2023
Journal Articles
Ioannidis Alexios I., Datsios Zacharias G., Gerodimos Apostolos K. and Tsovilis Thomas E.
IEEE Transactions on Electromagnetic Compatibility, pp. 1-11, 2023 Jan
[Abstract][BibTex][pdf] Lightning attachment can be modeled through a stochastic approach adopting a detailed representation of the lightning phenomenon. A fractal-based modeling technique can be used for this purpose, considering lightning discharge branched and tortuous behavior, as well as physical properties associated with downward and upward leaders’ inception and propagation. However, fractal-based simulations require substantial computational resources, especially for the accurate calculation of the electric field at all points of the discretized simulation domain at each simulation step. Thus, the considerable computational cost inhibits the extensive application of stochastic simulations for estimating lightning incidence to common structures and power systems. This work investigates optimization techniques for fractal-based simulations regarding total simulation time; these are applicable to both high-performance computing and personal computers. The proposed techniques consist of a C-MATLAB integration methodology, as well as a multi-color ordering algorithm enabling parallel execution using CPU and GPU programming. Applications associated with lightning incidence to overhead transmission lines are presented. The total simulation time is substantially reduced with respect to the original code. A reduction of up to 98% is achieved, enhancing the applicability of stochastic modeling to lightning incidence estimation problems. @article{IOANNIDIS2023TEMC, | |
Staikos Evangelos T., Peppas Georgios D. and Tsovilis Thomas E.
IEEE Transactions on Power Delivery, 38, (1), pp. 453-462, 2023 Feb
[Abstract][BibTex][pdf] The voltage-current characteristic of metal-oxide varistors is experimentally investigated for a wide frequency range. Concave exponential and rectangular impulse currents that resemble lightning current field records are employed to investigate their energy coordination with transient voltage suppression diodes, commonly integrated into printed circuit boards to protect sensitive electronic components. Thus, the effective coordination is experimentally evaluated against high- and low-frequency surge events for components used in power, telecom, and automotive applications. Experimental results supported by ATP-EMTP simulations show that reliable coordination of conventional varistors with bidirectional diodes can be challenging; this finding reveals a risk for the uninterrupted operation and safety of equipment with built-in diodes. The satisfactory agreement of ATP-EMTP results with experimental data shows that electromagnetic transient simulations can be an effective tool for designing coordination circuits and evaluating the risk of failure in case of surge events and electromagnetic pulses. @article{STAIKOS2023TPWRD, |
2022
Journal Articles
Zacharias G. Datsios, Pantelis N. Mikropoulos, Thomas E. Tsovilis, Emmanuel Thalassinakis and Grigorios Pagonis
Electric Power Systems Research, 213, pp. 108763, 2022 Jan
[Abstract][BibTex][pdf] This paper investigates the application of Line Surge Arresters (LSAs) to 150 kV double-circuit overhead lines through ATP-EMTP simulations. The 150 kV lines under study are the backbone of the autonomous electrical system of Rhodes island in southeastern Aegean Sea, Greece. Hence, lightning-related insulation flashovers causing outages of these lines may lead to a blackout of this isolated system. In this work, both Non-Gapped Line Arresters (NGLAs) and Externally Gapped Line Arresters (EGLAs) are evaluated. Two installation configurations with 3 and 6 LSAs per tower are considered protecting one circuit and both circuits of the line, respectively. Simulations were performed for both lightning strikes to phase conductors and tower; these may cause shielding failure flashover and backflashover, respectively. The conducted current through the LSAs and the voltage at their terminals are computed, enabling the estimation of the energy stressing the LSAs. The effects of the lightning current time to half value, the phase angle of the operating voltage, and the power frequency ground resistance of towers are assessed. The required LSA energy absorption capability is determined. The lightning performance of a critical overhead line of the Rhodes 150 kV system is estimated and its improvement due to LSA installation is quantified. @article{DATSIOS2022EPSR, | |
Martins-Britto Amauri G., Papadopoulos Theofilos A., Datsios Zacharias G., Chrysochos Andreas I. and Papagiannis Grigoris K.
IEEE Transactions on Electromagnetic Compatibility, 64, (6), pp. 2273-2282, 2022 Dec
[Abstract][BibTex][pdf] The electromagnetic interference (EMI) of overhead transmission lines (OHLs) to aboveground pipelines sharing the same right-of-ways has been a research topic for many years. Most studies focus on investigations of the induced currents and voltages at the mains frequency (50/60 Hz). However, significant voltage levels can also be induced, when the pipeline is subject to high-frequency excitation. The representation of earth conduction effects is very important to estimate accurately the level of the EMI. This article presents a detailed high-frequency analysis of OHL/pipeline configurations taking into consideration the frequency-dependent (FD) soil properties. Wise's earth formulation is adopted for the calculation of the earth return impedances and shunt admittances. Propagation characteristics, frequency-domain, and transient responses are calculated by using both the FD soil models and constant soil properties, as well as the classical transmission line approach of Carson. Frequency-domain responses calculated with Wise's formulation are compared against those obtained using the MoM-SO method of EMTP software. @article{DATSIOS2022TEMC, | |
Datsios Zacharias G., Mikropoulos Pantelis N., Staikos Evangelos T., Tsovilis Thomas E., Patsalis Diamantis G., Vlachopoulos Dimitrios and Ganatsios Stergios
IEEE Transactions on Industry Applications, 58, (1), pp. 212-223, 2022 Jan
[Abstract][BibTex][pdf] Soil ionization, that is, electrical discharges developing in the ground, may have a significant impact on the behavior of grounding systems under lightning currents, as it causes a reduction of the impulse ground impedance. This may have several implications on insulation coordination studies for power systems. The effects of soil ionization have not been completely clarified yet due to its complexity associated with soil characteristics and conditions, ground electrode configuration, lightning current characteristics, as well as difficulties in the accurate determination of discharge activity. This study deals with the experimental investigation of the lightning impulse behavior of wet sandy soil. An experimental setup and measurement procedure are introduced for this purpose. Experiments under lightning impulse voltages of negative polarity were performed on two wet sandy soils, both as obtained from their extraction sites, as well as after drying and manual addition of moisture; thus, the influence of the soil sample preparation procedure is evaluated. Results are discussed considering soil ionization inception, electrical breakdown of soil, impulse impedance, and soil electrical properties. A simulation model is proposed for the prediction of the instantaneous impulse impedance when soil ionization occurs; this model is suitable for time domain simulations in ElectroMagnetic Transients Program (EMTP)-type software. @article{DATSIOS2022TIA, | |
Ioannidis Alexios I., Mikropoulos Pantelis N., Tsovilis Thomas E. and Kokkinos Nikolaos D.
IEEE Industry Applications Magazine, 28, (4), pp. 20-28, 2022 Jul
[Abstract][BibTex][pdf] A fractal-based approach to the lightning protection of historical buildings and monuments against direct lightning flashes is introduced. The proposed methodology is based on a stochastic lightning attachment model that considers physical criteria on downward and upward leaders’ inception and propagation. The model foresees multiple competing upward leaders incepting from vulnerable points of the monument under protection and considers the branching and tortuous behavior of the lightning attachment phenomenon. Applying the proposed methodology to the Parthenon has shown that the risk of direct lightning flashes per year that cause physical damage to the monument is not acceptable without an external lightning protection system (LPS); two different LPSs are evaluated in terms of lightning interception efficiency. Lightning risk assessment results are discussed and compared with those obtained by implementing the procedures of the International Electrotechnical Commission (IEC) 62305. @article{IOANNIDIS2022IAM, | |
D. Khelil, S.Bouazabia, and P. N. Mikropoulos
COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, 41, (4), pp. 1159-1170, 2022 Feb
[Abstract][BibTex][pdf] The paper aims to estimate the instantaneous breakdown voltage of the lightning discharge from simulated figures in an energized rod-plane configuration protected by a lightning rod. The same configuration of electrodes has been the subject of experimental investigations for the measurement of the instantaneous breakdown voltage using oscillographic monitoring. This study validates the simulation model by making a comparison with experimentation and involves the role of the inception field of the upward discharge in the propagation of this last one. @article{Khelil2022COMPEL, | |
Emara Manal M., Peppas Georgios D., Pyrgioti Eleftheria C., Chronopoulos Demetrios D., Bakandritsos Aristides, Tegopoulos Sokratis N., Kyritsis Apostolos, Tsovilis Thomas E., Polykrati Aikaterini D. and Gonos Ioannis F.
IEEE Transactions on Dielectrics and Electrical Insulation, 29, (2), pp. 510-518, 2022 Apr
[Abstract][BibTex][pdf] This work reports on the significant enhancement of the thermal properties of the FR3 natural ester dielectric oil after the addition of pentyl-graphene nanosheets, as confirmed by thermal diffusivity and specific heat studies at different concentrations and temperatures (30 °C–90 °C). Experimental results of the dielectric constant demonstrated a constant value in the kHz region while increased in the low-frequency region, decreased with increased temperature, and saturated at 0.008% w/w concentration. In addition, light absorption is used for a better understanding of the properties variation upon changing graphene’s concentration as a method to estimate the agglomeration level. The optimum concentration for its best performance in terms of thermal and dielectric properties is 0.008% w/w, whereby the thermal diffusivity and the dielectric constant increased by 43.04% and 6.18%, respectively. @article{TSOVILIS2022TDEIS, |
2022
Conference Papers
Bousiou E.I., Karanikiotis N.C., Mikropoulos P.N. and Zagkanas V.N.
2022 IEEE International Conference on High Voltage Engineering and Applications (ICHVE), pp. 1-4, 2022 Sep
[Abstract][BibTex][pdf] A software application for the estimation of the corona inception field and voltage of typical ACSR transmission line conductors is presented. The software, developed in Python, runs as an executable Microsoft Windows application. It calculates the inception field and voltage of line conductors, based on a physical model that considers the ionization processes involved in corona discharge as affected by atmospheric conditions and operating voltage polarity. With a user-friendly interface, the developed software is a useful tool for the design of overhead transmission lines allowing for the evaluation of corona activity, through parametric analysis. @inproceedings{BOUSIOU2022ICHVE, | |
Datsios Zacharias G., Stracqualursi Erika, Araneo Rodolfo, Mikropoulos Pantelis N. and Tsovilis Thomas E.
2022 IEEE International Conference on Environment and Electrical Engineering and 2022 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe), pp. 1-6, 2022 Jun
[Abstract][BibTex][pdf] Frequency- and current-dependent effects dominate the response of grounding systems. This work investigates the influence of tower grounding system modeling on estimating the minimum backflashover current and backflashover rate (BFR) of a typical 150 kV overhead transmission line. The minimum backflashover current is determined through ATP-EMTP simulations. Four grounding system modeling approaches are evaluated, namely: (i) a constant ground resistance, (ii) the frequency-dependent (FD) response of the grounding system with constant electrical properties of soil, (iii) the FD response with FD soil properties, and (iv) a soil ionization model. Actual concentrated and extended tower grounding systems used in practice for the investigated 150 kV line are considered. The FD response of these grounding systems is obtained using a hybrid code based on electromagnetic field analysis and circuit theory. Results show that simulating the FD response is important for the extended grounding system. For the concentrated grounding system, the minimum backflashover current and BFR are affected considerably by including soil ionization in simulations; FD effects influence BFR results primarily for low soil resistivity values. @inproceedings{DATSIOS2022EEEIC, | |
Datsios Zacharias G., Mikropoulos Pantelis N., Tsovilis Thomas E., Antonaros Alexandros C. and Karamouslis Dimitrios A.
2022 2nd International Conference on Energy Transition in the Mediterranean Area (SyNERGY MED), pp. 1-5, 2022 Oct
[Abstract][BibTex][pdf] The critical lightning currents (minimum values) causing flashover of overhead transmission line insulation are required for computing the line lightning flashover rate, LFR. The latter comprises the shielding failure flashover rate, SFFOR, and backflashover rate, BFR. Hence, two critical currents associated with the lightning performance of the lines are defined: the minimum shielding failure flashover current and the minimum backflashover current. These currents can be calculated employing simplified analytical methods. More accurate estimates can be obtained via electromagnetic transient simulations performed iteratively, using detailed simulation models for fast-front transients. This work deals with the estimation of line critical currents through ATP-EMTP simulations by means of an external program developed in MATLAB, facilitating parametric investigations. An application to 150 kV double-circuit lines is presented considering tower height and insulator length as parameters. @inproceedings{DATSIOS2022MED, | |
Gektidis Konstantinos M., Ioannidis Alexios I. and Tsovilis Thomas E.
2022 IEEE Industry Applications Society Annual Meeting (IAS), pp. 1-9, 2022 Oct
[Abstract][BibTex][pdf] The transient behavior of commercially available low-voltage surge protective devices (SPDs) is experimentally investigated by employing standard lightning and switching impulse voltages. The response time of an SPD that integrates a triggered spark gap between the power lines and earth is on focus; a novel definition of the response time is proposed. Surprisingly, the experimentally derived response time varies beyond the upper limit declared by the SPD manufacturer. This work stresses the need for an update of international standards to incorporate a definition of the response time of SPDs covering a wide range of transients. @inproceedings{GEKTIDIS2022IASAM, | |
Ioannidis Alexios I. and Tsovilis Thomas E.
2022 IEEE Industry Applications Society Annual Meeting (IAS), pp. 1-16, 2022 Oct
[Abstract][BibTex][pdf] The energy stress of surge arresters installed in high voltage substations is computed by combining stochastic modeling of lightning incidence with an ATP-EMTP electromagnetic transients simulation model. An application is made to a 69 kV substation presented in IEEE Std 998. Results of this work indicate that the stochastic nature of the lightning attachment phenomenon shall be taken into account for the dimensioning and selection of the thermal energy rating of surge arresters installed in substations. @inproceedings{IOANNIDIS2022IASAM, | |
Ioannidis Alexios I., Mikropoulos Pantelis N., Tsovilis Thomas E. and Kokkinos Nikolaos D.
2022 36th International Conference on Lightning Protection (ICLP), pp. 479-484, 2022 Oct
[Abstract][BibTex][pdf] A literature review on lightning protection of historical buildings and cultural heritage monuments is conducted. Cases of lightning-related damages reported worldwide are presented to stress the need for an efficient lightning protection system (LPS) design, minimizing the risk of loss of human life and cultural heritage. The procedures adopted by the international standard IEC 62305:2010 for lightning risk assessment and LPS design are described. In addition, several cases of external LPS installed to monuments and landmarks worldwide are shown. The design of an LPS for the Parthenon monument in accordance with IEC 62305:2010 is presented; the proposed LPS is further evaluated by employing a stochastic lightning attachment model. @inproceedings{IOANNIDIS2022ICLP, | |
Ioannidis Alexios I., Datsios Zacharias G., Tsaousakis Georgios A. and Tsovilis Thomas E.
2022 36th International Conference on Lightning Protection (ICLP), pp. 36-41, 2022 Oct
[Abstract][BibTex][pdf] An analysis of the fractal dimension of lightning discharges simulated using a stochastic lightning attachment model is made. Two fractal dimension estimation methods are employed, incorporating developed algorithms in MATLAB software environment, namely the box-counting and sandbox methods. The statistical variation of fractal dimension results is discussed with respect to fractal dimension values reported in the literature and derived from 2D photographs of natural lightning observations. Fractal dimension results regarding lightning incidence to a 66 kV single-circuit overhead transmission line are analyzed. The effect of lightning discharge termination point to the overhead line in the estimated fractal dimension is discussed as well as the dynamic variation of the fractal dimension throughout the lightning discharge path. @inproceedings{IOANNIDIS2022ICLP2, | |
Karanikiotis N.C., Mikropoulos P.N., Samaras P.K. and Tsovilis T.E.
2022 IEEE International Conference on High Voltage Engineering and Applications (ICHVE), pp. 1-4, 2022 Sep
[Abstract][BibTex][pdf] Inception characteristics of partial discharges developing in a short sphere-ring gap bridged by polymeric insulating surfaces are investigated using positive ramp high voltages with variable rate of rise and several detection threshold discharge currents. Inception probability distributions of surface partial discharge voltage were obtained. A pronounced effect of material relative permittivity on partial discharge inception characteristics was mainly observed for the lowest detection current employed. The lowest measured values of inception voltage and pulse current amplitude could be considered as characteristics of streamers developing adhering to the insulating surface. A good agreement between theoretical and experimental results on partial discharge inception voltage is shown to exist. @inproceedings{KARANIKIOTIS2022ICHVE, | |
Patsalis D. G., Datsios Z. G., Mikropoulos P. N. and Tsovilis T. E.
2022 IEEE International Conference on High Voltage Engineering and Applications (ICHVE), pp. 1-4, 2022 Sep
[Abstract][BibTex][pdf] This work evaluates the influence of typical first return-stroke current waveforms of negative downward lightning flashes, as recorded in literature, on the computed fast-front overvoltages on a typical 150 kV overhead transmission line. The critical flashover currents are also assessed. The investigation is performed through ATP-EMTP simulations considering lightning strikes to towers (backflashover) and phase conductors (shielding failure). Results for recorded lightning current waveforms are compared with those obtained for the widely used CIGRE waveform; the front time, maximum steepness, and time to half value of the latter are varied according to their statistical distributions. A comparison between CIGRE and double-peak waveforms is also performed. It is shown that the use of actual recorded return-stroke current waveforms may affect considerably the computed overvoltages and critical currents. The leader development models employed for flashover prediction are discussed in terms of the criterion used to terminate leader propagation for withstand cases. @inproceedings{PATSALIS2022ICHVE, | |
Datsios Zacharias G., Patsalis Diamantis G., Mikropoulos Pantelis N. and Tsovilis Thomas E.
2022 36th International Conference on Lightning Protection (ICLP), pp. 338-343, 2022 Oct
[Abstract][BibTex][pdf] This work investigates with the aid of ATP- EMTP simulations the effects of lightning current waveform on the computed fast-front overvoltages and critical currents causing insulation flashover to a typical 150 kV overhead transmission line. First return-strokes of negative and positive downward lightning flashes are considered for shielding failure flashover and backflashover cases. The CIGRE current waveform is employed in simulations; recorded lightning current waveforms are used as well. The front time, maximum steepness, and time to half value are varied taking into account their statistical distributions. It is shown that the representation of lightning current affects considerably the waveform of the arising fast-front overvoltages and consequently the minimum currents causing flashover. The effects of waveform parameters are quantified and discussed for the 150 kV line under study. @inproceedings{PATSALIS2022ICLP, | |
Karanikiotis N.C., Mikropoulos P.N., Samaras P.K. and Tsovilis T.E.
2022 IEEE International Conference on High Voltage Engineering and Applications (ICHVE), pp. 1-4, 2022 Sep
[Abstract][BibTex][pdf] Partial discharge inception in a short sphere-ring gap bridged by polymeric insulating surfaces is investigated under positive ramp high voltages with variable rate of rise. Partial discharge inception probability distributions were obtained through successive inception tests, based on simultaneous applied voltage and discharge current measurements. The partial discharge inception voltage is lower for smaller sphere radius and higher material relative permittivity. These effects could be accounted for theoretically, based on electrostatic field simulations and the equivalent avalanche concept, by assuming a poor contact between the sphere and insulating specimen. Using the ratio of sphere radius to material relative permittivity, a modified Peek's formula yields satisfactory estimates of the partial discharge inception field. @inproceedings{SAMARAS2022ICHVE, | |
Mikropoulos P. N., Tsouris P. T. and Aristotelous G. K.
2022 IEEE International Conference on High Voltage Engineering and Applications (ICHVE), pp. 1-4, 2022 Sep
[Abstract][BibTex][pdf] Lightning impulse flashover characteristics of a typical 24 kV pin-type porcelain insulator are experimentally investigated aiming at a better understanding of the flashover mechanism as affected by the amplitude and polarity of the applied voltage. Flashover probability distributions under standard lightning impulses of both polarities were obtained and salient characteristics of the discharge inception, growth and flashover were measured. The insulator was overstressed to study the effects of the applied impulse voltage peak on discharge characteristics. Flashover occurs through a streamer-dominated mechanism involving however, necessarily, the inception of a small leader. Flashover characteristics are closely related to those of leader inception and growth; the latter is facilitated when overstressing the insulator. At relatively high applied voltages flashover occurs sooner and at lower voltages under negative than positive impulses. @inproceedings{TSOURIS2022ICHVE2, | |
Mikropoulos Pantelis N. and Tsouris Petros P.
2022 36th International Conference on Lightning Protection (ICLP), pp. 535-539, 2022 Oct
[Abstract][BibTex][pdf] Accurate modelling of the lightning impulse flashover of medium voltage overhead line insulators is of great importance for insulation coordination studies of distribution networks. This paper presents an application of the CIGRE leader progression model implemented in ATP-EMTP to the prediction of the positive lightning impulse flashover characteristics of a typical 24-kV pin-type porcelain insulator. A reasonable agreement between simulation and experimentally obtained results on the dynamics of discharge development as well as on flashover characteristics is achieved by using appropriate parameter values in the leader progression model. @inproceedings{TSOURIS2022ICLP, | |
Tsovilis Thomas E., Hadjicostas Alexandros Y., Staikos Evangelos T. and Peppas George D.
2022 IEEE Industry Applications Society Annual Meeting (IAS), pp. 1-6, 2022 Oct
[Abstract][BibTex][pdf] This work provides an electromagnetic transient model for low-voltage surge protective devices connected to the dc side of electric vehicle charging stations with a maximum operating voltage of 1000 V. An equivalent circuit model is developed based on standard impulse voltage ($1.2/50\ \mu\mathrm{s$) and impulse current ($8/20\ \mu\mathrm{s$ and $10/350\ \mu\mathrm{s$) experiments. The proposed model reproduces quite accurately the response of the combination type surge protective device under study in terms of sparkover voltage, residual voltage, and energy absorption, as illustrated through ATP-EMTP simulations. The developed simulation model can be an effective tool for surge protection and insulation coordination studies for electric vehicle charging stations. @inproceedings{TSOVILIS2022IASAM, | |
Emara Manal M., Tegopoulos Sokratis N., Pyrgioti Eleftheria C., Peppas Georgios D., Kyritsis Apostolos, Tsovilis Thomas E. and Gonos Ioannis F.
2022 IEEE 21st International Conference on Dielectric Liquids (ICDL), pp. 1-6, 2022 May
[Abstract][BibTex][pdf] Nowadays, nanoparticles are used in insulating oils to enhance their dielectric and thermal properties significantly. On the other hand, natural ester oil is considered one of the most environmentally friendly types of insulating oil. In this study, magnesium oxide nanoparticles with their excellent physical and thermal properties, are used to prepare natural ester oil-based nanofluids. Their electrical performance is investigated by subjecting samples of different nanoparticles concentration to lightning impulse voltage (1.2/50 µs) by following the step-up method. For the generation of the pulses, a one-stage impulse voltage generator was used, while measurements from 20 pulses per voltage level were applied to a needle-to-plane gap so as to estimate the relevant breakdown probabilities. Furthermore, relative permittivity and electrical conductivity are measured for a range of frequencies (0.1 Hz - IMHz) and a range of temperatures (30 °C – 90 °C) by means of broadband dielectric spectroscopy. The thermal properties are studied based on thermal diffusivity measurements by LFA (Laser Flash analysis) for different concentration values and a wide range of temperatures (30 °C – 90 °C). Results reveal the improved performance regarding the dielectric and thermal properties for the prepared natural ester oil-based nanofluids. A 15.15 % improvement in lightning impulse breakdown voltage, more specifically of the U50% voltage, is observed. Additionally, results show a 12.63 % improvement for thermal diffusivity. @inproceedings{TSOVILIS2022ICDL, | |
Datsios Z. G., Mikropoulos P. N. and Vasileiou M. G.
2022 IEEE International Conference on High Voltage Engineering and Applications (ICHVE), pp. 1-4, 2022 Sep
[Abstract][BibTex][pdf] Soil ionization is important for several engineering applications since when occurring dominates the impulse behavior of grounding systems. Thus, knowledge on electrical discharge characteristics developing in soil is essential; their accurate determination is performed experimentally due to the complex physical mechanisms involved and the widely varying soil properties and conditions. This work introduces a methodology for processing and analyzing the associated measured impulse voltage and current waveforms. Time instants related to soil ionization phenomena are identified along with current, voltage and impedance values. Characteristic curves are constructed in order to evaluate the dynamics of soil ionization growth. The recorded impulse waveforms are processed automatically using a code written in MATLAB software. Preliminary results for a wet sandy soil are presented and discussed. @inproceedings{VASILEIOU2022ICHVE, |
2021
Journal Articles
T.A. Papadopoulos, Z.G. Datsios, A.I. Chrysochos, P.N. Mikropoulos and G.K. Papagiannis
Electric Power Systems Research, 196, pp. 107249, 2021 Jan
[Abstract][BibTex][pdf] In surge analysis, an important issue is the influence of the imperfect earth on the propagation characteristics of the conductors. In this paper, the wave propagation characteristics and the transient performance of underground multiconductor cable systems in flat, vertical and trefoil arrangement are investigated. The Longmire and Smith frequency-dependent (FD) soil model as well as a generalized earth formulation are considered, taking into account in the analysis the impact of earth conduction effects on both the series impedance and shunt admittance of the cable conductors and sheaths. Comparisons are carried out with approximate earth formulations, neglecting the influence of imperfect earth on shunt admittances. Finally, resonance frequency analysis and transient simulations are performed for the different cable arrangements to evaluate the importance of FD soil modeling and earth formulation per cable arrangement. @article{DATSIOS2021EPSR, | |
Datsios Zacharias G., Mikropoulos Pantelis N. and Tsovilis Thomas E.
IEEE Transactions on Power Delivery, 36, (2), pp. 522-532, 2021 Apr
[Abstract][BibTex][pdf] The minimum backflashover current, IBF, of typical overhead transmission lines is estimated through ATP-EMTP simulations considering the tower ground resistance and AC voltage phase angle as parameters. Several single- and double-circuit lines are investigated with operating voltage from 66 kV to 765 kV and Basic Insulation Level from 325 kV to 1950 kV. The backflashover rate, BFR, of the investigated lines is obtained using an expression that accurately considers lightning incidence to the line for prospective currents higher than IBF; the relevant CIGRE expression underestimates BFR. BFR can be easily estimated using solely the phase angle values corresponding to zero AC voltage of the phase conductors. Based on the IBF and BFR results, simple expressions are introduced for the calculation of an equivalent minimum backflashover current as a function of insulator length and tower ground resistance or impulse impedance. These expressions enable straightforward estimation of BFR without the need for time-consuming simulations or laborious analytical methods adopting simplifying assumptions. @article{DATSIOS2021TPWRD, | |
Datsios Zacharias G., Ioannidis Alexios I., Papadopoulos Theofilos A. and Tsovilis Thomas E.
IEEE Transactions on Electromagnetic Compatibility, 63, (5), pp. 1433-1443, 2021 Oct
[Abstract][BibTex][pdf] A stochastic lightning attachment model for evaluating the lightning performance of overhead transmission lines is introduced. The proposed model considers the stochastic nature of lightning attachment by taking into account the lightning discharge branched and tortuous behavior. It integrates physical criteria on leader inception by adopting the Petrov and Waters model, as well as leader discharge progression considering also the competing interaction of multiple upward leaders. A generalized methodology combining stochastic modeling of lightning incidence with an electromagnetic transients (EMT) simulation model is proposed so as to estimate the backflashover and shielding failure flashover rates of HVDC overhead lines; an application to a monopolar −400 kV line sheds light on the basic parameters that affect the lightning performance of HVDC lines. The probability of shielding failure is higher than that obtained by the deterministic lightning attachment models. The stochastic nature of lightning attachment and the effect of lightning peak current distribution should be considered for the design and evaluation of the lightning performance of the emerging HVDC systems. @article{IOANNIDIS2021TEMC, | |
Ioannidis Alexios I. and Tsovilis Thomas E.
IEEE Transactions on Industry Applications, 57, (3), pp. 2317-2325, 2021 May
[Abstract][BibTex][pdf] A fractal-based approach is presented for the direct-stroke shielding analysis of high-voltage substations. The proposed method considers the effect of lightning polarity and the stochastic nature of the lightning attachment phenomenon. An application to a typical 69 kV substation reveals that shielding failures may occur even if the shielding design is realized with IEEE Std 998-2012 methods. This can be explained by the fact that the shielding design methods adopted by IEEE Std 998 do not consider the effects of lightning polarity and object height on striking distance. In addition, IEEE Std 998 methods adopt a deterministic approach on shielding failure analysis neglecting the branched and tortuous behavior of lightning discharges. Fractal-based simulation results show a considerable dispersion of striking distance and a significantly higher shielding failure probability for downward positive lightning than negative lightning. This work forms a discussion framework on shielding failure analysis following a stochastic approach; this approach may explain unexpected shielding failures, such as those reported in IEEE surveys, and can be used for the direct-stroke shielding design of mission-critical high-voltage substations. @article{IOANNIDIS2021TIA, | |
Papadopoulos Theofilos A., Datsios Zacharias G., Chrysochos Andreas I., Mikropoulos Pantelis N. and Papagiannis Grigoris K.
IEEE Transactions on Electromagnetic Compatibility, 63, (1), pp. 259-267, 2021 Feb
[Abstract][BibTex][pdf] The accurate estimation of the influence of the imperfect earth on the propagation characteristics of conductors is a crucial issue in electromagnetic (EM) transient analysis. In this aspect, the frequency-dependence of the soil electrical properties should be also considered. The effects of the dispersion of soil electrical properties on EM propagation have been investigated mostly for overhead transmission lines. This article presents a detailed EM transient analysis of underground cable systems taking into consideration the frequency-dependent (FD) soil properties. A generalized earth formulation of cable earth return impedance and shunt admittance is adopted. Propagation characteristics and transient responses are calculated by using both FD soil models and constant soil properties, as well as approximate earth formulations, neglecting the influence of the imperfect earth on shunt admittances; significant differences are observed. Guidelines for the accurate evaluation of earth conduction effects on the transient performance of underground cable systems are also introduced. @article{MIKROPOULOS2021TEMC, | |
Tsovilis Thomas E.
IEEE Transactions on Power Delivery, 36, (5), pp. 3055-3064, 2021 Oct
[Abstract][BibTex][pdf] Surge protective devices, SPDs, improve the reliability of power systems by mitigating the risk of equipment failure due to impinging overvoltages. The role of SPDs is more challenging today when considering the advent of smart grids and the associated integration of sensitive electronic equipment into modern low-voltage power systems. This work provides critical insight into performance requirements and test methods for surge protective devices according to IEC 61643 and UL 1449 standards; SPD ratings and fail-safe behavior are on focus. Experimental arrangements are proposed to represent in a laboratory environment the surge current and/or temporary overvoltage events that SPDs may be exposed to in the field; experimental evidence, ATP-EMTP simulation results and field experience are used to support these proposals. Grey zones of SPDs performance and failure mode are discussed in the context of the integrated components technology. @article{TSOVILIS2021TPWRD, |
2021
Conference Papers
Datsios Zacharias G., Mikropoulos Pantelis N., Tsovilis Thomas E., Thalassinakis Emmanuel and Pagonis Grigorios
2021 35th International Conference on Lightning Protection (ICLP) and XVI International Symposium on Lightning Protection (SIPDA), pp. 01-07, 2021 Sep
[Abstract][BibTex][pdf] The application of non-gapped line surge arresters (NGLAs) to the 150 kV double-circuit overhead lines of the electrical network of Rhodes island in southeastern Aegean Sea, Greece, is investigated through ATP-EMTP simulations. Several NGLA installation configurations are studied considering the power frequency tower ground resistance and AC voltage phase angle as parameters. The simulated scenarios include lightning strikes to shield wire, as well as to phase conductors (shielding failure). The improvement of the lightning performance of an 150 kV line is quantified. The current flowing through the NGLAs and the corresponding absorbed energy are computed. The energy stress of the NGLAs due to shielding failure is more severe as compared with the case of lightning strike to the shield wire; this holds even for the highest tower ground resistance of 200 Ω considered in this study. A significant improvement of the lightning performance of the investigated 150 kV double-circuit overhead line requires the installation of at least three NGLAs per tower, protecting one of the two circuits. For the relatively low tower ground resistance of this line (10 Ω), this configuration prevents backflashover of both circuits as well. However, for higher ground resistance values six NGLAs per tower are required to completely eliminate backflashover. @inproceedings{DATSIOS2021ICLP, | |
Ioannidis A. I., Karanikiotis N. C., Mikropoulos P. N., Samaras P. K. and Tsovilis T. E.
2021 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), pp. 663-666, 2021 Dec
[Abstract][BibTex][pdf] A fractal-based model for simulating the final stage of positive streamer flashover is introduced. The proposed model considers the stochastic nature of discharge growth along insulating surfaces and integrates physical criteria on surface discharge propagation. An application of the proposed model to simulate flashover along a Polyethylene (PE) insulating specimen bridging a short sphere-ring air gap has been made. With reference to experimental results, the proposed model well predicts the flashover voltage and spark path along the insulating surface. The statistical dispersion of the flashover voltage and spark path should be accounted for in determining the creepage distance of insulators utilized in critical electronic equipment. @inproceedings{IOANNIDIS2021CEIDP, | |
Ioannidis Alexios I., Mikropoulos Pantelis N., Tsovilis Thomas E. and Kokkinos Nikolaos D.
2021 IEEE Industry Applications Society Annual Meeting (IAS), pp. 1-5, 2021 Oct
[Abstract][BibTex][pdf] A stochastic approach for evaluating the risk of physical damage to the Parthenon due to direct lightning flashes is introduced. The proposed method is based on a fractal-based lightning attachment model that takes into account physical criteria on leader inception and propagation, multiple competing upward leaders, and also considers the lightning discharge branching and tortuous behavior. An application of the proposed methodology to the Parthenon has shown that the risk of loss of cultural heritage without a lightning protection system is not acceptable; different external lightning protection systems are evaluated in terms of lightning interception efficiency and lightning risk assessment results are discussed and compared with those obtained by IEC 62305. @inproceedings{IOANNIDIS2021IASAM, | |
Mikropoulos Pantelis N. and Samaras Pavlos K.
2021 IEEE Electrical Insulation Conference (EIC), pp. 277-280, 2021 Jun
[Abstract][BibTex][pdf] Partial discharge activity in a short sphere-plane gap bridged by PVC and POM insulating surfaces has been investigated under positive trapezoidal high voltages; the case of air alone was considered as reference. Distinguished modes of discharge activity., namely streamer and stable glow discharges., are determined., and their associated salient characteristics are measured as affected by the insulating surface. Inception of partial discharges occurs at a lower voltage in the presence of an insulating surface than in air alone., but the opposite applies for discharge extinction. Along an insulating surface the establishment of the stable glow discharge is hindered due to preceding intense streamer discharge activity. The discharge current., therefore also conductance., is higher for air alone and lowest for the PVC insulating surface. Results are discussed in terms of insulating surface material electrical properties and its affinity to surface charging. @inproceedings{SAMARAS2021EIC, | |
Staikos E. T., Tsovilis T. E. and Peppas G. D.
2021 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), pp. 77-80, 2021 Dec
[Abstract][BibTex][pdf] The frequency response of metal-oxide varistors and transient voltage suppression diodes is experimentally investigated; their voltage-current characteristics are measured by employing DC, sinusoidal, and pulse overvoltages. The effective coordination of varistors with transient voltage suppression diodes is evaluated by performing experiments with exponential and rectangular impulse currents; experimental results are in good agreement with preliminary ATP-EMTP simulations. @inproceedings{STAIKOS2021CEIDP, | |
Emara M. M., Peppas G. D., Tsovilis T. E., Pyrgioti E. C. and Gonos I. F.
22nd International Symposium on High Voltage Engineering (ISH 2021), pp. 1593-1596, 2021 Nov
[Abstract][BibTex][pdf] Using natural oils as a substitute for mineral oils has drawn the attention of researchers with respect to environmental regulations. In addition, the usage of natural ester based nanofluids helps in enhancing their properties. In this study, natural ester oil based nanofluids are prepared by employing magnesium oxide nanoparticles due to their excellent physical and thermal properties. Nanofluids with different nanoparticles concentration have been subjected to lightning impulse voltage to investigate their electrical performance. A one-stage impulse generator has been used to produce lightning impulse voltage of 1.2/50μs; the impulse dielectric strength of liquid insulation is investigated by using needle to plane configuration. The impulse voltage and the transient current are measured, while the time to breakdown is recorded, in order to investigate the lightning performance of the nanofluid in various concentrations by following step up method. In addition, 20 shots are performed at each level to help in obtaining the probability of the lightning breakdown voltage. The prepared natural ester oil based nanofluids show better performance, by means of increased U50% than the base oil. @inproceedings{TSOVILIS2021ISH, |
2021
Inbooks
Zumret Topcagic and Thomas E. Tsovilis
pp. 254-271, Elsevier, Oxford, 2021 Jan
[Abstract][BibTex][pdf] Varistors, their properties, and electrical behavior have been investigated extensively throughout the last 4 decades. In parallel, their usage in surge protection applications has become increasingly prominent, thus requiring a deeper understanding of their electrical properties and energy absorption capability. The following article attempts to elucidate microstructural effects on varistor electrothermal behavior as well as the advancements and future challenges on varistor technology and applications. The role of surge protection through varistor-based devices is becoming today even more important due to the increased sensitivity of the equipment integrated to smart power systems and the emerging low-voltage and high-voltage DC systems. @inbook{TOPCAGIC2021254, |
2020
Journal Articles
Evanthia I. Bousiou, Pantelis N. Mikropoulos and Vasileios N. Zagkanas
Electric Power Systems Research, 178, pp. 106032, 2020 Jan
[Abstract][BibTex][pdf] Corona inception field of line conductors is of major importance for assessing corona performance of overhead transmission lines. Using computational models that consider the ionization processes in corona discharge, the corona inception field of ACSR conductors typically utilized in overhead transmission lines is estimated. The interactive effects of line conductor geometry, voltage polarity as well as atmospheric conditions on corona inception field are assessed and discussed based on the ionization area around the conductor. It is shown that the corona inception field of bundle configurations can be satisfactorily approximated by that of the subconductor when considered single. Generally, the inception field of negative corona is slightly lower than that of positive corona and lesser affected by variations in atmospheric conditions. An empirical expression for the straightforward estimation of the corona inception field of line conductors has been introduced, accounting well for the effects of conductor geometry, voltage polarity and atmospheric conditions. @article{BOUSIOU2020EPSR, | |
Topcagic Zumret, Mlakar Miha and Tsovilis Thomas E.
IEEE Transactions on Power Delivery, 35, (3), pp. 1180-1188, 2020 Jun
[Abstract][BibTex][pdf] The energy absorption capability of metal-oxide varistors, decidedly influenced by the electrothermal processes occurring within their microstructures, is a vital parameter for the effective surge protection. This paper proposes a numerical model for the simulation of the electrothermal phenomena occurring in metal-oxide varistors. The model is based on a 3D representation of the varistor's polycrystalline microstructure and the finite element method analysis. With the aid of the proposed model, the interdependence of the varistor's energy absorption capability, nonuniform current conduction, and the thermal behavior is investigated. Results are in good alignment with experimental data and discussed in the context of electrothermal properties of the varistor's microstructure. An unambiguous dependency of the varistor's energy handling capability on the applied overvoltage is shown to exist. A quantitative evaluation of the effective volume decrease due to the severe current localization at temporary overvoltages is demonstrated. The presented work analyses varistor's current conduction under temporary overvoltages and provides the means for extension of the varistors IV characteristics into the time domain so as to accurately predict their dynamic electrothermal behavior. The introduced dynamic (IV t) model may have significant implications in energy absorption requirements and design principles for surge protective devices. @article{TSOVILIS2020TPWRD, | |
Tsovilis Thomas E. and Topcagic Zumret
IEEE Transactions on Power Delivery, 35, (5), pp. 2541-2543, 2020 Oct
[Abstract][BibTex][pdf] This letter provides evidence of a peculiar behavior of metal-oxide varistors under DC overvoltages. It stresses the need for extending the V-I characteristic of varistors in the time domain so as to accurately predict the dynamic performance of varistor-based surge protective devices under temporary overvoltages. Observations and mathematical formulation of DC overload behavior of metal-oxide varistors may have significant implications in energy absorption requirements for low-voltage surge protective devices and unlocks possible monitoring strategies in emerging DC distribution smart grids. @article{ZUMRET2020TPWRD, |
2020
Conference Papers
Bousiou Evanthia I., Mikropoulos Pantelis N., Samaras Pavlos K. and Zagkanas Vasileios N.
2020 IEEE International Conference on High Voltage Engineering and Application (ICHVE), pp. 1-4, 2020 Sep
[Abstract][BibTex][pdf] Simulation software for estimating the basic inception characteristics of air and surface discharges, namely inception voltage and electric field, is presented. The simulation software, called CSPDI, utilizes an electrostatic solver using the Boundary Element Method and integrates physical modeling of partial discharge inception, based on the growth of an equivalent electron avalanche, together with advanced numerical methods. Simulation results are validated against experimental results obtained for short gaps in air alone and bridged by an insulating surface. A very good agreement is shown to exist between computed and measured values of inception voltage, especially with decreasing gap length and for negative discharges. @inproceedings{BOUSIOU2020ICHVE, | |
Datsios Zacharias G., Mikropoulos Pantelis N., Staikos Evangelos T., Tsovilis Thomas E., Vlachopoulos Dimitrios and Ganatsios Stergios
2020 IEEE International Conference on Environment and Electrical Engineering and 2020 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe), pp. 1-6, 2020 Jun
[Abstract][BibTex][pdf] Electrical discharges occurring in the ground, commonly called soil ionization, may have a significant impact on the lightning impulse behavior of grounding systems causing a large reduction of the impulse ground impedance. The effects of soil ionization have not been fully clarified yet due to the dependence on excitation current characteristics, ground electrode configuration, as well as on soil characteristics and conditions. This study presents an experimental setup and measurement procedure for the investigation of the impulse behavior of soil. Experiments are performed on wet sand under lightning impulse voltages of negative polarity. Results are analyzed and discussed considering soil ionization inception, soil breakdown and impulse impedance. A preliminary attempt is made to develop a simulation model suitable for EMTP-type software so as to reproduce the temporal variation of the impulse impedance obtained through experiments. @inproceedings{DATSIOS2020EEEIC, | |
Datsios Zacharias G., Ioannidis Alexios I., Papadopoulos Theofilos A. and Tsovilis Thomas E.
2020 IEEE International Conference on Environment and Electrical Engineering and 2020 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe), pp. 1-6, 2020 Jun
[Abstract][BibTex][pdf] An ATP-EMTP simulation model for the evaluation of the lightning performance of the overhead lines of the ±533 kV Cahora-Bassa HVDC transmission system is presented. This model is used for the estimation of the minimum lightning currents causing flashover of the positive and negative pole insulators due to lightning strikes to shield wires (backflashover) and pole conductors (shielding failure flashover). A parametric analysis is conducted to investigate the influence on the critical lightning currents of several factors, namely, the span length, sag of pole conductors and shield wires, number of sub-conductors per bundle, tower ground resistance, soil resistivity and the pole operating voltage and polarity. It is shown that the minimum shielding failure flashover current of the HVDC lines is significantly affected by the polarity of the pole operating voltage only; the variation due to the other investigated parameters is found to be lower than about 10%. The minimum backflashover current, in addition to the polarity of the pole operating voltage, is influenced considerably by span length, lightning strike location along the span and tower ground resistance, thus also soil resistivity. @inproceedings{DATSIOS2020EEEIC2, | |
Datsios Zacharias G., Mikropoulos Pantelis N., Samaras Pavlos K. and Tsovilis Thomas E.
"Experimental Arrangement for Investigating the Surface Dielectric Strength of Insulating Materials"
2020 IEEE International Conference on High Voltage Engineering and Application (ICHVE), pp. 1-4, 2020 Sep
[Abstract][BibTex][pdf] An experimental arrangement for laboratory investigation of surface discharges along insulating specimens is presented. A sphere-ring and a needle-plane air gap bridged by PA insulating surfaces were stressed by positive slowly-varying high voltages with variable waveform parameters and by positive standard lightning impulse voltages. A flexible digital measurement and control system allowed for simultaneous monitoring of the applied voltage and discharge current, as well as of the UV radiation and temperature rise of the insulating surface associated with surface discharge activity. With the aid of the introduced experimental set-up, measurement procedures and analyses, the various surface discharge modes including flashover are easily identified, providing valuable information on their inception and spatial-temporal growth characteristics. @inproceedings{DATSIOS2020ICHVE, | |
Ioannidis Alexios I. and Tsovilis Thomas E.
2020 IEEE Industry Applications Society Annual Meeting, pp. 1-8, 2020 Oct
[Abstract][BibTex][pdf] A fractal-based model for the simulation of lightning incidence to high voltage substations is introduced. The proposed model takes into account the stochastic nature of lightning attachment by considering the lightning discharge branching and tortuous behavior and integrates up-to-date knowledge on leader inception and progression criteria. Fractal-based simulations are performed for the case of a typical 69 kV substation of the IEEE Std 998-2012. Simulation results show that the basic shielding design parameter, the striking distance, is stochastic in nature and that shielding failures may occur even for substations with shielding design in accordance with IEEE Std 998-2012. This work may shed light to unexpected failures of modern substations reported by utilities in a lightning protection survey held by IEEE. @inproceedings{IOANNIDIS2020IASAM, | |
Staikos Evangelos T. and Tsovilis Thomas E.
2020 IEEE International Conference on High Voltage Engineering and Application (ICHVE), pp. 1-4, 2020 Sep
[Abstract][BibTex][pdf] The low-frequency response of metal-oxide varistors, commonly used in telecommunication systems and networks, is investigated. The voltage-current characteristic and capacitance of varistors are obtained experimentally. The effects of frequency on the electrical characteristics of varistors on the pre-breakdown and the breakdown region are presented and discussed. Experimental results can be used for accurate modeling of varistor behavior under low-frequency electromagnetic pulses. @inproceedings{STAIKOS2020ICHVE, |
2020
Inbooks
P. N. Mikropoulos, J. He, and M. Bernardi
Charpter:5, 1st edition, pp. 165-215, Institution of Engineering and Technology, Energy Engineering, 2020 Jan
[Abstract][BibTex][pdf] Lightning is the main cause of unscheduled interruptions in overhead power lines, affecting reliability of power supply and thus, consequently, resulting in economic losses. Lightning-caused insulation flashover in overhead power lines is associated with the fast-front overvoltages across line insulation, arising due to direct lightning strokes or induced by nearby lightning. Shielding against direct lightning strokes to phase conductors of overhead power lines is provided by shield wires. The latter are metallic elements that are able to, by physical means, launch a connecting upward discharge that intercepts the descending lightning leader from a distance, called striking distance, commonly also called attractive radius or lateral distance. Lightning leaders intercepted by shield wires, increasing the potential of the transmission-line tower, may result in power-line outages due to backflashover, that is, insulation flashover between tower and phase conductors. However, some of the less intense lightning strokes, not being intercepted by shield wires terminating thus to the phase conductors, may cause powerline outages due to shielding failure. In addition, descending lightning leaders which are not intercepted by the line conductors, striking to ground nearby the power line or to adjacent structures may result in power-line outages due to induced voltages on line conductors causing insulation flashover. As the line operation voltage increases, a higher line insulation level is utilized, and the lightning performance of overhead power lines becomes increasingly determined by the direct stroke flashover rate. In this chapter, the physical process of lightning attachment to overhead power lines is presented and discussed. Engineering models of lightning attachment are described in detail. Finally, a general procedure for the estimation of lightning incidence to overhead power lines is presented. @inbook{Mikropoulos2020IETCh5, |
2019
Journal Articles
Datsios Z. G. and Mikropoulos P. N.
IEEE Transactions on Dielectrics and Electrical Insulation, 26, (3), pp. 904-912, 2019 Jun
[Abstract][BibTex][pdf] The electrical properties of soil at low radio-frequencies are important for engineering applications. In this work the effects of excitation frequency (42 Hz-1 MHz) as well as soil characteristics and conditions on the electrical properties of soil are experimentally investigated using remolded soil samples. Several sandy soils were tested with variable water content (dry up to saturation) using guarded two-electrode arrangements. A method is proposed based on the Nyquist plot to estimate the critical frequency above which measurements of the electrical properties of wet soil are free from electrode polarization effects. The latter result in extremely high real permittivity values, which do not correspond to the response of soil. The critical frequency is higher for smaller grain size and higher water content and varies according to a power law with soil power-frequency conductivity. The real and (effective) imaginary relative permittivity decrease with increasing frequency whereas the effective conductivity increases; this is attributed to the distributed relaxation of the interfacial polarization mechanism associated with the particulate nature of soil. The values of soil electrical properties increase with increasing water content and decreasing grain size (increasing specific surface) as a consequence of enhanced polarization and conduction phenomena. The effective imaginary permittivity varies with frequency according to a power law with an exponent approximately −1; the multiplier coefficient of this law expresses losses and has been formulated as a function of the degree of saturation and soil specific surface. @article{DATSIOS2019TDEIS, | |
Datsios Zacharias G., Mikropoulos Pantelis N. and Tsovilis Thomas E.
IEEE Transactions on Electromagnetic Compatibility, 61, (3), pp. 623-630, 2019 Jun
[Abstract][BibTex][pdf] Modeling of lightning return-stroke channel affects significantly the estimation of fast-front overvoltages arising across overhead line insulators, thus, also the lightning performance of power lines. This paper introduces a simplified method for estimating the minimum lightning currents causing shielding failure flashover and backflashover of overhead transmission line insulation, as affected by lightning channel equivalent impedance. The validity of the proposed methodology is demonstrated through ATP-EMTP simulations of typical 66 up to 765-kV overhead transmission lines with variable tower ground resistance. An assessment is made of the effects of lightning channel equivalent impedance on the lightning performance of overhead lines, that is, shielding failure flashover and backflashover rates. Lightning channel equivalent impedance values of 1000 and 400 Ω are suggested, respectively, for shielding failure and backflashover studies, based on the results obtained in this paper together with a discussion on the literature data regarding channel impedance. @article{DATSIOS2019TEMC, | |
I. F. Gonos, P. N. Mikropoulos, and P. Svarnas
High Voltage, 4, (3), pp. 159-160, 2019 Sep
[Abstract][BibTex][pdf] @article{Mikropoulos2018ICHVESel, | |
Mikropoulos Pantelis N. and Tsovilis Thomas E.
IEEE Transactions on Electromagnetic Compatibility, 61, (6), pp. 1793-1802, 2019 Dec
[Abstract][BibTex][pdf] General closed-form expressions for estimating lightning incidence to telecommunication towers are introduced on the basis of several lightning attachment models. The expressions consider the effects of tower height and lightning peak current distribution, as well as orographic and shielding effects. The estimated annual number of lightning strikes to towers, varying considerably among lightning attachment models, increases with tower height according to a power law and it is higher for lightning peak current distributions with high median value and standard deviation. A comparison is made between estimates and field data on lightning incidence; IEC geometric method, which is traditionally used in industry, by exaggerating the effect of tower height, overestimates lightning incidence. Literature lightning attachment models suitable for estimating lightning incidence to telecommunication towers are suggested based also on the observed failure rate of a transformer feeding a GSM base station. @article{TSOVILIS2019TEMC, |
2019
Conference Papers
T. A. Papadopoulos, Z. G. Datsios, A. Chrysochos, P. N. Mikropoulos, and G. Papagiannis
International Conference on Power Systems Transients (IPST), June 16 - 20, 2019, Perpignan, France, 2019 Jun
[Abstract][BibTex][pdf] In electromagnetic transient analysis, a major issue is the influence of the imperfect earth on the propagation characteristics of conductors. Although soil electrical properties present significant frequency-dependent (FD) behavior, in most cases earth is considered with constant properties. In this paper, the impact of the FD soil properties on the propagation characteristics of underground cables is investigated. For this purpose, generalized earth formulations are considered, taking into account the impact of earth conduction effects on both series impedance and shunt admittance of cable conductors. Comparisons are carried out using different FD soil models, also constant soil properties and with approximate earth formulations, neglecting the influence of imperfect earth on shunt admittances. Finally, transient simulations are performed to evaluate the impact of the different approaches. @conference{Datsios2019IPST, | |
Z. Topcagic, T. E. Tsovilis, and D. Krizaj
55th International Conference on Microelectronics, Devices and Materials, Ljubljana, Slovenia, pp. 112-118, 2019 Sep
[Abstract][BibTex][pdf] Nonuniform current distribution inside varistor ceramics is a key factor influencing its performance and failures. Therefore understanding, modelling and predicting of current distribution in varistor ceramics is of crucial significance. Moreover, the electrothermal processes occurring within varistors microstructure decidedly influence their energy absorption capability, as a vital parameter for the effective surge protection. In this paper, we discuss a 2D numerical model for the simulation of nonuniform electric current distribution inside Zinc Oxide Varistors. A numerical model is based on physical modelling of the varistor's grain-structured geometry presented by Voronoi network using Finite Element Method (FEM) simulation. In order to properly establish a FEM model a novel approach in defining grain boundary characteristic is proposed. Thus, a macroscopic model of the varistor microstructure has been developed and the grain micro-junction boundary characteristic has been derived. Furthermore, a 3D numerical model for the simulation of the electrothermal phenomena occurring in the metal oxide varistors is discussed. The model is based on a 3D representation of the varistor's polycrystalline microstructure and the finite element method analysis. With the aid of the proposed model, the interdependence of the varistor's energy absorption capability, nonuniform current conduction, and the thermal behaviour is investigated. An unambiguous dependency of the varistor's energy handling capability on the applied overvoltage is shown to exist. A quantitative evaluation of the effective volume decrease due to the severe current localization at temporary overvoltages is demonstrated. @conference{TsovilisICMDM2019, |
2018
Journal Articles
Djazia Khelil, Slimane Bouazabia and Pantelis.N Mikropoulos
Journal of Electrostatics, 95, pp. 42-52, 2018 Jan
[Abstract][BibTex][pdf] An experimental investigation on the lightning discharge interception probability of a vertical grounded rod when inserted in a rod-plane gap, as affected by the presence of a neighboring grounded object (rod) is presented. The height of the two grounded rods (simulating a protective and a protected object against lightning) and their separation distance and placement with respect to the energized rod were considered as influencing parameters on breakdown voltage and time, thus also on the discharge interception probability, under negative lightning impulse voltages. The discharge interception probability of the vertical grounded rod is strongly affected by the height and position of the neighboring rod; it significantly reduces when the separation distance between rods decreases, especially as the height of the rods increases. In the presence of the neighboring rod breakdown to the vertical rod occurs sooner at higher instantaneous voltages. A fractal model describing the lightning interception probability in the evaluated electrode arrangement is developed; the electrical discharges, emanating from both energized and grounded electrodes, evolve randomly in the space where the electric field is most intense. By considering also the voltage drop along the discharge path at each evolution step a satisfactory agreement between simulation and experimental results has been achieved. @article{KHELIL2018JELECTROSTAT, | |
Zumret Topcagic, Thomas Tsovilis and Dejan Krizaj
Electric Power Systems Research, 164, pp. 253-262, 2018 Jan
[Abstract][BibTex][pdf] Nonuniform current distribution inside varistor ceramics is a key factor influencing its performance and failures. Therefore understanding, modeling and predicting of current distribution in varistor ceramics is of crucial significance. This paper proposes a numerical model for simulation of nonuniform electric current distribution inside zinc oxide varistors. A numerical model is based on physical modeling of the varistor's grain-structured geometry presented by Voronoi network using finite element method (FEM) simulation. The presented method is solving complete electric field inside the modeled geometry and therefore provides a more physically accurate approach for better understanding and predicting nonuniform current distribution in the varistor. In order to properly establish a FEM model a novel approach in defining grain boundary characteristic is proposed. Thus, a macroscopic model of the varistor microstructure has been developed and the grain micro-junction boundary characteristic has been derived. The simulation results of nonuniform current distribution in a varistor agree well with measurement results for a typical ZnO varistor. The presented model enables investigation of influences of varistor geometry (shapes, sizes) and material properties on the current distribution. A new mathematical expression for varistor I–V characteristic based on Lambert function is proposed. @article{TOPCAGIC2018EPSR, |
2018
Conference Papers
Bousiou E. I. and Mikropoulos P. N.
2018 IEEE International Conference on High Voltage Engineering and Application (ICHVE), pp. 1-4, 2018 Sep
[Abstract][BibTex][pdf] Surge corona losses are of great importance in insulation coordination studies for high voltage transmission systems; corona losses are most often calculated based on charge-voltage curves, which follow a hysteresis loop. The enclosed area of the charge-voltage curves relates to the associated energy dissipation by corona for the full duration of the overvoltage surge. This study presents an experimental investigation on the charge-voltage characteristics of the lightning impulse corona in the coaxial cylindrical electrode arrangement. Corona inception characteristics namely time, voltage and charge were measured and the associated energy losses were estimated. To investigate the dependence of corona characteristics on the amplitude of the applied impulse voltage, the gap was overstressed. As the applied voltage increases, a transition from the glow to streamer mode of corona inception occurs. Where stable streamer corona is established, the corona charge and the associated energy losses are approximately two times lower for negative than positive corona. @inproceedings{BOUSIOU2018ICHVE, | |
Datsios Z. G., Mikropoulos P. N., Tsovilis T. E. and Angelakidou S. I.
2018 IEEE International Conference on High Voltage Engineering and Application (ICHVE), pp. 1-4, 2018 Sep
[Abstract][BibTex][pdf] The evaluation of the backflashover rate (BFR) of overhead power transmission lines requires knowledge of the minimum lightning current causing backflashover of line insulators. This work investigates the effects of concentrated tower grounding system modeling on this critical current as well as on BFR of typical 150 and 400 kV double-circuit power transmission lines through simulations using ATP-EMTP. Several models of concentrated grounding systems, which are based on a constant resistance or a current-dependent impulse resistance taking into account soil ionization effects, were employed in simulations; the low current and low frequency tower ground resistance was an influencing parameter. It is shown that the computed overvoltages arising across line insulators, therefore also the critical current and BFR, are significantly affected by tower grounding system modeling. BFR estimates are even more than 10 times lower for models that consider soil ionization effects. @inproceedings{DATSIOS2018ICHVE, | |
Datsios Zacharias G., Mikropoulos Pantelis N. and Karakousis Ioannis
2018 34th International Conference on Lightning Protection (ICLP), pp. 1-6, 2018 Sep
[Abstract][BibTex][pdf] The electrical properties of soil in the lower part of the radio-frequency range are important for many engineering applications. This work investigates the dependence of soil electrical properties upon frequency and soil parameters through laboratory experiments. The soils under test consisted of two natural silica sands of uniform gradations. Measurements were conducted by using two-electrode experimental arrangements with guard electrodes; emphasis was given on their calibration. A method is introduced to estimate approximately the critical frequency below which measurement results are affected considerably by electrode polarization effects. The principal low-frequency polarization mechanism is interfacial polarization; the latter causes with increasing frequency a decrease of the real relative permittivity and an increase of the effective conductivity due to polarization losses. @inproceedings{DATSIOS2018ICLP, | |
Mavrikakis N. C., Mikropoulos P. N., Siderakis K., Pellas I. and Thalassinakis E.
2018 IEEE International Conference on High Voltage Engineering and Application (ICHVE), pp. 1-4, 2018 Sep
[Abstract][BibTex][pdf] Bird pecking is one of the causes for deterioration of composite insulators. It concerns the removal of parts of the polymeric housing due to the attack by large birds. Such damages on the insulator housing rise questions concerning the efficiency and reliability of the bird-pecked insulators. This study evaluates the damages due to bird pecking activity detected on the housing of two 150 kV liquid silicone rubber tension insulators. Both insulators were operated for 15 years without experiencing faults in an overhead transmission line of Crete crossing an area highly populated by the griffon vulture. The impact of the deformed sheds on the electric field distribution along the housing surface is assessed through electrostatic simulations. The surface electric field is locally enhanced; this is of great concern when damages due to bird-pecking activity are detected along the high electric field areas of the insulator. @inproceedings{MAVRIKAKIS2018ICHVE, | |
Mavrikakis N.C. and Mikropoulos P.N.
2018 IEEE International Conference on High Voltage Engineering and Application (ICHVE), pp. 1-4, 2018 Sep
[Abstract][BibTex][pdf] Corona discharges along pure and room temperature vulcanized silicone rubber (RTV SIR) coated glass insulating surfaces, are experimentally investigated in a non- uniform electric field electrode arrangement under negative ramp high voltages. The insulating surfaces were bridging a short needle-plane gap which was stressed by applying voltages just sufficient for corona inception up to values causing flashover; the case of air alone was considered as reference. The salient corona discharge characteristics, namely inception voltage and current as well as the energy dissipated were obtained. Results are discussed based on different modes of corona growth as affected by applied voltage and presence of an insulating surface. Corona growth along an insulating surface is suppressed, thus flashover occurs at a higher applied voltage. @inproceedings{MIKROPOULOS2018ICHVE, | |
Gonos J., Kladas A., Labridis D., Mikropoulos P., Koulouridis S., Pyrgioti E., Kyriacou G. and Safigianni A.
2018 IEEE International Conference on Environment and Electrical Engineering and 2018 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe), pp. 1-5, 2018 Jun
[Abstract][BibTex][pdf] This work undertakes environmental impact analysis of high voltage overhead transmission lines, with respect to the produced electric and magnetic fields and the admissible reference levels for human exposure foreseen by international guidelines. The characteristics of magnetic and electric fields varying at the frequency of 50 Hz are described and the main calculation methodologies of the field distributions created by high voltage power lines are reviewed. Appropriate simulation techniques are proposed and the obtained results in cases of typical power line configurations are compared to the ones available in the literature. The main factors affecting compliance of the field distributions with the admissible limits and reference levels for human exposure to magnetic and electric fields are investigated and discussed. @inproceedings{MIKROPOULOS2018ICPS, |
2017
Journal Articles
Zacharias G. Datsios and Pantelis N. Mikropoulos
Electric Power Systems Research, 150, pp. 36-44, 2017 Jan
[Abstract][BibTex][pdf] Typical grounding configurations are used in MV/LV distribution substations often without evaluating their safety performance against the danger of critical electric shock due to touch and step voltages arising in case of a ground fault. A method for the straightforward safety assessment of typical grounding configurations of MV/LV substations is introduced on the basis of simple calculations. A safety performance curve is constructed by using proportionality factors, specific to each typical grounding configuration, and the time–current characteristic of the installed protective device. The safety performance curve relates ground fault current to upper limits of soil resistivity, thus also ground resistance, below which safety is ensured. Thus, safety of an existing or new MV/LV substation can be easily evaluated through the associated safety performance curve. In a similar approach, a method is introduced to determine the shortest separation distance between MV/LV substation and LV neutral grounding configurations ensuring safety against transferred potentials where common grounding is not applied. The use of the proposed methods is demonstrated through an application to typical 20/0.4kV distribution substations. @article{DATSIOS2017EPSR, | |
Datsios Z. G., Mikropoulos P. N. and Karakousis I.
IEEE Transactions on Dielectrics and Electrical Insulation, 24, (5), pp. 3063-3072, 2017 Oct
[Abstract][BibTex][pdf] Soil resistivity is an important parameter for engineering applications. In this work the effects of soil characteristics and conditions on the DC soil resistivity are investigated experimentally using remolded soil samples. Several natural silica and artificial glass sands of uniform gradations were tested under variable water resistivity and content, using the two-electrode and the four-electrode soil box methods for dry and wet soil, respectively. The dependence of DC soil resistivity on soil characteristics and conditions, such as grain size, specific surface, pore water conductivity and degree of saturation, is assessed. Soil resistivity decreases with increasing water conductivity and content. It also decreases with decreasing grain size as a result of the shorter current conduction paths (lower tortuosity) and the higher amount of available electrolytes; the contribution of the latter was quantified by measuring the resistivity of several soil:water suspensions. The effects of soil characteristics and conditions on soil resistivity have been well accounted for by considering soil resistivity at saturation as reference. For degree of saturation higher than the percolation threshold soil resistivity is well approximated by Archie's law; parameter values applicable to sandy soil are proposed. A new expression has been derived on a physical basis to describe soil resistivity for degree of saturation values lower than the percolation threshold. @article{DATSIOS2017TDEIS, | |
Mavrikakis N.C., Mikropoulos P.N. and Siderakis K.
IEEE Transactions on Dielectrics and Electrical Insulation, 24, (1), pp. 490-498, 2017 Feb
[Abstract][BibTex][pdf] Condition assessment of naturally aged composite insulators, aiming to better understand the ageing processes involved, is essential for maintaining high reliability in power networks. In this study field-ageing effects on insulating materials (EPDM and VMQ/HCR) of two 150 kV composite suspension insulators are evaluated. The insulators had been in service for 17 years on a coastal transmission network, exposed to seaborne salt spray, windborne soil deposits and intense UV solar radiation. Several diagnostic techniques, including visual inspection, wettability classification, FTIR spectroscopy, SEM and EDX analysis were employed to assess the condition of the insulators. Field-ageing effects were not assessed as critical to dictate insulator replacement. For both insulators morphological and material degradation due to field-ageing was restricted to the upper surface layer of the polymeric housing. The resistance of housing material against tracking and erosion remained unaffected by field-ageing. Surface deterioration of EPDM was more intense than that of VMQ/HCR, despite the fact that the EPDM insulator had been in operation at a site with a lower pollution severity. The EPDM housing was classified as hydrophilic; however, after removing pollutant deposits its hydrophobicity was improved. The hydrophobic properties of the VMQ/HCR housing were only slightly reduced. Field-ageing effects on insulator housing are discussed based on material structural changes caused by ageing stresses. @article{MAVRIKAKIS2017TDEIS, |
2017
Conference Papers
Bousiou E. I., Mikropoulos P. N. and Zagkanas V. N.
2017 52nd International Universities Power Engineering Conference (UPEC), pp. 1-5, 2017 Aug
[Abstract][BibTex][pdf] Negative DC corona on conductor bundles is experimentally investigated in the coaxial configuration. The dependence of the corona characteristics, namely inception voltage and current, thus also inception field and power losses, on bundle radius and number of conductors in the bundle is assessed. The corona inception voltage of conductor bundles is highest at a bundle radius that corresponds to the minimum electric field strength at the conductor surface. The corona inception field strength of conductor bundles can be considered, with reasonable accuracy, as equal to that of the single conductor. Polarity effects on DC corona characteristics are assessed through comparisons with positive DC corona. For both polarities of applied voltage, the corona current can be accurately estimated through a modified Townsend quadratic formula using appropriate values for ion mobility. @inproceedings{BOUSIOU2017UPEC, | |
Bousiou E. I., Mikropoulos P. N. and Zagkanas V. N.
2017 52nd International Universities Power Engineering Conference (UPEC), pp. 1-5, 2017 Aug
[Abstract][BibTex][pdf] Corona discharge causes the attenuation and distortion of lightning and switching surges propagating along overhead transmission lines. Therefore, knowledge on surge corona characteristics is of great importance for insulation coordination studies. Most of the studies pertaining to corona effects on wave propagation on overhead line conductors neglect the fact that surge corona inception is stochastic in nature. This can be accounted for by applying the well-established theory of critical volume, allowing for statistical distributions of impulse corona inception characteristics to be estimated. In the present study the critical volume theory is applied to estimate impulse corona characteristics in the coaxial cylindrical electrode arrangement; this configuration is most commonly used in scale model experiments for assessing corona performance of overhead lines. The developed model accounts well for the effects of steepness of the wavefront of the impulse voltage on corona characteristics. The dependence of the estimated impulse corona inception probability distributions on the density and lifetime of negative ions is assessed and discussed. @inproceedings{BOUSIOU2017UPEC2, | |
Mavrikakis N.C. and Mikropoulos P.N.
2017 52nd International Universities Power Engineering Conference (UPEC), pp. 1-6, 2017 Aug
[Abstract][BibTex][pdf] Positive corona discharge activity along glass surfaces, in pure form and coated with room temperature vulcanized silicone rubber (RTV SIR), bridging a short needle-plane gap is investigated under positive ramp high voltages. The case or air alone was considered as reference. At applied voltages just sufficient for discharge inception up to values causing flashover, the discharge current and the associated temperature rise of the insulating surfaces were measured; thus, I-U characteristics were obtained. In the presence of an insulating surface the glow discharge is suppressed but streamer formation is favoured. Surface corona inception, stable streamer formation and flashover occur at significantly lower voltages than those obtained in the case of air alone. Surface temperature starts to increase above the ambient value when the stable streamer discharge is formed. During the stable streamer regime the insulating surface temperature is closely related to the streamer current. Both the maximum temperature reached immediately before flashover and the cumulative energy required for flashover are higher for the RTV SIR coated than pure glass surface. The temperature rise on the RTV SIR coated glass surface never exceeded ~10 oC, thus it cannot be considered as crucial in terms of thermal degradation of the material. @inproceedings{MAVRIKAKIS2017UPEC, |
2016
Journal Articles
Zacharias G. Datsios and Pantelis N. Mikropoulos
Electric Power Systems Research, 139, pp. 37-46, 2016 Jan
[Abstract][BibTex][pdf] Evaluation of the dielectric strength of transmission line insulation subjected to fast-front overvoltages is of major importance for the insulation coordination of overhead lines and connected substations. Among models proposed in literature for the prediction of the dielectric behavior of long air gaps and insulators under lightning overvoltages, leader development models (also called leader progression models) have a greater physical significance. These models consider the predischarge current flowing in the gap during the leader propagation phase preceding breakdown. However, this current is often disregarded for simplicity in fast-front overvoltage simulations. In this study the effects of simulating predischarge current on voltage–time characteristics of long air gaps and insulators, critical currents of overhead transmission lines as well as fast-front overvoltages arising at substations are investigated with the aid of ATP–EMTP. Including predischarge current in simulations, affecting the flashover characteristics of air gaps and insulators, results in slightly higher estimates of the minimum backflashover current of overhead transmission lines. However, it does not affect the estimated minimum shielding failure flashover current of overhead lines. In addition, simulating predischarge current may affect the overvoltages arising at substations due to shielding failure of the connected overhead lines depending on withstand or flashover of line insulation. In the case of backflashover the wavefront steepness and amplitude of the overvoltages are lower. Thus, predischarge current effects should be considered in insulation coordination of overhead transmission lines and substations. @article{DATSIOS2016EPSR, | |
Mikropoulos P. N. and Zagkanas V. N.
IEEE Transactions on Dielectrics and Electrical Insulation, 23, (3), pp. 1322-1330, 2016 Jun
[Abstract][BibTex][pdf] Characteristics of negative DC corona threshold inception in the coaxial cylindrical electrode arrangement are investigated based on experimental data and computations on avalanche growth considering a field and atmospheric conditions dependent photoelectron emission coefficient. A transition region between glow and streamer regimes of inception of the self-sustained corona discharge could be identified on the basis of space charge field effects on avalanche growth. Approximate expressions are introduced for satisfactorily estimating the negative corona inception field strength as interactively affected by conductor radius and atmospheric conditions. Polarity effects on corona inception characteristics are elucidated. The establishment of the glow corona generally occurs up to larger conductors for negative than positive corona; the opposite may also apply depending on atmospheric conditions. The inception field strength as well as its dependence on atmospheric conditions differs only slightly between negative and positive streamer corona; a critical avalanche number per unit length of ~108 cm-1 is required for both negative and positive streamer formation. @article{ZAGKANAS2016TDEI, |
2016
Conference Papers
Bousiou E. I., Mikropoulos P. N. and Zagkanas V. N.
2016 51st International Universities Power Engineering Conference (UPEC), pp. 1-5, 2016 Sep
[Abstract][BibTex][pdf] The salient characteristics of DC corona discharge on conductor bundles, namely corona inception voltage, corona current and the associated power losses, are experimentally investigated in the coaxial cylindrical electrode arrangement in air. The corona inception voltage increases markedly with increasing number of bundle conductors. There is an “optimum” bundle radius, increasing with number of bundle conductors, for which corona inception voltage attains its highest value. Except for relatively small bundle radii, the corona inception field of a conductor bundle is approximately equal to that of a single conductor. For a fixed applied voltage and a given bundle radius the corona current decreases as the number of bundle conductors increases. An empirical expression is proposed for the estimation of the corona current, therefore also power losses, as influenced by the applied voltage and the geometry of the conductor bundles. @inproceedings{BOUSIOU2016UPEC, | |
Datsios Zacharias G. and Mikropoulos Pantelis N.
2016 33rd International Conference on Lightning Protection (ICLP), pp. 1-4, 2016 Sep
[Abstract][BibTex][pdf] Soil ionization, that is, electrical discharges developing in ground, occurs due to the high electric field associated mainly with lightning currents. Despite having attracted a great interest among researchers from the beginning of the 20th century, soil ionization is far from being completely understood owing to the complex nature and structure of soil. This study investigates breakdown of several dry natural silica sand samples in a quasi-uniform electric field electrode arrangement under standard lightning impulse voltages. The dependence of sand breakdown gradient and time delay on the grain size is assessed. Corona inception, thus also breakdown, is favored by the sand grains as compared with the case of air alone. @inproceedings{DATSIOS2016ICLP, | |
Zacharias G. Datsios, Pantelis N. Mikropoulos, Thomas E. Tsovilis, and Sofia I. Angelakidou
International Colloquium on Lightning and Power Systems, Bologna, Italy, 2016 Jun
[Abstract][BibTex][pdf] Estimation of the minimum lightning current causing backflashover of line insulation is of great importance for the calculation of the backflashover rate of overhead transmission lines. The minimum backflashover current can be estimated through simplified expressions or, more accurately, through computer simulations. The latter allow for the detailed modelling of the transmission line components as well as of the complex phenomena involved in backflashover, such as soil ionization around tower ground electrodes and flashover of line insulation under fast-front overvoltages of non-standard waveshape. In this work the minimum backflashover current of typical 150 kV and 400 kV overhead lines of the Hellenic transmission system is estimated through ATP-EMTP simulations by neglecting or considering soil ionization around the concentrated ground electrodes of transmission towers; the phase angle of the power frequency voltage and the low current and low frequency ground resistance are considered as parameters. It is shown that the peak of the limiting lightning overvoltage causing backflashover is found approximately equal 1.8 times the basic insulation level of the overhead line for both tower grounding system modelling approaches; this corresponds to a minimum average gradient required for backflashover of ~720 kV/m. The minimum backflashover current varies almost linearly with the reciprocal of the power frequency ground resistance. A new expression is proposed for the calculation of the BFR of overhead transmission lines considering only those lightning strokes to shield wires with prospective current higher than the minimum backflashover current; this is not the case for the traditional BFR expression of CIGRE. The latter yields lower BFR estimates especially for low power frequency ground resistance values. @conference{Datsios2016ICLPS, | |
Khelil D., Bouazabia S. and Mikropoulos PN.
2016 IEEE International Conference on High Voltage Engineering and Application (ICHVE), pp. 1-4, 2016 Sep
[Abstract][BibTex][pdf] In this paper, the influence of the height and position of a grounded object on the interception probability of a protective rod is experimentally investigated under standard lightning impulse voltages of positive polarity. By using a 77 cm energized rod-plane gap the interception probability of a protective rod of different heights is calculated when putting another object on the plane. It was found that the discharge interception probability of the protective rod is strongly affected by the height and position of the grounded object. The time to breakdown and the instantaneous breakdown voltage are two parameters deduced from experimental tests. It was noted that the discharge makes more time to occur when moving the protection far from the energized rod. The insertion of another rod reduces the time to breakdown. The discharge always happens during the tail of the applied impulse voltage making that the variation of the instantaneous breakdown voltage decreases with increasing the separation distance between rods. @inproceedings{MIKROPOULOS2016ICHVE, |
2015
Journal Articles
Pantelis N. Mikropoulos and Vasileios N. Zagkanas
IEEE Trans. on Dielectrics and Electrical Insulation, 22, (1), pp. 278-286, 2015 Feb
[Abstract][BibTex][pdf] The conditions for threshold inception of positive DC corona in the coaxial cylindrical electrode arrangement are investigated. The establishment of the self-sustained corona discharge in glow or streamer form, as influenced by conductor radius and atmospheric conditions, is evaluated through detailed computations that consider space charge field effects on avalanche growth. The salient corona characteristics at threshold inception are assessed and discussed through comparisons with literature experimental data. In a wide range of inner conductor radius and atmospheric conditions corona initiates in streamer form when a critical avalanche number per unit length of about 108 cm-1 is attained. Accurate formulation of the critical field strength required to sustain ionization allowed for the derivation of approximate expressions accounting well for the interactive effects of conductor radius and atmospheric conditions on the corona inception field strength in both glow and streamer regimes. @article{Mikropoulos2015TDEI, |
2015
Conference Papers
Zacharias Datsios and Pantelis N. Mikropoulos
19th International Symposium on High Voltage Engineering, Pilsen, Czech Republic, 2015 Aug
[Abstract][BibTex][pdf] The evaluation of the lightning performance of overhead transmission lines necessitates the estimation of the minimum lightning current causing backflashover of line insulation. In the present study an assessment is made on the effects of transmission tower modelling upon the minimum backflashover current of typical 150 kV and 400 kV overhead lines with the aid of ATP-EMTP simulations. Several tower models, classified in three categories namely vertical lossless single-phase frequency-independent distributed parameter line models, multiconductor models and multistory models, were employed in simulations. Simulation results indicate that tower modelling, affecting the computed overvoltages arising across line insulators, influences the minimum backflashover current and the phase insulator associated with the latter. These effects are greatly dependent on tower ground resistance as well as upon the configuration of the transmission line. @conference{Datsios2015, | |
Nikolaos Mavrikakis, K. Siderakis, Pantelis N. Mikropoulos and N. Katsarakis
19th International Symposium on High Voltage Engineering, pp. 253, Pilsen, Czech Republic, 2015 Aug
[Abstract][BibTex][pdf] Condition assessment results are presented for a field-aged 150 kV HTV SIR suspension insulator following its flashover due to bird nesting activity. The insulator, equipped with arcing horns, was operated for 10 years in a coastal transmission network under heavy environmental pollution. In order to evaluate flashover effects on insulator housing, several macroscopic and microscopic diagnostic techniques were employed including visual inspection, hydrophobicity classification, Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray (EDX) analysis. Arcing affected the morphological structure and elemental composition, thus also hydrophobicity of the housing surface in proximity to arcing horns. The protection offered by the arcing horns together with the synthesis of the insulator housing material resulted in flashover deteriorating effects solely restricted to the upper surface layer of the housing. However, arcing caused excessive damages to the arcing horns. In addition to flashover, ageing and environmental pollution effects were detected on the insulator housing and further analysed. @conference{Mavrikakis2015ISHVE, | |
Pantelis N. Mikropoulos, Thomas Tsovilis and V.S Victoratos
19th International Symposium on High Voltage Engineering, Pilsen, Czech Republic, 2015 Aug
[Abstract][BibTex][pdf] Estimation of lightning incidence to vertical slender structures, such as telecommunication towers and wind turbines, is a formidable task. It is, however, of great importance in terms of reliability and insulation coordination of the connected power systems. The present study introduces a general methodology for the estimation of downward flashes to vertical slender structures on the basis of the statistical and several electrogeometric and generic lightning attachment models. The methodology has been incorporated in a user friendly mobile application, called TLIC. Lightning incidence calculations show that the relevant IEC 62305 procedure yields results deviating significantly from those obtained according to several lightning attachment models. It also, implementing an oversimplified geometrical approach, does not account for the dependence of lightning incidence on lightning peak current distribution and lightning interception probability distribution. With the aid of TLIC mobile application the effects of structure height, lightning peak current distribution and, based on the statistical model, lightning interception probability distribution are easily quantified. TLIC can be a useful tool for lightning risk assessment of vertical slender structures. @conference{Mikropoulos2015ISHVE, |
2014
Journal Articles
Zacharias Datsios, Pantelis N. Mikropoulos and Thomas Tsovilis
Electric Power Systems Research, 113, pp. 141-150, 2014 Aug
[Abstract][BibTex][pdf] ATP-EMTP simulations are performed to estimate the minimum shielding failure current causing flashover in overhead transmission lines with operating voltage in the range of 66 kV up to 735 kV. This critical current, affecting shielding failure flashover rate, is of great importance for assessing the insulation coordination of overhead transmission lines and the connected substations. The minimum shielding failure current causing flashover of line insulation is highly dependent upon insulator string flashover modelling and, also, markedly higher than that calculated according to the relevant IEEE Std 1243-1997 simplified expression. A modification of the latter is suggested by using multiplication factors of 1.5 and 1.65 for first and subsequent lightning strokes, respectively, so as to account for the increased dielectric strength of line insulator strings under non-standard lightning overvoltage surges. Alternatively, the critical currents can be respectively estimated by using average negative breakdown gradients per unit length of insulator string of 680 kV/m and 750 kV/m. The shielding failure flashover rate of the overhead transmission lines, being greatly influenced by insulator string flashover modelling, is lower than that obtained based on the critical current according to IEEE Std 1243-1997. @article{Datsios2014, | |
Pantelis N. Mikropoulos, Thomas Tsovilis and Sotiria G. Koutoula
IEEE Trans. on Power Delivery, 29, (6), pp. 2570-2579, 2014 Jun
[Abstract][BibTex][pdf] Data on unscheduled electric service interruptions in an extended distribution network (20/0.4 kV) were analyzed in order to examine the causes contributing to distribution substation failures. A distribution substation feeding a Global System for Mobile Communications base station experienced the highest service interruption rate due to transformer sustained failures, the vast majority of which were categorized as lightning related. Thus, with the aid of detailed Alternate Transients Program-Electromagnetic Transients Program simulations, an investigation on the overvoltages surges impinging on the distribution transformer due to direct lightning strokes to the connected MV overhead line and to the nearby telecommunication tower has been made. Transformer failures are caused solely by fast-front overvoltages exceeding the basic insulation level of the LV side of the transformer. This is substantiated by the good agreement between estimated and reported transformer failure rates. The safe operation of the distribution transformer necessitates the installation of surge protective devices at its low-voltage terminals, also overcoming the need for extremely low values of telecommunication tower grounding resistance. Additional line surge arresters should be installed at the penultimate wood pole of the connected overhead line which, besides improving the lightning performance of the transformer, significantly increases the reliability of the distribution substation. @article{Mikropoulos2014, |
2014
Conference Papers
Zacharias Datsios and Pantelis N. Mikropoulos
2014 International Conference on Lightning Protection (ICLP), pp. 979-985, 2014 Nov
[Abstract][BibTex][pdf] Evaluation of the dielectric strength of transmission line insulation subjected to fast-front overvoltages is of major importance for the insulation coordination of overhead lines and the connected substations. Among models proposed in literature for the prediction of the dielectric behavior of air gaps and insulators, leader development models have a greater physical significance. In this study several leader development models are implemented in a new model in ATP-EMTP using MODELS simulation language. The new model is solved simultaneously with the rest of simulated system interacting with it as a circuit element; this is accomplished by using the model with a type-94 circuit component. The developed model is verified against literature data referring to breakdown of long air gaps. Shielding failure and backflashover simulations are conducted for a 150 kV and a 400 kV overhead transmission line to demonstrate the effects of modeling of the predischarge current flowing during leader propagation phase on the estimated critical currents. @conference{6973265, | |
Zacharias Datsios, Pantelis N. Mikropoulos, Andreas Teneketzoglou and Dimitrios Tzikas
49th Universities Power Engineering Conference, pp. 1-6, IEEE, Cluj-Napoca, Romania, 2014 Sep
[Abstract][BibTex][pdf] The design of the grounding configuration for the metal fence of a high voltage installation is important as the outside perimeter of the fence is accessible to the general public. In this work the safety provided by several fence grounding techniques commonly used in high voltage installations is evaluated for a 150/20 kV air insulated substation, a 400 kV step-up GIS substation and a large scale photovoltaic power station with the aid of grounding analysis software. A safe and cost-efficient fence grounding design depends on ground fault characteristics, soil conditions, installation area, distance between the fence and grounding grid as well as on the size and geometry of the latter. @conference{Datsios2014UPEC, | |
Nikolaos Mavrikakis, K. Siderakis and Pantelis N. Mikropoulos
49th Universities Power Engineering Conference, pp. 1-6, IEEE, Cluj-Napoca, Romania, 2014 Sep
[Abstract][BibTex][pdf] Evaluation of the field performance of composite insulators is essential for maintaining the desired levels of reliability in power networks. Field performance of composite insulators depends on many factors, including the insulator design, material quality and service conditions experienced. The most critical part of the composite insulator is its external housing, usually made of silicone rubber having the advantage of recovering its hydrophobic properties in polluted conditions. Thus, condition assessment of the hydrophobic properties of the housing material especially under erosion and tracking processes is of major importance. In this study performance evaluation of the housing material of 150 kV field-aged silicone rubber insulators is carried out through physical, electrical and material analysis techniques. The hydrophobic properties of the housing material were found degraded to a different extent between field-aged insulators due to differences in material structure and pollution conditions. Hydrophobicity can be better assessed if the relevant diagnostic techniques are also applied after inclined plane tests. @conference{Mavrikakis2014UPEC, | |
Pantelis N. Mikropoulos, Thomas Tsovilis and Aikaterini S. Pori
32nd International Conference on Lightning Protection, pp. 1212-1216, Shanghai, China, 2014 Oct
[Abstract][BibTex][pdf] The lightning performance of overhead distributions lines affects significantly the reliability of distribution power network. Lightning-related flashover of line insulation is caused by direct and nearby strokes. This paper presents a generalized methodology for the estimation of the flashover rate of overhead distribution lines that considers several lightning attachment and coupling models. Results of the proposed methodology are discussed and compared with A. J. Eriksson\'s field observations. Based on the consistency between estimated values and field data suggestions are made for the appropriate selection of lightning attachment and coupling models for the evaluation of the lightning performance of distribution lines. @conference{Mikropoulos2014ICLP, |
2013
Journal Articles
Pantelis N. Mikropoulos and Thomas Tsovilis
IEEE Trans. on Dielectrics and Electrical Insulation, 20, (1), pp. 202-211, 2013 Feb
[Abstract][BibTex][pdf] Lightning is a major cause of distribution line outages affecting reliability of power supply thus, consequently, resulting in economic losses. The lightning performance of overhead distribution lines is associated with line insulation flashover due to direct and nearby lightning strokes. The present paper introduces a statistical method for the estimation of the flashover rate of overhead distribution lines. The proposed method, implementing a recently introduced statistical lightning attachment model and the simplified coupling model suggested by the IEEE Std. 1410:2011, yields a range for the expected flashover rate of distribution lines associated with lightning interception probability distribution of the line conductors. It also provides the means to easily quantify the effects of line parameters, soil resistivity, shielding of nearby objects and lightning crest current distribution on lightning performance of distribution lines. Results of the statistical method, discussed and compared with that obtained by the IEEE Std. 1410:2011, are in close consistency with field data. @article{Mikropoulos2013TDEI, |
2013
Conference Papers
Zacharias Datsios, Pantelis N. Mikropoulos, Z. Politis, A.G Kagiannas and Thomas Tsovilis
18th International Symposium on High Voltage Engineering, Seoul, Korea, 2013 Aug
[Abstract][BibTex][pdf] The effects of the length of the surge arrester connection conductors on the lightning surges impinging on a typical wood pole-mounted 50 kVA, 20/0.4 kV transformer of the Hellenic distribution system are investigated through detailed ATP-EMTP simulations. By considering both first and subsequent direct lightning strokes to a connected overhead distribution line, the effectiveness of the common practice transformer protection scheme and of an alternative one utilizing shorter surge arrester connection conductors in suppressing fast-front overvoltages was evaluated. A shorter length of the surge arrester connection conductors results in a reduction in the amplitude of the overvoltages arising at the medium-voltage terminals of the transformer and in a slower rate of increase of the overvoltage amplitude with lightning return-stroke current. The overvoltages transferred to the low-voltage terminals of the transformer are practically not affected by the length of the surge arrester connection conductors. Protection against transferred overvoltages was provided by surge protective devices installed at the low-voltage terminals of the transformer. By utilizing shorter surge arrester connection conductors the transformer failure rate, estimated through risk assessment, is reduced by approximately 11%. @conference{Datsios2013ISHVE, | |
Pantelis N. Mikropoulos and Thomas Tsovilis
18th International Symposium on High Voltage Engineering, Seoul, Korea, 2013 Aug
[Abstract][BibTex][pdf] A methodology for the estimation of lightning incidence to free standing Early Streamer Emission (ESE) rods is introduced. The proposed method implements a general expression for the equivalent interception radius, which considers the ESE rod height, length of the triggered upward connecting leader and the lightning peak current distribution. Lightning incidence results are discussed and compared with that referring to conventional rods obtained according to Eriksson’s method and the statistical lightning attachment model. It is shown that the lightning interception efficiency of an ESE rod, even assuming an earlier initiated upward connecting leader, is similar to that of a conventional rod when considering a realistic value for the progression velocity of the upward connecting leader. The present work provides the means to easily evaluate the lightning interception efficiency of ESE rods through comparisons with available field data. @conference{Mikropoulos2013ISHVE, | |
Pantelis N. Mikropoulos and Vasileios Zagkanas
48th Universities Power Engineering Conference, pp. 1-5, Dublin, Ireland, 2013 Sep
[Abstract][BibTex][pdf] The effect of stranded conductor geometry on the salient characteristics of DC corona, namely corona inception voltage, corona conductance and the associated power losses is experimentally investigated in the coaxial cylindrical electrode arrangement in air. The number of strands of the conductor has a greater impact on the characteristics of positive than negative corona. Under conditions of high absolute humidity, corona conductance, thus also losses depending on conductor geometry can be higher for positive than negative corona. Breakdown, only slightly affected by stranded conductor geometry, is greatly facilitated by the space charge associated with multiple coronas occurring along the energised conductor. An empirical expression for the estimation of the irregularity factor of overhead transmission line conductors is proposed, accounting well for the effects of stranded conductor radius, stranding ratio and relative air density. @conference{mikropoulos2013UPEC, | |
Pantelis N. Mikropoulos and Vasileios Zagkanas
18th International Symposium on High Voltage Engineering, Seoul, Korea, 2013 Aug
[Abstract][BibTex][pdf] The effect of the steepness of overvoltage surges propagating along overhead transmission lines on corona characteristics is of great importance for insulation coordination studies. Corona inception voltage on line conductors under fast-front overvoltages is commonly estimated through Peek’s empirical formula, which however was obtained for steady or slow-varying electric fields. In the present study experimental results on impulse corona in the coaxial cylindrical electrode arrangement in air are presented, with the wavefront duration and the polarity of the applied voltage as parameters. Corona discharge has been investigated at both threshold and overstress conditions by obtaining inception probability distributions and U-t curves. An empirical expression describes well the experimentally derived U-t characteristic. A modified Peek’s formula is proposed taking into account the effect of the steepness of the applied impulse voltage on corona inception field strength. The integration method, commonly used for the estimation of the impulse breakdown voltage of non-uniform air gaps, has been implemented to estimate the corona inception time and voltage; a very good agreement exists between calculated and measured values. @conference{Mikropoulos2013Zagkanas, |
2012
Journal Articles
Petros Mavroidis, Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
IEEE Trans. on Dielectrics and Electrical Insulation, 19, (2), pp. 632-640, 2012 Apr
[Abstract][BibTex][pdf] The impulse behavior of composite short rod-plane air gaps with a dielectric-covered rod under positive lightning and switching impulse voltages is investigated, by monitoring the electric field strength at the earthed plane, by still photographs of corona discharges and through electric field computations. Experiments were performed in normal laboratory air at pressure around 0.1 MPa, temperatures in the range 19 to 28°C and absolute and relative humidity varied naturally between 11-21 g/m3 and 60-90%, respectively. Breakdown probability distributions were obtained for composite gaps with a dielectric cover made of either PTFE or epoxy resin and for simple air gaps with a bare rod. Also, basic characteristic parameters of coronas preceding breakdown in composite gaps, namely initial corona in the vicinity of the covering tip, surface coronas emerging along the dielectric cover and developing mainly in air, and secondary corona in the vicinity of the cover upper end, were measured. Surface corona development is greatly affected by initial corona growth and facilitates secondary corona inception. Breakdown, occurring at higher voltages for composite gaps, is closely related with the secondary corona inception; a similar dependence upon impulse waveshape and cover material was seen to exist. At breakdown, the spark channel bridges the gap that includes the dielectric cover length. The spark channel develops either along the cover surface or partly or solely in free air, being affected by surface corona development. @article{Mavroidis2012TDEI, | |
Pantelis N. Mikropoulos and Thomas Tsovilis
IEEE Trans. on Dielectrics and Electrical Insulation, 19, (6), pp. 2155-2164, 2012 Dec
[Abstract][BibTex][pdf] Shielding failure of overhead transmission lines is a major cause of transmission system outages, affecting reliability of power supply and resulting in economic losses. In this study the shielding performance of overhead transmission lines is evaluated with the aid of general expressions, derived by implementing in shielding analysis different categories of lightning attachment models. Thus, the effects of lightning attachment model, transmission line parameters and lightning crest current distribution on shielding failure rate of overhead transmission lines have been quantified. Alternative approaches to that proposed by IEEE Std 1243 for assessing the shielding performance of transmission lines, including computer simulations of lightning attachment, are evaluated. Shielding failure rate results are discussed and compared with field data reported in literature. For typical overhead transmission lines, an upper limit of the estimated shielding failure rate is 0.4% of the rate of lightning strokes to the line. More and reliable field data is needed in order to evaluate lightning attachment models with respect to the lightning performance of overhead transmission lines. @article{Mikropoulos2012TDEI, |
2012
Conference Papers
Zacharias Datsios, Pantelis N. Mikropoulos and Thomas Tsovilis
31st International Conference on Lightning Protection, pp. 1-5, Vienna, Austria, 2012 Sep
[Abstract][BibTex][pdf] ATP-EMTP simulations are performed to estimate the minimum shielding failure current causing flashover in 150 kV and 400 kV double-circuit overhead lines of the Hellenic transmission system. This critical current is of great importance for estimating the shielding failure flashover rate and assessing the insulation coordination of overhead transmission lines. It is shown that the minimum shielding failure current causing flashover varies significantly among the insulator string flashover models employed in simulations, which include volt-time curves and leader development models. The minimum shielding failure current causing flashover calculated on the basis of the relevant IEEE Std is significantly lower than that obtained through ATP-EMTP simulations. The computed shielding failure flashover rate of the 150 kV and 400 kV overhead transmission lines is greatly affected by the method adopted for the estimation of the minimum shielding failure current causing flashover. @conference{datsios2012, | |
Zacharias Datsios and Pantelis N. Mikropoulos
MedPower 2012, pp. 1-6, Cagliari, Italy, 2012 Oct
[Abstract][BibTex][pdf] A safe and cost-efficient grounding system design of a 3 MWp photovoltaic power station according to IEEE Std 80-2000 is presented. Grounding analysis is performed by considering the metal parts of the photovoltaic panel arrays foundations as auxiliary ground electrodes. Utilizing also horizontal ground conductors, required solely for the interconnections of the metal support structures of the photovoltaic panel arrays, both safety and cost-efficiency in grounding system design have been achieved. It is shown that in large-scale photovoltaic power stations where the metal parts of the panel arrays foundations are concrete encased the concrete resistivity is not an important parameter in evaluating the safety performance of the grounding system. @conference{datsios2012MP, | |
Zacharias Datsios, Pantelis N. Mikropoulos and Thomas Tsovilis
46th Universities Power Engineering Conference, pp. 1-5, VDE, Soest, Germany, 2012 Sep
[Abstract][BibTex][pdf] Accurate modeling of line insulation flashover is very important in evaluating the fast-front surges arising at overhead transmission lines and impinging on the connected substations. A new ATPDraw object, called ISF, has been developed with the aid of which insulator string flashover is modeled on the basis of several flashover models from literature. The ISF object was employed in ATP-EMTP simulations of a 150 kV GIS substation. The computed backflashover surges impinging on the substation vary considerably among the insulator string flashover models employed in simulations. The ISF object is a useful tool within the ATP-EMTP environment for insulation co-ordination studies. The effects of insulator string flashover modeling on backflashover surges arising at overhead transmission lines and impinging on the connected substations can be easily quantified. @conference{Datsios2012UPEC, | |
Pantelis N. Mikropoulos, Thomas Tsovilis and P.P Papaioannou
2012 47th International Universities Power Engineering Conference (UPEC), pp. 1-5, London, UK, 2012 Sep
[Abstract][BibTex][pdf] A useful application software for the evaluation of the lightning performance of overhead distribution lines is introduced. The SM-LPDL software has been developed in Matlab, runs as a Microsoft Windows application and features a user-friendly graphics interface. It incorporates a statistical method for the estimation of the flashover rate of overhead distribution lines, implementing a recently introduced statistical lightning attachment model and the simplified coupling model suggested by the IEEE Std. 1410:2011. The SM-LPDL yields a range for the expected flashover rate of a distribution line associated with the lightning interception probability distribution of the line conductors. It allows for the easy quantification of the effects of line parameters, soil resistivity, surge arresters, shielding of nearby objects and lightning crest current distribution on lightning performance of distribution lines. SM-LPDL results are discussed and compared with those obtained by the recently released IEEE Std. 1410:2011. @conference{Mikropoulos2012, | |
Pantelis N. Mikropoulos, Thomas Tsovilis and P.P Papaioannou
47th Universities Power Engineering Conference, pp. 1-5, London, United Kingdom, 2012 Sep
[Abstract][BibTex][pdf] A useful application software for the evaluation of the lightning performance of overhead distribution lines is introduced. The SM-LPDL software has been developed in Matlab, runs as a Microsoft Windows application and features a user-friendly graphics interface. It incorporates a statistical method for the estimation of the flashover rate of overhead distribution lines, implementing a recently introduced statistical lightning attachment model and the simplified coupling model suggested by the IEEE Std. 1410:2011. The SM-LPDL yields a range for the expected flashover rate of a distribution line associated with the lightning interception probability distribution of the line conductors. It allows for the easy quantification of the effects of line parameters, soil resistivity, surge arresters, shielding of nearby objects and lightning crest current distribution on lightning performance of distribution lines. SM-LPDL results are discussed and compared with those obtained by the recently released IEEE Std. 1410:2011. @conference{Mikropoulos2012UPEC, | |
Pantelis N. Mikropoulos, Vasileios Zagkanas and T.S. Koustoulidis
47th Universities Power Engineering Conference, pp. 1-6, London, United Kingdom, 2012 Sep
[Abstract][BibTex][pdf] Knowledge on the effects of air density on corona discharge is of great importance for many practical applications, including overhead transmission lines. In the present study the salient characteristics of both positive and negative DC corona on 7-stranded conductors, namely the corona inception voltage, corona current and the associated power losses, are experimentally investigated in the coaxial cylindrical electrode arrangement under variable air density. Theoretical predictions of the corona current and losses are in good agreement with experimental values for an ion mobility decreasing with relative air density according to a power law, the rate of decrease being higher for negative than positive ions. Irregularity factors for the 7-stranded conductors have been obtained based on electric field simulations and Peek\'s formula for smooth conductors. Logarithmic expressions, describing well the dependence of the irregularity factor on the product of relative air density and conductor radius, allow for a satisfactory estimation of the corona inception field strength of 7-stranded conductors. @conference{Mikropoulos2012Zagkanas, |
2011
Journal Articles
Lazaros Lazaridis and Pantelis N. Mikropoulos
IEEE Trans. on Dielectrics and Electrical Insulation, 18, (3), pp. 745-754, 2011 Jul
[Abstract][BibTex][pdf] Positive impulse flashover along smooth cylindrical insulating surfaces bridging a short rod-plane gap under standard lightning and switching impulse voltages is investigated under variable absolute humidity and by regarding the case of air alone as reference. Flashover is closely related to predischarge phenomena, specifically secondary corona under lightning impulses and corona streamers arrival at the earthed plane under switching impulse voltages. Under lightning impulses the dielectric strength of the gap is highest for air alone and decreases with material permittivity; the opposite is true, although less marked, under switching impulse voltages. Flashover voltage increases with absolute humidity, this being more pronounced for switching than lightning impulse voltages. The inhibitory effect of humidity on flashover, mainly determined by the trajectory of the spark channel with respect to the insulating surface, is similar to that observed in air alone where flashover occurs away from the insulating surface but reduced where the discharge develops close to the insulating surface. For insulating arrangements where at flashover the spark channel adheres to the insulating surface the IEC 60060-1:1989 atmospheric conditions correction procedure should be optimized by considering a reduced humidity correction factor. @article{Lazaridis2011, |
2011
Conference Papers
Zacharias Datsios, Pantelis N. Mikropoulos and Thomas Tsovilis
International Conference on Power Systems Transients, Delft, The Netherlands, 2011 Jun
[Abstract][BibTex][pdf] Tower grounding system accurate modeling is very important in evaluating the backflashover surges arising at overhead transmission lines and impinging on the connected substations. A new ATPDraw object, called TGIR, has been developed with the aid of which a concentrated tower grounding system can be represented on the basis of several tower grounding system models. The TGIR object was employed in ATP-EMTP simulations of a 150 kV GIS substation. The computed backflashover surges impinging on the substation vary considerably among the tower grounding system models employed in simulations, as a result of the variability in the grounding impulse resistance. The TGIR object is a useful tool within the ATP-EMTP environment for insulation co-ordination studies; the effects of tower grounding system modeling on backflashover surges arising at overhead transmission lines and impinging on the connected substations can be easily quantified. @conference{Datsios2011ICPST, | |
Zacharias Datsios, Pantelis N. Mikropoulos and Thomas Tsovilis
International Conference on Power Systems Transients, 2011 Jun
[Abstract][BibTex][pdf] The maximum shielding failure current of overhead transmission lines is an important parameter in evaluating the shielding performance of the lines and performing insulation coordination studies of the connected substations. A new ATPDraw object has been developed, by using MODELS language, that easily generates the maximum shielding failure current of overhead transmission lines, with amplitude and waveshape depending on line geometry and selected lightning attachment model. The new object, called MSFC, was employed in ATP-EMTP simulations of a 150 kV GIS substation. The computed shielding failure surges impinging on the substation, being dependent upon maximum shielding failure current, vary considerably among lightning attachment models. The MSFC object is a useful tool within the ATP-EMTP environment in assessing the shielding failure surges arising at overhead transmission lines and impinging on the connected substations. Shielding failure current of overhead transmission lines generated through an ATPDraw object (PDF Download Available). Available from: https://www.researchgate.net/publication/230817373_Shielding_failure_current_of_overhead_transmission_lines_generated_through_an_ATPDraw_object [accessed Feb 05 2018]. @conference{Datsios2011ICPSTMikropoulos, | |
Pantelis N. Mikropoulos and Vasileios Zagkanas
17th International Symposium on High Voltage Engineering, Hannover, Germany, 2011 Aug
[Abstract][BibTex][pdf] Corona discharge has attracted much interest among researchers as it has a lot of applications in industry and a number of effects on power systems. Corona inception in the coaxial cylindrical electrode arrangement, which finds many practical applications, depends on the electric field strength around the inner conductor and on atmospheric conditions. In the present study a new model for positive corona inception in a steady or slowly-varying electric field is presented. The model, implementing streamer criterion, assumes that an equivalent electron avalanche develops towards the anode by virtue of ionization by collision and photoionization in an electric field distorted by the avalanche space charge. Based on a great amount of literature experimental data, a new empirical expression for the estimation of positive corona inception field strength has been derived. The formulation of a photoionization coefficient as a function of inner conductor radius and relative air density enabled the investigation of the effects of the latter parameters on the basic characteristics of the avalanche at corona inception, namely critical avalanche length, radius, number and electron density. @conference{Mikropoulos2011ISHVE, | |
Pantelis N. Mikropoulos and Thomas Tsovilis
17th International Symposium on High Voltage Engineering, Hannover, Germany, 2011 Aug
[Abstract][BibTex][pdf] Lightning is a major cause of distribution line outages affecting reliability of power supply thus, consequently, resulting in economic losses. Line insulation flashover in overhead distribution lines may be caused by overvoltages associated with direct or nearby lightning strokes. In this paper a statistical method for the estimation of the induced-voltage flashover rate of unshielded overhead distribution lines due to nearby strokes is introduced. The proposed method yields a range for the expected inducedvoltage flashover rate of the line, by considering, besides line parameters and lightning crest current distribution, the lightning interception probability distribution of the line phase conductors. Results of the statistical method are compared with those yielded by the methods suggested in IEEE Std. 1410:2004 and its recent revision IEEE Std. 1410:2011; a satisfactory agreement is shown to exist. An application of the statistical method to a typical 20 kV unshielded line of the Hellenic distribution system is made. A statistical method for the estimation of induced-voltage flashover rate of unshielded overhead distribution lines (PDF Download Available). Available from: https://www.researchgate.net/publication/235986109_A_statistical_method_for_the_estimation_of_induced-voltage_flashover_rate_of_unshielded_overhead_distribution_lines [accessed Feb 05 2018]. @conference{Mikropoulos2011Tsovilis, |
2010
Journal Articles
Lazaros Lazaridis and Pantelis N. Mikropoulos
IEEE Trans. on Dielectrics and Electrical Insulation, 17, (5), pp. 1585-1591, 2010 Oct
[Abstract][BibTex][pdf] Negative impulse flashover along insulating surfaces bridging a short rod-plane gap is investigated under variable humidity. The specimens, cylindrical in shape and with a smooth surface, were made of PTFE, silicone-rubber, nylon and glazed porcelain and were bridging the gap, which was stressed by standard lightning and switching impulse voltages. Breakdown probability distributions were obtained and the breakdown voltage and time to breakdown were measured. The gap was overstressed by applying voltages higher than that causing 100% breakdown so as to study the effects of the applied peak voltage on breakdown characteristics. When breakdown occurs over an insulating surface the breakdown voltage is significantly lower compared to that obtained for air alone, especially at lower breakdown probabilities and under switching impulse voltages. It is also lower for lightning than switching impulse voltages, this being less marked with increasing material permittivity. Breakdown is closely related to negative corona growth. The effect of absolute humidity on breakdown voltage is minimal. The IEC atmospheric conditions correction procedure yields satisfactory results when breakdown occurs both in air alone and along an insulating surface. @article{Lazaridis2010, | |
Lazaros Lazaridis and Pantelis N. Mikropoulos
IET Sci. Meas. Technol, 4, (2), pp. 71-83, 2010 Mar
[Abstract][BibTex][pdf] The salient characteristics of the predischarge phenomena and flashover along cylindrical insulating surfaces bridging a short rod-plane gap under positive lightning impulse voltages were measured in a wide range of applied peak voltages. Materials used in the investigation were polytetrafluoroethylene (PTFE), silicone-rubber, nylon and glazed porcelain; the case of air alone was regarded as reference. Corona inception is favoured by the presence of an insulating surface, this being more evident for materials of high permittivity and for initial than secondary corona. At relatively high applied voltages, the initial corona characteristics are directly related to the field enhancement at the tip of the stressed electrode. However, near threshold inception conditions there is a marked reduction of the inception field with material permittivity; an assisting mechanism of initiatory electron production was put forward to explain this behaviour. Initial corona streamers require higher applied voltages to arrive at the earthed plane when propagating along an insulating surface than in air alone. Flashover, closely related to secondary corona characteristics, is always preceded by continuous corona growth, occurring mainly in free air away from the insulating surface because of possible positive surface charge deposition by the initial corona; the latter is characteristic for polymeric insulating surfaces. There is a reduction of the dielectric strength of the gap in the presence of an insulating surface, more pronounced for higher material permittivity, related to the facilitating action of the field enhancement close to the rod tip on continuous corona growth preceding flashover. @article{Lazaridis2010IET, | |
Petros Mavroidis, Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
IET Sci. Meas. Technol, 4, (2), pp. 52-61, 2010 Mar
[Abstract][BibTex][pdf] The breakdown mechanism of dielectric–covered rod/plane air gaps under positive lightning impulse voltages is investigated. Several gap lengths, varying between 2.5 and 15?cm, were employed and the simple air gaps were regarded as reference. The basic characteristics of coronas, namely inception time and voltage, were measured at applied voltages just sufficient for their inception up to voltages causing breakdown. Multiple level tests were conducted; thus, corona inception and breakdown probability distributions were obtained and time to breakdown was measured at several voltage levels. Interpretation of the results was made based on oscillograms of the electric field strength at the earthed plane, which was monitored through a capacitive probe, geometric field calculations and still photographs of the discharge at breakdown. In the dielectric-covered rod/plane gaps, breakdown occurs at higher applied voltages as a result of increase in both corona inception voltages and discharge path. The development of the discharge depends on the electric field distribution as modified by both space and surface charges associated with coronas preceding breakdown. Surface charge accumulation may affect the discharge path at breakdown. @article{Mavroidis2010, | |
Pantelis N. Mikropoulos and Thomas Tsovilis
IET Generation, Transmission and Distribution, 4, (12), pp. 1299-1313, 2010 Dec
[Abstract][BibTex][pdf] The maximum shielding failure current of overhead transmission lines is an important parameter in evaluating the shielding performance of the lines and in insulation coordination of substations. General expressions for the estimation of the maximum shielding failure current of transmission lines, derived by employing several lightning attachment models in shielding analysis, are presented. An application to typical 110?kV up to 1150?kV overhead transmission lines shows that there is a great variability in maximum shielding failure current among lightning attachment models. The importance of maximum shielding failure current in insulation coordination of substations is demonstrated with the aid of alternative transients program-electromagnetic transients program (ATP-EMTP) simulations. The computed overvoltages impinging on 150 and 400?kV gas insulated system (GIS) substations because of shielding failure of the incoming overhead transmission lines, being dependent upon shielding failure current, vary with the lightning attachment model employed in shielding analysis of the lines. Implementation of the electrogeometric model adopted by IEEE Std 1243:1997 in shielding analysis imposes high requirements on protection of the substations against incoming shielding failure surges. @article{Mikropoulos2010, | |
Pantelis N. Mikropoulos and Thomas Tsovilis
"Interception probability and proximity effects: Implications in shielding design against lightning"
IEEE Trans. on Power Delivery, 25, (3), pp. 1940-1951, 2010 Mar
[Abstract][BibTex][pdf] The effects of a neighboring object on the interception probability distribution of an air terminal are investigated through scale model experiments. The discharge interception probability of an earthed rod is influenced by the presence of a neighboring shorter one when both inserted in a rod-plane gap. This depends on the polarity of the impulse voltage, the height of the earthed rods and their displacement with respect to the energized rod. The experimental results are interpreted in terms of the breakdown mechanism and electric field calculations; their possible extension to shielding design is discussed. Proximity effects may result in a reduction in the striking distance and interception radius of an air terminal, especially at the lower interception probabilities. A new approach for shielding design is introduced, which considers, besides lightning parameters and height of the prospective struck objects, interception probability and proximity effects. @article{Mikropoulos2010TPD, | |
Pantelis N. Mikropoulos and Thomas Tsovilis
IEEE Trans. on Power Delivery, 25, (3), pp. 1855-1865, 2010 Jun
[Abstract][BibTex][pdf] General expressions for the estimation of lightning incidence to overhead transmission lines on the basis of electrogeometric and generic models are introduced, which consider, besides transmission-line geometry, lightning crest current distribution and, based on the recently proposed statistical model, interception probability distribution. An application to typical 115 kV up to 765 kV and large scale 500 kV and UHV overhead transmission lines is performed and the computed results, varying significantly among lightning attachment models, are validated through comparisons with field data from literature; the IEEE Std 1243 overestimates significantly lightning incidence to shield wires of large scale transmission lines. The expected annual number of lightning strikes to shield wires of transmission lines depends on lightning crest current distribution; this dependence, easily quantified with the aid of the introduced general expressions, is not considered by the relevant IEEE standard. Lightning incidence results are discussed in the context of the backflashover rate of overhead transmission lines. @article{Mikropoulos2010TPD06, |
2010
Conference Papers
Pantelis N. Mikropoulos, Thomas Tsovilis, Zacharias Datsios and Nikolaos Mavrikakis
45th Universities Power Engineering Conference, pp. 1-6, Cardiff, Wales, 2010 Aug
[Abstract][BibTex][pdf] Overvoltages arising in 150 kV and 400 kV GIS substations due to backflashover of the incoming overhead transmission lines were computed with the aid of ATP-EMTP simulations, by considering the effects of several simulation models of the basic transmission line components. The protection offered against impinging surges by surge arresters operating at the substation entrance is evaluated with respect to the basic insulation level of the GIS system. The computed overvoltages vary considerably among tower grounding system models and among insulator string flashover models whereas rather insignificantly among tower simulation models. There is no systematic variation in computed overvoltages among insulator string flashover models. Single vertical lossless line models and a constant rather than a current dependent resistance are considered, in terms of simulation simplicity and safe design, as satisfactory for simulating transmission line tower and its grounding resistance, respectively, in insulation coordination studies of substations. @conference{5649203, | |
Pantelis N. Mikropoulos, Thomas Tsovilis, Z. Politis and A. G. Kagiannas
7th Mediterranean Conference and Exhibition on Power Generation, Transmission, Distribution and Energy Conversion (MedPower 2010), pp. 1-6, Agia Napa, Cyprus, 2010 Nov
[Abstract][BibTex][pdf] Fast-front overvoltages arising at or transferred to the medium-voltage and low-voltage terminals of a 20/0.4 kV distribution transformer are evaluated with the aid of ATP-EMTP simulations. The effects of lightning crest current and of the transformer and load grounding resistances on the computed overvoltages are investigated. The protection against lightning surges offered by surge protective devices installed close to the low-voltage terminals of the distribution transformer is evaluated. The peak of the overvoltage arising at the medium-voltage terminals of the distribution transformer may exceed the corresponding insulation level even when surge arresters are operating close to the latter. The peak of the overvoltage arising at or transferred to the low-voltage terminals of the distribution transformer may exceed the corresponding insulation level when surge protective devices are not installed. When surge protective devices are installed, the overvoltages are significantly reduced and practically unaffected by transformer and/or load grounding resistances. @conference{5715996, | |
Petros Mavroidis, Pantelis N. Mikropoulos, Constantinos A.Stassinopoulos and Lazaros P. Tsirolias
45th Universities Power Engineering Conference, Cardiff, Wales, 2010 Aug
[Abstract][BibTex][pdf] Surface corona development in short rod-plane air gaps with a dielectric covered rod under positive lightning and switching impulse voltages is investigated. Discharge activity was recorded through still photographs and oscillograms of the electric field strength at the earthed plane. The gap length, impulse waveshape and material of the dielectric cover were considered as influencing parameters. The extent of development of the surface corona along the dielectric cover becomes greater with increasing applied voltage and field and with decreasing gap length. Also, it is greater for lightning than switching impulse voltages and occurs at significantly lower applied field for the PTFE than epoxy resin cover. Surface corona development, being greatly dependent on the characteristics of the initial corona emerging in the vicinity of the cover tip, affects the inception of the corona emerging at the dielectric cover upper end, thus also breakdown. @conference{Mavroidis2010UPEC, | |
Pantelis N. Mikropoulos and Thomas Tsovilis
30th International Conference on Lightning Protection, pp. 1-7, Cagliari, Italy, 2010 Sep
[Abstract][BibTex][pdf] Shielding performance of overhead transmission lines is evaluated by implementing in shielding analysis a statistical model of lightning attachment. The effects of transmission line parameters, lightning peak current distribution and interception probability on shielding failure flashover rate are investigated and discussed. An application has been made to several overhead transmission lines including typical lines the Hellenic transmission system. Results are compared with that obtained by employing in shielding analysis some commonly used electrogeometric models. The estimated shielding failure flashover rate, showing a great variability among lightning attachment models, is much more sensitive to transmission line geometry for the IEEE Standard 1243:1997, which yields the highest values among models. For all lightning attachment models employed in shielding analysis the estimated shielding failure flashover rate of several overhead transmission lines is in qualitative agreement but in quantitative inconsistency with field data. @conference{Mikropoulos2010ICLP, | |
Pantelis N. Mikropoulos, Thomas Tsovilis, Iordanis Manousaridis, Georgios Laloumis and Asterios Dramis
MedPower 2010, pp. 1-5, Agia Napa, Cyprus, 2010 Nov
[Abstract][BibTex][pdf] Lightning risk assessment of a 170 kV GIS substation connected to the Hellenic transmission system through underground cables has been performed. Fast-front overvoltages impinging on the substation due to shielding failure and backflashover of the incoming overhead transmission lines have been computed with the aid of ATPEMTP simulations and evaluated with respect to the insulation level of the substation equipment. The mean time between failures of the substation is greatly reduced for higher tower grounding resistance and varies significantly among lightning attachment models employed for the evaluation of the lightning performance of the incoming overhead transmission lines. Implementation of the IEEE Std 1243:1997 in lightning risk assessment of substations imposes high requirements on protection against incoming fast-front overvoltage surges. @conference{Mikropoulos2010medpower, | |
Pantelis N. Mikropoulos and Lazaros C. Tzimkas
45th Universities Power Engineering Conference, pp. 1-5, Cardiff, Wales, 2010 Aug
[Abstract][BibTex][pdf] Knowledge of surface streamer characteristics as influenced by the insulating surface and atmospheric conditions is important for the better understanding of the flashover mechanism, hence also for an efficient design of insulating systems under various environmental conditions. In the present study positive streamer propagation along PTFE and Nylon cylindrical insulating surfaces is investigated in a uniform field in air under variable absolute humidity. Streamers were initiated by applying at an auxiliary needle electrode, located at the earthed anode plane electrode, a pulse voltage variable in amplitude and propagated along an insulating surface towards the upper plane electrode, which was stressed by negative DC voltage. The electric fields required for threshold and stable surface streamer propagation and the velocity of stable streamer propagation, being higher than that for air alone and also slightly higher for PTFE than Nylon insulator, increase with absolute humidity. Empirical relationships have been derived, accurately expressing the effects of absolute humidity on surface streamer propagation field and velocity. Results are compared to that obtained in the case of streamer propagation in air alone based on previous work. @conference{mikropoulos2010UPEC, | |
Pantelis N. Mikropoulos, Thomas Tsovilis and D.E Zlitidis
45th Universities Power Engineering Conference, pp. 1-6, Cardiff, Wales, 2010 Aug
[Abstract][BibTex][pdf] A useful tool for the evaluation of the lightning performance of overhead transmission lines has been developed in Matlab. The software (LPTL) runs as a Microsoft Windows application and features a user-friendly graphics interface. For given overhead transmission line parameters, ground flash density and lightning crest current distribution the lightning performance of the line can be easily evaluated according to several lightning attachment models. Through an application to a typical 400 kV double circuit line of the Hellenic transmission system the effects of lightning attachment model and lightning crest current distribution on the lightning performance of the line are quantified. Generally, electrogeometric models yield the highest shielding failure flashover rate whereas the lowest backflashover rate. As the median value of the lightning crest current distribution increases the shielding failure flashover rate decreases whereas backflashover rate increases. The application software is a useful tool for utilities and can also be used for educational purposes in high voltage engineering courses. @conference{Mikropoulos2010UPECTsovilis, | |
Pantelis N. Mikropoulos and Vasileios Zagkanas
45th Universities Power Engineering Conference, pp. 1-5, Cardiff, Wales, 2010 Aug
[Abstract][BibTex][pdf] Corona discharge has attracted much interest among researchers as it has a lot of applications in industry and a number of effects on power systems. In the coaxial cylindrical electrode arrangement in air, simulating many practical applications, corona inception depends on the electric field strength around the inner conductor and on atmospheric conditions. In the present study a computational method for the estimation of the negative corona inception field strength in the coaxial cylindrical electrode arrangement under variable air density is presented. The method is based on streamer theory, involves Hartmann\'s expression for the effective ionization coefficient and considers the effect of the space charge field on avalanche growth. The computed negative corona inception field strength is in good agreement with literature experimental data for an avalanche number varying with the product of relative air density and inner conductor radius. Streamer formation occurs rather through a multi-avalanche process, assisted by subsidiary avalanches owing to secondary ionization processes at the cathode and in air. Peek\'s empirical formula for estimating corona inception field strength in the coaxial cylindrical electrode arrangement in air agrees satisfactorily with literature experimental data referring to negative corona inception. @conference{Mikropoulos2010Zagkanas, |
2009
Journal Articles
Pantelis N. Mikropoulos and Thomas Tsovilis
IEEE Trans. on Power Delivery, 24, (2), pp. 863-873, 2009 Feb
[Abstract][BibTex][pdf] A comprehensive analysis on shielding against lightning is presented. For an air terminal, the design of its protection zone and collection volume is introduced on the basis of simple working relationships which take into account, besides lightning parameters and air terminal height, the interception probability and use as a reference the striking distance to earth surface. The analysis, based on lightning scale-model experimental results, includes a comparison with previously reported models and field data; a satisfactory agreement is found. Lightning incidence calculations have been performed on the basis of lightning interception probability; a close conformity between the actual and calculated number of lightning strikes exists. Both striking distance and interception radius and their statistical nature should be considered for an accurate description of lightning interception. @article{Mikropoulos2009, |
2009
Conference Papers
Pantelis N. Mikropoulos Thomas Tsovilis
IEEE Transactions on Power Delivery, pp. 863-873, Uppsala, 2009 Apr
[Abstract][BibTex][pdf] A comprehensive analysis on shielding against lightning is presented. For an air terminal, the design of its protection zone and collection volume is introduced on the basis of simple working relationships which take into account, besides lightning parameters and air terminal height, the interception probability and use as a reference the striking distance to earth surface. The analysis, based on lightning scale-model experimental results, includes a comparison with previously reported models and field data; a satisfactory agreement is found. Lightning incidence calculations have been performed on the basis of lightning interception probability; a close conformity between the actual and calculated number of lightning strikes exists. Both striking distance and interception radius and their statistical nature should be considered for an accurate description of lightning interception. @conference{4783088, | |
Lazaros Lazaridis and Pantelis N. Mikropoulos
16th International Symposium on High Voltage Engineering, Cape Town, South Africa, 2009 Aug
[Abstract][BibTex][pdf] Positive impulse flashover of a short rod-plane gap bridged by cylindrical insulating surfaces has been investigated in a wide range of absolute humidity variation. Silicon rubber and porcelain insulators with a smooth surface were inserted parallel to the rod, which was stressed by positive standard lightning and switching impulse voltages; air alone was regarded as reference. A capacitive probe positioned at the centre of the earthed plane connected to a digital oscilloscope enabled the monitoring of the electric field strength at the plane. Flashover probability distributions were obtained and the time and voltage to flashover were measured. In the presence of an insulating surface the dielectric strength is reduced under lightning impulses but increased under switching impulses when compared to the case of air alone. Increasing humidity results in shorter time to flashover and increased surface dielectric strength, however, these humidity effects depend upon the trajectory of the spark channel. With the only exception of the porcelain surface under lightning impulses, the discharge develops away from the insulating surface in free air; hence, the effect of humidity on flashover is similar to that observed in the simple air gap. Where flashover occurs close to the insulating surface the atmospheric conditions correction procedure according to IEC 60060-1:1989 should be optimised by employing a reduced humidity coefficient. @conference{Lazaridis2009, | |
Petros Mavroidis, Pantelis N. Mikropoulos, Constantine A. Stassinopoulos and M Zinonos
16th International Symposium on High Voltage Engineering, Cape Town, South Africa, 2009 Aug
[Abstract][BibTex][pdf] The breakdown mechanism of short rod-plane gaps with a dielectric covered rod under positive standard lightning and switching impulse voltages is investigated. Two different dielectric covers, made of PTFE and epoxy resin, were used and the simple air gaps with a bare rod were regarded as reference. Breakdown probability distributions were obtained and the time and voltage to breakdown were measured. Under lightning impulses the increase of the dielectric strength due to the dielectric cover is little dependent upon the cover material and only slightly higher to that of a simple air gap including the cover length. Under switching impulses this increase is greater; the presence of a dielectric cover results in a reduced effect of the impulse waveshape on the dielectric strength. Most of the times, the spark channel develops along the dielectric cover under lightning impulses whereas, under switching impulses it develops either partly or solely in free air away from the cover surface. The increase in the dielectric strength of the gaps due to the dielectric cover is associated with the effects on the discharge development pattern of the coronas preceding breakdown. @conference{Mavroidis2009, | |
Pantelis N. Mikropoulos, Lazaros C. Tzimkas, T Giannopoulos and P Tsintikidis
16th International Symposium on High Voltage Engineering, Cape Town, South Africa, 2009 Aug
[Abstract][BibTex][pdf] Results on positive streamer propagation along smooth and profiled cylindrical insulating surfaces coated with different room temperature vulcanized (RTV) silicon rubber coatings are presented; nylon specimens were regarded as reference. Experiments were carried out in a three electrode arrangement consisting of a 12 cm long parallel-plane gap with an auxiliary needle in the earthed anode. Streamers were initiated by applying at the needle electrode a pulse voltage variable in amplitude and propagated over the insulators towards the upper plane electrode which was stressed by a negative DC voltage. When streamers propagate stably along an insulating smooth surface the propagation field and the associated velocity are both higher for RTV coated than bare insulators, however when they propagate along a profiled insulating surface with a step or a shed this reverses itself. The effect of a step or a shed on an insulating surface is to increase propagation field, with the only exception where a streamer crosses part of the gap in air alone, and to reduce the velocity of propagation at all applied fields. The increase of streamer propagation field due to surface profile is less marked for RTV coated than bare insulating surfaces whereas the reduction of propagation velocity is more pronounced. @conference{Mikropoulos2009ISHVE, | |
Pantelis N. Mikropoulos and Thomas Tsovilis
IEEE PowerTech 2009, pp. 1-8, Bucharest, Romania, 2009 Jul
[Abstract][BibTex][pdf] General relationships for the estimation of the maximum shielding failure current of overhead transmission lines have been derived by performing shielding analysis on the basis of several lightning attachment models including a recently introduced statistical one. The interdependence of maximum shielding failure current, transmission line geometry and factors employed in lightning attachment models is discussed through an application to typical 150 kV and 400 kV lines of the Hellenic transmission system. The maximum shielding failure current depends on transmission line geometry and shows a great variability among the lightning attachment models that are used in shielding analysis; electrogeometric models, thus also the IEEE Standard 1243:1997, yield higher values. These results are of great importance when considering that the maximum shielding failure current of transmission lines, besides being employed in estimating their shielding failure flashover rate, is an important parameter for insulation coordination studies. @conference{Mikropoulos2009PowerTech, | |
Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
44th Universities Power Engineering Conference, pp. 1-4, Glasgow, Scotland, 2009 Sep
[Abstract][BibTex][pdf] Positive corona inception in dielectric covered rod-plane air gaps stressed by lightning and switching impulse voltages is investigated. Corona inception probability distributions were obtained and the salient characteristics of the corona discharge, namely inception time and voltage, were measured as influenced by the gap length, waveshape of the applied impulse voltage and by the cover material, namely PTFE and epoxy resin. The simple air gaps with a bare rod were regarded as reference. The corona inception voltage increases significantly due to the insulating cover, especially for the PTFE cover under switching voltages. Electric field computations were performed. The corona inception field is, contrary to the inception voltage, lower for the dielectric covered rod-plane than simple rod-plane air gaps; an assisting mechanism for initiatory electrons production is suggested to explain this behaviour. @conference{Mikropoulos2009Stassinopoulos, | |
Pantelis N. Mikropoulos and Thomas Tsovilis
16th International Symposium on High Voltage Engineering, Cape Town, South Africa, 2009 Aug
[Abstract][BibTex][pdf] Lightning is the main cause of transmission line outages affecting reliability of power supply thus, consequently, resulting in economic losses. A statistical method for lightning incidence calculations in transmission lines is introduced. Simple expressions for the estimation of an expected range of lightning strikes to a transmission line depending on interception probability distribution have been obtained, based on a recently proposed statistical lightning attachment model derived from scale model experiments. The expected number of lightning strikes depends, besides transmission line geometry, on lightning stroke current distribution and interception probability. The results of the statistical method have been compared with those obtained by employing other models from literature, including that suggested by the IEEE Std. 1243:1997, in lightning incidence calculations, and with field observation data; a satisfactory agreement has been shown to exist. Results on lightning incidence calculations are further discussed through an application to typical 150 kV and 400 kV lines of the Hellenic transmission system. @conference{Mikropoulos2009Tsovilis, | |
Pantelis N. Mikropoulos and Thomas Tsovilis
44th Universities Power Engineering Conference, pp. 1-5, Glasgow, Scotland, 2009 Sep
[Abstract][BibTex][pdf] General relationships for the estimation of the perfect shielding angle of overhead transmission lines have been derived by performing shielding analysis on the basis of several lightning attachment models, including a recently introduced statistical one. The interdependence of perfect shielding angle, transmission line height and minimum current causing flashover of insulation is demonstrated as influenced by the lightning attachment model employed in shielding analysis. There is a great variability in perfect shielding angle among lightning attachment models; this is demonstrated for 150 kV and 400 kV lines of the Hellenic transmission system. The applicability of lightning attachment models in perfect shielding angle calculations is evaluated based on the shielding performance of transmission lines; the IEEE Std 1243:1997 yields consistent results with respect to the shielding performance of the lines. @conference{Mikropoulos2009UPEC, | |
Pantelis N. Mikropoulos and Vasileios Zagkanas
16th International Symposium on High Voltage Engineering, Cape Town, South Africa, 2009 Aug
[Abstract][BibTex][pdf] Corona discharge has many practical applications, thus it has been studied extensively experimentally as well through modelling in many electrode arrangements. In the present study a computational method for the estimation of the positive corona inception field strength in the coaxial cylindrical electrode arrangement in air is presented. It is based on streamer theory and involves Hartmann’s expression for the field dependent effective ionization coefficient and the known distribution of the geometric electric field. A very good agreement with literature experimental data referring to wire-cylinder air gaps has been observed for an avalanche number of 10^4 (ionization integral ~9.2) in a wide range of wire radii and under variable atmospheric conditions. A simple absolute humidity correction factor has been introduced in Peek’s formula, allowing for an accurate estimation of the corona inception field strength under variable humidity. A computational method for positive corona inception in the coaxial cylindrical electrode arrangement in air under variable atmospheric conditions (PDF @conference{Mikropoulos2009Zagkanas, |
2008
Journal Articles
Lazaros Lazaridis and Pantelis N. Mikropoulos
IEEE Trans. on Dielectrics and Electrical Insulation, 15, (3), pp. 694-700, 2008 Jul
[Abstract][BibTex][pdf] Results are presented concerning discharge development and breakdown in air and along cylindrical insulating surfaces in a 12 cm long rod-plane gap under positive switching impulse voltages. Discharge development and breakdown probability curves were obtained. The times taken for the discharge to cross the full gap and for breakdown were measured and the corresponding instantaneous voltages were calculated. The gap was over stressed so as to study the effect of the applied peak voltage on the discharge characteristics. In the presence of an insulating surface the discharge consists of a \'surface\' and an \'air\' component; the former hinders the development of the latter. At voltages causing 50% breakdown probability only the \'air\' component traverses the full gap and breakdown occurs always in free air. For higher applied voltages the \'surface\' component may become able to cross the full gap and breakdown may occur also along the insulating surface; under these conditions both the arrival of the discharge at the plane and breakdown occur at shorter times and at lower voltages than in air alone, depending on insulating surface material. @article{Lazaridis2008, | |
Pantelis N. Mikropoulos
IET Sci. Meas. Technol., 2, (4), pp. 187-195, 2008 Jun
[Abstract][BibTex][pdf] Results concerning streamer propagation along cylindrical insulators coated with room-temperature-vulcanised silicon rubber coatings are presented. Experiments were carried out in a three-electrode arrangement consisting of a 12?cm long parallel-plane gap with an auxiliary needle in the earthed anode. Insulators could be inserted between the plane electrodes adjacent to them and almost in contact with the needle. Positive streamers were initiated by applying at the needle electrode a pulse voltage variable in amplitude and propagated over the insulators towards the upper plane electrode which was stressed by a negative DC voltage. The streamer propagation field at conditions from threshold up to the stable streamer propagation and the associated velocity were measured. The dependence of the streamer velocity on the electric field was investigated with the type of coating as parameter. Both the streamer propagation field and the associated velocity of propagation are higher, when a streamer propagates along the coated insulators, than the reference bare nylon insulator depending on the coating employed. Streamers might be used as an effective probe for studying the surface dielectric behaviour of coated insulators hence also for evaluating the various coatings used to improve the contamination performance of outdoor high-voltage insulators. @article{Mikropoulos2008, | |
Pantelis N. Mikropoulos, Constantine A. Stassinopoulos and Barbara C. Sarigiannidou
IEEE Trans. on Dielectrics and Electrical Insulation, 15, (2), pp. 416-425, 2008 Apr
[Abstract][BibTex][pdf] The influence of humidity on streamer propagation at conditions from the threshold for propagation to those for streamer-induced breakdown was investigated in a uniform field in air at atmospheric pressure. Experiments were carried out in a three electrode arrangement consisting of a 12 cm long parallel-plane gap, with an auxiliary needle in the earthed anode. Positive streamers were initiated by applying at the needle electrode a pulse voltage which varied in amplitude. These propagated towards the upper plane electrode which was stressed by a negative dc voltage. Under natural atmospheric conditions, propagation and breakdown probability curves were obtained for several values of absolute humidity in the range between 5 and 22 g/m3. Thus, distributions of the electric field required for streamer propagation and breakdown were obtained and the associated velocity of propagation and time to breakdown were measured. Besides humidity, the amplitude of the voltage used for streamer initiation and the ambient electric field were considered as influencing parameters on streamer properties. Empirical equations are presented expressing the effects of the above parameters on the intrinsic streamer properties. A comparison with previous work in the literature is made and this leads to the conclusion that the influence of humidity on streamer propagation and breakdown can be placed in a sounder quantitative basis. @article{Mikropoulos2008TDEI, | |
Pantelis N. Mikropoulos and Thomas Tsovilis
IEEE Trans. on Power Delivery, 23, (3), pp. 1571-1580, 2008 Jul
[Abstract][BibTex][pdf] The relation between the striking distance and interception probability is experimentally investigated under standard lightning impulse voltages of both polarities. By using the rod-plane gap as a reference case, results are presented relating to the discharge interception probability of an earthed rod inserted in the gap. There is a critical separation distance between the stressed and earthed rods at which breakdown occurs either to the plane or to the earthed rod with the same probability. Besides the impulse voltage polarity, the length of the reference gap and the earthed rod height are considered as parameters influencing on interception probability. Results are discussed on the basis of the breakdown mechanism and electric field calculations. The striking distance is defined with the aid of an expression that takes into account, besides lightning peak current, the interception probability and the effects of lightning polarity and struck object height. The results introduce the design of lightning protection systems on the basis of lightning interception probability. @article{Mikropoulos2008TPD, |
2008
Conference Papers
Petros Mavroidis Pantelis N. Mikropoulos Constantine A. Stassinopoulos G. Smaragdakis
2008 43rd International Universities Power Engineering Conference, pp. 1-5, 2008 Sep
[Abstract][BibTex][pdf] Results are presented concerning breakdown of short rod-plane air gaps with a dielectric-covered rod under positive standard lightning and switching impulse voltages. Breakdown probability distributions were obtained through multiple level tests and the time and voltage to breakdown were measured with the gap length as a parameter. The simple air gaps with a bare rod were considered as reference cases. There is an increase in the dielectric strength of the gap due to the insulating cover, especially under switching impulse voltages. In the presence of the dielectric cover the effect of the impulse waveform on the dielectric strength of the gap is minimal. @conference{4651623, | |
Petros Mavroidis, Pantelis N. Mikropoulos, Constantine A. Stassinopoulos, A Dodos and P Zannias
XVII Int. Conference on Gas Discharges and their Applications, pp. 289-292, Cardiff, UK, 2008 Sep
[Abstract][BibTex][pdf] Results are presented concerning both prebreakdown phenomena and the breakdown mechanism in short rod-plane gaps with dielectric-covered rod under positive standard lightning impulse voltages. Characteristic discharge parameters, namely first and second corona inception time and voltage, and time and voltage to breakdown were measured, through multiple level tests, with the gap length as a parameter. The simple air gaps i.e. without any insulating covers were considered as reference cases. In the presence of the dielectric cover breakdown occurs at higher applied voltages as a result of increased both corona inception voltages and discharge path. Interpretation of the results is made based on the discharge development pattern and electric field calculations. @conference{5379232, | |
Lazaros Lazaridis Pantelis N. Mikropoulos A. Darras A. Theocharis
2008 17th International Conference on Gas Discharges and Their Applications, pp. 233-236, 2008 Sep
[Abstract][BibTex][pdf] Results are presented concerning discharge development and breakdown along cylindrical insulating surfaces in a 12 cm long rod-plane gap under positive standard lightning impulse voltages. Cylindrical insulator specimens, made of silicone rubber and glazed porcelain, could be inserted parallel to the rod electrode, bridging the gap; the case of air alone was regarded as reference. Discharge development patterns were obtained by oscillographic monitoring of the electric field strength at the earthed plane. An insulating surface, depending on material permittivity, may inhibit the development of the initial corona streamers but favour breakdown. @conference{5379263, | |
Pantelis N. Mikropoulos, Thomas Tsovilis, P Chatzidimitriou and P Vasilaras
MedPower 2008, Thessaloniki, Greece, 2008 Sep
[Abstract][BibTex][pdf] A user-friendly Windows application software has been developed for shielding design of high voltage substations against direct lightning strokes; shielding design can be achieved in a few minutes on the basis of a 3-dimensional analysis. With the aid of the software, an installed shielding system can be validated and/or a new system can be designed according to IEEE Standard 998:1996. The performance of different shielding design methods can be easily evaluated for various operating system voltages and equipment dimensions. The developed software has been applied to the shielding design of typical substations of the Hellenic Transmission System, 150 kV and 400 kV substations and a comparison of the design methods has been made. The application software is a useful tool for electrical engineers and can also be used for educational purposes in high voltage engineering courses. @conference{Mikropoulos2008MP, | |
Pantelis N. Mikropoulos, Thomas Tsovilis and T Ananiadis
MedPower 2008, Thessaloniki, Greece, 2008 Sep
[Abstract][BibTex][pdf] The effect of an earthed object on the interception radius of the Franklin rod is experimentally investigated under standard lightning impulse voltages of both polarities. By using a 75 cm rod-plane gap as a reference case, results are presented relating to the discharge interception probability of an earthed rod inserted in the gap together with a neighbouring shorter earthed rod. At certain separation distances between stressed and earthed rods breakdown occurs to either of the earthed electrodes, plane and two rods, with the same probability (33.3%); these critical separation distances depend on impulse volt¬age polarity and earthed rods height. The experimental results are interpreted in terms of the breakdown mechanism and their possible extension to shielding design is discussed. The interception probability dis-tribution of a Franklin rod is affected by the presence of a neighbouring earthed object. @conference{Mikropoulos2008MPTsovilis, |
2007
Conference Papers
Lazaros Lazaridis, Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
15th International Symposium on High Voltage Engineering, Ljubljana, 2007 Aug
[Abstract][BibTex][pdf] @conference{Lazaridis2007, | |
Petros Mavroidis, Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
42nd Universities Power Engineering Conference, Brighton, UK, 2007 Sep
[Abstract][BibTex][pdf] Results are presented concerning prebreakdown phenomena and breakdown in short rod-plane gaps in air under lightning impulse voltages of both polarities. Breakdown probability distributions were obtained and the discharge parameters such as first and second corona inception time and voltage, dark period, time and voltage required for the discharge to arrive at the earthed plane and for breakdown were measured as a function of gap length and impulse voltage polarity. Breakdown under negative impulse voltages is closely associated with the prebreakdown phenomena since there is a close correlation between coronas inception and breakdown voltages; this is not always the case under positive impulse voltages. For both polarities there is a tight correlation between the breakdown and discharge arrival voltages. At 50% breakdown probability, the mean electric field required for the discharge to arrive at the plane is roughly two times higher under negative than positive impulse voltages and for both polarities it decreases with gap length according to a power law. These explain the similar dependence of the 50% breakdown voltage on polarity and gap length. @conference{Mavroidis2007, | |
Pantelis N. Mikropoulos and Thomas Tsovilis
15th International Symposium on High Voltage Engineering, Ljubljana, 2007 Aug
[Abstract][BibTex][pdf] The protection zone of the Franklin rod is experimentally investigated under standard lightning impulse voltages of both polarities. By using a 75 cm rod-plane gap as a reference case, results are presented relating to the discharge interception probability of an earthed rod inserted in the gap. There is a critical lateral distance between the stressed and earthed rods at which breakdown occurs either to the plane or to the earthed rod with the same probability; this depends on impulse volt¬age polarity and earthed rod height. The Franklin rod protection zone is de¬signed at different interception probabilities on the basis of an expression defining its boundaries. The protection zone identified according to the rolling sphere method is overesti¬mated for positive lightning but underestimated in the case of negative lightning. An explanation of this behaviour is attempted relating to the breakdown mechanism which is dis¬cussed with the aid of electric field calculations. @conference{Mikropoulos2007ISHVE, |
2006
Conference Papers
Lazaros Lazaridis, Pantelis N. Mikropoulos, Constantine A. Stassinopoulos, C Kerasaridis and I Lisaridis
41st Universities Power Engineering Conference, pp. 912-915, Newcastle, UK, 2006 Sep
[Abstract][BibTex][pdf] Results are presented concerning corona inception in air and in the presence of a porcelain insulator in a non-uniform field under positive switching impulse voltages. It is shown that in the presence of the insulator both first and second coronas start earlier, under lower inception voltages and with smaller associated charges compared to corona inception in air alone. Where the insulator is present, the first and second corona inception voltages and the required voltage increase during dark period increase linearly with the applied voltage. This is not so in the case of corona inception in air alone where the second corona inception voltage was found roughly constant, independent of the applied voltage variations. The apparent first and second corona charges were found to increase with the corresponding inception voltages according to a power and an exponential law respectively @conference{Lazaridis2006, | |
Pantelis N. Mikropoulos, B.C Sarigiannidou, M Stapountzi and Constantine A. Stassinopoulos
41st Universities Power Engineering Conference, pp. 916-920, Newcastle, UK, 2006 Sep
[Abstract][BibTex][pdf] Results are presented concerning the influence of humidity on streamer propagation and flashover along a PTFE cylindrical insulator in a uniform field in air. Experiments were carried out in a three electrode arrangement consisting of a parallel-plane gap (12 cm), stressed by negative DC voltage and a needle in the earthed anode. Positive streamers were initiated by applying a pulse voltage at the needle electrode and propagate along the insulator surface. Streamer properties investigated are the electric field required for stable streamer propagation and the propagation velocity with field values sustaining stable streamer propagation and also under \"overfields\". The electric field required for flashover and the corresponding time were measured. It is shown that the electric field required for stable streamer propagation and the associated velocity increase with increasing humidity, whilst under \"overfields\" high humidity causes streamers to decelerate. Time to breakdown tends to decrease while the required field to breakdown increases with increasing humidity @conference{Mikropoulos2006UPEC, |
2005
Journal Articles
D.E. Gourgoulis, Pantelis N. Mikropoulos, Constantine A. Stassinopoulos and C.G. Yakinthos
IEE Proceedings - Science, Measurement and Technology, 152, (4), pp. 155-160, 2005 Jul
[Abstract][BibTex][pdf] The positive impulse breakdown behaviour of conductor-rod gaps 50?cm in length is investigated while negative DC voltages pre-stress the gap. Breakdown voltage and time to breakdown variations are discussed in terms of the parameters influencing the discharge mechanism such as the gap geometry, the amplitude of the pre-stress negative DC voltage applied at the rod, the waveshape of the applied impulse voltage at the conductor and the variation of absolute humidity. It is shown that pre-stressing, by producing sufficient DC coronas at both electrodes, results in a significant increase in the breakdown voltage. There is a threshold value of the pre-stress DC voltage above which the gap factor against breakdown may double its value. Both absolute humidity and pre-stressing affect, in a combined way, the dielectric strength of the gaps. @article{Gourgoulis205, | |
Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
IEE Proc.-Sci. Meas. Technol., 152, (4), pp. 169-174, 2005 Jul
[Abstract][BibTex][pdf] The sparkover behaviour of sphere-rod gaps under standard impulse voltages is investigated by assessing the influence of gap spacing, impulse voltage waveshape and polarity, and atmospheric conditions on the distribution of the sparkover voltage. At sparkover the growth of streamers of both polarities can be estimated since a value of 2 MV/m is found to be characteristic for the average negative streamer gradient. The IEC atmospheric conditions correction is discussed and compared with a new optimised correction procedure. The feasibility of using the sphere-rod gap as substandard for measuring impulse voltages, replacing the conventional more expensive sphere gap, is examined. @article{Mikropoulos2005, |
2005
Conference Papers
Pantelis N. Mikropoulos, Constantine A. Stassinopoulos and Charalambos Yakinthos
"Αύξηση της δυνατότητας μεταφοράς ενέργειας σε υψηλές τάσεις μέσω της συμπίεσης των διακένων"
1o Πανελλήνιο Συνέδριο Διπλ. Μηχανολόγων – Ηλεκτρολόγων, Αθήνα, 2005 Jan
[Abstract][BibTex] @conference{Mikropoulos2005AthensPan, | |
Pantelis N. Mikropoulos, B.C. Sarigiannidou, Constantine A. Stassinopoulos and C Tsakiridis
40th Universities Power Engineering Conference, pp. 803-807, Cork, 2005 Jan
[Abstract][BibTex][pdf] Results are presented concerning the influence of humidity on streamer propagation and breakdown in a uniform field in air at atmospheric pressure with atmospheric conditions varying naturally. Experiments were carried out in a three electrode arrangement consisting of a parallel-plane gap, 12 cm spacing, and a needle in the earthed anode. Positive streamers are initiated by applying a pulse voltage, varying in amplitude, at the needle electrode and propagate towards the upper plane electrode which is stressed by negative DC voltage. Streamer properties investigated are the electric field required for stable streamer propagation and the propagation velocity under field values sustaining stable streamer propagation and under overfields. Time to breakdown and the corresponding field are also measured. Propagation and breakdown probability curves are obtained for several values of absolute humidity in the range between 5.5 and 18 g/m3. It is shown that increasing humidity results in higher field required for streamer propagation and breakdown and in greater propagation velocity. Time to breakdown decreases with increasing humidity. @conference{Mikropoulos2005UPEC, | |
G D. Sergiadis, D S. Aleksiadis and Constantine A. Stassinopoulos
"Η αρχή της συνετής αποφυγής – Μια πρόταση αντιμετώπισης των πιθανών κινδύνων από την έκθεση σε πεδία γραμμών ΥΤ"
1o Πανελλήνιο Συνέδριο Διπλ. Μηχανολόγων – Ηλεκτρολόγων, Αθήνα, 2005 Jan
[Abstract][BibTex] @conference{Sergiadis2005Athens, |
2004
Conference Papers
Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
39th Universities Power Engineering Conference, pp. 207-210, Bristol, UK, 2004 Sep
[Abstract][BibTex][pdf] The influence of atmospheric conditions on the dielectric strength of external insulation is a complicated matter. Investigations carried out resulted in a correction procedure for atmospheric conditions that is currently adopted by the IEC standard 60060-1/1989. Despite its widespread applicability, many of the factors employed in this standard are still under consideration and several authors have argued about its validity, especially on short air gaps. The paper presents data concerning the breakdown characteristics of rod-plane gaps under positive impulse voltages. Emphasis is given on the influence of atmospheric conditions, the effect of gap spacing and the wavefront duration of the applied impulse voltages. Empirical expressions relating to these parameters are presented. An optimised atmospheric correction procedure is introduced, which employs an iterative concurrent correction for both air density and humidity. It estimates the influence of atmospheric conditions more accurately than the IEC procedure. @conference{Mikropoulos2004, | |
Pantelis N. Mikropoulos, Constantine A. Stassinopoulos, I Katarachias and A Tsetoglou
WSEAS Transactions on Circuits and Systems, pp. 1197-1200, 2004 Jan
[Abstract][BibTex][pdf] The sparkover behaviour of sphere-rod gaps under standard impulse voltages is investigated by assessing the influence of gap spacing, voltage waveshape and polarity, and atmospheric conditions on the distribution of the sparkover voltage. A new correction procedure for atmospheric conditions is introduced and the related IEC standard is discussed. The feasibility of using the sphere-rod gap as measuring substandard, replacing the conventional more expensive sphere gap, is examined. @conference{Mikropoulos2004WSEAS, | |
Pantelis N. Mikropoulos, Constantine A. Stassinopoulos and Charalambos Yakinthos
X International Symposium on Gaseous Dielectrics, pp. 229-234, Athens, Greece, 2004 Jan
[Abstract][BibTex][pdf] The influence of the superimposition of positive impulses on negative DC pre-stressed conductor-rod gaps with spacing of 50 cm is investigated. Previous experiments have shown that when a conductor of 2 cm in diameter is used a marked increase in the dielectric strength of the gap is observed when negative DC voltages between 100 kV and 125 kV in value are applied at the rod; this is not the case for a 3 cm conductor. This paper provides new data concerning the above phenomenon; by applying higher values of pre-stressing voltage a similar behaviour as with the 2 cm conductor is observed for the 3 cm conductor. The discharge mechanism is discussed taking into consideration parameters affecting the above behaviour, such as the value of the pre-stressing DC voltage, the waveshape of the applied impulse voltage and the variation of absolute humidity. @conference{Mikropoulos2004XISGD, |
2003
Conference Papers
D E. Gourgoulis, Constantine A. Stassinopoulos, G D. Tonozlis, Charalambos Yakinthos and S Chondrogiannis
"A comparative presentation of sphere gaps and sphere-rod gaps under standard lightning impulse voltages"
13th International Symposium in High Voltage Engineering, Netherlands, 2003 Jan
[Abstract][BibTex] @conference{Gourgoulis2003, | |
G Sergiadis and Constantine A. Stassinopoulos
"Consequences of overhead lines on public health"
38th Universities Power Engineering Conference, pp. 225, Thessaloniki, Greece, 2003 Jan
[Abstract][BibTex] @conference{Sergiadis2003, |
2002
Conference Papers
Constantine A. Stassinopoulos, G D. Tonozlis and Charalambos Yakinthos
37th Universities Power Engineering Conference, pp. 401, Stafford, 2002 Jan
[Abstract][BibTex][pdf] As a part of a programme of work on overhead line compaction, at the High Voltage Laboratory of the A.U.Th., a tower - line clearance stressed by impulse voltages has been studied. The effect of a pre - stressing negative voltage was also studied as in our previous work concerning a positive conductor - rod gap with the rod pre - stressed by a negative D.C. voltage; this work showed a higher gap factor than other gap configurations. Since in a conductor - plane gap the existence of a pre - stressing negative D.C. voltage shows no influence, we investigate the effect of inserting rods on the plane in order to study the breakdown mechanism of such gaps in atmospheric air. The length of the rods, and the values of the negative D.C. voltage were taken as parameters. Furthermore the above mentioned results compared with the results taken from a conductor - plane gap stressed only by a positive or negative D.C. voltage in order to obtain more information concerning the breakdown mechanism. Also photographs were taken for gaps stressed with both D.C. polarities as well as for conductor - plane gaps. @conference{Stassinopoulos2002, |
2001
Journal Articles
N. L. Allen and Pantelis N. Mikropoulos
IEEE Transactions on Dielectrics and Electrical Insulation, 8, (5), pp. 812-817, 2001 Oct
[Abstract][BibTex][pdf] In a uniform field arrangement, under direct voltage, positive streamer propagation and breakdown are investigated along cylindrical insulators with different profiles, inserted perpendicularly between two parallel plane electrodes. The basic properties of streamer propagation and breakdown, namely the electric field required for a stable propagation together with the associated velocity and the breakdown field together with time to breakdown, are measured as influenced by the pulse voltage amplitude used for the streamer initiation and by the insulator profile. It is shown that a strong relation between streamer propagation and breakdown exists, because the insulator profile exerts a similar influence on the breakdown and propagation fields. The effect of a shed on an insulating surface, forming an `obstruction\' to streamer progress, is to increase the stability for propagation and breakdown fields, and to reduce the propagation velocity at all applied fields compared with those in the case of a smooth insulator. Along the surface of a smooth insulator, a streamer system propagates with a `surface\' and an `air\' component; however, a shed on an insulating surface modifies this system, resulting in only one component reaching the cathode @article{Allen2001, |
2001
Conference Papers
D E. Gourgoulis, Constantine A. Stassinopoulos and Charalambos Yakinthos
36th Universities Power Engineering Conference, Swansea, 2001 Jan
[Abstract][BibTex][pdf] In overhead lines it is desirable to find the minimum practicable clearances to be used when a composite rather than a simple impulse voltge is applied. In our previous work the conductor - rod gap has been studied; this shows a higher gap factor than other gap configurations. As a part of a programme of work on overhead line compaction at the High Voltage Laboratory of the A.U.Th. the possibility of finding other gap configurations displaying high gap factors has been studied. For this reason the impulse breakdown of a conductor - rod gap with insulator strings as an application analogus to some overhead line situations and a conductor - sphere gap as an alternative configuration of the conductor - rod gap when the rod or the sphere is pre - stressed with negative direct voltage have been investigated. It was found that the effect of pre - stressing depends on the diameter of the conductor, on the position of the rod, on the waveshape of the applied impulse voltage and on the value of the direct voltage. @conference{Gourgoulis2001, | |
Constantine A. Stassinopoulos and Charalambos Yakinthos
IX International Symposium on Gaseous Dielectrics, pp. 535, Maryland, 2001 Jan
[Abstract][BibTex][pdf] In order to investigate the breakdown mechanism of a conductor — tower gap under transient overvoltages in the laboratory, the simulation of overvoltages is done by the use of standard lightning or switching impulses. If these impulses are superimposed or preceded by a steady direct pre — stressing voltage it has been shown1,5 that this affects the dielectric strength of the configuration used. Previous study1 showed that the influence of the superimposition of positive impulses on a negative DC pre — stressing conductor-rod gap with a spacing of 50 cm is significant in that under certain conditions the overall sparkover voltage tends to increase. Several parameters affect this behaviour, i.e. the value of the pre — stressing DC voltage, the diameter of the energised conductor, the position of the rod with regard to the conductor, the waveshape of the applied impulse and humidity. All this was explained in terms of the various DC and impulse coronas that occur at the conductor and the rod which tend to create a more «uniform» field distribution in the gap. In order to have a better simulation of a tower — line clearance, a construction similar to a tower and a line has been constructed. Since a conductor — rod gap shows a gap factor of about l.610, rods were inserted in the gap and the influence of their length on the breakdown mechanism has been evaluated. @conference{Stassinopoulos2001, | |
Constantine A. Stassinopoulos and G Sergiadis
"Επιπτώσεις των εναερίων γραμμών ΥΤ στη Δημόσια Υγεία"
Παγκόσμιο ΣυνέδριοΜηχανολόγων – Ηλεκτρολόγων, pp. 116, Κοζάνης, 2001 Jan
[Abstract][BibTex] @conference{Stassinopoulos2001Kozanis, |
2000
Conference Papers
Z D. Giagridis, Dimitrios Gourgoulis, Constantine A. Stassinopoulos and Charalambos Yakinthos
"Impulse breakdown of positive direct voltage pre-stressing rod conductor gaps under negative impulse voltages"
35th Universities Power Engineering Conference, pp. 272, Belfast, 2000 Jan
[Abstract][BibTex] @conference{Giagridis2000, | |
Dimitrios Gourgoulis, Constantine A. Stassinopoulos and Charalambos Yakinthos
"The breakdown of negative pre-stressed conductor-plane gaps under positive switching impulse voltages"
35th Universities Power Engineering Conference, pp. 271, Belfast, 2000 Jan
[Abstract][BibTex] @conference{Gourgoulis2000, |
1999
Journal Articles
N. L. Allen and Pantelis N. Mikropoulos
IEEE Transactions on Dielectrics and Electrical Insulation, 6, (3), pp. 357-362, 1999 Jun
[Abstract][BibTex][pdf] Results concerning the propagation of streamers along insulating surfaces under uniform electric field are presented. The basic properties of streamers, namely the electric field required for a stable propagation and the propagation velocity, have been measured and compared with propagation in air alone as a reference. The results have shown that in the experimental arrangement used significant space charges due to streamer branching are absent, therefore the properties observed are considered as characteristic of a single streamer. Streamers propagate stably with an intrinsic propagation field and a characteristic velocity that depend on the nature of the insulating material. For electric fields higher than the minimum field required for a stable propagation, a streamer system propagates with a \'surface\' and an \'air\' component @article{allen1999, | |
N L Allen and Pantelis N. Mikropoulos
Journal of Physics D: Applied Physics, 32, (8), pp. 913, 1999 Jan
[Abstract][BibTex][pdf] Results concerning the dynamics of streamer propagation in air under a uniform electric field are presented and discussed. Experiments were performed in a plane-parallel electrode arrangement with positive streamers initiated at a sharp point in the earthed anode. The basic properties of streamers are described in terms of the electric field required for a stable propagation and the associated propagation velocity. Critical parameters are the ambient electric field, the voltage used for streamer initiation and the distance of traverse. The present experiments permit the separation between the effects of the above parameters upon streamer advancement and propagation over the whole path up to the cathode. It is shown that an intrinsic propagation field with an associated velocity can be defined, which determine the propagation of streamers of a limiting, minimum energy. The propagation velocity is a power function of the electric field and, with the aid of an empirical equation, values can be expressed accurately in terms of these intrinsic streamer properties. @article{Allen1999PDAP, |
1999
Conference Papers
N L. Allen and Pantelis N. Mikropoulos
Electrostatics 99, Institute of Physics, pp. 49-52, Cambridge, UK, 1999 Jan
[Abstract][BibTex][pdf] Under uniform electric field, the propagation of a single streamer along insulating surfaces was studied. The dynamics of streamer growth were investigated as influenced by the amplitude of the voltage, and therefore energy, used for initiation and the nature of the insulating material; in this case fibreglass and resin. It is shown that the stable propagation of the streamer can be described in terms of an intrinsic propagation field together with an associated velocity. These properties are characteristic of the medium employed and were used to formulate the relation between the propagation velocity and electric field. Along an insulating surface a streamer system propagates with a surface and an air component. @conference{Allen1999EIP, | |
N L. Allen and Pantelis N. Mikropoulos
11th International Symposium on High Voltage Engineering, London, UK, 1999 Jan
[Abstract][BibTex][pdf] Flashover results on insulator specimens with different profiles in a uniform electric field in air are presented. Under direct voltages, positive streamers, propagating along cylindrical insulators, inserted perpendicularly between two parallel plane electrodes, result in breakdown. Breakdown in air alone is studied as a reference. Breakdown fields and times to breakdown are measured as influenced by the pulse voltage amplitude used for the streamer initiation, and by the insulator profile. A higher electric field is required for breakdown along an insulating surface rather than in air. It is shown that a strong relation between the discharge propagation and breakdown exists; the insulator profile exerts similar influence on the breakdown field as on the propagation field. @conference{Allen1999ISHVE, | |
N L. Allen and Pantelis N. Mikropoulos
11th International Symposium on High Voltage Engineering, London, UK, 1999 Jan
[Abstract][BibTex][pdf] In a uniform electric field the propagation of a positive single streamer along insulators made of PTFE has been studied. The basic properties of a streamer, namely the minimum electric field required for stable propagation together with the associated propagation velocity, and the dynamics of streamer growth were investigated. These streamer properties are influenced by the amplitude of the voltage, and therefore energy, used for initiation and by the profile of the insulator. The streamer growth was studied for applied electric fields greater than the minimum required for stable propagation. Along a smooth insulating surface a streamer system propagates with a 'surface' and an 'air' component, however, a step on the surface results, depending on its position, in a modification of this system. @conference{Allen1999Mikropoulos, |
1998
Journal Articles
N.L. Allen, D.E. Gourgoulis, Pantelis N. Mikropoulos, Constantine A. Stassinopoulos and C.G. Yakinthos
IEE Proceedings - Science, Measurement and Technology, 145, pp. 105-109, 1998 May
[Abstract][BibTex][pdf] The sparkover of a 50 cm conductor–rod gap under positive impulses is investigated when a pre-stressing negative direct voltage is applied to the rod. Under lightning impulses the pre-stress has a small effect on the breakdown voltage of the gap. For long-front impulses, a considerable increase in the dielectric strength of the gap can be observed. Several parameters affect this behaviour, like the value of the pre-stressing direct voltage, the diameter of the energised conductor, the position of the rod with regard to the conductor and the waveshape of the applied impulse. @article{allen1998, | |
D.E. Gourgoulis and Constantine A. Stassinopoulos
IEE Proceedings - Science, Measurement and Technology, 145, pp. 147-151(4), 1998 Jul
[Abstract][BibTex][pdf] The influence of irradiation on the breakdown of sphere and sphere–rod gaps for short gap spacings, has been investigated under standard impulse waveshapes of both polarities. It is known that, for short gap spacings, in non-irradiated sphere gaps and sphere–rod gaps the values of the standard deviations of the breakdown probability distributions are relatively large, and the same is true for the influence of humidity on the sparkover voltage. However, the experiments showed that irradiation acts interactively with other discharge parameters, i.e. impulse shape, gap spacing, polarity, absolute humidity, diameter of the spheres and the shape of the earthed electrode. It was found that the breakdown mechanism of small gaps is influenced by irradiation and that the irradiated gaps in most cases become more reliable for measuring and/or calibrating purposes. @article{gourgoulis1998, | |
Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
IEE Proceedings - Science, Measurement and Technology, 145, pp. 141-146, 1998 Jul
[Abstract][BibTex][pdf] An attempt is made to assess the extent of influence of various parameters on the breakdown mechanism in short rod–plane gaps under positive impulses. Such parameters include front duration and peak value of the impulse voltage, gap length, profile of the rod and, in particular, absolute humidity. Depending on the above parameters, breakdown occurs either through a streamer-dominated breakdown mechanism or through one involving the development of a small leader. The second corona was found to predesignate which mechanism will take place, thus influencing the statistical behaviour of breakdown. Calculated humidity correction factors were found to be different from those proposed by IEC. @article{mikropoulos1009PSMT, |
1998
Conference Papers
N L. Allen and Pantelis N. Mikropoulos
CIGRE 33-98 (WG04/07), IWD, 1998 Jan
[Abstract][BibTex][pdf] Results concerning the propagation of streamers along insulating surfaces under uniform electric field are presented. The basic properties of streamers, namely the electric field required for a stable propagation and the propagation velocity, have been measured and compared with propagation in air alone as a reference. The results have shown that in the experimental arrangement used significant space charges due to streamer branching are absent, therefore the properties observed are considered as characteristic of a single streamer. Streamers propagate stably with an intrinsic propagation field and a characteristic velocity that depend on the nature of the insulating material. For electric fields higher than the minimum field required for a stable propagation, a streamer system propagates with a 'surface' and an 'air' component. @conference{Allen1998CIGRE, | |
Dimitrios Gourgoulis and Constantine A. Stassinopoulos
"Uncertainties of HV measurements using the Sphere and Rod gaps"
CIGRE 33-98 (WG03/07), IWD, 1998 Jan
[Abstract][BibTex] @conference{Gourgoulis1998CIGRE, | |
Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
33rd Universities Power Engineering Conference, pp. 169, Edinburgh, 1998 Jan
[Abstract][BibTex][pdf] In short rod - plane gaps under positive impulse voltages the properties of phenomena occurring during the early stages of the discharge, namely the first and second coronas, have been investigated. Measurements are reported of the variation of their inception time and voltage as a function of the wavefront duration, the gap length, the shape of the end of the rod and the absolute humidity. For purposes of further elucidation, the gaps were divided into two categories depending on to whether second corona emerged during the front or the tail of the applied impulse, and the properties of the coronas into two groups, on the basis of whether breakdown occurred or not. Special interest was given to the influence of the absolute humidity as the experiments and the analysis that followed showed that humidity acts interactively with the other discharge parameters. As a result, humidity exerts sometimes inhibitory sometimes facilitating action on the inception of the first corona whereas on the inception of the second its action is always inhibitory. @conference{Mikropoulos1998UPEC, | |
Constantine A. Stassinopoulos
"Points causing uncertainty in sphere gap breakdown"
CIGRE 33-98 (WG03/41), IWD, 1998 Jan
[Abstract][BibTex] @conference{Stassinopoulos1998, |
1997
Journal Articles
D. E. Gourgoulis, Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
IEE Proceedings - Science, Measurement and Technology, 144, (1), pp. 11-16, 1997 Jan
[Abstract][BibTex][pdf] The relative low cost of sphere-rod gaps compared to sphere gaps makes it worthwhile to study the breakdown mechanisms of the former, if only to find whether they could be used for calibrating or measuring purposes, Having this in mind, the influence of impulse shape, gap spacing and humidity on the sparkover voltage of sphere-rod gaps always in comparison with sphere gaps has been investigated under standard impulse waveshapes. It is found that breakdown is influenced by humidity, waveshape and especially by polarity. With these factors in view, the breakdown mechanism and the feasibility of using them as measuring substandards is discussed @article{gourgoulis, | |
D.E. Gourgoulis and Constantine A. Stassinopoulos
Facta Universitatis, Series: Electronics and Energetics, 10, (2), pp. 281-294, 1997 Jan
[Abstract][BibTex][pdf] @article{Gourgoulis1997, | |
D.E. Gourgoulis, Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
"On the corona inception in medium length positive rod-plane gaps under impulse voltages with long wavetails"
Facta Universitatis, Series: Electronics and Energetics, 10, (1), pp. 91-105, 1997 Jan
[Abstract][BibTex] @article{gourgoulis1997FUEE, | |
D.E. Gourgoulis and Constantine A. Stassinopoulos
IEE Proceedings - Science, Measurement and Technology, 144, pp. 273-279(6), 1997 Nov
[Abstract][BibTex][pdf] Sparkover voltages were measured for quasiuniform field sphere gaps consisting of 75 cm diameter spheres stressed by standard waveshapes of 1.2/50 µs and 250/2500 µs of both polarities. The work was undertaken with the aims of comparison with existing work with 25 cm spheres, and of investigating the breakdown mechanism of such gaps and the effect upon them of the applied impulse voltage, with emphasis on the waveshape, the gap spacing, the polarity, the diameter of the spheres and the absolute humidity. The factors that influence the breakdown mechanism have been studied systematically, in order to ascertain their reliability as measurement standards and, hence, their effect on the sparkover voltage values proposed by the IEC. @article{gourgoulis1997SMT, | |
D. E. Gourgoulis, Pantelis N. Mikropoulos, Constantine A. Stassinopoulos and C. G. Yakinthos
IEE Proceedings - Science, Measurement and Technology, 144, (5), pp. 209-214, 1997 Sep
[Abstract][BibTex][pdf] Results were obtained and evaluated so as to investigate the influence of various parameters on the breakdown mechanism of a 50 cm positive conductor-rod gap under impulse voltages. For such a gap it was found that several parameters affect its breakdown characteristics, notably humidity, waveshape of the applied impulse, diameter of the energised conductor and position of the earthed rod with respect to the conductor. Breakdown probability curves have been established, gap factors computed and their dependence on the aforementioned parameters investigated. Finally, the paths taken by the spark channel have been studied. Based on the information gained several suggestions concerning the breakdown mechanism are proposed @article{gourgoulis97, |
1997
Conference Papers
Dimitrios Gourgoulis and Constantine A. Stassinopoulos
"Effects of irradiation on the sparkover of sphere gaps under standard lightning impulses"
10th International Symposium on High Voltage Engineering, pp. 505-508, Montreal, Canada, 1997 Jan
[Abstract][BibTex] @conference{Gourgoulis1997ISHVE, |
1996
Journal Articles
D. E. Gourgoulis, Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
IEE Proceedings - Science, Measurement and Technology, 143, (3), pp. 187-194, 1996 May
[Abstract][BibTex][pdf] The influence of impulse shape, gap spacing and of humidity on the sparkover voltage of sphere gaps consisting of 25 cm diameter spheres has been studied for both polarities under standard waveshapes of 1.2/50 ?s and 250/2500 ?s. Results are compared with the values proposed by the IEC standard and an attempt to explain the breakdown mechanism and especially how it is influenced both by humidity and the waveshape has been made. Further suggestions are given concerning their use as calibrating gaps, especially under switching impulses. Also, under certain conditions, the inclusion in the calibrating gaps of 15 cm gaps is proposed @article{gourgoulis96, |
1996
Conference Papers
Dimitrios Gourgoulis, Constantine A. Stassinopoulos and Charalambos Yakinthos
"Impulse breakdown of positive conductor-rod gaps"
31st Universities Power Engineering Conference, pp. 1-4, Herakleion, Greece, 1996 Jan
[Abstract][BibTex] @conference{Gourgoulis1996Stassinopoulos, | |
Dimitrios Gourgoulis, Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
"On the breakdown parameters of medium rod-plane gaps stressed by positive impulse voltages with long wavetails"
31st Universities Power Engineering Conference, pp. 1-4, Herakleion, Greece, 1996 Jan
[Abstract][BibTex] @conference{Gourgoulis1996UPEC, |
1995
Conference Papers
N L. Allen, M Boutlentj and Constantine A. Stassinopoulos
9th International Symposium on High Voltage Engineering, pp. 2096-1 – 2096-4, Graz, 1995 Jan
[Abstract][BibTex][pdf] The influence of the superimposition of positive impulses on negative DC pre-stressed conductor-rod gaps with spacing of 50 cm is investigated. Previous experiments have shown that when a conductor of 2 cm in diameter is used a marked increase in the dielectric strength of the gap is observed when negative DC voltages between 100 kV and 125 kV in value are applied at the rod; this is not the case for a 3 cm conductor. This paper provides new data concerning the above phenomenon; by applying higher values of pre-stressing voltage a similar behaviour as with the 2 cm conductor is observed for the 3 cm conductor. The discharge mechanism is discussed taking into consideration parameters affecting the above behaviour, such as the value of the pre-stressing DC voltage, the waveshape of the applied impulse voltage and the variation of absolute humidity. @conference{Allen1995Boutlentj, | |
N L. Allen, M Boutlentj, Constantine A. Stassinopoulos and Charalambos Yakinthos
"A new phenomenon occurring in the breakdown of pre-stressed conductor-rod gaps under impulse voltages"
9th International Symposium on High Voltage Engineering, pp. 2936-1 – 2936-4, Graz, 1995 Jan
[Abstract][BibTex] @conference{Allen1995ISHVE, | |
D E. Gourgoulis and Constantine A. Stassinopoulos
"On the influence of humidity on the impulse sparkover of sphere gaps"
Workshop on contemporary problems in power engineering, pp. 1-4, Thessaloniki, Greece, 1995 Jan
[Abstract][BibTex] @conference{Gourgoulis1995WCPPE, | |
Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
"Humidity influences on the breakdown of od-plane gaps under positive impulses in atmospheric air"
Workshop on contemporary problems in power engineering, pp. 1-5, Thessaloniki, Greece, 1995 Jan
[Abstract][BibTex] @conference{Mikropoulos1995WCPPE, |
1994
Journal Articles
Pantelis N. Mikropoulos and Constantine A. Stassinopoulos
IEE Proceedings - Science, Measurement and Technology, 141, (5), pp. 407-417, 1994 Sep
[Abstract][BibTex][pdf] To better understand the influence of atmospheric humidity on the breakdown mechanism of medium length rod-plane gaps when stressed by positive impulse voltages, emphasis was given to the initial prebreakdown phenomena (the first and second coronas) as well as the dark period. The salient events have been measured and assessed, especially the variation of their statistical distribution. Results were also taken and assessed to determine the influence of humidity on the breakdown probability curves, on the 50% breakdown voltages and on the distribution of the times to breakdown. During this investigation the main parameters, in addition to humidity, were the gap length, the geometry of the end of the rod and the front duration of the impulse voltage. Humidity was found to have a great influence on the breakdown mechanism, especially its streamer region. It influences not only the 50% breakdown voltage but also its standard deviation. It was also found to cause changes in the shape of the U-curves. The necessary correction for humidity was found to vary considerably with the front duration of the applied impulse @article{Mikropoulos1994, |
1994
Conference Papers
N L. Allen, M Boutlentj and Constantine A. Stassinopoulos
"Parameters affecting the gap factor in the conductor – rod geometry"
CIGRE 33-94, WG 07, 22 IWD, pp. 1-8, Mulhouse, 1994 Jan
[Abstract][BibTex] @conference{Allen1994Boutlentj, |
1992
Conference Papers
Constantine A. Stassinopoulos, Pantelis N. Mikropoulos and C J. Bagavos
"Positive impulse correction factor for medium rod-plane gaps"
X International Conference on Gas Discharges and their Applications, pp. 600-603, Swansea, 1992 Jan
[Abstract][BibTex] @conference{Stassinopoulos1992, | |
Constantine A. Stassinopoulos, Pantelis N. Mikropoulos and C J. Bagavos
"On the influence of humidity on positive impulse breakdown of medium rod-plane gaps"
X International Conference on Gas Discharges and their Applications, pp. 596-599, Swansea, 1992 Jan
[Abstract][BibTex] @conference{Stassinopoulos1992ICGDA, |
1990
Journal Articles
Constantine A. Stassinopoulos, K. Andreadou and A Sergaki
"Influence of humidity on small rod-plane gap breakdown"
ETEP, etz-Archiv, 12, pp. 273-277, 1990 Jan
[Abstract][BibTex] @article{stassinopoulos1990, |
1988
Conference Papers
Constantine A. Stassinopoulos
"Impulse breakdown of sphere gaps"
IX International Conference on Gas Discharges and their Applications, pp. 463-466, Venice, 1988 Jan
[Abstract][BibTex] @conference{Stassinopoulos1998ICGDA, |