Damage to 500 kV surge arresters occurred due to direct and multiple lightning strokes. The present paper initially analyzes the mechanism of how the surge arresters were damaged based on the accident investigative results and evaluates the energy absorption capacity of existing surge arresters by analyzing the energy absorbed when the surge arresters were damaged. Consequently, the damage was confirmed as attributable by the crack of ZnO elements due to the thermal stress sustained when absorbing the energy of direct and multiple lightning strokes. The damage energy was estimated at about 5.4 MJ. Subsequently, based on the lightning observation data according to the lightning location system and the lightning outage rate of transmission lines, the standard lightning-stroke conditions were determined, the required energy absorption capacity of the surge arresters was analyzed and determined to be less than 5.3 MJ. Although the energy absorbed in the above damage cases exceeds this required energy absorption capacity, it is still considered within the variable range of lightning events. Consequently, existing surge arresters have the required energy absorption capacity and the cases involving damage to surge arresters are considered extremely rare.

The accuracy of lightning overvoltage evaluation of electrical equipment has been improved based on circuit analysis such as the Electro-magnetic Transients Program, but analyzing phenomena whose plane wave propagation (TEM) mode cannot be assumed remains unsolved. Since numerical analysis of electromagnetic fields such as the finite-difference time-domain (FDTD) method directly solves Maxwell's equations, it is an appropriate means for solving this issue. In this paper, the lightning surge waveform due to the back-flashover is analyzed using the FDTD method; bearing detailed modeling of transmission towers and incoming substation lines in mind. An open end of a circuit breaker of a 500 kV air-insulated substation was selected as the subject of analysis, and ac operation voltage was considered as an analysis condition. Following FDTD analysis, a 150 kA lightning stroke to the first tower, which is the standard lightning stroke of the lightning protection design, does not cause back-flashover, but a 200 kA lightning stroke to the first tower and a 150 kA lightning stroke to the second did do so. The flashover occurred in the later timing than the result of conventional circuit analysis, and the rise of the lightning surge was also slower. The voltage waveform of the open end of the circuit breaker reached its peak after repeating reflections, and the overvoltage value became lower than the circuit analysis. According to the FDTD analysis, the required withstand voltage value after the waveform evaluation with a 200 kA lightning stroke is 1,337 kV, which is lower than the present lightning impulse withstand voltage (LIWV) 1,550 kV. The lightning stroke current 200 kA is the value adopted in the lightning protection design of the UHV system. Therefore, the existing air-insulated substation equipment is considered highly capable of withstanding overvoltage at the time of a back-flashover.

In this paper, a numerical procedure for computing electromagnetic fields in a three-dimensional space using the constrained interpolation profile (CIP) method is presented. Then, this method is applied to computing electromagnetic fields, which are generated by an engineering lightning return-stroke model such as the transmission-line (TL) model, the modified TL model with exponential current decay (MTLE) or the traveling-current-source (TCS) model located on flat perfectly conducting ground, and the CIP-computed electric- and magnetic-field waveforms are compared with the corresponding waveforms computed theoretically and using the finite-difference time-domain (FDTD) method.

Photovoltaic (PV) power plants and wind turbines are eco-friendly power generators that utilize solar energy and wind energy, respectively. Many large-scale PV power plants have been constructed using government subsidies. Large-scale PV power plants are usually constructed in large open spaces that contain some tall structures. Therefore, such large-scale PV power plants are likely to attract lightning, which may result in the malfunction or breakdown of electrical and electronic equipment. In this investigation, overvoltages generated when a lightning strikes a structure anchoring PV panels were measured using a 1:10 scale model. The measurements were also verified using the finite-difference time-domain method. The mechanisms of overvoltage generation on an actual-scale PV power plant were also clarified.

To establish an optimal lightning protection method for power distribution lines, factors such as the mechanism behind lightning surges as well as power distribution network and insulation level of power distribution lines should be taken into consideration.This study experimentally clarifies the voltage-time (V-t) characteristics of currently used 6.6-kV power distribution insulators having higher lightning impulse withstand voltage (LIWV) by considering the differences in polarity and the presence or absence of slurry.Furthermore, in this paper we propose approximation formulas based on the sparkover model for calculating the flashover characteristics of 6.6-kV power distribution insulators, which can contribute to insulation coordination throughout the power distribution system.

In recent years, residential solar power systems have been increasingly introduced at a rapid pace. To date, lightning surge currents have been considered to intrude into houses via four kinds of routes, power lines, communication wires, antenna wires, and ground wires respectively. However, if a residential solar power system is installed in a house, an additional lightning surge current will eventually come from the residential solar power system. On the other hand, it is thought likely that more electronic watt-hour meters, or so-called smart meters, will be installed in future. Since electronic watt-hour meters may potentially be more vulnerable to lightning compared to conventional mechanical watt-hour meters, more attention must be paid to the influence of lightning on electronic watt-hour meters. In this paper, lightning impulse tests were conducted for houses where a solar power system was installed. To study the influence of lightning on an electronic watt-hour meter, it is crucial to clarify the condition of the lightning surge current flowing from a residential solar power system hit by a lightning stroke. During these tests, the propagation condition of the lightning surge current flowing from the residential solar power system through the distribution line and the watt-hour meter was studied.

Higher accuracy in the lightning-surge analysis has been pursued; based on circuit analysis. However, the need to analyze phenomena where a plane wave propagation mode cannot be assumed is an outstanding issue. The finite-difference time-domain (FDTD) method is a dominant measure to solve such issue. This study evaluated surge waveforms intruding into a 500 kV air-insulated substation due to a back-flashover through FDTD simulation. The lightning surges were calculated with the inclined angle of the incoming line changed from 0 to 69 degrees and the voltage of the lightning surge intruding into the substation decreased with increasing incline angle of the incoming line. At the open end of the incoming line to the substation at the circuit breaker, the voltage was minimized and maximized when the span length was 20 m and 200 m respectively. This result differed in terms of characteristics from that obtained using the conventional circuit analysis model, whereby the voltage was minimized when the span length was 200 m. The lightning overvoltage at the circuit breaker terminal based on FDTD analysis was lower than that based on circuit analysis. Their relative ratio is 0.557 for a standard incoming line span length of 150 m, showing a 44 % reduction in FDTD analysis from the circuit analytical result. Since the current lightning impulse test voltage is evaluated based on this circuit analytical result, it was clarified that the lightning impulse test voltage level could be potentially reduced with consideration of the inclined conductors at the incoming line span, the vertical conductors of the tower and lightning path, and their mutual coupling with the transmission line.

A transmission tower model that can reproduce the lightning surge response is important for analyzing the lightning surge. In developing such tower model, however, studies have been conducted using a stand-alone tower or a condition where the tower and transmission lines are orthogonally crossed. This could be attributable to the difficulty in handling a complex layout in conventional experiments and theoretical studies. The present paper verifies the accuracy of the FDTD analysis, based on a comparison with the experimental results. Subsequently, it studies the influence of the layout and the inclined angle of the incoming lines to the substation on the surge response of the tower under near-real facility conditions via electromagnetic field analysis using the FDTD method. As a result, the voltage of the insulator strings peaked with a zero-degree incoming angle and it declined with increasing angle, namely by about 20% when the inclined angle was 37.5 degrees. Finally, the current waveform was analyzed in addition to the voltage characteristics and the generation mechanism of the line voltage was explained.

The insulation performance of an oil-immersed power transformer against lightning surges is verified by applying a lightning impulse (LI) voltage alone. However, the surge voltage generated at the transformer terminal in an actual system is superimposed over the ac operating voltage. Particularly for UHV- and 500 kV-class, where the ratio of ac operating voltage to the LI withstand voltage is high, the insulation characteristics for this LI and ac superimposed voltage are crucial factors to study the insulation design. Accordingly, this paper reviewed the research results of insulation characteristics of transformers for the superimposed voltage. Subsequently, these results were evaluated from perspectives of an insulation coordination and transformer insulation test. The insulation elements of transformers covered were the turn-to-turn and section-to-section insulation, for which the LI test is key for insulation design. As a result, for the section-to-section insulation for a shell-type transformer and the turn-to-turn insulation, the breakdown (BD) voltage for the superimposed voltage remained unchanged from the result when the LI was applied alone. Conversely, for the section-to-section insulation of a continuous disk winding for a coretype transformer, the BD voltage attributable to the superimposed voltage declined by about 10% to 20% from that when the LI was applied alone if the oil-impregnated paper component ratio compared to the oil-gap length was low. This is because the oil gap was primarily responsible for the BD and flaws were generated there when the ac voltage was applied. On the other hand, when this ratio was increased, the oil-impregnated paper part was primarily responsible for BD and the decline in BD voltage could be suppressed. For the section-to-section insulation for the interleaved disk winding, the BD voltage attributable to the superimposed voltage remained constant from that when the LI was applied alone. This is because the BD was determined by the LI partial discharge inception at the turn-to-turn part of the section-to-section insulation, where the superimposed voltage made little impact on BD. Based on the above, the LI test is considered adequate to verify the insulation performance of the section-to-section insulation for a shell-type transformer and for an interleaved disk winding and the turn-to-turn insulation against surge overvoltage. Conversely, for the section-to-section structure of a continuous disk winding, the influence of the ac voltage must be taken into account. These results are key findings for rationalizing transformers while maintaining their insulation reliability.

Secondary arc extinction time is an important factor, which influences system stability because it directly affects the reclosing time. However, few reports exist on a field data of the secondary arc extinction time on transmission lines. This paper describes the investigation results of secondary arc extinction characteristics by analyzing voltage wave shapes during the lightning faults on 550 kV transmission lines. Recovery voltages and secondary arc currents on each transmission line during faults were calculated to consider correlation with the secondary arc extinction time. The secondary arc extinction time is estimated by the existing formula, the secondary arc current and the recovery voltage required for one second reclosing are evaluated.

The lightning protection design of a substation is generally based on the surge overvoltage incoming to the substation, which is generated by the back-flashover across an insulator string of the transmission tower that is closest to the substation and struck by a lightning return stroke. In this case, surges propagate along non-horizontal or non-uniform lines such as the tower and the inclined lines incoming to the substation. Although the surge characteristics of a tower have been intensively studied as of today, those of inclined incoming lines to a substation have not yet been investigated. In this paper, experiments have been conducted using a reduced-scale model to clarify the surge characteristics of the conductor system that is composed of horizontal transmission line, two towers, inclined incoming line and a substation gantry. It turns out from the experiments that the potential (voltage) generated at the tower arm rises gradually, compared with the current injected in the tower top. Furthermore, it is found that the power line potential at the gantry is smaller than that that at the tower where the back-flashover occurs, while the opposite trend is obtained from a circuittheory- based simulation in which the inclined incoming line is represented by a horizontal line. The latter approximation has been usually employed in representing inclined incoming lines in lightning surge simulations using the Electromagnetic Transients Program (EMTP) or its alternatives. The fact that the power line potential at the gantry, evaluated by the present experiment, is smaller than the EMTPcomputed value would contribute to a more economical and rational design of a substation.

The type-C constrained interpolation profile (CIP) method has been applied to analyzing lightning electromagnetic fields. The CIP method is one of the finite-difference methods. Differently from the finite-difference time-domain (FDTD) method, however, it considers not only electric- and magnetic-field values at each discretized points in a working space but also their spatial-derivative values there. Therefore, in principle, it can compute fields accurately even when a relatively coarse grid and a relatively large time increment are used. In section 2 of this paper, a numerical procedure for computing electromagnetic fields in a three-dimensional space using the CIP method is presented. In section 3, the type-C CIP method is applied to computing electric fields in a uniform grid, which are generated by a lightning return-stroke current wave propagating upward along a vertical straight channel located on flat perfectly conducting ground, and the CIP-computed waveforms are compared with the corresponding waveforms computed theoretically and using the FDTD method. In section 4, the method is applied to computing lightning electric fields in a nonuniform grid, and a similar comparison is made.

The lightning-impulse voltage test of electrical equipment is specified in IEC 60060-1 "Highvoltage test techniques", whereby the standard waveform has a front time and a time to halfvalue of 1.2/50 μs. These values have been unchanged from IEC Ed. 1 in 1962 through to Ed. 3 in 2010, and further study is also ongoing with 1.2/50 μs as a starting point in the currently active WG "Adaptation of TC 42 standards to UHV test requirements". The present paper initially reviewed how studies had been conducted to establish the lightning-impulse test in the U.S.A. and investigated the flow of how the study results linked to IEC Ed. 1 together with the standards in Europe. Eventually, it seems that, in terms of the flow from the U.S.A., the current numerical values of 1.2/50 μs were most probably derived from the lightning surge observation results at the Wallenpaupack-Siegfried 220-kV system of the Pennsylvania Power & Light Company in 1929 and so forth. Subsequently, major characteristics of recent lightning surge observation results were analyzed from the perspective of current actual electrical facilities and equipment. Consequently, points common to the data of 1929 in terms of the average values and the breadth of the distribution emerged in the crest value - front time and crest value - time to half-value plots. At the same time, differences due to the individual conditions of the individual measurement positions were also recognized. The detailed analysis and study of the standard waveform of the lightning-impulse test based on the analysis results are considered issues to be addressed.

In the condition settings of a power-frequency withstand voltage test for substation equipment, an approach based on insulation reliability evaluation using Weibull distribution is available. In this method, temporary overvoltage is evaluated using an "independence model". This "independence model" assumes no remaining influence of voltage application (i.e. the model obeys the failure probability distribution starting at time 0 each time the voltage is applied). However, the authors have conducted insulation characteristics tests by applying a voltage multiple times at intervals and clarified that the influence of voltage application remains to a certain extent (i.e. the effect assumed in the "accumulation model" appears) as well as the degree of influence depending on the conditions for oil-immersed transformer. The present paper proposes an evaluation method with the degree of influence of voltage application history taken into consideration. In the proposed method, the portions following an "independence model" and an "accumulation model" are respectively assumed and combined after multiplying the relevant coefficient representing the respective degrees of influence. According to the trial calculation based on the proposed method, the required withstand voltage decreased by several percentage points, while it was confirmed that the existing method is on the safer side as a means of evaluating the insulation reliability of temporary overvoltage.

We summarize the lightning data for 17 years from 1992 to 2008 obtained with lightning location systems of nine electric power utilities in Japan and analyze them. The observed annual number of lightning flashes of which the current is more than 10 kA is 400 000–800 000 and the 50% value of the cumulative distribution of lightning peak currents is about 23 kA in recent times. The variation of lightning occurrence characteristics by areas, seasons, and so on, is clarified. Comparison of the obtained data with those obtained by another lightning location system is also made. The relationship between lightning occurrence and climate is discussed. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

A simplified model of corona discharge on overhead wire has been proposed for propagating surge computations using the finite-difference time-domain method. The radial progression of corona streamers from the wire is represented as the radial expansion of cylindrical conducting region whose conductivity is several tens of microsiemens per meter. Two wire radii are considered: 5 and 2 mm, in order to simulate two experimental con- figurations by Noda. The critical electric field on the surface of a 5-mm radius wire for corona initiation is set to E 0 = 1.8 or 2.9 MV/m. For a 2-mm radius wire, it is set to E 0 = 2.2 MV/m. The critical background electric field necessary for streamer propagation is set to E cp = 0.5 MV/m for positive voltage application, and E cn = 1.5 MV/m for negative voltage application. The computed waveform of radial current (including both conduction and displacement currents) agrees well with the corresponding measured waveform. Also, the computed relation between the total charge (charge residing on the wire and emanated corona charge) and applied voltage (qV curve) agrees well with the corresponding measured one, except for relatively low applied voltages. Additionally, the increase of coupling between the energized wire and another one nearby due to corona discharge is well reproduced.

A simplified model of corona discharge for finite-difference time-domain (FDTD) computations has been applied to analyzing lightning surges propagating along overhead wires with corona discharge. The FDTD computations simulate the experiments of Inoue and Wagner . In Inoue's experiment, a 12.65-mm radius, 1.4-km-long overhead wire was employed, and in Wagner 's experiment, a 21- or 25-mm radius, 2.2-km-long overhead horizontal wire was employed. The critical electric field on the surface of the 12.65-mm-radius wire for corona initiation is set to E 0 = 1.4, 2.4, or 2.9 MV/m, and those for 21- and 25-mm-radius wires are set to E 0 = 2.2 and 2.1 MV/m, respectively. The critical background electric field for streamer propagation is set to E cp = 0.5 MV/m for positive voltage application and E cn = 1.5 MV/m for negative voltage application. The FDTD-computed waveforms (including wavefront distortion and attenuation at later times) of surge voltages at three different distances from the energized end of the wire agree reasonably well with the corresponding measured waveforms. Also, the FDTD-computed waveforms of surge voltages induced on a nearby parallel bundled conductor agree fairly well with the corresponding measured waveforms.

In this paper, a simplified model of corona discharge for finite-difference time-domain (FDTD) computations has been applied to analyzing lightning surges propagating along a 25 or 21 mm radius, 2.2 km long single overhead horizontal wire, which simulates the experiment of Wagner et al. [1954]. The critical electric field on the surface of the 25 mm radius wire for corona initiation is set to E0=1.3, 2.1 or 2.5 MV/m, and E0=2.2 MV/m for 21 mm radius wire. The critical background electric field for streamer propagation is set to Ecp=0.5 MV/m for positive voltage application and Ecn=1.5 MV/m for negative voltage application. The FDTD-computed waveforms of surge voltage at three different distances from the energized end of the wire agree reasonably well with the corresponding measured waveforms.

The transient grounding impedance of a gas-insulated switchgear (GIS) substation was investigated through measurements on a commercial 300-kV underground substation. Based on the results, the macroscopic transient impedance of the grounding grid was clarified to be the inductance component and estimated at approximately 0.2 μ H. In the low-frequency region where the frequency is almost zero or so, the impedance is shown to be lower than the general concrete resistance value by one digit due to the complexity of grounding systems specific to underground substations. Hence, the simple model of the grounding grid can be expressed mainly by inductance. The detailed model was expressed by using a π-type equivalent circuit, where each circuit constant was calculated using the specific low resistivity of concrete. In addition, the validity of both models was confirmed by comparing the measurement results. The proposal models are applicable to the Electromagnetic Transients Program analysis on the surge phenomena within the GIS grounding system.