Lightning Stroke Current Research Articles

Study on lightning protection scheme of multi‐terminal MMC‐MVDC distribution system

Based on a ±10 kV three-terminal MMC-MVDC (medium voltage DC distribution system based on modular multilevel converter) system, in this study, the authors mainly study on the influencing factors and protection schemes of the lightning intruding overvoltage (including direct lightning and back-flashover lightning). Firstly, a lightning intruding overvoltage simulation model of the MMC-MVDC distribution system using overhead lines is established based on the PSCAD/EMTDC program. The influence of steady-state operating voltage and the number of converter stations on the simulation results are simulated and analysed. Meanwhile, the proper simulation modelling method of the lightning intruding overvoltage for multi-terminal MMC-MVDC system is proposed. Secondly, the lightning intruding overvoltage is simulated when the line is struck by the lightning stroke current that occurs once in 20 years and the different lightning protection schemes are proposed. Finally, based on the lightning impulse withstand voltage, lightning trip-out rate and the cost of the protection schemes, the lightning protection schemes in different scenarios are proposed. The simulation results show that if the cost of the system is prioritised, the protection scheme of increasing the number of parallel stacks of the DL arresters can be selected, and if the power supply reliability of the system is prioritised, the protection scheme of installing the overhead ground wire as well as reducing grounding resistance can be selected.

Determination of Cumulative Distribution Function of the Crest Value of the Lightning Current Circulating Through Line Surge Arresters

For the selection and design of line surge arresters (LSA), it is essential to know the characteristics of the lightning current circulating through LSA. When lightning strikes a transmission line, only a part of the lightning current circulates through LSA.This part mostly depends on the point of impact, and the characteristic of the lightning stroke current. The determination of the cumulative distribution function of the lightning current circulating through arresters is presented in first part of the paper. It can be applied on transmission lines where LSAs will be installed to protect the line against the effect of atmospheric discharges.Second part of paper presents the calculation results of the cumulative distribution function of the lightning current circulating through arresters for particular 110 kV transmission line located in an area with high lightning activity.

Current Observation Results of Downward Negative Flashes at Tokyo Skytree From 2012 to 2018

Direct observation of lightning current is a fundamental approach to evaluating lightning parameters, which are among the most basic factors for the lightning protection design of various grounded objects. However, for a tall grounded structure, upward lightning flashes initiated from the top of the structure have usually been observed, and the direct observation results of downward flashes have been limited. We developed and installed a pair of Rogowski coils at Tokyo Skytree, which is a 634-m-high freestanding broadcasting tower in Japan (35.71°N, 139.81°E), and have conducted direct observation of lightning flashes striking the tower. As of November 2018, 70 lightning flashes striking the tower, 26 downward and 44 upward, have been observed since the end of February 2012. In this paper, we focus on the downward negative flashes that occurred at the tower for seven years from 2012 to 2018 and report on the observed results of typical waveform parameters of lightning stroke currents in comparison with other observed results on downward negative flashes.

First ground-based observations of sprites over southern Africa

Sprites are the optical signatures of electrical discharges in the mesosphere triggered by large lightning strikes associated with thunderstorms. Since their discovery in the late 1980s, sprites have been observed extensively around the world, although very few observations of sprites from Africa have been documented in the literature. In this paper, we report the first ground-based recorded observations of sprites from South Africa. In 2 out of the 22 nights of observations (11 January and 2 February 2016), about 100 sprite elements were recorded from Sutherland in the Northern Cape, comprising different morphologies (carrot (55%), carrot/column (11%), unclassified (21%), column (13%)). The sprites were triggered by positive cloud-to-ground lightning strikes, which had an average peak value of ~74 kA and were observed at distances from ~400 km to 800 km. The estimated charge moment change of the lightning discharges associated with these events was in agreement with the threshold for dielectric breakdown of the mesosphere and correlates well with the observed sprite brightness.
 Significance: 
 
 The first ground-based recording of sprite events over southern Africa.
 It is suggested that the intensity of the events is proportional to the lightning stroke current.

뇌격전류에 의한 수평접지극의 전위상승 계산

An electric potential rise of the grounding electrode developed by the lightning stroke currents should be calculated for the purpose of effective protection of electrical and electronic equipment. In this paper, the electromagnetic model was applied to calculate the harmonic impedance of grounding electrode. Also the empirical equation related to the permittivity and resistivity of soil was used. The lightning current waveforms, which are expressed by the Heidler"s equation, were used in order to calculate accurately transient electric potential rises. The transient voltage was obtained by using the simulated harmonic impedance and the lightning current in frequency domain. Finally, the transient voltages of horizontal grounding electrode(10m) under lightning stroke currents were calculated by IFFT(Inverse Fast Fourier Transform).

Relation Among Velocity of Lightning Travelling Wave, Lightning Stroke Current, and Tower Footing Resistance to Study Back-Flashover on the Insulators in Transmission Tower

This paper studies the impact of back-flashover on the insulators with various velocities of lightning travelling wave, the lightning stroke current, and the tower footing resistance. The impedance of transmission tower section such as top tower, upper phase, middle phase, and lower phase that is calculated with lightning velocity dependent parameters is also considered. The velocity of lightning travelling wave at 300 m/μs and 200 m/μs is compared to consider back-flashover including maximum voltage at the cross arm and voltage across insulators. The results is shown that the velocity of lightning travelling wave plays an important role for the back-flashover voltage across insulator as well as the tower footing resistance and the lightning stroke current.

New Functions for Representing IEC 62305 Standard and Other Typical Lightning Stroke Currents

New functions for approximating various lightning currents, either measured, assumed or generalized in the standard IEC 62305, are presented in this paper. The channel-base current function and its parameters, as well as analytical expressions of this function derivatives, integrals, and integral transformations are given. Parameters of new functions for representing first stroke currents, subsequent stroke currents, and long stroke currents from the standard IEC 62305 are calculated, so as of two-rise front function typical for experimentally measured first negative stroke currents. Results for lightning electric and magnetic field at different distances from the channel-base obtained by using the proposed function and the Modified transmission line model with exponential decay with height are in good agreement with the results from literature, but any other lightning stroke model can be used as well.

Laboratory Study of the Lightning Attractive Width for Transmission Lines

This research focuses on an investigation of the attractive width of high voltage transmission lines to lightning strokes. In order to design the optimal lightning protection, the estimated number of lightning flashes to the line, which is based on its attractive width, needs to be determined. The investigation was performed using experiments with tested models at the Mississippi State University High Voltage Laboratory. For laboratory experiments, a total of 1,900 negative and positive switching impulse voltages were applied to a conducting rod, which represented a lightning downward leader. Different tested models of transmission lines on a scale of 1:100 were used. The effect of overhead ground wires, phase conductors, and the magnitude and polarity of lightning strokes were studied. The attractive width increased gradually with the height of overhead ground wires as well as the magnitude of the lightning stroke current. Impulse polarity had an impact on the attractive width and the attractive width for negative polarity was larger than that for positive polarity. The experimental results satisfactorily coincide with other published works, based on different methods and also with the actual transmission line observations. The new expressions of the attractive width of transmission lines, based on the experimental results, were established. The accurate estimation of the attractive width can help electric power utilities plan transmission systems reliably and economically. The detailed description of the background problem, methodology, experimental results, and analysis were presented in this paper.

Critical Length Estimation of Counterpoise Subjected to Lightning Stroke Currents

The conventional grounding impedance of a counterpoise is calculated as a function of the length of the counterpoise by use of the distributed parameter circuit model with an application of the EMTP(Electromagnetic Transient Program). The adequacy of the distributed parameter circuit model is examined and verified by comparison of the simulated and the measured results. The conventional grounding impedance of the counterpoise is analyzed for the first short stroke and subsequent short stroke currents. As a result, the simulated results show that the minimum conventional grounding impedance gives at a specified length of the counterpoise. The shorter the time taken to reach the peak of injected currents, the shorter the length of the counterpoise having the minimum conventional grounding impedance. We also present the critical lengths of the counterpoise for short stroke currents as a function of soil resistivity. Based on these results, it is necessary to compute the length of the counterpoise in a specified soil resistivity which satisfies both the low conventional grounding impedance requirement whilst also providing a suitable ground resistance in order to obtain an economical design and installation of the counterpoise.

Lightning Surge Overvoltages at Substations Due to Backflashover With Assumed Lightning Current Waveforms Based on Observations

Recent lightning current observations have suggested that a front duration of 1.7 s is more appropriate than the conventional 1.0 s for the lightning protection design of ultra-high voltage (UHV) systems in Japan. This study examined overvoltages at gas-insulated subsystems (GIS) and transformers in a UHV (the rated voltage of 1100 kV) substation during backflashovers, with the front duration of lightning stroke current waveforms taken as a parameter. The dependence of overvoltages on the front duration of the lightning stroke current is significant at GIS and relatively small at the transformer. Generally speaking, the shorter the front duration is, the higher the voltage will be. The transformer capacitance, ranging from 0 to 1000 pF, equivalently increases the distance to the surge arrester, and a voltage increase was observed at the transformer terminal. However, the steepness of the intruding surge waveform is reduced and the voltage increase suppressed at 1000 pF and over. The effect of overvoltages on insulation design was also evaluated and the results thereof indicated the possibility of reducing the lighting impulse withstand voltage.

Study of Lightning Surge Overvoltages at Substations Due to Direct Lightning Strokes to Phase Conductors

Accurate predictions of lightning surge overvoltages are essential to power equipment insulation design. Recent observations of lightning strokes to ultra-high-voltage designed transmission lines confirmed direct lightning strokes caused by shielding failure and found phenomena unexplainable by conventional shielding theories. However, there are few detailed studies of direct lightning surge overvoltages. This study assumed direct lightning stroke currents based on observational data and performs electromagnetic transient program analysis of the gas-insulated switchgear (GIS) and transformer overvoltages at substations to study the basic characteristics of overvoltages due to direct lightning strokes and evaluate lightning protection design. Consequently, the maximum GIS overvoltages were found during back-flashovers, and the locations of maximum overvoltages from direct lightning strokes and back-flashovers differ. Direct lightning strokes may be more severe than back-flashovers for transformers. This paper also studied the overvoltage generation mechanism and showed the relationship of the maximum voltage to lightning stroke current and transformer capacitance.

Possible Impacts of Earthing Path Impedance on Lightning Return Stroke Currents

Effects of the impedance of lightning earthing path on lightning currents are investigated by computer simulation. Distributed-circuitry transmission line models with adequate values of inductance, resistance and capacitance are chosen to represent lightning channels, upward connecting leaders, structures and lightning protection systems (LPS). Both the current and voltage as a function of time and height of the lightning channel are simulated. Results show that for a lightning stroke without an upward connecting leader, the large lightning stroke current is firstly generated at the channel base and then propagates upward as its amplitude decreases. For the case with an upward leader, however, the return stroke current appears firstly at the connecting point of the upward- and downward- leaders, and then propagates bidirectionally down and up as its amplitude decreases. The existence of an upward leader makes both the lightning current and the rate of change of the current at the channel base smaller than...

Air-Gap Discharge Characteristics in Foggy Conditions Relevant to Lightning Shielding of Transmission Lines

The features of lightning shielding of transmission lines have been calculated using the electrogeometric model (EGM) proposed by Armstrong and Whitehead. Discrepancies, however, have been found in the case of ultra-high voltage (UHV)-designed transmission lines. UHV-designed transmission lines often pass through high-altitude mountain areas, where foggy or rainy conditions are common when there is lightning. While the electrogeometric model determines the striking distance based on the lightning stroke current, environmental conditions, and how they might affect lightning discharge paths, they are not considered. It is possible, therefore, that foggy conditions may cause differences in the performance of transmission-line lightning shielding. This study used scale models of transmission lines for discharge tests with a 1-m air gap and analyzed differences in discharge paths and locations in dry and foggy conditions. The results showed that the polarity of the discharge had a significant influence, but differences in dry and foggy tests were negligible.

The Simulation of Failure Modes on ZnO Varistors

There are three main failure modes of ZnO varistors; thermal runaway, puncture and cracking. It is important from the operational point of view for user of ZnO surge arresters to know the fundamental mechanisms of these failure modes. I led many equations on these failures and simulated failure modes. I have been experienced the only failures of cracking which were occurred by lightning strokes operating our power systems. As the result of simulations, I found that this cracking results from that the highest thermal tensile stress is over the tensile strength and the relative expansion becomes longest too when the maximum temperature is shifted and the hole or the melt is occurred by the large lightning stroke current on the ZnO varistor.

Observational Results of Lightning Current on Transmission Towers

Lightning parameters, particularly the amplitude and the front duration of lightning stroke current, are the basic requirements for lightning protection design, and identifying lightning stroke current waveforms in detail is essential for rational lightning protection design. Between 1994 and 2004, Tokyo Electric Power Company directly measured the current waveforms of lightning strokes on 60 transmission towers (mainly 500-kV transmission lines) and obtained 120 data sets, including waveforms exceeding 100 kA. This paper quantitatively evaluates the characteristics of each lightning waveform parameter calculated from the observed waveforms as well as correlations between parameters, together with comparisons with previous data. In terms of the correlation between the current amplitude and the front duration, the front duration corresponding to the maximum rate of rise is defined, and the relationship that greater current amplitude results in a longer front duration is formulated for the first time. Quantifying the relationship of the current amplitude and the front duration is very useful to rationalize lightning protection design

봉상 접지전극에시 전류유입위치에 따른 임펄스 접지임피던스의 특성

본 논문은 전류유입위치에 따른 봉상접지전극의 과도 및 실효임펄스임피던스의 특성에 관한 것으로 뇌격전류를 인가하여 실규모 접지봉에 대한 시간영역에서의 성능을 평가하였다. 임펄스전류가 가해진 봉상접지전극의 과도 접지임피던스는 접지저항보다 높게 나타났으며, 접지전극의 길이가 길어짐에 따라 접지저항과 실효임펄스접지임피던스는 감소되었다. 또한 실효임펄스접지임피던스는 짧은 시간범위에서는 급격하게 증가하였다. 접지저항의 저감은 접지시스템의 임펄스임피던스 특성의 개선에 결정적인 역할을 한다. 임펄스전류를 접지봉의 하단에 인가하였을 때 접지봉 전위의 파두부에 고주파의 진동 파형이 포함되고 실효임펄스임피던스는 다른 경우보다 높게 나타났다.

Modeling of the transient behavior of a resistive type high T/sub c/ fault current limiter

The potential distribution in electrical equipment during transient excitation is an important criterion for the design of the insulation. Transients in electric power networks can be caused by lightning strikes, disconnecting operations or system disturbances. In this work the transient behavior of a resistive superconducting fault current limiter (SFCL) based on Bi-2212 tubes, which are connected in series, has been modeled. The SFCL will be used in a 10 kV bus tie of a German utility. A lumped network model of the limiter has been developed and implemented in PSpice to investigate the transient behavior. The model includes inductive- and capacitive coupling, respectively. An AC analysis is performed to obtain the frequencies which will cause the highest overvoltages between the windings of the limiter. Furthermore a lightning impulse voltage and a lightning stroke current are applied to the limiter to investigate its transient behavior. A simplification of the model is performed to reduce the computing time. Both models are compared and a good agreement of the results is obtained.

The Effect of Thunderstorm Cloud Quasielectrostatic (QE) Field on the Nighttime Lonospheric D‐Region

AbstractUsing a self‐consistent quasi‐electrostatic (QE) field model, the magnitude of QE is calculated at altitudes from 0km to 90km due to a sudden discharge of thunderstorm cloud. It is assumed that a positive charge of 200C is displaced to ground within 1ms. The numerical results show that the QE field obtained is greater than the breakdown field of neutral atmosphere at height above the thunderstorm about 65~78 km, 1 ms after the initiation of the discharge, and it decreases very quickly 0.5 s later. Because the thermal and ionization time scale are very short at the ionospheric height, the local nighttime lower ionosphere should be substantially affected by the relative large QE field. By solving the Boltzmann equation numerically, it is shown that the electron distribution function has a high‐energy tail at some altitudes, for example at 73 km, and the averaged electron energy is about 3~6 eV at heights of 63~78 km. The results also show that the electron density increases between 65km and 78 km, and the maximum peak becomes three orders larger than the ambient value at about 73 km. Such an effect is much larger than that caused by the electromagnetic pulse which is produced by the lightning stroke current.

Lightning protection of transmission lines: optimal shielding design procedure

The paper first derives a set of shielding constraints which must be satisfied for achieving effective shielding against lightning for all of the phase conductors of an overhead transmission line in relation to earth-wire placement. The shielding constraints are obtained from the analysis related to the rigorous proof of the premise that, once the earth-wire position has been determined to achieve effective shielding for a nominated critical lightning stroke current, then shielding of the phase conductors is still maintained for stroke currents greater than the critical value. An optimal shielding design procedure is then developed in which the cost function relating to earth-wire position(s) is minimised subject to shielding constraints and specified clearance constraints. Results of lightning protection designs using the procedure, to achieve effective shielding for a range of transmission-line configurations, are presented.

Assessment of protection system positioning and models using observations of lightning strikes to structures

This paper presents the results of an analysis of the observed incidence of lightning strikes to a wide range of earthed structures in Hong Kong. The data were obtained for 161 structures and span the period 1988–1996. These structures were protected with lightning air terminals, placed in the optimum locations on each structure using a new positioning method which is an improvement of the simple ‘electrogeometric model’. The aims of the paper are fourfold, namely to assess (i) the effectiveness of this new lightning protection positioning method, (ii) the validity of various attractive radius models, especially since many of the structures are located in high–density city blocks, (iii) the validity of a Poisson model for describing the strike frequency, and (iv) the effect of any assumed height dependence of the median peak current on the attractive radius models. The results show a significant positive correlation between expected and actual strike frequency and confirm that the interception efficiency of the lightning protection system is in accord with the specified protection levels. In general, attractive radius and Poisson strike models for ‘free–standing’ structures are found to be valid except for structures of height less than 100 m in dense city blocks. The results also show an influence due to positive flashes and a decrease in attractive radius if the peak lightning stroke current is assumed to be dependent on the structure height.