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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. [ABSTRACT FROM AUTHOR]

Lightning peak current is one of the most important parameter concerning the studies of the lightning phenomena. Nowadays, with a continuous dissemination of elevated structures, such as telecommunication towers, the study of the lightning peak current could be intensified with the installation of measurement devices in large scale. Thus, it is useful to develop a device that is robust, compact, low cost, and allows data collection. This paper describes a high-current sensor operating in a range up to 100- and 7.7-kA resolution. The system consists of a self-integrating Rogowski coil connected to the electret sensor by a coaxial cable. The electret sensor is installed in a sturdy and inexpensive casing at the tower base. Measurements indicate a linear and precise correlation between the voltage generated by the coil, installed on the top of the tower, and the impulse current from lightning. [ABSTRACT FROM AUTHOR]

In this paper, we present current pulses from upward lightning, which have been measured since 2011 at the new top structure of the Peissenberg Tower, Germany. The study comprises 38 negative and two positive flashes, which contained 199 current pulses. About 49 of them were return stroke current pulses, 133 of them were current pulses, which superimposed the initial continuous current (ICC-pulses), and 17 of them were M-component current pulses, which superimposed the continuing current of a preceding return stroke. The current pulses are used to evaluate the performance of the European lightning location system EUCLID. Fifty one (25.6%) out of the 199 current pulses were detected by EUCLID, 40 (81.6%) return stroke current pulses, and 11 (8.5%) ICC-pulses or M-component current pulses. The peak currents ranged from 0.1 to 40.8 kA. Two groups of current pulses could be identified. The first group is related to branches of nearby downward lightning which got in contact with the tower. Therefore, EUCLID reported much higher peak currents (more than 100%) compared to the peak currents measured at the Peissenberg Tower. The first group comprises the total of nine current pulses (six ICC-pulses, three return stroke current pulses). The second group of current pulses is related to upward lightning initiated from the top of the tower. The peak current inferred from EUCLID deviates much less from peak current measured at the Peissenberg Tower. The peak current was overestimated by about 20% by EUCLID. The second group comprises the total of 42 current pulses (4 ICC-pulses, 1 M-component current pulses, and 37 return stroke current pulses). The peak currents ranged from 3.1 to 40.8 kA, the geometric mean (GM) was 9.4 kA. About 30% of these events were misclassified as intra-cloud pulses by EUCLID. The GM of the location error was 161 m for all events, and 132 m considering only the return stroke current pulses. [ABSTRACT FROM AUTHOR]

With the development of the power system automation and the smart grid, intelligent monitoring sensors are widely used in the high-voltage power transmission lines (HVPLs). To ensure the stability and effectiveness of the monitoring sensors, the method of power supply should be solved urgently. In this paper, a three-coil wireless power supply system is proposed by considering the insulation problem. By comparing the insulation characteristics of the HVPLs with configuring the relay coil or not, the feasibility of the three-coil wireless power supply system in the application is validated. On the basis, the impedance matching conditions to achieve maximum efficiency and receiving power are analyzed. Particularly, a method to design the relay coil, used as an impedance matching window, is introduced so that the efficiency and the receiving power can be optimized simultaneously in different application situations. The theoretical analysis is confirmed by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

In this paper, we present the currents, which have been measured since 2008 at the new top structure of the Peissenberg Tower, Germany, and the associated electric fields in a distance of about 180 m from the tower. The study comprises 17 negative lightning, which contained 44 subsequent return strokes, 108 initial continuous current (ICC)-pulses, and 26 M-components. The analysis, based on the current waveform, revealed three different types for both the M-component current and the ICC-pulse. The impulsive current of type 1 has a more or less symmetrical wave shape. For this type, the electric field occurred on average 15.7 μs prior to the current pulse. The impulsive current of type 2 has a bipolar wave shape with current reversal. The impulsive current of type 3 has a wave shape, which exhibits a fast rise to peak and a much longer decay to low current values. For all types of impulsive currents (return strokes, ICC-pulses, and M-components), the electric field exhibits a first field change (ΔE1) followed by a second field change (ΔE2) of opposite polarity. For the ICC-pulses and M-component currents of types 1 and 3, the first field change (ΔE1) has typically an initial slow-rising section, which is followed by a fast-rising section. The transition point was time-correlated with the onset of the current. The transition point was at about ΔE1/3 for type 1 and at about ΔE1/2 for type 3. For type 2, the onset of the current pulse occurred during the second field change (ΔE2) of opposite polarity. Similar to type 1 and 3 pulses, the slow-rising electric field changed into a fast-rising electric field. The transition point for type 2 pulse was at about ΔE2/3. From the 44 subsequent return strokes, 8 of them contained one negative M-component of type 1. In that case, the M-component current was extremely strong. The arithmetic mean (AM) was 8.5 kA (GM: 5.4 kA) for the peak current and 747.8 mC (GM: 614.0 mC) for the transferred charge. The return stroke was also very strong, with an AM of 16.7 kA for the peak current (GM: 15.0 kA). In comparison, the AM was 10.4 kA (GM: 8.3 kA) considering all subsequent return strokes. [ABSTRACT FROM AUTHOR]

This paper presents the computed lightning-radiated vertical electric field and azimuthal magnetic field at the ground level at observing distances ranging from 0.3 to 50 km from the lightning channel for striking the cone-shaped mountain top, by using the two-dimensional finite-difference time-domain method in cylindrical coordinate systems. It is found that the mountain height and the inclination angle have a significant effect on the lightning-radiated electromagnetic field both for the close and far observing distances. For the lightning-radiated vertical electric field, the enhancement of the far field beyond several kilometers (mainly radiation field component) is due to the reflection process in the transition between the mountain terrain and the flat ground, but the reduction of close field near the mountain terrain (mainly quasi-electrostatic field component) is due to the shadowing effect, but not due to such reflection. For the lightning-radiated azimuthal magnetic field, the field values for different mountain terrains, including the mountain height and inclination angle, increase both for close and far observing distances. [ABSTRACT FROM AUTHOR]

An unusual negative lightning flash was recorded at the Säntis Tower on June 15, 2012. The flash did not contain an initial continuous current typical of upward negative lightning, which is the most common type of event at the Säntis Tower. The flash contained four strokes, the last three of which were normal while the current associated with the first stroke resembled a Gaussian pulse with an unusually high peak value of 102.3 kA, a long risetime of 28.4 μs, and a pulsewidth of 53.8 μs, which was followed by an opposite polarity overshoot with a peak value of 8.5 kA. Our current records suggest the involvement of a long upward connecting positive leader in response to the approaching downward negative leader in the formation of this flash. Lightning location system (LLS) data indicate that a positive cloud-to-ground stroke occurred 1 ms prior to the first stroke of the flash. In this paper, we present a detailed description of the data associated with this event. Moreover, both a return stroke model and an M-component model are used to reproduce the far-field waveform of this bipolar stroke. The simulations result in a radiated electric field waveform that is similar to those of large bipolar events (LBEs) observed in winter thunderstorms in Japan. A sensitivity analysis of the used simulation models reveals that, by proper selection of the input parameters, all field waveform characteristics, except for the positive half-cycle width, can be made to fall in the range of LBE field characteristics reported in Japan. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Lightning surge propagation on telecommunication towers is essential to lightning protection design. Analysis of very fast surges in a telecommunication tower requires a full-wave solution of Maxwell's equations. This paper proposes a full-wave time domain partial element equivalent circuit (PEEC) method considering the effect of ground to evaluate the surge currents and voltages on vertical structures. The PEEC of the formulation is provided by using the method of image. This method can take into account the attenuation of the lighting surges, and has the potential to be implemented as a new type of solution for general lightning surge analysis. The proposed method is validated numerically with the finite-difference time domain method, and is used to analyze the surge propagation on cables mounted on two typical grounded telecommunication towers. The simulation shows that both the location of cable installations and the type of towers have a significant influence on the lightning protection performance. [ABSTRACT FROM AUTHOR]

In this paper, we are interested in the study of electromagnetic (EM) field waveforms generated by a lightning strike to a tower located on a trapezoidal mountain. The latter has a height of 500 m and a steepness angle of slope of 45°. The EM field components are calculated at six points and in three directions from the tower. Among these six points, four of them are placed on a flat ground and located at close distances from the mountain bottom while the other two points are located on the mountain at close distances from the tower. Also, because of the three-dimensional (3-D) geometry of the problem being treated, the computation is performed in three dimensions by using the finite-difference time-domain (FDTD) method. In this computation, the lightning channel is represented by the transmission line model extended to include a tall strike object. To evaluate the influence of the presence of mountain on the EM field waveforms, a comparison between the results obtained in the presence and absence of the mountain has been done. On the other hand, the ground conductivity effect on the EM field components has been also studied. At the end of this study, we show that the trapezoidal mountain shadowing effect causes a reduction of the vertical electric field calculated on a flat ground at close distances from the mountain bottom, while the field is enhanced on the top of the mountain. The same conclusion is drawn for the azimuthal magnetic field. Furthermore, the initial peaks of the vertical electric field and the azimuthal magnetic field, above the ground, have been attenuated because of the finite conductivity of ground. The horizontal electric fields above the ground are characterized by oscillations due to the presence of tower and mountain. The underground horizontal electric field and azimuthal magnetic field have the same waveforms as those obtained above the ground but with smaller magnitudes. Thus, the underground vertical electric is initially bipolar and then essentially zero. Finally, the 3-D-FDTD developed program was validated (see the Appendix). [ABSTRACT FROM AUTHOR]

This paper gives the overview and review of the traveling current source (TCS) model, which describes the electrical processes during the lightning return stroke. It is shown that the main characteristics of the measured electric and magnetic fields can be reproduced with the TCS model. These are the ''initial peak” of the electric and magnetic field for near, intermediate and far distances, the ''ramp” (up to the maximum) of the near electric field, the ''hump” of the near magnetic field after the initial peak, and the ''zero crossing” of the far distant electric and magnetic field. The TCS model is based on the assumption that the lightning current is injected at the top of the increasing return stroke channel represented by a transmission line. The original model is presented and then extended to take into account the current reflections occurring at ground and at the upper end of the return stroke channel. To this end, the ground reflection factor ρ and the top reflection factor R are introduced. Due to the increasing return stroke channel, the top reflection factor is a function of the return stroke velocity. The total current is composed of the source current according to the original TCS model and the reflected currents. An example shows that the ground reflection causes significant variation in the peak values of the channel-base current and of the maximum current derivative. A major effect was also found for the initial peak of the electric and magnetic fields calculated at 3 km distance. [ABSTRACT FROM AUTHOR]

In this paper, we present an analysis of electromagnetic fields generated by a lightning return stroke to a tall tower in presence of a horizontally stratified two-layer ground. The electromagnetic fields are evaluated at a distance of 50 m from the tower for two observation points above and below the ground surface, by using the finite-difference time-domain method. The developed numerical model is validated using available experimental data obtained at the CN Tower in Toronto. To illustrate and discuss the effect of the soil stratification on the electromagnetic fields, we adopt two different cases characterized, respectively, by an upper layer less conductive than the lower level, and vice versa. The obtained results show, for the considered distance range (50 m), that the electromagnetic fields above ground at such close distance are nearly insensitive to the ground stratification. However, the underground electromagnetic fields are markedly affected by the properties of the soil layers. In the presence of a lower layer of higher conductivity, the horizontal electric field is characterized by a faster rise time, a significant decrease in amplitude and a bipolar wave-shape compared to that in the case of a homogeneous ground with the upper-layer characteristics. On the other hand, the presence of a lower layer with lower conductivity results in an increase of the peak value of the underground horizontal electric field. [ABSTRACT FROM AUTHOR]

To study the coupling effect of an antenna near the lightning channel when the wireless base station lightning rod is attacked by lightning, the simulation models of lightning channel–communication tower and dipole antenna working on the communication frequency of 900 MHz are constructed in this paper based on the CST Studio Suite and FEKO. The results of $S_{2,1}$ calculated by the two simulation software are compared to verify the reliability of the models, then the coupling characteristics of the 900 MHz dipole antenna is discussed in terms of the heights of tower, the heights of the antenna, the horizontal distances of the antenna from the tower, and the polarization directions of the antenna. We find that the induced voltage of the antenna in vertical polarization is much larger than that in horizontal polarization. The further the antenna from the base station tower top, the smaller the induced voltage. When the antenna is within the range of 5 m below the tower top with set heights of 30, 25, 20, and 15 m, the induced voltage of the antenna decreases greatly in response to the reduction of antenna's height, and the closer the antenna to the tower, the greater the change. While outside the range, the induced voltage decreases slowly as the antenna's height reduces, until it almost remains unchanged, and the effect of antenna's horizontal distance from the tower on the induced voltage is not obvious. The induced peak voltage of the antenna is almost linearly decreased with its polarization rotation from vertical to horizontal polarization. [ABSTRACT FROM AUTHOR]

Nowadays, the analysis of the lightning performance of high-voltage (HV) underground sections has become increasingly important, thanks to their increasing usage with overhead transmission lines. In this way, the objective of this paper is to investigate the sensitivity of the overvoltages, at the terminal of underground cables (UCs), due to the incidence of negative lightning flashes at the shield wire or the tower top. It is done by means of different representations of the grounding behavior, different points of lightning incidence, different values of soil resistivity, and considering or not the variation of the soil electrical parameters with frequency. It is observed that a reliable investigation on lightning overvoltages is important and it must consider a suitable representation of the grounding behavior. An improper modeling can lead to nonrepresentative results. In this way, it is highlighted how the frequency dependence of the soil parameters influences the results in many different situations. For long distances from the UCs and low soil resistivity regions, all the grounding models produce similar results. On the other hand, for regions with high soil resistivities, the use of a proper model for the tower grounding is important, since the discrepancies between the results produced considering or not the dependence of the soil parameters with frequency become substantial. The inclusion of the grounding behavior with frequency allows to obtain reliable simulations of the transient behavior of the insulated cables, which constitute the underground section under study. [ABSTRACT FROM AUTHOR]

This paper presents a probabilistic evaluation of energy absorption capability of transmission line surge arresters (SAs), based on Monte-Carlo method. In the presented approach, a wideband model of tower-footing grounding system is adopted taking to account both constant and frequency-dependent soil electrical parameters. Furthermore, the effect of multistroke lightning flashes on the energy stress experienced by SAs is taken into account. To this aim, simulation is performed for a typical 400-kV transmission line which is modeled in EMTP-RV. From the simulation results, it is found that the absorbed energy is significantly affected by the modeling type of grounding system, i.e., static or wideband model. This effect seems to be more pronounced for the soil characterized by frequency-dependence electrical parameters. The presented results show that wideband modeling of grounding system can affect the estimated lifetime and the energy absorption capability of SAs. Hence, the wideband model of grounding system is suggested to be taken into account for the proper selection and sizing of SAs. [ABSTRACT FROM PUBLISHER]

This article proposes the deconvolution method to evaluate the lightning channel-base current from the lightning magnetic field. We have verified the method using the magnetic field with/;without noises. The deconvolution results are both in good agreement with the simulated current. Also, we have discussed the deconvolution results when the condition number of the deconvolution matrix, $U_{{0}}$ , is different, and found that the deconvolution results will oscillate if the condition number of $U_{{0}}$ is very large. Note that the deconvolution method presented in this paper also works when using other engineering current models, such as transmission line (TL) model, and the modified TL model with exponential current decaying with height model, and so on. The deconvolution method is an efficient method to evaluate the lightning channel-base current from the electromagnetic field. This approach is also useful in research related to lightning characteristics and lightning protection. [ABSTRACT FROM PUBLISHER]

This paper proposes the Powell (PPSO) method. The particle swarm optimization (PSO) algorithm is combined with the Powell algorithm to identify the parameters of lightning channel-base current function. The method can overcome the problem of premature convergence for PSO algorithm, and improve the analysis accuracy. The Heidler function is used to represent the lightning channel-base current. We have compared the PPSO method and genetic algorithm (GA) on reaching the desired peak value of the current Im and the maximum time rate of change of current (di/dt)max. The results show that the parameters of Heidler function evaluated by the PPSO method can achieve more accurate values of Im and (di/dt )max than those evaluated by GA. Also, we have compared the PPSO method, the Nelder–Mead particle swarm optimization (NMPSO) method, and PSO method using the measured channel-base current. The results show that the PPSO method is better than the NMPSO and PSO method to determine the channel-base current function parameters. The PPSO method is an efficient method to identify the channel-base function parameters, which can improve the digitalization of lightning monitoring equipment. This approach is also useful in research related to lightning characteristics and lightning protection. [ABSTRACT FROM AUTHOR]

Wind power plants are one of the most widespread sources of electric energy during the last few decades. Wind towers are quite often exposed to lightning strikes due to their tall height and long blades. In this paper, the lightning-induced voltages (LIVs) on a three-phase overhead line are computed for both first and subsequent strokes to a nearby grounded wind tower using the three-dimensional finite-difference time-domain method with homogeneous and horizontally stratified grounds. The horizontal electric fields are computed on the line and on the ground surface considering the transient grounding and characteristic impedances of the struck wind tower. The impact of the existence of wind tower on LIVs and horizontal electric fields is illustrated by removing the tower (i.e., return stroke to the ground surface). Finally, the influence of ground permittivity on the peak values of LIVs is investigated. [ABSTRACT FROM PUBLISHER]

This paper presents the results of a radiated electromagnetic field due to lightning strike to a tall tower sitting on a mountainous terrain when considering both the first and subsequent return strokes. A cone-shaped ground with finite conductivity represents the mountainous terrain; and a cylindrical two-dimensional finite-difference time-domain (FDTD) scheme is used to determine the lightning-generated electromagnetic fields. The return stroke channel is modeled using the antenna theory model with fixed inductive loading which is appropriately incorporated into the FDTD algorithm. Simulation results are presented for different values of the cone angle and height, and for different values of the tower height. It is shown that when the first and subsequent return strokes hit a tower on a cone-shaped ground, the radiated electric and magnetic fields experience an enhancement in their amplitudes as compared to the case where the tower sits on a flat ground. Also, the current reflections from the tower base, influencing the current distribution along the tower and radiated electromagnetic field waveforms, depend on the cone angle and height, as well as the tower height. [ABSTRACT FROM AUTHOR]

Due to the current spreading of wind farms all over the world and their vulnerability to lightning strikes, it is important to investigate the lightning electromagnetic transients in wind farms. Underground cables are one of the essential parts in wind farms that link the turbines with the electrical grid. This paper investigates how the ground conductivity and relative permittivity, struck wind tower position, and rise time of lightning current influence the lightning electromagnetic fields impinging the underground cable sheath. The three-dimensional finite-difference time-domain method is implemented for this study. The lightning current through the cable sheath and its associated electric field can be effectively mitigated by connecting the grounding systems of the wind towers by underground bare wires called as counterpoise. Accordingly, the mitigation effect of counterpoise on the lightning current through the sheath and its associated electric field is also investigated. The results show that the lightning current through the cable sheath and its associated electric field is higher with lower ground conductivity. Moreover, it is revealed that the effect of both ground permittivity and struck wind tower position on the associated electric field and the sheath current is dependent on the ground conductivity. [ABSTRACT FROM AUTHOR]

In this paper, we present a theoretical analysis of the propagation effects of lightning electromagnetic fields over a mountainous terrain. The analysis is supported by experimental observations consisting of simultaneous records of lightning currents and electric fields associated with upward negative lightning flashes to the instrumented Säntis tower in Switzerland. The propagation of lightning electromagnetic fields along the mountainous region around the Säntis tower is simulated using a full-wave approach based on the finite-difference time-domain method and using the two-dimensional topographic map along the direct path between the tower and the field measurement station located at about 15 km from the tower. We show that, considering the real irregular terrain between the Säntis tower and the field measurement station, both the waveshape and amplitude of the simulated electric fields associated with return strokes and fast initial continuous current pulses are in excellent agreement with the measured waveforms. On the other hand, the assumption of a flat ground results in a significant underestimation of the peak electric field. Finally, we discuss the sensitivity of the obtained results to the assumed values for the return stroke speed and the ground conductivity, the adopted return stroke model, as well as the presence of the building on which the sensors were located. [ABSTRACT FROM AUTHOR]

Microwave relay stations are key components in controlling power grids and maintaining their stability, but lightning strikes to the stations may cause faults, malfunctions, or even physical damage to microwave radio equipment. To protect equipment from lightning, it is necessary to predict surge phenomena in a microwave relay station, and design effective lightning protection methodologies. Recently, numerical electromagnetic field computation methods to solve Maxwell's equations have entered widespread use for analyzing surge phenomena in 3-D structures such as buildings and towers and in grounding structures such as grounding grids. In this paper, we apply the finite-difference time-domain (FDTD) method to the surge analysis of a microwave relay station. First, to validate the applicability of the FDTD method, we set up a reduced-scale model of a microwave relay station. Using this model, we measured the distribution of the currents flowing through the station and compared the measured results with those simulated by the FDTD method. Second, through FDTD-based surge simulations, we analyzed the effects of the reinforcing bars of a building, the route of the ground wire of a waveguide, and the layout of a deep earth electrode on the lightning current distribution. [ABSTRACT FROM AUTHOR]

Subject matter of this paper is the analysis of the high-frequency oscillation of the lightning currents which have been measured at the top of the Peissenberg Tower, Germany. The oscillations appeared only during the initial period of fast-rising currents. In 2007, the tower top section was removed and replaced by a smaller construction. As a result, the frequency of the oscillation changed from formerly ∼12.5 to ∼6 MHz. The oscillations could be reproduced with simulations using the computer code CONCEPT II. It was found that the high-frequency current oscillation is caused by the transient response of the top structure of the Peissenberg Tower. The currents at lower sections of the tower as well as the nearby electric and magnetic field (∼190 m from the tower) contained less significant pulsation. As a major result, the presence of the tower increased the risetime of the fast-rising currents. Probably for this reason, the highest maximum current steepness ever recorded was limited to 155 kA/μs. [ABSTRACT FROM AUTHOR]

This paper presents the evaluation of lightning performance of transmission lines considering the wide-band modeling of their associated tower-footing grounding systems. To this aim, first, the grounding system admittance matrix over the frequency range of interest is obtained by making use of the method of moments solution to Maxwell's equations. In the next stage, the matrix pencil method is used to infer the pole-residue identification of the obtained admittance matrix. Finally, the obtained pole-residue model is incorporated into the EMTP-RV in the form of a state-space block. The back-flashover analysis is done for a typical 132-kV transmission line, while the tower-footing grounding system is modeled in three different ways namely: 1) static-model, 2) wide-band model assuming constant electrical parameters for the soil, and 3) wide-band model assuming frequency-dependent electrical parameters for the soil. From the simulations, it is found that the inclusion of the wide-band model of the tower-footing grounding system can markedly affect the total probability of back-flashover in transmission lines. This effect is more pronounced when the frequency dependence of soil electrical parameters is taken into account. It is shown that considering the wide-band modeling of tower-footing grounding system can affect (either decrease or increase) the total back-flashover probability of transmission lines. [ABSTRACT FROM AUTHOR]

In this paper, the transient impulse performances of a 330-kV composite transmission line tower under direct lightning strokes are comprehensively presented. An equivalent distributed parameter model combined with lumped capacitance elements for the tower is established. The wave impedances of the hybrid model are determined by using analytic equations. The lumped capacitances are calculated by 3-D finite element method (FEM). An accurate model for extended grounding structure (EGS) of the tower base considering the soil ionization is used to simulate its impulse performances. The wave process of the tower is analyzed by using the electromagnetic transient program (EMTP). The proper grounding conductor system is determined for the case of a superior lightning impulse performance considering three diverse grounding configurations. The influence of radius of the grounding conductor is assessed. The numerical electromagnetic field analysis, finite-difference time-domain (FDTD) simulation is applied to verify the validity of the presented hybrid model. Then, the influence of the wave-front time of the lightning current, the soil resistivity, the dimension of the EGS, and their combined effect on the transient impulse performances for the EGS are analyzed and discussed. [ABSTRACT FROM AUTHOR]

Subject matter of this paper is the analysis of the total of six upward positive lightning initiated from the Peissenberg Tower, Germany. All of them occurred during the cold season from February to April in the years 1997 to 1999. Three of them were initiated without nearby preceding lightning activity (called “self-initiated” upward lightning) and the other three occurred during nearby lightning activity (called “other-triggered” up-ward lightning). The analysis suggests that the other-triggered upward lightning is a downward lightning involving a relatively long upward connecting leader. The first current component, however, was different from the current of a first return stroke of a positive cloud-to-ground flash. On average, the duration was 15.7 ms, the maximum was 4.37 kA, and the charge was 13.3 C. Due to the long duration and the relatively low current, the first current component is more consistent with the initial continuous current (ICC) of an upward lightning. The initial period of the ICC exhibits a slowly rising portion lasting about 1 ms. During that period, the ICC was superimposed by weak current pulses. The arithmetic means of the pulse peak and the pulse duration were 0.49 kA and 9.6 μs, respectively. The average leader velocity was \bf \bf 2.3 \, \bm \times \,\bf 10^\bf 5 m/s and the average leader charge density was \bf 1.02 \, \bf \times\, \bf 10^\bf -3 C/m. Much stronger current pulses were observed after that initial period. Then, the arithmetic means were 5.3 kA for the pulse peak and 46.6 μs for the pulse duration. The ICC of the self-initiated upward lightning did not exhibit such an initial slowly rising portion with weak superimposed current pulses. The ICC immediately increased to several kilo-amperes involving strong current pulsation. For the ICC, the arithmetic means were 58 ms for the duration, 6.4 kA for the maximum, and 105 C for the charge. For the current pulses, the arithmetic means were 5.7 kA for the pulse peak and 19 μs for the pulse duration. The leader charge density was estimated to be up to several 10 mC/m. [ABSTRACT FROM PUBLISHER]

This paper presents a procedure for evaluation of lightning performance of overhead distribution lines. Because both voltages from direct strokes and nearby strokes may cause flashovers in distribution lines, flashover rates due to them need to be analyzed. The procedure is implemented in electromagnetic transient program, and the Monte Carlo method is used to take into account the random nature of lightning parameters. The lightning-induced voltages are calculated with an equivalent circuit derived from Agrawal formula. The influence of insulation level and spacing between surge arresters on lightning flashover rates is analyzed with the procedure. For a line with low-insulation level about 150 kV above high conductivity ground or with high-insulation level about 300 kV above low conductivity ground, the spacing between arresters is best less than 400 m. But for a line with low-insulation level above low conductivity ground, it is better to reduce the spacing to 200 m. [ABSTRACT FROM AUTHOR]

This paper analyzes the slow-varying electric fields and the associated currents of a total of 35 negative upward lightning initiated by the Peissenberg tower, Germany. Thirty-four of which were from winter upward lightning and only one from summer upward lightning. It appears that all of the winter upward lightning were initiated without nearby preceding lightning activity (called “self-initiated” lightning) and only the summer lightning was triggered by nearby lightning activity (called “other-triggered” lightning). The slow-varying electric fields of the winter upward lightning showed a fast rise characterized by the 10–90% risetime, with an arithmetic mean of 13.8 ms. After attaining the maximum, the electric field turned into a slow decay being characterized by the time on half value which was evaluated to having the arithmetic mean of 441 ms. Transported charges to ground were on average 44.8 C and on maximum 165 C. The maximum value of the electric field was 39.9 kV/m on average, with the highest value being 64.5 kV/m. For the electric fields, higher values were prevented by recovery effects such as the corona from objects at ground and the redistribution of the charge in the thundercloud. Due to these effects, no or only weak correlations were found between the 10–90% risetime, the time on half value, the charge, and the maximum of the electric field. From additional measurements with a field mill, it was found that the electric field recovers to the starting level within some seconds. [ABSTRACT FROM PUBLISHER]

We discuss in this paper the propagation of lightning current pulses along conical tall structures. Although the dominant mode of an infinitely long conical transmission line is transverse electric and magnetic (TEM), such a structure can also support higher order TE and TM modes which display a gradual cutoff frequency variation with height. Recently, Baba and Rakov's finite-difference time domain numerical analysis revealed that for a perfectly conducting conical structure, while the current pulses suffer no attenuation as they travel from the cone's apex to its base, the attenuation is significant when pulses propagate from the base to the apex. Adopting an analysis method using 1) the COMSOL Multiphysics simulation environment based on the finite element method and 2) the partial equivalent element circuit method, we study the same reduced-scale structure analyzed by Baba and Rakov. The obtained results confirm the conclusions drawn by Baba and Rakov. We also perform simulations for the case of a 100-m tall tower considering different tower-base radii. It is shown that the upward current pulses are affected by a strong attenuation resulting from the field scattering near the discontinuity at the tower base, followed by a weaker attenuation resulting from the propagation along the cone from its base to the apex. A simple way to modify the engineering lightning return stroke models to account for the attenuation of the upward current pulses is suggested. Finally, we report on experiments to study the current pulse propagation along a 1/582 reduced scale model of the Toronto, CN, tower. The obtained experimental data support the numerical simulations. [ABSTRACT FROM AUTHOR]