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The lightning-related outages remain a significant factor affecting overhead-line reliability in the Israel Electric Co. (IECo) Power Grid 170 kV. The estimates derived for years 2000–2013 show that the actual failure rate for some lines does considerably exceed the accepted indices. This paper reports on the lightning study whose primary goal was to examine relevant environmental data, including topography, tower footing resistance, and lightning incidence records provided by the IECo lightning location system. This paper presents long-term monitoring experience and local statistical data patterns gained for cloud-to-ground return strokes. The 295 outage-related flashes (265 of negative and 30 of positive polarity) were identified in the IECo database. The median peak current of the negative and positive flashes causing line outages is -12.0 kA and +26 kA, respectively. The local tower footing resistances are found to be lognormal distributed with a median of 4.77 \Omega and an SD of 1.44. The findings imply that revealed failure currents statistics, in combination with local route topography, are key factors controlling shielding performance of IECo lines. The acquired data will be involved in further case studies on IECo lines. [ABSTRACT FROM AUTHOR]

This paper presents a numerical method for calculating the resistance, inductance, and capacitance matrices of transformer windings. Importance of their precise calculation is shown in the simulation of voltage distribution over the windings for a lightning-impulse test. The results obtained in frequency domain analysis are in good agreement with the measurement data. All the parameters are calculated using the self-developed solvers, the theory and the novelty of which are described in this paper. The presented approach allows fast and accurate high-frequency modeling of transformer windings. [ABSTRACT FROM AUTHOR]

This paper presents a closed expression for the lightning induced voltage in short loops, which considers the effect of the return stroke speed. It is shown that the traditional expression that provides the induced voltage as the product of the current time derivative by the mutual inductance is a particular case of the expression developed in this paper, which holds when the return stroke propagates with the speed of light. The comparison between the results of the traditional expression and the new one is carried out for different distances from the lightning flash and different stroke current waveforms. The effect of the return stroke speed is also investigated, showing that the higher the speed, the higher the induced voltage. The effect of loop length is investigated, showing that the loop can be considered as electrically short if its dimensions are smaller than one-tenth of the product between the current front time and the speed of light in free space. [ABSTRACT FROM AUTHOR]

The groundings of the power distribution, signaling, and power systems of a railway system are individually performed to realize fail safe, and the groundings are often installed in close proximity. Thus, when a grounding electrode is invaded by a lightning current, its ground potential rises together with the potential of the adjacent grounding electrodes; hence, there is a possibility of a large overvoltage being applied to the connected devices. In this paper, we have investigated the potential spread between two rod-shaped electrodes widely used in the grounding of the power, signal, and distribution systems of a railway system using the finite-difference time-domain method. The results of this paper are organized in such a way that the extent of the potential spread to the neighboring grounding electrodes can be understood from information such as the grounding resistivity at the installation location of the ground electrode and the wavefront duration of the lightning current, and these findings will be useful for grounding design. We also investigate the effect of the insulator between two neighboring electrodes to prevent the potential spread. [ABSTRACT FROM AUTHOR]

Unlike most electrical systems, electrical submersible pump (ESP) system grounding has its unique feature: it must be divided into two zones, i.e., surface and downhole zones, grounding practices for the two zones are significantly different. In this paper, the current practice and future trend for ESP system grounding is presented, which is based on an extensive literature review, including the industry practice, published technical papers, and the patent search. This paper will be extremely useful for field engineers and ESP system design engineers to understand requirements, techniques, and future development directions for ESP system grounding. [ABSTRACT FROM PUBLISHER]

This paper applies a rigorous electromagnetic model to determine the transient distribution of potentials along a substation earth grounding grid subjected to lightning currents. The obtained results show that, in the initial period of the transient, equipment pieces that are earth grounded at distinct points of the grid and are electrically linked (for example, by aerial communication cables) experience impulsive loop currents. Such loop currents can cause equipment malfunctions, failures, and damage. A remarkable conclusion of this paper is that such loop currents can reach substantial values even in the case of soils of low resistivity. Some practical aspects are highlighted in order to reduce the risks due to the nonuniform distribution of potentials along earth grounding. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to wideband modeling of tower footing grounding impedances. Appropriate representation of transmission tower footing impedances is essential in electromagnetic (EM) transient simulations for proper evaluation of overvoltages and flashovers in the system during fast-front transient conditions such as lightning strikes. In this paper, a field solver is used to precisely model the most popular types of tower footing grounding systems, i.e., rods, counterpoises, and ring electrodes, for a variety of dimensions and soil parameters. Results are stored in a lookup table and used for generating frequency-dependent models that are exported to EM transient simulators. The table and model generation tool can be used by utility companies to model tower footings while taking into account local variations along the right-of-way, such as local variations in soil resistivity. The presented examples show close agreement of results of lightning studies using developed electrode models included in EM tools, e.g., PSCAD, EMTP-RV, and ATP-EMTP. A sensitivity study shows that the maximum voltage at the tower top during a direct lightning strike can be up to 19% higher when using the adopted modeling procedure, as compared to a standard approach of using a fixed resistor equal to the power frequency resistance. [ABSTRACT FROM AUTHOR]

Lightning is a substantial cause that leads to serious lightning failures, which has a significant influence on the normal operation of the entire power grid. This paper mainly focused on several regions of China with serious lightning activity, presenting the lightning performance of power grids by statistics obtained from long-term monitoring data, and intended to indicate some general characteristics. The lightning tripout rate, the shielding failure tripout ratio, the occurrence frequency corresponding tripout failures of different phases of single-circuit or double-circuit transmission lines, and the multicircuit simultaneous tripout failures of multicircuit transmission lines were analyzed. These statistical results presented a panorama of the lightning protection effect of transmission lines in China. The statistical data in this paper are informative to guide the future research or engineering practice of lightning protection of transmission lines, and will be helpful to evaluate the analysis methods of lightning performance of transmission lines. [ABSTRACT FROM AUTHOR]

In the companion paper (Part I), a new tool for lightning-induced voltage calculations, called CiLIV, has been presented. In this paper (Part II), predictions made with the new tool are compared to experimental data and to outputs of analytical procedures/numerical codes found in the literature. [ABSTRACT FROM PUBLISHER]

The operation experiences of power transmission lines show the lightning outage is still the main part of the total outage rate. So it is very important to calculate the lightning overvoltage across the insulators precisely and evaluate the lightning outage of the transmission lines correctly. Lightning flashover criterion of the insulator/gap is one of the most important factors that influence the precise calculation results of the lightning withstand level of transmission lines. In China, several ?800 kV ultra high voltage direct current (UHVDC) power transmission projects have been set up in recent years, and the altitude of the regions that the transmission lines across ranges from 0-3650 m. The paper mainly analyzed the influence of the modelling methods of insulator/gap on the lightning withstand level of ?800 kV UHVDC transmission lines by PSCAD/EMTDC program. The compared lightning flashover criteria of insulator/gap include the leader propagation model recommended by CIGRE, the volt/time curve recommended by IEEE and an improved leader propagation model, which is proposed based on the lightning flashover experiments of the ?800 kV UHVDC line insulators carried out at an altitude of 2100 m. Meanwhile, the influences of lightning current waveform and insulator structure were also considered and compared. The simulation results show that the calculated back-flashover lightning withstand level is much lower when using the improved leader propagation than that using other flashover criterions in the paper, it is lower under the 2.6/50 ?s double exponential lightning current than that under the 2.0/50 ?s Heidler function lightning current, and it is higher when using V-string than that using I-string insulator. Besides, the influences of the lightning current waveform and the insulator structure on the calculation of shielding failure lightning withstand level are little, but the flashover criterion has obvious influences on the shielding failure lightning withstand level. [ABSTRACT FROM AUTHOR]

In the companion paper, a methodology for computing transmission-line short circuits caused by direct and nearby ground lightning incidence was described. This paper presents the application of methodological and computational procedures of this methodology, regarding the calculation of lightning performance of transmission lines. From the computed results, focusing on 138- and 230-kV typical three-phase transmission lines, the effectiveness of the described process is clear, even when the line is modeled three-dimensionally or when nonlinear elements are present, for example, when arresters are installed in the line. [ABSTRACT FROM AUTHOR]

This paper is divided into two main parts. The first one describes the computation of the number of lightning strokes that directly hit transmission lines as well as those strokes that hit the earth’s surface near a line and can provoke very high overvoltages. The second one describes a process for computing the consequent short circuits in a line caused by both types of stroke incidence. In the companion paper, some application examples are presented. [ABSTRACT FROM AUTHOR]

This paper discusses the influence of stroke current propagation velocity on the characteristics of lightning horizontal electric fields, considering different types of soil and distances to the stroke location. The MTLE model is adopted for the determination of the current distribution along the return stroke channel, whereas the effect of the finite-ground conductivity is taken into account by using the modified Cooray–Rubinstein approximation. This paper also discusses the effect of the propagation velocity on each of the horizontal electric field components. The results show that the horizontal electric field is strongly influenced by the stroke current propagation velocity even for the case of good conductive ground and observation points relatively close to the stroke location. Regardless of the ground conductivity, the peak value of the static component decreases and the negative peak of the radiation component increases with the propagation velocity. Therefore, for short distances to the lightning channel, the absolute peak value of the horizontal electric field tends to decrease as the velocity increases, while for distances of few kilometers or larger its behavior is just the opposite, i.e., the amplitude increases with the propagation velocity. [ABSTRACT FROM PUBLISHER]

Models of one or several extremely simple transmission towers (pylons) are usually used for analyzing the influence of lightning strikes on power network. Models of more complex transmission towers with transmission lines, ground wires and even lightning channel are required. In this paper, first of all, the reason why one only focuses on the magnetic field at the observation points is briefly explained. Secondly, a method used to get the time-domain results from the frequency-domain results by Antenna Design Framework Electromagnetic Satellite (ADF?EMS) software is established and its validity is proved. Thirdly, the effects of the lightning channels with different geometries are discussed. Finally, this paper comes up with a complex multi-tower system under the following fault types of lightning strikes, 1) direct lightning strikes to the edge phase wire without flashover, 2) direct lightning strikes to the edge phase wire with flashover, 3) lightning strikes to the top of the tower without flashover, and 4) lightning strikes to the top of the tower with back flashover. The magnetic field waveforms from these fault types are very important for the follow-up activity to achieve the fault type identification of lightning strikes in the observation system automatically. [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 presents experimental results obtained from the Guangdong comprehensive observation experiment on lightning discharge during summer 2014. Residual voltages and current flows in a surge protective device (SPD) connected to an overhead distribution line were observed due to nearby M-components of a triggered lightning flash. Residual voltages with varying characteristics caused by different M-components are analyzed at two terminals of the SPD, and corresponding formation mechanisms for the different characteristics are also discussed. Our results show that the residual voltages at two terminals of the SPD caused by three types of M-component are determined from both the line induction and the ground potential rise (GPR) in a nearby triggered lightning at 40 m distance. The M-component with a large peak current would produce large surge energies in the power line. Under a given peak current, the M-component has greater surge energy than the return stroke. The ground terminal of the SPD is still affected by the GPR, and our results also show that the continuing current superimposed with M-components is an important factor in determining the magnitude of line coupling in power distribution lines when a lightning flash occurs nearby. [ABSTRACT FROM PUBLISHER]

In this paper, we present a new solution for the evaluation of the horizontal electric field in the presence of finitely conducting ground in the time domain. The solution is general, numerically robust, and overcomes the problems related to previously proposed approaches. [ABSTRACT FROM PUBLISHER]

During operation transformers are typically subjected to overvoltages with different wave shapes. Even though overvoltage protection systems, such as metal oxide surge arresters, are often employed, the overvoltages generated in power systems can still have a significant impact on the insulation systems of the windings of a power transformer. There are numerous examples of transformer failures as a result of overvoltages occurring during operation, even in cases that standard impulse voltage tests show no indication of potential problems and the transformers are protected by surge arresters. Comparisons of the internal overvoltages generated in transformers during voltage tests as well as those generated during standard operation of electrical networks provides fundamental insights into these overvoltages; insights which in turn can be used to improve the construction of insulation systems and overvoltage protection approaches and ultimately increase the reliability of transformers. In this paper, internal overvoltages occurring in the windings of selected transformer during standard voltage tests are compared with those which occur during typical operation of a transformer in an electrical power system. Overvoltages measured in the windings of the transformer form the basis of this comparison. Measurements were conducted with the transformer being subjected to voltage impulse tests, as well as transient voltages with waveforms simulating overvoltages generated in electrical power systems. In order to investigate the response of the windings to voltage strokes, full and chopped lightning voltage impulses were applied to the transformer. The waveforms of overvoltages generated in the electrical power systems were modelled as a rectangular voltage stroke, sinusoidal voltage, voltage with shape of “sweep sinus” also often referred to as a chirp signal and voltage with shape of “sweep ramp”. [ABSTRACT FROM AUTHOR]

In this paper, the lightning shielding performance of a newly designed 400-k \textV double-circuit composite tower is investigated. Based on a revised electrogeometric model (EGM) method, traditional shielding failure regions located at both sides of a traditional tower are no longer a big issue for the fully composite tower, due to its unusual ^\prime Y^\prime configuration. Instead, a new unprotected region exists in the tower center. The maximum lightning current that can lead to shielding failure and the shielding failure rate of the new tower are calculated. To verify results from the revised EGM method, a scale model test is conducted. Spatial shielding failure probability around the tower is calculated based on the ratio of discharge paths recorded in the test. Moreover, based on test results, the maximum shielding failure lightning currents are obtained. Analysis and results derived from the revised EGM method and scale model test have a small deviation, verifying the feasibility of these two methods in the lightning performance evaluation of the fully composite tower. Both methods confirm that the unusual negative shielding angle of -\text60^\circ in the newly composite tower provides good lightning shielding performance. The feasibility of the novel composite tower is verified from the lightning protection point of view. [ABSTRACT FROM PUBLISHER]

Recently, Andreotti et al. (2015) have presented a new tool for lightning induced voltage calculations on power networks. This tool, named Circuit for Lightning Induced Voltage (CiLIV), has been initially developed for straight and vertical lightning channels; afterwards, the tool has been extended to evaluate induced voltages produced by tortuous lightning channels. However, in the aforementioned studies, only simple power network configurations have been examined. Therefore, aim of this paper is twofold: 1) to apply CiLIV to more complex network configurations, that is, complex networks equipped with transformers, surge arresters, groundings, and so on; 2) to investigate the effects of channel tortuosity on the voltages induced in these complex networks. [ABSTRACT FROM PUBLISHER]

This paper describes the results obtained in the three sets of experiments. The laser emission and microwaves have been obtained almost with the same experimental setup. The ultraviolet radiation coming from the current carrying the spark channel pumps the N2 molecules to the upper-excited C3πu level to yield the nitrogen laser pulses at 337.1 nm of long (>220 ns) duration in the experimental setup used. The electromagnetic waves observed at the single microwave frequency close to 1 GHz and at 337.1 nm (=prominent nitrogen laser line) are the coherent radiations due to the maser action and the laser action, respectively. An attempt is made to relate one of these concepts to the lightning phenomena. [ABSTRACT FROM AUTHOR]

This paper presents a hybrid method based on the transmission line modeling method (TLM) aiming to represent the soil ionization effect for grounding systems simulation. This natural phenomenon can be better represented by taking into account the variation of the conductive components present in the TLM circuit and considering the residual resistivity remaining in the soil. The proposed analytical formulation is developed with a focus on the computational implementation of the method. The model is validated by comparing synthetized test results with measured data and other numerical models (residual resistivity, TLM, and analytical model). High precision together with an easy to implement formulation indicates that the methodology presents potential for real-life applications. [ABSTRACT FROM AUTHOR]

In order to solve the frequently occurring lightning flashover problems on ±500 kV dc transmission lines in China, the authors have conducted the research on the dc line arrester since 2011. In this paper, the structure and installation, technical parameters, and protection performances, as well as their deterministic processes of the arrester are presented and analyzed in detail. In 2013, the authors successfully developed the arrester products, and the type tests show that they have excellent performance parameters and can act effectively against the lightning impulse and cutoff the dc follow current. By now more than 500 dc line arresters have been installed and used on seven ±500 kV dc transmission lines in eight provinces of China. About four years of operating experience shows that the arresters work safely and reliably over a long period of time, and have been effectively reducing the lightning flashover rate of the ±500 kV dc lines. [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]

In this paper, a hybrid approach of the constrained interpolation profile (CIP) method and the transmission line modeling (TLM) method has been proposed for analyzing lightning electromagnetic fields and surges in the three-dimensional Cartesian coordinate system. The TLM method is employed locally in the working space for representing thin-wire conductors, and the CIP method is used for computing fields in the rest of the working space. Waveforms of lightning electromagnetic fields and surges computed using the CIP-TLM hybrid method agree well with corresponding ones computed using exact analytical expressions or with the finite-difference time-domain method. [ABSTRACT FROM PUBLISHER]

In this paper, a novel mapping algorithm by applying electromagnetic time reversal (EMTR) technique to broadband very high frequency (VHF) for the direction-of-arrival (DOA) estimation of lightning radiation sources is proposed and validated. Based on the theory of array signal DOA estimation and time reversal (TR) principle, the lightning radiation receiving model with broadband VHF array is established, and thereafter the TR synthesized signal for arbitrary direction is derived. It is proved that the direction with the maximum norm of synthesized signal is the optimal estimation for the incident direction, and hence the procedure for the EMTR-VHF method is derived. Numerical simulations are conducted for testing the algorithm and investigating the relationships between the array spatial resolution and the available signal frequencies, robustness of the algorithm, et al. Two metrics, amplitude ratio and energy ratio, are devised to filter false locations, and the acceptable ranges of them are further estimated by simulation. In order to further validate the EMTR-VHF algorithm, field experiments are carried out. The results show that the EMTR-VHF method performs well, especially for the sources with low elevations, with the error less than 1°. Finally, the application of EMTR-VHF method in locating a negative cloud-to-ground flash is presented. Temporal and spatial development of the leader-return stroke sequence could be well depicted. The results are generally consistent with the VHF interferometry technique, which confirm its ability in lightning localization. Besides, the discrepancy between this algorithm and broadband interferometry method are documented. [ABSTRACT FROM PUBLISHER]

Winding deformation is a critical power transformer issue that needs to be detected as soon as it emerges due to its progressive nature and severe consequences it may lead to. Frequency response analysis (FRA) is the only reliable technique currently used to detect such deformation. However, the technique is conducted offline that may cause interruption to the electricity grid when taking an operating transformer out of service for testing. Moreover, as the current FRA technique is only conducted on suspected units, a mechanical fault may emerge and progress before the utility becomes aware of. To overcome these limitations, this paper presents a practical feasibility study to detect transformer winding deformations online. The technique relies on utilizing transient overvoltage signals that a transformer is subjected to during its normal operation as a natural variable frequency excitation source. The feasibility of utilizing various transient overvoltage signals as excitation source for transformer FRA signature measurement is firstly investigated and optimum signal parameters are recommended based on signal voltage and energy spectrum analyses. Secondly, the proposed technique is verified through simulation analysis by comparing the transformer frequency response signatures when transient overvoltage and conventional sweep frequency voltage are used as excitation sources. Also, experimental testing is conducted to assess the feasibility of the proposed technique to identify various winding deformations such as radial buckling, telescoping and short circuit turns. Custom-made capacitive voltage divider is developed to accurately detect the response of transient overvoltage signals generated due to environmental conditions or power system switching operations. The proposed technique along with the developed capacitive voltage divider is implemented on a 3-phase Wye-Delta, 50 Hz, 31.5 MVA, 110/10.5 kV power transformer to measure the frequency response signatures of the high voltage winding. [ABSTRACT FROM AUTHOR]

The field lightning impulse withstand voltage test is an important step to ensure the safe operation of the gas insulated switchgear (GIS). The oscillating lightning impulse voltage is recommended in field test by IEC standard due to its high generating efficiency and lower impulse ratio. The insulation condition of GIS can be evaluated overall by detecting the partial discharge (PD) when conducting the field impulse withstand voltage test. In this paper, the protrusion defect was set in a 330 kV real GIS to study the PD characteristics under lightning impulse voltages, including SLI (standard lightning impulse) voltage and OLI (oscillating lightning impulse) voltages with different oscillating frequencies. The PD under impulse voltages was effectively detected by using the internal UHF sensor. The 50% probability PD inception voltage (PDIV50), maximum discharge amplitude, and discharge number were analyzed based on the measurement results. It was concluded that the PD number is significantly larger and the PDIV50 of OLI voltage is lower when the oscillating frequency is low by comparing the results of oscillating and standard impulse voltage. The PDIV50 increases and discharge number decreases with the increasing of oscillating frequency of the OLI voltage. [ABSTRACT FROM AUTHOR]

This paper presents an examination on the electrical properties of Palm Oil (PO) and Coconut Oil (CO) under the presence of semi-conductive nanoparticle, Titanium (IV) Oxide (TiO2). The type of PO used in this study was Refined, Bleached and Deodorized Palm Oil (RBDPO) Olein. TiO2 was dispersed into RBDPO and CO at volume concentrations ranging from 0.001% to 0.05%. The effect of surfactant, Cetrimonium Bromide (CTAB) was also examined and the morphology of RBDPO and CO based TiO2 nanofluid was observed through Transmission Electron Microscope (TEM). A number of measurements were carried out including the AC/lightning breakdown voltages, dielectric dissipation factor, relative permittivity and resistivity. Statistical analysis was carried out through Weibull distribution to determine the AC and lightning withstand voltages at 1% probability for RBDPO and CO. It is found that without CTAB, there are only slight improvements on the AC breakdown voltages of the RBDPO and CO with introduction of TiO2 but could decrease with presence of CTAB. The same pattern is found for lightning breakdown voltages of RBDPO and CO under non-uniform field where the highest percentages of increments decrease with introduction of CTAB while the effect is not apparent under quasi-uniform field. Significant effect of CTAB is found on the dielectric dissipation factors and resistivity of RBDPO and CO based TiO2 nanofluid while the relative permittivity are not affected. The statistical analyses reveal that RBDPO and CO experience apparent increments of the AC breakdown voltages at 1% probability after the introduction of TiO2 regardless with or without CTAB. The improvements done by TiO2 on the lightning breakdown voltages at 1% probability for all samples with CTAB under quasi-uniform field are more apparent than non-uniform field. [ABSTRACT FROM AUTHOR]

The leader progression model (LPM) is employed to investigate the shielding system performance of high-voltage substations against direct lightning strokes in the presence of substation instruments. The substation is simulated in detail for high accurate calculation of the shielding failure rate. Almost all of the apparatuses are modeled as fictitious charges in the stepwise simulations of LPM. The charge simulation method is used for finding the electrical field during the lightning movement. The probability of upward leader propagation is considered from all apparatuses. For more practical simulation, the environmental conditions are also included in simulations. The investigations are implemented on a test case and a practical high-voltage substation. The results are compared to those of the electrogeometric model. It is very likely that the results of this paper better simulate reality because lots of parameters have been taken into account. The results reveal that the presence of substation instruments increases the striking distance and the SF since they attract the lightning moving down near the substation. [ABSTRACT FROM PUBLISHER]

In this paper, streamer and breakdown phenomena and their mechanisms of an inhibited Gas-to-Liquid (GTL) transformer oil under standard negative lightning impulse voltages were studied. A conventional inhibited mineral oil was also tested as the benchmark. Experiments were carried out in 25 mm and 50 mm point-plane gaps. Streamer and breakdown phenomena of both oils were observed from the streamer inception voltage level up to the voltage level at which fast streamer appears with a velocity of over 10 km/s. The results showed that the GTL oil has a higher breakdown voltage and a higher acceleration voltage compared to the mineral oil. This is due to the fact that the GTL oil has a much lower aromatic content compared to the mineral oil. The streamer investigations showed that the development of fast streamers in both oils is the consequence of transition from dark streamer channels to bright streamer channels. By comparing with the results obtained under positive polarity [1], the differences in the propagation mechanisms between the fast negative streamers and fast positive streamers were explained. [ABSTRACT FROM PUBLISHER]

As the greenhouse effect of SF6 gas, the research on seeking alternative insulating gas to SF6 has become an imperative case. CF3I and its mixtures have been considered as the most promising insulating gas to replace SF6 gas. In this paper, the discharge characteristics of gas gap and insulator in CF3I/N2 gas mixtures under lightning impulse and alternating voltage were investigated. The effect of voltage, pressure as well as decomposition product after flashover were studied. Experimental results showed that in inhomogeneous electric field the breakdown voltages of CF3I/N2 with 30% CF3I gas is lower than SF6/N2 mixtures with 20% SF6. However, the flashover voltage of insulator in CF3I/N2 is higher than that in SF6/N2 mixtures. When compared to CF3I/N2 itself, the 50% breakdown voltage under positive lightning impulse were lower than that under negative lightning impulse. The CF3I/N2 gas mixtures with insulator also had polarity effect and appear polar reversal phenomenon. Under lightning impulse, there is no decomposition product on the surface of insulator after flashover but under alternating voltage, obvious iodine was produced on the surface of insulator. [ABSTRACT FROM PUBLISHER]

The use of sensitive electronics in avionics and wind generation systems, as well as the introduction of lower-conductivity composite materials make it important to ensure adequate lightning testing of airplanes and wind turbines. Evidence exists suggesting that standardized testing lightning waveforms produce damages that differ from those observed in actual strike events. The applicability of the present standard current waveforms for lightning testing is assessed in this paper and it is argued that waveforms based on upward flashes may be better suited as a basis for testing than the currently used tests, which are based on downward lightning and on airborne measured current bursts. Upward lightning data obtained at the Säntis Tower in Switzerland are also presented to support the need to revisit current waveforms used in standardized aircraft testing. [ABSTRACT FROM AUTHOR]

This paper presents an enhanced method used to deliver the 50th percentile location uncertainty ellipse given by lightning locating systems for lightning flash density maps with very fine detail of about 100 m $\times100$ m (or less) over a vast land region spanning thousands of kilometers. Because it is founded on a rigorous mathematical method (without using convolution operators), this new technique for computing the probabilistic lightning density map coverage represents a significant improvement in terms of precision compared with other techniques identified in the literature. The technique was adapted from a method used to calculate the probability of debris collision for spacecraft, and is based on a probabilistic approach to lightning flash impact over a facility. As a proof of concept, a Java language algorithm was implemented. This algorithm was applied to a set of 11.34 million lightning flashes over the territory of Spain registered between 2003 and 2012, producing a lightning density map coverage with a cell size of 2 arcsecond (~60 m). [ABSTRACT FROM PUBLISHER]

This paper comprises the first systematic investigation into the factors that render ultra-high voltage and double-circuit extremely high voltage transmission lines more vulnerable to direct lightning strikes by shielding failure. Such lines are typically characterized by one or more of the following features: massive conductor bundles, extreme conductor heights, and exceptionally high operating voltage. The model addresses the effects of the upward connecting leader onset of conductor proximity, ground field due to cloud charges prior to negative leader descent, positive space-charge generation at ground wires, as well as the operating voltage during the positive half cycle. It has been found that such factors have significant effects on the lateral attractive distance of both conductor bundles and ground wires. An agreement between model findings and field experience is found to be generally satisfactory. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of structure on the failure of full-scale metal–oxide arresters under successive lightning impulses. Typical structures of arresters are compared by simulation and experiment. With a finite-element model for the electrical-thermal multiple-field analysis, the thermal characteristics of typical structures of full-scale arresters under successive impulses are obtained. It is revealed that the filled solid insulation can contribute to more radial heat dissipation than filled gas. Experimentally, two full-scale arresters with different structures were exposed to successive nominal lightning impulses until failure, and it is found that the impulse failures of arresters are dominated by the structure and component. Surface flashover is the most common destruction for the varistor column. The cylinder type of varistors is suggested rather than hollow type, and the sleeve for position constraint of the cylinder varistor column should not be organic in order to avoid carbonization by arc discharge. It is found that the metallic spacers can contribute to sprayed-electrode protection, arc extinction, and heat dissipation. Based on the aforementioned results, an advanced arrester with structure optimization is proposed. [ABSTRACT FROM AUTHOR]

This paper presents the performance and protection of medium-voltage (MV) aerial cables against lightning faults by means of laboratory experiment and digital modeling. With the series of laboratory tests, practical examination of lightning hazard to shielded and unshielded aerial cables is conducted, and the need for shield wire protection is established. For the purpose of simulation studies, digital models are developed by using Alternative Transient Program-Electromagnetic Transient Program (ATP-EMTP) and its transient analysis of control system features. The performance of lightning flashover overvoltage on shielded and unshielded aerial cable is evaluated with the developed digital models. The evaluation is made by considering a direct lightning strike on wooden poles, messenger wires, and nearby trees. Based on the experimental and simulation results, practical recommendations are proposed for improvement in lightning performance of aerial cables. This study offers possible solutions for the protection of aerial cables against lightning flashover, induced overvoltage, and direct lightning strike, which may improve electricity reliability and availability to customers. [ABSTRACT FROM AUTHOR]

This paper describes observation of lightning overvoltages in a 500 kV switching station at Kansai Electric Power Co., Japan. Three types of lightning overvoltages, such as back flashover, direct lightning hit to a phase conductor, and lightning-induced voltage have been observed. The lightning overvoltages due to a back flashover were lower than operation voltage of a surge arrester. The observation suggests that induced voltage caused by electromagnetic fields radiated from a lightning channel affects lightning overvoltages in a station. [ABSTRACT FROM AUTHOR]

It is essential that the insulation system of the overhead distribution lines should be properly designed to ensure their immunity against lightning-induced overvoltages (LIOVs) caused by nearby return strokes. Therefore, accurate calculation of the peak values of LIOVs is important for the insulation design. In this paper, a formula is proposed to calculate the peak values of LIOVs for both first and subsequent strokes. The typical waveforms of the first and subsequent return strokes are adopted for this study considering a wide range of ground resistivity, from 0.25 to 20 k $\Omega $m. The 2-D finite-difference time-domain method associated with the Agrawal coupling model is employed for the calculation of LIOVs. In addition, the effect of ground permittivity on the peak values of LIOVs is also investigated. Finally, the proposed formula is applied to calculate the annual number of flashovers per 100 km of the overhead line. [ABSTRACT FROM AUTHOR]

When lightning strikes an aircraft, the electromagnetic (EM) field penetrates inside the aircraft, and induces currents and voltages on the onboard cables, resulting in the risk of equipment failure, which is a serious safety hazard to the flight safety. With the wide use of low-conductivity composite materials in aircraft manufacturing, the EM shielding effectiveness of the aircraft is weakened. As for the helicopter, the proportion of windows and doors is relatively larger than the fixed-wing aircraft, thus the EM shielding effectiveness is much weaker. Proper lightning protection design must be validated to eliminate the risk of electrical and electronic equipment failure. This paper describes the lightning indirect effects related to the modeling and simulation process of the composite UH-60 helicopter. The external and internal EM field environment together with the induced currents and voltages on cables are discussed. Moreover, in order to validate the simulation, an iron helicopter model was tested and the comparison between simulated and measured waveforms was carried out. [ABSTRACT FROM PUBLISHER]

The Cooray–Rubinstein formula is most widely used to evaluate the horizontal electric field generated by a lightning return stroke over a lossy ground. In this paper, a new method for fast evaluation of the Cooray–Rubinstein formula in time domain is proposed, by means of approximating the integral form of the modified Bessel function of the first kind using Gauss numerical integral. In the proposed method, the integral form of the modified Bessel function of the first kind is expressed by a summation of exponential functions, and a recursive convolution is achieved, which makes the calculation of the Cooray–Rubinstein formula in time domain much more efficient. Besides, the residues and poles due to the expression of the kernel function K( s) can be obtained directly for any ground conductivity and permittivity which makes the method proposed very simple and easy to program. The numerical examples demonstrate the validity and efficiency of the proposed method. [ABSTRACT FROM PUBLISHER]

For the application of SF6/N2 in power equipment such as GIS and GIL, the breakdown characteristics of SF6/N2 in varying electric field non-uniformity under standard lightning impulse were studied in this paper based on a lightning impulse experimental platform. The research indicates that the reversal of polarity effect appears in SF6/N2 gas mixtures. That is, when the pressure is relatively low, the 50% breakdown voltage under positive polarity is lower than which under negative polarity. When gas pressure reaches the critical pressure, the situation would be opposite. The augment of SF6 mixing ratio or decrease of electric field non-uniformity would both result in the decline of the critical pressure. Meanwhile the change of polarity effect with SF6/N2 is later than that with pure gas with the increase of electric field non-uniformity. In addition, the phenomenon of critical radius of SF6/N2 gas mixtures was found. The critical radius reduces with the increase of gas pressure and is smaller under positive lightning impulse than negative. And the phenomenon of critical radius with pure gas is more obvious than that with gas mixtures. [ABSTRACT FROM AUTHOR]

An efficient approach to evaluate the radiated electromagnetic field of a lightning channel over a horizontally stratified conducting ground is proposed in this paper. The electromagnetic field component produced by a lightning channel, expressed in the form of generalized Sommerfeld integral (GSI) with a complicated integrand, is calculated along a newly proposed path in the complex plane. Due to the change of the integration path, the integrand in the GSI turns out to decay dramatically fast and without any oscillation at all. As explained in this paper, the larger horizontal distance will become the benefit to achieve a quicker convergence, which is just opposite to the case that the integration path is along the real axis. The validity of the proposed methodology is justified by the extensive comparison with the results in other publications. As a matter of fact, the methodology in this paper can be generalized to evaluate stratified conducting ground with any number of layers. [ABSTRACT FROM AUTHOR]

Inductive fault current limiters (FCLs) have several advantages, such as significant current limitation, immediate triggering and relatively low losses. Despite these advantages, saturated core FCLs have not been commercialized due to its large size and associated high costs. A major remaining challenge is to reduce the footprint of the device. In this paper, a solution to reduce the overall footprint is proposed and discussed. In arrangements of windings on a core in reactors such as FCLs, the core is conventionally grounded. The electrical insulation distance between high voltage winding and core can be reduced if the core is left at floating potential. This paper shows the results of the investigation carried out on the insulation of such a coil-core assembly. Two experiments were conducted. In the first, the behavior of the apparatus under high voltage conditions was assessed by performing power frequency and lightning impulse tests. In the second experiment, a low voltage test was conducted during which voltages of different frequencies and pulses with varying rise times were applied. A finite element simulation was also carried out for comparison and further investigation. [ABSTRACT FROM AUTHOR]

In this paper, we present an improved and extended approximate formula for estimating the peak value of lightning-induced voltages in an overhead line, considering the horizontally stratified conducting ground. The approximate formula proposed in this paper is based on the return stroke transmission-line model (TL) and a trapezoidal lightning return stroke current waveform with the typical representative front time of 3.8 ~\mus and the return stroke velocity of 120 m/ \mus according to CIGRÉ and the IEEE Standard 1410 Guide. The extended approximate formula is validated by using the 2-D finite-different time-domain method and Agrawal field-line coupling model. The results show that the proposed approximate formula in this paper is simple and suitable for estimating the lightning-induced voltage peak value considering the horizontally stratified ground with satisfied accuracy. [ABSTRACT FROM AUTHOR]

This paper proposes a new method of risk assessment for lightning shielding flashover in transmission lines. This is used to improve the performance of lightning shielding failure which is a frequently serious problem. The method can be efficiently implemented in the optimization of a 3-D model. Three-dimensional laser scanning is used to derive the analytical 3-D model to high precision. This includes the data of the whole span line's structure and terrain parameters. In this study, the evaluation of lightning shielding flashover risk of each tower is calculated using the whole span calculation method associated with the laser scanning data and the given parameters of lightning activities. The evaluation results for the Gechen line in the zone near the Three Gorges area are presented based on the proposed method. Using a comparison of theoretical values and actual statistical data, this paper concludes that the proposed new method has better performance than the traditional method. [ABSTRACT FROM PUBLISHER]

This paper proposes approximate formulas to estimate voltages on a horizontal grounding conductor. The formulas are derived in the time domain using Bewley's lattice diagram method based on transmission and reflection coefficients. The expression of the approximate formulas is simple, and the formulas are useful for engineers to carry out grounding system design for lightning protection. This paper concerns a voltage source with step waveform. A formula for an arbitrary voltage waveform can be calculated by using Duhamel's integral. Surge characteristics of voltages and an effective length of a grounding conductor are discussed using the proposed formulas. It is easy to understand experimental and simulation results of a grounding system using the approximate formulas. [ABSTRACT FROM PUBLISHER]

An improved finite difference time-domain (FDTD) method based on the telegraph equations of transmission lines is proposed. The original time-domain simulation method that resembles the well-established FDTD scheme based on the Maxwell's equations has been used in this paper to tackle the modeling problems of buried and overhead transmission lines. In this paper, a group of time domain responses of the ground impedance or ground admittance can be extracted analytically by means of a correlation between the ground impedance and the ground admittance. Thanks to the analytical technique, the accuracy of this time-domain solution is improved significantly. As a result, the application of this time-domain algorithm can be greatly expanded beyond the modeling of common transmission lines. By combining with the shunt and series connection difference equations, the method can be used to analyze an entire buried grounding network. Because the correlation between the ground impedance and the ground admittance is related to the propagation constant of electromagnetic waves, the analytical technique makes the propagation velocity unchanged during the iterative calculation. Therefore, the improved FDTD method allows the grounding network to be analyzed more accurately and efficiently. [ABSTRACT FROM PUBLISHER]

Environmental factors, such as weather, trees, and animals, are major causes of power outages in electric utility distribution systems. Of these factors, wind and lightning have the most significant impacts. The objective of this paper is to investigate models to estimate wind and lighting related outages. Such estimation models hold the potential for lowering operational costs and reducing customer downtime. This paper proposes an ensemble learning approach based on a boosting algorithm, AdaBoost^+, for estimation of weather-caused power outages. Effectiveness of the model is evaluated using actual data, which comprised of weather data and recorded outages for four cities of different sizes in Kansas. The proposed ensemble model is compared with previously presented regression, neural network, and mixture of experts models. The results clearly show that AdaBoost^+ estimates outages with greater accuracy than the other models for all four data sets. [ABSTRACT FROM PUBLISHER]

In the companion paper (Part I), an analytical approach for calculating lightning-induced voltages for the case of lossy ground has been developed. In this paper (Part II), predictions of the new formulation are compared to those based on other approaches found in the literature. [ABSTRACT FROM PUBLISHER]