Lightning-induced Overvoltages Research Articles

Efficiency of Surge Arresters as Protective Devices Against Circuit-Breaker-Induced Overvoltages

The possible occurrence of transient overvoltages depends on the interaction between different components in a power system. In a cable system, circuit breaker (CB) operations may cause overvoltages, depending on the system configuration and the type of CB operations performed. Protective devices may be required during certain conditions. Surge arresters are a well-known product that could be applied. Surge arresters were originally developed as protection against lightning-induced overvoltages on overhead lines. However, they can also be used for protection against vacuum CB-induced transients in cable systems, and this is what the current publication reports on. Different surge arrester configurations were evaluated and two different surge arrester states are discussed; a “high current state” when the CB is closed and a high current passes through the surge arrester and a “low current state” when the CB is open and only a low current passes through the surge arrester. Finally, a new surge arrester configuration was evaluated and found to be advantageous in preventing amplification of internal resonances in the transformer.

Influence of Highly Resistive Ground Parameters on Lightning-Induced Overvoltages Using 3-D FDTD Method

It is important for the proper insulation design of the distribution system that lightning-induced overvoltages ( LIOVs ) are accurately computed. This paper investigates the impact of ground resistivity, considering wide range up to 20 kΩm, on LIOVs impinging an overhead line due to nearby return stroke using the three-dimensional finite difference time domain (3-D FDTD) method. The investigation considers two values of both ground permittivity as well as the rise rate of lightning current. Subsequently, it is inferred that the influence of both ground permittivity and rise rate of lightning current on the peak values of LIOVs depends on the ground resistivity. Furthermore, horizontal conduction and displacement current densities are also calculated on the ground surface under the line to analyze the behavior of ground surface impedance. Consequently, it is deduced that the behavior of the impedance changes from inductive to capacitive at high values of ground resistivity, thus increasing the time to the peak value of LIOVs . The peak values of LIOVs computed using the 3-D FDTD method are compared with those calculated using Darveniza's formula. It has been revealed that this formula considerably underestimates the peak values of LIOVs at high values of ground resistivity. Thereby, an interpretation is presented for the reason of this underestimation from an electromagnetic perspective. Accordingly, Darveniza's formula is appropriately modified to improve the computation accuracy.

Calculation and experiment of induced lightning overvoltage on power distribution line

Induced lightning is the major cause of interruptions in power distribution lines. To reduce lightning accidents and improve the power supply reliability, it is significant to study the characteristics of the induced lightning overvoltage by experiment and calculation. In the paper, a calculation method of lightning induced overvoltage, considering lightning leader progress, non-ideal ground corona effect, field-line coupling, was introduced. The accuracy of the program was verified by comparison between calculated results and the practical experimental results, the calculation results are close to the experimental data. A scaled experiment was carried out to obtain the basic relationship between lightning and overvoltage on distribution lines. Influence factors on overvoltage were analyzed.

Flashover Probability Distribution and Volt-Time Curves of Medium Voltage Overhead Line Insulation Under Combined AC and Lightning Impulse Voltages

Lightning overvoltages are considered as one of the major causes of insulation failure in medium voltage overhead lines. Therefore, the evaluation of the dielectric strength of overhead line insulation is of great importance for insulation coordination studies. This paper presents the flashover probability distributions and the volt-time characteristics of different types of insulator gaps subjected to both positive and negative polarity standard impulse (SI) and short tail lightning impulse (STLI) voltages. In practice, the transient overvoltages generated by a lightning stroke are superimposed over the power frequency AC voltage. Accordingly, the flashover characteristics of the insulator gaps under combined AC and lightning-induced overvoltages are also presented in this paper. The results indicate that superimposition of the impulse voltage on the power frequency AC voltage changes the flashover characteristics of the insulation gaps. Therefore, it is recommended that the effect of power frequency AC voltage should be considered in the risk assessment of insulation for the insulation coordination studies.

Probabilistic Risk Assessment of MV Insulator Flashover Under Combined AC and Lightning-Induced Overvoltages

The effect of lightning-induced overvoltages is more profound in overhead distribution lines due to their limited height and low insulation level. Consequently, there is a high risk of line insulation flashover when exposed to lightning-induced overvoltages. This paper presents a probabilistic method to assess the risk of insulator flashover in medium-voltage overhead lines due to lightning-induced overvoltages. In order to accomplish this, a modified Gaussian cumulative distribution function has been used to predict the probability of single-phase, two-phase, and three-phase flashover of insulators under combined ac- and lightning-induced overvoltages. The validity of the modified probabilistic model is confirmed through experiments carried out in the high-voltage laboratory. Next, Monte Carlo simulations were performed on the simplified Rusck's model to generate the distribution of peak lightning-induced overvoltages. Finally, the risk of insulator flashover is calculated based on the distributions of lightning-induced overvoltages and insulator flashover voltages. The proposed procedure could be considered beneficial to select the optimum insulation level required against lightning-induced overvoltages by distinguishing between single-phase and multiphase flashover faults.

Effect of combined AC and lightning-induced overvoltages on the risk of MV insulator flashovers above lossy ground

Soil resistivity is one of the prevailing parameters associated with the flashover of line insulation in medium voltage (MV) overhead lines due to nearby lightning strikes. This paper investigates the influence of lossy ground to determine the level of lightning-induced overvoltages and the corresponding risk of insulator flashovers. Experiments are performed in the high voltage laboratory to evaluate the flashover characteristics of a 24-kV pin-type insulator under combined AC and lightning-induced overvoltages. Based on experimental results, a modified Gaussian cumulative distribution function has been employed to estimate the probability of single-phase, two-phase and three-phase flashover of insulators based on the assumption of ground resistance close to zero. Monte Carlo simulations are performed on Rusck's and Darveniza's models to obtain the probability density function of peak lightning-induced overvoltages for both ideal and lossy grounds, respectively. The results indicate that lossy ground increases the risk of insulator flashovers. The risk indices are further aggravated with increasing soil resistivity and become significantly high for soil resistivity above 3000Ωm. The advantage of the proposed method is its simplicity and ability to distinguish between single-phase and multi-phase flashover faults with increasing soil resistivity. Thus, the proposed model can be successfully employed for insulation coordination studies of MV overhead lines.

The Influence of the Horizontally Stratified Conducting Ground on the Lightning-Induced Voltages

In this paper, we analyze the influence of the horizontally stratified conducting ground on the lightning-induced overvoltage on the overhead line by using the 2-D Finite-Difference Time-Domain method and the Agrawal coupling model. In order to clearly understand the propagation characteristics of the induced voltage waves along the line, we split the induced overvoltage into the scattered induced wave (Us) and the incident induced wave (Ui), and the latter is further decomposed into two subcomponents. When the conductivity of the first layer (σ1 = 0.001 S/m, er1 = 10) is less than that of the second layer ( σ2 = 0.1 S/m, er2 = 10), the lightning-induced overvoltage increases obviously with the increase of the depth of the first layer due to the increase of the total effective impedance, and we should consider the influence of the stratified ground if the depth of the first layer is more than 2 m. However, the lightning-induced overvoltage decreases sharply with the increase of first layer depth with much higher conductivity ( σ1 = 0.1 S/m, er1 = 10; σ2 = 0.001 S/m, er2 = 10). Also, we find that when the lower different conductivities between the two layers (i.e., 0.01 and 0.001 S/m) are assumed, the characteristics of the induced voltages are similar to that from the higher difference.

An Approximate Formula for Estimating the Peak Value of Lightning-Induced Overvoltage Considering the Stratified Conducting Ground

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 μs and the return stroke velocity of 120 m/ μs 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.

Analytical investigation of parameters effect on lightning-induced overvoltages on overhead lines

The evaluation of induced overvoltages from indirect lightning has been for more years one of the most important problems in designing and coordinating the protection of overhead power lines. In this paper, we discuss a modeling procedure that permits calculation of lightning-induced voltages on overhead lines starting from the channel-base current. The calculation is based on two main points: the calculation of the electromagnetic field radiated by lightning in a given point and a coupling model already presented in the literature based on the transmission line theory for field-to-overhead line coupling calculations.

Investigation of Wave Propagation to PV-Solar Panel Due to Lightning Induced Overvoltage

Investigation of Wave Propagation to PV-Solar Panel Due to Lightning Induced Overvoltage

Investigation of Wave Propagation to PV-Solar Panel Due to Lightning Induced Overvoltage

Lightning produces extremely high voltages that generated induce overvoltage which have a high tendency to effect the electrical apparatus especially renewable energy plant that directly expose to this source. This study was performed through experimental work by investigating the effect of induce overvoltage upon the photovoltaic system. The induce voltage was performed by using lightning impulse generator. It is found that the maximum voltage of the unwanted signal is proportional with the distant of the specimen. The closer distant between solar panel material and spark discharge, the more serious effect would occur due to the induced overvoltage.

Electro-Thermal Behaviour of a SiC JFET Stressed by Lightning Induced Over-Voltages

SiC JFETs are experimentally tested to verify their robustness against lightning induced strokes. The experimental setup is fully described. A lightning surge generator is built and a SiC JFET is stressed. The full thermal response of the SiC JFET internal temperature is obtained from an specific temperature estimation technique at different time steps during the surge test. This short time thermal response is compared and validated by a conventional 1D thermal model. This work shows that for a moderate lightning stroke, according to standards [1], the JFET temperature rise is less than 60 °C, which is acceptable in most circumstances.

Calculation of Lightning-Induced Overvoltages on Overhead Lines Based on DEPACT Macromodel Using Circuit Simulation Software

One of the simple and accurate methods for calculating the lightning-induced overvoltages is based on the Agrawal et al. held-to-wire model, in which the coupling mechanisms are presented by distributed voltage sources along the lines. There is a difficulty in calculating the lightning-induced overvoltages with the built-in transmission line models or other circuit elements of various circuit simulation software such as the PSCAD/EMTDC, EMTP/ATP, PSpice, etc., as the distributed voltage sources due to the horizontal component of the electric held caused by the lightning channel are in series with the line and not in between two transmission-line segments. In this paper, a simple circuit approach for efficient calculation of the lightning-induced overvoltages using the circuit simulation software is proposed. The delay extraction passive compact circuit (DEPACT) macromodel is applied and the transmission line is divided into a cascade of DEPACT subnetworks which can be represented by a cascade of two lossless transmission lines and a lossy network. By assuming the incident held only couples with the lossless transmission line sections, the distributed equivalent voltage sources due to the horizontal component of the incident electric held can be lumped at the termination of the lines, which makes it convenient for the engineering technologist to calculate the lightning-induced overvoltages in various circuit simulation software. Furthermore, in order to treat the nonlinear element such as metal oxide arrester (MOA) directly, the DEPACT macromodel is improved and the macromodel of multiconductor transmission lines excited by the external electromagnetic held can be solved in the actual phase domain instead of in the modal domain. Compared with the existing method for calculating the lightning-induced overvoltages, the benefit of the proposed algorithm is that it can be used to calculate the transients of the transmission line more efficiently. Considering the PSCAD/EMTDC is a powerful simulation software which providing lots of equipment models in power system, such as transformer, generator, and protection modules et al., an implementation procedure in the PSCAD/EMTDC is provided in this paper, which makes it more convenient for the electrical engineering technologists to analyze the lightning-induced overvoltages problems in the power system. Several numerical calculations of the line transient responses are provided and the CPU time is compared, which indicate the validity and efficiency of the algorithm proposed in the paper. At last, this algorithm is applied to analyze the influence of the ground wire and the MOA on the lightning-induced overvoltages of the overhead lines.

EMTP/MODELS를 이용한 지중 배전선로의 뇌유도 과전압 및 전류 분석

This paper analyzes the lightning-induced overvoltage and current in buried underground distribution cable. Based on analytical expressions, the lightning-induced overvoltage and current in buried underground distribution cable is calculated by EMTP/MODELS. The modeling is verified by comparing with the results in reference. Also, the type and buried arrangement of cables used in domestic distribution line are modeled by EMTP/ATPDraw. The various simulations according to the type and buried arrangement of cable are performed and the simulation results are analyzed.

Research on lightning overvoltages of solar arrays in a rooftop photovoltaic power system

Lightning overvoltages threaten the safe operation of the photovoltaic (PV) power system. This document uses the generalized modified mesh current method and establishes a time-domain multiport model of thin-wire system to simulate the lightning transient process of the solar arrays in a rooftop PV power system with and without the external lightning protection system. Different factors of the PV power system are simulated in order to study the effects of these factors on the induced lightning overvoltages. The simulation results show that the induced lightning overvoltage of the solar arrays in a rooftop PV power system is highly dependent on the lightning striking position, the lightning current amplitude, the building's height, the soil resistivity, and the distance to the external protection system. Therefore, when choosing the SPD configuration for a PV power system, the factors mentioned above should be considered comprehensively.

Time-Domain Implementation of Cooray–Rubinstein Formula via Convolution Integral and Rational Approximation

One of the most popular techniques to take into account the finite ground conductivity in the evaluation of the radial component of the electric field generated by a lightning return stroke is the Cooray-Rubinstein (CR) formula. As this formula is derived in the frequency domain, its application in time-domain simulation codes for the analysis of lightning-induced overvoltages on overhead lines might be challenging. In this paper, two methods allowing a simple time-domain implementation of the formula are discussed. The first one is an enhanced version of an algorithm recently proposed by two of the authors, while the second consists of a new technique, based on a suitable rational approximation of the impedance term appearing in the CR formula. This second approach is characterized by an intrinsic easiness in time-domain implementation and a considerable computational efficiency compared with conventional methods.

Electromagnetic Coupling of Lightning to Power Lines: Transmission-Line Approximation versus Full-Wave Solution

The problem of accurate prediction of lightning-induced overvoltages on power lines still attracts considerable attention. A variety of approaches of different levels of sophistication have been proposed. In particular, transmission-line (TL) approximation is widely used for describing electromagnetic coupling of lightning with power lines. In this paper, validity of this approach for lossless lines is demonstrated by analytically demonstrating that, under the assumptions that are typically justified for practical power distribution lines, the TL approximation and the more rigorous full-wave analysis lead to identical results.

Lightning-Induced Overvoltages Transmitted Over Distribution Transformer With MV Spark-Gap Operation—Part II: Mitigation Using LV Surge Arrester

When the distribution transformers are exposed to lightning overvoltages, it is worthy to study the low-voltage (LV) network response at the customer terminals using an accurate and simplified high-frequency transformer model. The impact of LV network feeder numbers, lengths, types, and loads on the lightning-induced overvoltage reached at the service entrance point is investigated. The high-frequency model representation of distribution transformer and the LV network are combined in a single arrangement in the environment of the Alternative Transients Programs/Electromagnetic Transients Program. Finally, a study is carried out to mitigate the overvoltages by allocating the surge arrester at the secondary side of the distribution transformer concerning the medium-voltage spark-gap operation. A simplified surge arrester model is represented and verified. This study can enhance the overvoltage protection of Finnish LV networks.

Lightning-Induced Overvoltages Transmitted Over Distribution Transformer With MV Spark-Gap Operation—Part I: High-Frequency Transformer Model

In Finland, distribution transformers are frequently subjected to lightning strokes. Therefore, it is worthy to study the voltage transferred to the secondary terminal of the transformer due to lightning strokes hitting the primary terminals. In order to do conduct this study, the high-frequency model of the distribution transformer is to be investigated. In this paper, an accurate and simplified high-frequency model of the distribution transformer under lightning strokes is presented. The proposed model is introduced based on two-port network theory where its parameters are calculated at two resonance frequencies experimentally measured. The model is suitable for unloaded and loaded conditions and it is experimentally verified under different balanced loads considering two different practical distribution transformers. Then, the model verification is extended to study the impact of medium-voltage spark-gap operation on the transmitted voltage. The experimental results have validated the proposed transformer model.

Lightning surge characteristics of an actual distribution line and validation of a distribution line model for lightning overvoltage studies

AbstractFor distribution lines in Japan, protection measures against lightning‐induced overvoltages have been taken and can be considered almost complete. The focus of lightning protection measures has moved to overvoltages due to direct lightning strokes. Studies of such overvoltages require simulations using the EMTP (Electro‐Magnetic Transients Program), and components of a distribution line must be modeled appropriately in the EMTP simulation environment. The authors have proposed an EMTP model of a distribution line in a separate paper. This paper consists of two parts. The first part presents surge characteristics of a distribution line obtained by measurement using an actual‐scale test distribution line. In particular, the result reveals noteworthy characteristics of the surge impedance of a reinforced concrete pole and the wavefront‐time dependence of insulator voltages. The second part presents a validation of the distribution line model previously proposed by the authors. The validation shows that the distribution line model accurately reproduces the measured voltage and current waveforms for various wavefront times of the injected currents. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 173(1): 1–10, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.21002