Probabilistic Evaluation of Optimal Location of Surge Arresters on EHV and UHV Networks Due to Switching and Lightning Surges

Switching surges are of primary importance in insulation coordination of extremely high voltage and ultra-high voltage networks. However, in regions of high lightning activity or high ground resistance insulation design, preferably, should be based on the risk of failure caused by lightning and switching surges and the probability of line outage, a combination of lightning and switching flashover rates (SSFOR). This paper describes an effective installation of transmission line arresters (TLAs) to obtain a better protection scheme (i.e., minimizing global risk to the network). As a consequence, protection costs are reduced in accordance with the costs of elements actually protected and the number of TLAs utilized. In order to accomplish this, a probabilistic method for calculating the lightning related failure and an artificial neural network for estimating the SSFOR are presented. A multicriteria optimization method based on a genetic algorithm is also developed to determine the optimum location of TLAs.     

Discrete-event simulation of the shielding failure of the arrester protected overhead-lines to evaluate risk of flashover

Damages caused by lightning stroke in power system networks are severe for insulations and result in less reliable energy supply. Knowledge of protection schemes and better selection of these devices in power systems is a goal of designers to reduce the risk of flashover in any risky point. In this paper, a statistical procedure is presented to evaluate risk of failure in an overhead-line which is protected by arresters in most risky towers. Main aim of the work is to present the modeling aspects for considering random nature of stroke and its simulation procedure. The random nature of a lightning stroke composed of proper discrete-event simulation of a stroke via its peak current, front time and tail time and accurate mathematical representation of such lightning stroke in a transient analyzer. In addition, the maximum lightning current which causes shielding failure for a specified tower design and probabilistic specification of lightning for discrete-event simulation is taken into account. As a study case, random nature modeled lightning strokes are applied to a 230 kV overhead-line which is located in a hilly area and the risk of failure is calculated when arresters are located beside the stroke point.     

Characteristics of lightning surges observed at 77 kV substations

In order to improve power supply reliability, it is necessary to prevent lightning faults in transmission lines and substation apparatus. However, faults are caused occasionally in lower-voltage power systems, particularly at the 77 kV level. The governing factor for insulation strength of substation apparatus is the lightning impulse voltage, and it is necessary to know the voltage level and distribution in a substation caused by lightning surges in order to investigate rational insulation coordination. For this purpose, the authors measured lightning surges at two 77 kV conventional substations from 1990 to 1993. In this paper, the characteristics of induced lightning surges and back flashover lightning surges are described. Comparisons of related surge voltages at two substations, the power line phases in grounding faults, and the equivalent capacitance of the substations are also discussed.     

Protecting load devices from the effects of low-side surges

Wherever lightning and poor utility power system grounds exist, distribution secondary systems are subjected to high-voltage surges due to lightning current seeking ground through low-voltage circuits. Utilities are becoming aware of this low-side surge phenomena and are taking measures to protect their distribution transformers' secondary windings. These measures can increase the voltage stress at the customer service entrance. If any ground paths exist on the customer side of the service entrance, surges can penetrate further into the customer's system and damage loads. Damage caused by low-side surges can be avoided if properly coordinated arresters are installed at the transformer secondary, at the service entrance, and at load devices. This work describes the secondary surge phenomena and the importance of protecting the service entrance and critical load devices effectively, especially when the transformer secondary is protected. A properly coordinated and effective protection scheme is described and recommended     

光伏组件受雷电影响的因数检测及仪器选择

鉴于雷电对太阳能光伏系统具有危害性,针对目前光伏发电系统专业防雷系统标准尚待完善,缺乏针对光伏发电防雷系统的专业检测设备,以及光伏发电防雷控制系统知识的专业培训,同时光伏组件设计生产过程中,没有将防雷检测作为产品设计检测的必备环节等现状,对光伏发电系统防雷结构设计及仪器选择进行阐述。本文简要叙述了雷电对光伏发电系统的危害及雷电分类,详细阐述了光伏发电系统防雷结构装置的设计方案,光伏发电系统监测方式以及光伏发电系统所需的检测仪器。     

Effective lightning protection schemes for distribution line

The causes of lightning outage are subdivided into direct lightning strokes and induced lightning strokes, which are identified by the characteristics of the lightning overvoltage. In the past, lightning protection devices were directed mainly toward the latter, and attention has been focused on the installation of lightning protection devices, ground wires, and reinforcement of insulators. However, lightning outages continue to occur. Thus it is extremely important to clarify the fault characteristics of lightning surges and to study the effectiveness of various lightning protection devices by considering both direct lightning stroke and induced lightning stroke in order to prevent lightning outage in the future. In this research, the electromagnetic transients program (EMTP) has been applied to the direct lightning stroke, and the induced lightning outage analysis program for multiple conductor systems has been applied to the induced lightning stroke to study the effectiveness of lightning protection devices provided by combination of various lightning protection devices. The most effective lightning protection schemes are analyzed and evaluated based on verification tests on the full scale models as well as economic considerations.     

Transformer insulation coordination using volt–time curve and limit–state surface formulation

This paper presents a novel method for the power transformer insulation coordination, based on the risk of failure analysis due to lightning surges, that uses its insulation strength volt–time curve and a limit–state surface formulation. The limit–state surface is derived in a novel way, from the optimal number of systematic numerical simulations of transformer terminal overvoltages—emanating from station impinging lightning surges—while accounting for the transformer insulation volt–time curve and surge arresters protective characteristics and disposition. The proposed method further employs a state-of-the-art transmission line (TL) and substation equipment models for lightning-surge transient analysis, constructed in the EMTP software package. It also uses the electrogeometric model of lightning attachment to TLs, in order to estimate the expected number of direct lightning strikes, along with a bivariate statistical distribution of lightning currents. The main aspects of the proposed method are demonstrated by means of the computational example featuring an air-insulated substation power transformer lightning insulation coordination. Simulation results exhibit many benefits of the proposed method. Sensitivity analysis further reveals different influences that the various model parameters have on the transformer insulation coordination design.     

Assessment of surge arrester failure rate and application studies in Hellenic high voltage transmission lines

The use of transmission line surge arresters to improve the lightning performance of transmission lines is becoming more common. Especially in areas with high soil resistivity and ground flash density, surge arresters constitute the most effective protection mean. In this paper a methodology for assessing the surge arrester failure rate based on the electrogeometrical model is presented. Critical currents that exceed arresters rated energy stress were estimated by the use of a simulation tool. The methodology is applied on operating Hellenic transmission lines of 150 kV. Several case studies are analyzed by installing surge arresters on different intervals, in relation to the region's tower footing resistance and the ground flash density. The obtained results are compared with real records of outage rate showing the effectiveness of the surge arresters in the reduction of the recorded failure rate. The presented methodology can be proved valuable to the studies of electric power systems designers intending in a more effective lightning protection, reducing the operational costs and providing continuity of service.     

变电站微机保护和监控系统电源干扰及抑制

雷击浪涌是低压电源线中发生最频繁的干扰源之一。为研究雷击浪涌对变电站微机保护和监控系统电源的干扰,首先通过分析电源线中雷击浪涌的入侵途径,提出了雷击浪涌危害的主要原因。然后基于过电压保护和电磁兼容两个方面的考虑,提出了低压电源线及低压电子设备的保护措施:一方面,根据低压电源系统防雷保护存在的问题,提出了完善低压电源系统的保护措施;另一方面,根据雷击浪涌的频谱中包含低频能量和高频能量的这一特征,提出了将瞬态抑制与滤波技术相结合的措施,即采用压敏电阻(MOV)消除低频能量,采用L-C低通滤波器滤除高频能量,从而有效地抑制雷击浪涌干扰。     

Prospective method of lightning protection schemes in distribution system

Grounding wires and enclosed ZnO elements have been incorporated generally in 6.6‐kV distribution systems by TEPCO for the reduction of lightning overvoltages. At present, the reliability to lightning surges is tolerably good. However, the facility of grounding wires is not inexpensive and its maintenance is hard due to corrosion and disconnection in some areas. A typical model simulating TEPCO field adopting enclosed ZnO elements has been developed and we have evaluated relative failure risks systematically according to conditions with and without grounding wires against lightning overvoltages. Two kinds of failures discussed in the paper are the flashover of insulation and the overduty of ZnO elements, and two kinds of induced and direct lightning overvoltages are studied in flashover. The greatest problem with no grounding wire is the increase of ZnO elements' duty, but it was demonstrated that a short partial grounding wire around ZnO elements or the selection of heavier ZnO elements provides a solution. The main objectives of this study are to clarify the relative failure risks systematically according to realistic field conditions, the risk of small stroke currents having long duration to ZnO elements' duty, and countermeasures against ZnO elements' overduty. © 1999 Scripta Technica, Electr Eng Jpn, 127(1): 1–10, 1999     

Electrical Surge-Protection Devices for Industrial Facilities—A Tutorial Review

Industrial facilities are becoming more and more dependent on computer control of their processes, and as a consequence, require an increase in cleanliness and reliability of the electrical power supply system. Electromechanical subsystems are being replaced by electronic logic. Harmonic interference, welding, variable speed drives, and other "in plant" noise have reliable mitigation procedures. However, lightning and other external sourced power disturbances rank high on the list of "uncontrollable" events that have shut down facilities in recent years. This paper provides an overview of the causes of power-line surges and their consequences for an industrial plant. The relevant international surge-protection standards will be briefly reviewed, and their differences will be analyzed. Different technologies utilized in the implementation of various commercially available surge-protection devices will be presented, followed by a comparative analysis. Finally, the latest trends and the most promising technologies in surge-protection systems as well as their ability to overcome the problems associated with conventional protection devices will be overviewed, and experimental data based on field trials are reported     

Statistical analysis of lightning surges on distribution lines based on the observation

Probability distribution of surge discharging current of arresters provided a basis for conventional theory of grounding systems. In order to rationalize the grounding systems, it is necessary to grasp the statistical data of lightning surges on distribution lines caused by direct lightning strokes and indirect lightning strokes. Lightning phenomena on TEPCO's distribution lines had been continuously observed for the rationalization of lightning protection design of distribution lines. The observation had been carried out with still cameras and monitoring sensors of lightning surges. This makes it possible to discover new interesting facts that can be useful for rationalization of lightning protection design of distribution lines. Cumulative frequency distribution of conventional data is close to that of ZnO discharging current in the case of direct strokes and indirect strokes through TEPCO's observation. Moreover, to verify the cumulative current distribution in concrete poles, the authors have compared the cumulative distribution of current through ground lines with that of current through ground lines and concrete poles. The results show that the distribution of current through ground lines and concrete poles is larger than that of current through only ground lines for high currents exceeding 1 kA. This fact suggests that lightning surge current flows not only in ground lines but also in concrete poles. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(2): 36–44, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20468     

Insulation coordination associated with distributed generation connected at distribution level

Insulation coordination is defined as the selection of dielectric strength of equipment, taking into account the over-voltages that could appear in the utility system and with the presence of protective devices. Electromagnetic transient (EMT) over-voltages are regarded as disturbances due to lightning surges and switching surges that result in the disruption and possible damage to equipments. The principal subject of this paper is to perform insulation coordination on the distributed generation (DG) by using methods of modeling lightning surges and switching surges. PSCAD/EMTDC is the main software used for the modeling and simulations.     

防雷元件的特性参数与其电容对通信信号的影响

微电子电路常因过电压损坏 ,其过电压保护与电气设备相比有不同的要求 ,因此文中介绍了过电压对微电子电路的侵入方式 ,测试了常用防雷元件的动作时延及其伏 -安特性 ,给出了防雷元件的电容对数字通信信号影响的计算公式。实测表明动作时延太长不能保护微电子电路 ,防雷元件的电容大于一定值后会使通信信号发生畸变 ,致使误码     

发电厂直配线路防雷保护措施的研究

对发电厂直配线路的防雷保护现状进行了分析和探讨，对发电机的耐雷水平进行了讨论，对目前一些直配线路的防雷保护缺陷进行了分析，提出了用避雷器、电抗器和电缆联合配置的发电厂直配线路的综合防雷保护措施，并且对直配线路所用避雷器选型、安装和运行维护以及防雷装置的接地问题都提出了一些改进建议．     

Review of generator surge coordination including generator breakers

The results of a utility survey on surge protection practices for large generators are presented. The surge environment, 60 Hz withstand test value, designated impulse withstand, arrester protective levels, and insulation breakdown tests on two machines were compared. Factors included in the surge environmental were lightning, faults, HV switching, ferroresonance. opening surges, breaker failure, and system-side resonance. Several topics are identified for further study     

Metal oxide arresters on distribution systems: fundamentalconsiderations

The authors compare the reliability of metal oxide and silicon carbide distribution arresters by examining the likelihood of failure as a result of moisture leakage and contamination, overvoltages, and lightning surges of high magnitude and long duration. It is found that metal oxide distribution arresters should be highly reliable in most applications because the arresters are far less likely than silicon carbide arresters to fail as a result of moisture ingress and contamination. Metal oxide arresters are more likely to fail as a result of system overvoltages because they conduct current in response to the overvoltages, and for this reason somewhat more care must be exercised in application to match the magnitude and time duration of system overvoltages to the temporary overvoltage capability of the arresters. Comparison of published metal oxide arrester energy absorbing capability against the energy absorbed in lightning surges that have been shown to exist indicates that the probability of failure may be high in areas of high lightning intensity. The authors suggest changes in the ANSI/IEEE C62.11 standard for metal oxide arresters to improve arrester reliability on lightning surges     

Estimation of shielding failure number of different configurations of double-circuit transmission lines using leader progression analysis model

The protection of overhead transmission lines from lightning strokes is one of the most important tasks of safeguarding electric power systems. In order to do this job effectively, the lightning performance of the transmission lines has to be evaluated accurately. This paper presents the development of a method for estimating the shielding failure number of power transmission lines in different configurations by using the charge-simulation method. The effects of towers, sags of conductors, and a perfectly conducting ground are represented in a 3-D computation. In addition, the stepwise descending nature of a downward negative leader-streamer systems is taken into account by using an appropriate progression model. Upward leader inception and propagation is also modeled utilizing critical equivalent streamer-length criterion. The method is applied to compute the shielding failure of power transmission line for different configurations.     

An experimental study of lightning overvoltages in wind turbine generation systems using a reduced‐size model

Wind turbine generation systems are built at locations where few tall structures are found nearby so as to obtain good wind conditions, and thus, they are often struck by lightning. To promote wind power generation, lightning‐protection methodologies for such wind turbine generation systems have to be established. This paper presents the result of an experimental study of lightning overvoltages in wind turbine generation systems using a reduced‐size wind turbine model. Overvoltages observed at wavefronts of lightning surges are focused on in this study. In the experiments, lightning strokes to one of the blades and to the nacelle were considered, and voltages and currents at various positions of the wind turbine model were measured. The following points have been deduced from the results: (i) The voltage rise due to the tower footing resistance can cause a significant voltage difference between the tower foot and an incoming conductor led from a distant point. Also, a voltage difference between the bottom of down conductors installed inside the tower and an incoming conductor can be of significance. (ii) The lightning current flowing through the tower body induces voltages in main and control circuits which form loops, and the induced voltages can cause overvoltages and malfunctions. (iii) Traveling‐wave phenomena in a wind turbine generation system for a lightning strike to the tip of a blade and to the nacelle have been clarified from the measured waveforms. This information can be used for developing an EMTP simulation model of wind turbine generation systems. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 158(4): 22– 30, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20466     

Experimental and analytical studies of lightning overvoltages in wind turbine generator systems

This paper presents the results of the experimental and analytical studies undertaken for the lightning protection of wind turbine generator systems by using a reduced-size wind turbine model. In the analytical studies, the FDTD (Finite Difference Time Domain) method is used. This study focuses on the overvoltages observed at the wavefronts of lightning surges. The lightning strokes on one of the blades and on the nacelle were considered, and the experiments and analyses were carried out by considering the cases of summer and winter lightning. The voltages and currents at various positions on the wind turbine model were considered.