Breakdown characteristics of gas‐insulated switchgear for nonstandard lightning impulse waveforms under nonuniform electric field

To improve the insulation specification of gas‐insulated switchgear (GIS), it is necessary to recognize the insulation characteristics of SF₆ gas during actual surges (called nonstandard lightning impulse waveforms) occurring at field substations. The authors observed the insulation characteristics of SF₆ gas gap under various types of nonstandard lightning impulse waveforms and compared them quantitatively with those obtained with standard lightning impulse waveforms. The experimental results were used to derive an evaluation method for real surges, which was applied to typical surges for various UHV and 500‐kV systems. In the preceding study, therefore, only the case of a quasi‐uniform electric field (with a typical range of field utilization factors in the bus of a GIS) was investigated. In the present investigation, the insulation characteristics of an SF₆ gas gap for a nonuniform electric field were observed experimentally and an evaluation method for converting nonstandard lightning impulse waveforms equivalently to the standard lightning impulse waveform was investigated. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 177(1): 11–18, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21144     

Insulation characteristics of CO2 gas for nonstandard lightning impulse oscillations: Evaluation method of nonstandard lightning impulse waveform for CO2 gas insulation

SF₆ gas is widely used in electric power apparatus such as gas‐insulated switchgears (GIS), because of its superior dielectric properties; however, it has been identified as a greenhouse gas at COP3 in 1997, and alternative insulation gases to SF₆ have recently been investigated. One of the candidates is CO₂ gas, which has lower global warming potential (GWP). However, CO₂ gas has a lower withstand voltage level than SF₆ gas; therefore, it is necessary to rationalize the equipment insulation level and reexamine the insulating test voltage for electric power apparatus as low as possible. From our previous investigation, in SF₆ gas insulation system, we obtained that the insulation requirements of the real surges (called nonstandard lightning impulse waveform) are not as severe as those of the standard lightning impulse waveform. This paper describes the evaluation method for real surges, based on insulation characteristics of CO₂ gas gaps. Furthermore, the method was applied to typical field overvoltage waveform in the lightning surge time region for 500‐kV systems and it is obtained that the equivalent peak value of the standard lightning impulse waveform is possibly reduced by 10 to 15%. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(3): 1– 9, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20560     

Insulation characteristics and its evaluation method of N2 gas for nonstandard lightning impulse waveforms

Until recently, SF₆ gas has widely been used as the best insulating medium in substation equipment. However, SF₆ gas was specified to be a greenhouse gas at COP3 in 1997 because of its high global warming potential (GWP), and alternative insulation gases to SF₆ have been sought for a long time. Alternatives using the natural gases are considered to be suitable, but none of them show better properties for insulation as well as good environmental compatibility. Therefore, it is necessary to rationalize the equipment insulation level and reduce the test voltage of electric power apparatus to as low a level as possible. The actual lightning surge waveform (so‐called nonstandard lightning impulse waveform) occurring in the actual field is different from the standard lightning impulse waveform (1.2/50 μs). There are many cases in which the actual lightning surge waveform has a steep rise and large decay of overvoltage, and the insulation requirements are not as severe as those for the standard lightning impulse waveform. In this paper, we focused our research on N₂ gas as an SF₆ substitute and investigated the insulation characteristics of N₂ gas for a single‐frequency oscillatory waveform with various frequencies from 2.7 to 20.0 MHz and damping ratios. Based on the experimental results, it might be possible to reduce the test voltage of N₂ gas insulation by evaluating the crest value of the actual lightning surge waveform that has been converted into an equivalent standard lightning impulse waveform. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 10–20, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20754     

Evaluation of Breakdown Characteristics of Gas Insulated Switchgears for Non-Standard Lightning Impulse Waveforms - Breakdown Characteristics for Non-Standard Lightning Impulse Waveforms Associated with Lightning Surges

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of a gas insulated switchgear (GIS) and thus cut the equipment cost while maintaining the high reliability of its insulation performance, it is necessary to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding paper, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five to six non-standard lightning surge waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. In this paper, the dielectric breakdown voltage - time characteristics were measured under several different conditions mainly for the quasi-uniform SF₆ gas gaps that represent an insulation element of a GIS toward four kinds of non-standard lightning impulse waveforms associated with lightning surges. As a result, in the tested range, the dielectric breakdown values for nonstandard lightning impulse waveforms were higher than for the standard lightning impulse waveform by 3% to 32%.     

Laboratory and analytical studies of the effects of multipulselightning current on metal oxide arresters

Multiple stroke lightning ground flashes can impose surges of exceptional severity on the arresters used to protect exposed distribution system equipment. This paper reports laboratory and analytical studies of the effects of representative multiple impulse currents on zinc-oxide surge arresters of distribution class. The results indicate that sextuple 8/20 μs currents can cause damage to arresters not evident with standard lightning current tests and so are worthy of inclusion in testing Standards     

Dielectric characteristics of oil‐filled transformer in the presence of nonstandard lightning surge waveforms

To achieve a rational insulation design for transformers, it is important to evaluate dielectric strength against surges actually impinging on equipment on‐site. This paper deals with the breakdown voltage characteristics of an oil gap under nonstandard lightning surge waveforms combined with oscillatory voltages. It is found that the breakdown voltages of the oil gap under nonstandard impulse waveforms are higher than standard lightning impulse voltages. The results can be ascribed to V–t characteristics of the oil gap in short‐time impulse voltage ranges. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(3): 39–45, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10229     

Evaluation of Breakdown Characteristics of Oil-immersed Transformers under Non-standard Lightning Impulse Waveforms - Method for Converting Non-standard Lightning Impulse Waveforms into Standard Lightning Impulse Waveforms

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of oil-immersed transformers and thus reduce equipment cost while maintaining high insulation reliability, it is required to identify the insulation characteristics under non-standard lightning impulse waveforms that are associated with actual surge waveforms in the field and quantitatively compare them with the characteristics under the standard lightning impulse waveform. In the previous research, field overvoltages in the lightning surge time region were analyzed, and four typical non-standard lightning impulse waveforms were defined. These four waveforms were used to measure the breakdown voltages and the partial discharge inception voltages on three models of the winding insulation elements of oil-immersed transformers. The average breakdown voltages were evaluated in terms of the overvoltage duration. This paper describes a method for converting of non-standard lightning impulse waveforms into standard lightning impulse waveforms with equivalent stress for the insulation. The constructed algorithm was applied to four examples representing two types of non-standard lightning waveforms. Due to the conversion into standard lightning impulse waveforms, the crest values were reduced by 14% to 26%. This seems to be a potential for reduction of lightning impulse insulation specifications of oil-immersed transformers.     

Results of lightning impulse tests for a 275‐kV full GIS substation

This paper describes the outline and results of the lightning impulse tests for a 275‐kV full GIS substation. The behavior of lightning surges is a very important factor for the rational design of substations and low‐voltage and control circuits inside the substations. For the above reason, we carried out lightning impulse tests for a new 275‐kV full GIS substation. In these tests, we measured voltage induced in low‐voltage and control circuits, transient characteristics of grounding grid, injected voltage and current waveforms, and so on. By investigating these data, we confirmed the behavior of lightning surges inside the substation. We also compared simulated waveforms by EMTP analysis with the measured waveforms. The simulated results agreed well with the measured results. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(1): 46–58, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10230     

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.     

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms -

To lower the lightning impulse withstand voltage of gas insulated switchgear (GIS) while maintaining the high reliability of its insulation performance, it is important to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In the preceding researches, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five to six kinds of non-standard lightning impulse waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. Then, the dielectric breakdown voltage ? time characteristics were measured under several different conditions on the quasi-uniform SF6 gas gaps and partly the coneshaped insulating spacers that represent insulation elements of GIS for six kinds of nonstandard lightning impulse waveforms. In this paper, the resultant breakdown voltages were evaluated in terms of the overvoltage duration, which led to their formulation in a unified way. On the basis of these insulation characteristics and their unified formulation, the paper investigated a method for converting non-standard lightning impulse waveforms into standard lightning impulse waveforms with equivalent stress for the insulation. When the constructed algorithm was applied to five examples of representative two type waveforms in the lightning surge time region, they were converted into standard lightning impulse waveforms with crest values reduced by 20% to 34%, suggesting potentiality for reduction of lightning impulse insulation specifications of GIS.     

低压变频器线线间雷击浪涌6kV防护回路设计

变频器常规浪涌防护回路在线线间雷击浪涌6kV时,变频器的绝缘栅双极晶体管(IGBT)模块通常会损坏。介绍了一种低压变频器线线间雷击浪涌防护回路的设计,在常规雷击浪涌防护回路基础上外加一级电感构成LC低通滤波回路,在雷击浪涌6kV时可以保护变频器的IGBT模块免受击穿。利用图解法确定了压敏电阻上的残压,通过理论计算确定了电感量,并给出了线线间雷击浪涌6kV的实例分析。结果表明,在雷击浪涌为6kV时,压敏电阻与LC低通滤波回路能将变频器线线间残压限制到1200kV以内。     

Quantitative evaluation of lightning surge range voltage–time characteristics in high‐pressure SF6 gas

Gas‐insulated switchgear (GIS) is subjected to very fast transient overvoltages such as lightning surges or disconnector switching surges. Therefore, the sparkover voltage and time (V?t) characteristics of SF₆ in a very short time range of less than are of great interest from the viewpoint of insulation design and coordination for a GIS. This paper describes the V?t characteristics of SF₆ at a gas pressure of 0.5 MPa using a steep‐front square impulse voltage under a quasi‐uniform field gap and presents a quantitative evaluation of the V?t characteristics for a nonstandard lightning impulse voltage. In the case of a square impulse, the V?t characteristics of positive polarity were observed to be almost flat over a long time range from 80 ns to , and rose steeply over a short time range from 80 ns down to 20 ns. For negative polarity, the V?t characteristics exhibit a gentle rise from 200 ns down to 40 ns. In the estimation of V?t characteristics, the equal‐area criterion parameters were quantitatively estimated using the square impulse. For a nonstandard lighting impulse, we found that application of the equal‐area criterion with these parameters for the nonoscillating impulse and oscillating impulse of up to 5.3 MHz as a model of lightning surge and disconnector switching surge is possible. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(4): 8– 17, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20309     

Insulation characteristics of SF6 gas for nonstandard impulse voltage polarity reversal pulse waveforms

Evaluation of insulation strength for lightning surge that actually enters into substations is important in estimating insulation reliability of gas‐insulated equipment. The standard lightning impulse voltage (1.2/50 µs) is used for factory tests. However, the actual lightning surge waveforms in substations are complex and are usually superimposed with various oscillations. Insulation characteristics of SF₆ gas as a function of such complex voltages have not been sufficiently clarified. This paper deals with gap breakdown characteristics in SF₆ gas under submicrosecond pulses. Breakdown voltages are lower under a polarity reversal condition than under a monopolarity condition. The cause of this difference is discussed while observing discharge propagation using an image converter camera. The electrode size effect is also discussed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 146(4): 18–25, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10246     

High-voltage testing on UHV equipment: Overshoot and base curve for oscillating lightning impulse

As the higher impulse testing voltage, residual inductance of the test circuit or the stray capacitance of the test object increases with size. This means that the overshoot superposed on standard lightning impulse voltage would not be neglected because of its larger value during the lightning test. This paper describes the analysis of overshoot and oscillation based on the equivalent circuit containing a residual inductance. The waveform parameters such as relative overshoot magnitude, oscillation frequency are also derived to evaluate the influence of the residual inductance in the impulse testing circuit. The oscillating impulse waveform is related to the base curve of the standard lightning impulse. Furthermore, the base curve for oscillating impulse is proposed by the analysis. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Evaluation of breakdown characteristics of oil-immersed transformers under non-standard lightning impulse waveforms - definition of non-standard lightning impulse waveforms and insulation characteristics for waveforms including pulses

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of oil-immersed transformers and thus cut the equipment cost while maintaining the high reliability in its insulation performance, it is necessary to grasp in an organized way the insulation characteristics under non-standard lightning impulse voltage waveforms that represent actual surge waveforms encountered in the field and compare them with the characteristics under the standard lightning impulse waveform quantitatively. As described in this paper, the first step in a series of study for the purpose above was taken by analyzing lightning surge waveforms and restriking surge waveforms such as disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations and identifying four typical non-standard lightning impulse waveforms with basic frequencies of 0.24 to 1.0 MHz. Then, two of these non-standard lightning impulse waveforms, the single-pulse waveform which is the most basic type and the waveform with a pulse in the crest and a subsequent flat section, were used to measure the breakdown voltage and the partial discharge inception voltage while changing the parameters, on three models that represent the insulation elements of windings of oil-immersed transformers. Then, the resultant average breakdown voltages were evaluated in terms of the overvoltage durations, leading to a result of formulating them in a unified way. In the tested range, the dielectric breakdown values under non-standard lightning impulse waveforms were higher, marking 52% at the maximum, than those under standard lightning impulse waveforms in all the cases, suggesting a possibility of lowering the insulation specifications of an oil-immersed transformer     

The influence of wave front duration of impulse voltage on creeping discharges along aerial insulated wire

In high‐voltage aerial distribution systems, creeping discharges progress along the cable surface from the free end of the binding wire when overvoltages caused by a lightning surge have invaded the central line of an insulated cable. Consequently, various accidents such as punch‐through breakdown, melting, or snapping of a cable, often occur at these systems. In our previous studies, it has been clarified that the lengths and aspects of creeping discharges under a 1.2/50 µ s impulse voltage condition can be markedly affected by changes in the electric field strength on the cable surface. However, lightning impulse surges which may invade the central line of a cable have various wave front durations. This will further complicate creeping discharge phenomena due to lightning. In this paper, we report the influence of the wave front duration on both the lengths and the aspects of the creeping discharges which progress on the cable on application of lightning impulse voltages. It has been shown that the behavior of negative creeping discharges reveals pronounced changes in response to the duration of the wave front of the applied voltage. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(2): 30–38, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10263     

基于L-M法的BP神经网络在电抗器雷电冲击波形调整中的应用

建立了电抗器匝间绝缘雷电冲击调波参数组合寻优模型。为了克服传统BP神经网络训练收敛太慢以及容易陷入局部最小值等问题,采用了正交试验设计方法结合基于Levenberg-Marquardt法的BP神经网络对建立的数学模型进行了仿真训练并对设备雷电冲击调波参数组合进行了寻优,获得了较为精确的标准雷电冲击波形,对实际试验具有一定的指导意义。     

Evaluation of breakdown characteristics of gas insulated switchgears for non-standard lightning impulse waveforms - analysis and generation circuit of non-standard lightning impulse waveforms in actual field

To lower the insulation specifications (specifically, the lightning impulse withstand voltage) of a gas insulated switchgear (GIS) and thus cut the equipment cost while maintaining the high reliability of its insulation performance, it is necessary to define in an organized way the insulation characteristics for non-standard lightning impulse voltage waveforms that represent actual surge waveforms in the field and compare them with the characteristics for the standard lightning impulse waveform quantitatively. In this paper, first, lightning surge waveforms and disconnector switching surge waveforms at UHV, 500 kV, and 275 kV substations were analyzed and five non-standard lightning surge waveforms with basic frequencies of 0.6 to 5.0 MHz were identified. Next, high-voltage circuits that generate these non-standard lightning surge waveforms were designed and constituted using EMTP (electro magnetic transients program) based on a circuit with a gap, inductors, and resistors connected in series and resistors and capacitors connected in parallel. Further, circuits were actually constructed, to obtain voltage waveforms approximately equal to those designed. Finally, the dielectric breakdown voltage-time characteristics were measured under several different conditions for the quasi-uniform SF₆ gas gap that represents an insulation element of a GIS. As a result, it was found that, in the tested range, the dielectric breakdown values for non-standard lightning impulse waveforms were higher than for the standard lightning impulse waveform by 6% to 32%     

特高压变压器雷电冲击伏秒特性研究

随着750 kV、1000 kV输电技术的发展,相应的电力变压器和并联电抗器的容量、尺寸和入口电容随之增大,试验回路尺寸亦相应扩大,这使雷电冲击试验电压的波前时间拉长,无法达到国内外标准的要求。根据500 kV、750 kV和1000 kV变压器和电抗器的实际雷电冲击试验波形,结合油纸复合绝缘结构的雷电伏秒特性,分析了不同波前时间对特高压变压器和电抗器绝缘水平的影响。目前变压器的设计计算和试验电压的选取一般按照标准波头进行,而充油设备的雷电冲击伏秒特性表明,雷电冲击试验电压波前时间的长短与绝缘强度有密切关系,波前时间延长可能会对某些纵绝缘的考核偏松,同时对主绝缘的考核偏严。因此,应在特高压变压器、电抗器的设计研制和试验中,考虑和重视雷电冲击波形波前时间延长所带来的影响。     

Review of research on nonstandard lightning voltage waves

Although the impulse insulation level of a power apparatus is specified under the standard 1.2×50-μs voltage wave, the apparatus seldom encounters such a voltage wave in the field. A wealth of knowledge exists on the behavior of air gaps under nonstandard lightning impulse voltages. The objective of the Task Force was to compile a bibliography on the nonstandard lightning impulse voltages and review the present state of research. This paper reviews the present status of research including the behaviour of air gaps under transient voltages, and the generation and measurement of fast-front impulse voltage waveforms