Numerical electromagnetic field analysis of unit step response characteristics of impulse voltage measuring systems

Unit step response characteristics of impulse voltage measuring systems are studied with the help of numerical electromagnetics code (NEC-2). Prior to this analysis, the accuracy of a transient analysis by this method is investigated for a simple structure. An impulse voltage measuring system, under application of step voltage, behaves like an antenna until a traveling wave makes several roundtrips in its lead wire. NEC-2 code can analyze such dynamic electromagnetic field around a three-dimensional (3-D) conductor system. In the present paper, the role of a shield ring of a divider for lightning impulse voltage is intensively investigated and discussed.     

冲击电压下电缆终端的非线性电场数值分析

基于后退欧拉法和变分原理推导了非线性电场的暂态有限元方程。利用暂态有限元方法分析了含不同应力控制管时的电缆终端冲击电压下的电场分布。分析结果表明,在冲击电压下电缆终端采用由电容性和非线性电阻性材料复合绝缘结构的应力控制管时,电场分布最为均匀。     

电磁脉冲测量技术分析

本文设计了一种时域天线,具有超宽带特性,在频带范围内天线端口反射系数小于-10dB（VSWR〈2）,可以确保电磁脉冲测量的不失真。并且在脉冲测量中用了一种对此时域天线的新的分析方法,即引入了转移函数。根据现有理论可以计算出测量系统所用的同轴传输线的损耗。最后利用宽带示波器显示的测量信号的结果,通过此显示的信号能很容易的计算出需要测量的脉冲信号。     

反向恢复期脉冲作用下高压晶闸管失效分析

本文搭建了高压晶闸管反向恢复期脉冲作用实验平台与特性参数测试平台,研究了高压晶闸管在反向恢复期不同阶段遭受脉冲冲击过程中的特性参数变化规律,并对退化和失效晶闸管拆片分析,结果表明：反向恢复期脉冲作用下高压晶闸管退化或失效表现为阻断能力的退化或丧失,由此引起晶闸管漏电流剧增,漏电流可作为表征晶闸管状态变化的特征参量;反向恢复期初期和中期冲击失效器件芯片上可见明显击穿点;反向恢复期中期冲击阻断能力退化芯片上可见热应力作用形成的圆斑;反向恢复期末期冲击失效器件可在芯片边缘与绝缘橡胶相接处见雪崩击穿闪痕。#$NL关键词：高压晶闸管; 电压脉冲; 反向恢复期; 失效分析#$NL中图分类号：TM461.4     

低阻抗冲击电压标准波源

介绍了可产生IEC60060-1中规定的雷电全波的低阻抗冲击电压标准波源的原理及其不确定度评定。冲击电压标准波源为小型的Max发生器,其电压峰值Up、波前时间T1、波尾时间T2都可以根据脉冲形成回路的元器件参数计算得到。该标准波源的输出电压波形峰值为10~1000V,输出波形参数不确定度(置信概率95%,包含因子k=2)为:峰值UUp为5×10-4,波前时间UT1为4×10-3,半峰值时间UT2为4×10-3。采用PTB校准过的14bit数字记录仪测量低阻抗标准的输出波形,并将测量结果与理论计算值进行比较。连续重复20次,最大相对标准偏差为2.7×10-4。在六个月内各电压点峰值长时稳定性在0.2‰内。负载分别为7.95kΩ和1MΩ,理论计算波形参数的区别与测量结果吻合。表明该低阻抗冲击电压标准波源既可校核数字记录仪也可校准电阻分压器。     

Insulator surface charge accumulation under impulse voltage

The surface charge distribution under impulse voltage is measured using a static capacitance probe. A probe with very small charge leakage is designed. The condition of surface charge accumulation under impulse voltage is analyzed, and it is concluded that micro discharges in the gas near the insulator surface such as the corona caused by free and fixed metal particles is usually a prerequisite condition. The dynamic equation describing the relationship between surface charge density and the applied voltage is established, and the process of surface charge accumulation under impulse voltage is analyzed. Theoretical analysis and experimental results show that the decrease of wave front time of the impulse voltage can result in an increase of surface charge accumulation. A GIS spacer is used to investigate the influence of charge accumulation on the flashover characteristics. It is shown that the 50% impulse flashover voltage can be reduced by 23.4%, and the lower limit of the V-t characteristics can be lowered drastically if the polarity of the surface charge is opposite to that of the applied voltage.     

Comparisons between impulse voltage calibrators and digitizers

Impulse voltage calibrators are important instruments for the calibration of impulse voltage digitizers and other measurement devices. The impulse digitizers, on the other hand, are often sufficiently accurate for checking the performance of impulse voltage calibrators. Comparisons between impulse calibrators and digitizers are useful in determining the uncertainties of the instruments, especially when multiple devices are being cross compared. In this paper, comparisons among calibrators and digitizers from Nippon Institute of Technology (NIT), Japan, National Measurement Institute (NMI), Australia, and Korea Electrotechnology Research Institute (KERI), Korea, are reported. Comparisons of full lightning impulse and switching impulse waveforms were performed. The results of the comparisons are reported with an analysis of the sources of the uncertainties. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

An impulse voltage calibrator of low output impedance

A calibrator that produces full lightning impulses and chopped lightning impulses with variable chopping time is described. The calibrator uses series-connected power metal-oxide field-effect transistors as the main impulse switch and insulated gate bipolar transistors (IGBTs) as the chopping switch, and its output impedance is low to drive a termination impedance of 50 /spl Omega/. The performance of the calibrator is verified by comparing the simulated calibrator output parameters based on the calibrator component values and output parameters calculated from measured output waveforms using a calibrated digitizer.     

Low energy single stage high voltage impulse generator

High voltage (HV) impulse generators are employed widely for testing of HV apparatus, as such tests are codified in a range of standards. As a result, insulation properties under impulse waveforms are of interest in the design of HV apparatus. This creates a need for very low energy laboratory impulse generators which can be used to test laboratory scale samples, often in conjunction with sensitive electronic instrumentation to measure sample dielectric properties. Since the sample is often the only isolation between the impulse generator and the electronics, failure of the sample will result in exposure of the electronics to the energy stored in the generator. This paper provides design details for a very low energy (/spl sim/1 nF storage), single-stage impulse generator which provides "clean" double exponential waveforms.     

Electroluminescence due to impulse voltage in cable-grade XLPE

Underground power cables in service are inadvertently subjected to impulses generated by lightning and switching surges that are superimposed on the ac voltage at which they operate. HV transients caused by lightning and switching operations not only radiate large electromagnetic fields but also impose additional stresses on the insulation and could initiate deterioration which can continue under normal operating conditions. Electrical breakdown of HV cables is a local phenomenon and electrical aging at local sites in the polymeric insulation occurs by molecular dissociation of the polymer and formation of new chemical bonds. This process usually involves the electronically excited states of the molecules that give rise to radiative phenomena, such as electroluminescence (EL). Analysis of EL can help to clarify the degradation mechanisms that occur at points of electrical stress enhancement and lead to cable breakdown. The EL technique is several orders of magnitude more sensitive than the commonly employed partial discharge detection and can provide a better understanding of the various time dependent mechanisms such as space charge injection, trapping and decay that can lead to insulation failure. The characteristics of EL in crosslinked PE subjected to impulse voltage, are described in this paper. Impulses having the same polarities as the half cycles of the ac voltage on which they are superimposed give rise to the largest number of EL pulses. Also, more EL pulses are emitted when impulses are applied at the peaks of the positive and negative half cycles than at the zero crossing of the ac voltage. This suggests that the amount of charge injected and trapped into the polymer plays a crucial role for EL emission     

Precision digital filters for high voltage impulse measurementsystems

This paper reports the design, testing and practical applications of two types of high order FIR digital filters for noise reduction and data smoothing of high voltage impulse waveforms. Particular attention is paid to the estimation of the error limits introduced by the digital filters. The error estimation involves the analysis of the frequency components of the impulse waveforms, the ripple calculation of the filters and testing of the filters with simulated and real impulse waveforms. The relationships between the filter parameters and the required filter accuracies are established     

直流电缆雷电冲击电压安全裕度研究

高压直流电缆是柔性直流输电技术的关键装备,直流电缆的绝缘厚度设计以雷电冲击电压安全裕度为重要依据。为了获得直流电缆的安全裕度,文中提出了直流电缆雷电冲击电压安全裕度试验方法,建立了相应的试验回路,对冲击电压波形参数进行了计算、仿真和验证,获得了波前时间为1~5μs、半峰值时间为40~60μs的冲击电压波形;提出了直流电缆雷电冲击电压安全裕度的分析方法,计算了电缆绝缘的电场分布。研究表明,文中所提方法可以获得直流电缆的雷电冲击电压安全裕度,为高压直流电缆绝缘厚度设计提供了依据。     

100kV单级冲击电压发生器的研制

冲击电压试验系统是研究纳米复合材料电击穿性能的前提,冲击电压发生器是试验系统的核心装置.一般来说,多级超高压冲击电压发生器的放电电压高于1 000 kV,进行局部放电的小型脉冲发生器的放电电压低于10 kV,而纳米复合材料击穿电压大约在100 kV.因此,为适应高压设备投运前试验需求,研制了100 kV低储能单级冲击发生器,介绍了其工作原理.通过仿真计算,确定了冲击低压发生器主回路元件参数.经实测,该单级冲击发生器能够满足标准雷电波要求.     

Streamer propagation under impulse voltage in long point-plane oilgaps

A 67 mm point-plane gap immersed in transformer oil, at atmospheric pressure, stressed with a 1/180 μs impulse, has been studied by recording gap current and light emission. Time-resolved images were obtained by use of an image converter camera. Minimum breakdown voltages were twice as high for negative as for positive points. All streamers at these and higher voltages were supersonic, with negative streamer velocities ⩽50 km/s. The speed of the positive streamer gradually increased to 19 km/s with increasing voltage, where it saturated. At high stresses the propagating positive streamer has been observed to switch to a faster mode which propagates with speeds in the 65 to 200 km/s range. Positive streamers were bush shaped to 2× the minimum breakdown voltage, the branching diminishing with increased voltage. Negative streamers were coarsely bush shaped or usually tree shaped. For both polarities, light emission consisted of a background light, with superposed pulses corresponding to 15 ns wide current pulses of up to 10 A. The pulses are caused by very bright, brief re-illuminations of single streamer channels. The tips of positive streamers are considerably more luminous than the channels, indicating that electron multiplication may take place at the tips. A model of the streamers as being plasma filled channels may explain the re-illuminations     

溯源用低阻抗冲击电压标准波源

本文介绍了可产生IEC60060-1中规定的雷电全波的低阻抗冲击电压标准波源的原理及其不确定度评定。冲击电压标准波源为小型的Max发生器,其电压峰值U_p、波前时间T₁、波尾时间T₂都可以根据脉冲形成回路的元器件参数计算得到。该标准波源的输出电压波形峰值为10V-1000V,输出波形参数不确定度(置信概率95%,包含因子k=2)为：峰值U_Up：5×10_-4,波前时间U_T1:4×10_-3,半峰值时间U_T2: 4×10_-3,。采用PTB校准过的14Bit数字记录仪测量低阻抗标准的输出波形,并将测量结果与理论计算值进行比较。连续重复20次,最大相对标准偏差为2.7×10_-4。在六个月内各电压点峰值长时稳定性在0.2‰内。负载分别为7.95kΩ和1MΩ,理论计算波形参数的区别与测量结果吻合。表明该低阻抗冲击电压标准波源既可校核数字记录仪也可校准电阻分压器。     

特高压冲击电压分压器线性度测量方法比较

线性度为冲击电压分压器的关键技术参数,随着额定电压的不能提高,对于不能在全部电压范围内进行比对校准的冲击分压器,必须进行单独的线性度试验。本文介绍了两种不同的测量高压冲击分压器线性度的方法：测量冲击电压发生器输出电压与充电电压的比值变化;使用球形电压测量仪来测量冲击分压器的线性度。研究充电电压测量准确度、充电时间、充电电压补偿以及充电电压不均匀程度等因素对冲击电压发生器输出电压的影响;球形电场测量仪的输出电压与被测电场成正比,在均匀场与非均匀场中都可以测量冲击电压波形,其线性度≤±1%,可通过改变测量仪的布置位置来扩大测量电压范围;使用上述两种方法测量同一台弱阻尼冲击电压分压器的线性度,测量结果一致性好,因此球形电场测量仪也可用于进行特高压冲击分压器线性度的现场校准。