Development of an identification system for location of free metallic particles in GIS based on analysis of Lamb waves

We investigated propagation properties of Lamb waves in a gas‐insulated switchgear (GIS) tank to diagnose insulation performance of GIS. The acoustic signals excited by a free metallic particle colliding with the tank sheath were measured using AE sensors. The wavelet transform was applied to decompose the wave data into its time–frequency components. As a result, difference of propagation properties of Lamb waves is clearly seen with different sizes of GIS tank. Based on the characteristics of Lamb waves, algorithms for location identification of a free metallic particle were examined in model GIS using two AE sensors. Herein, we propose a new system for location identification of a free metallic particle in GIS. Moreover, it is verified that the new identification system is suitable as a diagnostic technique for GIS. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(3): 28–35, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20676     

Resonance characteristics and identification of modes of electromagnetic waves excited by partial discharges in GIS

Electromagnetic waves are used for detection of partial discharges (PD) in GIS (gas‐insulated substations). A very wide frequency band up to 1.5 GHz is utilized for detection. There are three categories of electromagnetic wave which can be excited and propagate in coaxial cylindrical structures like GIS, namely, TEM, TE, and TM modes. The characterization and identification of each mode is indispensable to understanding the partial discharge phenomena in GIS. In this paper, peaks in the frequency spectrum excited by PD are identified in each mode and the resonant characteristics of each mode are studied. The following are the major results: (1) The resonance peaks appear at the frequencies defined by the spacer distance. (2) The intensity of each mode depends on the position of discharge source along the radial direction. The lower‐order modes including TEM are excited when a discharge source is located near the center conductor. On the other hand, higher‐order modes are excited when the discharge source is at the enclosure surface. (3) The experimental profile of each mode excited by PD along the radial direction approximately agrees with the general theory of electromagnetic wave propagation in coaxial cylindrical cavity. © 2000 Scripta Technica, Electr Eng Jpn, 131(2): 1–11, 2000     

Motion and size estimation of a free moving metallic particle in GIS based on propagation properties of acoustic waves

We have investigated the propagation properties of Lamb waves and motion characteristic of free moving metallic particle in a gas‐insulated switchgear (GIS) tank to diagnose the insulation performance of GIS. We have proposed a new identification technique for defect location in GIS based on the time–frequency analysis of the Lamb waves using the Wavelet Transform. In this paper, we measured the acoustic signals excited by a metallic particle colliding with the tank sheath. Furthermore, we measured the moving particles under a high electric field in GIS using a high‐speed video camera. As a result, we examined the relationship between maximum lifting height and the flight time during subsequent impacts of a moving particle. Moreover, we estimated particle size based on the propagation properties of Lamb waves. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 26–33, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20023     

GIS局部放电的超宽频检测系统初探

针对GIS运行中存在的潜伏性绝缘缺陷,根据GIS局部放电脉冲所激发的电磁波传播特性的宽频带特诊,对一种新型超宽频带天线局部放电检测系统实验方案作了探讨.     

Time‐frequency analysis of a pressure wave caused by impulse tree using wavelet transform

This paper describes results of time‐frequency analysis of a pressure wave caused by impulse tree extension using wavelet transform. Pressure waves were measured by a piezo sensor which was located on the back of the plane electrode when high‐voltage nanosecond pulses were applied to a point electrode in a low‐density polyethylene block. Frequency of the pressure wave from induced charges on the plane electrode was higher than that of the pressure wave from tree. In addition, the frequency of the pressure wave from tree tended to decrease with increasing gap length because of the dispersion of the pressure wave during its propagation. When a large tree extension occurred between a 5‐mm gap, pressure waves of about 10 MHz propagated from the tree tip and a pressure wave of 1 MHz propagated from the tree stem. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(1): 1–7, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10097     

Auto‐detection of partial discharges in power cables by discrete wavelet transform

One of the serious problems that can occur in power XLPE cables is destruction of insulator. The best and conventional way to prevent this is ascertaining partial corona discharges occurring at small voids in organic insulators. However, there are some difficulties in detecting those partial discharges due to the existence of external noise in detected data, whose patterns are hardly identified at a glance. For this reason, there have been a number of researches into detecting partial discharges by employing a neural network (NN) system, which is widely known as a system for pattern recognition. We have been developing an NN system for auto‐detection of partial discharges, and have input numerical data of the waveform itself and obtained appropriate performance. In this paper, we employed the discrete wavelet transform (DWT) to acquire more detailed transformed data in order to use them in the NN system. Employing the DWT, we were able to express the waveform data in time–frequency space, and achieved effective detection of partial discharges by the NN system. We present herein the results using DWT analysis for partial discharges and noise signals which we obtained. Moreover, we present results out of the NN system which dealt with those transformed data. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(1): 24–30, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10315     

基于ANFIS的GIS设备局部放电故障辨识

为了实现气体绝缘组合电器设备局部放电故障类型的辨识,本文通过分析四种典型绝缘缺陷局部放电时SF6气体分解组分特点,选取四种气体分解物含量比值作为特征向量,阐释了气体含量比值的物理意义,构造了三输入单输出的自适应模糊神经推理系统(ANFIS),对该模型的有效性进行了测试。测试结果表明局部放电类型的ANFIS辨识系统识别效果好,收敛速度快,且对样本数量要求低。     

GIS中金属微粒诱发沿面局部放电发展过程的研究

局部放电的检测和识别对气体绝缘全封闭组合电器(GIS)运行状况的监测起着至关重要的作用。金属微粒缺陷是一种极易引发GIS局部放电的典型缺陷。文中主要研究金属微粒诱发的GIS内局部放电沿面爬电的发展过程。为此,根据GIS实际运行条件,搭建GIS模拟实验平台,采用阶梯升压法划分试验阶段,利用脉冲电流法检测各阶段下的局部放电模式,与此同时架设增强型电荷耦合检测器相机(ICCD)实时记录金属微粒局部放电的沿面发展过程,并采用K-Means聚类算法结合特征参量对其发展过程进行划分。结果表明GIS盆式绝缘子上金属微粒的沿面局部放电演变过程分为3个阶段:电晕放电主导阶段、电晕与流注放电并存阶段和流注放电主导阶段。     

气体绝缘开关设备局部放电检测及定位实例分析

对现场使用的气体绝缘开关设备(GIS)局部放电检测手段进行了介绍,通过对各种局部放电检测手段的比较,确定了采用超声波和超高频同时进行局部放电的检测和定位的方法。对现场实例进行分析,确定文中采用的定位方法有助于对故障进行精确定位。     

GIS在线检测中局部放电和外部干扰信号的识别

采用小波时频分析的方法对发生在气体绝缘金属开关设备(GIS)内部局部放电而激发的电磁波和外界的电晕干扰进行了分析,讨论了区分和识别外部和内部放电及外界干扰的可能性。在单一信号存在的情况下,发生在GIS变电所的电晕干扰一般在130MHz以下,频宽小于70MHz,而内部放电激发的电磁波信号无论何种缺陷以及类型如何,其频宽至少是电晕干扰的2倍以上,所以,从信号的带宽上可以判别是内部放电还是外部干扰。当电晕和放电信号共存时,可以通过信号的带宽和信号到达的前沿综合判断。结果表明,该方法简单有效,可以满足在线检测中信号识别的要求。     

实测信号激励条件下GIS局部放电的电磁波传播特性研究

笔者主要分析GIS典型绝缘缺陷引起的局部放电(PD)过程,并应用FDTD算法,分别以理想的高斯脉冲信号和真实PD电流信号为激励源,研究电磁波在GIS内部的传播特性,结果表明:PD实际电流信号与理想高斯脉冲激励下的电磁渡相差较大,PD超高频电磁波传播特性仿真研究宜采用实测PD信号作为模拟激励源.     

基于尺度-能量熵特征对的特高频局部放电辨识方法

对气体绝缘组合电器(GIS)进行局部放电(PD)检测,可以发现GIS内部早期绝缘缺陷和隐患,并预防绝缘事故发生。文中采用复小波分解(CWT)对GIS内部特高频(UHF)PD信号进行多尺度分解,分析了CWT能量熵(CWT-EE)随CWT尺度的变化规律,发现UHF PD信号信息主要分布在能量熵变化梯度较大的尺度下。为此,文中提取CWT-EE及其对应尺度,构建尺度-能量熵(SP-EE)特征对,既保留了PD信号能量特征信息,又保留了UHF PD信号小波尺度信息。最后,采用支持向量机(SVM)进行UHF PD类型辨识,结果表明:SP-EE特征对不但可以有效识别GIS内部4种典型绝缘缺陷,而且能够有效降低UHF PD信号分解层数和PD特征维数。     

GIS局部放电测试技术比较

通过介绍GIS局部放电测试经常使用的几种方法的基本原理及优缺点，建议现场GIS局部放电检测应采用声-电联合使用的办法，才能更好的发现GIS内部局部放电缺陷。     

小波分析在气体绝缘组合电器局部放电检测中的应用

采用两种检测手段,测量了在气体绝缘组合电器(GIS)局部放电模拟系统中,由内导体固定突起所产生的局部放电。一种有效的滤除干扰的信号处理方法——小波分析法被应用于这个系统。结果表明,在背景有较强干扰情况下,由于小波分解的局部特性,在检测局部放电时优于传统的付里叶频谱分析方法及在单纯频率范围滤波的方法。     

GIS中电磁波传播特性的试验研究

GIS内部的局部放电会在腔体中激励超高频（UHF）电磁波信号,局部放电信号可通过超高频传感器进行检测。为研究UHF信号在GIS中的传播特性,在GIS内设置了导体尖端和悬浮电位放电模型,内置式传感器的信号与用示波器在盆式绝缘子浇注孔测试到的UHF信号进行比较。试验结果表明,UHF信号在GIS内有一定的衰减,外置式传感器测得的信号比内置式的衰减大。     

局放脉冲信号的三种小波去噪方法的研究

介绍了三种小波去噪的方法:小波分解与重构法、非线性小波阈值法、小波模极大值法,分析了各自的特点和优劣。针对从高斯白噪声中提取的局部放电脉冲信号给出了仿真试验结果。为局部放电脉冲信号检测方法的选择提供了参考依据。     

基于小波和高阶PDE的电缆局部放电去噪研究

局部放电(PD)试验是检测电力电缆绝缘性能的重要手段,由于试验现场电磁环境比较复杂,提取所得的PD信号已被噪声淹没。为得到较为真实的PD信号,提出了一种基于小波变换和高阶偏微分方程(PDE)相结合的去噪方法。利用小波变换提供较好的局部放电信号预处理和后处理平台,对低频子信号进行四阶PDE迭代去噪,同时采用效果评价指数信噪比(SNR)作为迭代终止条件。将该方法的去噪效果与传统的小波阀值去噪效果进行了比较,经过计算和仿真分析表明,文中方法能够较好的保留信号边缘与细节,比传统小波阀值去噪具有更优越的去噪性能。     

运行GIS设备的局部放电检测技术及其应用

超高频局部放电测量技术(UHF法)可有效检测运行GIS设备局部放电信号,及时发现GIS设备内部存在的绝缘缺陷。UHF法弥补了GIS设备缺乏有效试验手段的不足,可作为现行高压电气设备预防性试验方法的补充,有助于GIS设备的运行维护。本文采用自行研制测量装置成功地捕获到运行GIS设备产生的超高频局部放电信号,为推广应用UHF法积累了经验。     

GIS绝缘缺陷局部放电的联合检测研究

建立了GIS（Gas Insulator Switchgear气体绝缘体全封闭组合电器）局部放电模型,通过在GIS腔体盘式绝缘子上制作人工气泡模型,运用脉冲电流和气相色谱分析检测两种方法对GIS内局放进行了检测。获得了绝缘缺陷局部放电的分布图谱和局部放电时SF6气体分解组分。最后,通过曲线拟合研究了绝缘气泡缺陷下SF6放电各分解组分的变化规律。     

Effect of spectrum analyzer's impulse bandwidth on the measurement of EM waves emitted from partial discharges in multipath‐rich environment

Superheterodyne spectrum analyzer (SA) has been widely used for receiving EM waves emitted from partial discharge (PD) because of its high sensitivity. Generally, resolution bandwidth is shown as a measurement parameter because the pulse response depends on the receiver's bandwidth. In this paper, we measure the impulse bandwidth of SA and describe the effect of the impulse bandwidth of SA on the measurement of EM waves emitted from PD in multipath‐rich environment. The results showed that the field strength of the EM waves emitted from PD is proportional to the impulse bandwidth higher than about 200 kHz and signal‐to‐noise ratio (SNR) increases with the impulse bandwidth as in the measurement of pulsed RF signals. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.