Characteristics of partial discharges in artificial simulated treechannels during tree propagation

In order to clarify partial discharge (PD) mechanism in an electrical tree, we investigated PD pulse sequence and light emission from a single PD in an artificially-simulated tree channel during the tree propagation in low-density polyethylene (LDPE). For positive PD, the light emission was observed near the needle-tip and there was a positive correlation between the PD magnitude and the length of luminous region. The pulse-sequence analysis showed that PD took place at constant voltage increments. These results suggest that PD starts at the needle-tip and the PD magnitude is determined by the PD length. On the other hand, for negative PD, there was no correlation between the PD magnitude and the length of luminous region. The PD pulse sequence can be explained by a simple PD model, since the voltage increment is related to the magnitude of preceding PD. These results suggest that there is a difference between positive and negative PD characteristics and their mechanisms in an artificial channel during tree propagation     

Examination and location of partial discharge sites in severelyaged underground distribution cables

This paper presents the results of laboratory investigations of partial discharge (PD) in field aged XLPE underground power cables. PD measurements were made on sixty-one cable samples over a three year period. When PD was detected, the magnitude was measured and a site location was determined. PD site locations were predicted using time delay estimations between PD pulses arriving at opposite ends of the test cable. Fourteen of the samples tested had detectable levels of PD. Some of these PD sites extinguished during the measurement period and were returned to rated voltage aging. When samples had continuously active PD sites, they were either dissected or returned to the aging test. Four sites of this type were found allowing two for dissection and two for aging. Seven of the samples failed after PD measurements. All seven failed near the predicted PD location. During the PD testing, no test cables contained PD which initiated at or below operating voltage. When PD detection equipment was monitoring cables which failed, the failures occurred from 2 to 80 minutes after the presence of PD pulses was detected     

电机局部放电超声特性

为探索电机局部放电检测新方法,分析电机局部放电机理和国内外对电机局部放电监测研究状况,提出利用超声法对电机局部放电进行监测.为此,构建电机定子绕组存在的几种典型局部放电模型和实验硬件系统,并进行放电实验.在局部放电实验室,采用一种窄带超声传感器对几种典型局部放电超声信号进行采集.对相同条件下采集到的各种模型局部放电超声...     

气体绝缘系统中典型缺陷的超宽频带放电信号的分形分析

要提高气体绝缘系统(GIS)放电在线监测与诊断的准确性，需要研究其典型缺陷的超宽频带放电特征。但GIS中放电频率高、频带宽，基于IEC60270标准的常规低频局部放电统计分析方法难以对放电特征进行分析。文中提出应用基于小波提取技术的放电信号的分形分析方法，对GIS中典型缺陷放电的各频段信号进行分维数计算，用分维数来量化分析GIS中超宽频带局部放电的频谱特性，发现了GIS中不同金属性表面缺陷的超宽频带放电分形特征的明显差异，对进一步将超宽频带放电检测技术用于GIS局部放电在线监测具有重要意义。     

基于样本加权FCM聚类的未知类别局部放电信号识别

针对电力变压器待识别局部放电信号中可能存在不属于已知类别的未知样本的问题,提出了一种基于样本加权模糊C均值(FCM)聚类的未知类别局部放电信号识别方法。对已知类别的局部放电信号进行FCM聚类,确定各已知类的聚类中心;分别计算已知类别和待识别局部放电信号的样本权值,并根据Otsu准则确定样本权值的自适应阈值;将各待识别局部放电信号的权值与确定的阈值进行比较,判断其是否属于已知类别;采用支持向量机(SVM)对得到的属于已知类别的待识别局部放电信号进行分类,对未知类别样本进行人为分析判断。采用所提方法对实验室条件下的放电信号进行分析,实验结果表明,所提方法可以有效地区分待识别局部放电信号中的未知类别样本。     

周期性脉冲电压作用下绝缘局部放电的测量与分析

局部放电是导致变频电机绝缘失效的主要原因之一.逆变器输出的脉冲方波上升沿陡、频带宽,使局部放电测量更加困难.文中采用脉冲电流传感器有效地测量出脉冲方波下的局部放电,利用小波包方法提取局部放电信号,并根据其统计结果,探讨了脉冲方波幅值和频率对放电次数、最大放电量、平均放电量的影响,为研究绝缘材料在脉冲方波下的老化机理创造了条件.     

Partial discharge characteristics and tree inception in artificialsimulated tree channels

In attempt to clarify the mechanism of electrical treeing degradation and tree propagation, partial discharge (PD) characteristics in an artificially-simulated tree channel in a low-density polyethylene (LDPE) were investigated. The PD pattern and PD pulse sequence showed that the PD in artificial channel with diameter of 10 μm was useful for clarification of PD in actual tree. The PD formed a PD pulse train whose magnitude changed with time. In the samples where tree propagation was seen at the tip of the artificial channel, pulse trains with large PD magnitude sometimes occurred and the region of light emission reached the vicinity of the channel tip before tree propagation. In the samples where tree propagation was not seen, the region of light emission due to PD did not reach the channel tip. These results suggest that tree propagation takes place when the PD with large magnitude and long luminous region occur in an artificial channel and damage the channel tip     

超高频方法在变压器局部放电检测中的应用

为了探讨局部放电超高频检测技术的应用,将数字化测量和超高频检测技术相结合,分析了局部放电超高频检测技术的原理。在简要介绍了局部放电超高频检测系统硬件和软件的组成后,实测并分析了检测系统的抗干扰性能。通过变电站电力变压器的现场局部放电测量,及时发现了设备的局部放电水平异常,避免了事故的发生。分析和实测表明,超高频方法较其它方法相比能有效避开电晕干扰,更易于发现设备绝缘系统早期绝缘缺陷,检测结果能准确反映设备绝缘状况,适用于电力变压器局部放电在线监测。     

Pattern analysis of partial discharges in SF6 GIS

The measurement of partial discharge(PD) of several faults in gas-insulated system (GIS) is discussed. Phase-resolved PD patterns have been measured using three different PD detection measuring systems: according to the IEC 270 recommendations, a VHF/UHF measuring system with narrow band filtering, and the UHF measuring system with wide band filtering. PD patterns are compared using computer-based discrimination tools. The influence of the selected center frequency on the PD patterns is discussed for the narrow band VHF/UHF measuring system. The influence of the number and type of GIS components between the discharging defect and the capacitive coupler on the shape of the PD patterns is analyzed. For several GIS components the signal reduction is studied. It was found that the shape of PD patterns is independent on the used PD detection circuit and the propagation path of the PD signals. As a result, discrimination and classification of PD distributions of several studied defects are possible using digital tools     

发电机定子离线局部放电试验的现场操作与数据分析

离线局部放电试验通常用于发电机定子绕组绝缘的老化鉴定.离线局部放电试验一般需要无局放电源将定子绕组加至一定电压,通过局部放电传感器和检测阻抗,检测系统测量局部放电信号.停机后热态下的发电机所处的状态与运行时发电机所处的状态差异很大,因此不能以停机之后的热态来比拟运行状态,离线局部放电试验应该在定予清扫之后进行.应采取抗...     

Random sampling and data processing for PD-pulse height and shapeanalysis

A measuring system for the digital acquisition of partial discharge (PD) pulse signals, based on the last generation of oscilloscopes, has been developed in order to perform both PD pulse shape and PD pulse height analysis. Wide-band, fast sampling rate and individually-triggerable memory blocks are available for the acquisition of PD pulse signals. However, a problem of sampling the population of PD pulses arises from the limited available on-line storage memory. Four sampling techniques are investigated and evaluated in order to record an amount of PD pulses which enables PD stochastic inference for a minimum of the on-line memory use. Some statistical indexes based on the pulse-height and pulse-phase distributions are used to compare performances of the different techniques. It is shown that a technique based on the Poisson law provides the most accurate sampling of PD pulses, while minimizing the memory, particularly in the presence of two simultaneously active PD phenomena. The developed procedure enables an accurate analysis of the shape of a large number of PD signals, but also stochastic processing of height distributions, which is becoming a reference for PD pattern analysis     

电力电缆局放定位中波速确定方法研究

由于电缆中局放脉冲传播速度很快,对电缆局放定位误差影响很大。由于电缆参数不同导致其中局放脉冲的传播速度有所差别。波速微小的差别会使定位结果偏差较大。针对不同电缆,局放定位应该采用基于实验确定的波速。在分析了广泛应用的交联聚乙烯(XLPE)绝缘电缆中局放脉冲传播特性后,提出了电缆局放定位中波速确定方法。基于实验数据拟合,得到局放脉冲在电缆中的传播时间与电缆长度的表达式,为局放点精确定位打下基础。     

波形匹配追踪算法在多局放脉冲提取中的应用

针对现场实际中可能存在多个放电源同时放电的情况，利用基于Laplace小波的匹配追踪算法，提取出每个局部放电信号的起始时刻、振荡频率和衰减系数等信息，根据这些结果来确定其是同一个放电源的多次放电，还是不同放电源的各次放电。仿真及对实验数据的分析结果显示在多个放电脉冲同时存在的情况下，用该方法提取和辨识多个局部放电脉冲信号是有效的。     

局部放电数字化在线检测诊断系统

局部放电（PD）是导致高压电工设备绝缘击穿的主要原因。局部放电 在线检测是保证电力设备可靠运行的有效手段。本文以西安交通大学绝缘国家重点实验室研制的一套数字化局部放电在线检测诊断系统为例,在高压屏蔽室内对典型试样的放电进行采集,并绘制其放电谱图,进行指纹识别、放电模式识别分析。     

Influence of supply voltage frequency and magnitude on PD pulse parameters

A study on the influence of supply voltage magnitude and frequency on partial discharge (PD) pulse shapes is presented in this paper. Ultrawide band (UWB) timeresolved PD pulse measurements were carried out on artificial PD defects using test voltage frequency range of 10 ? 400 Hz and voltage range of 2 - 11 kV. The manner in which the PD pulse shape responded to changes in the test voltage characteristics depended on the defect type. The observations can be interpreted using the generally agreed theory of PD mechanisms. The knowledge generated in this work is valuable in the interpretation and comparison of PD measurements made at different voltages and frequencies. It also contributes to development of PD defect classification techniques based on the correlation between test voltage frequency and time-resolved PD.     

基于模极大值小波域的局部放电信号重构算法

局部放电信号是奇异信号，利用模极大值原理，可以对局部放电信号去噪，然而，对于单个的局部放电脉冲信号，如何由保留下来的少数模极大值点重构局部放电信号是一个重要课题。为此，该文提出一种基于模极大值小波域的局部放电信号重构算法，该算法先根据模极大值小波域的定义求出局部放电信号的模极大值小波域，从而得到局部放电信号的小波系数，然后逆变换得到局部放电信号，实例分析表明，该算法程序简单，易实现，速度快，能满足局部放电在线监测的需要。     

GIS局部放电故障诊断试验研究

建立了模型GIS中局部放电在线检测的测量系统,采用特高频(UHF)电磁波测量、常规局部放电测试以及相位分析等方法,对GIS中典型的几种局部放电特征进行了研究,以求识别放电类型.通过常规局部放电测试与UHF特高频局部放电测量结果对比,可估计UHF信号的放电量,提高UHF特高频局部放电测试在工程中的实用性.     

Partial discharge. XXV. Calibration of PD measurements for motorand generator windings-why it can't be done

In most types of high voltage apparatus, a PD acceptance test is required. In contrast, the PD test is very rarely used as an acceptance test for new motor and generator windings. The closest that machine manufacturers come to a PD acceptance test is the power factor tip-up test (IEEE Standard 286), which is an indirect PD test. The tip-up test is sensitive to PD sources when testing individual coils/bars but is relatively insensitive when testing complete windings, due to the presence of stress relief coatings. The lack of a direct PD acceptance test fundamentally results from the inductive nature of a stator winding. This article discusses the reasons for the lack of an absolute PD measurement criteria for stator windings, after a discussion on measurement methods and the quantities used to measure PD activity     

Detection and location of partial discharges in power transformers using acoustic and electromagnetic signals

The measurement of partial discharges (PD) is a non-destructive and sensitive diagnostic tool for the condition assessment of insulating systems. Two major tasks of PD measurements may be distinguished, (i) PD detection, hence providing evidence and the type of the PD and (ii) the location of the PD. The question "Where is the PD source?" is amongst others tremendously important for scheduling and starting maintenance/repair actions cost and time efficiently or to perform a risk analysis. Here the possibility to geometrically localize the flaw, by means of arrival times of acoustic PD signals, gets an extremely interesting option. Precise acoustic arrival times are consequently essential to accurately locate PD in a power transformer. The averaging of acoustic PD signals helps to enhance the acoustic sensitivity. The acoustic detection limit is lowered significantly and the determination of the arrival times is made possible for weaker PD. Supplementary steps, like automatic objective arrival time determination or additional wavelet-based de-noising further improve the overall location accuracy. A new location approach works with pseudo-times and allows for the use of robust direct solvers instead of the previously used iterative algorithms.     

Partial discharges in a cavity at variable applied frequency part 1: measurements

In this paper partial discharges (PD) in disc-shaped cavities in polycarbonate are measured at variable frequency (0.01 ? 100 Hz) of the applied voltage. The advantage of PD measurements at variable frequency is that more information about the insulation system may be extracted than from traditional PD measurements at a single frequency (usually 50/60 Hz). The PD activity in the cavity is seen to depend on the applied frequency. Moreover, the PD frequency dependence changes with the applied voltage amplitude, the cavity diameter, and the cavity location (insulated or electrode bounded). It is suggested that the PD frequency dependence is governed by the statistical time lag of PD and the surface charge decay in the cavity. This is the first of two papers addressing the frequency dependence of PD in a cavity. In the second paper a physical model of PD in a cavity at variable applied frequency is presented.