变压器局部放电在线监测技术的改进

设计了一种基于无线传输的变压器局部放电在线监测方案,解决了传输电缆不便安装和维修的问题。在网络协议中采取了节能措施,使检测器能够持续工作7年以上;在检测器中增加了一些硬件电路,可对局部放电产生的超声波信号进行预处理,有效地排除了各种干扰,大大压缩了数据量,降低了系统造价。采用AD8307对数放大器对超声波信号进行放大,既保证了检测精度,又扩大了检测范围。测试结果表明,该检测装置的检测范围为30～10 000pC,相对误差小于±10%,满足设计要求。     

局部放电在线监测相位外同步新技术的研究

为了克服传统相位同步技术在局部放电在线监测应用中的缺陷,研究了灯光相位同步和电源无线相位同步新技术。这两种相位外同步技术在硬件上综合采用光敏传感技术、电力电子技术、模拟信号调理技术和无线传输技术对电网相位信号进行采集、调理和实时传输,在软件上采用自适应数字消抖算法结合锁相环技术对相位波形进行分析。实际测试表明灯光相位同步技术在普通室内灯光强度下和电源无线相位同步技术在少遮挡环境下均能稳定的实现应用。相比传统同步技术,这两种相位外同步技术具有使用简单、安全、移动性好和相位实时同步的优点,在局部放电现场测量具有良好实用价值。     

JFY-3型变压器局部放电在线监测系统

ＪＦＹ－３型变压器局部放电在线监测系统能连续监测多台大型变压器的局部放电,并具有事故追忆、故障报警和定位等功能。它采用芝带多通道、大容量、高采样率数据采样;运用多种数字信号处理方法抑制干扰;采取电－声联合监测方式,以实现放电点定位。主控室的上位机与现场的数据采集装置之间的通信由网络舆系统实现,提高了信号传输的速率和可靠性,从而提高了系统的抗干扰能力。本文主要介绍了下位机相关的硬件部分。     

HSB-2型发电机局部放电在线监测系统的研究与应用

基于射频检测分析的旋转电机局部放电在线监测方法,具有实施的简便性、历史经验的可比性、信号分析的可视性和配备专家咨询系统的可行性.介绍了宝钢电厂HSB-2型基于嵌入式集成前端的发电机局部放电在线监测装置的研究与应用效果.     

750kV变压器局部放电超高频在线检测技术

电压等级的不断提高,对电力设备运行可靠性提出了更加苛刻的要求,电力设备绝缘在线检测,越来越得到人们的重视。因此,分析超高频局部放电在线检测系统的结构、原理及特点,介绍变压器局部放电在线检测的方法和超高频局部放电在线检测系统的现场应用就具有特殊意义。     

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。     

发电机局部放电在线监测中的抗干扰技术

大型发电机局部放电在线监测的关键技术之一是如何掏现场的各种电磁干扰。本文对现场干扰的特性进行了分析,并提出了相应的抑制方法。最后介绍了已成功用于发电机局部放电在经监测仪中的抗干扰系统。对现场实测数据的处理结果表明这些方法是有效的。     

变压器局部放电在线监测系统设计和干扰抑制

如何有效地去除各种干扰是变压器局部放电在线监测系统的关键问题．介绍了用FFT和级联二阶IIR陷波器剔除周期性载波干扰,用小波包方法去除白噪声和用小波分解方法有效地提取内部局部放电脉冲。由于DSP可做FFT变换、IIR滤波和小波变换,因此把采集的数据先由DSP预处理,然后判断处理后的数据是否为有用放电信号,若是则传送到后台工控机进行二次处理。由于本系统采用了一种较新的设计,能够做到处理的实时性。     

A novel wavelet transform technique for on-line partial discharge measurements. 1. WT de-noising algorithm

Medium and high voltage power cables are widely used in the electrical industry with substantial growth over the last 20-30 years ago, particular in the use of XLPE insulated systems. Ageing of the cable insulation is becoming an increasing problem that requires development of reliable methods for on-line condition assessment. For insulation condition assessment of MV and HV cables, partial discharge (PD) monitoring is one of the most effective techniques. However on-site and on-line PD measurements are affected by electromagnetic interference (EMI) that makes sensitive PD detection very difficult, if not impossible. This paper describes implementation of wavelet transform techniques to reject noise from on-line partial discharge measurements on cables. A new wavelet threshold determination method is proposed with the technique. With implementation of this novel de-noising method, PD measurement sensitivity has been greatly improved. In addition, a full AC cycle data recovery can be achieved instead of focusing only on recovering individual PD pulses. Other wavelet threshold de-noising methods are discussed and examined under a noisy environment to compare their performance with the new method proposed here. The method described here has been found to be superior to the other wavelet-based methods     

大型发电机定子绕组局部放电在线监测系统的研究

提出了一种用于现场的发电机局部放电在线监测系统的实现方案。这个方案采用客户机／服务机形式的局域网结构,以光纤传输作为局域网的连接。在系统设计中从局部放电监测点的选择、硬件结构和软件编程等多方面考虑了抑制噪声干扰的问题。这个监测系统在实验室和现场进行了测试,证明了该系统是可行的。     

抗干扰技术在电力变压器局部放电在线监测中应用

针对电力变压器现场干扰信号特点,采用了软件辅助的脉冲定向耦合法进行抑制,即利用每相高压套管底座和套管末屏接地线上的2个磁芯式电流传感器耦合信号,通过软件鉴别2路传感器所耦合到的脉冲信号第1个峰值的极性,判断2路传感器脉冲极性的异同,从而定向耦合变压器内部的放电脉冲,可有效去除随机脉冲型干扰;同时将动态阈值、数字滤波及相位开窗等抗干扰技术融合到在线监测系统中,综合去除背景噪声、固定频段干扰、周期性脉冲等,使监测数据真实可靠.通过在220 kV变电站的实践应用验证了系统监测的有效性及可靠性.     

Cost-effective on-line partial discharge of measurements for cables

On-line partial discharge (PD) measurements are an efficient method for detecting certain insulation defects of cables. These include defects in cable joints and terminations, and defects due to mechanical impact. Noninvasive, efficient, and widely applicable, portable on-line PD measurement techniques are strongly favored by the electricity industry. Three on-site PD measurements for cables are described in this article to illustrate how the techniques achieve cost-effective insulation diagnosis to protect the main assets.     

A novel wavelet transform technique for on-line partial discharge measurements. 2. On-site noise rejection application

For pt.I see ibid., p.3-14, (2007). Insulation assessment of HV cables requires continuous partial discharge (PD) monitoring to identify the nature of insulation defects and to determine any degradation trends. However to recover PD signals with sufficient sensitivity to determine such insulation degradation in substations with high levels of electromagnetic interference is a major challenge. This paper is the second of two papers addressing this challenge for on-line PD measurements in a noisy environment. The first paper described a wavelet transform-based method of interference rejection. This paper applies that method to the problem of on-site testing, using both laboratory tests and on-site tests. The laboratory tests were used to stimulate the noisy on-site testing environment, with use of transient pulse-like noise, discrete spectral interference (DSI) and white noise. These noise types have been successfully rejected by the method proposed in the first paper. In addition, on-site tests have been undertaken and have been able to detect PD signals in an old 11 kV substation multi-cable installation     

基于脉冲电流法的高压开关柜局部放电在线监测装置

脉冲电流法局部放电检测通常用于电气设备出厂时的型式试验以及其他离线测试中。在充分分析开关柜局部放电检测的现状与问题后,设计了基于开关柜高压带电显示装置的局部放电在线检测的电路原理和信号提取方法。搭建了基于脉冲电流法的高压开关柜局部放电在线检测回路,开发了具备实时监测、判断与分析功能的后台软件。并在10 kV开关柜真型局部放电缺陷仿真平台上进行了真实放电的模拟试验,验证了基于脉冲电流法的高压开关柜局部放电在线监测装置的灵敏度与有效性。该研究对开关柜状态检修以及脉冲电流法在线检测理论研究具有较大意义,为10 kV配网设备局部放电在线监测提供了良好的实现方法。     

局部放电信号检测的HHT-MDL自适应阈值算法

基于局部放电信号特征,将HHT与信息论的MDL 判据相结合应用于局部放电信号的提取。该算法以多分辨率的EMD为基础,结合MDL判据自适应地确定EMD得到的IMF的阈值,来提取局部放电信号,同时还得到局部放电信号的时间-相位-幅值谱。对于强周期窄带干扰,提出了先用FFT预处理后,再用HHT和MDL消噪的简单算法。该算法综合了这两种方法的优点：无需定义任何基函数,无需事先知道噪声的水平,不需要预置阈值、不需要选择阈值行为方式,有较强的自适应性。仿真结果表明,本方法能够有效地消除局部放电中的噪声,其效果优于基于小波和MDL准则的消噪算法,为局部放电信号的消噪提供了一种新思路。     

局部放电信号检测的HHT-MDL自适应阈值算法

基于局部放电信号特征,将HHT与信息论的MDL 判据相结合应用于局部放电信号的提取.该算法以多分辨率的EMD为基础,结合MDL判据自适应地确定EMD得到的IMF的阈值,来提取局部放电信号,同时还得到局部放电信号的时间-相位-幅值谱.对于强周期窄带干扰,提出了先用FFT预处理后,再用HHT和MDL消噪的简单算法.该算法综合了这两种方法的优点:无需定义任何基函数,无需事先知道噪声的水平,不需要预置阈值、不需要选择阈值行为方式,有较强的自适应性.仿真结果表明,本方法能够有效地消除局部放电中的噪声,其效果优于基于小波和MDL准则的消噪算法,为局部放电信号的消噪提供了一种新思路.     

Comparison of on-line partial discharge detection methods for HV cable joints

The capacitive coupler, acoustic emission (AE) sensor and radio frequency current transducer (RFCT) have been used to detect partial discharge (PD) activity within a 132 kV prefabricated cable joint containing a known defect. Although each of the three methods has been applied individually under different situations, a comprehensive investigation and comparison of these three methods has not yet been made. Results obtained were compared to measurements made using the conventional electrical detection method. The quantification of the capacitive coupler measured signal in mV with a discharge apparent quantity in pC has been investigated and an on-line quantification method proposed. The capacitive coupler has good detection sensitivity and PD location can be realised by studying the time of Right between signals from two sensors. The difference in pulse shape, spectrum and time of flight between an internal discharge and external interference has been investigated. The AE approach has the advantage of being free from electrical interference. However, investigation indicated that AE signals were significantly attenuated within the cable joint. RFCTs were used to detect the discharge current flowing through the cable sheath. Where the detection sensitivity was low, a wavelet de-noising method was applied to process the RFCT signals and proved to tie effective in increasing the measurement signal to noise ratio.     

基于分布式传感器的GIS局部放电在线监测实时数据传输方式的研究

针对检测GIS(Gas Insulated Switchgear,简称GIS)局部放电的分布式传感器采集局部放电信号的数据量大,通过RS-422串口进行数据传输时间长的不足。基于GIS局部放电分布式传感器在线监测系统,采用一种最大值数据压缩算法,将高速A/D采集到的大量实时数据,有效地传输到后台监测系统,解决了分布式在线监测系统中大量数据传输的瓶颈。通过实验验证,该数据传输方式速度快,性能安全、可靠,实用性强。     

On-line partial discharge calibration and monitoring for power transformers

Partial discharge (PD) is one of the major factors causing insulation damage of power transformers. This paper describes the development of on-line partial discharge monitoring system for transformers. The developed set can monitor up to four power transformers continuously. It uses various methods to reject interference and enhances monitoring sensitivity of PD effectively. The optical cable is applied to communicate between measurement system near transformers and the upper computer in the main control building. On-line calibration of partial discharge quantity is requisite for on-line detection or monitoring. This paper describes an on-line calibration method using pulse injection through tap of high voltage transformer bushings. It also discusses the influence of limit inductance and bushing capacitance, from tap of bushing to ground, in on-line calibration circuits. Influences of multi-grounding of the transformer tank for monitoring and calibration are also discussed. Simulation in laboratory and site test shows that the method is practically valid for on-line PD calibration of power transformers within permissible engineering error range under certain defined conditions. This system has been in operation steadily in 500 kV substations for more than 2 years.     

Partial discharge on-line monitoring for HV cable systems using electro-optic modulators

A technique for the remote inspection and monitoring of partial discharge (PD) activity using an optical network is described. The network uses a LiNbO/sub 3/, modulator to modulate the intensity of the transmitted laser light approximately proportional to the voltage applied across the modulator. The laser light is transmitted along an optical fibre and measured remotely by a high-speed optical receiver. A capacitive coupler has been used to detect partial discharge activity and act as the modulator's input voltage source. The electro-optic modulator is passive and does not require a power supply at the site of the PD detection sensor. The system has the additional advantages of being immune to electromagnetic interference, having very little signal transmission attenuation, with good sensitivity, compact size, as well as being convenient to use and safe. Both simulation experiments and practical PD tests on two cable systems have indicated that the optical system provides a feasible remote PD monitoring technique for high voltage cable systems.