A measurements-based discharge location algorithm for plain disc winding power transformers

A measurements-based electrical method for locating partial discharges (PD) in transformers is described in the paper. This location method relies on the series resonance frequencies of the signals produced at the transformer terminals by a discharge on the winding. Based on the equivalent circuit of plain disc type winding which consists of series inductance (L), series capacitance (K) and shunt capacitance to earth (C) of the winding, an analytical location algorithm is derived which gives the relationship between the location of a discharge and its terminal response's series resonance frequencies. LKC parameters of the equivalent circuit can be estimated using the series resonance frequencies of a calibration signal measured at the bushing tap during PD calibration. The PD location algorithm was tested on 11 kV transformer winding using signals produced by a discharge simulator and real discharges, and the results confirm its validity with a location accuracy of better than 10% of the winding length. However, blind area where this location algorithm is not applicable does exist near the neutral of the winding and far away from the measuring terminal. Since this location algorithm uses the series resonance frequencies below 500 kHz, it can be implemented with conventional PD measuring circuitry and instruments to detect and locate discharges in power transformers.     

电力变压器局部放电检测技术的现状和发展

本文概述了电力变压器局部放电检测技术的研究现状,着重论述了近几年发展起来的数学化测量和超高频（UHF）检测,并对电力变压器局部放电检测技术的发展前景作了探讨。     

用超高频局部放电测量法实现电力变压器局部放电的在线监测

高频局部放电测量法(UHF法)与传统的脉冲电流法完全不同，它采集的被测信号为局部放电过程所产生的超高频电磁波：利用UHF法可有效解决电力变压器局部放电在线监测中的抗干扰问题。文中结合变压器结构设计的放油阀式和人孔／手孔盖式超高频信号传感器安装在220kV和110kV电压等级变压器上，成功地捕捉到变压器内部局部放电产生的超高频信号。对变压器局部放电故障诊断的判据等问题进行讨论，为变压器超高频局部放电在线监测方法的应用积累了经验。     

Partial discharge testing on resin insulated voltage transformers

Contents The lifetime of resin insulated voltage transformers (RIVT) can be considerably shortened due to partial discharge activity taking place inside the insulation close to the active parts of the component. In that region the presence of voids, due to manufacturing processes, and the enhanced electric field stress lead to an intense partial discharge activity which determines accelerated degradation processes and eventually the ultimate failure of the device. Partial discharge measurements together with an estimation of the electric field distribution in RIVT seem to be indispensable in order to fully understand transformer performances. In this paper, a study of the electric field distribution inside the RIVT, together with results of partial discharge tests are presented. The influence of the various test arrangements and methods on the experimental results are investigated.

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Teilentladungsmessungen an Epoxidharz-isolierten Spannungswandlern

Übersicht Die Lebensdauer von feststoffisolierten Spannungswandlern kann beträchtlich durch innere Teilentladungen (TE) verkürzt werden. Ursache dieser inneren TE sind Gaseinschlüsse im Feststoffisoliersystem eines Wandlers, die sich auf konstruktive und fertigungsbedingte Mängel zurückführen lassen. Infolge des gewählten Isoliersystems-Feststoff-sind diese Wandlertypen für eine hohe Betriebsfeldstärke entworfen. Letztere bedingt wiederum, daß die TE-Aktivität in Gaseinschlüssen sehr hoch ist, was zu stark beschleunigter Materialalterung des festen Isolierstoffs und damit letztendlich zu frühzeitigem Ausfall des Geräts führt. Daher sind TE-Messungen vonnöten, die kombiniert mit Feldberechnungen für den jeweiligen Wandlertyp, zu einem besseren Verständnis der Alterungsvorgänge in diesen Geräten leiten sollen.Der nachfolgende Beitrag beschäftigt sich mit dem elektrischen Feld in einem feststoffisolierten Spannungswandler und den Resultaten von TE-Messungen an solchen. Ebenso wird der Einfluß von verschiedenen Versuchsanordnungen und-methoden auf die Resultate der Messungen untersucht.

     

Partial discharge detection in cables using VHF capacitive couplers

In order to detect and locate partial discharge (PD) activity within HV cables and in particular cable joints, the feasibility of using a very high frequency WHO capacitive coupler technique has been investigated. In addition, an alternative PD offline test method for cable joints or cable sections within long cable systems has been developed. By energising the joint or a short section of the cable screen only this method has the advantage of reducing the power supply requirement of the test source. The application of capacitive couplers for this PD offline test method has been investigated. In order to use this approach there must be an insulation gap between the coupler and the outer sheath of the test cable. The effect of this gap on measured sensitivity has been investigated experimentally and through the use of a simulation model. Obtained results are in good agreement. Cross-correlation techniques have been implemented to automatically estimate the signal time of flight from different-coupler outputs. Methods of calibrating the coupler applied to the alternative PD offline test method have also been investigated.     

变压器局部放电超高频检测方法的应用

阐述了电力变压器局部放电超高频检测方法的原理,分析了其抗干扰性能的优越性,并在变电站进行了实际应用。对测量数据进行了分析,结果表明,超高频方法可用于在线检测变压器局部放电,抗干扰性能好,测量结果能反映出变压器绝缘的真实状况。     

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.     

基于自适应神经模糊推理系统(ANFIS)的变压器超高频局部放电模式识别

对于变压器油中局部放电超高频测量系统所得到的局部放电的特征量,首先,选择优先权较高的6个特征量作为自适应神经模糊推理系统(ANFIS)的输入量,其次,构建6输入单输出的ANFIS,它采用了Takagi-Sugeno模糊系统的if-then规则,利用梯度下降和最优平方估计相结合的混合学习算法进行训练.最后,对于模型的有效性进行了检验,检验结果表明利用ANFIS系统进行局部放电的模式识别是可行的.     

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.     

电力电缆局部放电的高频与特高频联合检测

为了对已敷设的电力电缆进行局部放电在线检测,并抑制现场测量时的干扰,采用高频(HF)与特高频(UHF)联合检测的方法,建立一套局部放电在线检测系统。该系统主要由HF和UHF传感器、信号调理单元、数据采集系统和上位机软件组成,通过HF信号和UHF信号的相互鉴别来去除脉冲型干扰信号。同时根据干扰信号和局部放电信号在频带及工频相位上的分布特点,提出基于复小波的多周期叠加干扰抑制算法。对缺陷电缆的试验结果表明,该系统能有效检测到局部放电的HF信号和UHF信号,局部放电检测灵敏度小于10 pc;对局部放电采集数据的处理结果表明,所提出的干扰抑制策略可很好地消除测量时的干扰信号。     

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。     

Partial discharge. XXI. Acoustic emission based PD source locationin transformers

Acoustic emission-based partial discharge source location has been applied successfully to power transformers in both factory and field environments, and this method is becoming an established test procedure with a high success rate. With the aid of local utilities and utility laboratories that use acoustic emission apparatus daily, we expect further advances in this technology and an improved basis for determining suitable application conditions     

Transfer function-based partial discharge localization in power transformers: a feasibility study

Statistical studies have shown that failures of bushings, winding insulation, and online tap changers are the main causes for long-duration outages of transformers. This article investigates the development of an instrument for supervising the conditions of transformer units. The use of sectional winding transfer functions (SWTFs) for online PD evaluation in power transformers has several advantages: localization of PD sources, discrimination between PDs inside or outside of the transformer, and evaluation of actual PD amplitudes along the winding. Direct measurement of SWTFs-when different points along the coil are accessible-and use of these SWTFs for PD evaluation and localization has shown excellent results. In order to use this method at transformers on site, an appropriate modeling method is needed for the computation of the SWTFs using only measurements at the transformer terminals. A detailed modeling approach based on discrete RLC circuit elements has been studied and different algorithms used for parameter estimation and optimization. This model is applicable in practical cases for a limited frequency range if genetic algorithms (GAs) are used for parameter optimization. A new method based on traveling wave theory has been investigated using genetic algorithms to search for the optimum parameters of a partial differential equation that describes the transient behavior of the coil. This method has shown potential in solving SWTF calculation problems for different transformers.     

Partial discharges. XII. Partial discharge detection in rotatingelectrical machines

For pt.XI see ibid., vol.8, no.2, p.14 et seq. (1992). Partial discharge (PD) phenomena in the windings of rotating machines are examined. PD measurements on rotating machines, both offline and online, are described. Data acquisition and analysis requirements are briefly considered     

采用混沌振子和新相态判别法的局部放电检测

为了降低信号检测的信噪比,利用新型混沌振子作为检测工具,采用Lyapunov指数法分析动力学特性,通过提升临界混沌阈值精度减少在覆盖初始相位差方面混沌振子的使用数量。针对各主要相态判别方法的局限性,利用系统周期特点提出新相态判别法并设计仿真电路,实现相态的自动识别并记录间歇混沌状态周期。最后对单指数衰减振荡型局部放电信号进行检测。仿真结果表明,新型混沌振子动力学特性丰富,抗噪性能优越,能够实现更低的信噪比检测,新相态判别法不受过渡过程的影响,适用于任何混沌振子且具备电路实现的可行性,配合超高频传感器可以检测超高频毫伏级的变压器局部放电信号。     

Winding deformations detection in power transformers by tank vibrations monitoring

There is an increasing interest in applying monitoring systems and on line diagnosis techniques to power transformers, as these are one of the most expensive and critical components of a power system. Detecting failures in an incipient stage can avoid major transformer damages, allowing important savings in investing, and giving time enough to plan transformer outages. In recent years, a great number of monitoring systems have been reported. Some of them, make use of models as a tool to assess transformer condition. In this paper the use of a vibration model to be applied to transformer monitoring is proposed. In the paper, a review of the basic theory of transformer vibration is performed and the results of an experimental set of tests carried out in order to establish the model basis are reported.     

声发射技术测量变压器局部放电的现状与进展

介绍了近年来声发射（acoustic emission．AE)技术在变压器局部放电测量方面的发展及应用情况．详细说明了用声发射技术检测变压器局部放电的原理．对检测系统结构、定位测量方法及局部放电声发射信号的模式识别进行了概述．探讨了该方法的优缺点和今后的发展方向。     

Partial discharge measurement on three-core belted power cables

It is shown that the partial discharge (PD) characteristics of three-core belted-type cables determined using single-phase testing techniques may differ greatly from the actual discharge performance of the cable when subjected to three-phase voltage conditions in service. To achieve meaningful results concerning the voltage ratio and the life expectancy of the cable, careful considerations must be given to the way of energizing the cable and PD response characteristics of single-phase test configurations. An example of erroneous single-phase testing techniques is a circuit which gave an error of up to 88% lower discharge level as compared with three-phase detection. A novel technique was developed in which single-phase voltage was applied to one core, the other two cores were earthed, and the sheath was left floating. The PD detection used a coupling capacitor connected to the energized phase     

基于振荡波局部放电检测的电力电缆绝缘老化状态评价与故障定位

随着我国社会发展进步,电缆线路的铺设速度愈发加快.交联聚乙烯电缆凭借其优良的运行性能,在国内广泛铺设,但囿于复杂的运行环境,电缆常因此受到不同程度的绝缘老化.目前,在高压交联电缆线路现场试验和状态检测中,阻尼振荡波电压下的局部放电实验还未有重大突破,缺乏相关的实验数据.文中介绍了振荡波局部放电实验的原理及其实验装置,并...