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。     

变压器局部放电超高频信号外传播特性的试验研究

介绍了目前内置超高频传感器在电力变压器局部放电监测中的应用情况,分析了利用外部传感器检测局部放电产生的超高频信号的可行性,设计了一套基于超高频法的电力变压器局放测量系统。实验结果表明,超高频电磁波可以透过变压器夹缝衍射出来,为变压器局部放电检测提供了一种新途径。     

利用辐射UHF信号反演局部放电脉冲电流

获取局部放电(PD)特征信息是局部放电特高频(UHF)检测的关键问题之一,研究UHF信号与PD脉冲电流之间的关系有助于绝缘缺陷的诊断.文中从电磁辐射理论出发,计算了变压器油箱外壳等复杂环境影响下的PD脉冲电流辐射场,分析了PD脉冲电流辐射场的横电磁波特性.在此基础上,提出了利用检测UHF信号的时间积分反演PD点脉冲电流的新方法,并讨论了UHF传感器及检测系统频带对PD脉冲电流推测算法的影响.仿真和油中针-板型放电实验结果表明:文中所提出的方法能有效推测PD脉冲电流波形,对变压器PD信号UHF在线监测和智能化诊断有一定的参考价值.     

变压器局部放电超高频信号的外部检测

电力变压器局部放电超高频检测法中一般将传感器安装于箱体内部,这对已投入运行的变压器来说是有潜在危害的。为此,先分析了变压器箱体对局部放电超高频电磁波传播的影响,探讨了接收天线外部检测超高频信号的可行性,再实验研究了局放超高频电磁波的外传播特性。结果表明,超高频电磁波可以透过变压器箱体夹缝衍射出来,外部检测到的超高频信号强度随着变压器箱体缝宽增大而增大;变压器套管附近安装接收天线也能检测到超高频信号。     

Partial discharge monitoring for power transformer using UHF sensors. Part 2: field experience

Because of the large capital value of power transformers and their critical role in the electricity network, there is an increasing need for non-intrusive diagnostic and monitoring tools to assess their internal condition. The UHF technique is being applied increasingly to monitor partial discharges (PD) in power transformers and has been shown to be much more sensitive than acoustic techniques when the signal path passes through solid insulation. Field trials were performed on five power transformers ranging in size from 18 to 1000 MVA and in voltage from 25 to 400 kV. The results of PD tests on power transformers provide sufficient evidence to justify making provision for UHF sensors on new transformers to facilitate their monitoring when required during the service lifetime.     

变压器局部放电超高频检测中的混频技术研究

信号的提取和分析是局部放电超高频检测中的重点和难点，文中提出用混频技术提取局部放电信号超高频分量的新方法。用混频技术进行超高频数字信号处理的仿真实验，结果表明该技术既可保留信号包络的峰值和相位特征，又降低了超高频信号的频率。基于混频技术建立变压器局部放电超高频在线监测系统，并对典型局放模型进行实验，结果表明混频技术的应用可以有效地提取中心频率在400—800MHz之间(最小步长5MHz)、带宽为10、20、40或80MHz的局部放电超高频信号，准确地计算放电相关参数，抗干扰性强且提取的放电信息丰富，可用于变压器局部放电超高频在线监测和智能化诊断。     

特高频局部放电测量技术在变压器在线监测中的应用

通过220 kV变压器在线特高频局部放电和超声局部放电试验,认为将特高频检测技术应用到电力变压器在线局部放电检测,具有较好的有效性、抗干扰能力、安全性及适应性,可以满足变压器缺陷分析的需要。     

Two Types of Compact UHF Antennas for Partial Discharge Measurement

To investigate the partial discharge (PD) online monitoring of transformers by ultra-high-frequency (UHF) approaches,high-qualified UHF antennas are focused on as one key technique. The size of UHF sensor used for PD UHF online monitoring in transformer is excessively large,therefore,it is not convenient for internal installation of transformer. Two types of compact UHF antennas with small sizes,a Hilbert fractal antenna and a small loop antenna are presented. PD experiments of three typically artificial insulation defects are executed and both antennas are used for PD measurement. The spectra of power via frequency of detected PD signals are analyzed and compared. The experimental results show that the Hilbert fractal antenna and small loop antenna are qualified for PD online UHF monitoring.     

电力变压器局部放电检测技术现状与发展趋势

概述电力变压器局部放电检测技术现状,介绍超高频(UHF)法的测试原理、系统构成、标定方法及测量影响因素,指出UHF检测将是电力变压器局部放电检测的发展方向.     

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。     

变压器局放特高频检测中检测频率和带宽的影响

变压器局部放电特高频检测中,检测频率和带宽的选取对于放电信号的提取,进而对放电的标定及局部放电模式识别特征的保留具有决定作用.本文在实验室中建立了局部放电特高频检测系统和变压器典型局放模拟系统,对特高频检测中检测频率和带宽的选取原则进行了实验研究.实验结果表明,检测频率应选择局部放电特高频分量丰富且噪声小的频带,滤波器的带宽应在不引入干扰的前提下尽量选用较宽的带宽.     

变压器局部放电UHF信号传播特性的仿真分析

特高频(UHF)技术通过检测局部放电辐射电磁波信号来实现对设备局部放电的检测,抗干扰能力强,检测灵敏度高,是一种基于空间电磁场耦合的局部放电测试技术,能够实现真正意义上的局部放电在线检测,因此在变压器局部放电检测领域取得了日益广泛的关注及研究。由于变压器内部结构复杂,各种金属结构件都会对辐射电磁波的传播产生影响,因此变压器局部放电UHF检测技术有必要研究变压器内部电磁波的传播规律。为此在对变压器内部结构进行合理简化的基础上完成了变压器典型结构的计算机建模,以高斯电流元模拟局部放电源,合理设置各类仿真参数,利用时域有限差分法(FDTD)对特高频电磁波在变压器内部的传播特性进行了仿真分析。仿真结果给出辐射电磁波信号在铁心绕组之间的传播特点,铁心对电磁波传播造成的衰减和畸变作用,并通过时域及频域波形的对比给出不同脉宽、不同幅值电磁波信号在铁心绕组结构中传播的特点。     

Recognition of discharge sources using UHF PD signatures

This paper investigates utilizing zero span UHF PD detection. The findings suggest that the technique is a practical solution for on-line PD monitoring of transformers in the presence of noise and also permits the use of existing knowledge on PD defect signatures.     

Dielectric windows for UHF partial discharge detection

Increasing the permittivity of the propagation medium inside a hollow tube lowers its cut-off frequency, allowing it to transmit a wider range of signal frequencies. This principle is applied to the design of dielectric windows that can be used to facilitate partial discharge (PD) detection at ultra high frequency (UHF) in a HV metalclad plant such as gas-insulated substation (GIS), power transformers and circuit breakers. External UHF couplers mounted on such windows can be removed or replaced without compromising the integrity of the insulation system. By increasing the signal power level incident on a window-mounted external UHF coupler, higher sensitivity to PD can be achieved. The problem is analyzed using waveguide theory and, using GIS as an example, improvements of ≈6 dB are demonstrated by means of coupler sensitivity measurements and experiments using PD sources     

±800kV换流变压器现场局部放电试验的干扰监测

研究干扰识别和定位技术是解决换流变压器现场局部放电测量难题的关键。针对南方电网开展的国内外首次现场修复±800 k V换流变压器的试验要求,采用特高频(UHF)法对局部放电测量干扰进行了旁路监测,通过分析UHF检波信号的波形特征和相位分布统计特征验证了现场检修试验厂房对换流站电磁辐射的屏蔽效果,通过UHF天线阵列精确定位并妥善处理了厂房内的多种局部放电干扰源,支撑被试的±800 k V换流变压器顺利通过了各项试验,视在放电量满足了出厂试验的限值要求。为今后研究在无厂房条件甚至运行条件下实现换流变压器局部放电水平的精确评价提供了技术基础。     

电力变压器局部放电内嵌式监测系统研究

针对变压器内部局部放电产生的超声波信号特征,设计基于电-声联合检测法的内嵌式监测系统。该系统可以在线同步检测出变压器局部放电产生的2路电流脉冲信号和6路超声波信号。硬件上采用12芯光纤传输,有效抑制现场监测的电磁干扰,提高测量的灵敏度;软件上采用集成模块化设计,有助于提高系统运算的速率和可靠性。通过地下变电站3台主变在线运行,实测数据表明,研制的在线监测系统能够实现变压器局部放电信号的在线实时监测,为变压器的状态检修提供大量可信的数据依据。     

直流电压下油纸绝缘中局部放电的超高频特性

为研究直流电压下油纸绝缘中局部放电的超高频特性,组建了一套直流电压下局部放电试验系统以及由局放超高频检测和超宽带检测组成的测量系统,其中脉冲电流超宽带检测的作用是确保超高频检测获取的信号来自于试品自身的局部放电。试验设计了6种油纸绝缘局放模型以模拟换流变压器的典型缺陷,并引入毫瓦分贝(DBM)频谱分析对超高频信号进行了统一化处理,以比较不同缺陷模型对应的超高频信号。直流下试验结果表明:局部放电电流脉冲具有极快的上升沿,能激励起大于300MHz的超高频电磁波,它可以通过超高频传感器加以耦合接收。各种缺陷模型局部放电的DBM频谱分布各异,超高频段能量幅值最大处也不一样。因此若想以高信噪比实现直流下局部放电超高频信号的在线监测,需要使用中心频率可调的窄带滤波器。这些特性为直流输电系统中使用油纸绝缘的电工设备进行局部放电超高频信号在线监测提供了试验依据。     

Recent trend of the partial discharge measurement technique using the UHF electromagnetic wave detection method

The ultra high frequency (UHF) electromagnetic wave detection method has been widely studied and used in partial discharge (PD) measurement and as a diagnostic technique for insulation performance in gas‐insulated switchgears (GIS) and transformers. The UHF method has advantages such as high sensitivity, wide detection range and reduced external disturbances. On the other hand, there are still some issues to be solved in the UHF methods, such as a clear understanding of the propagation characteristics of electromagnetic waves arising from the structure of the equipment, optimization of antenna design, calibration of charge, etc. This article deals with the present status and future trend of the technology of this promising UHF method of PD measurement, together with recent activities and results from our laboratory. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Ultra-wide-band PD diagnostics of power cable terminations in service

During the past decade the PD probing in the ultra-high frequency (UHF) range has successfully been proven for on-site PD diagnostics of GIS cable terminations in service. Therefore it was decided to apply this non-conventional method also for condition assessment of the insulation integrity of outdoor cable terminations. In order to evaluate the minimum detectable PD level the paper deals with comparative PD studies using the IEC and the UHF method. Moreover, experimental studies on the attenuation of PD pulses traveling through power cables were performed in order to assess the spatial selectivity of the UHF method applied.