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.     

用极低频以局放和损耗因数测量来鉴定中压电缆的新成果

引　言本文介绍采用一个 0 .1周正弦波极低频电源诊断系统进行现场试验的真实结果。这一采用新技术的新型诊断工具为地下电缆系统和电网的用户提供高效的测量步骤以判断老化特性、更换的需要程度以及更精确的投资规划预测。此外 ,远在击穿发生前这个方法提供了适时更换和对初期故障的预测。普遍使用这种诊断工具可以戏剧般地降低拥有者的投资 ,更换、维护和‘停电’的成本 ,同时可以得到较高的系统可靠性和配电的冗余度。以往 ,中压和高压电缆是用直流做试验的。它的好处是现场试验设备重量轻、便携带、使用方便和经济。在引入如聚乙烯、交…     

老化中压电缆复合界面的放电特性研究

针对中压电缆热缩型中间接头界面受潮老化的放电特性做了相关研究,分别在不同的湿度环境下做了两类中间接头样本。通过对干燥电缆接头和受潮电缆接头界面间的放电特性做了对比,将整个放电过程分成了三个阶段,分别对比这三个阶段的不同放电特征。对击穿后的样本进行了解剖,观测到受潮界面和干燥界面绝缘失效后的电痕有差异。分析了造成放电特性和电痕差异的主要原因。得出了由于界面间水的作用,使得界面空腔被填满的同时降低了绝缘强度,虽然消弱了初始阶段的局部放电,但增加了后期的击穿概率。而造成不同的电痕特征的主要原因在于干燥界面间的放电对绝缘的劣化具有累积效应,所以放电主要集中在一条通道上。而潮湿界面在水的作用下,界面击穿发生在不同的位置,碳化痕迹分布较广。     

Partial discharge factory test requirements and in-field partial discharge testing of medium voltage cables

This article presents partial discharge testing of medium voltage cables. Utility engineers are faced with decision on whether to replace some of the older cables in their underground distribution systems. Today, measurement of PD at voltages above 1 Vg on extruded cables more than fifteen years old may not indicate that the cables have developed PD due to in-service aging. Removal of these cables based solely on PD measurements may not be warranted. Failure history of the cable, in conjunction with an analysis of the PD site, should be part of the utility engineer's decision-making process.     

电力电缆耐压和局部放电试验方法的改进

从理论和应用的观点讨论了电压等级35kV及以下的交联聚乙烯电缆耐压和局部放电试验时,杯型终端中使用氟里昂与水两种液体介质来替代单一氟里昂液体介质的新方法。利用时域有限元方法在理论上分析了该方法的可行性,并且试验验证了该方法的正确性。新方法能节约氟里昂,更重要的是能够减少对大气环境的污染。     

高压开关柜局部放电TEV信号传播衰减特性

高灵敏度状态感知是实现设备数字化运维的关键环节,也是实现设备状态分析与全生命周期管理的重要前提。局部放电暂态地电压(transient earth voltage,TEV)检测是实现开关柜绝缘状态感知的主要手段,其检测灵敏度受到放电类型与部位、检测位置的影响,目前缺乏系统研究。文中建立基于实测脉冲电流波形的时域有限差分法的电磁波仿真模型;分析局部放电脉冲电流波形上升沿时间、放电源位置及脉冲电流方向等因素对TEV幅值与衰减程度的影响;在实验室开展开关柜局部放电试验与TEV测量,得到影响TEV检测灵敏度的主要因素。结果表明,脉冲电流上升沿时间与放电源位置是影响开关柜局部放电信号幅值的主要因素。脉冲电流上升沿时间越长,TEV信号幅值越小,当2种脉冲电流波形上升沿时间相差10倍时,TEV幅值相差3.17~3.37倍;母排室局部放电的TEV衰减程度明显大于电缆室,前者衰减程度约为后者的9.5~10.0倍。该结论对检验TEV检测灵敏度具有参考价值。     

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.     

XLPE电缆及接头局部放电的超高频测量与分析

超高频的局部放电测量是目前国外电力设备绝缘检测研究的焦点问题之一。本文建立了一套超高频局部放电的测量系统，设计了XLPE电力电缆及其接头局部放电超高频测量的电容耦合传感器，分析了传感器的等效电路，测量了其频率响应，对电缆以及接头中的实际放电进行了测量分析。     

基于EMD-ICA的高压电缆局部放电信号去噪研究

为了解决高压电缆绝缘监测系统在实际工作环境中采集的局部放电(PD)脉冲信号含有噪声的问题,提出了一种融合ICA的EMD去噪算法。详细介绍了该算法的去噪原理。该算法的优点在于不仅有效地去除了局部放电脉冲信号中的噪声,而且还很好地保留了PD信号的完整性。经过实验室模拟实验和现场在线绝缘监测实验,可以看出该算法取得了很好的去噪效果,证实了该算法的有效性与可靠性。     

A new approach to partial discharge testing of HV cable systems

This paper describes the application of an innovative partial discharge (PD) detection and analysis approach to the diagnosis of HV polymeric cable systems. The results of PD measurements performed off-line on cable systems, rated from 220 to 400 kV just after laying or after some time in operation, are presented. PD generating defect identification and location are discussed, also in relation to forensic observations.     

Medium voltage cable defects revealed by off-line partial discharge testing at power frequency

This paper describes typical cable defects uncovered while testing over 9,000 km of medium voltage XLPE insulated cables. After a brief review of the testing method, the procedure that led to the identification, localization, and characterization of typical defects found in operating cables is described. The paper also discusses the "conversion" of water trees (WT) to electrical trees (ET) which are associated with partial discharge (PD) activity in the context of laboratory research. Based on actual service performance of cables, several cases in which ETs associated with WTs did not lead to cable failure even after several years of service in very harsh operating environments are cited.     

Single-phase voltage regulators and three-phase systems

Voltage regulators are applied on distribution systems to control the voltage delivered to customers within acceptable industry standards. Concerns about the quality of electric power delivered to customers by electric utility companies have raised the level of awareness of high- and low-voltage conditions at customer facilities. Normally occurring voltage drops through lines and transformers vary with the load level on the system. Voltage regulators, when properly applied, can compensate for these voltage drops and keep customer voltage within proper limits. Single-phase voltage regulators can be applied on three-phase systems in a variety of ways, including grounded-wye, open-wye, closed-delta, and open-delta. The capabilities of the regulator systems are affected by the system design. In this article, the authors review the characteristics of the closed-delta and wye applications, and discuss the advantages and disadvantages of each application scheme. The impact of the regulator connection on overcurrent protection is also reviewed     

高压电缆接头局部放电声光联合检测系统设计与实现

针对传统局部放电检测系统成本高、易受电磁干扰、检测距离和准确性有限等缺点,基于超声与紫外两种非电气局部放电检测技术,利用超声传感技术实现近端局部放电信号的高灵敏、动态和精确捕获,利用空气中紫外光比超声信号衰减慢弥补超声的检测距离极限,综合实现复杂电磁干扰环境下远距离、非接触、信息可靠和低成本的高压电缆接头处局部放电状态...     

Development of a method of partial discharge detection inextra-high voltage cross-linked polyethylene insulated cable lines

Deterioration in the insulation performance of extra-high voltage XLPE (cross-linked polyethylene) cables is believed to be attributable to the deterioration caused by partial discharges. After using an XLPE cable to investigate the behavior of partial discharges under various adverse conditions, the authors succeeded in developing a highly sensitive novel method of measuring partial discharge in XLPE cable lines. Partial discharges in a 275 kV XLPE cable live line have been measured using this method. As a result, a detection sensitivity of 1 pC has been achieved     

高压电缆屏蔽层局放信号定位检测试验及其应用

高频局放带电检测是预先发现110 kV及以上高压电缆线路本体或屏蔽层运行缺陷的有效手段之一。针对高压电缆线路屏蔽层局放检测易受外界环境干扰且信号定位缺乏有效经验问题,采用长2 m、截面积为400 mm²的9根110 kV电缆搭建一交叉互联接地形式的电缆线路局放检测试验平台,并用信号发生器模拟局放源;利用该试验平台,分别对设置于电缆屏蔽层接地线不同位置的局放信号进行检测,并根据检测到的信号幅值和波形特征判断屏蔽层局放源位置及其传播路径。试验过程及其结果为1条实际在运的110 kV电缆线路高频局放检测异常信号的分析提供了参考。     

Numerical simulation of partial discharge propagation in cable joints using the finite difference time domain method

In this second of a series of three papers, the authors investigate partial discharge (PD) detection and propagation in cable joints. The complex nature of cable joints leads to errors when PD analysis is carried out using conventional equivalent circuits. The authors use the finite difference time domain method to determine the transient electromagnetic fields caused by simulated PD in model cable joints.     

Technical trends in medium voltage URD cable specifications

It has been more than thirty years since high molecular weight polyethylene (HMWPE) was first introduced as a commercial insulating material for medium voltage (15-35 kV) underground residential distribution (URD) cables. That began a dramatic expansion of utility electrical service that has led to the installation of several million miles of URD cables by over 3,000 utility companies across America. When early cables began failing prematurely, the industry was challenged to diagnose the causes and find corrective solutions that would give utilities the confidence to continue their commitment to underground cable. The past 25 years have been a story of constant technical improvements, increasingly tighter industry specifications and positive advancements in URD cable life performance. This paper discusses the significant technical changes that have taken place during this period and their impact on cable performance. The results of a 1983-1993 ten-year study of the major technical specification changes of the 25 largest Investor-Owned Electric Utility Companies (IOUs) is also presented. The data illustrate how quickly new cable technology is specified by these leading utilities and provide a clear picture of the key technical trends occurring throughout the utility industry during the 1990s     

基于HFCT局放测试技术的高压电缆终端失效检测方法研究

针对高压电缆终端因缺陷造成的运行失效问题,分析局部放电的机理,采用HFCT(高频电流传感器)的局放测试技术并结合交流变频谐振耐压的试验方式,设计了一种通过监测电缆终端在不同试验电压下的局部放电图谱,以确定电缆终端发生失效状态的检测方法。通过现场化的试验验证,有效地发现了高压电缆终端缺陷。应用该检测方法,解决了高压电缆工程竣工验收问题,可以在电缆终端竣工验收中有效地发现微小缺陷,对于提前判断高压电缆终端失效具有明显效果。可避免因终端失效造成的电缆运行故障甚至是终端头爆炸等事故。     

Rebuilding of three-phase load voltage during single-phase auto reclosing in medium voltage distribution lines

Most faults in medium voltage (MV) distribution lines are temporary single line to ground (LG) faults. Single-phase auto reclosing (SPAR) may be used to remove the LG fault producing highly unbalanced and low voltage across the load during the reclosure dead time. The negative sequence voltage produced may cause severe over heating in three-phase induction motors. It is proposed to connect a zigzag winding grounding transformer at the remotest load bus to rebuild the three-phase voltage during the SPAR dead time. The zigzag transformer neutral should remain disconnected from the ground during normal operation.     

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.