The ac superposition method,a new hot‐line diagnostic method for 6‐kV XLPE power cables

Water trees are the most hazardous factor affecting the life of XLPE distribution cables and the major cause of insulation failure. It is well known that insulation failure causes stoppages in electrical service and requires extensive repair work. Up to now, deterioration of cable insulation has been diagnosed mainly by the dc leakage current method. However, application of this method for diagnostic measurements requires interruption of electrical service. Several types of hot‐line diagnostic methods (including the dc component current and dc superposition methods) were developed to detect water tree deterioration. However, these methods have some shortcomings, such as being subject to effects of stray currents and the accuracy of measurements not being sufficiently high. Therefore, we have attempted to develop a new hot‐line diagnostic method. We investigated whether the signals produced by superposition of voltages of various frequencies to the cover layer of energized cables were correlated with deterioration by the water treeing. As a result, we found that a deterioration signal of 1 Hz was observed when we superposed an ac voltage (commercial frequency × 2 +1 Hz) on the cover layer of cable where the water tree had occurred in the insulation. © 1999 Scripta Technica, Electr Eng Jpn, 130(2): 49–58, 2000     

XLPE老化过程中交流绝缘参数特性

介绍了实验室中,XLPE电缆绝缘水针法加速工频老化实验及所测绝缘交流特征参数(介损、电容和电导等)。研究结果表明XLPE老化过程中的交流绝缘特征参数与其老化程度相关,不同老化阶段的特性不同.根据特征参数的变化规律可有效判断XLPE电缆绝缘老化状况。     

XLPE电缆工频耐压试验探讨

试验研究了工频耐压诊断机械损伤类绝缘缺陷效果,评估损伤程度和受潮时间的影响。试验结果表明绝缘未受潮时,工频耐压试验不能检测出机械类甚至是很深的机械类绝缘缺陷。     

Application of the AC Superposition Method to Degradation Diagnosis of 22/33‐kV Class XLPE Cables

Water trees in the insulator of XLPE cable may considerably reduce the dielectric breakdown voltage, thus being an important lifetime‐governing factor. The ac superposition method we have investigated is a new technique for hot‐line diagnosis of 6.6‐kV XLPE cables, and the diagnostic apparatus using this technique is now widely used in the distribution line field. In order to study the application of the ac superposition method to degradation diagnosis of 22/33‐kV class XLPE cables, we measured deterioration signals of the cables with water trees by a modification of the above diagnostic apparatus. The deterioration signals, hereafter called “ac superposition current”, were generated by an amplitude modulation effect due to the nonlinear resistance of water trees. Moreover, we evaluated the relationship between the ac superposition current and the ac breakdown voltage. It is difficult to judge whether a correlation between then is present or not because of the uneven distribution of the measured data. However, the ac superposition current tends to increase linearly with a decrease in the residual thickness of the insulator. For example, the ac superposition current was about 40 nA when the residual thickness decreased to 3 mm. Thus, we consider that the ac superposition method is effective for degradation diagnosis of 22/33‐kV class XLPE cables.     

500kV XLPE电缆绝缘中树枝化现象的述评

介绍日本开发 5 0 0 k V XL PE电力电缆时研究树枝化现象的形成 ,评述 XL PE电缆形成电树和水树与场强的相关性、树枝引发场强和长期寿命特性的研究结果 ,说明由此确定 5 0 0 k V XL PE电力电缆的绝缘设计。     

Pulse response measurement for locating water tree degradation in XLPE cables

Water treeing is a degradation mode of power cable with polymeric insulation. A water tree is composed of small droplets filled with water. As the conductivity in a water tree is very high, it leads to dielectric breakdown when it grows. Because the inside of the water tree is filled with trap sites, it is polarized with a certain distribution of relaxation time when a DC poling voltage is applied. Although its depolarization process after removing the poling voltage depends on the ambient temperature, applying a “depolarizing voltage” with the opposite polarity can accelerate the process. If a short pulse propagating through the cable is employed as a depolarization voltage, we may locate the water tree by looking at the time‐resolved pulse response. This would lead to a diagnosis method with spatial resolution. In order to retain 100‐m spatial resolution, the response should be as sharp as 1 μs. As a preliminary study, a coaxial communication cable was aged to form water trees. A DC poling voltage was applied followed by a pulse voltage with opposite polarity. The rise time of the pulse was several hundreds of microseconds. A sharp pulse current response 50 μs wide was observed, suggesting that rapid depolarization took place. No such response was seen when the cable specimen was not aged. We concluded that the technique is quite feasible. Because the response was found to be as quick as several microseconds, an experiment using a cable 405 m long with 5 m of degraded length in the middle was performed. It was shown that the degraded point was successfully located. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 180(3): 18–24, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21294     

Diagnosis method for live-wire insulation of high-voltage XLPE cables by DC superimposition

Recent preventive maintenance for equipment has grown to include diagnosis of the insulation of cables under hot-line conduction. Much of the equipment constructed during the high-growth period in the 1960s has become obsolete. Recent circumstances make it difficult to obtain a longer service interruption time. Results of a study of the method that measures the live-wire insulation resistance by superimposing dc 50 V to a high-voltage busbar through GPT and forms a bridge with the resistance of a cable insulation are discussed. It is clarified that this live-wire insulation diagnostic method is highly effective at detecting degradation of a cable insulation resistance and is, therefore, suitable for so-called trend monitoring as well.     

XLPE电缆水树的影响因素及防范措施

针对交联聚乙烯电缆的绝缘层在潮湿和电场的同时作用下会产生水树老化的问题,分析水树形成的机理和影响因素,并提出应采取的防范措施,认为开发和使用TR-XLPE绝缘电缆是今后电缆行业的主要发展方向.     

一种加速XLPE电缆水树老化的新型水电极法

基于原有的水电极老化方法,提出了一种能有效加速XLPE电缆绝缘中水树生长的新型水电极法,并针对该方法的老化机制进行了讨论。采用改进后的新型水电极法老化XLPE电缆制作水树样本,测量老化过程中电缆样本的介质损耗正切角(tanδ)的变化。利用光学显微镜、红外光谱(IR)和扫描电镜(SEM)分析电缆样本中水树的微观结构和形貌变化,提出相应的微观老化模型。结果表明:采用改进后的水电极法生成的水树尺寸和微观形貌差异较小,水树长度在300~400μm之间,水树形貌为团状,水树缺陷内部微孔或通道的直径在几微米到几十微米之间。采用新型水电极法老化的电缆试样稳定有效,可生成符合典型结构和特征的水树,为进一步研究电缆绝缘老化机理提供了可靠的保证。     

含水树枝XLPE电缆的超低频谐波响应电流特性实验研究

本文对含水树枝XLPE电缆在0．1Hz超低频正弦高电压和在50Hz工频电压下的非线性漏导电流特性进行了对比实验研究,发现含水树枝电缆样品的漏导电流波形畸变出现的电位与电压对时间的积分有关。分析认为,在电场激励下水分进入连接水树枝微孔的微裂纹是造成电漏导电流含有谐波电流的原因,这种超低频正弦电压激励下的漏导电流检测诃用来XLPE电缆绝缘的水树枝老化状态进行了现场离线检测。     

交联聚乙烯电缆中水树枝诊断的研究现状

交联聚乙烯（XLPE）电缆因其具有优良的导电性、较好的耐热性和机械强度,自问世以来已广泛应用于输电线路和配电网中。然而,当电缆绝缘处于潮湿的环境中时,在电场的作用下会产生水树枝老化。随着水树枝的生长,电缆的绝缘性能下降并可能导致绝缘击穿,从而影响电网的安全运行。总结了交联聚乙烯电缆中水树枝老化的研究现状,概述了水树枝的产生机理及近年来水树枝老化的诊断方法,最后对各种诊断方法进行了简单比较。     

用于XLPE电力电缆局放检测的宽频带电磁耦合法的研究

对用于 XL PE电力电缆局部放电检测的宽频带电磁耦合法进行了研究 ,针对带铁氧体磁芯的罗哥夫斯基线圈型电流耦合器 ,讨论了几个主要参数对其传递函数的幅频特性的影响。模拟实验和电缆局放测量表明 ,应用此电流耦合器来检测 XL PE电缆的局放是可行的     

A study of the actual failure situation of XLPE cable and the order of priority of degradation diagnosis

We analyzed statistical data on failures due to dielectric breakdowns caused by water tree degradation in 6‐kV XLPE cables using the Hazard Analysis. The data used in this report reflect actual conditions of XLPE cables. The data are classified by the conductor size of the cables. Calculated failure rates were different for cables having different conductor sizes. In this report, the failure rates were calculated based on the information regarding conductor size, cable length, and cable age. The results obtained make it possible to quantitatively establish the order of the priority of degradation diagnosis. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(4): 50–58, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10301     

用电磁波速诊断XLPE电缆绝缘

XLPE电缆绝缘诊断的研究对于掌握电缆的绝缘老化状态,保证电力传输系统的安全可靠运行有着十分重要的意义。针对工程实际中大规模应用的诊断方法不多见的现状,提出了一种XLPE电缆状态检测的新方法,即用电磁波在一段XLPE电缆中的传播速度作为诊断这段电缆是否发生老化的依据。在阐明了该方法的原理和理论依据后介绍了所搭建的实验平...     

交联聚乙烯电缆水树枝修复技术研究

针对交联聚乙烯电缆水树枝老化的问题,介绍电缆水树枝形成和发展的过程,分析电缆水树枝修复技术的原理、修复液注入工艺和研究现状,提出该技术应用中需要解决的关键问题.     

Study on field demonstration of high‐sensitivity SF6 leakage detection method for gas insulated switchgear

SF6 gas is widely used in power equipment such as gas insulated switchgear or gas circuit breaker. However, its global warming potential is 23,500 times higher than that of CO₂. In consideration of environmental protection, detection of SF6 gas leakage with high sensitivity is necessary. The authors proposed an algorithm to accurately estimate the average gas temperature from the tank surface temperature for establishing a high‐sensitive SF6 slow leak detection technology. Since the gas temperature depends on the temperature of the conductor, the algorithm was characterized by estimating the gas temperature from the tank surface temperature and the load current. The relationship among the tank surface temperature, the gas temperature, and the current was preliminarily investigated by the use of the thermal fluid analysis and stored in the database. By use of this method, the fluctuation of the converted pressure in the basic examination test was suppressed to 20% as compared with that without considering the current. In addition, database was also created from the machine learning of field test result in substitution. In the field test, it was confirmed that the detection time of 0.5%/year slow leak could be detected in about 8 months by considering the load current.     

检测XLPE电缆绝缘水树老化状态的超低频方波-工频叠加法研究

本文提出了能有效检测ＸＬＰＥ电缆绝缘水树老化状态的超低频方波－工频电压叠加法新技术,对含水树ＸＬＰＥ电缆分别放加单极性方波和正负对称方波电压叠加工频电压所产生的响应电流特性进行了实验研究,找出了最佳叠加工频电压值,最后对产生超低频方波－工频电压叠加电汉响应的机理及其检测的影响因素进行了探讨。     

在线注入有机硅修复液对交联聚乙烯电缆中水树生长的影响

提出了水树老化电缆的在线修复方法,讨论了在交变电场下修复液对水树的抑制作用及其绝缘修复机理。采用高频高压水针电极法对新样本、预修复样本和在线修复样本进行加速水树老化。老化一个月后,使用显微镜观察样本中水树形态并测量其水树长度。通过差示扫描量热法分析样本绝缘层的劣化程度,同时利用扫描电镜和能谱分析仪对比水树区域的微观形貌及化学结构变化。研究表明,在线注入有机硅修复液能有效地抑制水树的生长。在电场的作用下,修复液分子和水分子同时向强电场区域(如微孔、水树区域等)进行扩散并发生反应,消耗水分并且生成凝胶颗粒填充微孔,一定程度上缓解了绝缘的劣化。     

在绝缘诊断试验技术的发展中了解水树机理

近来 ,有几种测量介电常数和介质损失的诊断方法已被发展为用来对水树枝劣化 XL PE电缆进行非破坏性试验。当所施加的试验电压超过一定值时 ,发现临界劣化不仅仅与介电性能成比例。本文采用一种力学模型来描述水树枝现象的这种非线性。绝缘中的水树枝被认为是由被微裂纹区隔离的一系列充水微孔构成 ,在相对较低的含水量和较低试验电压下 ,有的裂纹区即可能产生自愈合作用并且恢复绝缘状态。当试验电压上升时 ,Maxwell电机械应力将导致水分侵入裂纹区 ,并导致拉长的水滴间出现电接触。对电场和损耗的有限元法数值计算结果表明 ,这种影响将使导电通道端部的电场增强 ,同时导致含水树枝绝缘的介质损耗增加。