Detection of x-ray radiation of partial discharges in polymeric cable insulation

The experimental results related to the detection of X-ray radiation in partial discharges in polymeric cable insulation are presented (X-ray electric gas barrier discharges (EGBD) technique).     

Effect of water on aging of XLPE cable insulation

Cables as elements of power distribution system have great influence on its reliable service and overall planning requirements. During last years, crosslinked polyethylene (XLPE) cables have been more and more used in power systems. This paper presents the results of an investigation of changing of (XLPE) cables insulation breakdown stress (AC BDS) due to water absorption. The paper deals with AC BDS of the following kinds of XLPE cable insulations: steam and dry cured with water tree retardant crosslinked polyethylene (TR-XLPE) and non-tree retardant crosslinked polyethylene (XLPE). During tests, the tap water was injected into, (1) conductor with cable ends closed; (2) into cable conductor with ends opened; and (3) into metallic screen with cable ends opened. The presence of water in XLPE cables was subjected to electrical stress and heating. AC BDS tests were performed as a function of aging time and water content in the cable insulation at different aging temperatures. Also, in this investigation, tests with the changing of AC BDS in the radial direction of unaged and aged XLPE cable insulations were carried out.     

电缆绝缘层老化对接头界面压力的影响研究

为研究老化电缆绝缘层弹性模量变化对界面压力的影响,本文实测三根不同运行年限电缆绝缘的击穿场强与介质损耗角正切表征其电性能,以及在不同温度下的弹性模量表征力学性能。基于超弹性材料本构理论,计算电缆接头与本体装配后的界面压力,并建立电缆接头的二维轴向仿真模型,计算轴向上的界面压力。仿真与理论计算结果的对比表明,运用二维轴向仿真模型计算电缆接头与本体之间的界面压力的误差不超过3.2%,仿真模型计算的准确度可为研究接头轴向上的界面压力分布提供可靠的数据,虽然不同运行年限电缆绝缘层电性能不同,且弹性模量最大差异为29%,但界面压力仅变化0.275%。因此,全新接头与已运行一定年限的电缆装配后,仍能保证足够的界面压力。     

Application of oxidation induction time and compensation effect tothe diagnosis of HV polymeric cable insulation

Oxidative stability tests were performed on field and laboratory-aged crosslinked polyethylene (XLPE), ethylene-propylene rubber (EPR) and polypropylene (PP) insulations using differential scanning calorimetry. Flat films and miniature cables aged in the laboratory were subjected to a wide range of aging conditions that included thermal, electrical and a combination of thermal-electrical aging, in dry and wet environments. The results were analyzed using the Eyring rate theory. It is shown that for a given material the oxidative stability data can be described by a single linear relationship between the activation entropy ΔS and the activation enthalpy ΔH of the oxidative process, and thus are governed by the so called compensation effect. It is argued that the position of a data point representing a certain operating condition of an insulation on the ΔS vs. ΔH compensation plot is a measure of the degree of degradation and can be used as a diagnostic indicator of the operating conditions of the insulation     

电热联合老化对XLPE电缆绝缘特性的影响

为了探究达到设计寿命的高压交联电缆继续运行的可靠性,文中对一回实际运行32 a的110 kV高压交联聚乙烯(XLPE)电缆采用预鉴定试验方法,进行为期180 d的电热循环加速老化试验。通过综合分析比较试验过程中电缆绝缘内、中和外层的电场强度和温度场变化的差异,并将各绝缘层试验条件转化为导体芯表面得到相应的等效试验条件,发现电缆绝缘中层和外层的等效试验条件接近电缆的实际运行情况。通过相关理化实验分析比较试验前后电缆绝缘各层的微观和聚集态状况。结果发现:绝缘内层在严苛的试验条件下热氧化降解占主导;绝缘中层虽然发生一定的氧化降解,但晶体结构仍有所改善;绝缘外层的结晶形态在温度效应的热刺激下趋于完善。因此,可以评估该退役电缆的其余部分在实际运行条件下仍具有长期服役的潜能。     

Field and laboratory aging of polymeric cable terminations. II.Laboratory aging

For pt.I see ibid., vol.13, no.2, p.316-22 (1998). This paper presents the results of laboratory aging tests on polymeric cable terminations. The goals of the laboratory aging were two-fold: (1) develop an accelerated aging test that can simulate the changes produced in the field, and (2) provide an assessment on the magnitude of aging induced changes on the electrical performance of terminations. Monitoring leakage current and material changes during laboratory tests were useful for assessing the variations possible in aging due to experimental parameters used. It has been shown that a laboratory aging test that is based on evaluating the termination's leakage current suppression capability and the ability to withstand a moderate level of discharge activity is suitable not only for assessing the long term performance, but also for ranking the electrical performance in accordance with field exposure     

Statistical models for failure modes of polymeric materials for HVoutdoor insulation

In this paper, a methodology to build the required models for the performance comparison of materials that usually pass the standard inclined plane tracking and erosion tests, is presented. Samples made of silicone rubber and cycloaliphatic epoxy resin were evaluated to present the practical aspects of the proposed methodology. Factorial experiments, using the modified version of the inclined plane test method, were conducted to obtain the response variable. Generalized linear models provided the base for the proposed statistical models since the selected response variable was not normally distributed     

Thermoluminescence in XLPE cable insulation

Crosslinked polyethylene (XLPE) has been employed in underground transmission and distribution cables because of its excellent electrical and mechanical properties, such as low permittivity and dielectric loss, high degree of toughness, and good flexibility. An underground power cable operates at temperatures above ambient and the polymeric insulation is usually crosslinked to provide mechanical strength to withstand the high temperatures. Chemical crosslinking is commonly employed; however, chemical crosslinking creates byproducts such as acetophenone, α-methylene styrene, and cumyl alcohol. The general practice is to decrease the concentration of the volatile crosslinking byproducts from the newly manufactured transmission class cables before they are commissioned into service. The concentration of the byproducts is decreased by treating the cables at a high temperature in a vacuum oven. At present, to determine the residual concentration of the byproducts, the treatment has to be stopped, a sample of the polymer has to be cut from the treated cable and the byproducts have to be extracted for several hours from the polymer before they can be analyzed. This paper describes a novel, non-destructive optical method for determining the concentration of the byproducts in XLPE prior to cable installation. The method involves in situ detection and measurement of thermoluminescence emitted by the crosslinking byproducts during the pretreatment of the cable, It is shown that the measurement of the intensity of thermoluminescence provides a direct indication of the concentration of the byproducts and that it is more sensitive than mass spectrometry     

Application of a novel polypropylene to the insulation of an electric power cable

Cross‐linked polyethylene (XLPE) has been widely adopted as insulating material for high‐voltage power cables up to 500 kV. Further improvement of electrical and thermal properties on insulating material is required in order to increase cable operation efficiency. Therefore, the development of novel insulating material possessing high thermal properties will be necessary. Recent progress of catalysis technology contributes to obtain new polymeric materials which may be applied to electrical insulation. The authors investigated the basic properties of newly developed stereoregular syndiotactic polypropylene (s‐PP) which is synthesized with homogeneous metallocene catalyst. Though recycling of cross‐linked polymers such as conventionally used XLPE may be difficult because of their poor heat deformation, the s‐PP which is not cross‐linked must be suitable for recycling. A series of experiments on its physical and electrical properties gave the following results.

• (1) s‐PP has sufficient flexibility compared with isotactic polypropylene (i‐PP ).
• (2) Both AC and lightning impulse breakdown strength of s‐PP in spite of no cross‐linking are superior to those of XLPE in the temperature range from 25 to 90 °C.
• (3) Degradation by copper of s‐PP is less than that of i‐PP.
• (4) s‐PP/VLDPE blend shows sufficient brittleness temperature for use.

These results suggested that s‐PP should serve as insulating material for power cables at higher‐temperature operation. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(1): 18–26, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002//eej.10210     

基于图像特征和深度森林的乙丙橡胶电缆绝缘

为了更准确地对乙丙橡胶电缆绝缘老化状态进行识别,提出了一种基于局部放电图像特征和深度森林的识别方法。文中制备了不同老化状态的乙丙橡胶试样,搭建了局部放电试验平台,通过试验获得了不同老化状态的乙丙橡胶试样局部放电谱图,并从局部放电谱图中提取了19个特征参量,结合深度森林网络对不同老化程度的试样进行识别。结果表明：通过结合局部放电谱图特征和深度森林网络能够准确的识别电缆老化状态,且识别率优于其他传统分类算法。将局部放电图像特征与深度森林结合应用于电缆的绝缘老化诊断具有较好地工程应用前景。     

Weld lines in power cable insulation

The quality of XLPE insulation of power cables has improved markedly in recent years, and insulation failures caused by contamination have diminished. As a result, focus has shifted on the effects of insulation morphology. There are concerns about the weld lines regarding the anisotropy and frozen-in mechanical stress. The weld line that is formed has different properties than the matrix and the region is considered to be a mechanically weak point. In a recent study, seams were observed in the XLPE insulation of power cable. Their type and intensity vary because of the melt temperature and homogeneity in the extrusion. The mass distribution also has a certain influence. Typically, the seams are quite harmless for the dielectric properties of the insulation. Occasionally, severe weld lines may be considered as possible weak regions in the insulation construction. By performing electrical needle tests on four cable samples, it was found that the weld line containing sector of the cable is measurably weaker than the insulation in general. The rotating mass distributor, or more specifically, the conical extrusion was able to modify, level out and reduce seam effect. While there is no guarantee that the extrusion will have high insulation quality, it is possible to reduce the seams. The traditional extrusion process, however, should be considered as a less robust solution than the rotating mass distributor with respect to the seams.     

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...     

Applications of polymeric outdoor insulation in Japan

Intensive research and development concerning the application of polymeric outdoor insulations in Japan started about 10 years ago. Research on applying polymeric insulating materials to power systems covers various fields such as insulators and interphase spacers for overhead transmission lines, polymer housing of bushing and surge arresters for substation apparatus, insulators and interphase spacers for distribution lines and insulators for railways. Polymeric insulators and housings for electric power systems are being evaluated to extend their use, focusing on insulation characteristics such as withstand voltage against salt contamination and deterioration through prolonged use. For railways, trial uses of polymeric insulators have been started on commercial lines     

等温松弛法在三元乙丙橡胶绝缘电缆连接器的老化评估中的应用研究

本文采用等温松弛电流法测量了不同老化程度的电缆连接器绝缘的等温松弛电流,建立了基于界面极化理论的等温松弛电流模型,分析了老化引起的缺陷对总体的松弛电流的影响,定义了表征电缆连接器绝缘老化程度的参数——老化因子A,并且计算了不同老化程度的电缆连接器绝缘的老化因子。结果表明随着老化时间的增加,老化因子值也在增加。另外,基于ASTM E698标准测量了活化能,结果表明随着老化时间的增加,活化能减小,这与老化因子之间存在良好的对应关系,表明等温松弛电流法可对电缆连接器的绝缘老化程度进行有效评估。     

Electroluminescence-a technique to detect the initiation ofdegradation in polymeric insulation

The EL technique is at least two orders of magnitude more sensitive than PD detection and can detect the initiation of polymeric ageing. It can also detect the conversion of a water tree to an electrical tree     

交联聚乙烯电缆绝缘老化超低频介损试验及评价规程研究

本文基于通过检测电缆超低频介损值确定电缆老化程度的基本原理,结合某地实测得到的多组数据,通过国际规程IEEE 400.2—2013进行初步判断,分析处于不同状态下的电缆介损值的变化规律及其原因,并得出该规程仅适用于没有局部劣化的电缆.此外,由于我国电缆制造材料、结构和生产工艺与国外产品存在差异,采用国际规程判断电缆老化程度有时会变得不准确.为解决此类问题,本文建立更加全面的判据体系,给出最优判断阈值的确定方法,并对该地区实测得到的数据进行拟合,得到更加准确的分级判断阈值.此方法可为建立符合我国电缆实际情况的评价规程提供参考.     

混联等效电路在油纸绝缘老化诊断的应用

针对常规电路在油纸绝缘老化诊断中的局限性,提出应用混联等效电路来表征油纸绝缘介质极化响应特性,并将其用于油纸绝缘变压器老化诊断的分析中。该电路在扩展德拜模型的基础上加入混联支路来表征复杂的界面反应,由此提出混联电路参数辨识的数学模型,最后结合回复电压测试仪RVM5461测量得到的数据进行混联电路的有效性分析和混联支路数的探讨。研究结果表明,混联电路更能真实反映极化谱特性,其吻合度高于扩展徳拜模型,且当油纸绝缘变压器老化或受潮越严重时,混联支路数有增多的趋势。因此,论文提出的油纸绝缘混联等效电路模型为准确评估油纸绝缘老化状态提供一种可靠有力的分析手段,具有一定的参考价值。     

电发光检测聚合物绝缘起始劣化的方法

电缆聚合物绝缘的劣化 (电树枝 )有两个阶段 :第 1是诱导期或起始期 ;第 2是扩展期。文中论述了劣化初始期聚合物内电场强度增强点会有发光 ( EL )现象 ,它不同于局部放电( PD)引起的发光现象 ,至少比 PD检测灵敏度高两个数量级。文中详细介绍了 EL现象发生的机理 ,以及进行实验和检测 ,最终认为 :EL是一种可在电树枝起始之前检测聚合物劣化的有效方法 ,并成功地用于 50 0 k V XL PE电缆的研究     

Space charge accumulation in power cable XLPE insulation

The accumulation of space charge in the crosslinked polyethylene (XLPE) insulation of a power cable sample under dc stress was investigated. The sample was held at 82°C and atmospheric pressure, and at 82°C and 0.1 Pa, for periods up to several days. Such conditioning removed pre-existing space charge, When an external dc field was applied after conditioning at atmospheric pressure and 82°C, space charge accumulated at a rate considerably faster than that observed before conditioning. However the rate of accumulation following conditioning at 82°C under reduced pressure was much slower than that observed before conditioning. The faster rate could be recovered by reconditioning the sample at atmospheric pressure after conditioning under reduced pressure. Inversion of the equilibrium space charge profile, following reversal of the applied field, was observed. This observation is consistent with a model incorporating a spatially-inhomogeneous polarization in the amorphous volume of the XLPE, and electron injection/extraction at the electrodes. The electron transfer between electrode and XLPE in either direction involves the same narrow window of combined donor and acceptor states in the insulator, centered on the Fermi level. The spatially-inhomogeneous polarization in the XLPE originates in a spatially-inhomogeneous distribution of dipole complexes. It is suggested that the dipoles are formed by a process equivalent to nonpermanent oxidation of the XLPE, requiring water as a catalyst     

Recommendations in HV DC testing of MV cable insulation

Research and field reported data supports the theory that high voltage DC testing can reduce the life of both unaged and aged medium-voltage cross-linked polyethylene (XLPE) cable insulation. This research led an industry movement to eliminate factory DC testing, and reduce the field level and frequency of DC testing. DC factory testing identifies an imperfection in the insulation wall as well as mechanical damage. The test sequence in the factory is to perform the AC voltage withstand and corona tests first, followed by the DC withstand test. The AC withstand and corona test levels today are very demanding and locate the same insulation imperfections. Therefore, it can be inferred that today's level of AC withstand and corona testing positively locates insulation imperfections and the following DC testing is redundant and not required. Statistical analysis of factory testing shows that DC testing after AC withstand and corona tests has no additional benefit. The changes and recommendations made by the Association of Edison Illuminating Companies to DC testing are outlined