Effects of crosslinking byproducts on space charge formation in crosslinked polyethylene

Space charge is formed in cables insulated with crosslinked polyethylene. It has not been clear whether the crosslinking byproducts or the crosslinked polymer morphology is responsible for the space charge formation. In order to clarify this point additive-free noncrosslinked low-density polyethylene, additive-free crosslinked polyethylene, and degassed crosslinked polyethylene were soaked in the crosslinking byproducts and the space charge distribution was measured after DC voltage application. Samples tested are divided into two categories. The first category is a soaked single-layered sheet and the second category is a two-layered specimen consisting of a soaked sheet and a nonsoaked sheet. As a result, the following conclusions were obtained. (1) Cumyl alcohol is responsible for homocharge layers in front of the electrodes in both low-density and crosslinked polyethylene sheets. (2) Acetophenone is responsible for heterocharge formation in crosslinked polyethylene, presumably as a synergistic effect with water. (3) alpha -methylstyrene has no effect on space charge formation in low-density polyethylene, while it assists charge trapping in crosslinked polyethylene. (4) Charge trapping occurs easier in degassed crosslinked polyethylene than in low-density polyethylene, probably because of carbonyl groups induced by crosslinking     

Effect of testing parameters on the outcome of the acceleratedcable life test

The effects of various testing parameters on the accelerated life test results of 15 kV underground residential distribution cables prepared from thermoplastic and crosslinked polyethylene insulation are considered. Testing parameters included dry versus water in the strand, voltage stresses 4X(34.6 kV) and 3X(26.0 kV), and hot spot temperatures of 90 and 75°C. The effect of shelf aging on the life of crosslinked polyethylene insulation is reported. Microscopic examinations were made for a number of the tested samples, and tree observations are discussed. The data presented provide insight to a number of the factors which reduce the life of polyethylene cable insulation used in the URD applications     

Chemical group in crosslinking byproducts responsible for charge trapping in polyethylene

It is known that space charge is formed in cables insulated with crosslinked polyethylene. It is probable that the crosslinking byproduct or the crosslinked polymer morphology is responsible for the space charge. In order to examine the former possibility, an additive-free low-density polyethylene sheet was soaked in various liquid chemicals including the crosslinking byproducts and space charge distribution inside the sheet was measured under DC voltage application. As a result, space charge appears in the vicinity of the injecting electrode only in the case that the sheet was soaked in the liquids with at least one hydroxyl group in their structures. Therefore, it is concluded that cumyl alcohol, which is the only byproduct with a hydroxyl group in its structure, is responsible for the formation of space charge in polyethylene on the assumptions that chemical functions of a given molecule act separately from each other and that other contributions such as the crosslinked polymer morphology are negligible.     

Interfacial properties of XLPE/EPDM laminates

Interfacial properties such as space charge accumulation and breakdown characteristics in crosslinked polyethylene (XLPE)/ethylene propylene diene terpolymer (EPDM) laminates were investigated. Homocharge is observed in EPDM containing 1,4-hexadiene while heterocharge is observed in EPDM containing 5-ethylene-2-norbornene. Interfacial charge develops when the EPDM is laminated with XLPE. The polarity of this interfacial charge reverses at less than a few tens of hours heat treatment at 80°C dc breakdown voltage shows a sequential change of an increase, a decrease and a slight increase as a function of heat treatment time, which holds true for both interfacial and volume breakdown voltages. A maximum breakdown voltage is observed at 20 to 24 h heat treatment. After long heat treatment, silicone grease used in the interface shows lower interfacial breakdown voltage than silicone oil for the dc case, which was attributed to the additives in the grease and the molecular weight of silicone molecules in oil and grease. Details of the results are given and their origins discussed     

Polymer insulated cable systems up to 220 kV

The state-of-the-art of polymer insulated cable systems in Switzerland is presented. The construction and the features of high-voltage power cables with crosslinked polyethylene (XLPE) or ethylene-propylene rubber (EPR) insulation, accessories such as joints and terminations, and some special laying techniques are discussed. Results of type tests, long duration tests, and field tests are presented     

硅烷交联聚乙烯电缆料的开发与应用

本文研究了硅烷对聚乙烯的交联技术，开发了硅烷交联聚乙烯电缆料。     

Loss evaluation for underground transmission and distribution cablesystems

The design, manufacture and testing of crosslinked polyethylene (XLPE) cables for voltages of 245 kV and above are described. The operational reliability of a cable connection is decisively codetermined by the reliability of the cable accessories. The state-of-the-art and development trends regarding cable-sealing ends and cable joints are discussed in detail. Knowledge of the lifetime curve of XLPE (essential for designing reasonable qualification tests) is discussed, and test results which show that service stresses of 12-13 kV/mm can be realized are described. The design of accessories, especially joints and terminations for enclosed switchgears is addressed, and service experience is reported     

The Development and Commercialization of Ignition Suppressant, Moisture Barrier Instrument, Control and Power Cables

Plastic coated metal shielding tapes are becoming more and more prevalent in the wire and cable industry. When these tapes are bonded to a chlorinated polyethylene jacket, a moisture/chemical barrier sheath is created that can be utilized in cables for above, ground applications such as in cable trays, in conduit or for aerial use on messengers. These designs can also be used for direct burial and inside buildings. The physical properties of the shielding tapes, combined properties of the tape and jacket, and the properties of various cable designs are all discussed. Additionally, case histories are reviewed which describe the use of these cables in various industrial environments. Specifically, the development of such coated tapes and chlorinated polyethylene jackets provides wire and cable users with additional sheath designs which can be used to reduce expensive maintenance and extend cable service life.     

Space charge distributions in EPDM compounds

The formation of space charge in EPDM (ethylene-propylene-diene terpolymer) filled with ATH (alumina trihydrate) or clay has been investigated by measuring charge distributions. It is found that the type and amount of space charge developed in crosslinked EPDM or its compounds is governed by the type of diene in EPDM and the composition of the semicon electrodes. The amount of charge in the EPDM compounds containing 1,4-hexadiene decreases with an increase of ATH content and increases with an increase of clay content. The heat treatment of EPDM compounds in a vacuum oven increases the amount of space charge in them. These features were explained by the effects of low molecular weight molecules present at the surface of fillers. It is found that the homocharge increases as the clay content increases, while EVA decreases the homocharge in the EPDM compounds. Possible reasons for these results are discussed     

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.     

The influence of the water on water absorption and density of XLPEcable insulation

This paper presents the results of a continuing investigation into effect of water on water absorption and density of crosslinked polyethylene (XLPE). The experimental set up was made for the following XLPE cable insulations: steam and dry cured with water tree retardant crosslinked polyethylene (TR-XLPE) and without water tree retardant crosslinked polyethylene (natural XLPE). During tests, the tap water was injected (1) into the cable conductor with cable ends closed, (2) into the cable conductor with cable ends opened, and (3) into the metallic screen with cable ends opened. The XLPE cable insulation together with the water present in the cable was subjected to electrical stress and heating. The results were analyzed theoretically and experimentally. The aim of this paper is to present the results of the influence of the water on water absorption and density of various kinds of XLPE cable insulation in different service conditions     

Evaluation of service aged 35 kV TR-XLPE URD cables

This paper provides information on the aging of URD power cable insulated with a tree-retardant crosslinked polyethylene (TR-XLPE) compound, installed in a typical utility environment, Numerous evaluations were performed on samples of power cables aged up to 7 years in-service. AC and impulse voltage breakdown data are compared with data for similar 35 kV ethylene propylene rubber (EPR) and crosslinked polyethylene (XLPE) insulated cables removed from the same utility system. The data show that, to date, the rate of degradation of TR-XLPE cables is less than that of the EPR and XLPE insulated cables. Extrapolation of the data, assuming the same rate, indicates TR-XLPE cable will have the longest life     

输电线路悬索式跨越架抗冲击性能影响规律研究

目前悬索式跨越架的设计未考虑动态冲击效应。为了探究悬索式跨越架在不同工程参数下抗导线冲击的影响规律,文中以悬索式跨越架承载索常用的超高分子量聚乙烯绳为例,建立了绳索受冲击的仿真模型。文中研究不同工程参数对跨越架在事故工况下(断线和跑线)的抗冲击性能影响规律,得到基于桁架单元的动力学仿真与试验的最小误差为0.67%。仿真结果表明:因牵引板的作用,断线对跨越架产生的冲击载荷大约为跑线的2～3倍;跨越架冲击载荷随落线高度而增加,但具有一定随机性,其弧垂变化水平在4～4.5 m;中间承载索和绝缘网安全系数较小;1 250 mm~2导线比630 mm~2导线的线密度、配套使用的牵引板大,故1 250 mm~2导线对跨越架的冲击较大。     

Ethylene-vinyl acetate (EVA) copolymers: a general review

Ethylene-vinyl acetate (EVA) copolymers are used extensively in the wire and cable industry for making heat shrinkable insulation, semi-conductive insulation jackets, and flame retardant insulation. A general review of EVA copolymers is given. The following items are reviewed: EVA copolymer development, methods of manufacture, fundamental structural attributes, typical properties, processing and applications     

基于面阵CCD的聚乙烯薄膜缺陷检测方法研究*

电线电缆是现代经济及国家建设正常运转的基础保障,也是与人们日常生产生活息息相关的产品。电缆料,即绝缘及护套用塑料,是电线电缆产品的重要组成部分,其质量及性能直接影响电气设备的安全性及可靠性。的聚烯烃薄膜是典型的电缆绝缘材料,具有相对密度小、耐腐蚀性强、耐水性好等特性。然而,薄膜加工过程中会在表面产生的微小凸起,形成缺陷,这是引起电缆局部放电的主要因素。因此,及时准确地检测及控制表面凸起,对电力安全至关重要。以聚乙烯半导电屏蔽膜为研究对象,采用面阵CCD图像传感器摄取微小凸起的原始图像,运用形态学图像处理方法获取微小凸起的特征信息,基于八邻域连通检测原理设计算法实现缺陷的提取与标记,最终依据三角形原理计算获得微小凸起的高度和体积。实验结果表明,该检测方案是完全有效的。     

Electrical properties of silane crosslinked polyethylene incomparison with DCP crosslinked polyethylene

The electrical properties such as water tree length, electrical conduction, ac breakdown strength and space charge of silane crosslinked polyethylene (SXLPE) were investigated, with a purpose to compare this material with ordinary dicumyl peroxide (DCP) crosslinked polyethylene (XLPE). Experimental results show that SXLPE has a smaller water tree length, much lower conduction current density, a little bit higher ac breakdown strength than XLPE, and on SXLPE only a very small homocharge is seen. The better behaviour of SXLPE under electric stress is attributed to the absence of residual curing byproducts present in XLPE and the change of chemical structure by grafting and curing reactions     

南京城网10kV XLPE绝缘电力电缆现状试验研究

针对南京城网中的10 kV交联聚乙烯(XLPE)绝缘电力电缆线路,进行了综合试验研究。取自三条在役线路作为样品进行全面试验,在这基础上结合各项试验结果及理论分析,对线路评价及风险管理等问题进行讨论,并提出若干建议。     

A Comparison of Medium-Voltage Cable Insulations

This paper presents a review of solid dielectric insulations suitable for use in medium-voltage power-cable applications. Comparative electrical and physical characteristics are presented on high molecular weight polyethylene, butyl, and oil-based insulations with special emphasis on ethylene propylene rubber and cross-linked polyethylene.     

输电导线覆冰与绝缘子串覆冰的关系分析

绝缘子串发生覆冰桥接闪络是影响架空输电线路安全运行的主要因素之一。根据不带电绝缘子串及同期导线覆冰的观测数据,分析了玻璃、陶瓷及复合绝缘子串的覆冰质量与导线覆冰质量的关系,研究了绝缘子串发生桥接与导线标准冰厚的关系。