Stress induced electrochemical degradation of the inner semiconlayer of XLPE-insulated cables and model samples

A degradation phenomenon of the inner semicon layer of extruded cable insulation occasionally has been observed in different service aged as well as in laboratory aged polymer insulated cables. To investigate this effect, accelerated aging tests on XLPE-insulated cable cores as well as on a new type of model sample (aluminum wires, semicon and XLPE insulation layer) were performed. It is shown that under the influence of an electrolyte and mechanical strain, channel-like structures develop in the semicon of both test objects, and that vented trees are initiated when these structures reach the interface to the insulation. Thus, this type of degradation also is of particular importance for the long time aging behavior and testing procedures of polymer insulated cables. It is demonstrated that the newly developed model sample test arrangement is a valuable tool for the study of aging of insulation systems     

Field monitoring of parameters and testing of EP and TR-XLPEdistribution cables

Five commercial ethylene-propylene rubber (EP) and one tree-retardant cross-linked polyethylene (TR-XLPE) 15 kV cables are being aged in the laboratory, and in field service on a utility distribution system. The cables were obtained from six different manufacturers. This study subjects commercially available, widely used EP cables, and one TR-XLPE cable to similar conditions at three different sites. Two test sites are located at Orange and Rockland Utilities' (O&RU) distribution system. The first is in normal 15 kV service; the second is a normal 35 kV service site, with the cable aging under accelerated voltage conditions. Line voltage, voltage surges, load current, earth, duct and cable temperatures on the systems are being field monitored. Cable Technology Laboratories (CTL) has provided an accelerated aging set-up for the third site. This paper describes the methodology, characterization testing and some preliminary results from this project     

煤矿井下梭车用金属屏蔽橡套软电缆的研制

煤矿井下梭车用电缆的工作环境比较恶劣,在实际应用中寿命较短,通常会影响采煤和掘进作业的正常进行。梭车电缆的断芯故障在许多煤矿是比较棘手的问题,严重地影响了＂房柱式＂采煤方式的推广。新型金属屏蔽橡套软电缆通过改变传统电缆缆芯结构,着重提高电缆导体的抗张能力,采用特种合成纤维束作为加强芯,结合添加纤维束对导体绞合结构进行优化设计,较好地解决了由于断芯造成梭车电缆使用寿命短的问题。     

一种新型的港口机械用拖曳软电缆研制

港口机械吊装频繁,配套的电缆经常需要做高速移动,承受较大的拉力和弯曲,而传统的软电缆通常使用半年左右即发生各种破损故障,影响使用.根据港口机械用拖曳软电缆的使用条件及其相关的国内外资料,对其主要技术要求、产品结构设计和材料选择进行了分析,研制了一种新型的港口机械用拖曳软电缆,经国家电线电缆质量监督检验中心检验,产品符合...     

Retrofitting-new high voltage XLPE cables substitutingpaper-insulated power cables in steel pipes

Many utilities still have paper-insulated pipe type cables in service. In the near future they may have to replace some of these systems due to local increases in electric power demand or aged cable insulation. In many cases the steel pipes are well protected against corrosion and thus suitable for further use. For retrofitting in such installations, XLPE-insulated cables offer several advantages. Felten & Guilleaume Energietechnik AG has developed a new three-core XLPE-insulated 64/110 kV cable with reduced insulation thickness (10 mm), that can be pulled into a pipe. In co-operation with VEW ENERGIE AG, the cable performance is being investigated in a field test, that started in October 1996. This long-term loading cycle test will last for three years. The test voltage, applied between conductor and earth, amounts to 127 kV. The temperature is measured with the help of an optical-fiber measurement system. This device is computer controlled and works as a remote monitoring system     

Performance of reduced wall EPR insulated medium voltage powercables. I. Electrical characteristics

Paper-insulated lead covered power cables (PILC) have had a long and successful heritage. After almost 100 years, this design of cable is still in operation and continues to be manufactured. However, electric utilities are now looking for a reliable replacement for PILC cables. This is due to two primary reasons: (1) the difficulty in installing and maintaining this type of cable; and (2) increasing pressure to replace these cables due to environmental concerns. To date, diameter limitations of conventional extruded dielectric cables has impeded their replacement in existing PILC conduits. This paper describes a study for the evaluation for reliably reducing the insulation thickness to achieve a lower diameter cable to effectively replace PILC cable in existing conduits. Part I of the investigation reviews the theory of insulation wall determination and the test program carried out to evaluate electrical performance of reduced wall EPR cables. Additionally, cable design concepts and constructions are discussed     

Service aged 69 and 115 kV XLPE cables

Five 69 kV XLPE cables, 6 to 23 years in service and two old vintage cables from storage plus a 115 kV XLPE cable from service together with a spare cable from the same production, kept in storage, were evaluated. All components of the cables were found to show little signs of deterioration except for AC breakdown. The 69 kV XLPE cable from service has breakdown levels ranging from 10.2 to 18.2 kV/mm, the spare cable 15.0 to 17.7 kV/mm compared to 27.2 kV/mm, the only previously reported value for a new cable. The 115 kV XLPE cable had a breakdown level of 16 kV/mm and the spare 10 kV/mm. The above cables are low-stress cables. Most modern cables operate at higher voltage stresses, taking advantage of cleaner insulations with smoother shields and moisture barriers. Caution is advised in using older, low-stress cables placed in storage     

Extending the service life of 15 kV polyethylene URD cable usingsilicone liquid

The authors describe methods and materials used to extend the useful life of extruded polyethylene insulated cables rated at 15 kV that have developed electrochemical trees in the insulation of sufficient severity to cause service failures. Earlier rehabilitation methods treated extruded dielectric cables with both gases and insulating liquids. This new method fills the cable and impregnates the insulation with a silicone liquid. This liquid, which is reactive, significantly improves the voltage breakdown strength of the cables, which had been reduced by electrochemical trees, and extends the useful service life of the cable. A review of the criteria used to develop the silicone liquid for this application and the methodology used to inject it into the cable are presented. An assessment of the costs for this life extension indicates a significantly lower cost than conventional cable replacement with little disturbance to the service and property of the customer     

高压电缆缓冲层的设计与工艺研究

高压与超高压交联电缆金属护套与电缆缆芯之间的缓冲层是电缆的重要组成部分,对电缆的机械、热性能具有重要的影响。为研究缓冲层对电缆性能的影响,分析了不同的阻水带的热阻特性与工艺特点,对国产两种同型号不同厂家的电缆进行了对比温升试验,最后讨论和分析了现在国内外高压交联电缆缓冲层的结构与工艺特点。研究表明,具有不同结构与材料的缓冲层,对电缆本体的热阻有显著影响,也对电缆载流量有着很大的影响。在此基础上,对国产电缆的缓冲层设计与工艺提出了一些建议。     

Successful testing of 345-kV XLPE cables and premolded joints atIREQ

Extruded polymeric cables and accessories are an alternative to self-contained fluid filled (SCFF) cables for extra-high-voltage (EHV) systems. Crosslinked polyethylene (XLPE) insulated cables have many advantages over the traditional fluid-filled pressurized cable system with the elimination of the hydraulic system and the associated equipment and complications during the installation and operation/maintenance of such systems. Other advantages of the extruded cable system arise from the new accessory technologies and the use of splices and terminations that are prefabricated and pretested in the factory and require less time to install on site. Concerns over the long term reliability of high voltage cable systems, in particular the accessories and the lack of service experience above 300 kV led to the decision of Hydro-Quebec to carry out a prequalification (long-term) test program to assess the reliability of the cable materials and to verify the cable and accessory installation methods to be employed. The cables were installed in duct banks and manholes simulating actual installation conditions used in Hydro-Quebec underground cable network. This paper describes the program and results of the prequalification tests of 345-kV XLPE cables and accessories performed at Hydro-Quebec's Research Institute (IREQ) in partnership with three international cable manufacturers, Alcatel, Fujikura and Pirelli     

Evaluation of Locomotive Cable Insulation Life Under Varying Temperature Loading

A method is described for evaluating the life of cable insulation subjected to the varying temperature and time electrical service conditions of a locomotive. This type of evaluation becomes more important as the current ratings of higher fuel efficiency locomotives are increased, subjecting cable insulation materials to higher operating temperatures. Insulations evaluated by this proposed technique are first tested at several elevated constant temperatures to determine their thermal aging characteristics. Based on the material performance data, the insulation life consumed by the thermal stresses imposed by the locomotive duty cycle is calculated. This method can be readily applied to measure the effects of temperature cycles on cable life, objectively compare the performance of different insulations, and assess the design margin of locomotive cables. It may also be used to establish Association of American Railroads (AAR) specification requirements for thermal aging tests based on the conditions of actual field application. A method for evaluating cable life through testing and duty cycle analysis has been developed and verified by examination of cables in service. A new high performance insulation developed by the General Electric Wire and Cable Business Department is shown to offer reliable service life under the varied and demanding operating conditions of today's higher performance locomotives.     

抗水树交联聚乙烯绝缘电力电缆的研究

分析了国内外交联聚乙烯(XLPE)绝缘电力电缆的使用情况,以及容易产生水树的原因机理。从如何避免水树的产生和发展,以提高电缆运行寿命,提出了抗水树的机理和抗水树XLPE电缆的设计理念,并对其试验流程和试验结果进行了统计分析。     

The control of intermetallics in Pb-Cu-Te cable sheathing alloys

Lead alloys are used extensively as sheathing materials for high voltage power cables, especially in long undersea installations. Excellent extrusion properties, high ductility, a low re-crystallization temperature, good fatigue properties, and creep resistance make these alloys ideal for this application. Other service requirements, such as grounding of the cable, conduction of the short circuit currents, and waterproofing of the plastic insulators, are also met by a lead sheath. However, the lead layer in the cable is often a limiting factor both during cable production and during its service phase. The production of several hundred miles of long, single-piece cables is limited by cracking that takes place in the lead sheath during cable extrusion. Cracking of the lead sheath due to repeated vibration, creep, and re-crystallization becomes a limiting factor during the service life of these cables. Large precipitates that appear in the cable sheath after several hours of extrusion seem to be responsible for the premature cracking. A detailed examination of the alloy composition and cable sheathing operation is required to understand the origin of these precipitates     

Investigation of Water Tree Degradation in Dry‐Cured and Extruded Three‐Layer (E‐E Type) 6.6‐kV Removed XLPE Cables

Dry‐cured and extruded three‐layer (E‐E type) 6.6‐kV cross‐linked polyethylene (XLPE) cables were introduced into electric power systems more than 30 years ago, but they do not experience failures because of water tree degradation. Also, the degradation index of water treeing for these cables has not been established. Therefore, investigating results of residual breakdown voltage and water tree degradation of these cables will help us plan for cable replacement and determine water tree degradation diagnosis scheduling, and will be fundamental data for cable lifetime evaluation. In this study, the authors measured the ac breakdown voltages of dry‐cured and E‐E type 6.6‐kV XLPE cables removed after 18 to 25 years of operation and observed the water trees in their XLPE insulation. As a result, it was observed that breakdown voltages were larger than the maximum operating voltage (6.9 kV) and the ac voltage for the dielectric withstanding test (10.3 kV). Water trees were mainly bow‐tie water trees and their maximum length was approximately 1 mm. Although the number of measured cables was limited, the lifetime of this type of cable was estimated to be approximately 40 years, even experiencing water immersion.     

Application of dielectric response measurement on power cable systems

Water treeing is one of the factors leading to failure of medium voltage XLPE cables in long-term service. Increased moisture content inside oil-paper insulated cable is not desirable. To identify water tree degraded XLPE cables or oil-paper cables with high moisture content, diagnostic tests based on dielectric response (DR) measurement in time and frequency domain are used. Review of individual DR measurement techniques in the time and frequency domains indicates that measurement of one parameter in either domain may not be sufficient to reveal the status of the cable insulation. But a combination of several DR parameters can improve diagnostic results with respect to water trees present in XLPE cables or increased moisture content in oil-paper cables. DR measurement is a very useful tool that reveals average condition of cable systems. However, it is unlikely that DR measurement will detect few, but long water trees. In addition, DR cannot locate the defect or water tree site within the cable system. Combination of DR and partial discharge (PD) measurements can improve diagnostic results with respect to global and local defects. However, it is doubtful whether PD test can identify the presence of water trees inside a cable in a nondestructive manner. Further research is needed for more detailed conclusions regarding the status of a particular insulation and for predicting the remaining life of the insulation system.     

高压XLPE电力电缆绝缘老化状态评价研究进展

高压交联聚乙烯（XLPE）电力电缆的绝缘老化状态关系到供电可靠性,故电缆绝缘老化状态检测及评价方法的研究意义重大。对于高压电缆的绝缘老化状态检测及评价,国内外已有相关研究成果,文中总结了目前常用的高压电缆绝缘状态离线、在线检测及评价方法。离线检测手段准确性高,但不适于对在役电缆进行大面积取样检测;在线监测的环境干扰因素太多,存在的干扰会对监测结果产生影响,有一定检测局限性,且缺乏大量的实验数据支撑;而对于电缆绝缘老化状态评价方法,尚未有广泛认可的评价标准和体系。文中在总结概述现有方法的基础上,提出了目前电缆老化绝缘状态综合评价方法存在的难点及未来电缆绝缘老化评价研究可提升的方向。     

Long - Term Behavior of XLPE Insulated Cable Models

A test cycle with electrical, thermal and combined stresses has been performed on models of XLPE insulated: cables in order to characterize this type of cable from the viewpoint of endurance to combined stresses. For this purpose the method of Combined Analysis of experimental data has been used, thus permitting the goal to be reached in less than two years. The experimenrtal methods and theoretical procedures are illustrated in the paper and the results shown by means of the three basic graphs for combined stresses. The material Under test has shown good endurance : values; of electrical and thermal threshold high enough to provide a reference for operating stresses. Some values for the stresses applicable in service are suggested.     

一种新型的电力电缆用半导电屏蔽阻水带

叙述了一种新型的半导电屏蔽阻水带,适用于电力电缆的绝缘屏蔽。它集均匀电场、缓冲机械应力及阻水功能于一体,可延长电缆使用寿命。产品结构简单,技术性能稳定,实用性强。     

Effects of voltage surges on extruded dielectric cable life projectupdate

Electric utility engineers have commented that extruded distribution cables frequently fail during or shortly after a thunder storm. These engineers also comment that failures often reoccur on cable circuits where previous failures were located with a thumper. Linemen at Georgia Power often make similar comments. To investigate this observation, crosslinked (XLPE) and tree retardant crosslinked (TRXLPE) power cable designs were subjected to accelerated water treeing tests. Samples were subjected to simulated lightning surges or simulated thumping surges. Crosslinked cables removed after 15 years of service operation were also subjected to these surges. The results show that, in some cases, lightning surges do reduce extruded distribution cable life. Also, high level thumping surges appear to reduce cable life once cables are well aged     

15kV热塑性塑料绝缘导引电缆及附件的研制

介绍导引电缆设计要求,论述了产品结构设计和材料选用的特点,重点论述在强电磁场作用下使用导引电缆的突出特性,提出了电缆设计总体思路,电缆电气性能指标以及研制开发技术方案。