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     

Condition assessment of cable insulation systems in operatingnuclear power plants

Four crosslinked polyethylene (XLPE) and ethylene propylene rubber (EPR) insulated cables were subjected to accelerated thermal, radiation, and sequential radiation and thermal exposure to simulate 20, 30, and 40 yr in-service environments in Ontario Hydro Nuclear Plants. Two sets of samples were evaluated. The first set contained 15 cm cable specimens in tubular form with the conductors removed, while the second set was made up of 4.3 m cable samples wound on mandrels. The cable samples were sequentially irradiated and thermally aged and subjected to an additional accident radiation exposure followed by a simulated loss of coolant accident (LOCA)/main steam line break (MSLB) steam test. During the steam test, samples were energized and their electrical characteristics continuously monitored. The material performance of the insulation was assessed using the 15 cm specimens during the various stages of aging exposure by conventional elongation measurement and by the use of micro-specimens with differential scanning calorimeter (DSC), oxidation induction time (OIT) and infrared carbonyl absorption techniques. The results from these samples were compared with the electrical performance of the cable samples wound on mandrels that had been subjected to the LOCA/MSLB steam test. The test results indicate that with the use of micro-specimens meaningful changes were obtained until the elongation values of the samples were reduced to 50% absolute. Electrical test data obtained for XLPE and EPR during the steam tests indicate that 50% absolute elongation values provide sufficient margin to withstand additional accident radiation, and to function electrically during design basis events     

电力电缆绝缘挤出胀大率对其性能影响的研究

本文针对电力电缆绝缘挤出胀大现象 ,研究了加工工艺对挤出胀大率的影响 ,结果发现 :加工温度和挤出速率对挤出胀大率有较大的影响 ;同时研究了挤出胀大率对电力电缆各项性能的影响 ,发现减小挤出胀大率能够明显地提高其性能。最后提出了减小挤出胀大率的几种方法。     

高压电力电缆绝缘故障定位分析

随着电力电缆在电网建设中运用越来越多,由外力、施工等原因引起的电缆绝缘故障明显增长,而故障的隐蔽性给恢复送电造成极大的麻烦。文章根据在电缆故障查找中的实践经验,全面分析了各类绝缘故障精确定位方法,并以110 kV上旭线及湖南110 kV某湖底电缆故障为例,再现故障定位全过程。     

电力电缆绝缘击穿点定位的新方法

探讨了电阻法对高压击穿点定位的原理,寻求一种简便可行的电缆定位技术,并找出一种可用于电力电缆绝缘击穿点定位的新方法,结果表明该方法精度高,且简便易行,其定位结果的精度不受击穿点电阻和测试导线电阻以及接触电阻的影响。     

一种电力电缆绝缘击穿点定位的新方法

本文介绍了一种电力电缆绝缘击穿点定位的新方法。该方法简便易行,其定位结果的精度不受击穿点电阻和测试用连接导线的电阻及其接触电阻的影响。     

电力电缆讲座：第五讲 电览线路的运行管理

1　运行管理的基本任务电缆线路的运行管理工作是多方面的 ,其最基本的任务就是要确保电缆线路安全供电和减少事故发生。基本任务可以归纳为以下两方面。1 .1　使电缆适应电网和用户供电的需求电缆运行管理部门必须严密监视电缆设备的运行状态 ,使电缆线路始终适应电网和用户供电的需求 ,运行管理人员要使管辖范围的电缆线路处于受控状态。电缆的绝缘、导体和护层这三大组成部分 ,必须符合运行要求。( 1 )绝缘一定要合格。电缆及其附件的绝缘 ,必须与电网的绝缘水平相匹配 ,它的 U0 /U要与系统的中性点接地方式相一致。而且 ,绝缘要有一定…     

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     

Study of space-charge characteristics in polyethylene for power cable insulation by laser-induced pressure-pulse technique

By utilizing the laser induced pressure-pulse (LIPP) technique, the behavior of space charge in low-density polyethylene (LDPE) and crosslinked polyethylene (XLPE) films in contact with metal or carbon-loaded semiconducting layers was studied quantitatively to clarify the space-charge characteristics in power cables. Negative heterospace charge near the anode and positive space charge in the bulk were observed in unoxidized LDPE under the fields above 120 kV/mm. The amount of negative space charge increased with applied field, while positive space charge in the bulk disappeared with increasing applied field. This indicates that electron injection and ionization are enhanced by applied field. Prominent negative homospace charge was formed near the cathode in oxidized LDPE, which indicates that oxidation enhanced electron injection. The depth of charge centroid from the cathode became larger with increasing temperature. This indicates that the effective electron mobility increases with temperature. Negative space charge also was formed in the bulk in XLPE films with metal electrodes, which indicates that crosslinking enhanced electron injection. XLPE films with a carbon-loaded semiconducting layer showed both negative and positive homospace charges near the semiconducting layers, which indicates that both electrons and holes were injected from the semiconducting layer.     

煤矿6kV动力电缆绝缘在线监测系统研究

针对煤矿井下6 k V供电系统电缆离线检测的不足,设计了一种电力电缆在线监测系统,并进行了实验验证。在供电系统中注入低频电压作为系统的激励信号,运用设计的监测单元对分支电缆的低频电压和低频电流信号进行调理和精确测量,采用高性能信号处理器结合矢量方程和全波傅里叶算法,计算出所有电缆分支的对地绝缘电阻值。同时运用CAN总线建立监控系统实现了电缆线路的故障选线。实验结果表明,监测系统有效的解决了线路电抗和互感器电抗参数以及不平衡电流对测量精度的影响,可以实时监测所有电缆分支的对地绝缘电阻值,测量误差在3%以内。     

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     

电力电缆绝缘监测中的低频交流电压叠加法研究

电力电缆绝缘损坏主要由水树枝劣化引起,对电力电缆进行带电检测是非常必要的,低频交流电压叠加法是目前比较好的一种检测方法,本文对该方法的原理和软硬件设计方法作了介绍。     

Aging of 154 kV underground power cable insulation under combined thermal and electrical stresses

This work the combined electrical and thermal stresses of the 154 kV XLPE power cable used in the underground power transmission in Turkey. The dependence of aging on electrical and thermal stresses is given by a straight line in a certain range of electric field (E) values which indicates that the aging is a thermochemical process. Furthermore, cable tests are conducted in oil, and the results are valid for immersed insulation but might not be completely representative of XLPE used in service in a "dry" environment. Therefore, each cable insulator has to be tested and the parameters must be determined for each cable separately.     

Electrical treeing characteristics in XLPE power cable insulation in frequency range between 20 and 500 Hz

Electrical treeing is one of the main reasons for long term degradation of polymeric materials used in high voltage ac applications. In this paper we report on an investigation of electrical tree growth characteristics in XLPE samples from a commercial XLPE power cable. Electrical trees have been grown over a frequency range from 20 Hz to 500 Hz and images of trees were taken using CCD camera without interrupting the application of voltage. The fractal dimension of electric tree is obtained using a simple box-counting technique. Contrary to our expectation it has been found that the fractal dimension prior to the breakdown shows no significant change when frequency of the applied voltage increases. Instead, the frequency accelerates tree growth rate and reduces the time to breakdown. A new approach for investigating the frequency effect on trees has been devised. In addition to looking into the fractal analysis of tree as a whole, regions of growth are being sectioned to reveal differences in terms of growth rate, accumulated damage and fractal dimension.     

线缆绝缘故障定位技术的探析

绝缘故障是线缆的常见故障之一 ,当两个绝缘线芯之间处于低绝缘 (或不完全击穿 )条件下其定位技术更为复杂。本文主要讨论了线缆在这种条件下的绝缘故障定位的基本原理和方法 ,分析了提高定位精度的几种方法 ,并以实例介绍了实践中的测量技术。     

110kV交联电缆绝缘层晶体结构研究

通过X -射线衍射方法研究了110kV交联聚乙烯绝缘电缆绝缘层的结晶结构。发现电缆工艺中的热过程和热历史会造成超高压交联电缆绝缘层各部分结晶形态分布不均,中层聚集态结构均匀性较好,内层外层结晶程度低于中层。热应力改变了晶区中的晶面间距,显示出绝缘径向应力以张力为主     

The application of novel polypropylene to the insulation of electric power cable (3)

Having a higher melting temperature than polyethylene, polypropylene has been expected to be an insulation material for power cables. But isotactic polypropylene (i‐PP) used generally is unsuitable as cable insulation because it shows poor flexibility, low breakdown strength due to growing spherulites, and so on. But stereoregular syndiotactic polypropylene (s‐PP) newly developed with metallocene catalyst shows quite different properties than i‐PP. In our previous paper, we investigated the basic properties of s‐PP and the initial properties as a cable which was manufactured using s‐PP insulation. It was revealed that s‐PP had superior thermal and electrical properties to cross‐linked polyethylene and the s‐PP insulation table showed satisfactory initial properties. However, in order to apply to an actual cable, the properties must be maintainable over 30 years after construction. In this paper, we estimated the long‐term remaining properties for s‐PP insulation table. A series of experiments on long‐term properties gave the following results: (1) s‐PP cable shows longer life over 30 years; (2) the breakdown strength of s‐PP cable after a long‐term experiment equal to 30 years is slightly lower than the initial breakdown strength, but it is sufficient as a remaining property. Furthermore, water‐tree resistivity of s‐PP was investigated and it was revealed that s‐PP significantly suppressed the water tree propagation compared with XLPE. These results suggested that s‐PP cable would serve as a next‐generation cable. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(3): 1–8, 2006; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20114     

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...     

Dielectric insulation characteristics ofliquid-nitrogen-impregnated laminated paper-insulated cable

The electrical characteristics and insulation design strength of liquid-nitrogen-impregnated synthetic insulation were considered. The impregnation of liquid nitrogen into insulation paper can be monitored by measuring the electrostatic capacitance of the cable. ∈ tan δ, an index of the dielectric loss, was 0.31% for cellulose paper and 0.18% for semisynthetic paper, polypropylene laminated semisynthetic paper, and biaxially oriented polypropylene laminated paper. It was found that the decline of the thickness dependence of the breakdown strength of the liquid-nitrogen-impregnated insulating cable was steeper than that of the oil-filled cables. It is possible to design the insulation strength of the 66 kV cable to be 10 kV/mm     

采用不平衡绝缘方式提高同塔双回线路供电可靠性

从线路设计和运行统计等方面论证了广东省广电集团公司珠海供电分公司原有标准型杆塔的空气间隙有足够的裕度,因此可在同塔双回线路上采用不平衡绝缘的保护方式,从理论和实际运行情况分析了不平衡绝缘方式对提高供电可靠性的作用,结论是：同塔双回线路采用不平衡绝缘方式能提高线路的耐雷和防污水平,能降低双回线路同时跳闸率。