Accelerated aging of extruded dielectric power cables. II. Lifetesting of 15 kV XLPE-insulated cables

For pt.I see ibid., vol.7, no.2, p.596-602 (1992). Preliminary results are described in which 15 kV XLPE cables were subjected to accelerated aging tests under a variety of controlled voltage stress and thermal load cycle conditions, with loss of life being calculated for each set of conditions in terms of the geometric mean time to failure (GMTF). The relative influence of voltage stress and load cycle temperature are discussed. Accelerated aging results show a reduction in GMTF for 15 kV XLPE-insulated cables as the voltage stress or conductor load cycle temperature is increased in a controlled manner. The relative influence of voltage stress versus load cycle temperature can be compared. The GMTF increases more in going from 90°C to 60°C at constant applied voltage stress than in going from 4X to 2X rated voltage at constant load cycle temperature conditions     

Electrical aging of extruded dielectric cables: review of existingtheories and data

Despite the huge amount of data on so-called electrical aging of extruded HV cables, the fundamental phenomena responsible for it or evolving with aging time, are still far from well understood. It is therefore not surprising why it is so difficult to predict reliable cable lifetimes in service from accelerated aging experiments in the laboratory. The objective of this paper is to review critically the existing theories of electrical aging of solid dielectric materials. A relatively large number of models and theories exist but none of the most often used is known to yield reliable life predictions. One conclusion is that there is a need for a more comprehensive model of electrical aging of extruded dielectric cables. In order to develop this model, an extensive review of existing literature data was undertaken. This paper summarizes the data collected from more than 200 papers on aging of PE, XLPE and EPR cables. It appears that cable breakdown strength should not be plotted on log field vs. log time graphs to yield long-time (i.e. low-field) values, since results obtained over a long time period do not obey an inverse power law. In fact, high-field results are better described by an exponential relation between time and field. The models of Simoni, Montanari and Crine seem to give the best fit to experimental results obtained under a wide variety of experimental conditions. It is also shown that the lower field limit for the exponential regime with XLPE cable is in the 8 to 15 kV/mm range, which corresponds to the onset of strong charge injection. The influence of environment, insulation nature and morphology, and testing temperature are discussed     

Accelerated aging tests for polymer insulated cables under wetconditions

The effectiveness of various aging test procedures utilized in the past to evaluate aging in polymeric cables under wet conditions is examined. It is pointed out that the prime parameters affecting the aging rate and its mechanisms are those of electrical stress, frequency, water solution, temperature, mechanical strain, and testing time duration. Any valid fixed-time or time-to-breakdown test procedure that is based on the stress/frequency acceleration concept must, therefore, be carefully specified and defined in terms of these parameters     

Skin effect and dielectric loss models of power cables

In power electronics applications, power cables spread paths of conducted disturbances throughout the system. This paper proposes a high frequency modeling method for power cables that takes into account phenomena which appear when the switching frequency of the static converter increases, such as skin effects, proximity effects and dielectric losses. The proposed power cable models are obtained by the seriesassociation of n identical RLCG basic cells. The skin and proximity effects are represented as the impedance of an R-L ladder and the dielectric losses as the admittance of an R-C ladder. The proposed method was successfully applied to a threewire unshielded cable and extended to a four-wire shielded cable.     

Influence of post-manufacturing residual mechanical stress andcrosslinking by-products on dielectric strength of HV extruded cables

Residual mechanical stresses from manufacturing always exist in freshly extruded HV cables. These stresses are not uniformly distributed in the cable insulation bulk material. Five different HV cables were analyzed with respect to residual mechanical stresses and dielectric breakdown strength. Photoelastic measurements have been carried out and show that maximum residual stresses range from 4.5 to 6 MPa and are located near the conductor shield. Breakdown strength measurements with respect to mechanical stresses have also been performed up to, and above the maximum stresses observed. A significant decrease in ac breakdown strength was observed for stresses higher than 6 MPa. Typical crosslinking by-products from dicumyl peroxide (DCP) have been measured by FTIR spectroscopy at five radial positions in the insulation bulk. Measured by-products consisted in acetophenone and cumyl alcohol. FTIR measurements show that crosslinking by-products content is higher in the bulk of the insulation than near the conductor and insulation shields thus showing a diffusion process. Moreover, residual amount of cumyl alcohol is generally between 1 and 3 times that of acetophenone. No important effect of both by-products on the ac dielectric breakdown strength was observed     

Technological progress in high-voltage XLPE power cables in Japan.I

The author reviews technological progress in the design and production of cross-linked polyethylene cable and discusses the present status of the products taking advantage of this technology. A brief historical background is given. The methods for determining or choosing cable characteristics, such as insulation thickness, service life, and cable quality, are discussed. Progress in production technology is discussed, covering improvements in polyethylene, three-layer common extrusion, dry curing, and smoothing of the semiconductive shield layers     

Thermal analysis of power cables in multi-layered soil. I.Theoretical model

The heat dissipation and temperature distribution in multilayered soil surrounding a buried cable are calculated using the finite difference method and the energy conservation principle. The numerical technique proposed is very suitable for modeling any real cable installation configuration in multilayered soil. The development of the model and the effect of the parameters that influence the conversion and the stability of the numerical solution of the heat dissipation from the underground cable system are studied     

规模化电动汽车充电对配电网电缆老化的影响

电动汽车规模化且带有随机特性的充电行为将给城市电网运行和维护带来新的挑战。提出了计及充电随机特性的电动汽车充电负荷模型,考虑了电动汽车接入水平、用户出行和充电习惯,在此基础上,研究了规模化电动汽车充电对配电网电缆老化的影响。所提出的电缆老化模型计及了不同季节、不同环境下每一负荷周期内电缆所承受电应力、热应力的随机特性,提高了电缆剩余寿命估算的准确性,解决了规模化电动汽车入网后如何确定电缆寿命所受影响这一技术难题。     

10 kV电力电缆绝缘在线监测的一种新方法

在简述现有的电力电缆绝缘监测方法的基础上,提出了一种基于模型参数识别的电力电缆绝缘在线监测的新方法,对10 kV电力电缆每条线路的每一相分别建立数学模型,基于模型参数识别方法建立以线路参数为未知量的微分方程,利用实时采集到的电压、电流求解最小二乘意义下的模型参数估计值,依据得到的电缆线路对地绝缘电阻值,从而判断电缆的绝缘水平.经EMTP仿真结果验证,该方法正确、可靠,并且可以和馈线保护合为一体,满足自动化的要求.     

10kV电力电缆绝缘在线监测的一种新方法

在简述现有的电力电缆绝缘监测方法的基础上,提出了一种基于模型参数识别的电力电缆绝缘在线监测的新方法,对10 kV电力电缆每条线路的每一相分别建立数学模型,基于模型参数识别方法建立以线路参数为未知量的微分方程,利用实时采集到的电压、电流求解最小二乘意义下的模型参数估计值,依据得到的电缆线路对地绝缘电阻值,从而判断电缆的绝缘水平。经EMTP仿真结果验证,该方法正确、可靠,并且可以和馈线保护合为一体,满足自动化的要求。     

自承式光缆的施工

结合在自承式光缆施工中的实际经验,具全介绍了电力系统中自承式光缆架设以及熔接施工的程序及方法,从光缆的施工准备,光缆展放,光缆紧线,附件安装到光纤接头熔接施工,介绍了施工的方法,使用的工机具及注意事项。     

无线分布式开关电源老化监控系统设计

设计了一款以单片机C8051F020为主控芯片,采用端口扩展技术和Zigbee无线组网技术的开关电源老化监控系统。通过8组16选1的芯片用来分别实现128路电压和温度的采集以及继电器的关断控制,能够实现较低代价的大规模扩展;通过Zigbee模块将上位机、主控板和通信子板联系起来,并以Modbus协议为格式来传输数据和命令,并通过上位机软件实现数据显示和老化命令设置。现场调试表明:系统可检测到0~50 V的电压和0~125℃的温度,检测精度分别为0.01 V和0.1℃,且功耗低、效率高、成本低,可以满足工业生产的要求。     

Accelerated cable life testing of EPR-insulated medium voltagedistribution cables

This paper presents results aimed at developing a reliable accelerated aging tank test for EPR-insulated cables. Aging was performed at 2 to 4 times rated voltage on load cycling to temperatures of 45°C, 60°C, 75°C, and 90°C at the conductor with water in the conductor strands and outside the cable. Results show that cable failure is more rapid at the highest electrical stress and lowest conductor load cycle temperature. Cables aged at higher temperatures and various levels of electrical stress rarely failed and retained in excess of 40% of their original breakdown strength after 1500+ days of aging. Aging performed at 90°C load cycle temperature and 4 times rated voltage with air on the outside and water at the conductor of the cable showed more rapid loss of life than with water outside. Results indicate the optimum aging conditions for EPR-insulated cables in the accelerated cable life test (ACLT) differ significantly from those previously observed for XLPE-insulated cables, and that the appropriate test methodology for EPR-insulated cables requires additional study     

Research and development of electrical insulation ofsuperconducting cables by extruded polymers

This is a review to show the importance of electrical insulation in ac superconducting cables. An attractive superconducting cable has to be designed for the voltage range of 60-270 kV. Therefore, a reliable insulation design is imperative. Two types of insulation have been compared. One is composite insulation, namely laminar paper or plastic tape, impregnated with coolant. The other is solid insulation of extruded polymer on the conductor. The composite insulation has a lengthy history and, in the constructions to date, has been the insulation design used for superconducting cables. Some prototype superconducting cables with this type of insulation have been developed and successfully tested. However, the partial discharge in butt gaps may affect their long-term reliability. The solid insulation, on the other hand, can separate the coolant from the electrical insulation and can exploit the benefit of the super electrical insulation characteristics of polymers in the cryogenic region. Some attempts have been made to use this design with liquid nitrogen and liquid helium. One example incorporating extruded ethylenepropylene rubber (EPR) for insulation was found to satisfactorily go through the cool-down to a liquid helium temperature and to endure the simultaneous voltage and current tests. EPR, and possibly some other polymers, seem to be promising materials for solid insulation in the cryogenic region     

交联聚乙烯电力电缆的绝缘在线监测技术

本文介绍了国内外交联聚乙烯 (XL PE)电力电缆绝缘在线监测技术的研究现状。讨论了 XL PE电力电缆绝缘在线监测技术所面临的一些技术问题。根据对交流叠加冲击电压下 XL PE绝缘放电特性的研究 ,探讨了 XL PE电力电缆绝缘在线监测技术的发展方向。     

电力电缆安全监测中温度场和电场数值关系分析

首先采用有限元法分别计算了8.7/15 kV YJV 1×400 mm2直埋式电缆的温度场以及电场分布,在此基础上分析了二者之间的数值关系。计算结果表明电缆的温度场与电场之间呈近似的线性关系。从而在实际工程中,可以通过在线监测电缆的温度场分布,首先可以推算其负荷,对电缆负荷进行监控。并根据电缆电场与温度场之间的线性关系,推算其电场分布,得出电缆绝缘介质内的电场分布规律,判断内部电场是否超过安全限值,可以更好地监测电缆的绝缘状态,确保电缆的安全运行。     

电力电缆安全监测中温度场和电场数值关系分析

首先采用有限元法分别计算了8.7/15 kV YJV 1×400 mm2直埋式电缆的温度场以及电场分布,在此基础上分析了二者之间的数值关系.计算结果表明电缆的温度场与电场之间呈近似的线性关系.从而在实际工程中,可以通过在线监测电缆的温度场分布,首先可以推算其负荷,对电缆负荷进行监控.并根据电缆电场与温度场之间的线性关系,推算其电场分布,得出电缆绝缘介质内的电场分布规律,判断内部电场是否超过安全限值,可以更好地监测电缆的绝缘状态,确保电缆的安全运行.     

光纤光栅测温系统在电力电缆温度在线监测中的应用

介绍了电力电缆温度在线监测系统目前的现状,光纤光栅测温系统的工作原理、主要技术指标及基于光纤光栅测温传感器的电力电缆温度在线监测系统在实际中的应用情况。