抗氧剂300对交联聚乙烯水树枝老化特性的影响

将受阻酚类抗氧剂300(4,4′-硫代双(6-叔丁基-3-甲基苯酚))与低密度聚乙烯(LDPE)、交联剂进行熔融共混并热压成型,制备出一系列抗氧剂含量不同的交联聚乙烯(XLPE),并对其凝胶含量、热老化前后力学性能及水树枝老化特性进行测试。结果表明:添加抗氧剂可以降低XLPE的交联度、提高材料热老化后的力学性能、减缓水树枝的生长速率。当LDPE与抗氧剂质量比为100∶0.2时,XLPE中水树枝在横向和纵向上的平均长度综合最短,抑制水树枝生长的效果最好。     

低密度聚乙烯/纳米蒙脱土复合材料的水树枝生长特性

低密度聚乙烯是高压电力电缆的主要绝缘材料,水树枝生长特性与聚乙烯高压电力电缆绝缘击穿具有紧密联系。采用熔融插层复合法制备了一种低密度聚乙烯/蒙脱土纳米复合材料;设计制作了纳米复合材料的水树枝老化试样及试验装置,在试验中观测了试样的水树枝生长长度,并对试样的水树枝引发率进行了统计,分析了低密度聚乙烯/蒙脱土纳米复合材料的吸水率对水树枝生长的影响;采用差示扫描热法分析了试样的结晶度和晶粒尺寸均匀性,通过分析低密度聚乙烯/蒙脱土纳米复合材料的结晶行为,说明了纳米蒙脱土对纳米复合材料中水树枝的抑制机理。试验与分析结果表明:掺杂质量分数为3%的纳米蒙脱土粒子能够有效地提高低密度聚乙烯的结晶度,使晶粒尺寸分布均匀,吸水率减小,延缓水树枝在低密度聚乙烯中的引发与生长。     

交联聚乙烯绝缘水树枝老化实时观测系统设计

设计了一套可用于实时观测XLPE绝缘中水树枝老化过程的实验系统,对XLPE及其纳米复合材料中的水树枝引发及生长特性进行了研究,探讨了纳米复合材料微观结构对水树枝的抑制机理。采用实时显微数字摄像系统对水树枝引发和生长过程进行实时观测。结果表明:整个系统能够满足水树枝生长过程实时观测的要求,从可视化角度为深入研究XLPE绝缘中水树枝的引发和生长机理提供了试验研究平台。     

绝缘材料水树产生及发展机理的研究现状

本文介绍了水树枝的定义、分类以及影响因素,在参考了16篇中外文献的基础上综述了常用绝缘材料中水树的生长过程和引发机理,推导出水树长度与老化时间、电场强度等因素的关系式。     

热处理对聚乙烯水树枝老化特性的影响

为研究热处理对聚乙烯(PE)中水树枝老化特性的影响,选用低密度聚乙烯(LDPE)、过氧化物交联聚乙烯(XLPE)作为试验材料,采用热循环和热冲击两种方法对试样进行处理。用水针电极法培养水树枝,用金相显微镜观测水树枝形态,并统计水树枝尺寸和引发率;同时测试试样的力学性能,观测结晶形态,测定XLPE的交联度。结果表明:热处理后,LDPE的力学性能变化不大,XLPE的力学性能明显下降;LDPE的晶块尺寸变小且趋于均匀化,XLPE的晶块尺寸变大且趋于不均匀化;LDPE和XLPE中水树枝都容易发展,XLPE水树枝的老化特性受热处理影响更大。热处理导致材料中微孔聚集、力学性能下降,是造成热处理后材料抗水树枝化性能下降的主要原因。     

LDPE结晶形态对水树枝老化特性的影响

为研究结晶形态对聚合物中水树枝生长规律的影响,选用低密度聚乙烯(LDPE)作为实验材料,采用不同冷却速率和添加成核剂两种方法来改变LDPE结晶形态,并用水针电极法培养水树枝。实验研究发现:(1)对纯LDPE而言,冷却速率越快,结晶度越低,球晶尺寸越小;而采用成核剂可以获得远高于冷却速率影响的高结晶度和小球晶尺寸。(2)当试样的球晶尺寸大、数量少时,水树枝的生长速度较快;球晶尺寸小、数量多时,水树枝的生长速度较慢。实验研究表明,合理的结晶形态对聚合物的抗水树枝性能具有至关重要的影响。     

水树枝影响交联聚乙烯电缆绝缘可靠性的试验研究

水树枝生长速度较慢,主要影响聚烯烃绝缘电力电缆的寿命;电树枝生长速度较快,主要影响电缆的可靠性。在高频恒定电压(15k V、20k V)下研究交联聚乙烯电缆中水树枝的生长规律,发现聚烯烃绝缘中的水树枝或电树枝存在相互转化的可能性。试验结果表明:干燥的水树枝引发电树枝的几率最高,湿润水树枝引发电树枝的几率最低,水树枝会影响电缆绝缘的可靠性。     

温度对聚乙烯水树枝老化特性的影响

为研究温度对PE水树枝老化特性的影响,选用低密度聚乙烯(LDPE)、过氧化物(DCP)交联聚乙烯(XLPE)作为试验材料。在室温(20°C)、40°C、60°C、80°C 4个温度下,采用水针电极法培养水树枝,用金相显微镜观测水树枝形态,并统计水树枝尺寸和引发率。研究发现,在60°C以上,温度对PE水树枝老化特性影响显著;水树枝的引发率随温度的升高先减小后增大;水树枝的尺寸随温度的升高总体呈现增大的趋势;LDPE和XLPE的试验得到类似的结果,但XLPE的抗水树枝老化性能优于LDPE。同时研究发现,随温度的升高,材料的力学性能大幅下降。经分析认为,交联限制大晶块的形成,使材料的力学性能增强,是XLPE抗水树枝化性能优于LDPE的两个主要原因;高温下两种材料力学性能下降、微孔膨胀、水分和盐离子的加速扩散是高温下水树枝劣化加速的主要原因。     

交联聚乙烯电缆中水树枝诊断的研究现状

交联聚乙烯（XLPE）电缆因其具有优良的导电性、较好的耐热性和机械强度,自问世以来已广泛应用于输电线路和配电网中。然而,当电缆绝缘处于潮湿的环境中时,在电场的作用下会产生水树枝老化。随着水树枝的生长,电缆的绝缘性能下降并可能导致绝缘击穿,从而影响电网的安全运行。总结了交联聚乙烯电缆中水树枝老化的研究现状,概述了水树枝的产生机理及近年来水树枝老化的诊断方法,最后对各种诊断方法进行了简单比较。     

化学交联方式对聚乙烯水树枝老化特性的影响

为研究化学交联对聚乙烯水树枝老化特性的影响,选用低密度聚乙烯（LDPE）、过氧化物交联聚乙烯、硅烷交联聚乙烯作为试验材料。采用水针电极法培养水树枝,用金相显微镜观测水树枝的形态,并统计了水树枝的尺寸和引发率;同时观测了试样的结晶形态,测定了试样的结晶度、交联度和杂质质量分数,并对比分析了交联前后及不同交联方式试样的电气...     

Suppression of electrical treeing by addition of lithium carbonate to low-density polyethylene

Low-density polyethylene (LDPE) is used widely as an electric insulating material in electric power cables. The generation of electrical treeing due to aging of LDPE may lose the reliability of its insulating capability. Therefore it is important to suppress its treeing and to improve its electrical properties so that the reliability of cables can be improved. For this purpose, the authors prepared LDPE to which various inorganic materials were added. This investigation focuses particularly on lithium carbonate and quartz which were effective in suppressing the treeing when added to LDPE. Lithium carbonate-added (0.25 phr) LDPE in two hours of discharge showed the tree length 150 μm shorter than that (560 μm) of nonadded LDPE, exhibiting an obvious suppressing effect on treeing generation. It was found that this effect was more significant than quartz-added LDPE and even at elevated temperatures lithium carbonate-added LDPE exhibited suppression of treeing. The thermal decomposition temperature at which lithium carbonate-added (1 phr) LDPE loses 50 percent of its weight rose 100°C more than nonadded LDPE and 60°C more than that of quartz-added LDPE, which showed improvement in heat resistance of LDPE.     

Water treeing in binary linear polyethylene blends: the mechanicalaspect

Water treeing tests were performed on low density polyethylene (LDPE) and four different binary blends of sharp linear polyethylene (LPE) fractions (M_w=2500 and 76000), which were either quenched in air from the melt or isothermally crystallised at 123°C. Although the morphology and initial mechanical properties of the materials tested were significantly different, the vented tree growth characteristics were similar for all of them. This is in disagreement with the electromechanical models of water treeing, which correlate water tree growth with the fracture toughness of the material. Time to breakdown distributions were also similar for both LDPE and the binary LPE blends, which indicates that, regardless of the initial material morphology and the actual structure of water trees, the length of water trees is one of the controlling factors in insulation failure. The visible light image of water trees in LPE blends did not disappear upon drying as it usually does in LDPE and crosslinked polyethylene insulation     

热老化对交联聚乙烯电缆绝缘中水树的影响研究

热老化过程不但会影响交联聚乙烯电缆绝缘的电磁学和物理化学性能,还对绝缘内水树的产生与生长有着一定的影响。通过研究热老化过程对XLPE电缆绝缘中的水树现象的影响,以及在几个有可能的影响因素当中,哪个因素对水树现象的影响最大。实验结果表明,在与XLPE电缆绝缘的热老化有关的各种因素对水树现象的影响中,热氧化对XLPE电缆绝缘表层水树的产生和生长的影响最大。尽管热氧化所引起的缺陷有可能就是XLPE电缆绝缘中水树生长过程中的起始点,但是它在一定程度上抑制着水树的成长,甚至有着"水树延迟效果"的美称。     

A water treeing model

A new model for water treeing is introduced. It assumes that when the field-induced stress applied on nano cavities filled with a liquid is larger than the yield strength of the polymer, bonds will be broken and the nano cavity will expand. The growth of the water trees is enhanced by the fatigue induced by the alternating electric field. The diffusion of the liquid is also a parameter affecting the water tree length. A simple equation relating the water tree length with field, time, frequency, and the nature of the solution is presented. A very good agreement between theory and experiments for a wide variety of results obtained with low density polyethylene (LDPE) tested under various fields, frequencies and ionic solutions is observed. This model also predicts the growth of water trees under DC fields after very long times or after many polarity reversals. Some aspects of this model requiring further refinements or experimental data are also pointed out.     

Aging of polymeric insulating materials in power cables

More than 160 years of history go with the use of polymers in the cable industry. Polyethylene of low and high density and crosslinked polyethylene gradually succeeded paper and polyvinylchloride. This review discusses some aspects of the aging processes of polyethylene under working conditions. Electrical and water treeing are considered, dependent upon the morphology and the induced characteristics of the insulating material     

The Performance of Strippable and Bonded Screened Medium-Voltage XLPE-Insulated Cables Under Long-Term Accelerated Aging

XLPE high-voltage underground cables are being extensively used in Arabian Gulf countries. Most of these cables are being manufactured locally. Although XLPE has excellent dielectric characteristics, extensive premature failures have been reported by the local power utilities. The main causes of such premature failures are related to manufacturing defects and insulation degradation mainly caused by water treeing phenomena. In this research work, five types of 15-kV, XLPE-insulated cables were subjected to accelerated aging under simultaneous electrical, thermal, and environmental stresses for periods of 60, 120, and 180 days. After each aging period, partial-discharge (PD), mechanical properties, ac dielectric strength and the extent of degradation due to water treeing of these cables were measured. The results show that PD and mechanical properties show just little variations whereas the ac-retained dielectric strength decreases rapidly in the first 60 days after which the rate of its decrease retards. Correlations are established between the retained dielectric strength and the lengths of the longest water trees. Pros and cons of the insulating materials that are used as well as the role of strippable and bonded semiconducting screens are also discussed     

固体绝缘中空间电荷测量装置的研制和应用

介绍了电声脉冲法空间电荷分布测量装置的测量原理和性能，并利用此装置测量了试样中的空间电荷密度分布，运用有限元法计算空间电荷对试样内部电场的畸变。为了研制超高压直流塑料电缆料，以少量的极性聚合物混炼到低密度聚乙烯中，降低了交联聚乙的空间电荷效应，大幅度提高了５０％直流预压短路树枝的起始电压。     

Influence of internal mechanical stress and strain on electricalperformance of polyethylene electrical treeing resistance

Crosslinked polyethylene (XLPE) and low-density polyethylene (LDPE) insulations used in HV cables are not only subjected to electrical and thermal stresses, but also exposed to mechanical stresses, whether residual internal stresses created during the cooling process of the fabrication, external forces when cables are bent during installation or thermomechanical stresses caused by differential thermal expansion between the conductor and the polymeric material. In order to investigate the possible influence of mechanical stresses on dielectric properties of polyethylene, measurements were conducted on pin-plane XLPE and LDPE samples with various magnitudes of residual mechanical stresses around the embedded electrode. The time to inception, the growing rate and the shape of the electrical trees under different voltages are reported in this paper. Specimens with the highest values of residual stresses were found to have the shortest inception times and the longest trees after one hour of aging under different voltages. When the mechanical stress was allowed to relax, the treeing resistance was measured to be significantly improved     

交联聚乙烯电缆热老化与电树枝化相关性研究

热老化过程不但会影响交联聚乙烯（XLPE）电缆绝缘的物理化学性能,还对绝缘内电树的产生与生长有着一定的影响。研究了热老化后XLPE电缆绝缘中的电树行为．探讨XLPE电缆绝缘中电树枝过程与材料热老化的关系。采用带循环通风的热老化箱对XLPE电缆绝缘进行3个温度等级的热老化实验：采用针板结构电极进行电树枝实验,并利用数码显微镜观察电树枝的产生和发展情况;利用差示扫描量热法（DSC）、傅里叶红外光谱分析（FTIR）测试了不同温度热老化下XLPE电缆绝缘的物理化学性能;最后探讨了几种不同结构电树枝的生长机理．认为热老化并没有加速电树枝的生长．反而有一定的抑制作用．