表面修饰纳米SiO_2/XLPE的电导电流和空间电荷特性

为研究纳米颗粒表面修饰对纳米二氧化硅/交联聚乙烯(SiO2/XLPE)电导电流和空间电荷特性的影响,分别将未经表面修饰和经钛酸酯偶联剂TC9修饰的纳米SiO2颗粒添加到XLPE基体中进行了实验。显微观测和成分分析表明,TC9的非极性有机官能团取代了纳米SiO2颗粒表面的羟基,降低了羟基间的相互成键作用,从而改善了纳米SiO2与XLPE基体之间的相容性,纳米SiO2颗粒在XLPE基体中的粒径范围从几十到100 nm;同时,TC9表面修饰提高了纳米SiO2/XLPE复合介质的介电常数和介质损耗,降低了电导电流,抑制了空间电荷的注入;而未经表面修饰的纳米SiO2/XLPE复合介质的电导电流和空间电荷特性相较于XLPE并未得到改善。分析认为,由于经TC9表面修饰的纳米SiO2分散性的改善,增大了纳米颗粒与XLPE基体之间的界面区域,因而在纳米复合介质内产生了更多的深陷阱;电极与介质界面附近的大量深陷阱捕获注入的电荷,形成固定的空间电荷层,降低了其与电极间的局部电场,从而提高了注入势垒,抑制了空间电荷的进一步注入。     

半导电材料对纳米MgO/XLPE复合介质空间电荷影响的研究

聚合物纳米复合介质中空间电荷的注入与半导电电极材料密切相关,文中采用电声脉冲(PEA)法测量了预压-60 kV/mm电场1 h后,对比研究了六种不同半导电电极材料下交联聚乙烯(XLPE)和MgO/XLPE复合介质中的空间电荷分布;并对不同半导电电极材料下MgO/XLPE复合介质中的平均电荷密度进行了计算。对比实验表明:配方不同的半导电电极材料确实对试样中空间电荷的分布以及空间电荷量影响很大;以乙烯醋酸乙烯共聚物(EVA)为基础材料、添加30wt%炭黑的第二种半导电材料对MgO/XLPE复合介质中空间电荷的抑制效果最好。     

MgO/LDPE纳米复合材料抑制空间电荷及电树枝化特性

应用经硅烷偶联处理后的纳米氧化镁(MgO)粉末与低密度聚乙烯(low density polyethylene,LDPE)共混,制得MgO/LDPE复合介质。高成分衬度扫描电镜(scanningelectron microscope,SEM)中图像表明,粒径为100 nm左右的MgO纳米粒子均匀的分散于介质中。通过电声脉冲法(pulsed electro-acoustic,PEA)测试发现,当纳米MgO填料的质量分数为4%时,可以有效抑制空间电荷的注入,伏安特性的实验结果表明,复合介质拥有更高的空间电荷注入阈值场强。通过电树枝实验,发现复合介质可以抑制电树枝的引发和生长。最后,对实验结果进行了分析,探讨了纳米复合介质抑制空间电荷和树枝化生长的机制。纳米颗粒与基体材料界面电荷行为可能是复合介质电学性能改善的原因。     

纳米MgO掺杂聚乙烯中空间电荷行为的研究

介绍了采用电声脉冲法测量纯低密度聚乙烯以及氧化镁／低密度聚乙烯（MgO／LDPE）纳米复合介质中的空间电荷,讨论了不同含量的MgO以及不同型号LDPE作为基础材料对复合介质内空间电荷分布的影响。实验结果表明：随着直流电场的增加,在纯聚乙烯中产生电荷注入现象,且随着加压时间的增加,注入的同极性电荷有向另一电极移动的趋势。少量的MgO可以有效抑制复合介质中的空间电荷注入,随着MgO含量的增加,对复合介质的空间电荷注入抑制效果逐渐减弱。     

不同表面处理剂对纳米MgO/LDPE空间电荷行为的影响

为研究不同表面处理剂对纳米MgO/低密度聚乙烯(LDPE)复合介质空间电荷行为的影响,将经过不同表面处理的纳米MgO颗粒以不同质量分数填充到低密度聚乙烯中,制得纳米复合介质,并对不同纳米复合介质的微观特性结构和空间电荷分布进行了实验研究。微观特性研究表明,经过表面处理,无机纳米颗粒与聚合物的结合作用得到增强,复合介质结晶度增加;空间电荷实验表明,添加经过不同表面处理的纳米MgO后复合介质在短路时阴极和阳极均积累了同极性电荷。此外,在不同无机纳米颗粒填充质量分数下,经过不同表面处理剂修饰后的纳米复合介质内部积累的空间电荷得到不同程度的抑制。总体而言,铝酸酯偶联剂对纳米MgO颗粒的表面处理效果相对较好。     

基于空间电荷的纳米MgO/LDPE中电荷输运的计算方法研究

为定量分析研究纳米氧化镁(MgO)/低密度聚乙烯(LDPE)复合介质的空间电荷行为,将粒径20 nm的纳米MgO颗粒以不同浓度填充到LDPE,并对纳米复合介质的空间电荷分布进行了实验研究。通过空间电荷实验的结果,对其进行多种方法的计算分析,计算分析结果表明:1)浓度为0.5wt%和2wt%的积累空间电荷的平均体电荷密度最大,而浓度1wt%的纳米MgO/LDPE的平均体电荷密度最小;2)浓度为2wt%的纳米MgO/LDPE的视在迁移率和体电荷密度衰减速率最高,其次是浓度为0.5wt%的,最低的是浓度为1wt%的纳米复合介质;3)浓度为1wt%的纳米MgO/LDPE的陷阱深度最大,其次是浓度为0.5wt%的,而陷阱深度最小的是浓度为2wt%的纳米Mg O/LDPE;4)浓度为2wt%的纳米MgO/LDPE试样中的场强畸变最大,其次是浓度为1wt%的,而场强发生畸变幅度最小的是浓度为0.5wt%的纳米MgO/LDPE。     

纳米MgO/环氧复合电介质的空间电荷特性研究

环氧复合材料在高温高场等复杂的工况下易积聚空间电荷，造成局部场强畸变，严重时将引发局部放电乃至绝缘击穿。通过纳米MgO颗粒与环氧树脂（EP）混合制备不同掺杂率的纳米MgO/EP复合电介质，采用差示扫描量热分析（DSC）测试环氧复合电介质的玻璃化转变温度；采用热刺激去极化电流法（TSDC）拟合计算环氧复合电介质的陷阱特性；采用电声脉冲法（PEA）测试环氧复合电介质的空间电荷特性。结果表明：纳米MgO颗粒的添加可以提高环氧树脂的玻璃化转变温度，抑制环氧树脂内空间电荷积聚。随着纳米MgO掺杂率的增加，纳米MgO/EP复合电介质的玻璃化转变温度先上升后下降，深陷阱能级和密度均先增大后减小；空间电荷密度先下降后上升，电场畸变的变化趋势与空间电荷的变化趋势相似。当纳米MgO掺杂率为3%时，纳米MgO/EP复合电介质的玻璃化温度达到最大值，抑制空间电荷积聚和场强畸变的能力最好。     

纳米颗粒接枝密度对纳米复合XLPE空间电荷特性的影响

为研究纳米颗粒接枝密度对交联聚乙烯(XLPE)纳米复合介质空间电荷特性的影响,分别将未接枝和经不同含量硅烷偶联剂(MDOS)接枝的胶体SiO2纳米颗粒通过熔融共混法添加到XLPE中。扫描电镜观测表明未接枝组别出现数微米尺寸的严重团聚,接枝后纳米颗粒分散性改善;红外光谱分析表明接枝后的纳米颗粒出现MDOS吸收峰,随接枝密度增大而增强;由热重分析结果计算得到了纳米颗粒的接枝密度;差示量热扫描测试结果表明随接枝密度的提高,纳米复合XLPE的熔点略呈上升趋势。-50 kV/mm电场下,XLPE和MDOS/XLPE试样均出现正极性空间电荷包现象,说明仅仅添加MDOS并无捕获或抑制空间电荷的效果。纳米复合后空间电荷受到抑制,随接枝密度的提高抑制效果更加明显。分析认为,MDOS接枝SiO2纳米颗粒,减小SiO2纳米颗粒与基体的表面能之差,促进纳米颗粒的分散,增大了纳米颗粒-聚合物的界面面积,产生的更多陷阱所捕获的电荷进一步降低电极-电介质界面附近的局部电场,但也减小了去极化过程残余电荷的消散速度。     

纳米填充浓度对LDPE/Silica纳米复合介质中空间电荷行为的影响

为研究纳米颗粒填充浓度对复合介质内部空间电荷特性的影响,以低密度聚乙烯(low-density polyethylene,LDPE)为基料,纳米二氧化硅(Silica)为填充颗粒,制备了浓度在0%～5%范围的纳米LDPE/Silica复合介质,并测试了复合介质的准稳态直流电导和空间电荷分布。当LDPE内填充不同浓度的纳米silica后,复合介质内部的平均体空间电荷密度均得到有效抑制,且其平均衰减速度随填充浓度的升高而下降,但复合介质的准稳态直流电导在填充浓度低于0.5%时比纯LDPE时要大,当填充浓度高于0.5%时,准稳态直流电导随着填充浓度的升高而快速下降。结果表明试样内部的空间电荷分布存在3种趋势:当纳米silica填充浓度为0%～0.1%时,试样内表面侧的异极性空间电荷量随填充浓度升高而下降;当填充浓度为0.5%～2%时,试样内表面侧积累同极性电荷,并随填充浓度升高而增大;当填充浓度高于2%时,同极性空间电荷量下降。最低空间电荷密度和准稳态直流高场电导对应的纳米填充浓度分别为0.5%和5%,表明在应用纳米颗粒对聚合物的绝缘性能改良时,为获得最佳的介电性能,应根据实际需求来选择适当的填充浓度。     

脱气处理对XLPE及MAH/XLPE复合介质直流电场下空间电荷分布的影响

为了研究脱气处理对XLPE及其复合介质中空间电荷的影响,采用螯合荆与线性低密度聚乙烯接枝马来酸酐(MAH)作为填料,与XLPE共混制成掺杂浓度为0.5wt%的MAH/XLPE复合介质,并用电声脉冲法(PEA)测量了XLPE及MAH/XLPE复合介质在不同脱气时间下的空间电荷分布.通过实验发现,增加脱气处理的时间可以减少...     

Properties of Space Charge Distributions and Conduction Current in XLPE and LDPE under DC High Electric Field

Space charge behavior and conduction current in polyethylene under dc stress were investigated. One of the reasons for the different breakdown property in cross‐linked polyethylene (XLPE) from that in low‐density polyethylene (LDPE) may be based on the existence of cross‐linking by‐products in XLPE. Furthermore, a thermal history in cross‐linking process for XLPE may also cause of the difference. It is generally accepted that the existence of the cross‐linking by‐products increase the conduction current in XLPE under dc stress. It is also said that an anneal treatment in air atmosphere may affect to the electrical properties under dc stress. Therefore, we investigated the effect of the cross‐linking by‐products and the anneal treatment on space charge behavior and conduction current in polyethylene under dc stress. In our research, it is thought that the increasing dissipation power in XLPE is the cause of the breakdown in it under dc stress. Therefore, to calculate the dissipation power in the bulk of test sample, we measured the space charge distribution and the external circuit current simultaneously. Based on the results, we discussed the reason of the difference of the space charge properties in XLPE and LDPE focusing on the cross‐linking by‐products and the oxidation of the test samples.     

氯化聚乙烯共混对聚乙烯的空间电荷效应的影响

在直流电场作用下 ,用电声脉冲法测量了低密度聚乙烯 (LDPE)中空间电荷的分布 ,计算结果表明 ,异极性空间电荷严重畸变试样中的电场的分布。以少量氯化聚乙烯 (CPE)混入低密度聚乙烯中 ,大大降低了试样中的空间电荷 ,电场分布趋向均匀。在正负极性直流预压短路树枝试验中 ,分别提高试样短路树枝起始电压 2 6 8%和 36 3%。通过直流预压和电晕电荷注入后 ,短路过程中空间电荷分布的测量 ,提出氯化聚乙烯的作用机理在于降低了聚乙烯中陷阱的深度和密度。     

Factors of hetero space charge generation in XLPE under dc electric field of 20 kV/mm

This report deals with the mechanism of space charge accumulation in cross‐linked polyethylene (XLPE) under dc electric field. Space charge was measured by the pulsed‐electroacoustic method with applying dc stress of 20 kV/mm. A large amount of hetero space charge accumulated in fresh XLPE samples. Factors influencing the space charge accumulation were analyzed in regard to cross‐linking by‐products and antioxidant. No space charge was seen when the fresh sample was degassed to remove cross‐linking by‐products. Introducing acetophenone, one of the cross‐linking by‐products, in a degassed sample produces no space charge, suggesting that acetophenone itself could not be the direct factor of space charge formation. However, heating this sample up to 150 °C results in formation of hetero space charges as in virgin samples. Hence, it is concluded that hetero space charges may be formed when impurities, such as an antioxidant, dissociate thermally with the help of acetophenone and that the dissociated products are attracted toward both electrodes under a dc field to form the hetero space charges. © 1999 Scripta Technica, Electr Eng Jpn, 129(2): 13–21, 1999     

Some factors for the space charge formation in polyethylene

Information on space-charge behavior in thick insulated samples aids in understanding the dc characteristics of polymer-insulated dc cables. The pulsed electroacoustic method is used to investigate several space charge formation factors in 2 mm-thick polyethylene (PE). The following results were obtained. For measurement factors: (1) A polymeric semiconducting electrode provides a more accurate measurement than does a metal electrode as a result of better matching of acoustic impedance with PE. (2) Within a dc electrical stress range of several tens kV/mm, the space charge distributions under and after dc voltage application are almost the same; this is due to a comparatively long time of space-charge decay. (3) The space-charge distribution of a plate sample agrees with that of a cable sample having the same insulation thickness. For insulating material factors: (1) The amount of space charge in crosslinked polyethylene (XLPE) is much larger than that in low-density PE (base of XLPE). The space charge of XLPE continues to increase even after dc voltage application (24 h); that of LDPE reaches equilibrium with a few hours. (2) The aforementioned space charge difference between XLPE and LDPE is assumed to be caused by ionic impurities in XLPE, not by the additives themselves (acetophenon and cumylalcohol as byproducts of cross linking and antioxidant).     

应力对诱发空间电荷击穿的作用

电介质在生产和使用过程中通常会受到各种应力的作用,而应力作用与电介质的老化和击穿密切相关.本文利用电子束辐照的方法将空间电荷引入聚甲基丙烯酸甲酯(PMMA)和低密度聚乙烯(LDPE)样品中,在无外加电场下通过外加应力,可能诱发空间电荷脱陷导致树枝化击穿.讨论了应力诱发空间电荷击穿的机理,分析了影响应力诱发的空间电荷击穿的诸多因素,如样品中空间电荷分布情况,机械应力的作用形式(如压缩应力或是拉伸应力),样品中的水份,样品的介电常数等因素在空间电荷树枝化击穿过程的作用.     

拉伸对电缆接头双层介质中空间电荷的影响

为了研制冷收缩预制式电缆接头并改善其介电性能,研究了拉伸对乙丙橡胶和交联聚乙烯所组成的双层介质中空间电荷的影响。将不同拉伸状态下的乙丙橡胶试样分别和交联聚乙烯试样组成双层介质试样,测量了不同双层介质在加压和短路后的空间电荷分布。实验结果表明,从空间电荷的角度看,一定的拉伸有利于减少聚合物中空间电荷量;分析了实验现象和机理以及在电缆中的应用价值。     

聚酰亚胺薄膜中电荷输运机理和空间电荷特性

通过测量比较耐电晕型和普通聚酰亚胺薄膜空间电荷积聚的阈值电场,分析温度对空间电荷分布的影响,以此来研究聚酰亚胺薄膜中电荷输运机理和空间电荷的特性.试验结果表明:耐电晕型聚酰亚胺薄膜空间电荷积聚的阈值场强高于普通聚酰亚胺薄膜,纳米粒子的加入有效地提高了耐电晕型薄膜的介电性能.此外,温度的升高促进电极发射电荷,增大电荷的能量和电导率,使得空间电荷的数量不断地增加,入陷的位置逐渐向介质体内移动,这与聚酰亚胺薄膜绝缘老化、击穿关系密切,是空间电荷的重要特性.     

Electrical Breakdown and Space Charge Formation at High‐Temperature Region in Long‐Time Heating Treatment PVC

Polyvinyl chloride (PVC) is widely used as an insulating material in various electrical products. It is reported that an exothermic reaction reaching temperatures above 150 °C can be caused by overload currents or inferior electrical wire connections before the ignition of electrical products. The exothermic phenomenon may cause deterioration of insulating properties in PVC due to its chemical decomposition. It is necessary to clarify the degradation of insulating properties in PVC under thermal stress exceeding 150 °C for the safe use of electric products. In this investigation the space charge distribution and conduction current in the heat‐treated PVC sheet were measured in the range from room temperature to 200 °C in the presence of a dc electric field, using a high‐temperature PEA system. Positive charge injection and increasing conduction currents were observed before breakdown above 100 °C in 100 °C 300‐h heat‐treated samples and in non–heat‐treated samples. The results indicate the thermal breakdown process from the analysis of conduction currents and electric fields. In samples exposed to higher temperatures (150 °C 100 h), the breakdown strength deteriorated strongly in the range from room temperature to 90 °C. Increases in conduction current were observed in the entire temperature range before breakdown of the 150 °C 100‐h heat‐treated PVC. This indicates that heat treatment above 150 °C degrades the breakdown properties in the range from room temperature to 90 °C due to thermal decomposition accompanied by dehydrochlorination in PVC. The electric field is intensified near the cathode due to positive charge accumulation, and the breakdown strength begins to deteriorate only above 90 °C. This shows that thermal stress exceeding 150 °C causes deterioration of insulating properties and that the breakdown process is affected by space charge formation in PVC.