基于Kerr电光效应测量的液体空间电荷产生及其分布特性

空间电荷是影响绝缘介质耐电强度,导致电场分布畸变和电介质击穿的重要参数之一。为了更深入地开展液体中空间电荷产生及其分布特性的试验及相关机理研究,采用基于Kerr效应的空间电荷高速CCD(charge-coupled device)测量系统,实现了碳酸丙烯酯中黄铜、不锈钢、铝3种电极材料在冲击电压下光强分布特性的测量;结合改进的图像处理技术,对极间电场随时间变化的动态发展过程进行反算;同时依据传统电击穿理论和双电层理论对空间电荷产生及发展的微观机理进行分析。研究表明:在不同材料以及不同电压极性下,空间电荷分布呈现出双极注入、正电荷注入及负电荷注入3种显著的注入特征,其中双极注入提高了液体电介质的冲击绝缘性能,正电荷注入和负电荷注入使得液体电介质绝缘性能降低,其注入特性的差异与外加电压大小、电极材料、电极表面状态等因素有关。     

第十届全国工程电介质学术会议征文通知

中国电工技术学会第十届全国工程电介质学术会议定于2005年10月28～30日在四川成都西南交通大学举行。会议旨在为国内工程电介质领域的研究人员和企业界知名人士提供一个平台,以分享知识、经验和创新思维。会议将组织专题研讨会并邀请相关专家,对一些热点问题展开讨论。详情请见网址:http://madil.swjtu.deu.cn/conference/conference.html一、征文内容(1)电介质理论及应用进展综述(2)介电性能、空间电荷、表面与界面现象(3)局部放电、树枝化与预击穿(4)老化与寿命评估(5)新型电介质功能材料(陶瓷、复合材料、纳米、生物材料等)(6)微电子、…     

第六届国际电介质材料性能和应用会议

第六届国际电介质材料性能和应用会议将于2000年6月21～26日在西安交通大学召开,会议将讨论当前国际绝缘技术的基础研究和应用,电介质的介电现象和应用,绝缘及其产品的测试技术和诊断。会议还将邀请高压、绝缘学科世界著名的权威人士作专题报告,邀请世界著名的电力设备制造商和仪器厂在会场展览先进产品。欢迎国内有关单位参展,欢迎踊跃投稿。征文内容如下:(1)电介质的介电现象及其应用。(2)介电现象:极化、介质损耗、电导和击穿。(3)空间电荷、表面和界面现象。(4)电力设备和电力传输系统的绝缘。(5)绝缘材料的树枝化和老化。(6)局部放电、…     

水分和温度联合作用时油浸绝缘纸空间电荷特性

油纸绝缘介质内部积聚的空间电荷与其绝缘性能密切相关,它可以导致介质内部电场分布的畸变,对局部电场起到削弱或加强的作用,若电场畸变严重,将引起绝缘材料的击穿和老化,直接影响绝缘系统的可靠性和安全性。水分和温度被认为是危害油纸绝缘介电强度和绝缘寿命的最主要因素,为了解它的特性,采用电声脉冲(PEA)法研究了油纸绝缘介质在温度和水分联合作用下空间电荷的注入、迁移、积聚和消散特性,进一步分析了水分和温度联合作用对油浸绝缘纸直流击穿和电荷积聚行为的影响。结果表明:油浸绝缘纸的水分含量和温度越高,其内部正负电荷的注入和迁移就越显著,而且油浸绝缘纸内部积聚的空间电荷在撤去外加场强后消散得也越快;对于未被外加场强击穿的油浸绝缘纸,其内部慢速运动电荷的量随着水分含量和温度的升高而减少;而对于被外加场强击穿的油浸绝缘纸,在击穿前其内部仅积聚极少量的负电荷。     

基于Kerr电光效应的冲击电压下液体电介质空间电荷高速CCD测量

空间电荷的存在直接影响液体电介质的绝缘击穿性能,为了更好地研究空间电荷的动态变化过程,建立了基于Kerr电光效应的冲击电压下液体电介质空间电荷的高速电荷耦合器件(CCD)测量系统。运用高精度光电传感器的测量方法,得到了室温下液体碳酸丙烯酯的Kerr常数。进而通过高速CCD的动态光电测量,并结合图像处理技术,求取了冲击电压下平行板铜电极间电场和空间电荷的动态分布曲线。实验研究表明:在平行板铜电极间,当液体介质中电场达到一定程度时会出现空间电荷的注入与输运,使得极间电场呈现出中间高两边低的分布情况。另外还分析了空间电荷的分布和输运对液体绝缘特性的影响,该研究为分析冲击电压作用下液体介质中空间电荷的产生机制及空间电荷对流注放电的影响奠定了基础。     

空间电荷碰撞电离退陷阱化导致介质击穿的理论

引言聚合物介质在高电场或电子束辐照下会产生带电现象,建立空间电荷。当时带电的介质进行短路放电时,可引起介质的击穿或接地树枝的产生。为什么这些空间电荷在形成过程中没有引起介质击穿,反而在短路释放瞬时引起介质的击穿破坏呢? 本文针对这一现象开展研究,探讨空间电荷在退陷阱化过程中引起介质击穿的机理,并从实验上进行研究和验证。 1.理论介质中的空间电荷由自由电荷和陷阱电荷组成。其中陷阱电荷可由场发射、热发射或者热、场发射实现退陷阱化,成为自由电荷。最近,有作者指出,入陷载流子还可以通过     

固体电介质空间电荷研究进展

随着空间电荷测量技术在近30年的巨大进步,固体电介质空间电荷研究成为国际研究热点.本文论述了固体电介质空间电荷检测技术从有损发展到无损的过程,分析对比了目前应用较普遍的压力波法和电声脉冲法的原理及特点,介绍了国内空间电荷测量技术研究的发展特点.在此基础上,从预电压效应、形态效应、空间电荷包现象、空间电荷的动态测量等方面论述了空间电荷效应对电介质电气性能的综合影响,对利用空间电荷进行固体电介质陷阱深度等性能参数的研究进行了探讨,强调了空间电荷在电介质材料的开发和评估中的重要作用以及不同应用领域对空间电荷特性的不同要求.指出空间电荷测量技术的进步为固体电介质的研究提供了新的有力手段,但仍需更多的深入研究,以完善电介质理论和促进空间电荷的工程应用.     

环氧及其复合物的空间电荷研究进展

空间电荷在电介质内部的积聚会导致其内部电场的畸变,从而明显的影响绝缘电介质其他方面的电性能,如电导、老化和击穿特性等。环氧树脂由于具备优异的机械性能、热性能和介电性能,所以在电气绝缘领域被广泛使用,其空间电荷的研究,也是近几十年来国际研究的一个热点。文中综述了环氧及其复合物中空间电荷的研究概况。从固化剂类型、电场强度、电极材料、温度、湿度、掺杂粒子等方面论述了这些因素对环氧中空间电荷的影响,并探讨了这些因素影响空间电荷的原因和影响的强弱。     

环氧树脂绝缘电树枝劣化研究进展

环氧树脂因具有优良的耐热性、机械强度、电气绝缘性能和良好的可加工性而广泛应用于电工装备绝缘的浇注、浸渍和封装等领域.该文根据国内外参考文献综合论述了由环氧树脂绝缘电树枝劣化引起的绝缘击穿现象.基于环氧树脂空间电荷集聚与迁移、局域电场形成、紫外辐射和机械应力断链理论,阐述了环氧树脂电树枝引发机理和劣化过程.结合电气设备运...     

基于分形理论的SF_6/N_2混合气体放电仿真

为了研究SF_6/N_2混合气体电介质击穿现象,利用编写的Matlab程序对放电通道发展过程进行数值模拟,并结合分形几何原理计算放电树枝的分形维数。基于分形理论,建立了考虑空间电荷分布和引入物理时间的棒-板分形放电仿真模型,通过有限元方法(FEM)计算空间电场,并首次结合通量校正传输(FCT)法求解带电粒子连续性方程,研究了不同发展概率指数、不同放电阈值和SF_6含量变化下分形放电特性。结果表明:概率指数越大,SF_6含量越高,则分形维数越小,放电树枝分叉也越少;体积含量50%/50%的SF_6/N_2混合气体放电分形维数D=1.219 2,整个放电过程流注发展平均速度为1.15Mm/s,并得到了不同时刻空间电荷及轴向电场与电子浓度的分布。     

油纸绝缘介质的空间电荷积聚与消散特性

油纸材料的绝缘问题在换流变压器、直流套管、直流电缆等高压大型直流设备大量应用的情况下显得十分突出。为探讨高压直流设备绝缘的最主要问题—空间电荷效应,应用电声脉冲法(PEA)对油纸绝缘材料的空间电荷特性进行了研究。有关外加场强对油纸材料中空间电荷积聚情况的影响和在较高场强下油纸材料的击穿破坏与空间电荷关系的研究结果表明:①低场强下油纸材料中空间电荷以电离产生为主;而在较高场强下,先后在阴极和阳极产生了同极性载流子注入。②相对于聚乙烯而言,由于油纸材料的电导率较大,材料内的空间电荷在外加电场撤去后很快消散。③空间电荷的注入和运动会导致油纸材料的劣化和破坏。油纸材料中的空间电荷快速消散现象有利于直流设备在极性反转条件下的运行,为阐释油纸绝缘良好的长期性能提供了有重要意义的试验依据。     

Evidence of strong correlation between space-charge buildup andbreakdown in cable insulation

Many processes have been considered over the years to explain the origin of breakdown in cable insulation. Such effects as space charge build-up, tree growth, charge injection, etc. have all been discussed. Various techniques are now available to measure, in a nondestructive way, space charge distributions in insulators. These techniques, for instance the pressure wave propagation (PWP) method, can be used under applied electric stress and thus make it possible to follow the development of space charge in selected regions of the insulators. In this paper we present new evidence linking space charge buildup, tree growth and breakdown in XLPE. We have used the PWP method to monitor the charge distribution as a function of time under dc stress in high insulating thickness cable. We show that for certain insulation systems the space charge buildup can increases the local field to a value which is more than 8× the applied electric field, leading to breakdown. Post-mortem analysis followed by optical microscopy shows the presence of electrical trees, the breakdown channel being centered on one of them. The study of space charge evolution in practical insulations permits an understanding of the role of space charge in dc breakdowns. This understanding enables the development of technologies to suppress this effect and hence realize practical dc XLPE transmission cables     

The contribution of field-induced morphological change to the electrical aging and breakdown of polyethylene

A brief review of the early literature is given which provides evidence that electrically-induced mechanical stresses make an important contribution to the electrical breakdown of solid dielectrics. Special attention is given to polyethylene and the manner in which this semi-crystalline polymer yields under mechanical stress by microvoid, crack and craze development in the amorphous phase between the lamellar crystallites. The nature of the forces induced by an electrical field is considered and it is shown that a significant component of tensile stress is generated in a direction orthogonal to the field and can become large as breakdown is approached. This suggests a correlation between the responses of the polymer to mechanical and electrical stresses and consequently the importance of morphology in determining the latter. The likely effect of field-induced morphological change on charge transport and electrode processes is described and its underlying contribution to possible aging markers for polyethylene, such as high field conduction, electroluminescence, space charge and charge packets is considered.     

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.     

Space charge in XLPE power cable under dc electrical stress andheat treatment

It is well known that the existence and accumulation of space charge in insulation can be harmful to polymer power cable. Although there is much research done on space charge distribution in various samples, there are still some important problems left unsolved, such as the mechanism of formation and elimination of space charge in dielectrics. Because of its superiority, the pulsed electro-acoustic (PEA) measurement method is used widely in the measurement of space charge in various geometries of samples such as the multiple layer plate and cylindrical cables. The space charge in crosslinked polyethylene (XLPE) power cable under dc voltage and heat treatment is investigated by the PEA method in this paper. After heat treatment, the space charge, which previously formed in cable insulation under the applied voltage, disappears. If electrical stress is applied to the insulation again, space charge will appear once more. However, after the cable is heated and degassed in vacuum for a long time, no matter how long the dc voltage is applied to the cable, no more space charge will be formed in the cable. The mechanism of formation and elimination of space charge under the effect of electrical and thermal stress is discussed     

Dynamics of voltage polarity reversal as the controlling factor inspace-charge induced breakdown of insulating polymers

Our investigation is focused on the understanding of high-field phenomena in polymers. In highly insulating materials such as polyethylene, space charge has a strong influence on both the short and long term breakdown strengths. The aim of this report is to demonstrate and discuss the importance of the dynamics of voltage polarity reversal at the injecting needle electrode on space charge induced breakdown. Evidence of space charge injection is provided by the observation of local breakdown generated by grounding of the sample after the polarization (so-called `grounding' tree). The effect which is polarity dependent, can be observed only when the sample is short-circuited immediately after charging. Field computation is performed versus injected charge and a critical charge density is derived in order to explain polymer breakdown upon grounding. The time dependence of the effect is explained by space charge relaxation. Polymer degradation under ac voltage is discussed on the basis of this interpretation     

Temperature effect on space charge dynamics in XLPE insulation

This paper reports on space charge evolution in crosslinked polyethylene (XLPE) planar samples approximately 1.20 mm thick subjected to electric stress level of 30 kV_dc/mm at four temperatures 25, 50, 70 and 90 degC for 24 h. Space charge profiles in both as-received and degassed samples were measured using the laser induced pressure pulse (LIPP) technique. The DC threshold stresses at which space charge initiates are greatly affected by testing temperatures. The results suggest that testing temperature has numerous effects on space charge dynamics such as enhancement of ionic dissociation of polar crosslinked by-products, charge injection, charge mobility and electrical conductivity. Space charge distributions of very different nature were seen at lower temperatures when comparing the results of as-received samples with degassed samples. However at higher temperature, the space charge distribution took the same form, although of lower concentration in degassed samples. Space charge distributions are dominated by positive charge when tested at high temperatures regardless of sample treatment and positive charge propagation enhances as testing temperature increases. This can be a major cause of concern as positive charge propagation has been reported to be related to insulation breakdown     

纳米ZnO对聚乙烯电老化过程中空间电荷及击穿特性的影响

聚乙烯是电气绝缘领域应用最广泛的聚合物材料之一。根据电老化过程中电子和空穴复合产生的紫外辐射能导致聚合物降解理论,将少量纳米ZnO与低密度聚乙烯熔融共混,研究了电晕老化不同时间后复合材料空间电荷以及击穿特性的变化。结果表明添加纳米ZnO能有效提高聚乙烯绝缘的耐电晕老化寿命。     

Measurements of acoustic waves generated by electrical breakdown in a polypropylene film

Electrical breakdown of a polymer film generates a pressure wave that is believed to include information about the breakdown initiation point. We measured the breakdown pressure wave and the space charge distribution up to the electrical breakdown field by using the pulsed electro‐acoustic method in a 30 µm thick polypropylene film. We discuss electrical breakdown phenomena based on the breakdown pressure wave and the dependence of the space charge distribution on the applied field and temperature. At room temperature, the observed breakdown pressure wave had a pulse‐like shape with a width that depended on the polarity of the applied field. Positive space charge accumulation was observed near the cathode as a hetero space charge near the electrical breakdown field. At 60 °C, the width of the breakdown pressure wave showed no dependence on the applied field polarity and positive space charge accumulation was observed inside the film near the electrical breakdown field. These experimental results suggest that electrical breakdown phenomena are affected by hetero space charge accumulation and that the initiation point of electrical breakdown corresponds to the position of hetero space charge accumulation in 30 µm thick polypropylene film. ©1999 Scripta Technica, Electr Eng Jpn, 126(3): 1–8, 1999     

±320kV直流电缆交联聚乙烯/三元乙丙橡胶附件击穿特性

高压直流电缆接头与终端为电缆系统故障的多发点,其击穿强度为直流输电系统安全稳定运行的重要基础。文中以±320 kV高压直流海底电缆中交联聚乙烯(cross linked polyethylene,XLPE)/三元乙丙橡胶(ethylene propylene diene monomer,EPDM)附件为研究对象。首先,研究电缆及附件负荷循环耐压试验,发现附件界面为击穿薄弱环节;其次,研究绝缘材料电导率随温度变化特性对电场分布的影响规律,通过有限元仿真模拟电缆空载和满载运行时附件的温度分布与电场分布,发现最大电场出现在电缆绝缘靠近附件应力锥一侧,为29.5 kV/mm,低于附件材料的击穿场强;最后,研究界面在直流电场下空间电荷特性对电场分布规律的影响,通过电声脉冲法测试复合叠层片状样品介质界面的空间电荷及其电场分布,发现场强畸变率约为100%~200%。同材料本征绝缘匹配相比,界面空间电荷积聚对附件内部电场造成的畸变程度更严重,在后续附件提升中应更注重开发抑制空间电荷的绝缘材料。