表面氟化聚乙烯中的空间电荷分析

根据在高场强下聚合物中的空间电荷主要来源于电荷的注入，而电荷的注入决定于聚合物的界面特性，用氟气表面处理聚乙烯试样改变表面层化学结构，来研究表面层的极性对空间电荷形成和注入的影响。测量了在不同场强下加压一定时间后短路条件下聚乙烯和表面氟化聚乙烯中空间电荷的分布情况，发现表面氟化聚乙烯的电荷注入的起始场强比聚乙烯试样的低，而且在相同场强下界面和介质中的空间电荷比聚乙烯多，在80kV／mm的高场强下表面氟化聚乙烯产生了空穴的注入，并通过测量材料的红外谱图对以上现象给出了微观的物理解释。     

不同直流场强下乙丙橡胶的空间电荷特性

乙丙橡胶在电缆绝缘中的应用日益广泛,空间电荷积聚成为影响其绝缘性能的关键因素之一。为了明确乙丙橡胶中空间电荷的行为特性及形成机制,文中基于PEA法对乙丙橡胶在直流场强下的空间电荷分布进行了研究,分析并讨论了不同场强下乙丙橡胶内空间电荷的分布规律以及其消散特性。实验结果表明:乙丙橡胶的电荷注入的阈值场强为2.5～5 kV/mm。根据不同场强下乙丙橡胶内空间电荷的行为特性,可将其分为4个阶段,分别为无电极注入阶段、双电极注入阶段、注入电荷迁移复合阶段、阳极注入主导阶段。此外,不同场强下陷阱密度及深度的差异会影响乙丙橡胶内部空间电荷的消散特性。在较高场强下,正极性空间电荷包的形成引起乙丙橡胶内部电场畸变,这可能会影响其介电强度,并使绝缘老化。     

水分含量对直流电场下油纸绝缘空间电荷动态特性的影响

为研究水分含量对直流电场下油纸绝缘内部空间电荷积聚特性与消散特性的影响,使用快速空间电荷测量系统与极化去极化电流测量系统分别测量了不同水分含量的油纸绝缘试样在直流电场下的电导情况与加压短路过程的空间电荷分布情况。结果表明:0. 91%水分含量条件下,油纸电导与场强呈现线性关系; 5. 21%水分含量条件下,电导与场强呈二次抛物线关系,且水分含量的上升使油纸绝缘电导提升多个数量级;相同水分含量条件下,外加场强的上升能增加电极处积累的同极性空间电荷。0. 91%水分含量条件下,油纸内部积聚的正极性空间电荷在加压过程中不断增加,且正极性空间电荷注入的深度不断提高; 5. 21%水分含量条件下,随加压持续,阴极积聚的同极性空间电荷向油纸内部迁移;不同水分含量条件下,加压过程中水分含量的上升使电极处积聚的同极性空间电荷与感应电荷增,而原先油纸内部积聚的正极性空间电荷减少。且油纸靠近电极处积聚的异极性空间电荷增多;短路过程中,水分含量的上升加快了油纸的放电过程,并抑制了电极处极性反转现象的出现。     

温度梯度效应对油纸绝缘材料空间电荷分布特性的影响

针对换流变压器及直流套管中油纸绝缘系统存在的内外温度不同的温度梯度效应对油纸绝缘中空间电荷分布的影响,利用电声脉冲法(PEA)研究了不同温度差下(△θ=0～40c),在场强分别为10～40 kV/mm时单层油纸中空间电荷特性及场强分布.实验结果表明:在各个电压及温度梯度下异极性电荷始终存在,这表明油纸绝缘中的杂质电离在...     

温度梯度下双层油纸绝缘系统的空间电荷分布特性

换流变压器为直流高压输电系统中的重要设备,但因其运行工况的特殊性,其内部油纸等绝缘材料往往承受较大的内外温度差异作用。针对换流变压器中双层油纸绝缘系统存在的内外温度不同的温度梯度效应对油纸绝缘中空间电荷分布的影响,利用电声脉冲法测量了不同温度梯度下（Δθ=0、20、40°C）,电压分别为-3.4、-10.2、-20.4kV（即平均电场强度分别为10、30、60MV/m）时双层油纸中空间电荷在20min内随时间变化规律及电场分布。实验结果表明：在低场强下,上下电极均有明显的同极性电荷注入;温度梯度使低温侧出现异极性电荷,并且随着温度梯度的增大、电压的升高,低温侧异极性电荷越来越多,从而使低温侧的场强畸变越来越大;加压后,2层油纸界面处开始积累与上电极相同极性的电荷,并且界面处电荷量随温度梯度及电压的增大而增大,但电荷密度出现饱和现象。经分析可知,油纸界面起到阻挡正负电荷通过的作用,而温度对电极注入特性及试样电导特性的影响为温度梯度影响空间电荷分布的主要原因。     

温度梯度对直流电压极性反转过程中瞬态电场的影响

高压电缆运行中由于导体发热而引起绝缘由内到外形成温度梯度。直流电压下温度梯度的存在必然会影响电荷的注入和迁移、加剧了位于绝缘层外表面的电荷积聚和场强畸变,降低绝缘击穿强度,也造成了电缆在断电或电压极性反转时的早期破坏。为此,基于电声脉冲(PEA)法,测量了聚乙烯板状试样在不同温度梯度场、50kV/mm直流电场协同作用下加压和极性反转过程中的空间电荷分布和最大瞬态场强。结果表明:温度梯度场-直流电场协同作用下,最大稳态电场出现在试样低温侧;而温度梯度场-电压极性反转协同作用下,最大瞬态电场却出现在高温侧。     

热老化对XLPE电缆绝缘空间电荷分布特性的影响研究

对110 k V XLPE电缆绝缘进行100℃和160℃加速热老化实验,通过电声脉冲法(PEA)测量了不同热老化试样的空间电荷分布特性。结果表明:当XLPE试样中有抗氧化剂存在时,氧化反应被抑制,试样中没有出现明显的空间电荷积聚。当抗氧化剂被消耗完毕后,100℃热老化试样内部靠近电极附近出现了明显的异极性电荷积聚,160℃热老化试样内部靠近电极附近出现了大量的同极性电荷积聚,试样中间出现了明显的异极性电荷积聚。热老化试样中的异极性电荷主要来自于热老化产物在电场下电离产生的离子对,而160℃热老化试样内出现的同极性电荷来源于电极的注入。在相同的条件下,未老化试样和100℃热老化试样中并不能观察到明显的同极性电荷的存在,因此,160℃热老化可能会降低XLPE的空间电荷注入阈值场强。     

直流和工频电压下油浸纸绝缘系统空间电荷特性的差异

绝缘材料在交流电压下的空间电荷特性和直流电压下的空间电荷特性同等重要。输电系统中交流变压器的数量巨大,变压器内绝缘用油纸绝缘材料在交流电压下的空间电荷特性如何,尚未见研究报道。首先采用直流电声脉冲测试系统研究了油浸绝缘纸在正/负极性直流场强下的空间电荷特性,然后采用改进的基于电声脉冲法的空间电荷测试系统研究了油浸绝缘纸在工频电压下的空间电荷特性。结果表明:电场极性对油浸绝缘纸内部的空间电荷分布有决定性影响,在正极性直流场强下,积聚在靠近铝板电极侧绝缘纸-绝缘纸界面处的电荷极性是正极性,而在负极性直流场强下,其是负极性;在工频加压的正半周,铝板电极处的电荷极性为负,而在工频加压的负半周,铝板电极处的电荷极性为正,90和270相位下油浸绝缘纸内部界面处积聚的电荷极性相反;与直流电压下相比,工频电压下油浸绝缘纸内部积聚的电荷显著减少。     

电极材料对高密度聚乙烯中空间电荷的影响

用电声脉冲法(PEA)测量了不同电极材料对高密度聚乙烯(HDPE)中空间电荷的影响.试样厚度为100μm,实验场强为50kV/mm,电极材料为铝(Al)和半导电橡胶(SC).实验发现对于Al-SC电极系统负压下电子和空穴注入较正压下少,并且镀铝电极可以有效抑制电荷的注入.     

温度梯度影响高压直流电缆用交联聚乙烯中空间电荷分布的作用机理

实验结果显示温度梯度会加剧交联聚乙烯(XLPE)低温侧的异极性电荷积聚,而在高温侧仅形成少量的同极性电荷。针对这一问题,分别基于杂质电离和注入载流子抽出受限这2种理论,探讨了温度梯度影响XLPE中空间电荷分布的机理,并指出介质内部存在的温度梯度可以通过影响载流子的迁移率来影响空间电荷分布,而两侧电极上的温度差会通过影响两侧载流子的注入和抽出来影响整体空间电荷的分布。为了验证以上推论,测量了不同厚度的试样在不同温度条件下的空间电荷分布,结果显示:在相同温度差和不同温度梯度下,薄试样中会积聚更多的异极性电荷,由此验证了介质内部的温度梯度可以促进低温侧异极性电荷的积聚;在相同温度梯度和不同温度差下,厚试样中会积聚更多的异极性电荷,由此验证了两电极间的温度差可以促进低温侧异极性电荷的积聚。     

变频电机用聚酰亚胺薄膜电老化特性研究

为研究变频电机用耐电晕型聚酰亚胺材料耐局部放电老化机理,采用电导电流法分别测量了普通聚酰亚胺薄膜(100HN)和耐电晕型聚酰亚胺薄膜(100CR)电晕老化前、经10kV/mm、20kV/mm电晕强度8h老化后的电老化阈值。结果表明,2种薄膜的电老化阈值随电老化强度的增加而减小,且耐电晕型薄膜的电老化阈值始终高于普通膜的阈值;在2种薄膜的空间电荷限制电流区内,耐电晕型薄膜的电流增长率较大,说明其中含有更多的浅陷阱,测试结果与其170°C下退极化电流测试结果一致。这些浅陷阱有效调节了聚酰亚胺薄膜中电场的分布,改善其耐电晕性能。     

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。     

Space charge and anomalous discharge currents in crosslinkedpolyethylene

Transient currents in cross-linked polyethylene (XLPE) have been investigated by using different parameters: temperature T, electrical field E_p and hydrostatic pressure P. Anomalous discharging currents flowing in the same direction as charging currents were observed from T=30 to 70°C, P=0.1 to 30 MPa and E_p=13 to 33 kV/mm. The space charge was measured using the pressure wave propagation method (PWP). Theoretical calculation revealed that this anomalous behavior can result from charge migration under a partial blocking condition at the electrodes. We discuss theoretical results which are in reasonable agreement with our discharge current measurements     

热老化对纤维素绝缘纸的空间电荷及陷阱特性的影响

为理解变压器用纤维素绝缘纸在其热老化过程中的空间电荷特性演变规律及其影响机制,采用电声脉冲法研究不同老化程度绝缘纸在不同电压等级(30、15和5kV/mm)下的加压和去压后的电荷密度分布规律,分析了绝缘纸热老化程度与其空间电荷特性演变规律间的联系。结果表明:纤维素绝缘纸体内电荷注入量及注入速率与外施电场等级成正比关系。热老化能够降低纤维素绝缘纸空间电荷注入的起始阈值,并减缓绝缘纸体内电荷注入和迁移的速率,从而削弱了体内电荷的复合现象。随着热老化程度的增加,纤维素绝缘纸体内陷阱的分布密度和陷阱能级的深度都将增大,致使材料体内残留电荷不仅总量逐渐增大,而且衰减速率逐渐降低。研究成果为理解热老化对纤维素绝缘纸空间电荷积聚和消散的影响机制提供了理论支撑。     

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。     

Effect of semiconducting screen on the space charge dynamic in XLPE and polyolefin insulation under DC and 50 Hz AC electric stresses conditions

In the past two decades, significant advances in space charge measurements in polymers have resulted in a better understanding of charge dynamics and their effect on material selection and processing. However, little attention has been given to the effect of semiconducting screens on space charge formation in the bulk insulation. This paper reports on space charge measurements on /spl sim/ 1.5 mm thick XLPE and polyolefinic plaques with different treatments and semicon electrodes, using the modified laser induced pressure propagation (LIPP) system. Samples were subjected to DC or 50 Hz AC electric stresses in the region of 25 kV/mm at ambient temperature. Emphasis has been placed on comparing the space charge characteristics of the two insulation systems with different semicon electrodes using an established method termed "X-plots" for analyzing data. The effects of sample treatment (i.e. degassing) on the space charge dynamics are also presented.     

空间电荷对低密度聚乙烯电气击穿特性的影响

为解决聚乙烯用作电线电缆绝缘材料时所受空间电荷问题的困扰,采用在低密度聚乙烯(low density po-lyethylene,LDPE)试品上施加直流预电压使其中积聚一定量的空间电荷,然后测量试品击穿强度的方法,研究了空间电荷对LDPE击穿特性的影响。结果表明,与未经过预电压处理的LDPE的击穿强度相比,在经过较低场强(50 kV/mm)预电压处理后,预电压与击穿电压极性相同时击穿强度提高了约9%,极性相异时击穿强度降低约14%;而经过较高场强(150 kV/mm)预电压处理后,预电压时LDPE中出现空间电荷包现象,预电压后同极性击穿强度提高约19%,而异极性击穿强度反而上升约16%。分析认为空间电荷包在LDPE中的运动导致了部分空间电荷的中和,使得空间电荷积聚量减少,同时LDPE中可能的缺陷得到了一定程度的老炼而使介质得到了均匀化,从而使LDPE的击穿强度得到了提高。     

Electric field criteria for charge packet formation and movement inXLPE

The formation of space charge packets in crosslinked polyethylene (XLPE) tapes from un-aged cable insulation has been studied utilizing the pulsed electroacoustic (PEA) technique. The 150 μm thick sheets were studied under constant applied DC field of 120 kV/mm at a temperature of 20°C for a period of 48 h. After an inception period of ~3.5 h, during which heterocharge accumulates at the anode and increases the local field there, a sequence of positive charge packets was observed to transit the sample starting from near the anode. Calculation of the internal field showed that the packets required a field of ⩾140 kV/mm for their initiation. Reduction of the applied field step-wise from 120 to 80 kV/mm indicated that the charge packet would keep moving as long as the local field at its front was >100 kv/mm, but with a reducing magnitude. A return to an applied field of 120 kV/mm confirmed that the local field required to initiate a new packet was >135 kV/mm. The results are discussed in terms of current theories of charge packet formation. The first packet appears to be a moving front of field ionization. The generation of subsequent packets is governed by the field at the anode and the balance of charge injection and extraction process, which occur there. The nature of the negative charges produced at the ionization front is not clear, but they are unlikely to be electrons     

Breakdown conditioning characteristics of long gap electrodes in a vacuum

An improvement in dielectric strength is required in vacuum circuit breakers (VCBs) intended for use in higher voltage systems. In order to develop higher voltage VCBs, it is important to improve the dielectric strength in a vacuum based on consideration of the vacuum breakdown mechanism. Particularly for gaps longer than 10 mm, little is known about the breakdown mechanisms and their quantitative analyses in a vacuum. This paper discusses the breakdown conditioning characteristics of long gap electrodes, under a non-uniform electric field in a vacuum. We treat gap lengths of up to 50 mm in this paper. The conditioning characteristics are investigated under impulse voltage applications. A negative standard lightning impulse voltage was applied to rod-plane electrodes made of Cu-Cr and SUS304 for different tip radii and gap distances until the conditioning effect was completed. We observed illumination spots on electrodes at each breakdown during the conditioning process and calculated the corresponding breakdown field strengths. Experimental results revealed that the tendency of breakdowns associated with long gaps is different from that for the short gaps. As a result, we clarified that the breakdown field strengths are nearly constant at 110-120 kV/mm at the distances longer than 10 mm, and the breakdown field strength is at its maximum when the gap distance is about 5 mm.     

Aging and polarization phenomena in PE under high electric fields

The influence of high electrical DC fields (>20 kV/mm) on aging, polarization and on the morphology of polyethylene (PE) is discussed. Infrared and positron annihilation spectroscopy measurements as well as capacitance measurements tend to suggest that the polymer morphology is modified by high fields. The author shows that the accelerated electrical aging characteristics of PE are linked directly to the morphology changes induced by the field. Below a so-called critical field, the activation volume of the aging process is dependent on the field-induced strain. Above the critical field, the amorphous phase is deformed significantly, and weak van der Waals bonds are broken, leading to another, faster, aging regime. There is an excellent agreement between the proposed model and experimental data obtained with various PE samples. The possible relation between the submicrocavity formation proposed in his aging model and various polarization measurements is discussed. It is his contention that strong charge injection occurs only after submicrocavity formation, i.e. after weak bond breakage. As is well known, the polarization currents obtained under high fields are controlled by space charges. It seems that the wave packets and the negative resistance observed at >100 kV/mm in PE are associated with a steady state in field-induced defect formation. This suggests that space charges are related to the formation of submicrocavities and, therefore, are a consequence, not a cause, of high field aging.