Investigation of space-charge effect on the AC treeing mechanism in an LDPE film by tsc and TSSP measurement

When an ac voltage is applied to a low-density polyethylene (LDPE) film placed under a needle-plane electrode system, there is a possibility of the formation of the space-charge field in the vicinity of the needle electrode by electrons (or holes) injected from the needle electrode. In this paper we investigated the properties of the space charge, e.g., the total amount of trapped charge formed in the vicinity of the needle electrode by using electrical measurements of thermally stimulated current (TSC) and thermally stimulated surface potential (TSSP). From the investigation, it was concluded that a space-charge field is formed in an LDPE film by the application of the ac voltage, and that the total amount of trapped charge by the application of the ac voltage is less than that by the application of the dc voltage, etc. Finally, on the basis of the present experimental results, we studied the space-charge effect on the ac treeing mechanism.     

基于α松弛分析CB/LDPE纳米复合介质空间电荷特性

分别以导电炭黑(C-CB)和绝缘炭黑(I-CB)作为纳米填充相,研究不同性能炭黑(CB)对低密度聚乙烯(LDPE)空间电荷特性的影响。采用多种测试方法对CB微观形貌和表面化学特性进行表征。利用电声脉冲(PEA)法测量LDPE及其纳米复合介质的空间电荷分布,并结合动态机械分析法(DMA)和热刺激电流法(TSC)探索CB改善LDPE空间电荷特性的作用机理。结果表明:C-CB比I-CB具有更长的链状结构和较少的表面基团,可与LDPE产生更强的相互作用;C-CB/LDPE和I-CB/LDPE纳米复合介质均能够有效地抑制空间电荷积聚,其中前者的空间电荷抑制能力更强。分析认为复合介质空间电荷性能改善是由于CB与LDPE相互作用,减少了参与α松弛的分子形成的缺陷数量,降低了LDPE内的陷阱密度。     

Charge storage in corona-charged polypropylene films analyzed by LIPP and TSC methods

Negatively corona-charged 50-/spl mu/m-thick polypropylene (PP) film is measured using laser-induced pressure pulse (LIPP) and thermally stimulated current (TSC) in order to study the charge storage mechanism in the PP film. The LIPP can reveal the space-charge distribution in the depth direction of the PP films and the TSC can be used to measure the energetic depth of the charge trap. The LIPP shows that negative charge is deposited on the charged surface of the sample. Almost all surface charges are removed by soaking the sample in ethanol. However, about 5% of the surface charge is injected into the sample up to a depth of about 7 /spl mu/m from the surface. The injected charge is not removed by the dip-in-ethanol method because the ethanol does not penetrate into the sample. The injection of the surface charge increases with corona-charging temperature. Besides the negative charge injection, the injection of positive charge from the opposite surface is also observed when the sample is charged at higher than 60/spl deg/C. In addition, negative bulk charge is formed when the sample is charged at higher than 80/spl deg/C. The LIPP profile is compared with the TSC spectrum. It is shown that the space charge observed using LIPP disappears when the temperature of the sample exceeds 80/spl deg/C. However, TSC is observed at even higher than 80/spl deg/C. This indicates that the TSC is observed even after the disappearance of the space charge measured using LIPP.     

蒙脱土改性聚乙烯复合材料的高场介电性能研究

利用熔融插层法制备了聚乙烯/蒙脱土纳米复合材料,研究蒙脱土对聚乙烯介电性能的影响。研究分析了纯聚乙烯和不同的聚乙烯/蒙脱土复合材料的树枝化性能,通过直流预电应力电树引发试验,探讨了空间电荷的极性效应对不同材料树枝化性能的影响。试验结果表明:与纯聚乙烯和其他复合材料相比,加入相容剂的聚乙烯/蒙脱土纳米复合材料的电树潜伏期更长,电树生长速度更慢,而且显示出与LDPE不同的极性效应。不同材料的热激电流(TSC)试验结果显示:聚乙烯/蒙脱土纳米复合材料的松弛时间分布展宽,峰值增高,说明在纳米复合材料中引入了更多的陷阱能级,这些陷阱调制了载流子浓度和迁移率,从而抑制了树枝的起始与生长。     

High-field conduction and carrier traps in polyethylene copolymerized with various monomers

The electrical breakdown and electrical conduction of ethylene copolymers have been studied. The electric strength of ethylene copolymers containing an optimum content of halogen moieties such as bromophenyl and fluoroethylene groups was found to be higher than that of LDPE over the wide temperature range from ?196°C to 90°C. Also, conduction currents in the copolymers were suppressed at high electric fields. X-ray-induced thermally stimulated currents (TSC) revealed that halogen comonomers act as carrier traps with a depth of about 0.4 eV. Consequently, the introduction of comonomer-containing halogen groups into polyethylene suppresses electron acceleration as a result of an increase in trapping and scattering of conduction electrons. This leads to an increase in electric strength which is determined by the electron avalanche breakdown.     

What is TSC?

The technical background for the thermally stimulated current (TSC) technique is presented. The effect of metal polymer contacts on the TSC method is discussed. The transitions in amorphous polymers are described. The dynamic properties of polyethylene using TSC method are given     

Thermally-stimulated current and dielectric loss measurement ofpolypropylene and Teflon-FEP films immersed in diarylethane

Some properties of oil/PP (biaxially stretched polypropylene) and oil/FEP (Teflon FEP) composite insulators have been investigated with TSC (thermally stimulated current) techniques. The oil/PP system showed three TSC peaks originating from carriers captured in the swollen surface region of the PP. The TSC spectra depended strongly on the polarity of the poling voltage and on the impregnating temperature. Their analysis yielded information on the carrier traps existing near the PP surface in the oil/PP interface region. On the other hand, the TSC spectrum of the oil/FEP system has a small impregnating temperature dependence and a small effect of the poling voltage polarity. The difference in TSC between oil/PP and oil/FEP systems is closely related to the difference in the oil-polymer interaction. The TSC is a useful method for investigating carrier traps in the surface region and their change due to the oil-polymer interaction. To investigate further the relation between the carrier traps and tanδ, collecting bias TSC was measured on a specimen to which an ac voltage was applied. The results indicate that the decrease in tanδ during the ac voltage application depends on the amount of trapped carriers near the polymer's surface or, the decrease in carriers in the oil     

Charge carrier trapping in a one-dimensional system

Theoretical models for one-dimensional structures, consisting of traps and recombination centers, are considered. The kinetics of trapping and recombination is studied numerically, especially in the case of thermal relaxation phenomena such as thermoluminescence (TL) and thermally stimulated current (TSC). Some peculiarities of TL and TSC are shown, which result from specific spatial arrangement of traps. The possibility of occurrence of an additional 'displacement' peak on TL and TSC measurement curves is predicted. Possible consequences for experimental studies of TL and TSC are discussed     

高压脉冲电压下聚酰亚胺的电老化机理

在高压脉冲电压下对聚酰亚胺膜的绝缘寿命、不同条件老化后试样的表面形貌及热刺激电流(thermally stimulated current,TSC)进行了测试。TSC曲线在20~200℃温区内由I峰和II峰两个单峰叠加而成。通过图谱分析发现聚酰亚胺膜早期电老化时陷阱的发展可用陷阱理论解释,但老化后期陷阱理论中陷阱密度变化规律的描述不再适用。电老化主要破坏聚酰亚胺内II峰对应的大分子链,I峰对应的分子链中小运动单元破坏并不严重。聚酰亚胺膜的寿命与频率成反比,频率越高对大分子链的破坏速度越快,表明通过II峰对应的活化能和电荷变化量来判断聚酰亚胺的绝缘老化程度是可行的。     

A review of thermo-stimulated current

Various areas of application of thermo-stimulated current (TSC) spectroscopy, used for studying insulating materials, are reviewed. The characteristics of this technique are compared with those of the other thermally stimulated spectroscopies. The origins of TSC are briefly cited. Examples of the identification of TSC peaks with ionic or molecular movements (inorganic or organic materials) are given     

复合热激电流曲线陷阱参数的计算

首先介绍了一种从单一热激电流曲线估计载流子的陷阱参数 ,如活化能E、频率因子s和动力学级数b的方法。然后将该方法用于计算复合热激电流曲线 ,以获得相应于各峰的陷阱参数 ,通过将它们代入单峰理论公式进行计算 ,最后完成复合热激电流曲线的分解。     

Determination of Activation Energies and Electric Dipole Moment of In‐Plane Highly Electrically Conductive Hetero‐C12TCNQ/C20 LB Films Using Thermally Stimulated Current

The activation energies of in‐plane highly electrically conductive 2‐dodecyl‐7,7,8,8‐tetracyanoquinodimethane (C₁₂ TCNQ)/arachidic acid (C₂₀) hetero‐LB films and C₁₂TCNQ homo‐LB films were determined by thermally stimulated current (TSC) measurement. The TSC curves for the upper Al electrode/C₁₂TCNQ/C₂₀/lower Al electrode were nearly of the same shape as those for the upper Al electrode/C₁₂TCNQ/lower Al electrode. The activation energies of the upper Al electrode/C₁₂TCNQ/C₂₀/lower Al electrode and upper Al electrode/C₁₂TCNQ/lower Al electrode were 0.9–1.3 eV at 55–80^°C and 1.6–1.8 eV at 105–120^°C, respectively. The TSC curves for the upper Al electrode/C₁₂TCNQ/C₂₀/lower Al electrode and upper Al electrode/C₁₂TCNQ/lower Al electrode had two peaks at 55–80^°C owing to the depolarization of the electric dipole and two peaks at 105–120^°C owing to the movement of space charges in the C₁₂TCNQ molecule. Copyright © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

纳米复合绝缘材料的热剌激电流测试研究

研究纳米复合聚酰亚胺薄膜热剌激电流(TSC)测试的影响因素和陷阱参数计算方法，并对不同样本和不同老化条件下的TSC结果进行分析。通过对不同的测试条件(包括不同的数据平滑方法、极化温度，极化电压、极化时间等因素)的TSC曲线特征分析，研究不同测试条件对纳米复合绝缘样本TSC测量结果的影响，并用高斯拟合对TSC曲线进行峰分离和陷阱参数计算。根据这些结论，对不同样本和老化条件下的热刺激电流特征进行分析和比较，得到热刺激电流和PWM脉冲电压下绝缘微观特征之间联系。结果表明，测试条件对TSC结果有明显影响，合适的测试方法有助于研究纳米复合聚酰亚胺薄膜在PWM电压作用下的微结构变化。     

A study of dielectric relaxation in aluminosilicate-filledlow-density polyethylene

Space charge formation in low-density polyethylene (LDPE) filled with zeolites and clays has been investigated by the thermally stimulated current method. The presence of fillers affects the dielectric properties due to additional dielectric relaxation phenomena, which depend on the structure of the inorganic filler. Pores or cages existing in the zeolite frame enable their compensated ions to move away from their neutral position under electric field to form dipoles of very low activation energy and high attempt-to-escape frequency. The activation energy is related to the pore sizes of zeolites. However, kaolin-based clay which has movable cations on its surfaces form an interfacial dipole between the LDPE and clay. A `Maxwell-Wagner' interfacial relaxation behavior was observed in the clay-filled LDPE system. The activation energy of interfacial relaxation of the clay-filled LDPE system is higher than that of dipole relaxation of the zeolite-filled LDPE     

Thermal instability of electromechanical films of cellular polypropylene

An investigation has been undertaken into the thermal instability of electroactive, cellular polypropylene, in particular concentrating on the interaction between mechanical and electrical properties. A range of mechanical and electrical techniques have been applied including, dynamic mechanical analysis (DMA), thermo mechanical analysis (TMA), thermally stimulated currents (TSC) and admittance spectroscopy. Evidence is presented which indicates that the initial stages of a TSC spectrum is dominated by thickness changes in the foam. Changes in mechanical dimensions correlate well with temperature-induced changes in resonator parameters.     

Analysis and discussion on conduction current based on simultaneousmeasurement of TSC and space charge distribution

A new analysis of conduction current distributed in dielectrics based on simultaneous measurements of thermally stimulated current (TSC) and time dependent space charge distribution is proposed. A new system pulsed electro-acoustic (PEA) method has been developed to enable simultaneous measurement of the TSC and the dynamic space charge and electric field distributions as a function of temperature within insulators. With the new system, the relationship between the TSC and the time dependent electric field distribution in electron beam (e-beam) irradiated PMMA has been investigated. From the time dependent electric field, the displacement current in dielectrics is obtained. The TSC is a typical external current which is represented as an addition of the displacement current and a conduction current in dielectrics. This paper makes it clear that the conduction current as a function of position is determined by the simultaneous measurement of the external current and the dynamic space charge distribution     

基于TSC测试的硅橡胶复合绝缘子伞裙材料老化特性研究

为利用热刺激电流(thermally stimulated current,TSC)测试手段对复合绝缘子老化特性进行评估,以现场运行复合绝缘子为研究对象,进行了TSC测试及憎水性等级喷水分级测试。初步探寻了伞裙位置、运行年限及环境污秽等级等因素对现场运行复合绝缘子伞裙材料TSC特性的影响规律。结果表明,绝缘子串上场强分布较高的位置、有较长运行年限及重污区的绝缘子,其伞裙材料的TSC曲线峰值较大,相应的陷阱电荷量也较大。对2种评估复合绝缘子伞裙材料老化的测试手段进行了对比分析,可知TSC测试结果能更加明显地区分复合绝缘子伞裙材料老化程度的不同,对于老化性能的评估更具优越性。     

DC electrical treeing phenomena and space charge

Influence of space charge on dc tree propagation is studied using many insulating polymer materials under divergent fields. The inception voltage and the propagation of dc treeing are affected strongly by space charge. Space charge formation in polymers was observed directly by using thermally stimulated current (TSC) techniques under divergent field. These results of the space charge effect on dc treeing phenomena are consistent with those obtained by the TSC method. From these results, the origin of space charge in polymers and the suppression techniques for space charge formation were discussed     

Surface potential on LDPE and PP films after removal of the upperdisk electrode

The potential distribution was measured on the free surface of low-density polyethylene (LDPE) and polypropylene (PP) films which had been inserted between plane electrodes after the removal of the upper brass disk electrode. The polarity of the surface potential was always the same as that of the applied step voltage which had been subjected to the upper electrode for a while and then shorted. The absolute value of the surface potential tended to increase to a constant value of ~650 V with increasing applied voltage and application time for both polarities. There was no appreciable difference in the surface potential between PP and LDPE when the applied voltage and its application time changed. However, the increase in the shortcircuit time tended to increase the surface potential for LDPE only, while it did not change that for PP. The effect of a longer shortcircuit on the surface potential increase for the LDPE films for both polarities could be explained by bipolar injection     

合成绝缘子材料的TSC试验研究

通过采用热刺激电流法对合成绝缘子材料进行热刺激电流(TSC)的探索性对比测试,力图探索热刺激电流法在评价合成绝缘子特性中的应用可能性.文中对比了同一厂家的两批合成绝缘子试样的TSC特性,初步的试验发现,新旧合成绝缘子之间的TSC测试结果是明显不同的,结合试样的憎水性试验以及微观结构的分析,表明TSC测试结果在一定程度上能够与合成绝缘子材料的老化联系起来.通过深入系统的研究合成绝缘子的TSC特性和合成绝缘子材料的老化特性之间的关系,将能够为合成绝缘子老化特性及老化程度的评价提供新的方法.