Three-dimensional PEA charge measurement system

The pulsed electroacoustic (PEA) method already has been used widely to measure the space charge distribution in the pulsed electric field direction of sheet specimens. We have developed a new PEA measurement system which can observe the space charge distribution in three dimensions. Since the PEA system is not damaged if the specimen breaks down, the new PEA system can measure the space charge distribution of dielectric materials safely and nondestructively within a short time     

Electrical Breakdown Properties and Space Charge Formation in High Temperature Region in Ultraviolet Ray Irradiated PVC

Polyvinyl chloride (PVC) is the most popular insulating material for electric wiring instruments. However, an exothermic reaction above 150 °C may cause deterioration of the insulating properties of PVC. Therefore, it is important to clarify the heat degradation in PVC, not only to investigate the ignition of electrical wiring products but also to use electrical products safely. It is known that ultraviolet (UV) irradiation causes chemical deterioration of PVC and an increase in its conductivity. Generally, it has been thought that the electrical breakdown properties, electrical conduction, and insulating performance are affected by space charge accumulation in an insulating material. A high temperature pulsed electroacoustic (PEA) system usable up to 250 °C has been developed, and the PEA system can measure the space charge distribution and conduction current in the high temperature range simultaneously. In this investigation, the space charge distribution and conduction current were measured up to electrical breakdown in a non‐UV irradiated sample (normal PVC) and in 353 nm and 253 nm UV‐irradiated PVC samples in the range from room temperature to 200 °C in a DC electric field. In the short wavelength UV irradiated PVC sample (253 nm, 300 h), a deterioration of breakdown strength at 90 °C to 150 °C and negative packet‐like charges were observed at 60 °C and 100 °C, a positive charge accumulated in front of both the anode and cathode above 90 °C, and a higher electric field near the cathode side because the positive charge of the cathode side was greater.     

High‐sensitivity PEA system with dual‐polarity pulse generator

The pulsed electroacoustic (PEA) method has been widely used to observe space charge distributions in various solid dielectric materials. The sensitivity of the conventional PEA system is around 1C/m³. When the charge density is less than 1C/m³, however, it is difficult to obtain an accurate result because the signal due to the Maxwell stress becomes comparable with the signal to be measured. The Maxwell stress is generated by applying the pulsed electric field to the dielectrics, and independent from the existence of either induced charges by DC bias voltage or internal charges. In order to eliminate the influence of the Maxwell stress, we have developed a new PEA system with a dual‐polarity pulse generator. The system allows measurement space at a charge density of around 0.03C/m³. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(2): 1– 7, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20496     

High repetition rate PEA system for in-situ space charge measurement during breakdown tests

In order to investigate transient space charge phenomena, it is essential that the space charge profile be observed at a high repetition rate. We have developed a new space charge measurement system using the pulsed electroacoustic (PEA) method, which can measure the space charge profiles every 10 /spl mu/s. It employs the most recent digitising oscilloscope model and a semiconductor switch. The effect of prestressing on impulse breakdown voltage of a low-density polyethylene sheet was investigated by using the new system. Experimental results suggest that positive charge injection was dominant immediately before the breakdown, and charge injection during the prestressing causes distortion of the electric field near the electrode, and enhances the subsequent charge injection due to the impulse voltage.     

电声脉冲法中脉冲对空间电荷分布测量的影响

首先阐述了目前已广泛应用的电声脉冲法(PEA)测量电介质中空间电荷的原理,介绍了一台新型的PEA空间电荷测量装置(其电脉冲幅值和宽度可调),并利用此装置在相同的测试条件下测量了相同的试样。研究发现:对固定厚度的传感器来讲,空间电荷分布信号随脉冲幅值增加而增加,且其波形随脉冲宽度增加而展宽和增强。最后根据PEA测量空间电荷的原理合理分析了上述的现象。     

Influence of oil aging on the space charge dynamics of oil‐immersed paper insulation under a DC electric field

The formation of space charge in oil/paper insulation system can lead to material degradation in the region of high electric field. Therefore, it is important to understand the factors that affect space charge formation in oil/paper insulation system. In this paper, the effect of oil aging on space charge dynamics in oil/paper insulation system is investigated using the pulsed electroacoustic (PEA) technique under a DC electric field at room temperature. The ultraviolet/visible (UV/vis) spectrum of the oil shifts to longer wavelengths, and the oil acidity increases as the aging time increases. It has been found that the oil property has a significant effect on the space charge distribution in the oil/paper insulation sample. The more the deterioration of the oil, the larger amount of negative and positive charges accumulated in the bulk of the oil/paper insulation sample. The total amount of slow moving charges, the surface trap energy density, and the electric field distortion of the oil/paper insulation sample increased with the degree of deterioration due to oil aging. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Electrodes and charge injection in low-density polyethylene usingthe pulsed electroacoustic technique

The effects of electrode materials on space charge formation in low-density polyethylene (LDPE) have been investigated experimentally using the pulsed electroacoustic (PEA) technique. Common electrode materials used in either the laboratory or power cable industry were selected, i.e. aluminum, gold and carbon loaded crosslinked polyethylene (XLPE), and space charge accumulation after the application of high electric stress was monitored. Experimental results demonstrated that charge injection processes take place in all cases once the applied stress has exceeded a threshold. However the amount of charge, and the polarity of the dominant injected charges showed a significant dependence on the electrode materials under the same applied electric stress     

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     

Space charge behavior under ac voltage in water-treed PE observedby the PEA method

The pulsed electroacoustic method (PEA) has been applied to observe space charge formation under ac application (7 kV_pk, 50, 0.1 and 0.001 Hz) in water-treed polyethylene samples in order to understand the degradation mechanism of water trees. A system with phase-resolving capability has been developed to measure the space charge distribution at any phase angle of the applied ac voltage. By comparing the observed charge distributions with theoretically predicted ones, it has been shown that the interfacial polarization due to the difference in conductivity between the treed and the regions without trees dominate the space charge behavior. It has become clear that the PEA method can be a powerful nondestructive method for evaluating water tree length     

±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。     

Industrial applications of space charge measurement in Japan

Industrial applications of space charge measurement using the pulsed electroacoustic (PEA) method were introduced. The materials are not only insulating materials affected by internal charges but also new functional polymers that effectively use internal charges. Users of the space charge measurement have had the method advanced to obtain suitable experimental conditions for a variety of materials. The space charge research field has been continuously expanding in Japan, and there are still many prospective materials for space charge measurement specimens     

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     

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。     

全尺寸直流电缆脉冲电声法（PEA）空间电荷测量系统设计及声信号衰减与色散补偿

脉冲电声法（PEA）空间电荷测量是交联聚乙烯（XLPE）绝缘直流电缆材料选型与评价的主要技术手段,被广泛应用于直流电缆薄膜试样。但应用该方法测量厚尺寸平板试样和大尺寸同轴试样以研究材料体效应对空间电荷的影响时,声波信号在材料中传播时的衰减与色散将直接影响电荷密度测量的精度和空间分辨率。提出了在空间电荷校准过程中利用理论计算直流电场的方法确定内外电极表面的电容电荷密度,然后计算确定在绝缘介质中传播的脉冲声波信号传递函数（该函数含有衰减和色散系数）,再对原始信号进行反卷积分运算以去除系统响应。在频域利用测量信号乘以传递函数获得脉冲声波信号经过衰减、色散恢复后的信号,从而保证大尺寸直流电缆试样测量中电荷密度及空间分辨率的测量精度。同时,设计了全尺寸直流电缆空间电荷测量系统,并在LabVIEW环境下开发了数据采集与处理系统。     

Phase-resolved pulsed electro-acoustic technique to detect space charge in solid dielectrics subjected to AC voltage

The PEA technique has been modified to study the space charge development in solid dielectrics subjected to AC electric field. Narrow (5 ns) electrical pulses are applied at various phase angles of the AC waveform. Special software, developed to precisely synchronize the pulse generator with the high voltage supply, applied the narrow pulses at 0deg phase angle and then in steps of 10deg till 360deg. By processing the PEA data at various phase angles of the AC waveform, without resorting to complex mathematical analysis, the electric field at which charges are injected into the polymeric insulation was determined. The phase resolved PEA technique can also provide the dynamics of space charge development under AC fields     

Space charge trapping in electrical potential well caused by permanent and induced dipoles for LDPE/MgO nanocomposite

Space charge accumulation in low-density polyethylene film containing a small amount of MgO nanoparticles (LDPE/MgO nanocomposite film) subjected to an electric field greater than 100 kV/mm has been studied using an improved pulsed electroacoustic (PEA) system. No marked space charge accumulation was observed in LDPE/MgO nanocomposite films. To determine the mechanism of no space charge accumulation in the LDPE/MgO nanocomposite film, we compared electric potential wells produced by a permanent dipole moment such as that of carbonyl groups (C=0) and an induced dipole consisting of MgO nanoparticles (spherical dielectrics) under a high electric field to create a trapping site for electric charge carriers. The trapping depth created by the permanent dipole moment such as that of the carbonyl groups (C=0) of chemical defects is approximately 0.45 eV. However, the potential well induced by high-permittivity dielectric nanoparticles (MgO) is about 1.5 to 5.0 eV, which is much deeper than that induced by chemical defects. The suppression of space charge formation is explained using the potential well model consisting of a dipole induced by a high-permittivity dielectric nanoparticle. We explained the suppression mechanism of charge accumulation in the LDPE/MgO film that contains deep traps.     

形态对聚乙烯中空间电荷包运动特性的影响

空间电荷相关研究是直流电介质材料特性研究的重要领域,聚乙烯则是主要的内绝缘材料之一。为了对高压直流条件下聚乙烯中的空间电荷现象进行深入研究,应用电声脉冲法空间电荷测量系统对高场强下低密度聚乙烯中的空间电荷现象进行测量,观察到了空间电荷包现象。研究结合不同热处理方法得到了不同微观形态的聚乙烯试品,并在不同场强下结合微观形态的变化对低密度聚乙烯的空间电荷包运动速率进行了分析。结果表明,聚乙烯的微观形态对空间电荷包特性有显著的影响,也对空间电荷包运动速率有明显的影响,结晶度越高,空间电荷包运动速率越小。     

Comparison between the PEA method and the PWP method for spacecharge measurement in solid dielectrics

The principles of both pulsed electro acoustic (PEA) and pressure wave propagation (PWP) methods for measuring the space charge distributions in solid dielectrics are summarized. The relationship between the charge distribution in a specimen and voltage signal of the PEA method or the current signal of the PWP method are expressed in the time and frequency domains. Furthermore, the calibration method of the amount of accumulated charge density using deconvolution techniques is described for both methods. To compare these two methods, PMMA samples with and without space charge are measured using both methods. In addition, the electric field and electric potential distributions are calculated and discussed. The experimental results obtained using both methods are almost the same     

A finite element method for the determination of space chargedistributions in complex geometry

Electrical breakdown in insulators very often initiate near high field regions of the structure, as found near small-radius impurities or at electrode defects. This is attributed to the development of localized space charges. For this reason many efforts have been made to determine such charge. Various techniques are now available, but they are not directly applicable to complex geometries where it is difficult to determine analytically the field configuration and thus the relation between the measured variables and the space charge distribution. To solve this problem, we propose to use a numerical simulation using a finite element method (FEM). In this paper we describe how it can be implemented in the case of the pressure wave propagation (PWP) method. It is shown that measured signals in insulating samples with divergent electric field regions are well fitted by simulations. We show that this allows for the determination of space charge distribution in such samples     

直流电场下油纸绝缘介质界面处的空间电荷特性

换流变压器是直流输电系统的核心设备,其油纸复合绝缘结构的空间电荷特性复杂,工程实践表明其对绝缘放电的影响不可忽略,因此针对油纸复合绝缘开展空间电荷特性的研究对换流变绝缘结构设计和运行分析有指导意义。为此,应用电声脉冲（PEA）法研究了电场对双层油浸纸介质中空间电荷特性的影响以及界面处的空间电荷特性。指出在双层油浸纸的界...