热老化XLPE电缆绝缘的介电击穿行为的研究

击穿强度通常是用来表征检测和使用过程中的绝缘材料状态和质量的指标之一。尽管有许多报道对聚乙烯(PE)和交联聚乙烯(XLPE)的击穿电压进行了研究,但是对热老化后的交联聚乙烯电缆的击穿行为的研究不是太多。表征威布尔统计分布参数,即范围和形状参数与分子结构、物理和化学缺陷的含量和形状以及其他的物理化学性能有密切的关系。本文的目的是研究不同热老化程度的XLPE电缆的威布尔统计分布参数的变化行为。研究结果显示威布尔参数变化对XLPE绝缘材料的热老化程度是非常敏感的,利用威布尔参数与热老化程度的关系可以有效地诊断PE和XLPE电缆绝缘材料。     

Long term accelerated aging tests on distribution cables under wetconditions

Two accelerated aging test procedures are proposed for use on solid dielectric extruded distribution cables under wet conditions. One test method is a fixed time duration test in which the degree of cable specimen aging is assessed in terms of breakdown tests, while the other test method is a time to breakdown test in which the cable specimens are voltage stressed until failure ensues     

Dielectric strength of series connected vacuum gaps

A simple procedure to obtain an analytical equation for the distribution function of breakdown voltage in devices containing an arbitrary number of identical elements in series is proposed. The obtained results make possible to analyze an influence of static properties of the elements and their number on the dielectric strength of a device as a whole. The probability of the breakdown of the switching device is calculated using the empirical distribution functions of breakdown voltages of each TVS. The Weibull plots are used to analyze the breakdown test results. The measurement of the dielectric strength performed for AC and DC devices shows a good agreement with the calculated data.     

Dielectric behavior of aged polyethylene under UV radiation

The present paper reports the results of a study of dielectric aging of low-density polyethylene (LDPE) by UV radiation. The extruded polymer contained carbon black particles, approximately 3% in weight. The aging studies were made for polymer without and with carbon black. LDPE flat specimens were aged under UV radiation for up to 300 h, resorting to dielectric spectroscopy measurements in the frequency range from 10/sup -5/ Hz to 10/sup 5/ Hz. The dielectric susceptibility behaviors indicate the presence of relaxation peaks obeying the asymptotic forms of Dissado and Hill susceptibility functions. As the aging progresses, quasi-DC and flat loss processes may be observed in the low frequency range, for the LDPE specimens without and with carbon black, respectively. In addition, dielectric spectroscopy results have been compared with other results obtained with additional techniques such as Fourier transform infrared spectroscopy and scanning electron microscopy.     

Influence of Voltage Application History on Insulation Test with One-Minute Step-up Method

For the development of test conditions for a short-duration power-frequency withstand voltage test, which is one of the insulation specifications of substation equipment, there is a precise method of evaluating reliability using a Weibull distribution function. For this method, "independence method" and "accumulation method" have been proposed in order to handle the coexistence of multiple voltage levels. In this paper, an insulation test based on the one-minute step-up method as condition for the coexistence of multiple voltage levels is used to calculate and evaluate the test results using these two methods. Consequently, the insulation characteristics obtained from the one-minute step-up test are found to have differences from the true values. If the independence method is adopted, there is a certain deviation regardless of the Weibull time shape parameter "a-value" and, the smaller the Weibull voltage shape parameter "m-value", the larger the deviation. If the accumulation method is adopted, on the other hand, the larger the "a-value" or the smaller the "m-value", the larger the deviation. The 50% breakdown voltage value, the standard deviation "σ-value", and the ?m-value? that can be obtained from the insulation test based on the one-minute step-up method were evaluated for their deviations from the true values. The results suggest that, when a test is conducted on an oil-filled transformer, the design may turn out to be on the dangerous side due to overestimation of the dielectric strength by around 8%.     

EFFECT OF ADDITIVES ON THE PERFORMANCE OF CABLE OIL AND KRAFT PAPER OIL COMPOSITE

ABSTRACT

This study investigates the effect of 1-Methylenaphthalene and Benzophenon as additives in cable oil used in extra high voltage paper insulated underground cable in service in Riyadh area. Samples containing different concentrations of these additives were used. Impact of variation of temperature and additive concentrations was evaluated for conduction current and burst current. Virgin samples of the dielectric paper used in this cable were impregnated in these oil samples for the investigation of power factor and breakdown voltage. The results indicate that an optimum concentration of the additives improves the performance of paper-liquid composite.     

Dielectric strength of series-connected triggered vacuum switches

An HV switching device consisting of two series-connected triggered vacuum switches (TVS) of type RVU-43 is tested. This device is intended for operation at a voltage up to 80 kV and its maximum switched current is 200 kA. The breakdown voltage of each TVS is measured separately and that of the series connection presented. Weibull plots are used to analyze the breakdown test results. Our investigations allow the determination of experimental and theoretical distribution functions for the breakdown voltages of the individual switches and the combined switching device. The probability of breakdown of the switching device is calculated using empirical distribution functions of breakdown voltages of each TVS. A comparison of the calculated distribution function of the breakdown voltages of the switching device with the experimental distribution function shows good agreement. The proposed method allows estimating the dielectric strength of the switching device depending on the degree of nonuniformity of the voltage distribution between series-connected TVSs.     

ns脉冲液体介质击穿实验研究综评

介绍了目前液体介质击穿研究的实验内容(电压极性、电压波形、外界静态压力等)、实验方法(电学与光学结合)、研究成果(经验公式、击穿机理);指出单次ns脉冲击穿的电压脉宽窄(ns级)、击穿电压幅值高,重频ns脉冲电压击穿下液体介质的电场累积效应(极化效应)显著,这些ns级液体介质击穿的特点有助于揭示液体介质击穿的本质特性。结合研究成果讨论了窄脉冲电压液体介质击穿的概率与击穿机理。     

Surface flashover characteristics of diamond-like carbon thin filmsin vacuum

Synthetic thin films such as diamond-like carbon (DLC) and polycrystalline diamond thin films can be used to increase surface flashover voltage of dielectric materials used in HV devices operating in vacuum. This work presents experimental results identifying some surface flashover characteristics of diamond-like carbon (DLC) thin films in space vacuum conditions. The DLC samples used in the experiments are produced by a microwave plasma deposition technique. The electrode material was copper, and a dc voltage was applied between the electrodes. Surface flashover voltage characteristics and the breakdown voltage wave forms of DLC thin film samples were determined. The results showed that DLC thin films may not be suitable materials for HV applications as dielectric materials in vacuum when coated onto semiconductor materials. Additionally, these results were compared with the surface flashover characteristics of polycrystalline diamond thin film and quartz samples     

电缆中聚乙烯界面微观结构对击穿强度的影响

本文选用特殊添加剂对电力电缆中半导电层以化学改性，为减薄电缆绝缘厚度，提高交联聚乙烯电缆的击穿强度，提供了有效途径。从理论上定性解释了聚乙烯的击穿强度与界面片晶取向角的关系。由微观结构分析结果表明，改性半导电层经热压后，会改变聚乙烯界面结晶取向，改善半导电层中碳粒凝聚状态。最后，由电缆模型试片的击穿强度结果予以证实：改性半导电层比普通半导电层，可使聚乙烯的１％威布尔击穿强度提高８９％。平均击穿强度提高４０％。本文结果对提高交联聚乙烯电缆质量是有意义的。     

Failure distributions of successive dielectric breakdown events

Experimental time-dependent dielectric breakdown (TDDB) distributions of standard CMOS hardware are used to demonstrate the problem of detecting a range of successive breakdown events, e.g., from the 5th to the 20th. Specifically, the range and the statistical distribution of successive breakdown events significantly change the shape of the cumulative failure distribution, which is crucial for the low percentile extrapolation. The observed behavior affects the correlation of integrated circuit failure distributions to dielectric breakdown as it is expected that circuit malfunction is caused by a range of successive breakdown events.     

茂金属聚乙烯改善低密度聚乙烯的介电性能

针对高压、超高压直流塑料电缆中存在的空间电荷效应,大多数直流电力电缆常采用改性方法提高其介电性能,如空间电荷特性、体积电阻率和击穿强度等。常用的改性方法主要有添加剂、共混、接枝和二元共聚4种。共混技术较广泛用以改性聚乙烯电缆,提高其介电性能。因此用电声脉冲法(PEA)测量了MPE与LDPE共混试样中的空间电荷分布;用高阻计测量了共混物的体积电阻率,用阶梯电压测量了共混物的交流击穿场强。试验结果表明,1%MPE与LDPE共混能有效降低空间电荷效应,提高交流击穿场强7.9%,略降低体积电阻率。最后讨论了共混物的物质结构、电荷陷阱及介电性能间的关系。     

Investigation of dielectric breakdown characteristics of double‐break vacuum interrupter and dielectric breakdown probability distribution in vacuum interrupter

To investigate the reliability of equipment of vacuum insulation, a study was carried out to clarify breakdown probability distributions in a vacuum gap. Further, a double‐break vacuum circuit breaker was investigated for breakdown probability distribution. The test results show that the breakdown probability distribution of the vacuum gap can be represented by a Weibull distribution using a location parameter, which shows the voltage that permits a zero breakdown probability. The location parameter obtained from Weibull plot depends on electrode area. The shape parameter obtained from Weibull plot of vacuum gap was 10 to 14, and was constant irrespective of the nonuniform field factor. The breakdown probability distribution after no‐load switching can be represented by Weibull distribution using a location parameter. The shape parameter after no‐load switching was 6 to 8.5, and was constant irrespective of the gap length. This indicates that the scatter of the breakdown voltage was increased by no‐load switching. If the vacuum circuit breaker uses a double break, the breakdown probability at low voltage becomes lower than the single‐break probability. Although the potential distribution is a concern in the double‐break vacuum circuit breaker, its insulation reliability is better than that of the single‐break vacuum interrupter even if the bias of the vacuum interrupter's sharing voltage is taken into account. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(2): 13–20, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21060     

单断口和三断口串联真空灭弧室绝缘击穿统计特性

建立了由3个真空灭弧室串联后组成的三断口真空灭弧室模型。通过施加工频交流高压和冲击高压，重点研究在相同的总开距下，与单断口真空灭弧室模型相比，三断口真空灭弧室模型的静态击穿电压增益特性和静态击穿统计特性，包括三断口真空灭弧室在工频交流电压下的静态电压分布特性。试验研究表明，不同的串联布置方式表现出不同的断口电压分布特性。断口电压分布特性越均匀，则击穿电压增益倍数越高。击穿统计特性试验研究表明，三断口真空灭弧室相比单断口真空灭弧室具有更低的击穿概率。试验结果与理论分析相吻合，证明了理论模型的有效性。     

Application of functionally graded material for solid insulator in gaseous insulation system

Functionally graded materials (FGM) have spatial distribution of a material property in order to achieve efficient stress control. An application of the FGM to a solid insulator (spacer) for a gaseous insulation system, like gas insulated switchgear, is expected to improve electric field (E-field) distribution around the spacer. In this paper, we describe the applicability of the FGM spacer to gas insulated power equipment. In the FGM spacer, we gave spatial distribution of dielectric permittivity to control the E-field distribution inside and outside the spacer. This paper includes following key results for the applications of the FGM. Firstly, E-field simulation results when applying the FGM by a finite element method are presented, in which we show the effective reduction of the maximum field strength by applying the FGM. Next, a fabrication technique of the FGM spacer sample with not only step-by-step but also continuous changes of permittivity is presented by use of centrifugal force. Finally, dielectric breakdown tests using FGM samples which are accurately controlled the spatial distribution of permittivity are carried out under lightning impulse voltage applications. The test result indicates the increase of breakdown voltage (BDV). From these results, we verified the applicability and the fabrication technique of FGM spacer for improvement of the dielectric strength in the gaseous insulation system.     

Effect of surfactants on superstructure and dielectric breakdown strength of crosslinked polyethylene insulation

This paper describes the influences of a surfactant on crosslinked polyethylene (XLPE) insulation. Several kinds of additives are mixed into the insulation in order to improve the dielectric breakdown strength of XLPE cables. It has been verified that the interfacial diffusion method, which modifies the interfacial region between the insulation and the semiconducting layer by a surfactant, is effective. The effects of the surfactant on the morphology in the XLPE insulation were studied with two kinds of specimens. In the first kind of specimens, a mill was used to disperse the surfactant throughout the insulation material. Alternating current dielectric breakdown tests were performed on disk specimens. Their average breakdown strengths were improved, but the breakdown strengths were not increased at the low probabilities of the hazard function. In the other specimens, the surfactant was milled into the semiconducting layer, and later allowed to enter the insulation by diffusion during the high-temperature crosslinking process. It was found that the average breakdown strengths were improved further. Moreover, the breakdown strengths were found to increase significantly at the low probabilities of the hazard function. The two kinds of specimens were followed by material analysis using analytical methods, such as TEM, FT-IR, etc. Results from the milled specimen indicated that the improvement in property was probably due to the increase in density of the amorphous portion, the increase in the lamella thickness, and the increase in spherulite radius created by the additive content. Therefore the insulation near the interface where a concentration gradient was established by diffusion from the semiconducting layer is considered to have similar morphological changes caused by the additive. In addition, the diffusion specimen was observed to have an absence of introduced microdefects that existed in the milled specimen.     

Influence of surface shape on DC surface breakdown characteristics under metallic-particle contaminated conditions in SF6 gas

The influence of a metallic particle attached to a supporting insulator is remarkable in decreasing the dielectric strength in an SF₆ insulated apparatus. To solve this problem, a series of studies has been conducted on a method of improving the particle-initiated breakdown performance. In this paper, dc breakdown voltage characteristics and the breakdown mechanism are investigated under metallic-particle contaminated conditions in SF₆ gas by varying the particle condition and the surface shape of the acrylic plate with a rod-plane electrode. The main results show that a rib increases the breakdown voltage by a corona stabilization effect and the elongation of discharge path, but a groove decreases its effect drastically at lower gas pressures. The breakdown voltage at pressures higher than 4 atm may be estimated on the basis of the discharge-maintaining field and the discharge length which depend on the gas pressure and the surface shape.     

Effect of annealing and polishing on flashover characteristics ofceramic in vacuum

Experiments were carried out to study the effects of surface polishing and annealing of ceramic specimens on the dielectric breakdown characteristics of their surfaces. It was found that when the samples were annealed at 1000°C, allowing the residual stresses in their surfaces to decrease, the breakdown voltage rose, whereas with the polished samples, reductions of residual stresses resulted in a slight rise of the breakdown voltage. Prior to dielectric breakdown, a surface glow was observed, due to luminescence from electron bombardment and insulator surface defects. The starting voltage of luminescence rose when residual stresses were reduced. It is suggested that the mechanical strain due to surface defects contributes to dielectric breakdowns on ceramic surfaces     

Electrode protrusions and particle chaining as factors affectingthe dielectric strength of air

Electrode protrusions and free particles have been demonstrated to reduce dramatically the breakdown voltage of insulating fluids. This paper examines two factors which affect the dielectric strength of gaseous insulators: (1) shape and size of electrode protrusions, and (2) particle chain formation. A computer program, based on the boundary element method, was employed for the computation of the electric field modified by an electrode protrusion and/or a particle chain. The results regarding field enhancement were used as input data of another program that evaluated the dielectric strength of the air-gap. Two types of protrusions were studied: hemispheres and hemispherically ended rods. One to ten conductive spheres were considered to be attracted to such protrusions and chain at the top of them. The computations showed that the large protrusions are more harmful than the small ones and that the dielectric strength of the air-gap decreases with the number of particles in a chain     

Development of the new polymer insulating materials for HVDC cable

The properties of modified HDPE, selected from various polymer materials by evaluations of DC characteristics, were examined in both sheet and cable samples. It was found that the modification, which introduced a small amount of polar group into HDPE, considerably enhanced DC breakdown strength to as high as 1.5-2.0 times those of XLPE (cross-linked polyethylene). Under a poling voltage of up to 30 kV/mm, the modified HDPE exhibits particular behavior, with its space charge decreasing as stress is increasing. In addition, the additives in HDPE have a large influence on space-charge characteristics, thereby affecting the DC breakdown strength. The evaluation of cable insulated with optimum modified HDPE was conducted to determine the breakdown strength under various voltage applications. Compared with the XLPE cable, modified HDPE cable exhibited excellent characteristics under all kinds of voltage applications, particularly DC dielectric breakdown strength, which was almost twice that of XLPE