Use of inductive energy storage for electric pulse destruction ofsolid materials

An inductive energy storage switch system for the destruction of solid materials is reported. This is based on creating a pulsed electric breakdown in the solid dielectric, which then propagates in the specimen. This scheme provides a higher destruction effectiveness compared to a capacitive energy storage system. The higher energy efficiency is attributed to a different discharge behavior during the discharge build-up in the solid material. A higher applied voltage causes a breakdown of a larger number of voids in a heterogeneous solid dielectric. The energy transfer to partial discharges, when using the inductive storage system, is faster than for the capacitive energy storage system, due to a shorter risetime of the discharge current     

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.     

提升纳米复合电介质击穿强度的理论与方法

聚合物复合电介质材料在电工领域有着广泛的应用。在电力设备运行过程中,电介质材料在温度、电(磁)场、机械力以及环境的作用下会发生击穿现象,造成电力设备失效以及由此引起的损失。因此,提升复合电介质的击穿强度一直是电工领域的重要问题。纳米复合电介质代表未来电力设备绝缘的发展方向。该文首先简述聚合物电介质的基本击穿理论,并总结提升纳米复合电介质击穿强度的基本策略及原理。接着,聚焦纳米粒子对电荷产生、输运以及电场分布的作用,总结几种提高纳米复合电介质击穿强度的方法,包括纳米粒子的表面工程、调控纳米粒子的维度和排列、制备多层结构的复合电介质、制备核壳结构纳米粒子复合介质,以及利用金属纳米颗粒的纳米效应。最后,对提升纳米复合电介质击穿强度未来的研究方向进行展望。     

液氮温区超导复合绝缘材料沿面放电特性

随着超导输电技术的不断发展,对各种超导设备中使用复合绝缘材料的绝缘特性提出了更高要求。复合绝缘的放电击穿往往发生在固体绝缘材料和液氮2种工作介质的交界面。而在液氮温度下,绝缘材料又有着相对独特的放电特性。针对这种情况,设计了极不均匀沿面电场,研究了3种不同的固体绝缘材料在液氮环境中沿面放电的特性,包括其放电起始电压、放电随电压发展过程、击穿电压等特性,并进一步分析3种材料差异的原因,为实际应用提供了参考。     

Structure,Ferroelectric, Dielectric and Energy Storage Studies of Ba0.70Ca0.30TiO3, Ba(Zr0.20Ti0.80)O3 Ceramic Capacitors

Ba_0.70Ca_0.30TiO₃-(BCT),Ba(Zr_0.2Ti_0.8)O₃-(BZT) ceramics were fabricated by conventional mixed oxide route to develop inorganic dielectric materials suitable for use as an insulator with high dielectric constant and low energy loss for capacitor applications. The structural phase transition, ferroelectric, dielectric and energy storage properties of BCT, BZT ceramic capacitors were investigated. Room temperature X-ray diffraction (XRD) patterns revealed prominent peaks corresponding to tetragonal perovskite crystal structure for both BCT, BZT solid solutions. Slim ferroelectric hysteresis (P-E) loops were observed for BCT, BZT solid solutions. Temperature dependent dielectric property measurements of BCT, BZT solid solutions have shown a high dielectric constant and low dielectric loss. Room temperature (300K) breakdown field strength and energy densities were obtained from the integral area of P-E loops. For the BCT ceramics, the largest recoverable energy (unreleased energy) density is 1.41 J/cm³ with dielectric breakdown strength as high as 150 kV/cm. For the BZT ceramics, the largest recoverable energy (unreleased energy) density is 0.71 J/cm³ with dielectric breakdown strength as high as 150 kV/cm. Bulk BCT, BZT ceramics have shown interesting energy densities; these might be the strong candidate materials for capacitor applications.     

Breakdown strength at the interface between epoxy resin and silicone rubber-a basic study for the development of all solid insulation

As a key component for a future power substation system entirely consisting of solid insulating materials, a special connection system between different pieces of power equipment has to be developed. A soft dielectric such as silicone rubber and a hard one such as epoxy resin are to be used for this connection. This paper describes the interfacial breakdown strength between silicone rubber and epoxy resin using two types of model samples on which the electric field can be applied in parallel or perpendicularly to their interface. Partial discharge characteristics at the interface and the effect of air penetration on the breakdown voltage along the interface are discussed.     

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.     

Comparative Laboratory Evaluation of Premolded Joints for Medium Voltage Cables

This paper provides information on laboratory performance of 15 and 35 kV premolded joints from three manufacturers. Data on partial discharge, ac and hot impulse voltage breakdown tests, and dissection of breakdowns are presented for joints that were tested immediately after their assembly and after one year aging immersed in room temperature water (15-30degC), under operating voltage. The test program was repeated twice using joints acquired with a two-year interval. The two batches showed similar performance indicating that all three manufacturers provide consistent quality joints. AC breakdown strength of the joints practically did not change with aging. In contrast, their impulse breakdown strength decreased noticeably. Joints having partial discharge levels up to 5000 pC were included in the study. No obvious correlation was found between the presence of partial discharge and the joints ultimate dielectric strength.     

High voltage studies of dielectric materials for HTS power equipment

The discovery of high temperature superconductors (HTS) has triggered renewed interest in the study of dielectric materials at cryogenic temperatures. While considerable work was done in the 1970s and 1980s on dielectrics immersed in liquid helium for low temperature superconducting applications, there remains a need for dielectric research at liquid nitrogen temperature for HTS applications, requiring experimental data oriented toward practical situations. We report on AC breakdown (puncture and/or flashover), and impulse breakdown of solid materials in either vacuum or in liquid nitrogen. Solid materials which we examined, include fiberglass reinforced plastics, epoxies with and without filler, and polymeric tape. Combinations of some of these materials have also been studied at low temperatures. Additionally we have measured permittivity and dissipation factor for materials for which these parameters are not available at 77 K. Finally, we also discuss specific applications for HTS cables including breakdown and aging studies on model cables, with lapped tape electrical insulation, immersed in liquid nitrogen.     

Surface flashover of oil-immersed dielectric materials in uniform and non-uniform fields

The applied electrical fields required to initiate surface flashover of different types of dielectric material immersed in insulating oil have been investigated, by applying impulses of increasing peak voltage until surface flashover occurred. The behavior of the materials in repeatedly over-volted gaps was also analyzed in terms of breakdown mode (some bulk sample breakdown behaviour was witnessed in this regime), time to breakdown, and breakdown voltage. Cylindrical samples of polypropylene, low-density polyethylene, ultra-high molecular weight polyethylene, and Rexolite, were held between two electrodes immersed in insulating oil, and subjected to average applied electrical fields up to 870 kV/cm. Tests were performed in both uniform- and nonuniform- fields, and with different sample topologies. In applied field measurements, polypropylene required the highest levels of average applied field to initiate flashover in all electrode configurations tested, settling at ~600 kV/cm in uniform fields, and ~325 kV/cm in non-uniform fields. In over-volted point-plane gaps, ultra-high molecular weight polyethylene exhibited the longest pre-breakdown delay times. The results will provide comparative data for system designers for the appropriate choice of dielectric materials to act as insulators for high-voltage, pulsed-power machines.     

电容器介质直流、交流击穿电压值的对比研究

与交流电场不同,在直流电场下,除介质中的空间电荷效应增强之外,电场强度在串联介质中的分配主要由体积电阻率的比值决定.电力电容器常用的液体介质、固体介质由于其相对电容率和体积电阻率存在明显的区别,这给它们复合后在直流电场和交流50 Hz电场的使用上不可避免地带来影响.通过对电容器用液体介质、固体介质以及由他们组成的复合介...     

纳米添加剂对聚合物击穿性能的影响

击穿性能是电介质材料最基本的要求,提高材料的电气强度是电介质研究最为重要的任务之一.理想电介质的本征击穿强度远高于实际材料的水平,工程击穿问题的研究实际上是集中在对缺陷体系的研究.就物理机理而言,电子陷阱与散射模型似乎应给予更多的关注.添加剂不仅可用于改善和平衡凝固态聚合物电介质的综合性能,也可以用来明显的提高材料的击穿强度.特别是纳米材料和技术研究的扩大与深入,一方面为击穿研究的发展奠定了一个新的物质基础,另一方面也促进了击穿机理研究的深化.氧化物纳米添加剂/聚酰亚胺基耐电晕漆包线漆、浸渍漆明显地提高了原漆的电压耐受寿命;纳米添加剂也提高了电缆绝缘的工作场强或可靠性.纳米金属粒子也可能明显提高聚合物的电导和击穿性能,本文用散射-陷阱模型对此作了讨论.绝缘结构的时间与空间节律不仅在宏观上具有主宰能力,在微观上也显示出了某种端倪.     

Electrical properties of biodegradable polylactic acid film

We measured the basic electrical insulation characteristic of biodegradable polylactic acid (PLA), and the following results were obtained. The volume resistivity, dielectric constant, and dielectric loss tangent measured at room temperature were almost the same as those of crosslinked polyethylene (XLPE) currently used as insulating material for cables and electric wires. The mean impulse breakdown strength of PLA was about 1.3 times that of XLPE. Also, space charge accumulation in PLA and XLPE was measured. The amount of space charge accumulation in PLA was one-half that in XLPE when a DC voltage was applied for a short time.     

AC breakdown strength of aromatic polymers under partial dischargereducing conditions

Partial discharge occurring at HV in AC electric breakdown field measurements on insulating polymeric films strongly reduces the breakdown field strength of the material and conceals the intrinsic breakdown process. By performing AC electric breakdown field measurements on polymer films in phthalic diesters, it was possible to suppress partial discharge and obtain breakdown field data of more intrinsic character. This is valuable for the evaluation of the influence of the structure and the properties of polymers on their insulating behavior. The AC electric breakdown field strength of five aromatic polymers at different film thicknesses was measured in dibutyl phthalate. The results from these measurements showed about a twofold increase in the breakdown field strength at sample thicknesses >50 μm, compared to data obtained in transformer oil. The breakdown field strength for thick samples showed a linear decrease with increasing sample thickness for all polymers except PEEK, which showed a constant breakdown field strength in the thickness range investigated. The breakdown field strength of thin samples was independent of the polymer structure. Measurements of the breakdown field strength of the polymers under dc conditions show no obvious correlation between chemical structure or polymer property and the breakdown field strength     

Dielectric properties of nanostructured polypropylene-polyhedral oligomeric silsesquioxane compounds

This paper presents the results of the dielectric measurements conducted on polymer nanocompounds consisting of polypropylene (PP) and polyhedral oligomeric silsesquioxane (POSS). The material compounds were analyzed with a scanning electron microscope (SEM) and Raman-atomic force microscope (Raman-AFM). Ac and lightning impulse (LI) breakdown strength of the material compounds were measured. Relative permittivity, loss factor and volume resistivity measurements were also conducted on the material samples. Two types of POSS, octamethyl and isooctyl, were used in different quantities. The thickness of the samples was approximately 600 mum. Statistical analysis was applied to the results to determine the effects of the additive type and amount on the breakdown strength of polypropylene. The paper discusses the possibilities and restrictions in order to achieve advantages in high voltage applications using polyhedral oligomeric silsesquioxanes.     

Deterioration characteristics of insulating spacer model in repeating impulse voltage

To discuss the UHV GIS test voltage, the deterioration characteristics of the GIS insulating spacer model were studied by repeating lightning or switching impulse voltage. The deterioration factor indicating the decrease of lightning or switching impulse breakdown voltage applied up to 1000 times was found to be 35.7/45.5. The relationship between the partial discharge inception voltage and the breakdown voltage after 1000 impulse applications was also studied. It was found that the partial discharge inception voltage increases despite a decrease in breakdown voltage due to the impulse voltage. In addition, to elucidate the deterioration phenomenon, a study was made of the breakdown characteristics of models with various boundary conditions between the electrode and epoxy resin, as well as the relationship between the boundary conditions. Microdischarge was also studied. The results of the investigation suggest that the deterioration by repeating voltage is caused by microdischarge due to electric field intensification on microprotrusions of the electrode surface.     

Insulation optimization by electrode contour modification based onbreakdown area/volume effects

This paper shows how to determine the electrode contour with the best insulation performance on the basis of an area effect and a volume effect in the breakdown field strength. Previous electric field optimization techniques have provided us only with an optimum electric field distribution, For the design of power apparatus insulation, we have to consider the dielectric breakdown characteristics rather than the electric field distribution. As a first step, we developed a new optimization technique which enables us to obtain an optimum electrode contour with the highest breakdown strength while taking into account the area and volume effects of breakdown strength of insulating media. From the results, we have confirmed that the proposed optimization method improved the breakdown voltage more than did the electric field optimization. This leads to an effective insulation design of electric power apparatus     

Nanosecond streak photography of discharges on spacer surface ingases

Results of an investigation to clarify the process of surface flashover in gases are reported. Two hemispherical capped rods of 12 mm diameter, separated by a half-cylindrical spacer of 50 mm diameter, formed the samples. The spacer materials were polytetrafluoroethylene, acrylic and nylon. High-speed streak photographs of impulse flashover indicate that the presence of a spacer not only lowers the impulse breakdown voltage but also reduces the breakdown time. The discharge on spacers may be initiated anywhere between the electrodes and develops rapidly into a flashover in ~5 ns for an 18 mm gap     

Electrode conditioning characteristics in vacuum under impulse voltage application in nonuniform electric field

In this paper, we quantitatively investigated the impulse conditioning mechanism under nonuniform electric field electrodes in a vacuum. A negative standard lightning impulse voltage was applied between rod and plane electrodes whose materials were Cu-Cr, stainless steel and Cu and the gap lengths were d=5 and 10 mm, respectively. Experimental results revealed the transition of the breakdown (BD) sport region on the rod electrode and the corresponding BD field strength in the conditioning process. As a result, we found that the BD spot region started at the tip of the rod electrode and moved to the wider region of the rod electrode with lower electric field as the shots of the voltage application increased before the saturation of the BD voltage. Finally, by analyzing the results with an electric field strength, we propose that "the conditioning degree" along the electrode surface distributed directly proportional to the electric field distribution under a nonuniform electric field in a vacuum, irrespective of the electrode materials     

Computer modeling of interaction of gas discharge plasma with solid dielectric barriers

A computer model describing charge transfer in a system consisting of two parallel-plate metallic electrodes covered with solid dielectric barriers immersed in gas medium is proposed. The material of the barriers is supposed to be a non-ideal insulator whose properties correspond to polyethylene and air is considered as a gas phase. The model is based on continuity equations for fluxes of charge carriers and accounts for their drift and diffusion and also for different sources of their generation and losses in different media. The continuity equations are coupled with Poisson's equation for computing electric fields affected by temporal and spatial variations of space charges in the system. Results of the computer simulations are obtained for the case when the applied field in the gas exceeds its breakdown threshold, i.e. charge transfer in the gas phase takes place in the form of an electrical discharge (electron avalanche and streamer). Evolution of generated discharge plasma is analyzed taking into account conditions on gas-solid interfaces and in the bulk of the solid dielectric barriers.