Effect of filler concentration on electrical conductivity andultralow-frequency dielectric properties

The effect of filler concentration on the dielectric properties in the ultralow-frequency region and on the electrical conductivity was studied for ethylene propylene rubber. First, we investigated the relation between the electrical conductivity and filler concentration: as the volume fraction of fillers q_a increased, the conductivity decreased in the low filler concentration region but increased abruptly in the high filler concentration region. The decrease and increase in conductivity can be explained with the action of carrier traps at the interface between EPR and fillers and with the formation of highly conductive paths of filler across the sample, respectively. Secondly, we studied the dielectric properties in the ultralow-frequency region which was obtained from the discharge current. As q_a increased, the relaxation time decreased in the low filler concentration region and then rose in the high filler concentration region. The polarization in the high filler concentration region can be explained by two-layer interfacial polarization between filler and rubber     

Influence of switching on dielectric properties of vacuuminterrupters

This paper deals with the influence of switching operations `closing without current/breaking without current', `closing without current/breaking with rated current', and `closing without current/breaking of rated short-circuit current' on vacuum interrupter dielectric strength. Two types of commercially available vacuum interrupter with transverse magnetic field CuCr contacts were tested. Breakdown voltages and emission currents, which appear before and after switching operations, were determined experimentally. The corresponding characteristics were determined after conditioning. The voltage shapes, dc, lightning impulse voltage (1.2/50 μs), and 50 Hz ac were applied. The obtained results were statistically treated. After taking into account theoretical considerations, it was concluded which physical mechanisms determine the influence of switching operations on the dielectric strength. It was found that in interrupters with poor contact material, the dielectric strength can deteriorate below the limits required by standards     

掺杂物对瓷介电容瓷料性能的影响

研究了La2O3,WO3对于0.90(Sr0.54Pb0.26Ca0.20)TiO3———0.1Bi2O3·3.5TiO2和0.90(Sr0.64Pb0.20Ca0.16)TiO3———0.1Bi2O3·3.5TiO2为系统的中高压瓷介电容瓷料的介电性能的影响,研究表明掺加La2O3对于前者的ε-t曲线有压峰作用,并能降低损耗;WO3的添加对于后者也具有压峰作用,并且同时可以降低高温段(的温度系数。     

An overview of electrical properties for stress gradingoptimization

The scope of the following paper is to present, both from a theoretical and a practical point of view, some aspects involved in stress grading in the general configuration where insulated HV conductors pass through a grounded screen. The difference between capacitive and resistive materials is discussed; particular attention is devoted to the rules governing the potential and the field distribution in both cases. The case of a capacitive varnish with nonlinear permittivity is discussed and a comparison with materials of constant permittivity is made. The experimental behavior of nonlinear semiconducting materials used in practice are examined and a discussion is given on the possible use of resistive materials of constant conductivity. Finally, practical considerations are listed as basic rules for optimizing the grading effect     

Influence of aging on electrical properties of polyethylenenaphthalate-2,6 dicarboxylate films

Poly(ethylene naphthalate 2,6 dicarboxylate), thanks to its heat resistance, may be used as insulating material in motors and laminated chip capacitors. In these specific applications the occurrence of partial or corona discharges leads to insulation aging and possible breakdown. An experimental investigation has been carried out to determine the changes in dielectric properties as function of the aging conditions, e.g. the temperature of irradiation. Dielectric loss values have been determined in the 10² to 10⁶ Hz frequency range from 150 to 200°C. Three relaxation peaks were found α,β*,β, in the order of decreasing temperature     

Influence of post-manufacturing residual mechanical stress andcrosslinking by-products on dielectric strength of HV extruded cables

Residual mechanical stresses from manufacturing always exist in freshly extruded HV cables. These stresses are not uniformly distributed in the cable insulation bulk material. Five different HV cables were analyzed with respect to residual mechanical stresses and dielectric breakdown strength. Photoelastic measurements have been carried out and show that maximum residual stresses range from 4.5 to 6 MPa and are located near the conductor shield. Breakdown strength measurements with respect to mechanical stresses have also been performed up to, and above the maximum stresses observed. A significant decrease in ac breakdown strength was observed for stresses higher than 6 MPa. Typical crosslinking by-products from dicumyl peroxide (DCP) have been measured by FTIR spectroscopy at five radial positions in the insulation bulk. Measured by-products consisted in acetophenone and cumyl alcohol. FTIR measurements show that crosslinking by-products content is higher in the bulk of the insulation than near the conductor and insulation shields thus showing a diffusion process. Moreover, residual amount of cumyl alcohol is generally between 1 and 3 times that of acetophenone. No important effect of both by-products on the ac dielectric breakdown strength was observed     

分散剂对钛酸钡介电性能的影响

通过水煮损耗测试、温度特性、电导率和化学分析、瓷片表面显微结构等测试手段,研究了在固相反应制备钛酸钡的工艺中,向BaCO3粉体和TiO2粉体的混合球磨的浆料中加入聚乙烯醇作为分散剂对合成的钛酸钡粉体均匀性的影响。研究结果表明,碱性聚乙烯醇改善合成BaTiO3粉体均匀性的效果最好,介电常数峰值提高了2313、游离BaO含量降低了93.33％。     

Influence of internal mechanical stress and strain on electricalperformance of polyethylene electrical treeing resistance

Crosslinked polyethylene (XLPE) and low-density polyethylene (LDPE) insulations used in HV cables are not only subjected to electrical and thermal stresses, but also exposed to mechanical stresses, whether residual internal stresses created during the cooling process of the fabrication, external forces when cables are bent during installation or thermomechanical stresses caused by differential thermal expansion between the conductor and the polymeric material. In order to investigate the possible influence of mechanical stresses on dielectric properties of polyethylene, measurements were conducted on pin-plane XLPE and LDPE samples with various magnitudes of residual mechanical stresses around the embedded electrode. The time to inception, the growing rate and the shape of the electrical trees under different voltages are reported in this paper. Specimens with the highest values of residual stresses were found to have the shortest inception times and the longest trees after one hour of aging under different voltages. When the mechanical stress was allowed to relax, the treeing resistance was measured to be significantly improved     

Basic electrical processes in dielectric liquids

The basic processes of electrical conduction in dielectric liquids are reviewed, attention being drawn to the similarities between conductive electrolytes and insulating liquids. The concepts of the electronic amorphous solid state are employed to provide a framework for the review. The conditions at metal electrodes can be incorporated naturally into the scheme, and it is known that the space charge layers occurring on them can control conduction. Although electrical breakdown itself is not considered, the underlying electronic processes which will develop when breakdown electrical fields exist in the liquid are considered     

High temperature piezoelectric materials: Defect chemistry and electro-mechanical properties

Langasite (La₃Ga₅SiO₁₄, LGS) and gallium orthophosphate (GaPO₄) resonators exhibit piezoelectrically exited bulk acoustic waves at temperatures of up to at least 1400^∘C and 900^∘C, respectively. Their mass sensitivity at elevated temperatures has been found to be about as high as that of quartz at room temperature. Within its operation temperature range, GaPO₄ shows significantly lower losses than LGS. Factors restricting application relevant properties of LGS at elevated temperatures, such as the mass resolution, include excessive viscous damping. Therefore, the effective viscosity is determined as a function of the temperature by fitting the calculated complex impedance to the experimental data in the vicinity of the resonance frequency. The viscosity shows an Arrhenius-like behavior if a temperature independent contribution is subtracted. The activation energies of the viscosity for LGS and GaPO₄ correspond to those of the bulk electrical conductivity for each material. Viscosity and conductivity are obviously correlated. Therefore, it is highly likely that the predominant conductivity mechanism also controls the mechanical damping. First attempts to minimize the viscosity of LGS by doping are undertaken. Very light doping does, however, not change the conductivity and viscosity of LGS. Higher doping levels have to be applied and tested. Based on the electromechanical properties given for undoped LGS, the applicability of this material as resonant gas sensor at 600^∘C is demonstrated.     

Influence of anatase-rutile phase transformation on dielectric properties of sol-gel derived TiO2 thin films

The phase transformation behavior and resulting dielectric properties of sol-gel derived TiO₂ thin films were investigated. Thin films showed a typical behavior of mixture systems during the phase transformation; a kinetic investigation on the isothermal curve of pre-crystallized thin films revealed that the phase transformation was a first-order reaction with an Avrami time component of 1. Dielectric constants of TiO₂ thin films increased with the increasing amount of the rutile phase while the dielectric losses showed the opposite relationship. From a fitting process using the parallel mixing rule, dielectric constants of two end members of the mixture system were calculated to be 41.4 and 145.2 for the pure anatase and rutile phase thin films, respectively.     

温度和微水对变压器油及油纸绝缘介电性能的影响

开展了极寒环境下变压器油及油纸绝缘介电性能的研究和典型油-纸绝缘系统的电场分析.建立了极寒环境试验系统,在-60～～ 25 ℃温度范围内,研究不同微水含量下的变压器油及油纸绝缘结构的绝缘性能随温度的变化情况,并对试验结果进行了分析.     

The dielectric properties of meat

The permittivity and conductivity of beef and chicken samples were measured in the frequency range of 1 Hz to 1 MHz. Differences were observed in these dielectric spectra for commercially purchased, as compared to freshly slaughtered samples. In particular, fresh samples display a greater directional anisotropy in their electrical properties and a smaller, frequency-dependent conductivity. Changes in the dielectric properties are also produced by freezing and cooking procedures. These results indicate that measurement of the low-frequency dielectric properties of meat products could serve as a monitor of their storage and preparation history     

Effect of re-oxidation on dielectric properties in Ni-MLCC

The effect of re-oxidation treatment on the solubility of dopants and the dielectric properties of rare-earths (La, Ho) and V-substituted BaTiO₃ solid solutions, assuming the shell phase of X7R dielectrics, was investigated. Ho-V-substituted samples showed larger increase of the lattice parameter and T _c by re-oxidation treatment compared with La-V-substituted samples. Electron spin resonance measurements revealed that the oxidation of V³⁺ to V⁴⁺ or V⁵⁺ appeared in the range in which the increase of lattice parameter by re-oxidation treatment was observed. This suggests that the increase of T _c is due to the change of preferential occupational site of Ho ion from A-site to B-site, being accompanied with the oxidation of V³⁺. We also investigated the effect of re-oxidation treatment on the electrical properties and microstructure in Ni-MLCC samples, using rare-earths (La, Ho, Yb) and acceptors (Mn, V) doped BaTiO₃ based X7R dielectrics. The change in temperature characteristic of the dielectric constant by re-oxidation treatment was observed for the MLCC samples containing V with smaller content. In the case of Ho-V- and Yb-V-doped samples showed larger increase of the dielectric constant at around 120 °C compared with La-V-doped samples. The relationship between the microstructure and electrical properties of the MLCC sample was investigated by impedance measurement at elevated temperature.     

Polyethylene under electrical stress

Fifty years ago, the concept of an intrinsic electric strength for insulating solids was fashionable. It was supported by the sophisticated theoretical models of von Hippel, Frohlich and others for the interaction of electrons with crystal lattices in an electric field. The models came to be applied, rather implausibly perhaps, to polymers such as semi-crystalline polyethylene (PE). In that climate, the work of van Roggen on the high-field conductivity of single lamellar crystals of PE was notable. Since then, the picture of the insulating properties of PE has had to be painted with an increasingly complex palette in which the electrical elements have had to be supplemented by mechanical, chemical, and optical ones. The present review of the conducting properties of the polymer considers these other features, but concludes that the fundamental characteristics of the lamellar PE crystal are still the determining factors.     

Modeling of dielectric relaxation spectra of polymers in thecondensed phase

Discusses models and their possible implication in the interpretation of the relaxation spectra of polymers, particularly involving the concept of order/disorder systems. Furthermore, some examples of the application of the Dissado-Hill model have been provided in this work to explain quasi-dc (QDC) conduction processes, which have been observed in crosslinked polyethylene (XLPE) and low density polyethylene (LDPE), showing an ageing behavior with continuing use with an ac field in a humid environment. It is also shown in this paper how a measurement of dielectric relaxation properties on a wide frequency range may be used as a tool to investigate the ageing of polymeric power distribution cables with an ac field in a humid environment. Equivalent electrical analog circuits of dielectric relaxation spectra are also shown     

Fire test methods for electrical and dielectric materials

Methods intended for the measurement of combustibility are briefly reviewed. The need for fire safety assessment to address parameters that extend beyond a material's tendency to burn is discussed. Emphasis is placed on recent developments in fire testing which provide a more complete characterization of a material's fire behavior and associated fire hazards. Fire test apparatus and toxicity and corrosivity of combustion products are considered     

电容性电器设备介质损耗角实时测量方法

叙述了用矢量乘法技术在电力设备绝缘在线监测与诊断中的应用.测量系统采用数字合成波形发生器技术、模拟-数字乘法器技术对电力设备绝缘的漏电流进行正交分解,提高了小电流信号的测量分辨率;用以小波变换技术构成的数字滤波器对正交分解后的矢量进行数字滤波以提高系统的抗干扰能力.