Liu Fuyi

Study on improving the tracking and erosion resistance of silicone rubber

Metal hydroxide filler has an evident influence on the electrical properties of silicone rubber used for outdoor insulation. This paper investigates the influence of alumina trihydrate (ATH) and magnesium hydroxide on the tracking and erosion resistance of silicone rubber. The research shows that the insulation performance improves with increase of filler concentration of ATH and magnesium hydroxide, but that adding excessive filler depresses the performance again. The results show that the tracking and erosion resistance of compound hydroxide filler is superior to that of single hydroxide filler. The effect of hydroxide filler level on vulcanization characteristics of silicone rubber is also investigated. The filler decreases the vulcanization speed and the vulcanization degree, which affects the tracking and erosion resistance. The results can be explained by the presence of an active center in the silicone rubber.

Studies on degradation mechanism of ZnO varistor under impulse stress by thermally stimulated current

The degradation mechanism of a ZnO varistor under impulse current stress has been studied. It is found that the impulse degradation, like DC degradation, arises from the variation of double Schottky barriers at the grain boundary which has been investigated by thermally stimulated current (TSC). It is concluded that the differing change of Schottky barriers is due to the high concentration of carriers injected into the grain boundary layer and accumulation of trapping effects in the layer, ultimately resulting in the change of Fermi levels.<<ETX>>

The influence of varistor disk capacitance of MOV arrester on its voltage distribution

The influences of varistor disk capacitance and its distribution on the voltage distribution along an MOV arrester column were investigated. The numerical computation of voltage (or gradient) distribution of the 110 kV-class arrester with a composite housing (or shell) and a porcelain housing were presented respectively. The finite element method (FEM) was used for this computation. The measurement and statistical analysis of processing varistor disk capacitances were also taken. After rearranging the varistor disks, according to their capacitance, the voltage distribution of the arrester became more uniform. The optimal voltage distribution was described using an adaptive method.

Study of dielectrical properties of a new high permittivity material

High permittivity material is usually used to achieve larger stored energy in capacitors. In particular, many high permittivity materials has been used to achieve excellent stress control at cable terminations. In our paper we have investigated the dielectric properties of a new high permittivity BaTiO/sub 3//Al/LDPE composites with volume fraction of metal Al 0.20 and volume fraction of BaTiO/sub 3/ from 0.10 to 0.40 at various temperatures and frequencies. Resistivity of the materials as a function of volume percent BaTiO/sub 3/ powder were measured at temperatures. Dielectric constant of the materials are compared with the two-component composites containing Al/LDPE and BaTiO/sub 3//LDPE over a wide rang of volume loading. In theory we propose to improve the effective cluster model for disordered suspension of conducting particles exhibiting substantial permittivity enhancements, and to extend it to be applicable to three-components systems, containing conducting particles, ferroelectric ceramic and polymer insulator. Dielectric experimental data are needed for meaningful comparison between theory and experiment.

SrTiO/sub 3/ capacitor-varistor ceramics exhibiting surface effect

The electrical properties and microstructure of SrTiO/sub 3/ capacitor-varistor ceramics sintered in different atmospheres are investigated. The results show that samples sintered in a strong reducing atmosphere of 25%N/sub 2/+75%H/sub 2/ and heat-treated in air have a low-resistive core with a high-resistive surface layer around it, which we name the surface effect. XPS results reveal that the surface effect results from an oxygen diffusion process during heat treatment.

An automatic measuring device based on PC for MOVs' aging test

A new kind of system based on a PC for the metal oxide varistor (MOV) aging test has been developed, which can detect and analyze the leakage current signal with the aid of the computer. The principle of the system is presented in brief.

The mechanism of degradation of polymer under electrical stress

The mechanism of polymer degradation was studied by means of an accelerated electrical aging test of polypropylene. The microchemical structure and physical structure of the sample before and after aging were investigated by small angle X-ray scattering, electron paramagnetic resonance, and infrared spectroscopy. The trap parameter was evaluated using the photoconductive current spectrum and surface potential. The macromolecules were scissored under high electrical stress. The free radicals initiated further decomposition, and micropores resulted from chain reactions involving macromolecules. Micropores, free radicals, short groups, and the terminals of scissored groups formed in aged samples and increased in number with aging time. The free radicals and micropores were the manifestations of the traps created by electrical stress. The relations among the chemical structure and the trap density and depth are discussed.<<ETX>>

Polarization absorption currents and conduction response characteristics of zinc oxide varistors

The absorption currents and conduction response characteristics of zinc oxide varistors were measured with step voltage pulses of different amplitude, and a series resistance was used to stimulate the ZnO grain resistance of zinc oxide varistors. Based on an analysis of the experimental results, three kinds of absorption current were found, and an equivalent circuit describing the electrical properties of zinc oxide varistors was developed. It is deduced that conduction response time results from the equivalent capacitance of the grain boundary, and there is a close relation between the conduction delay phenomenon and the polarization absorption current. The larger the ZnO grain resistivity the shorter is the conduction response time.<<ETX>>