04_avlanche_ analysis - Conference Record of the 2004 IEEE...

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Conference Record of the 2004 IEEE Intemational Symposium on Electrical Insulation, Indianapolis, IN USA, 19-22 September 2004 Numerical Analysis of Effect of Avalanche Space Charges on Corona Onset Voltage Dianchun Zheng, Chuntian Chen, Xueyong Sun, Huawei Liu, Jiaxiang Yang Harbin University of Science & Technology Harbin China 150040 zhenzdianchun@.sina.com Abstract: Based on the Townsend collision theory, the number and field strength of the space charges have great effect on the onset voltage of partial discharge in gaseous insulated apparatus. The facts have not only been proved by many researchers' work, but also been demonstrated by mathematical analysis. In fact, the effects of space charge field created by both the positive ions and the electrons are largely different. The electrons of the head avalanche cause the avalanche to forther gmw because the electron field strengthens the electric field between the head avalanche and the anode. And positive ion field also reinforces the electric field between the tail avalanche and the cathode, and the middle areas of the electron avalanche are full the equivalent ions and electrons, which are called the zone plasma. With growing of the zone plasma in great speed, the gap of electrodes quickly breakdown. Computer programs are developed to calculate the onset voltage. The space charge fields both the positive ions and the electrons are considered in the calculations. The calculation procedures are represented in details. Meanwhile, Results are gained for the air and the SF6 for a wide range geomehical parameters and gas pressures. The results show that the electrons promote the growth of the avalanche whlle the positive Ions retard the growth of the avalanche. INTRODUCTION Air and SF6 are widely used as insulation and arc quenching dielectrics. In order to avoid power accidents, improve the insulation performance of power equipments, research the new technique of insulation and discover new insulation medium, it is important to study the mechanism of gas discharge and the factors influencing the course of discharge. According to the electron collision ionization theory of Townsend, the electron avalanche is the basic process in gas discharge [I, 21. However, the effect of the space charge fields caused by electron avalanche is neglected in the calculations of the onset discharge voltage. The effects of space charge fields on applied field are shown in Figure I.
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This note was uploaded on 06/08/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

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04_avlanche_ analysis - Conference Record of the 2004 IEEE...

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