Research on the SF6 decomposition components of the GIS bus spike PD and the insulator surface PD

Abstract

According to the problem that the intelligence is not high of the recognition of GIS PD types by SF6 decomposition components, using the real 110kV GIS platform, simulating two kinds of insulation defects PD of SF6 gas, and making the research on the change of the four kinds of gases of CO2,CF4,SO2F2,and SOF2,then making the research on the ratio of components of c(SOF2)/c(SO2F2), and c(CF4+CO2)/c(SOF2+SO2F2). The results show that the two types of ratio of components of the GIS bus spike PD and the insulator surface PD are significantly different. Therefore, the two types of ratio of components can as the features to identify the GIS bus spike PD and the insulator surface PD. Introduction SF6 gas is widely used in gas insulated switchgear (GIS) as an excellent insulating medium. Under normal circumstances, the chemical property of SF6 is very stable, and not easy to break down. But in the case of the GIS device has internal insulation defects and partial discharge, SF6 gas will break down and produce a trace of the gas. [1]. High energy electron impact caused by high electric field in the partial discharge will cause SF6 gas decomposition. 6 (6 ) , 1 ~ 5 X e SF SF X F X      (1) 1 X X e SF SF F     (2) Most primary decomposition products SFX (X=1,2,... 5) will compound to SF6 molecules, but there is water, oxygen and other impurities in the electric chamber. The water, oxygen and other impurities will be associated with the SFX (X=1,2,... 5) to generate CF4, SO2F2, SOF2, SO2, SOF4 and other products [2]. If the discharge area is surrounded by carbon material (such as stainless steel metal electrodes, solid insulating materials, etc.), the F and O atom in the gas chamber will react with C atom, producing CF4 and CO2 and other products. At high temperature, the C atom also reacts with CO2 to generate CO [3]. In this paper, using the real 110kV GIS platform, two kinds of insulation defects GIS of bus spike PD and the insulator surface PD will be tested. This paper will focus on four kinds of gases of CO2,CF4,SO2F2 and SOF2,and the ratio of components of c(SOF2)/c(SO2F2) and c(CF4+CO2)/c(SOF2+SO2F2). Finally find out the methods to identify the GIS bus spike PD and the insulator surface PD. 3rd International Conference on Machinery, Materials and Information Technology Applications (ICMMITA 2015) © 2015. The authors Published by Atlantis Press 1010 Overview of experimental system The whole experimental system is composed of the GIS experimental model, the pressure device, the SF6 component analysis device and the PD monitoring device. The structure of the GIS experimental model is a three phase, and the insulation level is 110kV which is divided into 6 gas chambers. The gas chamber is separated by a basin insulator, and each gas chamber is provided with the air outlet and the barometer. The gas chamber which is horizontally placed is 1# and the gas chamber which is vertically placed is 2#. Gas chromatograph of Huaai GC9760B will be used to analysis SF6 components. Fig.1.GIS experimental model Construction of insulation defect In the 2# gas chamber, the electric wire is arranged on the edge of the surface of the insulator. Wire ground clearance is 60mm, and the surface distance is 63mm. The bus spike partial discharge model is set up in the 1# chamber. Spike length is 4.7cm, and the gap length is 2.4cm. (a) 2# gas chamber (b) 1# gas chamber Fig.2. The construction of insulation defect Experimental data acquisition and data processing In this experiment, high purity SF6 gas (99.999%) was used. In this paper, the SF6 gas was measured after filling in the electric chamber. The results show that the content of CO2 in 2# was 1.5895ppm, the content of CO2 in 2# was 1.5771ppm, the content of CF4 in 1# was 1.4895ppm, the content of CF4 in 1# was 1.4762ppm. In order to compare the trend of SF6 decomposition components of two kinds of insulation defects, a constant volume of PD will be ensured as far as possible by adjusting the voltage. The experiment used the mode of three phases of the common pressure, and the experimental voltage was maintained between 31kV~35kV, and the volume of PD of the gas chamber of 2# and 1# was1300pC to 800pC. The SF6 gas pressure of two gas chambers was 3.5MPa. The experimental voltage was maintained to 240h continuously of insulation defects in 2# and 1# gas chambers, and gas chromatography was used to trace the SF6 discharge (every 12h~24h), and the quantitative results were obtained.