Study On Surface Charge Accumulation And Dissipation On Cone-Type Spacer For220kV GIS

Gas Insulated Substation (GIS) has been widely used in the newly-built substation of all the big cities attributed to its advantages of less land occupied and good insulation performance. GIS mainly operates under AC and impulse voltage. And a lot of surface charge will accumulate on the spacer surface. Surface charge will not only enhance the local electric field but also provide charge for creeping discharge, which finally causes flashover. Therefore, it is very important to study the surface charge accumulation and dissipation characteristics on the cone-type spacer in SF6under AC and impulse voltage for solving a lot of surface flashover accidents of GIS with unknown reasons, improving the operation reliability and making the manufacturing technology of GIS better.Based on the actual252kV GIS, a cone-type spacer surface charge measurement experimental platform has been established. The surface charge on the cone-type spacer has been measured using the static capacitive probe. And three issues have been studied:1) the relationship between the surface charge distribution and AC voltage amplitude and duration.2) the relationship between the surface charge distribution and impulse voltage amplitude and applied times.3) the dissipation characteristics of the surface charge of the cone-type spacer in SF6.According to the principle of static capacitance probe method, a surface charge measurement system has been designed and manufactured. Through improving the insulation portion design of the static capacitance probe and manufacturing an anti-leakage and high resistance box, the charge resolution could be up to0.0187pC/(m2·nV) and the space resolution could be up to1.97085mm2. In order to measure the cone-type spacer surface charge surrounding SF6gas, this paper developed a three-dimensional control device, which can drive the probe to scan the insulator surface in the circumferential and radial direction with high precision(lmm of radial direction and1°of circumferential direction).This paper has studied the insulator surface charge distribution under different AC voltage values and different AC voltage application time. It is been founded that under AC voltage, the accumulated surface charge on spacer is mainly negative. And under high voltage stress, the growth of the surface charge with AC voltage duration time is obvious. Under impulse voltage, the accumulated surface charge on insulator is also mainly negative. And the growth of the surface charge with impulse voltage applied times is obvious. Through analysis of the test result, the surface charge on spacer is mainly produced by micro discharge which triggered by micro defects on the insulator or electrode surface. Based on that, surface charge distribution on the cone-type spacer is uniform, with local outstanding. The surface charge dissipation characteristics on the cone-type surrounding SF6gas is also be studied. It is be found that surface charge dispersed more quickly in the beginning period, with the velocity of0.09584μC/m2·h in the first hour. But later, dissipation rate greatly reduced. And finally, there is no-dissipation. This shows that the spacer surface charge is not easy to dissipate in SF6.