Design Of Surface Charge Measurement System And Test Of Polymer Insulating Materials

In recent years, polymer insulating material is widely used in the gas insulated equipment, plays the roles of supporting and insulating. Surface charge can gradually accumulate on insulator surface under the stress of high voltage. Surface charge accumulated on insulator will not only make the local electric field aberrant, it also provides a number of free charges for the formation of the creeping discharge process. Surface charge may lead to surface flashover occurred along insulator in serious cases.The reduced dielectric strength has been attributed to the presence of such charge. Compared with the AC system, surface charge accumulated on insulator more seriously under the DC voltage, it hindered the extensive application of dc gas insulated equipment. Therefore, it is very important to study the surface charge accumulation and dissipation characteristics on the cone-type spacer in SF6 under DC voltage for improving the operation reliability.A surface charge measurement system based on the active electrostatic probe method was developed in this paper. This system can be used to explore the mechanism of surface charge accumulation and dissipation through simulating the process of surface charge accumulation under the DC voltage. It mainly included static potentiometer, measuring probe, GIS simulation tank, 3D motion control system, control mechanism, data storage systems. The measuring probe and electrostatic potentiometer is used for surface charge measurement. GIS simulation tank is used for simulating the running environment of the SF6 gas insulated equipment, it could withstand-0.1~+0.5MPa pressure. The 3D control device is developed to drive the probe to scan the insulator surface in the circumferential and radial direction with high precision. The radial accuracy can reach 1mm, the circumferential accuracy can reach 1°.On the basis of previous research, two methods of surface potential- surface charge transformation are introduced in this paper. The first method is based on the finite element matrix analysis, the second method is based on charge simulation. The results of this two methods is relatively close. Then the calculate course of the second method is more simple and the result is more accurate. The method based on charge simulation is recommended for surface potential-surface charge transformation calculation. The surface charging behavior of two different types of insulators was investigated by applying a DC voltage between two parallel electrodes. Experimental results show that the average charge density increases with the increase of the amplitude and time duration of the applied voltage, and surface charge distribution is closely related with the polarity of the applied voltage. The normal-field strength on the surface of insulator is the essential factor for the deposition of surface charges at the interface of gas-solid dielectrics. The charges on the surface of insulator are mainly derived from the free charges in gas side.The surface of the cylindrical insulator sample is charged by external corona. The results show that the total surface charge is in the tendency to the exponential decay along with time. It dispersed more quickly in the beginning period, then the decay rate of the surface charge become slower with time. Probably bulk neutralization was the dominant decay mechanism for corona charged polymer insulating material. The negative charge decays more quickly than the positive charge under certain conditions.