Research On The Electromagnetic Interference Due To Switching Operation In Gas Insulated Substation

Supported by National Natural Science Foundation of China (No.50077006) and Natural Science Foundation of Hebei Province (No.503424), the setup method of circuit model for instrument transformer and transient electromagnetic interference to the secondary equipments through conductive coupling due to switching operations in Gas Insulated Substation (GIS) are researched in this paper. The main contributions are as follows: 1. The method to setup high frequency transfer function model for instrument transformer in GIS by means of Vector Fitting is presented. According to the practical condition, the order reduction method for the high frequency transfer function model of instrument transformer is proposed. 2. The setup method for instrument transformer's circuit model is proposed . We use a special R L C synthesis method for transfer function based on the real part decomposition technique to set up the high frequency circuit model for instrument transformer. The circuit model for a 110kV potential transformer in GIS is built. Time domain and frequency domain simulation results have validated this method. 3. In using the FDTD method to research the transient process of the overhead line, for the convenience of the time domain convolution, the Vector Fitting method is adopted to expend the frequency domain form of ground return impedance into a sum of finite exponential functions which are easy to be treated and test to be valid. Compared with EMTP, the method proposed is demonstrated to be effective. 4. The modeling methods for every primary equipment in GIS are discussed and summarized . A primary system model for a 125kV GIS is built by EMTP, the VFTO and TGPR as well as the transient current in the grouding conductor are calculated. There is a good agrement between the simulation results and measurement results. 5. An whole conductive coupling model for a 110 kV GIS which containing three-phases in one encapsulation is built by EMTP, the VFTO and TGPR as well as the interference voltages on the port of the secondary equipment are calculated. The simulation results are consistent with the measurement results of another 110 kV GIS. The magnitude of the disturbing voltages are not big(about 100V ), but their main frequency is very high(30 MHz ～40MHz ), This phenomenon can't be neglected by the secondary equipment designer. 6. The 3D-electromagnetic field of a 220kV GIS are calculated by means of Numerical Electromagnetic Code. In order to decrease the workload, the "modified coefficient"method are adopted. According to the practical conditions of this GIS, the method to decrease the computing error are put forward. Compared with the measurement results, the method proposed is demonstrated to be effective.