Research Of The Influence Of The Residual Charge On The VFTO In The GIS

Under the promotion of the rapid development of our country's power utilities, the gas insulated station(GIS) has been widely used, meanwhile, the voltage level is also rising. Due to the specific structure and electrical characteristics of the GIS, although it has many advantages, it also has many negative effects inevitably. The very fast transient overvoltage (VFTO) generated by the operation of the disconnector is a typical phenomenon in GIS. Its wave-front time is short, shocking intensely, and it may do harm to the insulation of the internal components. When the disconnector of the GIS operated, the residual charge will be left on the bus. When the discharging of the residual charges is superimposed on the VFTO generated by power source due to the disconnector operation, it may generate more serious over-voltage, or even an accident.In this thesis, for the phenomenon just mentioned, firstly, the causes of residual charge, manifestation mode and the discharge process are analyzed. Based on transmission line theory, the equivalent analysis formula are analyzed and derived for responses generated by the residual voltage and residual current along the line theoretically. Secondly, based on the MATLAB, the numerical Laplace inverse transform (NILT) method is applied to conducting the simulation of the VFTO of the bus caused by the residual voltage, and the results are compared with the that of reference experiment to verify the correctness of this method. The comparison with the equivalent model established in ATP-EMTP is also done. Through comparison the method presented in this paper is more accurate than the lumped capacitance method in the description of the discharge process of the residual charges. Thirdly, the straight line GIS bus and GIS net is simulated separately. Under the different residual voltage amplitude or different lengths of the line, the nodal voltage variation is studied. Some valuable conclusions are obtained. Finally, with the actual GIS, the residual voltage discharge test has been experimented, and the discharge voltage is measured at the specific location, and compared with the simulation result by the method presented in this paper. Then a further verification of the correctness of this method is obtained. Through all these researches, the more accurate simulation model which describs the impact of the residual charge to the VFTO in the GIS is established. At the same time, some useful conclutions are obtained. It is laid a good foundation to future research, design and manufacture of the gas insulated station.