Simulation Analysis Of Air Gap Defect Discharge Of Solid Insulating Material In GIS

Solid insulation materials are widely used in high-voltage equipment of Gas Insulated Switchgear（GIS）.However,many solid materials inevitably have insulation defects during the manufacturing process,resulting in partial discharges.Partial discharge is one of the important factors that cause aging and breakdown of insulation materials.Due to the small number of partial discharge test samples,high cost and inaccurate statistical law,it helps to detect and evaluate the insulation status and service life of power equipment by establishing a partial discharge simulation model to study the characteristics and development law of partial discharge of insulating materials.In this thesis,the discharge characteristics of air gap defects inside solid insulating materials are studied by combining with partial discharge theory.Firstly,the air gap defects in the basin insulator are extracted;the physical model of partial discharge is established and the various parameters required for the simulation model of partial discharge are calculated and described.The classical three-capacitor model is used to build the air-gap partial discharge simulation circuit through Simulink;the voltage waveform and pulse current of the partial discharge are analyzed and the effect of the change of supply voltage amplitude on the partial discharge is discussed using the three-capacitor simulation model.Secondly,the simulation process of partial discharge is simulated by COMSOL Multiphysisc controlled by MATLAB to establish the finite element simulation model.The microscopic partial discharge phenomenon is combined with the macroscopic physical model.The electric field and potential distribution in the model are solved by using the finite element method.Based on the existing research results,the randomness of the partial discharge is simulated by the difference of the discharge delay time according to the law of the generation of free electrons and the decay of the charge on the air gap surface.And the simulation results of the two simulation models are compared and analyzed.Nextly,the finite element model is used to simulate the partial discharge at different applied voltage amplitudes,different applied voltage frequencies and different insulation defect sizes.The parameters characterizing partial discharges,such as the discharge phase,the repetition rate and the charge magnitude of the positive and negative discharge pulses,are statistically analyzed according to the discharge pattern to study the development law of partial discharges under different conditions.The simulation results show that with the increase of applied voltage amplitude and applied voltage frequency,the number of discharges and the charge magnitude increase.With the increase of air gap defect radius,the number of discharges decreases and the charge magnitude increases sharply.Finally,air gap discharge characteristics under lightning impulse voltage are simulated and analyzed.The Fourier transform is used to decompose the lightning wave.Considering the high frequency characteristics of the medium,the potential distribution of the model under the lightning impulse voltage is obtained through the superposition of the transient electric field calculation results,and the discharge situation is simulated and analyzed.Compared with the working frequency voltage,the lightning surge voltage wave has a short action time and fewer discharges.But the maximum discharge volume is about 1.97 times of the maximum charge magnitude under the working frequency voltage.