Computer Simulation Of Electron Avalanche Process For Gas Insulation In Short Gap And Discharge Signal Acquisition

Gas discharge is a subject of researching the motion law and its application of charged particle in electrical field. Experimental research and theoretical analysis of the gas discharge are important in understanding the law of gas discharge, making use of electrical characteristic of gaseous dielectric, developing new type high voltage apparatus, implementing monitor online and safety operation.Scientists have done lots of researching work in questing phenomena of gas discharge and gained great achievement,but there is no an ideal model to describe the gas discharge because the process of gas discharge concerns lots of affecting factors and different aspects of substance microstructure (including electron, atom, molecule and photon). According to the electron collision ionization theory of Townsend, the electron avalanche is the basic process in gas discharge. After investigating literatures of gas discharge domain at domestic and abroad and based on the Townsend and streamer theory, in the thesis, the mathematics model of gaseous electron avalanche in short gap is constructed according to the Raether and Meek criterion and the processes of electron avalanche growth are simulated by computer. For the plane-to-plane and pin-to-plane electrode systems which are filled with air and SF6, respectively. The avalanche growth processes are numerically computed and analyzed under fully considering the space charge fields of the electrons and the positive ions, meanwhile the behaviors of charged particles in electrical field have been taken into account in the calculation procedures, which include ionization, attachment, drift, diffusion and density of gas molecule. Simulation results show that the space charge fields affect the electron avalanche development greatly; the effect to negative pin is greater than that of positive pin and the effect degree is relative to the characteristic of dielectric and density of gas molecule. Electromagnetic wave signals are eradiated with the development of electron avalanche and the signal characteristics are different with the shapes of electrode systems and environmental conditions. The acquired signals are analyzed in the time-frequency domain to gain the patterns of gas discharge under different conditions and characteristic quantities used for recognizing defects of high voltage apparatus with gas insulation.In this thesis, not only a new method is provided to research mechanism of gas discharge, but also theoretical foundation and technological reference are given in estimating the electric strength of gas dielectric and monitoring online for high voltage apparatus with gas insulation.