High frequency model of metal-oxide surge arrester for researching on VFTO

In the simulation of very fast transient over-voltage (VFTO), establishing the accurate equivalent model of electrical equipments in GIS has a major effect on the calculation results. At present, nonlinear resistance model based on static V-I characteristics is used for metal-oxide surge arrester (MOA) when simulating the VFTO in GIS. But the result is not accurately, because polarization in high frequency electric field is neglected by this model. In this paper, combined with the conductive process of grain and grain boundary in the microstructure of arrester valve piece, based on the polarization theory in alternating electric field, the high frequency circuit model of arrester is proposed, and the model can accurately simulate polarization process of arrester in high frequency electric field by comparing the simulation and the actual waveform. Then based on a GIS in China, the VFTO is simulated with the high frequency model, and the effect of MOA on VFTO amplitude, spectrum characteristics and gradient are analyzed. The simulation results show that, MOA has some inhibitory effect on the amplitude and steepness of VFTO, especially for the equipments that nearing the arrester. In addition, the nearer equipment from the arcing disconnector, the greater steepness on it, conversely, the farther from the disconnector, the steepness is lower. The result has some practical significance for calculating and analyzing VFTO.