Electric field distribution of UHVAC basin-type insulator with very fast transient overvoltage in GIS

UHV AC GIS Basin type insulator is the key component of the gas insulated substation (GIS). The stability and reliability operation determines the insulation strength level of GIS. However, because of the characteristic of switchgear in GIS, the very fast transient overvoltage (VFTO) occurs with high frequency, amplitude and gradient, which will threaten the safety of insulation. In the past time, electric field distribution with VFTO was calculated by traditional method which used the peak voltage as the boundary condition. In this paper, a transient method which have the effect of wave front in consideration was proposed. A circuit model of GIS was built to simulate the VFTO, and than a equivalent bevel flat top wave of VFTO was used to be a boundary condition. Eventually, a basic finite element model was established by using COMSOL, and the electric field was obtained when the wave pass through center conductor in instantaneous condition. Electric field distribution in different time were shown. Results indicated that when the wave process was in consideration, the electric field will be distorted and comparing with traditional method, it will make the electric strength increase.