Research on VFTO Characteristics of Substation using GIL-GIS-oil/SF6 Bushing Structure

GIL is one of the important ways to connect GIS substations through existing overhead lines in urban substations, and GIS is directly connected to the main transformer through oil/SF6 bushings, which is one of the important means to make the substation layout more compact. The research object of this paper is based on a 500kV substation. When VFTO is generated by the operation of the disconnector, the modeling methods of GIL and GIS busduct based on their geometric dimensions to obtain the unit-length-to-ground capacitance and unit-length conductor inductance, together with the travel time and surge impedance. The oil/SF6 bushing can be simulated as a multi-layer equivalent model considering its structure, and other GIS components makes use of electrical equivalent circuits composed by lumped elements (capacitances, inductances and resistances). Finally, the equivalent model of the whole substation for VFTO simulation is established in EMTP, and the VFTO waveform characteristics of the substation are analyzed through different operation modes. Furthermore, the influencing factors of VFTO are analyzed, and the suppression of VFTO waveform is simulated by means of damping resistance and magnetic ring.