Research on Very Fast Transient Overvoltage During Switching of Disconnector in 550kV GIS

This paper establishes a circuit-simulation model about 550kV gas insulated switchgear (GIS) of Hongping pumped storage power station by using Electro-Magnetic Transient Program (EMTP). Then, the very fast transient overvoltage (VFTO) is calculated when the transformer, the bus line and the outgoing line are switched. As to the calculation results, the influence of VFTO on transformer as well as the influence of cable on VFTO are analyzed. Analysis shows that VFTO amplitude at transformer port is small, but it may excite significant internal resonance voltage under high-frequency oscillation which may harm the turn insulation of power transformer. Besides, long cable connecting the ground part and underground part of GIS accelerates the attenuation of the transient progress. Finally, the case in which the most serious VFTO of transformer port appears is chosen as a model to research the VFTO's suppressing measure. The research reveals that building a 3-meter-long overhead line between GIS bushing and transformer can effectively keep the wave front steepness below the restriction level. The wave front steepness of VFTO decreases by 30.2% from
$\mathbf{1631}\ \mathbf{kV}/\mu\mathrm{s}$
to
$\mathbf{1138}\mathbf{kV}/\mu \mathbf{s}$
.