VFTO Suppression by Selection of a Combination of Initial Phase Angle and Contact Velocity

The magnitude of very fast transients (VFTs) generated in disconnector operation in gas-insulated substation (GIS) is mainly determined by breakdown voltage between stationary and movable contacts. Moreover, the initial phase angle of source voltage and the movable contact operation velocity of disconnector are two important factors of affecting the breakdown voltage. The combination of initial phase angle and contact velocity to suppress VFTs is theoretically studied. With 3-D electrostatic simulation model, the capacitance parameters are calculated at different separations between stationary and movable contacts. Taking measured relation between the breakdown voltage and the separation of contacts as criterion, VFTs can be analyzed under different combination of initial phase angle and movable contact velocity. The effectiveness of the method is verified by comparing with experimental data. Based on this method, the effect of initial phase angle, movable contact velocity, and residual charge on repeated breakdown voltage in GIS is discussed and analyzed, and the optimum phase angle for closing and opening operations are selected. The very fast transient over voltage is remarkably suppressed with selection of optimum initial phase angle when disconnect is operated under enough fast velocity of movable contact.