Very fast transients in 1000 kV gas insulated switchgear

For 1000 kV transmission system, disconnecting switches (DSs) fitted with resistors and high-speed grounding switches (HSGSs) were developed. At the UHV Equipment Test site, DS surge and HSGS closing surge tests were conducted. Then, the very fast transient overvoltage (VFTO) controlling performance of the DS and the surge voltage level due to HSGS closing were confirmed. In the same tests, the surge level transferred into the protecting and controlling components were confirmed to be low enough for them to operate properly. The transferring mechanism was clarified by an electromagnetic wave propagation analysis.