For lOOOkV 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 low enough for them to operate properly. The transferring mechanism was clarified by an electromagnetic wave propagation analysis.

Insulation level (LIWV 2250 kV) of loo0 kV gas insulated switchgear will be adopted by installing high performance loo0 kV surge amsters. But when temporary overvoltage (TOV) is generated in power systems at line faults and load rejection including Ferranti effects, high performance surge arresters flow discharge current according to the value of TOV. Therefore, it is important to check TOV discharge capability of surge arresters. This paper describes the screening of zinc oxide elements using thermography (thermal uniformity factor) obtained by an infrared radiation camera, with discharge capability of surge arresters for loo0 kV power system.

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