Surface potential sensing for 320 kV high-voltage direct current gas-insulated system

A system for the measurement of surface potential on epoxy insulator within a direct-current (DC) gas-insulated system (GIS) of 320 kV nominal voltage is presented. Challenges encountered were the operating conditions: applied voltages up to 250 kV -and hence elevated electric field stress-, elevated temperature generated by the full load conductor current of 4600 A, pressurized gas atmosphere, and continuous operation for periods up to 6 months. Furthermore, a positioning system integrated within the GIS enables sequential scanning of two insulator surfaces while minimally disturbing the original system geometrical and electrical configuration. The sensor itself is modified non-contact voltmeter, using a miniature electrostatic field chopper probe. We demonstrate the capability of the system by following the time evolution of the surface potential on DC epoxy partition insulators, as well as recording its spatial distribution in the final resistive state.