Investigations on Requirements for UHV/EHV AC Switchgear by CIGRE Study Committee A3

On request of IEC Technical Subcommittee 17A, CIGRE Study Committee A3 “High Voltage Equipment” investigated the requirements for ultra-high voltage ac switchgear, especially for parameters which cannot be extrapolated linearly from the corresponding equipment characteristics with lower-rated voltage, namely 800 kV. For circuit breakers, such aspects are the first pole-to-clear factor, the amplitude factor, the time to peak to define the transient recovery voltage envelope, the surge impedance of overhead lines, the damping and refraction of traveling waves, long-line faults, transformer-limited faults, initial transient recovery voltage, and the influence of shunt and series compensation. Disconnectors utilized for interrupting the bus transfer currents, bus charging currents and very fast transients, ground switches used for interrupting induced line currents, and high-speed ground or earthing switches have been studied as well. Based on these system and substation studies and simulations, recommendations have been provided to IEC SC 17A.