A New HVDC Circuit Breaker System Design For -+ 400 kV

A HVDC circuit breaker based on the commutation concept is under development. Tests of components indicate the breaker is capable of interrupting a fault current of 8 kA on a 400 kV system and absorbing up to 10 Megajoules of system energy without generating more than 1.6 P.U. voltage on the system. An ultrafast hydraulic actuator enables the breaker, which is independent of terminal actions, to respond rapidly to a trip signal and to initiate the current limiting, process within 5 miseconds after receipt of a trip signal. A new hydraulic valve design minimizes the delay before motion begins. Interruption occurs in series connected vacuum interupters chosen because of their unique ability to interrupt high dl/dt before current zero followed by a high RRRV with a short contact gap. System energy isabsorbed by Zn0 surge arrestors mounted across the breaker. Their extremely non-linear current-voltage characteristic allows them to be utilized with no series gaps. The overall design is a dead tank type using SF6 gas as a dielectric medium. The actuator and all control functions are located at ground potential with easy access for inspection or adjustment. Operational specifications such as duty cycle and operating temperature range have been carried over from NEMA standards for ac circuit breakers where applicable.