PURPOSE: To enable reclosing of a circuit breaker according to the kind of an accident by finding zero-phase currents from the currents of two terminals and, if the zero-phase current of either of said terminals exceeds the preset value, forming judgement to be a grounding accident.
CONSTITUTION: In a transmission system with single-line indication of a three- phase AC wire, transmission lines 18 and 20 are equipped with circuit breakers 22, 24, 26, and 28. When for example the circuit breaker 24 is tripped by an accident in a protected area, it is inspected whether or not zero-phase currents are generated in terminals A and B and, if a zero-phase current generated in terminal A exceeds the preset value, judgement that a grounding accident has occurred is formed and the circuit breaker 24 is reclosed by the high-speed multi-phase reclosing method. If no zero-phase current is generated in the terminals when the circuit breaker 24 is tripped, judgement that a short-circuit accident has occurred is formed and the circuit breaker 24 is reclosed by the medium-speed three-phase closing method.
IWATANI FUMIO
KOBAYASHI JUNJI
SATOU KESAO
TOHOKU ELECTRIC POWER CO