Abstract: In Huaneng Jinghong Hydropower Station, during the transmission test of the 500kV GIS breaker before it was put into operation, it was found that there were some problems existed in closing circuit of the breaker. The parasitic circuit, which was caused in match of the operation mechanism of the breaker with antijump device and the protection device, and its hazards were analyzed briefly. The antijump function of the protection device and the internal antijump function of the operation mechanism were compared. A more rational improvement scheme was put forward, and the importance of the antijump function in the secondary circuit was pointed out.

Key words: breaker, control circuit, protection, anti-jump circuit, parasitic circuit