Through the investigation on the accident resulted from generator-transformer unit misoperation

find that the length of the cable in protection loop is too long and the distributing capacitance of the cable is too big. When the severe mutual interference between DC and AC circuits effects as DC grounding

the sudden discharge of distributed capacitance

as a disturbance source

activates the output relay. Countermeasures are suggested

shorten the length of DC control cables

increase the voltage of intermediate output relay and breaker trip coil

avoid the repetition of such problems.