Plant power supply device in an atomic power plant

Object: To avoid tripping of a 6.9 kV class bus line and to decrease a large electric current momentarily flown into a start transformer, in despite of the fact that the bus line is not changed over resulted from actuation of a generator lock-out relay. Structure: An atomic power plant comprising a bus line for a two-system plant power supply and a start transformer receiving power from an exterior system, characterized by the provision of a breaker for effecting the change-over of only one system bus line simultaneously with the reactor scrum and a breaker for effecting the change-over of the other bus line before a generator is tripped as a result of actuation of a generator lock-out relay in a predetermined period of time after the reactor scrum, to thereby reduce the momentary large current to the start transformer. (Kamimura, M.)