A circuit switcher is installed on an input circuit by a substation, and only the one of two circuit switchers maintains an ON contact point. When the substation which supplies and receives electricity to and from a first transformer, a second transformer, and a third transformer is blacked out, the contact point of the circuit switcher is changed to the opposite contact point of the circuit switcher to receive electricity from the other substation. When errors occur in an adjacent ground transformer, the first transformer and the second transformer are operated in parallel by maintaining a transformer switcher in the ON contact point. Therefore, the power is supplied via a DC converter and a lead-in circuit breaker, and the third transformer supplies the output of a common load to a tram station via a low voltage panel.COPYRIGHT KIPO 2016회로절체기는 변전소별로 입력회로상에 설치하여 2개 중 하나의 회로절체기만 ON접점을 유지하여 제1변압기, 제2변압기, 제3변압기에 전력공급 및 수전 받는 변전소가 정전될 경우 다른 변전소로부터 수전 받게 회로절체기의 접점을 반대접점으로 전환하며 인접 지중변압기에 고장이 발생할 경우 변압기절체기를 ON접점을 유지하여 제1변압기와 제2변압기를 병렬운전하여 직류변환기, 인입차단기를 거쳐 전력 공급 및 제3변압기는 상용전원 출력을 저압반을 거쳐 트램정류장에 상용 부하에 공급한다.
