The 35kV side of the total step-down substation (the high-voltage side) adopts the connection mode of the outer bridge. There are two main transformers, one is running and the other is running in hot standby mode (switching periodically and not running in parallel with each other). The 6kV side (low-voltage side) is supplied by the main transformer in operation, which adopts the single-bus (switch) sectional wiring mode, and supplies 9 lines of outgoing load through the switch, among which 6 lines reduce 6kV to 380V through the transformer.According to the above comparison and discussion on the main junction mode of the high-voltage side and low-voltage side of the substation; The selection of transformer determines the master wiring diagram of the total step-down substation.