Protective circuit for expansion unit wiring system

The invention relates to a protective circuit for an expansion unit wiring system. The protective circuit comprises a line protection device connected to a 110 kV power system through a voltage transformer and two transformers with 110kV voltage classes. The two transformers share the same circuit to be connected with the 110kV power system. In the circuit, the 110kV side of each transformer is provided with an isolating switch, a current transformer and a circuit breaker which are connected in series. The output end of the line protection device is connected with the two circuit breakers of the 110kV sides of the two transformers. The input end of the line protection device is connected with an overvoltage protection and transfer trip local discrimination device. The invention firstly provides the expansion unit wiring system with a protection method suitable for the two transformers with 110kV voltage classes sharing the same circuit of a transformer station and a power station boosting station, solves the