Operating circuit anomalies are one of the main reasons for protecting system failures and protection incorrect actions. However, the operating circuit still doesn’t have the functions of on-line monitoring and self-inspection. This paper proposes an effective method for the on-line monitoring and state evaluation of relay protection operating circuit. Firstly, the trip/close coil current is monitored on-line to detect faults in the operating circuit, such as poor contact and disconnection. Then cooperated with the auxiliary contact state, the precise positioning of the abnormal part in the operating circuit is realized. Besides, based on the dynamic fault tree method, the operating circuit reliability model is built. Combined with the online monitoring information, the operating circuit health assessment indicator is constructed. Simulation results prove that the method can effectively monitor and evaluate the state of the operating circuit, and provide theoretical and data support for the CBM implementation of the secondary equipment.

coil current,operating circuit,on-line monitoring,relay protection,state evaluation