Reliability analysis of protective relays in low voltage distribution network

A new reliability index is defined considering correct inaction, failure events and the failure probability of protected component in protective relays according to the risk theory. Relaying reliability is separated into the two different aspects of dependability and security in the calculation based on the losses resulted from failure events. A general 8-state Markov model is set up where resist-operation state is divided into extended state and no-extended state. The relation between relaying reliability and failure probability of protected component was drawn. Then, the optimal maintenance interval was derived by taking the minimum of risk assessments for protection as target function. The general and detailed reliability model with its algorithm was validated with the protective relays test. Compared with the traditional method, the proposed index and model are more effective in low voltage distribution network.