On the risk evaluation of HV line protection based on Markov model

It is a significant problem to evaluate the running protective relay devices. This paper proposes a novel risk evaluation method for HV line protection. Firstly, six states of the system are established. Considering the self-check of the protective relay, four risk indexes are derived. Then, according to the state division of the system, ten state Markov model is established and then the risk and unavailability indexes of the system can be calculated. Finally, based on some real grid data, the unavailability and risk indexes is analyzed under different maintenance cycles, failure-rates and self-check rates. The conclusion is drawn: the risk and unavailability has different changing trend with the maintenance cycle increasing; a smaller failure rate or a larger self-check rate can keep risk and unavailability at a lower level.