Reliability of digital relays with self-checking methods

Abstract

This paper addresses the reliability of protection system relays considering the self-checking resources. The operation of the relay is modelled by a Markov chain with the failure to operate and unnecessary operation states. The model applies to both conventional and digital relays. Data from the Brazilian transmission line protection systems were used for the determination of the conventional relay parameters. For the digital ones the total relay failure rate was estimated and the reliability indexes were calculated for different values of self-checking efficiencies and preventive maintenance intervals.