Protectability evaluation of protective relays based on a probabilistic model

This paper provides a novel view for the performance evaluation of protective relays. The paper starts with a Gaussian model for the protective relay setting to describe the effective zone of protection by considering the measurement errors, and introduces the performance index “protectability” for the protective relays. Protectability is defined including the correct trip probability (CTP) and no un-wanted trip probability (NUTP). The CTP and NUTP of different types of relays are analyzed based on their specific features through qualitative analysis, which aims to provide a basic understanding of the relay performance and make a basis for the further quantitative analysis.