Improved analytic model to detect hidden failure of protection relays

Abstract

Hidden failure of protection relays is one of the important reasons of cascading failure and disconnection of power systems. It is significant to improve the reliability for protection. So far, the hidden failure remains undetected. An analytic model based on protection signals is proposed to detect hidden failures of protection relays in this paper. In this model, fault location, protection start signal, protection action signal, breaker tripping signal, protection return signal and auto-re-closing signal are all treated as logic variables. To build the analytic model, the principles of protective relay settings and the rules of circuit breaker trips are expressed with a set of logic equations. As the model dimension is large, it is difficult to find out the analytical solution. Therefore, we use discrete particle swarm optimization to solve this model. The optimal solution of the model represents the fault location and the expected states of protective relays and circuit breakers. Finally, the comparison between the real state and expected state is used to detect hidden failures. An example demonstrates that this method can be used to check the hidden failure effectively.