Risk evaluation model for relay protection considering communication delay and bit error

This paper proposes a risk evaluation model to assess the impact of communication delay and bit error on relay protection. First, the mechanism of mal-function of relay protection caused by communication delay and bit error is introduced. In general, a channel´s consistent delay or bit error results in refuse-operation, while a channel´s inconsistent delay normally causes false trip. Based on the analysis of probability distributions of communication delay and bit error, the probabilistic models of false trip and refuse-operation are proposed. With the probabilistic models, risk of power system failure caused by relay protection´s malfunctions can be calculated. Simulations results, using current differential protection as an example, are given to validate the proposed evaluation model.