Failure Probability Methodology for Overdutied Circuit Breakers

With the expansion of the grid, fault current levels increase and circuit breakers are subject to increasing duties and stresses, and are more prone to failures. Because the performance of breakers is critically affecting the operation and protection of the power grid, it is important to quantify the probability of failure of the circuit breakers to assess the risks, prioritize maintenance and replace the equipment. This paper describes a methodology to compute the absolute, stress-induced failure probability for a given circuit breaker of a power system. We compute the breaker probability of failure that accounts for all the characteristics of the network in which the circuit breaker operates, including the physical properties of the system. The knowledge of this result is of paramount importance for utilities to pinpoint the circuit breakers that may become overdutied (underrated) as a result of increased fault currents due to generation capacity expansions. As a side benefit, appropriate actions can be defined to prepare the protective equipment to handle constraints imposed by higher fault currents.