Reliable life calculation of circuit breaker based on FTA and reliability function

Reliable life is defined as the average operation time of power equipment in a given reliability, and it is a significant parameter in reliability evaluation. This paper presents a reliable life calculation method for SF₆ circuit breakers. The reliability evaluation model is established based on Fault Tree Analysis (FTA) method. From FTA, all the bottom events which cause top event (failure of the SF₆ circuit breaker) are found. To estimate the reliability by inspection results and test results of the circuit breakers, Health Index (HI) is presented to calculate the failure probability of each bottom event, then the reliability of the top event is obtained. Collecting the failure probability and the age data of different SF₆ circuit breakers with the same type in power system, the data is applied to estimate the reliability function of two parameters Weibull distribution by the least square method. Finally, the reliable life of the SF₆ circuit breaker in a given reliability is estimated after inversion calculation by reliability function. To make further understanding of the method, an application example is presented, and the calculation result shows the effectiveness and accuracy of the model. According to the detailed analysis, the reliable life has more advantage than the physics life to reflect the reliability level of the power equipment.