A Study on the Statistical Life Span Estimation of Aged Low-Voltage Circuit Breakers

In this study, aged low-voltage breakers, including earth leakage breakers (ELBs) and molded case circuit breakers (MCCBs) with high rates of electrical fire occurrences, were collected from a field site and tested according to failure identification test criteria. Based on the International Electro technical Commission (IEC)’s failure judgment test criteria, pass or fail tests include lever repeat operations, the manual trip button for finding mechanical deformations and leakage sensitivity current test, the ELB earth leakage trip time test, and the MCCB overcurrent trip test to verify changes in electrical performance. The fault data obtained from the tests, expressed in years (yr), were analyzed for statistical life span prediction (SLP) using the Weibull distribution probability. The SLP analysis verified the fault data set’s distribution suitability and derived the mean time to failure (MTTF) using the Minitab statistical analysis tool. Sample analysis of aged low-voltage breakers determined that approximately 73% of the samples were found in homes, and their MTTFs were 19–23 year, longer than those suggested in the literature. The predicted life span of an ELB was also approximately 4 yr shorter than an MCCB, possibly due to the mechanical and electrical shock of internal electronic devices caused by the manual trip button test and the deteriorating electrolytic capacitors of some printed circuit boards (PCBs).