Lifetime estimation and surface degradation of MCCB contact tips due to multiple electrical interruptions

Abstract

This paper presents the surface degradation analysis of contact tips of commercial (20A, 110 V) molded case circuit breaker due to multiple electrical interruptions during experimental electrical test. In the experimental electric test, and according to the post arc current observation, the arc voltage and current were categorized. Multiple high-current interruption has been identified, and the phenomena that regulate the interruption failure have been established. Also, post-arc current sprinted for a short period of time (10–200 µs) during multiple electrical interruptions. These interruptions cause the failure of the contact tips of MCCB. The metallurgical changes were also observed on the contact tips. The braze joints between contacts tips and copper base is also affected by thermal and electrical conductivity during the electrical interruptions. The optical microscope reveals the typical metallurgical changes that occur during a breakdown, such as surface degradation, wear, cracks adjacent to the braze interface, oxide layer formation, cracks on the contact tips, and cracks that penetrate into the copper base. The experimental investigation of the factors influencing the post arc current was carried out to learn more about the link between the post arc current and the degradation of the interruption characteristics. This investigation’s primary objective is to explore the interruption performance and failure analysis of commercial MCCBs.