Molded Case Circuit Breaker Reliability Test And Failure Mechnism Analysis

Molded case circuit breakers，protected electrical equipments，are one of the mostcommonly used distribution appliances. Its structure is mainly composed of operatingmechanism, thermal magnetic releaser, contacts, Its main function is to break the over currentand protect the distribution line. Molded case circuit breakers are widely used, Therefore, thefailures of molded case circuit breakers will bring great harms to the industrial production andthe people’s life, so it is very important to study on the reliability test of the molded case circuitbreakers. Molded case circuit breaker’s reliability test and failure analysis are one of theimportant measures to improve its reliability.In this paper, it is introduced that the molded case circuit breaker reliability researchsituation at home and abroad, and finished M1series molded case circuit breaker reliability restbased on reliability verification test theory, according to the “Reliability test method for moldedcase circuit-breakers”. The failure products are analysed for reliability, including contact failureanalysis, thermal-magnetic trip failure analysis, operating mechanism failure analysis, etc. thecontact mechanism is the weaker part for molded case circuit breaker, using scanning electronmicroscope (SEM-S4800) analyses the contact surface degradation phenomenon and surfacecomposition after test. At last，it is put forward the improvement measures in this paper,including improving contact materials and arcing grid tablet, keeping contact clean, enhancingtoughness of traction rod and handle material, optimizing the component design and so on.