A new microcircuit breaker thermal trip unit design based on compliant mechanisms

Miniature Circuit Breakers (MCB) are protective devices used in low voltage applications. To perform their protection function, MCB contain two different trip systems: a thermal unit and an electromagnetic unit. Current thermal trip unit designs were introduced decades ago and are based on bimetal technology. This paper introduces a new technology based on compliant mechanisms that replaces bimetals in MCB. The proposed architecture uses a thermosensitive compliant mechanism whose design is calibrated to perform as traditional bimetal designs do, but with the advantage of reduced heat losses. An additional advantage of the new design is its monolithic construction, which reduces the number of parts and manufacturing costs. The design of an MCB equipped with this technology is presented and its performance is analyzed, with special attention to its protective function and thermal losses. Tests with prototypes are also presented.