A comparison of thermoset and thermoplastic arc chutes in molded-case circuit breakers under fault clearing

Abstract

Molded-case circuit breakers (MCCB) are vital devices that are used in many distribution systems for protection from faults in the network. During a fault, a large increase in current passes through the terminals of the MCCB and the contacts open by electromagnetic actuation. On opening, a low-voltage arc is struck between the contacts, forming a high-temperature plasma of thousands of degrees Celsius. The plasma causes thermal degradation of the insulating materials and erosion of the contacts and is a source of intense UV, which may further cause degradation of the insulating materials. In the case of a polyester based MCCB, electrically conductive soot is produced, which is detrimental to the long-term performance of the device.