The Effect of the Magnetic Grids and Arc Runner on the Arc Plasma Column in the Contact System of a Molded Case Circuit Breaker

This paper examined the extent of the dependence of the interrupting capability on the shape of the contact system in a molded case circuit breaker (MCCB). Thus, a simple analysis method was suggested for estimating the interrupting capability and used to investigate the magnetic flux density distribution in a contact system caused by a short-circuit current. However, the MCCB produced by a joint-research company turned out to have the poor interrupting capability and a low magnetic flux density distribution for driving arc plasma between two contacts in the contact system. To build up additional interrupting capability without making many changes, a new arc runner was devised to prevent arc plasma from returning to its original position in the contact system. The arc voltage characteristics were tested with a simplified synthetic testing facility using an LC resonant circuit. The result showed that the new MCCB had a much higher arc voltage than the existing MCCB. This implies that investigating the arc voltage is fairly comparable to predicting the arc plasma extinction and the interrupting capability.