I. Introduction
In recent years, most electric devices such as information technology (IT) devices, television (TV), Audio/Video (AV) devices, personal computer (PC) and facsimile (fax) are operated by direct current (DC) electrical power. Furthermore, renewable energy which generates DC power is increasing rapidly. Hence, the DC power distributed system has been attracting attention. DC magnetic contactors (DCMC) are essential devices to operate the DC power distributed system.