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A high voltage direct current (HVDC) system (300 V) was used for a demonstrative project on power supply systems by service level in Sendai, Japan, entrusted by the New Energy and Industrial Technology Development Organization (NEDO). In high-quality DC power systems, the existing DC protection devices, such as the fuse and the Molded Case Circuit Breaker (MCCB), cannot conduct quick and stable circuit breaking. Therefore, we developed a semiconductor switch that uses a metal oxide semiconductor-field effect transistor (MOS-FET) as a new DC protection device. However, although it is possible to quickly break a HVDC circuit using this semiconductor switch, the possibility of a malfunction still exists because the semiconductor switch is an active device. Therefore, we included a retry function that repeats the turn on and turn off of the MOS-FET at certain periods, thus devising a method of evading malfunctions. We present the characteristics for breaking a HVDC circuit when a semiconductor switch is used as the HVDC protective device in the demonstrative project on power supply systems by service level.