Abstract: A commercial power-system and a private power-generating system are connected via a high-speed current-limiting breaker. The commercial power-system supplies power to each important load via a first system. Each overlap switch is provided at each interlinkage point of the first system and a second system. Each overlap switch is switched step-by-step based on output of a private power generator so that the first system is disconnected, therefore, the private power-generating system supplies power to the important load. If there is a surge in the commercial power-system, the high-speed current-limiting breaker limits an over-current and interrupts power supply quickly to protect the important load.