UNINTERRUPTIBLE POWER SUPPLY SYSTEM

PROBLEM TO BE SOLVED: To shorten a period when electric power supply to a load is interrupted due to a delay in the operation speed of a relay when an electromagnetic relay is used for switching power in order to suppress power loss. SOLUTION: A second relay 13 is installed between a load line 5 for switching between commercial AC power and compensating AC power by action of a storage portion 8 and an inverter portion 7 for supply with a first relay 3 and a compensating AC power supply line 5. Under abnormal conditions such as a momentary voltage drop, compensating AC power is supplied to the load 40 by making the first relay 3 in an a-c connection state and the second relay 13 open, respectively. When returning to normal conditions, a control portion 20 initially stops energizing to the relay 3 so as to switch the first relay 3 to a b-c state and keeps the second relay 13 in a closed state. After time delay according to the switching time of the contact of the first relay 3 has elapsed, the second relay 13 is open. Therefore, compensation AC power continues to be supplied to the load 40 for the major part of time in the period during being switched to the first relay 3, and commercial AC power is supplied to the load 40 for a short time after power is interrupted. COPYRIGHT: (C)2009,JPO&INPIT