Uninterruptible power supply device

An uninterruptible power supply device, which is an uninterruptible power supply device provided between an essential load and a power system on an upper power supply side on a commercial or self-employed line and supplies AC power to the essential load, the uninterruptible power supply device comprising:

• a power supply part having an energy storage device connected to a power line for supplying power from the power system to the essential load;
• an open switch provided on a power system side of the power supply part on the power line to open and close the power line;
• a system abnormality detection part detecting a system abnormality which is at least one of a voltage rise, a phase fluctuation, a voltage imbalance, a harmonic abnormality, and a flicker in addition to at least one of a voltage drop including an instantaneous voltage drop and a frequency fluctuation, occurring on the power system side of the open switch;
• and
• a control part opening the open switch to supply AC power from the power supply part to the essential load when a detected system abnormality is equal to or greater than a tolerance of the essential load or the power supply part for the system abnormality.