Emergency power supply is composed of charger, inverter, storage battery, isolation transformer, transfer switch and other devices, which reverses DC power into AC power.

When the industrial and civil buildings are in the state of fire emergency, in order to ensure the success of fire fighting, the independent power supply which is responsible for the power supply of fire-fighting electrical equipment is called emergency power supply. "Code for electrical design of civil buildings" clearly stipulates that the first level load shall be supplied by two power sources, and when one power source fails, the other power source shall not be damaged; the power source form of the first level load includes two high voltage power sources, one high voltage power source and one low voltage power source, diesel generator set or battery pack; the particularly important load in the first level load is in addition to the above two power sources In addition, emergency power supply must be added