In the event of a power failure, the air switch will trip by itself, generally because the air switch has an undervoltage trip protection device. When the power fails, the undervoltage release will trip.

The working principle of undervoltage release (see the figure below):

1. When the line voltage is normal, the voltage release 11 generates enough suction force to overcome the action of the tension spring 9 to pull in the armature 10, and the armature and lever are separated, the lock and the hook can be locked, and the main contact can be closed. .

2. When the voltage on the line disappears or the voltage drops to a certain value, the suction force of the undervoltage release disappears or decreases, the armature is pulled apart by the tension spring 9 and hits the lever, and the main circuit power supply is disconnected.

3. For the same reason, when there is no power supply voltage or the voltage is too low, the automatic air switch cannot turn on the power supply.