1 Short-circuit protection: timely cut off the high-current short-circuit protection of the motor and its lines, otherwise, once a short-circuit occurs, the motor may be burned out and cause heavy losses.
2 Overload protection: For the overload current of the motor, the fuse may not be able to blow, so it is necessary to set a separate power-off protection device.
3 Phase failure protection: Although phase failure operation protection is also a kind of overload protection, it is also necessary to set up a phase failure operation protection device separately. There are many ways and devices for open-phase protection. There are mainly 5 common ones. They are:
① Use thermal relay with open-phase protection device for open-phase protection;
② Undercurrent relay open-phase protection;
③ Zero-sequence voltage relay off Phase protection;
④ Phase failure protection of the fuse-broken voltage relay;
⑤ Protection with fast saturation current transformer.
4 Loss of voltage and undervoltage protection: In order to prevent the motor from starting and running under too low voltage, or moving and restarting when the power supply is restored after a sudden power failure during operation, the loss of voltage and undervoltage protection are generally adopted.
5 Grounding or zeroing protection: When the motor shell is energized, it prevents people from touching the shell and getting an electric shock.