This series of motor protectors are suitable for the power supply circuit with AC 50Hz and rated working voltage 380V, and the motor control circuit is composed of AC contactors and other switching appliances. When the main circuit of the motor is out of phase, overload, blocking, three-phase unbalance, over-voltage, under-voltage, short circuit, leakage and other abnormal working conditions, timely disconnect the contacts of switching appliances, disconnect the three-phase power supply of the motor, and quickly and reliably protect the motor.