Three-phase motor phase loss automatic protection circuit

Working principle of the circuit: When the three-phase wires of the motor are passed through a transformer at the same time,
the inductive voltage is O. When one phase is missing, or two or three phases are seriously unbalanced, the induced voltage of the transformer rises rapidly, and a transistor base current
is generated after rectification. The transistor is immediately saturated and conducts, and the relay K is electrically closed, and the normally closed contact The point is disconnected, the contactor coil loses power, the contacts are disconnected, and the motor loses power and stops running. The action time does not exceed Is.