Transistor leakage release protection circuit

It is a phase failure protection circuit that uses the principle that the sum of the three-phase currents of the balanced load is zero. During normal operation, the sum current is zero, the transistors
VT1-VT3 are turned on, the switch tube VT4 is turned off, and the relay K is powered off . When a phase failure occurs (including the disconnection of a phase winding of the motor), and
the current is greater than zero and the system loses balance, the transistor is cut off, the switch is turned on, the relay is energized, and its contacts are opened, cutting off the original control
circuit . The contactor is released when the power is cut off, and the motor stops when the power is cut off . The selection of components is based on actual measured data.