Current transformer multi-function protection circuit a

The current transformer can be used to reflect the magnitude of the stator winding current. When the stator winding current exceeds the allowable value (avoiding startup
and current fluctuation time), the current signal detected by the current transformer acts on the relay through the electronic circuit , causing the contactor
to trip. , cut off the motor power. The multi-functional protection circuit
    of current transformer is shown in Figure 4-41. This circuit has overload protection, rapid braking, phase failure protection and alarm functions. Thermal relay FR serves as overload backup protection and phase failure protection.     When adjusting, connect the rated load and adjust the potentiometer RP so that the secondary voltage of TA is 1~2V (if it cannot be reached, the number of primary turns can be increased), that is, the base voltage of the transistor VTi is o. 2~0.4V, in a reliable cut-off state; when the motor is overloaded , it can ensure reliable conduction of VTi and the relay KA is closed.