Thyristor overcurrent protection circuit

When starting, press
the lock button SBi once. After the start is completed (
after the motor speed is stable), press SBi again, and
then the protection circuit will be put into work. For
motors with a short starting time (such as a few seconds), SBi can also use ordinary
buttons, as long as the SBi is pressed during the starting process
.
    When the motor is running normally,
the secondary induced potential of current transformers TAi~TA3 is small and is not
enough to trigger the thyristor V.