Star connection motor phase failure protection circuit

It is a Y-shaped connection motor phase failure tripping device. This circuit is suitable for motors below 7.5kW.
    Working principle: Press the start button SB2, the contactor KM is energized and self-locking, and the motor starts and runs normally. When
one phase of the three-phase alternating current is disconnected, a potential difference occurs at the neutral point of the motor. This voltage is rectified and stabilized, causing the relay KA to be energized and closed, and its normally closed contact
to be disconnected, causing the contactor to be de-energized and released, the main contact to be disconnected, and the motor M to be de-energized and stop.