One of the phase failure and overload protection circuits for detecting line current

This circuit has phase failure protection and overload protection functions. The circuit does not use a power transformer,
which can reduce the size of the device.
    Adjust RP. When the motor is running normally,
the voltage applied to the voltage regulator tube vsl is lower than its breakdown voltage,
the transistor VTi is cut off, Vtz is turned on, the intermediate relay
KA is closed, its normally open contact is closed, and the contactor
KM is self-locking. .
    When the W phase is powered off, the contactor KM is released and the motor
stops; when the U phase or V phase is powered off, VS1 breaks
down and the transistor VTi is turned on. VT2 cuts off, KA and
KM lose power and are released one after another, and the motor stops. When the motor is overloaded
, Vsl breaks down and also plays a role in shutdown protection.