Motor phase failure control and protection circuit

Working principle of the circuit: As can be seen from Figure a, RK, RV2, and Crown K are connected in parallel to form
a three-phase balanced network. When the three-phase power supply is normal, its common point potential is o, and RV4
is the common terminal varistor protection resistor, which is connected with RV ,—RV3-Qimachi constitutes overpressure protection.
SSR is a two-way solid state relay. The output end is connected to the input end of the moon K, and the other end is connected to the ground
through the current limiting resistor R. The entire circuit is divided into a four-lead structure. Pins 1, 2, and 3 are connected to any three-phase mains power, and pin 4 is connected to the ground . line or neutral line, so that among the three windings of the motor, RV and RV3 can limit the overvoltage, and RV4 can absorb and suppress the surge current and impact current (impulse current caused by lightning) that appears in any phase. When any phase is powered off, the potential of the common point is 0 and rises, the SSR is turned on, short-circuiting the external load, cutting off the power supply, and protecting the motor .