Simple and effective power supply phase loss protection circuit

If a three-phase motor runs without a phase for a long time during operation, the motor will be burned due to excessive winding current and heat. If there is a lack of phase when starting, the motor will buzz and not be able to turn the meter, or even heat up and burn out. If you use a cabinet air conditioner with a three-phase power supply, the lack of a phase may also cause the compressor to burn out, which will cause greater economic losses. The circuit introduced in this article can overcome this shortcoming, as shown in the figure.

Circuit composition: Use two relays of the same model (the main contacts should be able to meet the maximum current of the motor, and the coil voltage is 380V) for phase loss protection, and the effect is good. The wiring method is shown in the figure. Connect the main contacts of the two relays in series in the motor power supply circuit. When all three phases are powered, relays J1 and J2 are energized at the same time and close their main contacts to make the circuit safely connected. If phase A or phase B suddenly loses power during operation, relay J1 will lose power and trip. , if phase B or phase C suddenly loses power, relay J2 will lose power and trip, cutting off the power supply. Therefore, if any of the three phases A, B, and C is missing, the power supply to the motor will be cut off, thus playing a protective role.

Component selection: There are no special requirements for the components of this circuit, just select them according to the icons.