Any electrical product, including motor products, has specified rated voltage for normal operation. Any voltage deviation will have adverse consequences on the normal operation of the appliance.

For relatively high-end equipment, necessary protection devices are used. When the power supply voltage is abnormal, the power is cut off for protection. For very precise instruments, constant voltage power supply is used for adjustment. However, for motor products, especially industrial motor products, the possibility of using constant voltage devices is extremely small, and power-off protection is more common.

For single-phase motors, there are only two situations: high voltage and low voltage. For three-phase motors, there is also the problem of voltage balance. The direct impact of these three voltage deviations is increased current or current imbalance.

The technical conditions of the motor stipulate that the upper and lower deviations of the rated voltage of the motor cannot exceed 10%. The torque of the motor is proportional to the square of the motor terminal voltage. When the voltage is too high, the motor core will be in a state of magnetic saturation. The increase in stator current will cause severe heating of the winding and even quality problems such as winding burning. For the case of low voltage, there may be problems with starting the motor, especially for motors running under load. In order to meet the load operation of the motor, the current must also be increased. The consequence of the increased current is also the heating and even burning of the winding. Especially for long-term low-voltage operation, this problem is more serious.

Unbalanced voltage in three-phase motors is a typical power supply problem. When the voltage is unbalanced, it will inevitably lead to unbalanced motor current. The negative sequence component of the unbalanced voltage generates a magnetic field in the air gap of the motor that is opposite to the direction of rotation of the rotor. A small negative sequence component in the voltage may cause the current flowing through the winding to be much larger than the current when the voltage is balanced. The frequency of the current flowing through the rotor bars is almost twice the rated frequency, so the current squeezing effect in the rotor bars causes the increase in rotor winding losses to be much greater than the increase in stator winding losses. The temperature rise of the stator winding is higher than the temperature rise when running under balanced voltage.

When the voltage is unbalanced, the motor's stall torque, minimum torque and maximum torque will all decrease. If the voltage imbalance is severe, the motor will not work properly.

When the motor is fully loaded and running under unbalanced voltage, the speed will drop slightly because the slip rate increases with the increase of the additional loss of the rotor. As the voltage (current) imbalance increases, the noise and vibration of the motor may increase. The vibration may damage the motor or the entire drive system.

In order to effectively identify the cause of uneven motor voltage, it may be possible to detect the power supply voltage or current changes. Most equipment is equipped with a voltage monitoring instrument, which can be analyzed by data comparison. In the case of no monitoring device, regular detection or current measurement should be used; for motors that can be reversed, the two-phase power supply lines can be swapped at will without affecting the towed equipment, and the current changes can be observed to indirectly analyze the voltage balance. After eliminating the problem of uneven voltage, quality problems such as turn-to-turn and phase-to-phase may be involved.