Any electrical product, including motor products, of course, stipulates the rated voltage for its normal operation. Any voltage deviation will cause adverse consequences for the normal operation of the electrical appliance.

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

For a single-phase motor, there are only two situations of high voltage and low voltage, while for a three-phase motor, there is also a voltage balance problem. The direct manifestation of the influence of these three voltage deviations is current increase or current imbalance.

The technical conditions of the motor stipulate that the upper and lower deviation of the rated voltage of the motor cannot exceed 10%, and the torque of the motor is proportional to the square of the motor terminal voltage. When the voltage is too high, the iron core of the motor will be in a state of magnetic saturation, and the stator current will increase. It will lead to serious heating of the winding, and even the quality problem of the winding burning; and for the case of low voltage, one is that there may be problems with the start of the motor, especially for the motor running under load, in order to meet the load running of the motor, The current must also be increased, and the consequence of the current increase is also the heating and even burning of the windings, especially for long-term low-voltage operation, the problem is more serious.

Unbalanced voltage of three-phase motor 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 creates a magnetic field in the motor air gap that opposes the rotor turning. A small negative sequence component in the voltage may cause the current through the winding to be much larger than when the voltage is balanced. The frequency of the current flowing in the rotor bars is almost twice the rated frequency, so the current squeezing effect in the rotor bars makes the loss increase of the rotor windings much larger than that of the stator windings. The temperature rise of the stator winding is higher than that when operating at balanced voltage.

When the voltage is unbalanced, the stall torque, minimum torque and maximum torque of the motor will all be reduced. If the voltage imbalance is serious, the motor will not work properly.

When the motor runs at full load under unbalanced voltage, since the slip increases with the increase of the additional loss of the rotor, the speed will decrease slightly at this time. As the voltage (current) unbalance increases, the noise and vibration of the motor may increase. Vibration can damage the motor or the entire drive system.

In order to effectively identify the cause of the uneven motor voltage, it may be carried out by means of power supply voltage detection or current variation. Most equipment is equipped with a voltage monitoring instrument, which can be analyzed by data comparison. For the case where there is no monitoring device, regular detection or current measurement should be used. In the case of dragging the equipment, the two-phase power supply line can be arbitrarily exchanged, the current change can be observed, and the voltage balance can be analyzed indirectly.

By Jessica