The voltage of the three-phase motor is often encountered in the motor test and the user's use. If the three-phase voltage is unbalanced, there will be a reverse sequence current and a reverse sequence magnetic field in the motor, resulting in a large reverse sequence torque. Give a brief analysis of the voltage unevenness of the Y2 aluminum shell three-phase asynchronous motor. I hope to help you improve your work efficiency.

Increased current

The negative sequence component of the unbalanced voltage produces a magnetic field in the motor air gap that opposes the steering of the rotor. A small negative sequence component of the voltage may cause the current flowing through the winding to be much larger than the current at which the voltage is balanced. The frequency of the current flowing through the rotor cage is almost twice the rated frequency, so the current squish effect in the rotor cage causes the rotor winding loss increase to be much greater than the stator winding loss increase.

When the motor runs at rated speed under unbalanced voltage, the current imbalance is very large, about 6~10 times of the voltage imbalance; the current imbalance during the stalling is basically the same as the voltage imbalance, but the stall The apparent power increase is small.

Motor heating:

When the motor is operated under unbalanced voltage, the stator loss increases due to the negative sequence component in the current and voltage. Therefore, the temperature rise of the stator winding is higher than that when operating at the balanced voltage. The degree of increase in rotor loss increases due to the squish effect of the current. Furthermore, the voltage imbalance is usually associated with a decrease in the positive sequence component, which causes the current of the positive sequence component in the stator to increase.

Torque reduction:

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

The voltage imbalance is related to the generation of an oscillating torque having a frequency of 2 times the power frequency. The increase in the amplitude of the oscillating torque is linear with the product of the positive sequence component and the negative sequence component of the voltage. The peak value of the oscillation torque is within 25% of the rated torque. When the critical torsional frequency of the oscillating torque is close to 2 times the power frequency, the entire shafting system may generate impermissible torsional vibration.

Full load speed drop:

When the motor is running at full load under unbalanced voltage, the slip speed will decrease slightly as the slip rate increases as the additional loss of the rotor increases.

Increased noise and vibration:

As the degree of voltage (current) imbalance increases, the noise and vibration of the motor may increase. Vibration can also damage the motor or the entire drive system.




----- Editor-in-Chief: Dalan Oil Pump Motor 02-Procurement Consultant

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