A common influence of voltage unevenness on the operati […]
A common influence of voltage unevenness on the operation of a motor.
1. Effect on 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 rotation of the rotor. The small negative sequence component in the voltage may make the current flowing through the windings much larger than the current when the voltage is balanced. The frequency of the current flowing through the rotor bar is almost twice the rated frequency, so the current squeezing effect in the rotor bar makes the increase in the loss of the rotor winding much larger than the increase in the stator winding loss. When the motor is running at rated speed under unbalanced voltage, the current unevenness is very large, about 6-10 times the voltage unbalance: the current unevenness is basically the same as the voltage unevenness when the rotor is locked, but the current is locked The increase in power is small. Customers can use the motor running current to analyze whether the voltage is normal.
2. Influence on the heating performance of the motor
When the motor is running 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 running under the balanced voltage. The increase in rotor loss is due to the current squeezing effect. If the motor runs under this condition for a long time, it is easy to cause the motor to overheat, which may cause malfunctions such as burnout.