For single-phase motors for one phase, only the size and relative stability of the supply voltage need to be considered.
For three-phase motors, the balance of the supply voltage must also be considered.
The unbalance of the power supply will have different degrees of negative impact on the three phase motor's parameters such as current, torque, speed, temperature rise, vibration and noise.
Variation of current and temperature rise when the voltage unbalance
When the three phase system voltage of the power supply is unbalanced, the most obvious impact is the change of current, especially the variable frequency drives motor's in the rated voltage, rated speed state operation, the current unevenness is very large, the current unevenness is much larger than the voltage unevenness.
Unbalanced voltage will produce a magnetic field in the stator and rotor air gap of the three phase motor in the opposite direction of the rotating magnetic field of the three phase motor.
Thus changing the size of the current in the stator winding of the three phase motor, as well as the rotor part of the current frequency, especially the rotor part of the impact is greater, the rotor loss will also have a more obvious increase.
Due to the increase of current and derived from the loss increase problem, directly lead to the motor heat loss increase, and intuitive expression of the load for the three phase motor temperature rise, that is, the electric motor temperature rise performance becomes worse.
Variation of electric motor speed and torque when the phase voltages unbalance
In order to better understand the relationship between speed and voltage, we can analyze the electric motor according to the limit state of phase loss.
When the three phases motor is out of phase, the vibration increases, the temperature rises, the speed decreases, the current increases, and there is an abnormal sound, there is a lot of noise when starting and it cannot start successfully for the motor with voltage unbalances..
When the polyphase motors are out of phase, the three phases motor runs weakly.
The torque becomes smaller, and the motor stator winding will burn up soon. When the power supply voltage is unbalanced, the symptoms are the same as the phase loss, but the severity is slightly less.
Changes in electric motor vibration and noise when the three phase motor is with unbalanced voltage
Electric Motor vibration and noise can be divided into mechanical and electromagnetic, when the supply voltage is unbalanced, electromagnetic vibration and noise will be particularly obvious, the vibration and noise performance of the three-phase motor is out of phase, that is, the voltage unbalance limit state.
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