How do the parameters of a three-phase induction motor change under conditions other than nominal?
A low voltage at rated frequency leads to a reduction in no-load current and magnetic flux and therefore to a reduction in steel losses. The magnitude of the stator current, as a rule, increases, the power factor increases, the slip increases and the efficiency decreases somewhat. The motor torque is reduced because it is proportional to the square of the voltage.
When the voltage rises above the rated and rated frequency, the motor overheats due to increased losses in the steel. The rotating torque of the motor increases, the amount of slip decreases. No-load current increases and the power factor deteriorates. Stator current at full load may decrease and at low load may increase due to increase in no-load current.
With decreasing frequency and rated voltage, no-load current increases, leading to deterioration power factor… Stator current usually increases. Losses in copper and stator steel increase, motor cooling deteriorates slightly due to reduced speed.
As the mains frequency and nominal voltage increase, the current and torque at idle speed decrease.