Electrical motors are designed to operate with a high efficiency. Does voltage imbalance between phases affect motor's efficiency?

At first whatever the reason of imbalance voltage of course will affect the motor efficiency because It will affect motor characteristic as following: -

·         The imbalance voltage will produce a circulating current flow through the stator current depend on the amount of this imbalance which will cause an overheating on the stator winding which have a bad effect on winding insulation by the time.

·         Torque: will decrease depend on the amount of the imbalance voltage, may be at this mount the motor adequate for its application, so may be hear noise for the motor.

·         Current: due to the decrease of the Torque the motor will draw more current to produce the required torque, which cause overheating for motor windings.

·         Speed: Will decrease slightly due to this imbalance voltage.

·         Winding Temp: will increase depend on the amount of imbalance and we can know the ratio of tempe. Increase from the following equation.

Temp. rise % = 2 * (voltage imbalance %) ²,

Voltage imbalance = 100 * ((Max. voltage deviation from average voltage)/ (Average voltage))

Example: -

Measure line to line

L1 – L2 =392 v , L2 – L3= 400 v , L3 – L1= 412  v

Average voltage = (392+400+412)/3 = 401.33 v

Voltage imbalance = 100 * (12/401.3) = 2.99 %

Temp. rise % = 2*(2.99)² = 17.88 % , so voltage imbalance by 2.99% produce increasing temp. by 17.88 %.

For all above the motor efficiency will affect by the imbalance voltage.

Yes, if the imbalance is large and beyond the limit of allowable voltage variation. However, if if imbalance is so small, it very little effect on efficiency.

yes, as far as the electric motor is working 2 the range of 380v-415v