Effects of Unbalance Voltage on Induction Motors

Unbalance phase voltages on a three (3) power system produce negative sequence components of the voltage. Even a small voltage unbalance will result in large current unbalance during the running of motor by a factor of 6 to 10 times.

The effects of unbalance voltages are:

  • Negative phase sequence components causes motor overheating;
  • Negative phase sequence currents reduce motor output torque;
  • Motor runs at higher slip increasing rotor loss and reducing efficiency.

This is one of the reasons why in a three(3) phase distribution design, single phase loads should be distributed evenly on each phase. Unbalance single load distribution creates unbalance phase currents. The unbalance currents produce unequal voltage drop on each phase conductors leading to unbalance voltages on the load terminals.

Electrical engineers should always consider balancing single phase loads evenly across all phase when doing load distribution as voltage unbalance effects considerably the efficiency of induction motors which will affect the overall efficiency of the power system.

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