Unbalance is term related to three-phase systems and can refer to:

  • supply voltage unbalance
  • load current unbalance
  • receiver unbalance

In three-phase systems, the voltage (current) unbalance occurs when values of three component voltages (currents) are different and/or the angles between individual phases are not equal to 120 degrees.

The receiver unbalance occurs when impedance values of individual receiver branches are not equal. An unbalance can be particularly dangerous for three-phase motors, in which even a slight voltage unbalance can cause current unbalance that is many times larger. In this situation, the motor torque is reduced, heat losses in windings increase, and mechanical wear is faster. The unbalance also has an unfavourable effect on power supply transformers.