Low Load and High Current Imbalance

An unloaded motor can create a 10-15% current imbalance yet be perfectly healthy. This is a normal design response caused by unbalanced flux in the core iron between phases at low loads. When performing power or current analysis on three-phase induction motors, verify the percent loading at which the motor is operating. If possible, increase the load on the motor to determine the validity of a high current imbalance. A normal current imbalance for healthy motors operating at or near design load is 3% or less.

First published in "the Operator", January 2007