The effects of voltage and winding abnormalities on the measured performance of induction motors

The results of a test program are presented which was undertaken to measure the degradation of the performance of a specially prepared, cage-rotor, induction motor when subjected to operating conditions that are significantly nonideal. The 100 HP, 4-pole motor has connections that enable either regular balanced-phase windings or unbalanced windings by the removal of one turn per phase. This latter condition simulates an often employed, quickly and cheaply implemented, repair of a common failure mode. The performance (phase currents, power factor and efficiency, for a range of loads from 0 to 150% of rated) was established for ideal baseline conditions of balanced windings and rated, balanced voltages. This was compared to the performance at 10% overvoltage, 10% undervoltage, and 2.5% voltage unbalance. This entire range of commonly encountered, nonideal, voltage conditions was then repeated with the motor windings deliberately unbalanced. The test results which are difficult to predict, due to inadequate models and inherent motor nonlinearities, should serve as guides to derating for motor repairers and industrial users.