Power savings obtained from supply voltage variation on squirrel cage induction motors

This paper offers practical guidance about the nature of design and application engineering trade-offs that may be used to optimize motor efficiency to match a low load output shaft power condition and thereby achieve power savings by reducing the losses in squirrel cage induction motors (SCIM). This opportunity is the result of motor efficiency dropping off significantly at low load factors of mechanical output shaft power and can be explained by analyzing the balance between various components of the electric and magnetic power flows in the motor with respect to motor loading. This paper analyzes the possibility of obtaining minimum power losses at low motor loading and explains how iron losses, which usually are considered constant, can be made variable and optimized for power savings. The study was done using a typical 20 HP (15 kW), TEFC, 4 poles, 480 V, energy-efficient motor. This motor type is a common squirrel cage induction motor used in various industry applications and sometimes found operating at low loads for long periods of time. A squirrel cage induction motor design program was used to simulate the motor performance characteristics for low values of motor loading under various supply voltages. The study found that for this particular motor design, power savings of up to 2% and up to 20% of the total input power at motor loadings of 0.5 and 0.1 respectively can be achieved by varying the supply voltage. Minimizing motor losses by reducing the supply voltage could be realized with the advances and emerging technologies in power electronics. The findings of this study suggest a method of evaluating possible power savings for any SCIM prior to installing a specific control device.