DETERMINATION OF THE EFFICIENCY OF INDUCTION MACHINE WITH FIVE TESTED MACHINES

Abstract

Induction machines are mostly used as a motor but the manufacturer’s catalogue only mentions the motor efficiency values with no mention of values for generator mode. The paper uncovers that nevertheless induction machines can be used either in motor or generator mode, the efficiency curves for these modes are not necessarily the same. Several high- and low-efficiency induction machines with different power rating are compared for motor and generator mode. These experiments show that depending on the machine’s design, and thus also efficiency class, the efficiency for motor and generator mode can differ significantly. Special attention will be paid to differences between copper and aluminium rotors. In the paper the underlying phenomena causing this effect are elucidated. It can be concluded that the machines with lower stator and a non-saturated core, typical characteristics for high efficiency or machines with a high power rating, will have comparable efficiencies in both generator and motor mode. This is not the case for low power rated low efficiency machines, where the efficiency for generator mode can drop several percent. Whether for an induction motor or a generator, an efficiency increase of just one percent can represent a considerable economic benefit over the whole life-time.