AC induction motor efficiency

The author discusses those factors which determine the efficiency and rating of polyphase AC induction motors. The loss mechanisms are described and are related to the performance and design characteristics of the motor, such as the operating flux density, the winding turns distribution, the current density in the windings, the motor speed torque characteristic, and the motor efficiency itself. The author emphasizes the fact that induction motor design is an integrated process and that it is not in general possible to adjust one motor design parameter (such as the winding turns distribution) without changing a number of performance parameters (torque, efficiency, rating, etc.). In addition, the factors that together determine the rating of induction motors are discussed. The author also discusses the common pitfalls which occur when attempting to interpret induction motor performance measurements. The need to measure both the electrical input power and the mechanical output power of a motor to determine its efficiency is emphasized. Finally, the author presents a brief discussion of tests performed upon a set of AC induction motors which were rewound using the Unity-Plus winding technology. This technology has received considerable attention in the past few years because of claims that it can result in improved motor efficiency. The test results do not verify these claims