Reverse-Rotation Test for the Determination of Stray Load Loss in Induction Machines

Abstract

VARIOUS methods for the accurate determination of stray load loss in induction machines have been devised in recent years. Also older methods have been improved and developed as the nature of the loss has become better understood. The employment of different methods of testing on a given machine seldom shows complete agreement in results, due to minor discrepancies and inaccuracies inherent in the methods themselves. Another difficulty is that all of the plans proposed to date require a high degree of skill and experience on the part of the testing technician. Thus industry today finds itself in need of a test which will give highly accurate results and at the same time be simple and easy to perform. The purpose of this paper is to describe a new method of testing — termed the “reverse-rotation test” — which will more nearly meet these requirements. The theoretical basis and the assumptions involved are discussed. Tests to determine the accuracy of the method have been made on two squirrel-cage motors of somewhat different characteristics by various methods of testing. The results of these investigations are described and curves are given showing the degree of exactness obtained. While the method includes assumptions regarding compensating effects involving minor components of the loss, its over-all accuracy for the motors tested is shown by comparison with the values obtained by other methods having high precision.