Comparison of methods of making load tests on A-C. generators and on induction motors

This paper describes the most practical methods that have been employed for obtaining actual load temperatures of alternators and induction motors with an expenditure of power considerably less than that of their rated capacity. These methods are: Alternators. 1. Zero power factor method, (a) Leading current, (b) Intermittent leading and lagging current. 2. Open- and short-circuit method, (a) Continuous run, (b) Intermittent run. 3. Open delta method. 4. Phase displacement method. Induction Motors. 1. Feeding-back method. 2. Reduced voltage method. 3. Reversed rotation method. Data from actual tests are presented to show how closely the temperature rise by these equivalent load methods agrees with that of actual load. No attempt has been made to justify the use of equivalent heating tests through theoretical considerations. The chief advantages and objections of the different methods are stated and conclusions are drawn as to the most reliable substitute methods for actual load from a practical engineering and commercial point of view. Certain equivalent tests adapt themselves so well to commercial testing conditions that their use becomes imperative for a large proportion of alternating-current generators and motors.