Calorimetric method for determining efficiencies of electric machines

AMONG the methods available for determining losses and efficiencies of electric machines, many have been developed to their utmost capabilities. Some measure individual losses separately and with good accuracy,^1–10 but many have inherent drawbacks. There still remains the desirability of a satisfactory over-all test which will rate the performance of all sizes of machinery under actual conditions of loading and yet yield highly accurate results. This aim is largely met by the calorimetric method and is justified by its basic character. A simplification of the classical testing technique can be introduced in which the important measurements are all electrical. By this means, accurate measurements of heat values are obviated, and the calorimeter becomes in reality only a comparator for a substitution process. Test results of calorimetric measurements on small induction and d-c motors show excellent agreement with other tests on the same machines. Analysis of the method indicates that it is equally applicable to all classes of machines of any size and that it can be used more generally for over-all loss and efficiency measurements under loaded conditions.