Determining total losses and temperature rise in induction motors using equivalent loading methods

Conventional loading of induction motors is an extremely difficult and expensive process for large machines. In those cases, full load losses and temperature rise can be estimated by means of equivalent loading methods, which provide an accurate alternative, without the need of a mechanical load applied to the shaft. This paper describes three such methods, all using a commercial PWM inverter. The methods examined are described in detail and the results of tests performed on a 10 hp induction motor are presented. A calorimetric measurement facility was used in order to ensure consistency of result comparison between the different methods, as well as high accuracy for total loss measurement. The measured values of losses and temperature rise, although marginally larger, are in good agreement with those obtained through conventional loading.