Methods of no-load thermal testing of induction motors

A new method for determining the equivalent parameters of a simplified thermal model of induction motors (IM) based on the no-load testing of IM is presented. The full thermal network of IM is reduced to a system of only three simultaneous equations. By solving these equations, three equivalent thermal parameters of the simplified thermal model are obtained. The calculation is based on accurate measurements of the temperature rise in stator windings and the power absorbed by the tested motor. The thermal tests are done in the no-load running of IM (one test is like an open-circuit test and the other two are like short-circuit tests). Hence these methods of testing may be carried out without expensive equipment and their power consumption does not exceed the losses which occur under full load conditions. With the help of this thermal model the final temperature rise at the full load run according to rated losses, can be easily estimated. Three totally enclosed IM were tested by these methods and the difference in the predicted and measured temperature rise of the stator winding was within 2-3°C