International standards for the induction motor efficiency evaluation: a critical analysis of the stray-load loss determination

Motor efficiency has to be measured or calculated in accordance with international standards. The most important standards are the IEEE 112-B, IEC 34-2, and JEC 3 . In this paper, a comparison of the measurement procedures defined by these international standards is reported, together with some comments on the prescribed methodologies. The comparison is based on experimental results obtained by tests on four general-purpose three-phase induction motors. The stray-load loss measurement represents a critical key for the correct evaluation of the motor efficiency. For this reason, a critical analysis of this type of losses has been performed. In particular, in order to understand which are the most critical quantities that influence their evaluation, the stray-load loss sensitivity to the measurement errors is analyzed. In the final part of the paper the temperature influence, on the conventional iron losses, is experimentally analyzed. The performed tests show that the temperature difference between the no-load test and the motor real operative conditions is not negligible.