Comparative analysis of IEEE 112-B and IEC 34-2 efficiency testing standards using stray load losses in low voltage three-phase, cage induction motors

Since 1998, 817 motor efficiency test data sets, in the 1-500 hp (0.75-375 kW) range have been collected from several sources in different countries around the world, for 50 Hz and 60 Hz. The test data includes the motor efficiency using the IEC 34-2 and IEEE 112-B test standards, and the quantification of the stray load losses (SLL), using the IEEE 112B method. In 125 cases the test data includes the efficiency computed with both methods. The aim of this study, was the quantification of the discrepancy between the two mentioned standards, and to establish an approximate method to allow the comparison between motors tested with the two standards. Based on the significant number of collected motor data sets, it was concluded that when compared to IEEE 112-B standard, the IEC 34-2 standard is less accurate, and gives typically higher efficiency values, mainly because of the SLL estimation procedure. The IEEE 112-B SLL computed values are typically higher then the IEC SLL predefined values, on average by 1.0 and 0.8 percentage point for 50 Hz and 60 Hz motors respectively. Also, the average SLL values vary slightly with the motor power. Using efficiency measurements made with both standards on the same motors, it was possible to confirm that the SLL are the main reason for the observed discrepancy in the efficiency values. The results of the analysis carried out in this paper offers the possibility to compare the efficiency of motors tested under the IEC 34-2 standard with motors tested with IEEE 112-B, leading to a choice of the most cost-effective option. This paper also provides a key contribution to the ongoing revision of IEC 34-2 standard.