Induction motor efficiency test methods: a comparison of standards

Abstract

In this work, fundamental aspects regarding the efficiency of induction motors are treated. Improved efficiency is the task of the hour. Environmental challenges, which include climate change, global warming and greenhouse gas emission have been fuelling the need to increase energy efficiency in electrical rotating machinery. Furthermore, there is a need to establish a level platform for motor manufacturers globally where they can produce electric machines according harmonized standards. Not only does this establish trust with the market, but it allows legislators to enact policies which promote energy conservation and facilitate governments to provide incentives to organizations which make energy efficiency their priority. The efficiency data provided by manufacturers is measured or calculated according to different national and international standards. These standards use different means to incorporate the stray load losses and use different test methods; thus, the efficiency values obtained from different testing standards can vary. This leads to problems in competition and a potentially confusing situation for manufacturers and customers. Hence, there is a need to compare the standards and highlight the possible variations leading to these differences, their causes and recommend where possible, solutions on how they can be eliminated. A comparison of induction motor efficiency test methods according to the IEC 60034-2-1 and IEEE 112 standards is presented in this work. Standard direct-on-line squirrel cage induction motors rated at 3 Kw, 5.5 Kw, and 7.5 kW are tested according to the IEC and IEEE preferred standards. Data collected from tests carried out on the motors is used to calculate the efficiency for the various IEC and IEEE tests. The data obtained shows a similar variation in values of efficiency, stray load losses and excitation losses for the same machine, but calculated using different standards. These differences result from how stray losses are treated and calculated in the standards. As a result, there is a need to harmonize the international standards.