Application of induction machine efficiency testing standards in South Africa

This paper investigates the application of international induction machine efficiency testing standards in South Africa (SA). Motorized systems in SA account for up to 60% of the total electricity consumption. Recent power crisis in SA has accelerated the need for motor efficiency optimization. The applications of minimum energy performance standards (MEPS) to increase motor efficiency have become the norm around the world. Most electric motors in South Africa are still being rewound, with no consideration for the potential loss of efficiency and the most-likely increase in energy consumption. The status of motor rewinds is not good. Efficiency testing is underway at the University of Cape Town Machine Laboratory (UCTML) to investigate the impact of rewinding on motor efficiency in SA. As one of a very few testing labs, the power quality and instrumentation accuracy limits required in the standards were difficult to achieve. The result of this was errors and poor repeatability in testing. An alternative MG-set was used to create a supply that conforms to the standards. The impact of motor rewinding in SA is presented in this paper. It was found that procedures such as uncontrolled burnout temperatures result in efficiency drops of up to 4% at 25-50% loading points and up to 2% at rated loading points.