An Evaluation of Induction Machine Stray Load Loss From Collated Test Results

The international standards for determining induction motor efficiency are not in agreement with each other. At the heart of the differences is the stray load loss (SLL). The way this loss is quantified is continuously debated. For many years, the IEC standard for motor efficiency measurement has assigned a fixed percentage to stray load loss. This fixed percentage value has been criticized throughout the history of the standard. A new version of the standard published in September 2007 replaced the fixed percentage with one that is dependent on motor kW rating through a specific relationship. One of the goals of this paper is to determine whether the new formula for assigning the SLL can be confirmed with actual test data. This paper presents a collection of test data on about 1000 motors to show the distribution of stray load losses in induction motors. The analysis clearly demonstrates the need for determining stray loss from test measurements rather than assigning an arbitrary value.