Equivalent load test for large induction machines - the three step method

Induction motors with output ratings exceeding test floor capacity present difficulties when attempting to verify, by testing, their rated performance, more specifically, the stator temperature rise. This is due to the power supply capacity of the testing facility. The three-step method, as an equivalent load test, is a viable alternative to testing machines when they cannot otherwise be loaded to specific conditions, as in the dual frequency test method. The theory of the three-step heat run method is described and well documented in IEC 61986. A comparison of test results for large machines using the dual frequency single step method versus the three-step method is presented in this paper.