Locked-Rotor Test Methods for Induction Motors Investigated

Locked-rotor testing is a common end-of-the-line check performed on most motors used in the petrochemical industry. Despite its popularity as a verification of rotor integrity and to confirm the current draw and torque produced at zero speed, there can be much ambiguity in how the test is performed. This test is not required by the National Electrical Manufactures Association Motors and Generators Standard (NEMA MG1) or the Institute of Electrical and Electronics Engineers Standard 112 (IEEE 112). IEEE 112 contains a locked-rotor test method, but there can be variations in the results based upon the test conditions (duration of voltage application and magnitude of applied voltage, for instance). The purpose of this paper is to describe how the test procedure employed affects the locked-rotor test results for both current and torque. Model and test data are presented to illustrate the variations possible depending on the test technique.