Detection of Airgap Eccentricity for Induction Motors Using the Single-Phase Rotation Test

The single-phase rotation test (SPRT) is a simple and reliable offline test frequently used for detecting problems in the rotor cage of induction motors without motor disassembly. Airgap eccentricity due to bearing degradation, shaft flexing, etc., is another problem that is difficult to detect, which can cause catastrophic motor failure. In this paper, the feasibility of using the SPRT for detecting eccentricity, which has not been reported before, is investigated. The variation in the inductive component as a function of rotor position and time under static, dynamic, and mixed eccentricity conditions is analyzed. It is shown that airgap eccentricity can be detected in addition to rotor cage problems with the SPRT. An experimental study on a 7.5-Hp induction motor under controlled eccentricity and broken bar conditions shows that airgap eccentricity can be reliably detected with high sensitivity and distinguished from broken rotor bars.