This paper is proposed to estimate temperature of permanent magnet for PM machines and to detect eccentricity for induction machines. The rare earth type magnet is susceptible to irreversible demagnetization at high operation temperature. Online monitoring method of magnet temperature has many limitations since magnet is placed on rotating part, and model-based estimation method must consider motor’s precise design or other parameter. Linear hall-effect sensor, which shows linearly magnetic field, is adopted to estimate temperature and to diagnose partial demagnetization of magnet. It is shown that temperature of magnet can be estimated in addition to partial demagnetization problems using linear hall sensor. An experimental study on a 2.2kW interior PM motors with linear hall sensor shows that temperature of magnet can be reliably estimated and partial demagnetization can be detected.
The single phase rotation test (SPRT) is a simple and reliable off-line 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 5.5kW 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.