Estimation of the number of rotor slots and rotor speed in induction motors using current, flux, or vibration signature analysis

Abstract

Effective condition monitoring of induction motors requires knowledge of the number of rotor slots and the rotor speed. These were primarily obtained in the literature by multiple measurements and using design knowledge of the motor under test. Furthermore, the earlier studies have mainly concentrated on stator current analysis. This paper investigates the use of the stator current, axial flux, and vibration signals in order to provide accurate rotor speed and rotor slot number estimation by utilising the eccentricity harmonics, slip frequency, rotor frequency, and rotor slot passing frequency. The proposed simple methods are verified using an extensive series of measurements on a 2.2 kW squirrel-cage and a 5 kW wound-rotor induction motor over a wide range of loading conditions.