Stator current monitoring to detect mechanical faults in medium size induction motors

An investigation into the use of stator current monitoring to detect mechanical irregularities in a medium-size, skewed induction motor is presented. Through the use of analytical mmf and permeance functions, the frequencies of air gap flux density harmonics may be identified, allowing the prediction of induced voltage and current harmonics in the stator windings. The development of a test rig to create both static and dynamic eccentricity conditions is described. The test facility also allows rapid access to the motor bearings, allowing the investigation of faulty bearings. The presented experimental results confirm the theory related to static and dynamic eccentricity. Experiments carried out with a contaminated bearing indicate that techniques used to detect eccentric conditions may also be valid for the detection of bearing degradation.