Signatures of Electromechanical Faults in Stress Distribution and Vibration of Induction Motors

This paper develops a method for determining the signatures of electromechanical faults in the airgap stress distribution and stator vibration of induction machines. Two types of induction motors are analyzed; a 2-pole pairs, star connected and an 1-pole pair, delta connected motor. The radial electromagnetic stress distribution along the airgap is calculated and developed into double Fourier series in space and time. The computations show the existence of low frequency and low order stress distributions acting on the stator of the electrical machine when it is working under faulty conditions. These stress waves are able to produce forced vibration in the stator surface. The simulation results are corroborated by vibration measurements. Modal testing is also carried out to determine the natural frequencies. The measurements and simulations show that low frequency components of the vibrations can be used as identifiable signatures for condition monitoring of induction motors. The patterns presented by the faults allow to discriminate between them.