Detection of air-gap eccentricity and broken-rotor bar conditions in a squirrel-cage induction motor using the radial flux sensor

Abstract

A new method for detecting eccentricity and broken rotor bar conditions in a squirrel-cage induction motor is proposed. Air-gap flux variation analysis is done using search coils, which are inserted at stator slots. Using this method, the leakage flux in radial direction can be directly detected. Using finite element method, the air-gap flux variation is accurately modeled and analyzed. From the results of the simulation, a motor under normal condition shows maximum magnetic flux density of 1.3T. On the other hand, the eccentric air-gap condition displays about 1.1T at 60° and 1.6T at 240°. A difference of flux density is 0.5T in the abnormal condition, whereas no difference is detected in the normal motor. In the broken rotor bar conditions, the flux densities at 65° and 155° are about 0.4 T and 0.8T, respectively. These simulation results are coincided with those of experiment. Consequently, the measurement of the magnetic flux at air gap is one of effective ways to discriminate the faulted conditions of the eccentricity and broken rotor bars.