Broken bar indicators for cage induction motors and their relationship with the number of consecutive broken bars

The study presents analysis of the broken bar induction machine, through numerical, analytical and experimental investigations. Numerical finite element analysis is carried out with a commercial software in which coupling between the windings circuit equations and equations of the magnetic field has been implemented and verified through intensive measurements. An analytical model has also been constructed to understand and explain the origin of different frequencies detected in the case of broken bars. The analytical model enabled prediction of frequencies, in a new manner, when the number of consecutive broken bars increases. The novelty of this study arises from derivation of an expression linking stator current harmonics (using the wave number of a broken cage), slip harmonic and saturation harmonic, which is closely related to the number of consecutive broken bars. The model also takes into account the speed ripple. This expression has been validated by both finite element model (FEM) and measurements on a 22 kW induction machine with healthy and faulty rotors.