The Modeling and Investigation of Slot Skews and Supply Imbalance on the Development of Principal Slotting Harmonics in Squirrel Cage Induction Machines

A discrete winding function analysis (DWFA) based approach for the modelling of skewed rotor cage-type induction motor with minimal simulation time is presented in this paper. The rotor slot skew has a significant attenuating impact on principal slotting harmonics (PSH) or rotor slotting harmonics (RSH). These harmonics can play a significant role in sensor-less speed estimation and condition monitoring of induction machines. The advanced fault diagnostic algorithms are becoming increasingly dependent on the fast and accurate mathematical models of electrical machines. The most accurate models are based on the finite element method (FEM), but the computational complexity and the required simulation time make them unsuitable for model-dependent fault diagnostic algorithms. Moreover, as most models are 2D, they cannot incorporate axial asymmetries such as rotor slot skews. Furthermore, most analytical models, such as modified winding function analysis (MWFA), depend upon the continuous integration functions, increasing complexity while implementing them in the online environment in digital signal processing boards. To resolve all those issues, DWFA based model is proposed in this paper, which can simulate the majority of the faults in negligible time compared to the corresponding FEM models. The impact of slot skews and unbalanced power supply on the current spatial harmonics is studied, and the results are compared with the practical measurements taken from the laboratory setup.