Modelling of induction machines with skewed rotor slots

A model permitting the simulation of induction machines with skewed rotor slot is presented. The two-dimensional finite-element method is used for electromagnetic field analysis of the induction machine. The skew effects are considered by coupling several discs cut by planes perpendicular to the shaft. The solution of the resulting nonlinear time-dependent equation is obtained using step-by-step numerical integration. The paper also presents a method to avoid the singular matrices when rotor bar currents are solved from field and circuit equations. The model is verified by comparing measured and computed results for a 37kW cage induction motor. Current and voltage waveforms and torque-speed curves are discussed. According to the results the model gives good results when the slip value is under 0.9.