Stator Inter-turn Fault Modelling and Analysis on Induction Motor based on MCCM

A multiple coupled circuit model (MCCM) of a 3phase squirrel cage induction motor based on the winding function approach is presented in this paper. The model is based upon the motor's structure and associated physical parameters. The incorporation of the exact stator winding layout (winding distribution), skewing of rotor bars and the linear rise in the stator slot MMF, consolidates the space harmonics associated within the motor in the presence of fault. The fault is modelled as a gradual insulation degradation using appropriate fault parameters. The integration of the insulation degradation in the winding function based model, is the main contribution of the work. The stator current signature analysis is performed under different load torque conditions for healthy and faulty motor. The fault specific harmonics are observed, and the behaviour of the motor under unbalanced supply voltage is investigated. The slip dependent fault harmonics and the voltage imbalance in the supply causes harmonics at thrice the supply frequency. It has also been observed that, if occurring together, the voltage imbalance increases the amplitude of the fault as well as the slot harmonics. However, if both fault and voltage imbalances are observed as standalone conditions, a diagnosis can be performed using the fault harmonics appearing in the spectrum of line currents.