Multiple coupled circuit modelling approach for squirrel cage induction machine under single-broken-bar fault with stator winding functions decomposed in d-q rotor reference frame

Mathematical modelling is a fundamental issue in the condition monitoring and fault diagnosis of electrical machines. This study presents a multiple coupled circuit approach for the modelling of squirrel cage induction machines (SCIMs) with a single broken bar. Derived by means of winding function, the model is capable of incorporating all the harmonics of air-gap magnetomotive force and describing transient machine behaviours. A d-q reference frame fixed on rotor is introduced. Each stator winding function is decomposed into two parts, a q-axis and a d-axis component, both of which induce currents in each rotor mesh. The q-axis and d-axis equivalent circuits are developed for both healthy and faulty cage rotors. It is also shown that a single-broken-bar fault does not affect the q-axis rotor mesh current distribution. The d-axis equivalent circuit for healthy cage rotor is modified further to determine the deviations in the mesh currents due to bar breakage. A detailed model of a 2.2 kW, four-pole, three-phase, 28-rotor-bar SCIM is implemented in MATLAB/Simulink environment, and a laboratory test bed is set up for this machine. A comparison between the simulation and experimental results verifies the effectiveness of the proposed modelling approach.