The effect of inter-bar currents on the diagnostic of the induction motor

This paper presents a mathematical model of a three-phase induction motor. Many studies have been available for a long time about induction motor rotor faults but few include a part for the machine under defects in the model. The aim of this paper is to have a simulation tool of induction motors with rotor broken bars which, in spite of their increasing complexity, are able to provide with useful indications for diagnostic purposes. The tool is suitable for the simulation of motors behavior under rotor defect taking into account inter-bar currents. The proposed model is based on the mesh model analysis of the squirrel cage. As low power induction motors are the larger to be used in industrial plants, we pay a special attention on them. Notwithstanding, the additional currents are due to the contact between the non-insulated bar constituting the squirrel cage to the rotor iron core, they are very important. Traditionally, the motor monitoring is made thanks to the analysis of the stator current when the motor operates under nominal load. Moreover, this one has to be observed in steady state operating system knowing that the motor is generally fed by a sinusoidal supply. Consequently, simulation results show the effectiveness of the approach proposed and the impact of inter-bar resistance both on the model and the sidebands for the diagnostic.