Bindu, S.Sumam David, S.Thomas, V.V.2026-02-052021International Review on Modelling and Simulations, 2021, 14, 5, pp. 345-35819749821https://doi.org/10.15866/iremos.v14i5.19670https://idr.nitk.ac.in/handle/123456789/23408An accurate means of non-invasive condition monitoring of the popular industrial drive, three-phase squirrel-cage induction motor, can help to avoid unscheduled maintenance downtime and loss. Faults like air-gap eccentricity can exist even in a newly assembled drive and hence may co-exist with other internal defects. Despite it being a possible situation, the occurrence of simultaneous faults has seldom been studied. Therefore, there is a need for identifying fault signatures of combined fault conditions in a non-invasive manner. This paper presents a detailed model-based study on a three-phase squirrel-cage induction motor with the simultaneous existence of broken rotor-bar and air-gap mixed eccentricity faults using spectral analysis of stator current, instantaneous power, and estimated air-gap torque signals. The modelling of the machine is done using the Multiple Coupled Circuit method and modified to model the presence of the combined fault conditions. A comparative evaluation with various fault conditions and their severity is carried out by spectral analysis, and unique slip-dependent frequency components are identified in the spectra of diagnostic signals. This fault characterization is the most significant contribution of this paper. © 2021 Praise Worthy Prize S.r.l.-All rights reserved.Air-gap eccentricityAir-gap torqueBroken rotor-barCondition monitoringFault diagnosisInduction motorsInstantaneous powerMotor current signature analysisMultiple coupled circuit model