Comparison between characterization and diagnosis of broken bars/end-ring connectors and airgap eccentricities of induction motors in ASD's using a coupled finite element-state space method

This paper describes how a rigorous and comprehensive Time-Stepping Coupled Finite Element-State Space (TSCFE-SS) modeling technique can be utilized i n diagnostics and differentiation between induction motor rotor (cage) abno rmalities of broken bars/connectors and airgap eccentricities. The model is used for the computation of time-domain performance characteristics, such as the stator phase current waveforms and developed torque profiles includi ng these abnormalities. This is followed by analysis of the current wavefor ms and torque profiles using Fast Fourier Transform to obtain their corresp onding frequency spectra, Comparison between the TSCFE-SS model's simulatio n results, which correlate very well with theoretical results, clearly illu strate that rotor bar and/or end-ring connector breakages can be distinguis hed from static and dynamic airgap eccentricities. This paper also gives an interesting comparison between the effects and implications of these vario us rotor abnormalities on machine parameters and performance characteristic s, Furthermore, the results indicate that frequency components reported ear lier to be produced only by the combined effects of static and dynamic airg ap eccentricity could be observed in case of either static or dynamic eccen tricity. Finally, this paper demonstrates the possible opportunities that c an be made use of in noninvasive detection of airgap eccentricities via TSC FE-SS and current signature techniques.