Nabeel A. O. Demerdash

Induction Machine Broken Bar and Stator Short-Circuit Fault Diagnostics Based on Three-Phase Stator Current Envelopes

A new method for the fault diagnosis of a broken rotor bar and interturn short circuits in induction machines (IMs) is presented. The method is based on the analysis of the three-phase stator current envelopes of IMs using reconstructed phase space transforms. The signatures of each type of fault are created from the three-phase current envelope of each fault. The resulting fault signatures for the new so-called ldquounseen signalsrdquo are classified using Gaussian mixture models and a Bayesian maximum likelihood classifier. The presented method yields a high degree of accuracy in fault identification as evidenced by the given experimental results, which validate this method.

Modeling and Parametric Design of Permanent-Magnet AC Machines Using Computationally Efficient Finite-Element Analysis

Computationally efficient finite-element analysis (FEA) (CE-FEA) fully exploits the symmetries of electric and magnetic circuits of sine-wave current-regulated synchronous machines and yields substantial savings of computational efforts. Motor performance is evaluated through Fourier analysis and a minimum number of magnetostatic solutions. The major steady-state performance indices (average torque, ripple and cogging torque, back-electromotive-force waveforms, and core losses) are satisfactorily estimated as compared with the results of detailed time-stepping (transient) FEA. In this paper, the CE-FEA method is presented and applied to a parametric design study for an interior-permanent-magnet machine. Significant reduction of simulation times is achieved (approximately two orders of magnitude), permitting a comprehensive search of large design spaces for optimization purposes. In this case study, the influence of three design variables, namely, stator tooth width, pole arc, and slot opening, on three performance indices, namely, average torque, efficiency, and full-load torque ripple, is examined, and design trends are derived. One hundred candidate designs are simulated in less than 20 minutes on a state-of-the-art workstation.

Diagnosis and characterization of effects of broken bars and connectors in squirrel-cage induction motors by a time-stepping coupled finite element-state space modeling approach

In this paper, a comprehensive presentation of a time-stepping coupled finite element-state space modeling approach for diagnosis and characterization of effects of rotor (cage) broken bars and connectors in squirrel-cage induction motors is given. The model is used to compute/predict the characteristic frequency components which are indicative of rotor bar and connector breakages in the armature current waveforms and developed torque profiles, respectively. It was found that failures due to rotor connector breakages tend to degrade the developed torque of the machine considerably more than failures due to rotor bar breakages. Also, the effects and implications of rotor breakages on core loss distributions are quantified and described. Furthermore, this model has great potential in future applications to generate databases for use in overall noninvasive diagnostics of faults or troubleshooting in relation to quality assessments of the state of the motor and the overall drive.

Analysis and Diagnostics of Adjacent and Nonadjacent Broken-Rotor-Bar Faults in Squirrel-Cage Induction Machines

In this paper, faults associated with the rotor of an induction machine are considered. More specifically, effects of adjacent and nonadjacent bar breakages on rotor fault diagnostics in squirrel-cage induction machines are studied. It is shown that some nonadjacent bar breakages may result in the masking of the commonly used fault indices and, hence, may lead to a possible misdiagnosis of the machine. A discussion of the possible scenarios of these breakages as well as some conclusions regarding the types of squirrel-cage induction machines (number of poles, number of squirrel-cage bars, etc.) that may be more prone to these nonadjacent types of failures are presented. This discussion is supported through both simulation and experimental results. It is also shown that secondary fault effects can be used to diagnose such nonadjacent bar breakages.

Effects of load magnitude on diagnosing broken bar faults in induction motors using the pendulous oscillation of the rotor magnetic field orientation

The effects of load level on the ability to diagnose broken bar faults in squirrel cage induction motors are studied in this paper. The pendulous oscillation of the rotor magnetic field orientation is implemented as a fault signature for rotor fault diagnostic purposes. Moreover, the effects of load level on the low side band component of the stator current spectrum are reported as well. These investigations were performed through testing 2-hp and 5-hp induction motors over a wide range of load levels and control-drives. The results of these tests and investigations demonstrate that the pendulous oscillation signature can be used for a wide range of motor operating conditions.The effects of load level on the ability to diagnose broken bar faults in squirrel-cage induction motors are studied in this paper. The pendulous oscillation of the rotor magnetic field orientation is implemented as a fault signature for rotor fault diagnostic purposes at steady-state operations. Moreover, the effects of load level on the low-side band component of the stator current spectrum, and associated diagnostic difficulties in this approach particularly in the presence of motor operation from pulsewidth-modulation drives, are reported as well. These investigations were performed through testing 2-hp and 5-hp induction motors over a wide range of load levels and control drives. The results of these tests and investigations demonstrate the efficacy of the pendulous oscillation signature as a diagnostic means that can be used for a wide range of motor operating conditions.

Electric machinery parameters and torques by current and energy perturbations from field computations. I. Theory and formulation

In this first of a two-part article, the well-established energy/current (E/C) perturbation method of computation of machine winding inductances is reviewed. The methods efficacy in machine performance calculations is delineated and verified in a companion paper by comparison to experimental results. The critical role that winding inductance parameters have in modeling and simulation of the nonsinusoidal steady state time-domain (forced response) performance of electric machinery is demonstrated using state models in both the winding flux linkage and current-based frames of reference. The computed machine performance characteristics include profiles of winding inductances, induced terminal voltage waveforms, and instantaneous torque profiles that contain all the ripples due to the significant space harmonics in a machine. The method and associated formulations and techniques are shown to be very effective in both 2D-FE and 3D-FE electric machinery field solutions involving substantial degrees of saturation and complexity of construction. The machines analyzed in the comparison paper include a 15-HP permanent magnet brushless DC motor, a 1.2-HP three-phase induction motor, and a 14.3 kVA three-phase modified Lundell alternator possessing very complex magnetic circuit geometries. The well-posedness of the method held true for all these cases, as well as many other case-studies briefly reviewed here.

Calculation of Magnet Losses in Concentrated-Winding Permanent-Magnet Synchronous Machines Using a Computationally Efficient Finite-Element Method

The proposed hybrid method combines computationally efficient finite-element analysis (CE-FEA) with a new analytical formulation for eddy-current losses in the permanent magnets (PMs) of sine-wave current-regulated brushless synchronous motors. The CE-FEA only employs a reduced set of magnetostatic solutions yielding substantial reductions in the computational time, as compared with the conventional FEA. The 3-D end effects and the effect of pulsewidth-modulation switching harmonics are incorporated in the analytical calculations. The algorithms are applied to two fractional-slot concentrated-winding interior PM motors with different circumferential and axial PM block segmentation arrangements. The method is validated against 2-D and 3-D time-stepping FEA.

Interturn Fault Diagnosis in Induction Motors Using the Pendulous Oscillation Phenomenon

A robust interturn fault diagnostic approach based on the concept of magnetic field pendulous oscillation, which occurs in induction motors under faulty conditions, is introduced in this paper. This approach enables one to distinguish and classify an unbalanced voltage power supply and machine manufacturing/construction imperfections from an interturn fault. The experimental results for the two case studies of a set of 5-hp and 2-hp induction motors verify the validity of the proposed approach. Moreover, it can be concluded from the experimental results that if the circulating current level in the shorted loop increases beyond the phase current level, an interturn fault can be easily detected using the proposed approach even in the presence of the existence of motor manufacturing imperfection effects

Soft started induction motor modeling and heating issues for different starting profiles using a flux linkage ABC-frame of reference

In order to mitigate adverse effects of starting torque transients and high inrush currents in induction motors, a popular method is to use electronically controlled soft starting voltages utilizing series connected silicon controlled rectifiers (SCRs). Investigation of semi-optimum soft starting voltage profiles was implemented using a flux linkage ABC-frame of reference model of a soft started three-phase induction motor. A state-space model of the soft starter thyristor switching sequence for the motor and load was developed and implemented in a time-domain simulation to examine winding heating and shaft stress issues for different starting profiles. Simulation results of line starts and soft starts were compared with measured data through which validation of the model was established. In this paper, different induction machine soft start profiles are shown and comparisons of starting times, torque profiles, and heating losses are made. Discussion of these results and conclusions as to the near-optimum types of profiles are delineated based on peak torque, starting times, and winding heating criteria.

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

This paper describes how a rigorous and comprehensive time-stepping coupled finite element-state space (TSCPE-SS) modeling technique can be utilized in diagnostics and differentiation between induction motor rotor (cage) abnormalities 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 including these abnormalities. This is followed by analysis of the current waveforms and torque profiles using fast Fourier transform to obtain their corresponding frequency spectra. Comparison between the TSCFE-SS models simulation results, which correlate very well with theoretical results, clearly illustrate that rotor bar and/or end-ring connector breakages can be distinguished from static and dynamic airgap eccentricities. This paper also gives an interesting comparison between the effects and implications of these various rotor abnormalities on machine parameters and performance characteristics. Furthermore, the results indicate that frequency components reported earlier to be produced only by the combined effects of static and dynamic airgap eccentricity could be observed in case of either static or dynamic eccentricity. Finally, this paper demonstrates the possible opportunities that can be made use of in noninvasive detection of airgap eccentricities via TSCFE-SS and current signature techniques.