A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the Degree of Doctor of Philosophy. / Variable speed motors are achieved by varying the voltage of a DC machine or by varying the frequency of an AC machine, the former method being the simpler of the two. DC motors have the major disadvantage of brushes and commutators which require regular downtime for maintenance, a fact already recognised by Tesla [1] in 1888. Thus the AC motor, in particular the induction motor, is of a more rugged design and does not suffer from the commutator problem of its DC counterpart. Recent advances in the technology of the power electronics used to supply a variable frequency to the motor has allowed the induction motor to be a viable alternative to the DC motor in variable speed applications. Problems have been encountered in industry when an inverter is injudiciously selected to be combined with a motor. Such problems were highlighted by difficulties being experienced with some 400 kW inverter drives. The inverters had been bought from one supplier and the motors from another. When this system was coupled together, there was excessive heating in the motors and the overall plant was only able to operate well below its capacity, incurring a substantial weekly loss of income. The motor and inverter were evidently incompatible, and since the inverter could not be modified, the motor was redesigned to make it less susceptible to the harmonics present in the inverter waveform, These problems have led to the development of a variable speed drive simulation package at the University for use by the local industry which can accurately model the complete system of inverter, motor and its associated load. It is envisaged that this package could be used to predict the performance of a drive system and highlight problems that may occur. To be able to do this, an accurate model of the motor is required. This investigation gives the development of an induction motor model which is suitable . for variable speed drive system simulations. The model accounts for the deep bar effect by using lumped parameter circuits and includes saturation of the leakage paths using only information which is typically available from motor design data. A complete analysis is given of the different lumped parameter models and their suitability for use in this application. The thesis also shows the utilisation of the deep bar model to simulate reswitching transients and double cage motors. The author hopes that the models used in the simulation package wallow industry to predict problems prior to their occurrence, alter the designs and thereby avoid costly remanufacture of the system. / Andrew Chakane 2018

This thesis analyses the behavior of an induction motor based on a mathematical model created for its simulation. The model describes the interaction of its several non linear differential equations to present a simulated output of induced torque and mechanical speed. Considering the applications to marine propulsion, it is also the goal of the project to design and test a control system for the speed of the motor by maintaining a specific cruse speed regardless the perturbations. / by Camilo Carlos Roa. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Vita. / Includes bibliographical references. / Ph.D.

Thesis. 1977. B.S.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaf 84. / B.S.

Thesis. 1977. B.S.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / B.S.

In this dissertation, we investigate the theory and application of higher-order spectral analysis techniques to condition monitoring in shipboard electrical power systems. Monitoring and early detection of faults in rotating machines, such as induction motors, are essential for both preventive maintenance and to avoid potentially severe damage. As machines degrade, they often tend to become more nonlinear. This increased nonlinearity results in the introduction of new frequencies which satisfy particular frequency selection rules; the exact selection rule depends on the order of the nonlinearity. In addition, the phases of the newly generated frequencies satisfy a similar phase selection rule. This results in a phase coherence, or phase coupling, between the “original” interacting frequencies and the “new” frequencies. This phase coupling is a true signature of nonlinearity. Since the classical auto-power spectrum contains no phase information, the phase coupling signature associated with nonlinear interactions is not available. However, various higher-order spectra (HOS) are capable of detecting such nonlinear-induced phase coupling. The efficacy of the various proposed HOS-based methodologies is investigated using real-world vibration time-series data from a faulted induction motor driving a dc generator. The fault is controlled by varying a resistor placed in one phase of the three-phase line to the induction motor. First, we propose a novel method using a bispectral change detection (BCD) for condition monitoring. Even though the bicoherence is dominant and powerful in the detection of phase coupling of nonlinearly interacting frequencies, it has some difficulties in its application to machine condition monitoring. Basically, the bicoherence may not be able to distinguish between intrinsic nonlinearities associated with healthy machines and fault-induced nonlinearities. Therefore, the ability to discriminate the fault-only nonlinearities from the intrinsic nonlinearities is very important. The proposed BCD method can suppress the intrinsic nonlinearities of a healthy machine by nulling them out and thereby identify the fault-only nonlinearities. In addition, most machines contain rotating components, and the vibration fields they generate are periodic. These periodic impulse train signals may produce artificially high bicoherence values and can lead to ambiguous indications of faults in machine condition monitoring. The proposed BCD method can remove the artificially high bicoherence values caused by periodic impulse-train signals. With these advantages, the proposed BCD method is a new and sensitive indicator for condition monitoring. Second, we propose a novel method to estimate, from a measured single time-series data record, complex coupling coefficients in order to quantify the “strength” of nonlinear frequency interactions associated with rotating machine degradation. The estimation of the coupling coefficients is based on key concepts from higher-order spectral analysis and least mean-square-error analysis. The estimated coupling coefficients embody the physics of the nonlinear interactions associated with machine degradation and provide a quantitative measure of the “strength” of the nonlinear interactions. In addition, as an auto-quantity method utilizing a single time-series data record, the proposed method adds supplemental fault signature information to conventional tools. Such knowledge has the potential to advance the state-of-the-art of machine condition monitoring. Third, we propose a bispectral power transfer analysis methodology to quantify power transfer between nonlinearly interacting frequency modes associated with machine degradation. Our proposed method enables us to identify the relative amounts of power transferred by various nonlinear interactions, and thereby identify the predominant interactions. Such knowledge provides important new signature, or feature, information for machine condition monitoring diagnostics. / text

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Thesis (M. E. (Hons))--University of Western Sydney, 2002. / "A thesis submitted for Master of Engineering (Honours), School of Engineering & Industrial Design, University of Western Sydney, October 2002" Bibliography: leaves 147 - 149.