Date of Award

Fall 2007

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Electrical and Computer Engineering

First Advisor

Demerdash, Nabeel A. O.

Second Advisor

Yaz, Edwin E.

Third Advisor

Mirafzal, Behrooz

Abstract

In this thesis, faults associated with squirrel-cage rotor structures will be considered. More specifically, diagnostics of adjacent and nonadjacent squirrel-cage rotor bar breakages will be addressed. Effects of such faults on machine performance will be studied through a number of modeling approaches. Namely, an example of a simple 8-bar squirrel-cage induction machine will be used to visualize the effects of both adjacent and nonadjacent rotor bar faults on the magnetic field distribution in the induction machine. Then, more sophisticated models such as the magnetic equivalent circuit, and time-stepping finite element models of a case-study 5-hp induction machine will be developed. These models will be used to verify the assumptions used in the simple 8-bar example as well as to provide a more detailed picture of the fault effects on the motor performance. A number of both adjacent and nonadjacent fault scenarios will be considered. It will be shown that some nonadjacent rotor bar breakages may result in the masking of the commonly used indices of fault signals, hence, leading to possible misdiagnosis of the machine. It will also be shown that secondary effects that appear during such nonadjacent rotor faults can be utilized for purposes of fault identification using conventional rotor fault diagnostic approaches with modified indices. Moreover, a new rotor fault diagnostics technique based on the vibration signal obtained using a low-cost piezoelectric vibration sensor will be introduced. This technique will be used for successful diagnostics of both adjacent and nonadjacent squirrel-cage rotor faults. Both of these findings show a good deal of promise in practical applications.

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