On-line protection of electrical machines by microcomputer analysis of axial leakage flux
The work, of which this thesis is a record, is concerned with the development of condition monitoring and protection facilities for electrical drives and generators. There are two primary objectives, the first being the development of a consistent theory governing the production of axial - flux harmonics in electrical machines. This development proceeds with the identification of the harmonic spectra expected in machines which are running normally, and is then extended to predict the changes to be expected for a variety of fault conditions. Faults such as: stator winding interturn short circuits, negative phase sequence due to unbalanced supply, eccentric running due to bearing wear, fractured rotorbars in induction machines, and rotor winding short circuits are investigated and the predicted changes verified by test and experiment on machines varying in rating from 2 kW to 100 HW. The second, and overlapping, primary objective is the provision of an integrated, microprocessor-based condition monitoring system that will also afford protection for the machines under surveillance against the fault conditions mentioned above. Such a system based on the FFT analysis of the axial flux signal has been constructed to prototype Level, and has met said objective. The system comprises two 8 bit and one 16 bit processors and is designed to react extremely rapidly to the occurrence of a fault condition. Throughout the design phase, the aims of simplicity of operation and flexibility have been paramount. The provision of test facilities in the industrial environment afforded by the CF.GB proved invaluable in these respects. It is thought that the methods of monitoring and protecting machines, mentioned above, has significant attractions because it allows multi-functional protection from a single transducer to be achieved, and the form of the transducer is such that line voltages and currents need not be sensed.