All large turbo and hydro-generators are constructed using thin electrical steel laminations to minimise eddy current losses. However, there are circumstances, in which the lamination insulation can be damaged. Examples of these include: poor manufacturing technique; the ingress of foreign objects; and mechanical impact on the laminated surface. This can lead to high localised eddy currents in the damaged area and will affect the performance of the machine, hi extreme cases, unattended core faults can permeate at an extremely fast rate and the heat generated can be sufficient to melt the damaged area in the stator core. The repair and replacement of a severely damaged stator core is a time consuming and costly affair. This thesis describes a non-invasive method for detecting stator core faults during normal routine inspection of the machine, to ensure that its normal life expectancy is not compromised. The work is aimed at providing a deeper understanding of the electromagnetic aspects associated with core faults by developing new investigative techniques for modelling and predicting the fault behaviour. An analytical model was developed to predict the fault current distribution produced by the damaged core lamination insulation. This fault current can be detected by an electromagnetic instrument called the Chattock potentiometer. A separate analytical model was also developed to predict the field distribution profile produced by a fault current flowing in the stator core. The analytical model allows the estimated fault current to be determined from the Chattock coil output signal.
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