Detection of air-gap eccentricity faults in synchronous machines

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Recently, research related to on-line electric machine fault diagnosis (also known as Condition Based Monitoring (CBM)) has generated considerable interest. Fault prognosis, particularly at the incipient stage, can reduce machine downtime and maintenance considerably. Air-gap eccentricity faults occur in electrical machines when the air-gap between stator and rotor is no longer uniform. An air-gap eccentricity can be broadly classified into two types, namely, the static air-gap eccentricity and the dynamic air-gap eccentricity. Static and dynamic eccentricities tend to co-exist. Unless detected early, eccentricity may result in stator to rotor rub, causing a major breakdown of the machine due to core and winding damage. Normally, eccentricity related faults are associated with large machines. The detection and monitoring techniques available for eccentricity have been mostly restricted to induction machines because they usually have very small airgap. However, early and quick detection techniques of eccentricity for synchronous machines can also lead to their design with much smaller airgap. This will substantially reduce the cost of the machine due to a decrease in magneto motive force (MMF) requirements. It will also reduce short circuit currents and hence circuit breaker size and cost. It is therefore imperative that diagnosis techniques, preferably non-invasive in nature, are developed to monitor and detect these faults in synchronous machines. It is expected that the results of the investigation will shed new light in understanding how to effectively detect eccentricity of synchronous machines. This will benefit numerous manufacturers and users of synchronous machines and will surely translate into increased profit and enhanced productivity for Canadian industry.