Detection of stator core faults in large electrical machines

Abstract

Monitoring the health of large electrical machines, especially power station generators, is now an integral part of their operation to maintain and extend life. This work studies the use of electromagnetic sensors to detect inter-lamination insulation faults in the stator cores of large generators before they propagate to a level that can lead to catastrophic failure. The work develops a deeper understanding of the electromagnetic behaviour of core faults so that condition-monitoring sensors can be more specific about the location and severity of the fault. The study develops two new three-dimensional (3D) analytical models, one for predicting the fault current distribution in a stator core fault and the second for predicting the varying detection of such current by air-cored sensors. This further analysed the 3D detection efficiency of typical short fault lengths to compare with the two dimensional (2D) default of infinite-length faults. Different fault positions were modelled so that a clearer understanding of the location and severity of the fault is possible. These were validated on a specially constructed experimental test core that can impose controlled fault currents. The study also demonstrates how small core faults can escalate then self-limit radially, but may propagate axially into longer more damaging faults.