AN ACOUSTIC DIAGNOSTIC-TECHNIQUE FOR USE WITH ELECTRIC MACHINE INSULATION

Many of the electrical failures of large electric machines have mechan ical precursors. This premise has led to the attempts described here t o detect mechanical changes, such as groundwall delamination, by acous tic methods as a means of early detection of incipient failure. By opt imally launching an ultrasonic wave into a stator bar and using the co nductor as a waveguide, it has been shown possible to interrogate the groundwall insulation and the critical interface region adjacent to th e conductor. Laboratory studies using an epoxy mica stator bar subject ed to thermal cycling have demonstrated that the acoustic signatures o btained with this method are mirrored by conventional corona spectrosc opy conducted simultaneously, although earlier damage is clearly disce rnible. Based on the results of this study, the acoustic technique app ears to have substantial promise as an advanced detection tool.