Long term aging test on stator bars exposed to end arm discharges

Long term aging tests of stator bar end arms were carried out over several months. Six specimens affected by one of three types of defect were studied. Those defects were corona activity, surface tracking and bar-to-bar discharges. All the specimens were submitted to an aging voltage of 20 kV c.a. Phase resolved partial discharge (PRPD) and spectral analyses were performed periodically, to characterize each type of activity. After more than one year and a half of aging, we noted that some type of activity was very sporadic, while others were more permanent. Two failures occurred up to now, both of them on specimens with corona activity. Despite the fact that the failures both occurred in the straight portion of the bars, we suspect that the corona activity was, at least partially, involved in the failure mechanism. The aging test is still running with two new specimens replacing the failed ones.