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Vibration sparking, an ignored damage mechanism of high voltage windings

Partial discharge (PD) mechanisms are widely acknowledged damage threads to high voltage windings of electrical machines. The immense number of papers on this subject and the development of prosperous PD monitoring industries provide the impression that PD is the only electrical damage mechanism which threatens high voltage machine insulation [1]. However, this is wrong because another electrical insulation failure called vibration sparking (VS) exists. It is much more destructive than PD and destructs even bars at the low voltage end of high voltage phase windings. For suppressing slot discharge (SD), a variant of PD, outside corona layers have been introduced on the bar surfaces. Under certain circumstances, these layers allow for vibration sparking. The paper deals for the first time with both the theory of VS and experiences with the failure damages.