Design-dependent slot discharge and vibration sparking on high voltage windings

Partial discharge effects are widely acknowledged as a damage mechanism for deteriorating high voltage windings of electrical machines. Vibration sparking is another but scarcely known. Not only is vibration sparking significantly more damaging to electrical machine windings, unlike partial discharge deterioration it can occur at any position within the winding. Deteriorated winding insulation at the low voltage ends can only be detected via offline monitoring as online monitoring is not sufficient. Prevention of vibration sparking requires a reliably earthed outer corona layer of the winding bars or sufficiently large resistances of the outer corona layers. However the slot design needs to take account of both vibration sparking and partial discharge in order to mitigate these deterioration mechanisms.