On turbogenerator H.V. stator winding condition assessment by the analysis of PDHD detected on phases and insulated coils after untimely failure

The paper deals with the results of investigations performed in order to verify whether diagnostic tests, based on Partial Discharge Height Distribution (PDHD) analysis, are able to identify the causes of deterioration and to guide the repair of the insulation system of HV rotating machine stator windings. The insulation system of a turbogenerator was tested after a breakdown occurred in service. Partial Discharge (PD) measurements were performed both on the windings and on single coils. The analysis of the results of PD measurements evidenced that the breakdown was due to a defective impregnation of the winding.