Condition assessment of rotating machine winding insulation by analysis of charging and discharging currents

In order to assess winding insulation condition, a field instrument measuring the charge and discharge current of rotating machine stator winding insulation under DC high-voltage was developed at Niroo Research Institute (NRI). This method that is known as PDCA (polarization and depolarization current analysis) was applied on the stator winding insulation of an 87 MW gas-turbine generator and results were compared with on-line partial discharge (PD) measurements. The results obtained from the presented method were found to be very compatible with partial discharge measurements and visual inspection of end-windings and the ability of the PDCA in assessing the condition of the ground-wall insulation was validated