The condition of the phase-to-ground insulation as well as phase-to-ground insulation of a Stator can be assessed by the Polarisation Depolarisation Current (PDC) technique.
PDC evaluation results of Stator Insulation include:

• Insulation Resistance and Polarisation Index
• Frequency scan of Capacitance
• Frequency scan of Dielectric Dissipation Factor (DDF) or tan δ

PDC results of a good, new 11 kV air-cooled, Global VPI generator are presented in the charts below: