An attempt to correlate time & frequency domain polarisation measurements for the insulation diagnosis of power transformer

The insulation system of power transformers (oil and paper/pressboard) generally change their dielectric properties during the life of the transformer and dielectric measurements have therefore been applied to assess the quality or state of ageing of the system. Both time domain and frequency domain dielectric diagnosis techniques have recently gained popularity in providing information on the condition of transformer oil-paper insulation. The present paper aims at deriving a correlation between these two methods of diagnosis. Simulation results along with actual field test results have demonstrated a direct correlation between the time and frequency domain tools for insulation diagnosis.