To apply the polarization and depolarization current（PDC）method to state evaluation of transformer’s oil-paper insulation

a PDC test platform of oil-paper insulation was set up to obtain the PDC characteristic curves of the oil-paper samples with different aging degree and moisture content.Analysis on these curves shows that:1)the aging degree exerts effects on the front and middle segments of the of the polarization current curve and the whole depolarization current curve;2)the moisture content exerts effects on the whole polarization current curve and the middle and last segments of the depolarization current curve.It is suggested that the initial depolarization current idp1 and steady polarization current id（conduction current）be taken as the mapping characteristic quantities of oil paper’s degree of polymerization and moisture content

respectively to fit their functional relationship for the assessment purpose of the moisture content of oil-paper with different aging degree.