In order to assess the moisture content of insulating pressboard in oil-immersed transformer

and thusproviding reliable guidance for insulation condition and life estimation of oil-immersed transformer

in this paper

we made four groups of oil-paper insulation samples with different moisture content under laboratory conditions andstudied the relationship between pressboard and moisture content by using polarization and depolarization current（PDC）technique. The experiment result shows that PDC curve is very sensitive to the change of moisture content

and the

change of moisture content mainly affects the tail of depolarization current curve;the extended Debye modelparameters can be obtained from depolarization current curve

and as the moisture content increases the number ofbranches in Debye model increases

the largest time constant becomes large;by the sensitivity of the tail of PDCcurve to the pressboard moisture content

the insulating pressboard branches can be filtered from the Debye model;the characteristic quantity Q

paper

can show the internal polarization of insulating paper and has a linear fittingrelationship with moisture content

so Q

paper

can be used to assess the moisture content of insulating pressboard.