Moisture is a key factor affecting the insulating property of transformer oil-paper insulation and many current research efforts have focused on resolving the relationship between its insulation state and the moisture content in the oil. Firstly

the source and harm of moisture in the oil-paper insulation system were analyzed

and the proportional relationship between the frequency factor a and moisture content in the insulation paper was deduced based on the Taylor expansion of a

and then the modified Arrhenius law was obtained in which the moisture content was taken into account. Secondly

the quantitative expression moisture content in the insulation paper and d

egree of polymerization（DP） was obtained by chemical reaction kinetics

the modified expression between DP and moisture content in the oil was derived according to the influences of cellulose aging on the Oommen’s moisture equilibrium curves

and the rectified representation between DP and the moisture content in the oil was acquired. Thereby

the characteristic life prediction criterion of the insulation paper was concluded. Finally

the validity of the proposed method was verified by experimental data. The results show that the calculation errors of the expression between moisture content in insulation paper and oil are between 20% and 50% without considering the aging of insulation paper and the errors of DP based on the moisture content in oil are between 3.8%

3

8.4%

but the above errors will be reduced to 12.5% and 23.3%

respectively

if they are calculated with the modified expressions. When the aging temperature remains at 140 ℃ and the moisture content in the oil is 10

-6

and 13×10

-6

respectively

the insulation paper characteristic life will be 65 d and 12 d

respectively.