Life Assessment Of Oil-Immersed Transformers

The degree of polymerization (DP) of transformer insulation materials is the most accurate, reliable and effective criterion for insulation aging. Based on the average degree of polymerization of insulation paperboard to judge the degree of transformer aging, we use the following judgment criteria.
Evaluation criteria for average degree of polymerization of insulation paper
Classification Life level Danger level
Average DP < 450 < 250
1) Life level indicator When an external short circuit occurs, the maximum tensile strength residual rate that the insulation paper can withstand reaches 60% of the initial value; the dangerous level means that the maximum tensile strength residual rate reaches 15% of the initial value.
2) The DP failure probability standard of Japanese insulation paper fiber is:
① DP ≥ 450, failure probability = 0; ② 450> DP ≥ 250, failure probability = (450 - DP) / 200; ③ 250 > DP, failure probability = 1.
3) Use the average DP to estimate the remaining life of the transformer, that is, nL/n0=(1-r)L, where n0 is the average DP starting value; nL is the average DP after L; L is the number of years, a; r is the average DP decrease rate.