The Method for Improving the Effect of Oil-Replacement on Aging Assessment of Power Transformers Insulation Based on Methanol

Methanol was considered as a new chemical marker for estimating the aging state of transformer insulation paper, whereas oil-replacement could influent greatly the accuracy of the assessment results. In this paper, the 130 degrees C thermal aging experiment was carried out, and the oil-paper samples were divided into four groups for investigating the effect of the oil-replacement on assessment deviation of aging states of insulation paper. The results indicated that the present aging assessment model was not suitable for oil-replacement based on methanol in oil and the aging assessment errors of degree of polymerization (DP) had a decreasing tendency with increasing the aging time after oil-replacement. Furthermore, the oil-replacement correction factor was proposed as power-series expansion based on the experiment results, and a modified model was proposed by integrating the basic Methanol-DP model and the correction factor. Eventually, the verification experiment was prepared to test the accuracy of modified model and the results indicated that the relative assessment error of DP was within 4.8%. The accuracy of aging assessment are improved by oil-replacement correction factor.