New Method for Assessment Ageing Condition of Oil Impregnated Insulation Pressboard Based on Frequency Domain Spectroscopy

Abstract

It is important to assess the condition of the cellulose insulation in transformer. However, taking paper samples from a transformer is both impractical and destructive. In this paper, a new method for assessment ageing condition of oil impregnated insulation pressboard based on frequency domain spectroscopy (FDS) was proposed. The FDS measurements were taken on oil impregnated insulation pressboards with five ageing levels at moisture content of 1.22%, 2.06%, 3.02% and 3.87%. The dielectric loss of all the samples were calculated by tanδ (f) interpolation and the ageing condition assessment database which contains data of five ageing levels and 1%-4% moisture content was built. It is found that the tanδ (f) interpolation is more sencentive to ageing and moisture. It could realize the ageing condition assessment by comparing the tanδ (f) interpolation curve with the curves in the database.The assessing result of the middle-low main insulation life of a 220kV transformer valided that it is effective and time saving to use the new method for ageing condition assessment.