Ageing diagnosis of MV/LV distribution transformers via chemical indicators in oil

The assessment of the ageing state of MV/LV distribution transformers is an important issue for operators and managers of the electrical network. The objective of this study is thus to find a simple and robust method to assess the degradation of paper inside transformers. So, this article presents investigations carried out on some real MV/LV transformers about the use of methanol (MeOH) and 2-furfural (2FAL) as indicators of the transformer ageing state. In parallel, laboratory tests on paper-oil systems in sealed ampoules were performed to establish the relationship between the in-oil concentrations of MeOH and 2FAL and the degree of polymerisation (DPv) of the paper. Both approaches together allow showing up that MeOH is a promising candidate as early ageing indicator that could be considered during equipment operation.