Experience of oil re-generation on a 132 kV distribution transformer

Under current economic scenario, transformer replacement is not always feasible. Therefore, maintenance based intervention scheme is introduced such as oil re-generation as an option to extend transformer life. Oil re-generation could remove ageing by-products e.g. acids, moisture through physical and chemical processes. It is expected that the degradation rate of the oil/paper insulation system is slowed down after oil re-generation. In this paper, a complete oil re-generation process for a 132/33 kV transformer using both on-load and off-load configurations is presented. Oil sampling was carried out every two hours during the re-generation process. Multiple parameters including Total Acid Number (TAN), Low Molecular Weight Acid (LMA) and High Molecular Weight Acid (HMA), colour and water content were measured. Off-load re-generation was carried out first to improve the oil to a good condition; then on-load re-generation was conducted, which was expected to ‘clean’ the paper. Post monitoring of oil parameters 2 months, 8 months and 11 months after the oil re-generation confirmed that the oil condition remained in a good level as expected.