The Loss-of-Life Analysis: Impact of Moisture Content for NTUP in ONAN Transformer

This paper presents the Loss-of-Life (LOL) of a 132/33 kV Oil Natural Air Natural (ONAN) transformer with a power rating of 60 MVA, focusing on the impact of moisture content as an ageing accelerator. First, the loading and ambient temperature profiles were simulated and validated. Then, the Hot-spot Temperature (HST) was determined utilizing the differential equation specified in IEC 60076-7. The LOL is subsequently evaluated according to the computed relative ageing rate, considering the impact of moisture content within the insulation paper. The results indicate that the transformer under examination reaches a maximum HST of 67.3 °C. It is found that the LOL increases as moisture content increases. Specifically, for moisture contents of 0.5%, 1.5% and 3.5%, the computed LOLs are 0.0709 day, 0.2594 day and 0.7783 day, respectively, over a 15 days loading period. The moisture content of 3.5% has the most impact on the LOL compared to other moisture content levels.