Accelerated aging effects of mineral and vegetable transformer oils on medium voltage power transformers

The usage of vegetable oil for power transformer insulation has increased, compared to mineral oil, for its better environmental characteristics. However, although the temperature rise depending on load difference and the relationship between hottest spot temperature and life time depending on long-term operation for mineral oil immersed transformer has been studied, there is being established for vegetable oil immersed transformer. Therefore, the MV power transformers either filled with conventional mineral oil or with vegetable oil are thermally aged and the transformer oils are sampled regularly. With these samples, the chemical, mechanical and electrical characteristics of the two oils are investigated by the aging time. According to our experiment, the degradation rate of vegetable oil can be compared to that of mineral oil.