Comparison of Degradation Mechanisms and Aging Behaviors of Palm Oil and Mineral Oil during Thermal Aging

As a potential alternative to mineral oil used in transformer, palm oil is an eco-friendly choice while its aging behavior and internal aging mechanism are still unclear. Since the failure in transformer oil-paper insulation is mainly caused by heat, with the purpose of better understanding the similarities and differences of palm oil compared with mineral oil during transformer operation, oil-papers respectively made from these two oils were thermally aged for different duration and then experimentally analyzed. Through the analysis of experimental results, the following conclusions were drawn. Quite different aging mechanisms were revealed for each oil-paper insulation material. That means mineral oil had been degraded by scission of main chains followed with oxidation, whereas palm oil had been degraded by scission of ester bonds followed with loss of terminal carbonyl. The different degradation mechanisms further lead to different changes in dielectric properties during thermal aging. The electron transition energy of mineral oil is more pronounced with the increase of aging degree. Besides, palm oil has a shorter wetting time in paper, and the local damage can be repaired more easily after partial discharge. On the contrary, longer wetting time of mineral oil in paper relates to easily damaged for mineral oil-paper insulation in partial discharge. This work clearly shows that palm oil should be a good substitute for traditional mineral oil not only is it eco-friendly, but also possesses even better performance to some certain extent.