Research and Application of Integrated Oil Exchange Device for Natural Ester Retrofilled Transformer

Natural ester insulating liquid has gradually become an alternative liquid for mineral oil and is widely used in power transformers due to its high fire point and environmental friendliness. Traditional retrofilling needs to complete the removal of old oil, flushing and retrofilling of new oil step by step, which involves multi-device switching and manual operation. It takes a long time and is prone to excessive or insufficient filling of new oil. And improper treatment of waste oil causes pollution and waste of resources. Compared with traditional mineral insulating oil, natural ester insulating liquid has higher kinematic viscosity and hydrophilicity. The existing mineral oil insulating oil high vacuum oil filter has been unable to meet the requirements of purifying natural ester insulating liquid. Firstly, this paper introduces the difference of physical and chemical properties between natural ester insulating liquid and mineral oil, and puts forward the necessity of designing high vacuum oil filter. Secondly, combined with the shortcomings of the existing technology, an integrated oil change device is introduced to realize the comprehensive operation of oil discharge, flushing and oil injection of natural ester retrofilling transformer, which can simplify the process and save time. At the same time, it may reduce leakage and pollution, in line with environmental requirements. Then the high vacuum oil filter for natural ester was designed from the aspects of precision filter design, pumping system design, vacuum separation system design and condensation system design. Finally, the case of natural ester refilling was introduced. After using the integrated oil change device, the proportion of mineral oil residue was about $4 \text{wt} \%$, and the oil change efficiency was good. The oil filtration efficiency of the special high vacuum oil filter for natural ester can reach $\mathbf{1 2} \mathbf{m}^{\mathbf{3}} \boldsymbol{/} \mathbf{h}$, which greatly improves the oil filtration effect.