The lightning impulse breakdown properties of multi-component mixed insulating oil under long oil gaps are crucial parameters for evaluating its insulation performance. These characteristics provide valuable guidance for optimizing transformer structure design and serve as a key foundation for ensuring the safe and reliable operation of high-voltage and large-capacity transformers. This study investigates the lightning impulse discharge characteristics of long oil gaps in multi-component mixed insulating oil

focusing on the discharge point development speed

streamer development morphology

breakdown voltage

and Weibull distribution under oil gap lengths ranging from 25 mm to 105 mm. The findings reveal that

due to the acceleration effect of ester insulating oil flow within the multi-component mixture

the development speed of lightning impulse discharge under long oil gaps is significantly faster than that of mineral oil. Under short-gap conditions

the discharge point development speed of multi-component mixed insulating oil is also higher for both positive and negative electrodes compared to mineral oil. The streamer morphologies under positive and negative polarities exhibit multi-branched filaments and single filaments

respectively. For long-gap conditions

the streamer morphologies are bush-like for positive polarity and tree-like for negative polarity. In terms of breakdown voltage

the positive polarity lightning impulse breakdown voltage of multi-component mixed insulating oil is slightly lower than that of mineral oil but significantly higher than that of ester insulating oil. Furthermore

it is comparable to binary and ternary mixed insulating oils. The negative polarity lightning impulse breakdown voltage of multi-component mixed insulating oil is 16%~50% higher than that of existing mixed insulating oils. Specifically

it aligns closely with mineral oil at gaps between 85 mm and 105 mm.