Lightning Impulse Breakdown Behavior of Three-Element Mixed Insulating Oil Under Long Oil Gap and Its Weibull Model Analysis

The lightning impulse breakdown (LIB) characteristics of three-element mixed insulating oil (T-EMO) under long oil gap are crucial to the structural design of T-EMO transformer with high voltage level. The LIB characteristics of T-EMO were studied by using mineral oil (MO) in the control group at three gaps. The research results show that the average breakdown voltage of T-EMO and MO is not much different under the condition of positive polarity, while the average breakdown voltage of MO is about twice that of T-EMO under the condition of negative polarity. Weibull distribution is used to analyze the breakdown voltage data of the two insulating oils. Under positive polarity conditions, the streamer development speed of the two insulating oils is relatively slow and the difference is not obvious. Under negative polarity conditions, the streamer development speed of the two insulating oils tends to increase with the increase of the oil gap and the development speed of the streamer in MO is much faster than that in T-EMO. This paper gives a theoretical basis for the application of T-EMO to high-capacity transformers with higher voltage levels.