Analysis of Negative Polarity Lightning Impulse Discharge Characteristics of Ester-Based Insulating Oil and Mineral Oil Blends in Non-Uniform Field

High-voltage and large-capacity oil-immersed power equipment is the core hub of energy conversion and transmission of new power system, and is the cornerstone to ensure the safe operation of large-scale modern power grid. Mixed insulating oil can take into account the unique advantages of various oils. In this paper, the negative lightning impulse characteristics (LIBC) of low carbon multi-element insulation oil (MEMO) and mineral oil (MO) with a gap distance of 25–105 mm are studied. The results show that the fluctuation of peak current of MO is always significantly greater than that of MEMO. With the enlargement of gap, the lightning impulse breakdown voltage (LIBV) gap between MEMO and MO decreases from 56.9% to 6%, and the LIBV of MEMO is more dispersed than that of MO. The discharge development rate of MO is 27.6%-46.9% higher than that of MEMO. This paper lays an empirical foundation for the subsequent engineering implementation of MEMO.