Simulation Study of the Effect of Microscopic Disturbances on the Propagation of Initial Streamer and Branching Characteristics in Transformer Oil

The governing equations of charged carriers were formulated using COMSOL simulation software. Various ionization sources, including field ionization, impact ionization, ion dissociation, and microscopic disturbance ionization charges, were employed to perform numerical simulations on a 2-D model of a needle-plate electrode submerged in transformer oil. This investigation analyzed the distribution of charge generation rates under different ionization mechanisms and explored the effects of varying microscopic disturbance source positions, radii, and charge generation rates on streamer propagation. The study also examined the branch shape and characteristics of the streamer under different voltage peaks and disturbance source distributions. The results highlight the predominant role of the field ionization mechanism as the primary ionization source for streamer discharge in transformer oil. Regarding disturbance source properties, larger disturbance source radii exerted a more significant effect on the streamer, whereas distances exceeding 0.1 mm from the axis center and lower charge generation rates (below ${2} {}\times {}{10} <^>{{9}}$ A/ $\text{m}<^>{{3}}$ ) resulted in a reduced effect on streamer behavior. Furthermore, the research explored the effect of multiple stochastic disturbance sources on streamer propagation, revealing a close correlation between the shape of streamer branches and the distribution of disturbance sources within the discharge region. Higher voltage peaks were associated with extended streamer propagation distances and an increased number of streamer branches within the same rise time. This study provides a reference for advancing the propagation of partial discharge in liquid dielectric and the study of its branch formation mechanism.