No abstract

The transformer oil was taken as the object of study, and the finite element method (FEM) was employed to analyze and solved the partial differential equations (PDE) which was built by field ionization for describing the generation and transport properties of free charge carriers. The results showing that the dynamic characteristics of space charges in the liquid-gap discharge under DC were gained. According to the simulating results, the fundamental causes of the dielectric liquids breakdown by the electric field dependent molecular ionization are described as following; the pre-breakdown current is firstly formed by the generation and migration of the charge carriers in the oil gap, then the joule heat generated from it makes liquid-gap to form the low density region in the liquid, which facilitate initiated little streamer emergence as avalanche in gas discharge, meanwhile, the streamer is continuously evolving. Then these conclusions enable ones easily understand breakdown mechanism of the liquid dielectrics that are reasonably applied to power system fields.