Field Ionization Degree Influence on Discharge Streamer of Natural Ester Based on Ionization Energy Calculation Under Changing Electric Field

During the development of streamer discharge in transformer oil, field ionization is considered to be the main ionization mechanism that causes liquid dielectric streamer breakdown. With the change of the distortion degree of the space charge to the electric field (EF), the field ionization factor (ionization energy, IE) will also change, further affecting the generation and development of streamers. Therefore, in this paper, the change rule of IE of natural ester with EF is obtained by the DFT (density functional theory) calculation considered solvent effect; Based on hydrodynamic drift–diffusion approximation model, the discharge streamer for natural ester is simulated with field ionization as the source term, and the EF strength and positive ions density in the streamer process are analyzed. DFT results showed that the IE of triglycerides decreased significantly with the increase of EF. Compared with the fixed IE, the development speeds are higher and stop lengths are longer for streamers considering the changing IE in different field strength.