Streamer initiation and propagation in transformer oil under positive and negative impulse voltages

Electro-thermal hydrodynamic modeling of streamers formed by positive and negative impulse voltages in transformer mineral oil is presented. Negative streamers initiate at roughly two times higher applied voltages while positive streamers propagate about two times faster and occupy much less space. Charge carrier mobilities dependence on the temperature is taken into account as well as the electric field effect on the ionization potential of hydrocarbon molecules. Negative streamer dynamics greatly depend on the variations of electron mobility. On the other hand, positive streamers are mostly dependent on applied impulse voltage rise-time for a given applied voltage peak. Higher applied voltage peaks form faster streamers called higher mode streamers in both polarities.