Effects of molecular ionization energy on liquid streamer development under DC

Liquid as insulation medium is a kind of complex component mixture, and it has different characteristics when breakdown applied different electric fields. In order to explore the development processes of different streamers in liquid dielectric, the model of the needle-sphere electrode geometry is employed and the discharge fluid model of liquid dielectric under non-uniform field is also established, then the influences of liquid molecule of different ionization energy on streamer discharge process are revealed through the numerically analysis in this paper. The research results show that the space charges generated by field ionization drive electric field to propagate into the liquid bulk, and the migration of electric field not only leads to the formation and development of streamer, but also causes the pre-breakdown current and results in the temperature rise of the liquid medium due to the joule heating effect. Then the factors are demonstrated that liquid with the molecules of low ionization energy and low density can lead to the 2^nd mode streamer with the propagation velocities of 1~5km/s, and as the applied voltage is increased, the liquid with the molecules of high ionization energy and high density can produce 3^rd mode streamer with the propagation velocities of 10~30km/s, these achievements are great significant and useful for reasonable utilizing and development liquid electrics.