Effect of electrical conductivity on the ion mobility in dielectric liquids

Conduction process in dielectric liquids has been studied for many years because of its importance in understanding the process of dielectric breakdown. As a key parameter in conduction process, ion mobility has been measured by various methods. The reversal polarity method has been widely used to accurately measure the ion mobility in the dielectric liquids. In this paper, the effect of electrical conductivity of dielectric liquids on the ion mobility measured by the reversal polarity method is studied via the ion drift model based on the Poisson's Equation. The observed results indicate that ion mobility of dielectric liquids with high conductivity decrease with the increasing of the applied electric field. On the contrary, the ion mobility of those with the low conductivity nearly keeps constant. It is revealed that in dielectric liquids with high conductivity, it is easier to cause electric field distortion at the low voltage side, making the TOF (Time of Flight) value inaccurate and leading to a larger value of ion mobility than the actual one. Therefore, when measuring the ion mobility of nonpolar dielectric liquids, the distortion influence should be considered carefully. And the effect of the different conductivity on the ion mobility should be taken into account.