Electrical conduction in dielectric liquids

Abstract

Conduction current measurements have been carried out in a variety of highly degassed hydrocarbon liquids using plane and spherical electrodes, at field strengths between 50kV/cm and breakdown. These liquids have been analysed by means of a high resolution chromatography apparatus and a marked dependence of the reproducibility of the results and the purity of the liquid was found. Steady currents in the region of 10 -6 A have been recorded, these being greater by several orders of magnitude than those found by other investigators under similar conditions. This high value of current has been established to be due to the high degree of degassing of the liquids used in this project. Measurements were made on the instability of the current, fast pulses in the microsecond region, particle movement and breakdown. No relationship was found between any of the electrical properties of the gap and the state of the electrode surfaces or the material used, although there was a marked change in the maximum value of the conduction current and some variation in the pattern of the instability when different liquids were tested. When using 3mm diameter, stainless steel, parallel plane electrodes the breakdown strength was found to be approximately 400kV/cm and independent of the liquid used. A mechanism has been proposed, based on realignment of the liquid molecules under the influence of the high electric field, and appears to be well able to explain the majority of the experimental observations.