Breaking arc in dielectric liquids

The purpose of this paper is to report the effect of dielectric liquids on breaking arc phenomena in detail. The experiments were carried out for Cu vs. Cu electrodes in several kinds of dielectric liquids such as distilled water, methanol, n-hexane, and gasoline. The following can be obtained as findings in the switching tests with an inductive circuit (L=20 mH, load current=0.5-1.2 A). It was found that the dielectric constant of liquids affected the arc discharge types. In distilled water and methanol (which have high dielectric constant) showering arc was observed under the test conditions. On the other hand, in n-hexane and gasoline (which have low dielectric constant) steady arc occurred in air. The relation between dielectric constant and arc discharge types is discussed with a simplified model. Also, surface morphology was dependent on liquids. The contact surfaces in n-hexane and gasoline were smoother than those in distilled water and methanol, and much smoother than those in air with the same breaking current. It is considered to be due to the carbon (or carbonaceous material) covering the contact surfaces observed by the EPMA analyses. Furthermore, contact resistance in n-hexane and gasoline stay low during the test.