The Effect of Nitrogen Sparging on the Long Term Stability of the Breakdown Electric Field Strength in a Repetitively Pulsed Oil Dielectric Switch

Summary form only given. Oil dielectrics, particularly hydrocarbon fluids, are often employed in applications involving dielectric breakdown. The reliability of the breakdown strength of the fluid, in its role as a switching medium, is frequently of great concern because unexpectedly low or high breakdown strength can produce timing errors, or worse yet, equipment failures. It is known from published investigations of breakdown electric fields that significant water contamination of an oil dielectric may significantly influence the breakdown strength of the oil. The effect of lowering the concentration of water in the oil, on the other hand, is less well known for most of the published experimental investigations of oil breakdown do not report the concentration of water present at the time of the tests. This paper explores the effects of water concentration on the repeatability of the breakdown strength of 1-decene, dimmer, which is known by its generic name, poly-alpha olefin, or PAO. Water concentration is controlled by passing dried nitrogen through the oil in a process known as \´gas sparging," which reduces the dissolved water suspended in the oil. Water concentration is monitored by periodically sampling the oil, utilizing a Karl-Fischer coulometric (water) analyzer to ascertain the concentration of water. The l-decene, dimer test fluid was allowed to remain in contact with the humid ambient environment for several months in order to accumulate a concentration of water. Prior to testing, the system was operated for 80times10³ shots. Oil sampled before the experiment was found to have an initial water concentration of 19.9plusmn0.5 ppm_v, and oil sampled following the sparging process was found to have a concentration of 16.2plusmn0.7 ppm_v. The water content decreased to 10plusmn3 ppm following subsequent operation of the hydraulic pumping system and sparging. Our test results suggest that repetitive switching through a liquid di- electric may also reduce the water concentration of the dielectric.