Particle Contamination in Gas-Insulated Systems: New Control Methods and Optimum SF sub 6 /N sub 2 Mixtures

摘要

The feasibilities of two new separate techniques to control particle contamination in practical gas-insulated sytems were tested in a small-scale concentric cylinder geometry. In one technique an insulating coating was first formed on the particles in a contaminated system by low-pressure discharges in appropriate gases such as 1-C sub 3 F sub 6 and c-C sub 4 F sub 8 . When SF sub 6 was subsequently introduced into the same system at practical pressure as the operating insulation, the considerable harm ordinarily caused by particles was found to be eliminated. The nature of the coating formed also on the electrodes in this process was studied, with the conclusion that the observed benefits were primarily due to coating on particles, not on electrodes. In the second technique the particles, moved randomly by electrical stress, struck and adhered to the surface of a tacky insulating solid material; they were subsequently encapsulated in a melt-resolidify cycle without electrical stress. This trapping technique was also found to eliminate the harmful effects of particles in SF sub 6 at practical pressure. A technique for producing a trapping material with temperature characteristics appropriate for practical apparatus was devised. The effect of particle contamination on the dielectric strength of SF sub 6 /N sub 2 mixtures was studied as a function of total pressure and percentage of each gas. Optimum total pressure (approx. 6 atm) and optimum percentages (60% SF sub 6 /40% N sub 2 ) were observed in breakdown tests in particle-contaminated concentric cylinder geometry. (ERA citation 09:028828)