Design of Post Metal Shields Through Electric Field Distribution Analysis for a 154-kV SFCL

Korea Electric Power Corporation has developed a 154-kV superconducting fault current limiter (SFCL). This report is a part of the design process of the SFCL, particularly for fixation of posts supporting the superconducting element on the cryostat wall side. For supporting the superconducting element, the use of a post insulator is inevitable; however, the post insulator and cryostat with liquid nitrogen (L-N2) during operation of the SFCL form three junction points where electric field is intensified. In this study, we aim to design the metal shield in order to relax the electric field intensity at triple points (TPs) through numerical analysis of electric field distribution. For the electric field distribution analysis, a commercial software based on the finite-element method was employed. Each design for the metal shield was checked whether it makes the electric field intensity at the TP sufficiently lower than dielectric strength in L-N₂ for 750-kV input and whether there is any electrically weak point on the metal. The designs of the metal shields were improved through four critical steps where thermal contraction, manufacture tolerance, and insulation distance in L-N₂ were considered. It was experimentally verified that there was no electric breakdown in L-N₂ between the metal shield and the fiber-reinforced plastic post insulator for the lightning impulse test and the ac breakdown voltage test according to the IEC 60137 standard.