Conceptual Design and Feasibility Study of Flexible Gas-Insulated Transmission Line Using CF 3 I Gas Mixture

SF 6 is widely used in high voltage equipment because of its outstanding characteristics as insulation medium. However, SF 6 is a potent greenhouse gas, so its use and emission are regulated. CF 3 I has been investigated as a candidate for SF 6 alternative gas, whose environmental impact is much less than that of SF 6 and other fluorocarbon-based gases. In addition, a flexible gas-insulated transmission line (FGIL) is expected to be used for power transmission from offshore wind farms due to its high flexibility and low capacitance. In this paper, the feasibility of 22 kV class FGIL utilizing atmospheric pressure CF 3 I gas is evaluated from the viewpoint of withstand voltage with actual lightning impulse tests. The cross-sectional size of FGIL is determined by considering insulation condition, heat transfer condition, sheath electric field condition and spacer stress condition. The impulse tests for FGIL are conducted in straight and bent states, and it is revealed that the 50% breakdown voltage $V_{50}$ of straight state exceeded lightning impulse withstand voltage (LIWV) for 22 kV class, and that $V_{50}$ of bent state falls below LIWV.