Cooling capability of gas mixtures with fluorocarbon in a gas-insulated transmission Line Model

Because of its high-capacity, low losses and no electromagnetic interference, the gas-insulated transmission line (GIL), which is a replacement of an overhead line in special environments, has been used for over 40 years, mainly as bus ducts of gas-insulated substations or underground connections in power plants. The insulated and cooling gas in GIL is mainly SF₆ or its mixtures, which have high global warming potential (GWP) and are listed as restricted gases in the 3^rd Conference of the Parties to the United Nations Framework Convention on Climate Change in 1997. Therefore, a lot of researches have been made to find a substitute gas for SF₆. In this paper, the cooling capability of gas mixtures with fluorocarbon, which has a lower GWP than SF₆ and outstanding insulating performance, is investigated. Heat transfer coefficients of gas mixtures are calculated by measuring the surface temperature of a metal pipe under a certain current. The heat transfer coefficients of gas mixtures with fluorocarbon are analyzed and compared with that of SF₆ mixtures. Based on the heat transfer coefficients, the maximum permissible currents of our GIL model with fluorocarbon mixtures or SF₆ mixtures are also calculated and compared.