Uprating of High Pressure Gas-Filled Feeders by Fluid Filling and Rapid Circulation

Recent years have seen increasing utility interest in uprating of existing power transmission lines, both overhead and underground. This paper describes the results of a study conducted on a pair of existing 115 kV high pressure gas-filled cables in a downtown urban area. The results of a technical audit of cable ampacity showed that the cables had a lower ampacity than had originally been calculated and that major uprating was necessary to meet increased transnission requirements. Both existing and experimental approaches to uprating were considered. The most cost-effective option was found to be the conversion of the lines to fluid-filled operation, with rapid circulation of the dielectric fluid to anooth a serious thermal bottleneck. Design for the fluid-filled system included provisions for fluid circulation at different rates, depending upon feeder loading and availability of equipment. Special attention was paid to providing means for rapid detection of a fluid leak. The resulting program will provide a reliable cable system, with ampacities at least 35% greater than the original system, as well as the capability of further uprating if required in the future.