Underground Transmission

The ability to transmit power underground at a higher voltage, using a pipe-type cable. The cable, which has either a copper or aluminum conductor insulated by layers of oil-impregnated paper tape, is pulled through a coated steel pipe that is then filled with an insulating oil or gas. The electrical capacity of the cable can be increased by force cooling using heat exchangers and pumps to circulate and cool the oil contained within the pipe. In addition, there is a technique of using compressed gas as an insulating medium inside aluminum pipe.