Application of Heat Exchangers to Existing High-Pressure, Oil-Filled, Pipe-Type Cable Lines

The design and installation of six air-cooled heat exchangers to increase the capacity of existing double circuit pipe-type cable lines was completed on an emergency basis in ten months. Design increase in capacity ranges from 26 to 43 percent above the self-cooled rating. A method was developed for making connections to the cable pipe using liquid nitrogen to freeze the cable oil, a technique of cutting and prying to make a window in the pipe without danger of damaging the cable, and a special diffusion chamber that allowed the cable to be thermally insulated during welding. Coordination with the existing pressure maintenance plants was accomplished with the least trouble by maintaining pressure only on the line which is on the suction side of the nearest heat exchanger circulating pump. Transfer trip and sequential starting schemes were developed to minimize trouble on lines with more than one heat exchanger.