Some economic aspects of extra-high-voltage underground cables

Some of the factors affecting the cost of cable circuits in the main transmission network are discussed. The conclusions are reached that (a) voltage-dependent losses can assume an economic significance one order of magnitude greater than current-dependent losses, (b) optimum conditions have already been reached at a system voltage of 275 kV for existing cable designs and (c) technically improved designs are desirable at higher system voltages. An attempt is made to estimate the capital cost, total annual charge and current-carrying capacity of cable designs for 275 kV and 400 kV systems employing dielectric materials other than oil-impregnated paper. The conclusion is reached that considerable technical advantages and significant economic advantages should be achieved if designs employing either a gas-filled polyethylene-tape dielectric or a compressed gas as the cable insulation could be successfully developed.