Submarine dc cables

Since 1900 most of our power has been supplied by alternating current, but the high-voltage electron tubes and the rectifying equipment developed during the last decade have revived our interest in direct current. Because geographical factors have made most of our present-day dc cables submarine, we find that we are beset by the same problems that were involved with their historical antecedents- transatlantic telegraph, and later telephone, cables. Mechanical problems arise because of the complex structure of a cable, and because of all of the stresses to which it is subjected. There is also the problem of electrical stress. A comparison of the various types of cable shows that rugged, lightweight equipment is desirable, and that taped insulation insures reliability.