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.