Application of carrier to power lines

DURING the 20 years or so that have elapsed since power-line carrier was first introduced on a commercial basis, enormous advances have been made in the communication arts. In the somewhat specialized branch of power-line carrier, advances in technique and apparatus design have not been as highly publicized as those in some other branches of the art; nevertheless, they have kept pace with the field, with the result that power-line carrier is today one of the most useful and versatile tools available to the power-utility engineer. There are now over 1,300 terminals of power-line carrier in operation in the United States. These terminals provide channels for telephone circuits, pilot relaying, telemetering, load-control, supervisory, and other remote-control functions over transmission lines of all voltages, totaling over 40,000 channel-miles. The last several years have seen a rapid increase in the number of terminals and in channel-miles, and there is every indication that this rate of growth will continue to increase for some time. With very few exceptions, every new transmission line of any importance is now engineered to include power-line carrier for one or more functions. Many large integrated systems¹ have already made such extensive use of carrier circuits that the problem of channel space and frequency assignment is rapidly becoming of major importance.