Possibilities and methods of extending a carrier current relay channel to other uses

Carrier-current relaying is now well established as the most complete type of protection. It has had sufficient field experience to well justify the fundamental principles on which it is founded and the manner in which it has been worked out. As it often happens, the solution of one problem will lend itself to another similar problem. This seems to be the case of carrier-current relaying as it has provided the communication channel which might be available to solve other problems involving the transmission and reception of signaled information. This common solution to two problems naturally lessens the economic factors which relieves each problem of the strain of carrying the entire burden. Other problems involving the use of communication means which could be provided by the relay channel are: telemetering, supervisory control, load control, communication, remote tripping, etc. The addition of these other functions to the carrier channel, while not involving serious technical difficulties, nevertheless, requires the consideration of some problems. Methods are available and actual installations have been made involving various combinations of additional uses of the relay channel.