Electric, power systems, having outgrown simplicity a long time ago, continue to require more and better protection as the demand for power increases and the need for reliability becomes greater. Protective relaying has met this challenge by providing more sensitive, higher speed relay systems that are inherently reliable. Among the more significant protective developments that furthered the economic design of power systems are pilot, relaying schemes and direct, transfer tripping over telephone channels. In recent years a growing need developed for more versatile wire-pilot relay systems and more secure means for direct transfer tripping. These factors, in ...

This Guide contains information and recommendations for applying audio-tone communication over telephone channels for power-system relaying. It is intended to cover applications to both leased and private telephone systems but not applications to private microwave or carrier channels. Included are sections on transmitting and receiving equipment, leased telephone channels, application principles, installation, and testing. Reflected in this work is the knowledge and experience of equipment manufacturers and telephone companies as well as that of the users. Pertinent information previously published is also included

The primary purpose of correlating this information and experience is to guide the power-system user in applying, installing, and operating audio-tone protection systems, including considerations for the telephone-channel facility. In doing so, it will also provide a reference for the manufacturers and telephone personnel engaged in design and application of equipment and facilities. The Guide has been prepared not only for those considering audio-tone relaying for the first time, but as a reference for the experienced.