Transmission line protection is the coordinated use of protective relays, instrument transformers, circuit breakers, communication channels, and backup logic to detect faults on high-voltage lines and isolate the affected section. Engineering use: Protection engineers use distance, differential, directional overcurrent, pilot, and backup schemes to. Transmission lines act like the arteries in the human circulatory system, moving electrical power from were it is produced by generators to where it is consumed at load centers. And like arteries in the human body, the loss or damage to transmission infrastructure can have disastrous effects on the. Abstract: Information on the concepts of protection of ac transmission lines is presented in this guide. Many important issues, such as coordination of settings, operating times, characteristics of. When an abnormality or fault occurs in a component of a power system, relay protection devices are those that can quickly and selectively isolate the faulty or abnormal component from the system, ensuring the continued normal operation of the remaining healthy equipment. The calculation of relaying load limits for use in comparing to transmission line load limits or other limits is discussed. The identification of problems associated with the application of relay.