A sensitive relay improves the reliability of the system. Based on simple examples of the generator-transformer unit protection from symmetrical short circuits, it was shown that the sensitivity factor is not a sufficiently objective measure of sensitivity of the. The relay protection sensitivity is one of the determined factors in the power system, however, it is often overlooked in current distribution network (DN) planning. The relay protection sensitivity can be decreased to below the minimum values, failing to meet the requirements for electrical. speed, sensitivity, dependability, security, and selectivity. The paper considers the use of various communications channels, including direct relay-to-relay fib r-optic channels and multiplexed digital fiber-optic networks. For example, unselective protection operation during a medium voltage network fault will cause an outage for an unnecessarily large number of consumers. (For high-impedance differential relays).