Dependability can be improved by increasing the sensitivity of the relaying system. The protective system must have ability to detect the smallest possible fault current. 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. Selectivity is a mandatory requirement for all protection, but the importance of it depends on the application. For example, unselective protection operation during a medium voltage network fault will cause an outage for an unnecessarily large number of consumers. Sensitivity refers to the minimal changes in measured parameter that the system can react to. The paper considers the use of various communications channels, including direct relay-to-relay fib r-optic channels and multiplexed digital fiber-optic networks.
