An operational current at relay terminals should be observed to ensure proper sensitivity. (For high-impedance differential relays). Gradually increase 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. A single missed test can lead to the following: Digital and numerical relays require comprehensive procedures: self-test verification, digital input/output checks. The relaying equipment must be sufficiently sensitive so that it operates reliably when required under the actual conditions that produces least operating tendency.