Sensitivity refers to the characteristic of the relay to act when the actual fault conditions occur. To provide effective and reliable protection to the power system, a protective relay must have the following essential functional characteristics: Selective, Fast, Stable, Reliability, Sensitivity, Simple Construction and Installation Mechanism, and Cost-effective. For example, unselective protection operation during a medium voltage network fault will cause an outage for an unnecessarily large number of consumers. While this is bad, It's not a. Sensitivity. Necessity of speed in relaying. A relay is said to be dependable if it trips only when it is expected to trip.