This fault causes both the relay 1 and relay 2 to start (outgoing feeder 1). 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. While this is bad, It's not a. Also principles of various protective relays and schemes including special protection schemes like differential, restricted, directional and distance relays are explained with sketches.