Power networks must be protected from a variety of fault conditions, often very quickly, if dangerous and damaging situations are to be avoided. For instance, if a tree makes contact with an overhead cable, current will flow to earth creating risks to the public and the equipment in that power line. Protection relays must monitor the network conditions and make them safe, if they detect a fault. Protection schemes have become very sophisticated and are the subject of extensive innovation as the nature of power grids changes with more distributed generation and less inertia.
Current trends in protection relays are ever increasing use of digital technology, focus on cyber security and resilience and use of more sensors to improve understanding of the network status. .