  Future distribution systems are expected to display increased complexity,
mainly due to looped/meshed operation, switch between grid-connected and
islanded mode and considerable integration of distributed generation. This
paper investigates a plug-and-play protection solution for overhead
distribution systems with such variable operation conditions, employing
existing numerical relay capabilities. This solution is applied by designing
plug-and-play, communication-assisted, multifunctional relays with integrated
protection element settings, which apply universally to all distribution system
conditions, rendering the protection scheme independent of a specific system.
Hence, the need for user-defined settings or future revisions due to system
changes is eliminated. The scheme ensures coordination between main line relays
and backup protection of laterals, without a coordination study. There is no
need to replace or modify existing lateral protection means for this purpose;
only their known time-overcurrent curves are uploaded to the relays by the
user. The scheme is described and evaluated through simulations in two test
systems. Meaningful conclusions are finally derived.
