What are directional relays are typically used for?

[Mjeelemco]

I haven't had much if any experience with protective relays. Can someone explain what directional relays are typically used for?

[SecondGen]

This type of relay operates in on direction of current flow and blocks in the opposite direction. Three conditions must be satisfied for its operation: current magnitude, time delay and directionality. The directionality of current flow can be identified using voltage as a reference of direction.

Directional relays are commonly used to protect against generator motoring, such as preventing excess power flow from a small generating station into a larger system. They can also be used to protect systems with networks and/or closed bus ties.

[SecondGen]

Check out this cutsheet for a GE ICW power directional relay, it gives a good overview of it's theory and various applications. https://www.gedigitalenergy.com/products/brochures/icw.pdf

[JohnRaz]

GE's Art & Science of Protective Relay
downloadable PDF

http://www.gedigitalenergy.com/multilin/notes/artsci/artsci.pdf