A PROBABILISTIC APPROACH TO SETTING DISTANCE RELAYS IN TRANSMISSION NETWORKS

The setting of back up zones in distance relays has to deal with fault current infeeds between the relay and remote faults. Traditional appr oaches to this problem are conservative, some times leaving portions o f a Power System without sensitive or selective back up protection. In this paper a probabilistic model for the relay errors resulting from the variation of the infeeds is developed. Other measurement inaccurac ies are also considered in order to build a probabilistic approach to setting all zones of distance relays. The developed concepts are assoc iated to automatic tools for computer aided protection coordination an d applied to the Portuguese Transmission grid.