A New Directional Relaying Scheme for the Protection of Active Distribution Networks Against Asymmetric Faults

This paper presents a new directional protection scheme to provide protection against asymmetrical fault and over unbalance operating conditions. The proposed scheme detects the fault by monitoring the degree of system unbalance using the magnitude of negative sequence reactive power, and discriminates the fault using the direction of negative sequence reactive power. Computer simulation studies have shown that the proposed protection scheme detects the unbalanced fault at buses and produces high speed trip for all lines connected to the buses. When there is a fault within the line, the protecting scheme produces trip signals for CBs at each end of the line, and provides high speed protection if the communication facility is available. When the communication link is not available, a backup protection can be provided for the line.