A Transfer Trip Scheme to Supervise Zone 3 Operation

Zone 3 of distance relay provides remote backup protection for adjacent transmission lines using local information. At times, zone 3 is prone to maloperation under stressed system conditions, which may cause serious threat to grid security. Zone 3 decisions can be more accurate, if fault pickup information of the adjacent line relays is availed. In this paper, zone 2 pickup signals of adjacent line relays are unified using simple logic gates and the information is transferred to supervise remote backup protection; the zone 3. Proposed method is tested for WSCC nine-bus and two-area four machine systems under different conditions and found to be accurate.