Study on Wide Area Backup Protection to Prevent Cascading Trips Caused by Flow Transferring

Protective relays, pivotal devices that can quickly identify and isolate fault area in power systems, is of great importance for power network security and reliability. When relays trip a faulted line in the network, the flow on the faulted line will be transferred to the other lines. Those lines might be overloaded and then cascading tripped by the backup relays, which worsen the system state and even cause blackout. Studies on several well-known blackouts reveal that protective relays are involved and the most troublesome ones are backup protective relays. In this paper the defects of the existing backup protections are investigated in detail first. Then a new wide area backup protection scheme based on WAMS to identify flow transferring is presented. A new concept of flow transferring relativity factor (FTRF) is proposed to estimate the flow distribution after flow transferring occurs; and the method of calculating FTRF matrix on-line is also stated. The simulation of a three machines network shows that the wide-area backup protection scheme to identify flow transferring works well