With the expansion of scale and ever increasing complexity of power grids in China， such drawbacks and limitations of traditional backup protection as protection failures and cascaded trips are apparent. A centralized wide area backup protection algorithm is presented for power grids based on sequence component under the design philosophy that the algorithm should reasonably and effectively utilize communication resources and effort should be made to avoid communication congestion. With this algorithm， the global decision will be made using different wide area information in different fault locating stages. This novel protection scheme enjoys nice rapidity with no such problems as complex settings and coordination among traditional standalone backup protections， mal-operation of backup relays during large flow transfer and so on. The feasibility and validity of this algorithm has been verified by digital dynamic simulation results.