I. Introduction
ON-LINE FDI (fault diagnosis and identification) in power system is of great importance to the restoration of power system. A number of techniques have been developed, including artificial intelligence techniques, expert systems, rule-based systems and neural networks. Fault diagnosis of Large-scale power system, however, is still an unresolved problem. It mainly because of the large amount of information received after fault and the need for high accuracy, speed, especially the existence of hidden failures (which include misoperation of circuit breakers and false alarms from relays) and model's un-adaptability to topological changes.