Owing to its advantages such as high reliability for power supply, flexible operating and dispatching mechanism and convenient transfer breaker, the 3/2 mode of connection has been greatly put into use in 500kv power stations and some 200kv load-center substations. However, more equipment may be subjected to power cut caused by some fault modes as long as the mode of connection is linked with primary equipment or the breaker is under the prophylactic repair mode. Based on the analysis of network topology and on-line identification technology to deal with equipment risk for protection and operation logic, it enables itself to automatically identify the latent fault mode which is contained within power-failure equipment with N-2 qualification or more and remind relevant dispatching working staff in accordance of the prophylactic repair of primary equipment or breaker under the mode of connection, meanwhile, through the combination of static and dynamic security analysis and maintenance scheduling, it will achieve the on-line prevention and control mechanism for equipment risk in large power grid.