Owing to lots of advantages such as high reliability for power supply， flexible operating and dispatching mechanism and convenient transfer switching， etc， the 3/2 connection mode has been widely put into operation in 500 kV power stations and some 200 kV load-center substations. However， many equipments may be subjected to power cut caused by some fault modes as long as the connection mode is linked with primary equipment or the breaker under prophylactic overhaul. Using on-line identification technology of equipment risk based on network topology analysis and operation logic for protection， it is able to automatically identify the latent fault mode concerning N -2 or more power-failure equipments for primary equipment or breaker overhaul under 3/2 connection mode， and reminds relevant dispatching working staff. In the meantime， through the combination of static and dynamic security analysis and maintenance schedule， it will achieve on-line prevention and control mechanism for equipment risk in large power grid.