What is generator non full phase operation? (power plant)

Non full phase operation is a fault phenomenon that the main switch of the generator operated by three-phase mechanism is closed or tripped during the closing and tripping of the main switch of the generator, and the three-phase current of the stator is seriously unbalanced due to some reason. Large negative sequence current during long-time non full phase operation will damage the generator stator coil, burn out the rotor coil and break the main shaft in serious cases. Because large generators mostly use three-phase split phase operation main switch, non full phase operation has become the key prevention object of electrical operation in power plants.