Incomplete phase operation is a fault phenomenon in which, during the closing and tripping process of the main switch of a three-phase generator operated by separate phases, one or two phase switches fail to close properly or trip due to some reason, resulting in a severe imbalance of the three-phase stator current. Prolonged incomplete phase operation causes a large negative sequence current that will damage the generator stator coils, and in severe cases, burn out the rotor coils and break the main shaft. Since large generators mostly use three-phase separate phase operation main switches, incomplete phase operation has become a key focus of electrical operation prevention in power plants. In our plant, during a remote transmission process, when the main switch 212 of unit #22 was remotely tripped after remote tripping, the C-phase switch failed to trip normally, the incomplete phase protection activated, but the mechanism failed to respond, and the tripping circuit remained energized for a long time, causing both tripping coils to burn out. Our plant's incomplete phase protection uses switch-body protection, which is not subject to current-based interlocking. When the three phases of the switch are inconsistent, the incomplete phase protection should operate correctly; otherwise, it will fail to activate. After a non-full-phase protection trips, if the switch mechanism malfunctions and cannot trip, the adjacent switch can only be tripped through the failure protection. If the failure protection current judgment condition is not met and the tripping condition is not met, then manual intervention is required to trip the switch. Many causes of non-full-phase operation can be identified and mitigated early during routine maintenance and inspections. For example: 1. To prevent mechanism failure, regularly lubricate the internal drive shaft and locking pins to ensure flexible transmission. Ensure the mechanism box door is tightly closed to prevent coil moisture and corrosion of mechanism components. 2. During routine inspections, pay attention to air and SF6 pressure, strengthen regular maintenance of the main switch, and ensure proper operation of tasks such as draining water from the compressed air tank and starting/stopping the heater. 3. Have a dedicated person monitor the switch body during each switch operation. If all three phases are not fully closed, notify remotely to trip the switch and then inspect. If all three phases are not fully tripped or the coil is smoking, immediately disconnect the two-way control DC power switch at the A-phase mechanism box and manually operate the mechanism to trip the untripped phase. 4. After each switch is disconnected (including manual tripping and protection tripping), the switch tripping and closing coils and the mechanism pull rods should be checked. 5. After the unit is de-energized or during grid connection, after the main switch is engaged and before the magnetization and voltage build-up, check if the generator terminal voltage and current are 0. If not, suspect a non-full-phase switch, investigate the cause, and take appropriate measures. [b]Handling of Non-Full-Phase Switching:[/b] When the generator is connected to the grid, if the main switch is not fully closed, the non-full-phase protection will trip the switch. After excitation is removed, report to the unit leader and shift leader, switch the generator unit to cold standby, and notify maintenance to check the cause of the non-full-phase switch. When the generator is disconnected, if a phase of the main switch is not disconnected, immediately press the generator emergency trip button manually. If this is ineffective, reset the trip button and the "reverse power protection," and immediately request the shift leader to check for synchronization and grid connection. After successful grid connection, notify the grid control to disconnect the generator's connected bus and use the bus tie switch to disconnect it. If the main switch is not closed and the failure protection has not tripped, reduce the stator current to a minimum and manually disconnect the switch locally. If it does not trip, notify the turbine to maintain 3000 r/m and adjust the excitation to keep the stator current as close to 0 as possible. Report to the shift leader and notify the grid control to disconnect the bus and use the bus tie switch to disconnect Unit #22. If a non-full-phase event occurs during generator operation, pay special attention to prevent the excitation from being disconnected and do not close the turbine main steam valve. Immediately press the generator emergency trip button and simultaneously notify the turbine to quickly reduce the load to 0, maintaining the frequency consistent with the system. Rapidly reduce the excitation current to keep the stator current as close to 0 as possible. If the failure protection trips correctly, maintain the excitation current at no-load current and notify the turbine to maintain 3000 r/m. r/m, check that the 220kV bus tie switch and other switches on the bus connected to the generator have all tripped. Manually poke the switch on the spot, check that the three phases have tripped, and then disconnect the excitation. If it fails to operate, it should be handled according to the following principles: (1) If the excitation has not been disconnected and the main steam valve is not closed, notify the network control to vacate the bus connected to the generator and disconnect it using the bus tie switch. (2) If the generator excitation has been disconnected and the turbine main steam valve is not closed, the excitation should be put into operation immediately to pull the generator into synchronization. Then adjust the excitation current to the no-load rated value so that the stator three-phase current is close to 0. Notify the network control to switch the load and disconnect the generator. (3) If the generator excitation has been disconnected and the turbine main steam valve is closed, the network control should be notified to switch the load and disconnect the generator. (4) During the handling process, the temperature of each part of the generator should be closely monitored to ensure that the air cooler is normal. (5) Closely monitor the A value table data to ensure that the equipment is processed within the allowable negative sequence current value. (6) When the switch fails to trip after a non-full phase occurs, the main switch KM1± and KM2± should be disconnected as soon as possible to prevent the trip circuit from burning out the trip coil due to prolonged energization.