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1. Understanding the steam turbine major 1. Tasks of the steam turbine major: Use the steam sent from the boiler to maintain the turbine speed (not connected to the grid) or load (connected to the grid), condense the completed exhaust steam into water, use the extracted steam to heat it and then send it back to the boiler. 2. Steam turbine professional system (1) Steam turbine body: Convert the thermal energy of steam into mechanical energy to maintain high-speed rotation. (2) Auxiliary system: Support system necessary for turbine rotation ； Heat recovery system set up to improve thermal efficiency (heat water and then return it to the boiler) ； Auxiliary engine and generator cooling system. 2. Steam turbine main system 3. Steam turbine body 1. Steam turbine body: Rotor - the stationary part of the impeller and blades: Partition plate, nozzle, cylinder, others: In order to achieve the required power, the steam seal and bearing bush have several levels. 2. Summary of the clearance problem of the steam turbine body: u If the dynamic and static gap is too large, the steam will be lost without performing work, which is uneconomical. The efficiency of the steam turbine in converting thermal energy into mechanical energy will be reduced, that is, the thermal energy (heat consumption) consumed for each kilowatt hour of electricity generated will increase the required steam (steam consumption). u If the dynamic and static clearance is too small, dynamic and static friction is prone to occur, causing vibration of the unit, and in severe cases, damage to the steam seal, large shaft, and blades of the steam turbine. u It is necessary to be both economical and safe, and the gap should be controlled within a certain range (tens of microns) u - The steam turbine is a precision equipment and must prevent dynamic and static contact (anti-friction). When friction occurs, the friction protection (vibration, axial displacement, differential expansion) action will be taken and the machine will trip. 3. Steam turbine seal: 4. Steam turbine control and security system: Control the load (speed) of the steam turbine and shut it down when an accident occurs. (1) High main and middle main door control schematic (2) High and medium pressure door control schematic (3) AST control oil (4) OPC oil 5. Protection of the turbine body 1. Overspeed protection: 103% overspeed: Due to the power grid, the unit is shedding load and the turbine speed exceeds 3090r/min. Close the high and medium adjustment doors. When the speed drops below 3000r/min, reopen each adjustment door. If the speed exceeds 3090r/min again, it will act again. Prevent higher speeds from occurring. 110% overspeed: three sets of DEH, TSI and ETS, which act on the AST solenoid valve and trip the machine. The machine is overspeeding. After the operation, remove the oil pressure on the diaphragm valve, and then remove the AST oil pressure to stop the machine. Steam turbine overspeeding accidents can cause severe consequences such as shaft breakage, bearing damage, and even speeding, and must be strictly guarded against. 2. High-pressure cylinder protection: Due to structural reasons, the steam flow rate of the Beizhong unit is too small at low load and cannot effectively take away the heat generated by the friction loss in the cylinder. The equipment in the cylinder will be damaged due to overheating. Therefore, the medium-pressure cylinder is used to start. After the steam flow reaches a certain value, it switches back to the high cylinder steam intake. During the cold start process, the high cylinder needs to be fully warmed. In order not to generate blast friction heat above 1020 rpm, the high cylinder must be evacuated. High cylinder protection is designed to achieve the above purpose. 3. Condenser low vacuum protection: The condenser vacuum is low (exhaust steam pressure is high), that is, the exhaust steam temperature rises, which increases the temperature of the low-pressure cylinder, low-pressure rotor blades, and condenser, which will cause turbine vibration, dynamic and static friction, final-stage blade fracture, metal deformation, condenser steel pipe leakage and other consequences. 4. Low lubricating oil pressure protection prevents oil breakage and tile burning. 5. EH oil pressure low protection: If the EH oil pressure decreases, each door of the high and middle main tuners will move uncontrollably and must be shut down. 6. Bearing vibration protection Steam turbine static friction, rotor mass balance damage (such as blade breakage, etc.), bearing failure (such as poor lubrication, wear, etc.), coupling failure and other reasons will cause unit vibration. 7. Axial displacement protection against dynamic and static friction. 8. DEH power loss trip protection unit loses monitoring and must be shut down. 9. High bearing temperature protection to prevent damage to bearings and journals 10. Turbine differential expansion protection to prevent dynamic and static friction 11. Turbine manual trip protection button when there is an emergency situation where the turbine protection cannot respond (such as endangering personal safety, fire, etc.) or when the protection refuses to operate. There is an emergency safety device on the nose of the machine, which can be pressed to stop the machine nose, similar to the accident button of the auxiliary engine. 12. After the boiler MFT is activated, the joint trip of the steam turbine protection boiler-steam turbine-generator is a unified unit. If the boiler is abnormal, to prevent the accident from spreading to the steam turbine, the steam turbine should stop feeding steam. However, in order to reduce non-stop shutdowns of the unit and improve economy (even if the unit heats up, the loss is very large), the logic and plan for stopping the boiler without shutting down are currently implemented. Except for a few situations that directly endanger the safety of the steam turbine (such as high water level in the steam drum, sudden drop in steam temperature, etc.), the boiler MFT will not trip. 13. If the main and reheat steam temperatures drop, the turbine will trip to protect the main and reheat steam. The drop in temperature indicates that the steam contains water and the turbine is in danger of water impact. Water impact can cause serious consequences such as cylinder deformation, rotor bending, dynamic and static friction, etc. 14. The generator main protection action is linked to the steam turbine protection. The generator trips. If the steam turbine loses load, overspeed will occur. Therefore, the generator trip will link the steam turbine trip, close the main and regulating doors, and cut off the steam turbine power. 6. High and low pressure bypass 1. Bypassing the high pressure cylinder is called high bypass, and bypassing the medium and low pressure cylinder is called low bypass. 2. The role of high and low sides: (1) When the steam parameters do not meet the requirements or the steam turbine is not allowed to enter steam, provide a channel for the steam generated by the boiler to flow through the reheater to avoid dry burning of the reheater. The flow of steam brings the heat out of the furnace, and measures can be taken to adjust the steam parameters. (2) Pressure relief. When the boiler pressure rises suddenly, the high side is opened to relieve part of the pressure to prevent the boiler from overpressure. 3. High-side and low-side start-up modes (1) During the startup process of the unit in high-side cold start mode, this method is used to automatically control the valve opening and main steam pressure as shown below.: (2) Low side cold start mode. The control process during low side starting is similar to that of high side. It can be turned on automatically and the pressure can be set manually. Initially open a certain opening manually: Ø When the condenser is evacuated, it can be directly pumped to the boiler drum, which helps the water in the boiler superheater and reheater to evaporate, eliminates water seals, and is also conducive to the evaporation of drum water and establishing boiler water circulation as soon as possible. Ø Provide passage for steam and protect reheater ； Ø Low side opening and large opening are helpful to increase the main and reheat steam temperatures ； Ø As the reheat steam temperature rises, adjust the low bypass opening and gradually increase the reheat steam pressure. After reaching the overturn pressure, the low bypass pressure can be automatically turned on to stabilize the pressure for unit overturn. After grid connection, as the load increases, the reheat steam will flow to the middle and low cylinders, and the low side will automatically close. (3) Bypass non-cold start mode (the boiler has a certain pressure) Ø In non-cold start, the high side cannot be put into the start mode Ø In non-cold start mode, after the boiler is ignited, the high and low sides should be opened in time to provide a channel for steam and protect the reheater. Ø The control of high and low side openings should adjust the high and low side openings according to the boiler combustion conditions (that is, the increase in main reheat steam pressure), and gradually increase the pressure and temperature. Notice: During the adjustment process, if the turbine has not been hung up and the high side opening is less than 2%, MFT will occur in the boiler. 4. Normal operation mode Ø The high and low sides must be tightly closed for normal operation. ； Ø High side sliding pressure mode operation (the current actual pressure plus a certain offset is used as the constant pressure control value to ensure that it is closed) Ø Low side sliding pressure mode, the given value is converted from the regulating stage pressure to ensure that it is greater than the actual pressure, so that it is closed 5. Regarding high and low side protection (1) To prevent steam from carrying water, the high side opens the pressure reducing valve first before opening the thermostat valve. ； (2) To prevent the thermal shock of the condenser, the low side desuperheating valve should be opened first before the pressure reducing valve can be opened; (3) To protect the reheater, the high side side should be closed quickly when the temperature of the high side side exceeds a certain value; (4) To protect the condenser, the low vacuum side should be closed quickly when the condenser water level is high, the low side desuperheating water pressure is low, and the condenser temperature is high or low. 6. High-side quick opening. High-temperature and high-pressure steam causes strong mechanical and thermal shocks to the pipes behind the high-side. (If the high-side heating pipe is defective, it will be more serious.) There have been pipe rupture accidents caused by high-side quick opening, so the high-side quick opening function has been cancelled. 7. In order to achieve its function (pressure relief, protection of reheater) during normal operation, the high side switch will automatically open 20% under several circumstances.: Ø l The moment when the high-pressure cylinder cuts to the intermediate pressure cylinder Ø l The pressure in front of the machine is greater than the specified value Ø l The rising rate of the pressure in front of the machine exceeds the specified value 8. During normal operation, the low side automatically opens the pressure relief when the reheat steam pressure exceeds 4.4Mpa. 9. During normal operation, you should pay attention to check whether the high and low side is turned on automatically, otherwise it will refuse to move. 7. Generator sealing oil system: 1. Function: The generator sealing tile is supplied to form an oil film between the sealing tile and the shaft to seal the hydrogen in the generator. The sealing oil cannot be interrupted, otherwise the hydrogen should be discharged urgently. 2 Schematic diagram of the normal operating mode of sealing oil (main oil pump operation) (purple is oil supply, blue is oil return) 3 Main sealing oil failure, backup oil pump operating mode 4 Operating mode when both main and backup oil pumps are lost: rely on lubricating oil as sealing oil, because of its low pressure (0.16MPa), the pressure in the generator must be lower than 0.1, that is, emergency hydrogen drainage and pressure reduction are required 5 Lubricating oil interruption operation mode: 8. About heating and thermal equipment (steam turbines, pipelines, pumps, etc.) 1 Function Ø Drain the accumulated water, air, and impurities in the equipment to avoid vibration ； Ø Let the temperature of the equipment rise slowly to avoid sudden temperature rise, uneven heating of the inside and outside of the metal, and local cracks that may cause damage to the equipment. ； 2 Causes and elimination of vibration in pipelines Ø Vibration is caused by water hammer, that is, the water in the front (formed by the original water or the steam that passes in is condensed by condensation) is pushed by the steam and hits the water or congestion in the back (such as closed valves, pipe plugs, etc.) ； Ø The coexistence of steam (gas) and liquid phases in the pipeline is the root cause of vibration. Ø If the high-pressure bypass cuts the main pipeline and the main pipeline heating pipe is insufficient, there will be a temperature difference between the main and bypass water, that is, a density difference. After mixing, the total volume of water will shrink, creating a gap in the pipeline, and the water behind will hit the water in front, causing the pipeline to vibrate. Ø Prevent pipe vibration when heating pipes, and drain out the water and air in the pipes to eliminate the root cause of water hammer. 3 Operation of warm pipes Ø First, fully open all drain doors and air doors on the pipeline (including the main pipe and its users) Ø Check that no large water flows out of each drain point, and open the steam source slightly Ø Check the drain doors one by one from the steam source end to the user end. If only steam flows out but no water flows out, and the pipe does not vibrate, the opening of the drain door should be closed. Close the air door. Ø If there is no user, the last drain should be turned up to ensure a certain steam flow. ； Ø Adjust the opening of the steam source door according to the temperature rise. Ø Close all drain doors in time when there are users. Ø For pipes that are hot backup, drains from warm pipes should be taken along the main road with a drain, and the bypass should be closed to prevent heat loss.