Q&A on Turbine Operation Technology

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1. Why cannot the vacuum be too low or too high when starting a steam turbine? Too low vacuum: 1) It increases the resistance during the startup of the steam turbine, thereby increasing the thermal shock as steam enters areas such as the control stage steam chambers. 2) Increase the amount of steam required during startup ； 3) After barring the turbine, a large amount of steam enters the condenser; at the moment of barring, there is a risk of triggering the exhaust safety valve ； 4) Raising the exhaust temperature causes the copper tubes of the condenser to expand rapidly, leading to loose joints; this can result in leakage from the condenser or a change in the rotor’s center, thereby causing vibration in the unit. Excessive vacuum: The amount of steam required for barring in decreases, which is detrimental to warm-up. 2. What is the principle of the high and medium pressure cylinder temperature probes? How to handle an increasing probe indication? Principle: The temperature probe is a metal rod fixed to the cylinder wall, with four holes in its middle. The front end of the metal rod passes through the cylinder wall and enters the cylinder, where it comes into contact with the steam flowing inside the cylinder and turbine to perform work; as a result of being exposed to the steam, the outer part of the metal rod is insulated. One thermocouple is installed in one of the holes of the probe, with its hot junction located in the metal at the front end of the probe that is exposed to the steam. Another thermocouple is installed in another hole of the probe, with its hot junction placed at an appropriate distance from the front end of the probe. Two thermocouples are connected in reverse series, so that their output electromotive force is a function of the difference between the temperature at the tip of the probe and the temperature at the location where the other thermocouple is situated. In other words, they form a temperature difference thermocouple; the two other terminals of the probe can be used as backups for each other, or one pair of outputs can be used as a measurement signal while the other pair serves as a control signal. The temperature difference measured by the probe device is the difference between the surface temperature of the rotor in the regulating stage of the high-pressure cylinder or the rotor in the first stage of the medium-pressure cylinder and the average temperature. The probe reading increases; this is directly related to the rate of temperature change. During normal operation, the temperature changes rapidly. For the surface temperature of the rotor, the rate of temperature change is close to that of the steam temperature. However, for the average temperature of the rotor, the rate of change is slower than that of the steam temperature. This results in an increased difference between the rotor’s surface temperature and its average temperature, thereby causing the probe reading to rise. Additionally, during the startup process of the unit, the probe reading often becomes very high; this is mainly due to insufficient warm-up of the rotor. If an increase in the probe reading is detected, contact the furnace side to appropriately reduce the steam temperature. Meanwhile, during operation, try to control the rate of temperature change to avoid excessive fluctuations. To prevent an increase in the probe reading during startup, thorough warm-up is necessary. 3. Why should we try to avoid breaking the vacuum at 3000 rpm? Since the frictional blowdown loss generated as the rotor rotates is inversely proportional to the vacuum level and directly proportional to the cube of the rotational speed, breaking the vacuum at this speed increases the heat generated by the frictional blowdown loss of the blades in the subsequent stages. This leads to an increase in the exhaust temperature and the temperature of the cylinder block; in severe cases, it can cause deformation of the cylinder block, changes in the rotor’s center position, and affect the safety of the condenser. Therefore, it is necessary to avoid breaking the vacuum at 3000 rpm when shutting down the machine. 4. After the turbine is tripped, why does the rotational speed decrease rapidly at first, and then more slowly after it has dropped? The frictional blowing loss generated as the rotor rotates is proportional to the cube of its speed. Therefore, after the turbine is stopped, the frictional blowing loss at high speeds is extremely large, which causes the speed to drop very rapidly. Once the speed reaches around 1500 rpm, the energy of the rotor is primarily used to overcome mechanical frictional resistance; this resistance is much smaller than the frictional blowing loss at higher speeds, so the speed decreases more slowly. 5. What is the impact of high and low system frequencies on turbines operating under rated load? For a unit participating in frequency regulation, when the turbine is operating at its rated load and the system frequency is low, the turbine will generate an additional amount of power of △N = N0×ε/δ, which leads to overload. Conversely, when the system frequency is high, the turbine reduces its load by an amount of △N = N0×ε/δ, resulting in insufficient output from the turbine. 6. Why must the turbine quickly pass through the critical speed during startup? Because at the critical speed, the turbine experiences severe vibrations; prolonged vibration can lead to dynamic and static friction within the turbine, bearing damage, and even serious incidents such as shaft bending. Therefore, the steam turbine needs to quickly pass through the critical speed during startup. 7. Why is the shaft seal activated first and then the vacuum created during hot start-up? Since, in a hot state, the metal temperatures of the front and rear shaft seals of the high-pressure rotor and the front shaft seal of the intermediate-pressure rotor are relatively high; if vacuum pumping is initiated without first supplying steam to the shaft seals, a large amount of cold air will be drawn into the cylinder through the shaft seal areas. This causes the rotors in these areas to contract, resulting in an increase in the negative differential expansion value—to the extent that it may exceed the permissible limit. Consequently, the axial clearance between the stationary and rotating components on the steam inlet side of the initial stages decreases or even disappears. Additionally, this process can lead to cooling-induced loosening and deformation of the inner walls of the shaft seal casings. 8. What does the length of time it takes for the rotor to coast down after the steam turbine is stopped indicate? A short coastdown time indicates an increase in mechanical friction resistance within the steam turbine. This may be caused by deteriorated bearing performance, friction between the rotating and stationary parts of the turbine, or poor maintenance of the condenser vacuum. A long idling time indicates that the main steam valve is not tight or that the check valve on the extraction pipeline is not tight. 9. Why are oil coolers always installed at machine level zero? The oil cooler is placed at ground level for two reasons: one is to prevent it from losing cooling water. If the cooler were installed at a higher location, it would be prone to losing cooling water whenever the pressure of the cooling water drops significantly. The other reason is to ensure that the oil cooler remains constantly filled with oil, thereby preventing any air accumulation inside it. 10. Why is the oil inlet pipe of the bearing thin while the oil return pipe is thick? What are the effects if the return oil pipe is too thin? Since the oil supplied to the bearing is under pressure and flows at a high velocity, in such cases it is sufficient for the amount of oil supplied to the bearing to ensure an adequate supply of lubricant; therefore, the pipe used for this purpose does not need to be very large in diameter. On the other hand, the pressure inside the pipe that carries the oil back from the bearing is low, and the flow velocity of the oil is low, so the pipe used for returning the oil must be larger in diameter than the pipe used to supply the oil. If the oil return pipe of the bearing is too thin, oil return will be hindered, which will affect the lubrication effect and cause the bearing temperature to rise. 11. Why is a smoke extractor installed on the unit’s oil return tank? The main purpose is to remove smoke and water vapor from the oil, preventing water vapor from condensing within the oil tank. A slight negative pressure is created in the oil return pipes and within the oil itself, which ensures smooth oil return to the bearings. Without such smoke removal equipment, the accumulation of large amounts of gas and water vapor in the return pipes and oil tank will result in positive pressure, thereby affecting the oil return to the bearings or deteriorating the quality of the oil. 12. What is the purpose of warming up at medium speed? Prevent brittle damage to the material and avoid excessive thermal stress. 13. When should the high and low pressure heaters be brought online during startup? The low-pressure heater starts up along with the main engine, while the high-pressure heater is activated after the unit is connected to the grid and the cylinders are shut down. 14. What is the purpose of turning the gear? 1) Prevent thermal bending caused by uneven heating or cooling of the rotor ； 2) Perform a barring test before startup to check whether the turbine is in operational condition, such as whether there is friction between the moving and stationary parts and whether the bending deformation of the main shaft exceeds the specified limits. 3) Reduce inertial force during impulses. 15. Why is it strictly prohibited to supply steam to the shaft seal when the rotor is at rest? Supplying steam to the shaft seal when the rotor is at rest causes localized heating of the rotor, leading to bending of the main shaft. Since the gap between the shaft seal teeth is very small, even a slight bend in the main shaft can reduce or eliminate the gap between the moving and stationary parts. As the rotor rotates, this will wear out the shaft seal teeth. Similarly, if some steam leaks into the cylinder, it will also result in a large temperature difference between the upper and lower cylinders, causing the rotor to bend due to uneven heating. Therefore, it is strictly prohibited to supply steam to the shaft seal when the rotor is at rest. 16. After startup, when should the high-pressure heater drain water be introduced into the deaerator? Why? After the unit is started, when the load is >30% and the steam turbine stops operating, the drain water from the high-pressure heater can be directed to the deaerator. At this point, the pressure inside the high-pressure heater is sufficient to overcome the pressure losses in the pipelines, the height difference, as well as the internal pressure of the deaerator, thereby allowing the water to be pushed into the deaerator by its own pressure. Therefore, at a load of 30%, it is possible to direct the drain water from the high-pressure heater to the deaerator. 17. What are the common causes of high shaft seal pressure during normal operation? 1) The shaft seal control valve is not tight, allowing high-pressure steam to enter the low-pressure shaft seal header ； 2) Increased steam leakage from high and medium pressure shaft seals ； 3) Poor exhaust from the shaft seal ； 4) Pressure regulation failure ； 5) The pressure setpoint is high. 18. What should be done if the shaft seal pressure is low? Immediately shut down the shaft seal overflow valve manually; increase the auxiliary steam supply to the shaft seal control valve depending on the shaft seal pressure. Once the pressure is under proper control, identify the cause of the low shaft seal pressure in order to restore automatic control of the shaft seal system as soon as possible. 19. During cold start-up, when the shaft seal has just been installed, how can the shaft seal temperature be adjusted manually? When the shaft seal is first activated during a cold start, since the shaft seal supply pipe is also cold, the temperature of the shaft seal rises slowly. At this time, because the pneumatic valve for controlling the cooling water to the shaft seal is not sealed properly, the temperature of the shaft seal fails to increase. After manually closing the cooling water manual valve, pay attention to the increase in the shaft seal temperature; once the shaft seal temperature is close to its normal value, then open the cooling water manual valve again. At this time, the shaft seal temperature control should be automatic, set at 150°C. 20. Why is it said that operating at half load is more dangerous than operating at full load? Because when the unit operates at half load, the heat release coefficient of the steam is much higher than that at full load; as a result, the inner wall of the cylinder cools down rapidly. This rapid cooling generates significant tensile forces, which in severe cases can cause cracks or damage to the cylinder. 21. What determines the cold and hot states of the unit? How to determine it? The cold and hot states of the unit are determined based on the temperature T of the lower wall inside the first-stage high and medium pressure cylinders: Cold state: T＜305℃; Warm state: 305℃≤T＜420℃; Hot state: 420℃≤T＜490℃; Extremely hot state: 490℃≤T. 22. What criteria are used to determine the parameters for starting the unit in its cold state? The temperature of the reheated steam should be at least 50°C higher than the metal temperature of the first stage of the intermediate-pressure cylinder, and the main steam temperature should be 50°C higher than the metal temperature of the inner wall of the impulse chamber in the high-pressure cylinder. The selection of steam parameters is based on the need to ensure that the steam entering the cylinders meets the requirements for the turbine to reach its rated speed smoothly, as well as to enable overspeed tests to be conducted. To ensure uniform heating of all metal components, a relatively lower pressure is chosen, along with an appropriately high steam flow rate. Sufficient superheat should be maintained for the temperature, while also taking into account matching it with the metal temperature to prevent thermal shock. 23. For turbines with nozzle regulation, what is the relationship between the enthalpy drop in the regulating stage and that in the final stage? The sum of the two remains constant; when operating conditions change, the enthalpy drop is merely reallocated between the regulating stage and the last stage, with their sum staying unchanged. 24. What is the most dangerous operating condition for the regulating stage? Why? The condition in which the first control valve is fully open while the second control valve has not yet been opened. This is because the control stage has a very important characteristic under varying operating conditions: its enthalpy drop changes as the steam flow rate changes. As the steam flow increases from zero, the enthalpy drop of the control stage first rises and then falls. The enthalpy drop reaches its maximum value when the first control valve is fully open while the second control valve is still closed. Therefore, the most dangerous operating condition for the control stage is when the first control valve is fully open and the second one has not yet been opened. 25. What is the most dangerous situation in the last stage of the turbine? Why? Maximum load of the steam turbine. Since the sum of the entropy drop in the regulating stages and that in the final stage is a constant, the entropy drop in the regulating stages is minimum when the turbine is operating at its maximum load; as a result, the entropy drop in the final stage becomes maximum. Therefore, the most dangerous situation for the final stage of the turbine occurs when it is operating at its maximum load. 26. What measures have been taken to eliminate the induced currents caused by steam impact on the blades and the leakage magnetic field of the generator? 1) The front end of the generator rotor is grounded using carbon brushes ； 2) Insulation measures should be taken for the rear-end bearing and coupling of the generator rotor to prevent the formation of an electrical circuit between the rotor, the bearing, or the foundation. 27. What is the function of the external linkage of the low-cylinder exhaust duct in small turbines? The connecting rod has a pre-tightening force that maintains the connection of the steam guide tube in the cold state, and withstands the pressure of steam in the hot state. 28. What is the main function of the low-cylinder exhaust safety valve? Prevent the outer cylinder from being damaged due to overpressure. 29. What measures are taken to balance the axial thrust of the unit? 1) High and medium pressure cylinders arranged in reverse order ； 2) The low-pressure cylinder is arranged symmetrically along the steam inlet blades, thereby enabling flow diversion ； 3) Balance pistons for high and medium pressure cylinders, which generate counterforce to partially offset their thrust ； After implementing the above measures, the remaining axial thrust is borne by the thrust bearings. 30. How does the differential expansion change during the start-up and shutdown of the unit? Shaft seal thrust: As the rotor in the steam seal section is heated, and at the same time some steam leaks into the cylinder, the rotor expands more than the cylinder due to the difference in specific volume, resulting in a positive expansion differential. Ramp-up: From ramp-up to steady speed, the temperatures of the cylinder and rotor change sharply. However, due to the low specific volume of the rotor, its expansion is greater than that of the cylinder; yet the positive expansion difference is reduced as a result of the Poisson effect. Load increase: The steam parameters rise, resulting in an increased steam flow rate through the turbine; this intensifies the heat exchange between the steam and the rotor as well as the cylinders, causing the positive expansion difference to continue increasing. When the turbine reaches a quasi-steady state, the positive expansion difference attains its maximum value. Load reduction: As the steam temperature drops, the rotor and cylinder cool down. Due to the low specific volume of the rotor, it contracts at a faster rate than the cylinder, resulting in a decrease in the expansion difference. Idle running after shutdown: After the unit is shut down, the heat generated by the significant frictional aerodynamic losses cannot be dissipated; as a result, the rotor and cylinder are heated again. The rotor experiences the most pronounced thermal expansion, leading to a positive expansion difference. 31. During startup, why is it necessary to preheat the high-pressure heater before bringing it into operation? How to do it? The high-pressure heater is usually brought into operation after the unit is connected to the grid. If it is not preheated before being put into use, the very low temperature inside the heater will cause a large amount of steam to flow in and condense rapidly, resulting in thermal shock and vibrations in the pipes of the high-pressure heater and the drain system. Therefore, preheating is necessary before activating the high-pressure heater. The method of preheating involves slightly opening the electric valve for steam inlet to the high-pressure heater locally or via the DCS, as well as opening the continuous exhaust valve and the emergency drain valve of the heater tank, thereby achieving preheating and preventing vibrations when the heater is activated. 31. What principles are followed to select the surge steam temperature for hot start? Appropriate main and reheat steam temperatures should be selected based on the metal temperature of the first stage of the high- and medium-pressure cylinders, so that the temperature difference meets the requirements for thermal stress and thermal deformation. Generally, operation with a positive temperature difference is required; that is, the main steam temperature should be at least 50°C higher than the metal temperature of the inner wall of the impulse chamber, and the reheat steam temperature should be at least 30°C higher than the temperature of the medium-pressure blade shrouds. Meanwhile, to prevent heat release due to condensation, the superheat of the steam must not be less than 50°C, ensuring that after throttling through the control valves and expansion through the nozzles, the main steam temperature remains above the metal temperature of the control stage. During normal hot start, the main steam temperature is set at 400°C, and the reheat steam temperature is also around 400°C. 32. What are the reasons for frequent tripping of the low-pressure bypass during startup? 1) The low-pressure bypass was activated too late, resulting in high reheat steam pressure. 2) The low-pressure bypass cooling water flow is not properly regulated; the amount of cooling water is insufficient, resulting in high temperatures downstream of the low-pressure bypass valve and tripping of the same. 3) Excessively high level of the hot well water ； 4) The vacuum pump does not provide sufficient output, or there are leaks in the vacuum system, resulting in a low vacuum level. The pressure in the condensate water pipe is 33 lower. During the start-up and shutdown of the unit, when should the advanced treatment system be activated or deactivated? During the unit startup process, once the quality of the condensate water at the condensate pump outlet is satisfactory, notify the chemistry department to start the fine treatment. During the process of shutting down the unit, once the boiler stops receiving water, it is possible to inform the chemistry department to stop the fine treatment process. 34. During the startup process, how are reverse heating regulations stipulated? During cold startup of the unit, when the metal temperature on the inner wall of the lower high-pressure casing after the control stage is less than 150°C, the steam turbine must undergo high-pressure casing preheating. The preheating process is completed once this temperature exceeds 150°C. Before pre-warming the high-pressure cylinder, confirm the following items: 1) The turbine barring gear is operating properly. 2) The condenser pressure shall not be higher than 13.3 kPa (the vacuum shall not be lower than -88 kPa). 3) The metal temperature on the inner wall of the high-pressure cylinder after the regulation stage is less than 150°C. 4) The main steam valve is in the closed position, the high-pressure drain check valve is closed, and the first-stage extraction steam electric valve is closed. 5) The reverse warm steam pressure should be no less than 0.5 MPa, with a superheat of over 28°C. 35. When is vacuum pumping generally carried out during a cold start-up? After the barring gear is operational and functioning properly, before the main engine shaft seal is activated ； 36. What should be paid close attention to after the steam turbine starts to spin up? Monitor the expansion difference, vibration, eccentricity, oil temperature, and bearing metal temperature; conduct visual inspections of the cylinders. At low speeds, listen for any sounds of sliding or friction within the unit, as well as check for any steam leaks at the external flange joints and various valves, so that defects can be detected and addressed promptly. Additionally, during the speed-up process, the generator should also be carefully inspected. 37. After the unit is shut down, the lubricating oil pressure drops below 0.115 MPa. What should you do in this situation? Upon detecting that the oil pressure is below 0.115 MPa, check whether the AC lubricating oil pump has been activated. If the oil pressure remains low and below 0.07 MPa even after the AC lubricating oil pump is started, the vacuum should be broken immediately to rapidly reduce the unit’s speed and thus decrease the amount of oil used by the bearings. 38. After shutting down the machine, is it better to drain the water from the pipelines right away or after some time? Why? It is better to open the pipeline drain valve after a while following shutdown, as opening it immediately after shutdown causes the steam remaining in the pipeline to be discharged rapidly, leading to rapid cooling of the pipeline. This increases the thermal stress on the pipeline material, thereby affecting its lifespan. Therefore, it is better to wait for some time after shutdown until the temperature of the steam in the pipeline drops before opening the drainage valve. 39. During cold start, what is the idling speed of the unit while it is warming up? What is the basis for increasing the speed again? The holding speed is 1500 rpm. The basis for increasing the speed again is: when the temperature of the inner wall of the first stage of the high-pressure cylinder is ≥ 320°C, and the temperature of the inner wall of the first stage of the medium-pressure cylinder is ≥ 320°C, as well as when the thermal expansion of both the high-pressure and medium-pressure cylinders is ≥ 8 mm, then the medium-speed warm-up is complete. 40. What should be noted when performing maintenance on the main engine exhaust pressure transmitter? The input for the exhaust pressure transmitter comes from the condenser; a main pipe runs from the condenser to the exhaust pressure transmitter and another branch leads to the vacuum low-pressure trip device. Therefore, when closing the input valve of the transmitter, it is essential to be careful to avoid any mistakes. If the input valve for the vacuum trip device is closed by mistake, it can cause the main engine to shut down. In addition, the secondary valve of the exhaust pressure transmitter should also be closed, so as to prevent air from entering the vacuum trip device in case the connections of the transmitter become loose and the input valve does not seal properly, thereby causing the main engine to shut down. 41. Why is a safety valve installed at the outlet of the seal oil pump? The seal oil pump is a screw pump. Due to the very small gap between the screws, very little of the high-pressure liquid on the discharge side leaks back to the suction side. To prevent damage to the equipment in case the outlet valve closes or the liquid pipeline gets blocked, a safety valve is installed on the discharge side of the pump; when the pressure exceeds the specified value, the safety valve opens automatically, allowing the high-pressure liquid to flow back into the vacuum chamber. 42. What is the function of a vacuum chamber? 1) Recover the hydrogen partition box, as well as the oil returning from the air separation box. 2) The vacuum chamber is equipped with a vacuum pumping device; the oil is in a boiling state within the chamber, allowing air and other gases present in the oil to escape, thereby ensuring the quality of the oil. 3) Supply oil to the seal oil pump. 43. What is the working principle of the steam chamber vacuum pump? This pump is a water-ring vacuum pump, equipped with an impeller featuring eccentric blades arranged radially. As the impeller rotates, one part of the water ring is in contact with the hub, while the other part together with the impeller forms two sickle-shaped air chambers. The volume of some of these air chambers increases gradually as the impeller rotates, resulting in a decrease in pressure; they are connected to the suction pipe, thereby drawing in air. The volume of the remaining air chambers gradually decreases in the direction of the impeller rotation; they are connected to the pressure air ducts. The decrease in volume causes the pressure to rise, pushing the gas out of the pump. 44. What is the function of the partition plate inside the hydrogen separator box? Thanks to the presence of the partition, it is possible to measure the oil return volume on the turbine side and that on the generator side separately. Additionally, by knowing the total oil volume on the hydrogen side, it is possible to determine the oil leakage from the sealing rings, which helps to check whether these rings are in good condition. 45. What is the function of the safety valve on the steam side of the low-pressure heater? The low-temperature heater has its own design pressure; once the pressure exceeds this value, the heater will be damaged. During normal operation, if a heater tube ruptures and the drain regulation is not carried out in a timely manner, it can lead to overpressure damage of the heater. Therefore, to ensure the safety of the high-pressure heater, a safety valve is installed. 46. Why is an air pipe installed in the low-pressure heater? If air accumulates on the steam side of the low-temperature heater, it will form an air film on the surface of the heater tubes, severely affecting heat transfer efficiency and reducing thermal economy. Therefore, an air vent must be installed to remove the air. 47. How is the axial thrust of the condensate pump balanced? The balance system is balanced by a balance drum and thrust bearings. 48. What bears the radial force of the condensate pump? It is supported by upper and lower bearings; the upper bearing is a rolling bearing, while the lower one is a sliding friction bearing or bronze bush. 49. What is the function of the condensate pump recirculation? It is ensured that during startup or operation at low load, there is sufficient water flowing through the condensate pump, to prevent insufficient water flow or water interruption from causing friction between the condensate and the pump impeller, which in turn leads to cavitation, pump vibration, and damage. 50. Why is the condensate pump recirculation taken from after the shaft coupling rather than from the condensate pump outlet? To ensure that sufficient cooling water is supplied to the shaft during the startup of the turbine, and also to condense the steam discharged from the shaft seal, thereby facilitating the establishment and maintenance of vacuum in the main engine. 51. Why is the condensate pump recirculation pipe connected to the upper part of the hot water well? The water at the outlet of the condensate pump recirculation pipe is water that has been heated by the shaft seal heater, resulting in a higher temperature. If this water flows directly into the hot water well, vaporization will occur, affecting the proper operation of the condensate pump. 52. The inlet pressure of the condensate pump is higher than the pressure inside the condenser during operation; why can water still be drawn into the pump? Although the pressure at the inlet of the condensate pump is higher than the pressure inside the condenser, due to the head difference, the pressure inside the condenser together with the static pressure resulting from this head difference is greater than the pressure at the inlet of the condensate pump, allowing water to be drawn into the pump. 53. Why is a slight negative pressure required in the shaft? To ensure smooth exhaust of the shaft seal steam and prevent it from condensing within the shaft seal pipeline and thus failing to be discharged. 54. What are the reasons for a prolonged low stator water level signal? 1) Failure of the water supply system, including: A. The solenoid valve being stuck in the closed position or not being energized ； B. False activation of low water level signal ； 2) There is leakage in the system, including: A. Stator water pump gasket leakage ； B. Leakage at the flange joint of the system piping ； C. The system drain valve is not tight ； D. Stator water cooler leak. 55. What is the function of the glue ball cleaning device? A certain number of rubber balls are fed into the water side of the condenser using a centrifugal pump. As the rubber balls pass through the copper tubes, they remove loose scale and prevent the formation of hard scale, thereby keeping the copper tubes clean and ensuring effective heat transfer. This, in turn, improves the operational efficiency of the unit. 56. What is the purpose of the feedwater pump recirculation? It is ensured that when the outlet valve of the feed water pump has not been opened right after it starts up, or when the unit reduces its load significantly and the feed water flow drops to a certain level, some water returns to the deaerator through recirculation, thereby ensuring an adequate flow of water through the pump and preventing cavitation from occurring. 57. What is the purpose of installing a throttle orifice in the feedwater pump recirculation? Prevent vaporization in the pipeline during the gradual reduction of recirculation after the feed pump starts rotating. 58. How is the axial thrust of the feed water pump balanced? It is compensated by a self-balancing system, which uses a balance disc and thrust bearings together to balance the axial thrust. 59. How are the flow rate and head of the feed water pump designed? The capacity and head design of the pump are based on the scenario where, under the unit’s maximum load, the high-pressure bypass requires water injection for cooling due to a sudden load rejection. Flow rate of the feed water pump = Maximum output of the boiler + Water flow rate from the high-pressure bypass. Outlet pressure of the feed water pump = Maximum pressure that the boiler can reach when the high-pressure bypass activates after the unit’s load is reduced + Steam and water resistance within the boiler itself + Resistance in the feed water system. 60. What are the advantages of using a double-shell design for feed water pumps? 1) It has a high degree of symmetry with respect to the axis centerline in terms of structure, allowing it to withstand significant thermal shocks. This prevents wear on the pump due to uneven heating during startup, shutdown, or changes in operating conditions, and makes it easier to heat the pump ； 2) Since the outer shell is a single forged piece, water leakage is prevented; the inner shell is also held in place by pressurized water, which ensures a sealed condition and prevents leakage, as well as allowing excessive amounts of water to escape ； 3) It is easy to maintain, as the inner shell and rotor can be removed as a whole without the need to move the shell, pipes, or valves. 61. What is the function of the safety valve on the high-pressure side? The material used on the steam side of the superheater has certain requirements regarding pressure; excessive pressure can lead to damage to the superheater. During normal operation, if the tubes of the superheater rupture and the drainage system is not adjusted in a timely manner, this can result in overpressure and damage to the superheater. Safety valves are installed to protect the superheater from such hazards. 62. Why is it necessary to open the drain valve of the high-pressure heater drain pipe before connecting the unit to the grid? Before introducing the superheater drain water into the deaerator, it is necessary to drain the water accumulated in the normal drain pipes of the superheater until steam begins to emerge; only then should the drain valve be closed. It is not allowed to introduce the superheater drain water into the deaerator without first draining the water, as this will cause cold water from the pipes to enter the deaerator and lead to vibration in it. 63. What are the advantages of sliding pressure operation in deaerators? Reduced throttling losses ； By designing a regenerative system, the deaerator can be regarded as a regenerative heat exchanger, allowing for a rational distribution of the steam turbine extraction points and thereby improving the regenerative efficiency. 64. What are the basic conditions to ensure effective thermal deaeration? Deoxygenated water must be heated to the saturation temperature at the operating pressure of the deaerator ； The escaped non-condensable gases must be removed promptly ； The deoxygenated water and the heating steam should have a sufficient contact area ； Steam and deoxygenated water should flow in opposite directions. 65. When should the manual drain valves for the main, cold reheat, and reheating pipelines be opened and closed? The manual steam traps on the main, cold reheat, and reheating pipelines should be opened after the unit is disconnected from service ； During startup, it shuts off when the steam before the high and low bypasses is superheated. 66. What is the working principle of a hydraulic coupling? A hydraulic coupling contains a turbine and a pump impeller, with liquid filling the space between them. The turbine is driven by a prime mover; it is the component that drives mechanical equipment. As the turbine rotates along with the prime mover, due to the structure within both the turbine and the pump wheel, the fluid between them transfers the driving force. By adjusting the amount of fluid, it is possible to change the magnitude of this force transfer, thereby altering the speed of the driving mechanism. 67. Why is a recirculation pipe provided for the feed water pump? When the feedwater pump has just started and its outlet valve has not yet been opened, or when the unit is under a significant load reduction, there is no water inside the pump or only a small amount of water flows through it. The heat generated by the high-speed rotation of the impeller raises the water temperature to such an extent that it vaporizes, resulting in cavitation. By installing a recirculation pipe, it is possible for a portion of the water to flow back to the deaerator when the feedwater flow is low enough, ensuring that sufficient water flows through the pump. 68. What changes occur in the state parameters of water vapor before and after throttling? The throttling process can be considered an adiabatic process; the enthalpy of the working fluid remains unchanged before and after throttling. The pressure decreases, the temperature drops, while entropy and specific volume increase. For wet steam, the dryness ratio generally increases after throttling. Wet steam can turn into saturated steam after throttling, and saturated steam can turn into superheated steam after throttling. Although the enthalpy of the steam remains unchanged before and after throttling, the increase in entropy leads to a decrease in the quality of the steam and thus a reduction in its capacity to do work. 69. What are the advantages of centrifugal pumps? It has a simple structure, is not prone to wear, operates stably, produces little noise, ensures even water output, is easy to adjust, and offers high efficiency. 70. What are the losses of a centrifugal pump? 1) Volume loss: seal ring loss, balance mechanism leakage loss, inter-stage leakage loss ； 2) Hydraulic losses: impact loss, vortex loss, friction loss along the flow path ； 3) Mechanical losses: friction losses in bearings and shaft seals, as well as friction losses in the impeller disk. 71. What are the performance parameters of centrifugal pumps? Flow rate, head, speed, power, efficiency. 72. Methods for balancing the axial thrust of centrifugal pumps? 1) Dual-sided water inlet (single-stage pump) ； 2) Drill balance holes on the working impeller to reduce the pressure difference on both sides of the impeller, thereby decreasing the axial thrust ； 3) Use a balance disc or balance drum ； 4) The impellers of multi-stage pumps are arranged in a relative configuration. 73. What is the working principle of an axial flow pump? The theoretical basis of an axial flow pump is the lift theorem of isolated airfoils; as fluid flows over these airfoils, lift is generated. When the impeller of the axial flow pump rotates driven by a prime mover, the blades move within the fluid, exerting a force on it. This force has an equal magnitude but opposite direction to the lift generated by the airfoils. Under the action of this lift, the fluid moves in the direction of the pump shaft, from the inlet to the outlet. Through this continuous back-and-forth movement, the axial flow pump operates. 74 What is the working principle of a centrifugal pump? The main component of a centrifugal pump is the impeller, which has several blades. When the impeller and the entire pump casing are filled with water, the rotation of the impeller causes the blades to force the water to move in a circular motion, thereby generating centrifugal force. This centrifugal force drives the water from the center of the impeller toward its edges, increasing both the speed and pressure of the water flow. As the water enters the pump chamber, its speed decreases again while the pressure increases, before it is discharged from the outlet. The pressure at the entrance to the impeller drops, becoming lower than the pressure in the inlet pipe; under this pressure difference, water flows from the suction tank into the impeller. In this way, the pump can continuously draw in water and supply it continuously. 75. What are the advantages of axial flow pumps? 1) Adjustable blades are used, and efficiency is reduced only slightly after adjustment ； 2) Small external dimensions and reduced floor area, resulting in lower investment costs and shorter construction time ； 3) Compact structure, light weight ； 4) High traffic. 76. How does cavitation in water pumps occur? What impact does it have on the pump? When the liquid pressure in certain areas of the flow channel drops to near a certain limit, bubbles begin to form in the fluid. When these bubbles enter areas of higher pressure, they are compressed and destroyed by the surrounding high-pressure water. It re-condenses into water, resulting in a **reduction in volume**. On one hand, high-pressure water rushes with great energy toward the area where the bubbles burst, creating a water hammer effect on the walls of the flow channel ； On the other hand, as successive bubbles continue to arrive and cause continuous compression and condensation, the material forming the walls of the flow channel suffers from fatigue damage, leading to the formation of so-called honeycomb-like erosion and cavitation. After operating for a certain period of time, the components of the water pump are damaged by cavitation. When cavitation is severe, it can disrupt the continuity of the liquid flow, resulting in a decrease in the pump’s Q, H, and η values, and even leading to pump failure. In cases of severe cavitation, crackling noises can be heard inside the pump, along with vibrations of the pump body. 77. Why is self-cooling generally used for cooling the shaft bearings of circulation pumps? There are two sources of cooling water for these bearings: industrial water and the water coming from the outlet of the circulation pump. Using industrial water for cooling means that if the industrial circulation pump fails and the pressure of this water drops, it can cause the rubber bearings to be damaged; however, using the water from the pump’s outlet avoids this risk. 78. How is the axial thrust of the circulating water pump balanced? How many bearings support it radially? The axial thrust is balanced by two thrust pads inside the motor. Radially, it is supported by upper and lower rubber pad bearings, and there is also a guide bearing on the upper part of the motor. 79. What are the performance parameters of a water pump? Flow rate Q, head H, power N, efficiency η, speed n, specific speed ns, and net positive suction head Δh. 80. Why is the flow rate of each pump when they operate in parallel less than that when each pump operates alone, while the head generated by each pump is greater than that of a single pump? This is because, when two pumps operate together, the frictional losses in the pipes increase as the flow rate rises; as a result, each pump must increase its head to overcome these increased loss heads, which leads to a decrease in flow rate and an increase in pressure. 81. Why aren’t high-speed pumps used for circulating water pumps? This is mainly to meet the requirements of the condenser for a large flow rate and low pressure head; since the outlet water pressure of a pump is proportional to the square of its speed, using a high-speed pump would result in excessively high outlet pressure, which the copper tubes of the condenser cannot withstand, posing a risk to safe operation ； Furthermore, the power of a water pump is proportional to the cube of the pump’s rotational speed; if a high speed is used, the power consumed by the pump increases sharply, which is why circulation pumps do not operate at high speeds. 82. Why is it not allowed to start the circulating water pump when it is running in reverse? If a large pump is started while running in reverse, its pump shaft (including the coupling wheel) can be damaged, as the torsional torque generated during startup is much greater in this case than during normal startup. The motor is also prone to damage; the starting current of a motor is 5 to 6 times higher than its rated operating current. If the pump is started while running in reverse, the current will be even higher, and such high currents can cause damage to the motor. 83. How to conduct a vacuum tightness test? Steps: 1) Adjust the unit load to 80% ； 2) Stop the operation of the steam chamber vacuum pump ； 3) Observe the rate of vacuum drop and record the value of vacuum decrease per minute ； 4) If the vacuum drop rate is ≤ 2 mmHg column/min, the vacuum system has good airtightness ； If the vacuum drop rate is ≤ 3 mmHg column/min, the vacuum system is considered leak-free ； If the vacuum drop rate is ≤ 5 mmHg column/min, the vacuum system has severe leakage ； 5) The test duration is 8 hours, but the overall decrease in vacuum level must not be excessive, in order to prevent an increase in the exhaust temperature of the unit ； 6) Once the test is complete, the vacuum pump is put into operation. 84. What are the reasons for the unit to overspeed after the steam turbine is shut down? 1) The automatic main steam valve and throttle valve are not tight ； 2) The check valves and electric valves in the high-pressure extraction steam pipeline are not tight, allowing steam to flow back into the machine. 85. After the steam turbine is started, how can the speed be maintained at a constant level as it increases? How to operate when accelerating again? After the turbine is started up and its speed begins to increase, if it is necessary for the turbine to remain at a certain speed for warming up or for inspection, simply press the “HOLD” button on the DEH program control panel; once the button’s indicator light comes on, the turbine will stay at that speed. When accelerating again, simply press the “HOLD” button; the indicator light in the middle of the button will go out, and then press the “reset” button, and the unit will accelerate once more. 86. What are the reasons for low pressure in the deaerator during operation? 1) Fault in the steam source for the deaerator. 2) The low-temperature reheater is faulty and not in operation. 3) The load is low. 4) An accident drain from the high-temperature reheater opened, causing the drain water to flow into the hot water well. 87. What are the reasons why the speed cannot increase during startup? 1) The issued command was not delivered ； 2) Speed-up controller failure ； 3) The high-pressure bypass valve is open to a small degree, resulting in low pressure before the low-pressure bypass valve ； 4) The throttle oil actuator filter is clogged, causing the actuator to stick. 88. Why is the expansion difference in the lower cylinder large when the unit load is low, and small when the unit load is high? Because at low load the steam flow rate is low, the heat generated by frictional blowdown losses inside the lower cylinder cannot be removed promptly by the exhaust steam. Additionally, due to the difference in the mass-to-area ratio of the rotor and the cylinder, the rotor expands more than the cylinder, resulting in a large expansion difference. At high load, the steam flow rate is high, and the heat generated by frictional blowdown in the lower cylinder can be promptly carried away by the exhaust steam. Due to the difference in mass-to-surface area ratio, the expansion of the rotor is relatively small, resulting in a smaller expansion differential. 89. Under what conditions does the extraction check valve close? 1) High water level in the heater ； 2) Unit tripping ； 3) Compressed air interruption ； 4) Manual test 90. How many channels are there for making up water in the stator water system? How to use it? Two routes: 1) Condensate pump outlet ； 2) Outlet of the condensate transfer pump ； During normal operation, if the conductivity is high, water is added using the outlet of the condensate transfer pump; if the pH value of the cooling water is low, condensate is used for adding water ； 91. How to carry out maintenance measures for the stator water cooler? What to pay attention to? 1) Check that the standby cooler is filled with water; otherwise, start the condensate transfer pump and use the chilled water pump to fill it and drain any air from it ； During this period, pay attention to the water level in the chiller tank. 2) Open the cooling water inlet and outlet valves of the standby cooler as well as the stator water inlet and outlet valves. 3) Slowly close the inlet and outlet valves of the cooling water for the operating cooler, as well as the cooling water valve; during this process, pay attention to the flow rate of the cooling water and the water level in the cooling water tank. 4) Open the chilled water supply and chilled water drain valves of the cooler on the shut-down side; be careful to monitor the water levels in the chilled water tank and the closed expansion tank ； 92. What are the maintenance measures for the stator water pump? What should be noted during recovery? 1) Start the backup chilled water pump; once it is operating normally, stop the pump ； 2) Close the inlet and outlet doors of the stator water pump ； Open the water release valves on the pump body and pipelines ； 3) Stator water pump motor power connection ； 4) Hang warning signs on each door and the motor body ； During restoration, it is necessary to first manually fill the chiller tank to the high water level, and then slowly open the inlet and outlet valves of the pump, while paying attention to monitoring the water level in the chiller tank. 93. What are the maintenance measures to restore the stator water cooler? 1) Check that the cooler drain valve is properly closed ； 2) Manually refill the chiller water tank to the high level ； 3) Open the water injection valve on the stator water side of the cooler; the water injection valve leading to the stator water side of the operating cooler must be tightly closed ； 4) When continuous water flows out from the air valve, it indicates that the cooler is filled with water; pay attention to the water valve and the air valve ； 5) Slowly open the stator water inlet valve, paying attention to the stator water flow rate, until the pressure is equal to that on the operating side ； 94. After the stator water system is shut down and water is drained, how should the ionizer be protected? The resin inside the stator water ionizer must not be exposed to the atmosphere; therefore, when draining the stator water system, the ionizer should be isolated. 95. How to determine if the main stator water filter is clogged? 1) The outlet pressure of the stator water pump increases, and the stator water flow rate decreases ； 2) An alarm is issued when the blockage causes a severe pressure difference. 96. How to switch the stator water cooler? 1) The cooling water inlet valve of the standby stator water cooler is closed, the outlet valve is open; the stator water inlet valve is closed, the outlet valve is open ； 2) Check that the stator water pressure in the standby stator water cooler should be the same as that in the operating stator water cooler ； 3) Open the cooling water inlet valve of the standby stator water cooler, and slowly open the inlet valve on the stator water side, paying attention to changes in the stator water flow rate ； 4) After confirming that the installed stator water coolers are operating properly, put the previously in-use coolers into standby mode. 97. What are the reasons for the increased conductivity of stator water? 1) Ionizer failure, resin degradation ； 2) Cleaning the filter screen causes dirt to accumulate ； 3) The supplementary water quality is substandard. 98. If the stator water temperature at the generator inlet is high, which items should be checked? Is the outlet temperature high? 1) Check whether the cooling water valves of the operating stator water cooler are fully open ； 2) Check whether the inlet valve on the stator water side of the backup stator water cooler is properly closed, and whether there is any stator water that enters the generator without being cooled first ； 3) Check whether the cooling water temperature is normal, and whether there are any abnormalities in the control valve for the chilled water and the regulation of the closed-loop cooling water system ； 4) Check whether the generator is operating normally ； 5) Check whether the level of the chilled water tank is normal ； Is the electric heating for chilled water supply accidentally activated? ； High outlet temperature: 1) Check the stator water flow rate ； 2) Is it overloaded? ； 3) If the inlet temperature is normal, it may be a fault in the generator stator coil. 99. When should the stator water cooler be started and stopped? After the unit is connected to the grid, the stator water cooler is activated ； After the unit is disconnected, the stator water cooler is shut off ； 100. What are the maintenance measures for the seal oil pump? 1) Notify the controller to disable interlocking ； 2) Close the pump inlet and outlet valves ； 3) Motor power draw ； 4) Hang warning signs on each door and the motor body. 101. What are the reasons for the decrease in the outlet water temperature of the low-pressure heater? 1) The rise in the hydrophobic water level affects heat transfer efficiency ； 2) Low extraction steam pressure or sudden increase in condensate volume ； 3) Air trapped in the heater affects heat transfer ； 4) The bypass is not tight, allowing water to take a shortcut ； 5) The heater steel pipe is dirty, resulting in high thermal resistance ； 6) Heater leakage. 102. How to determine if a heater is leaking? 1) Increase in heater terminal difference ； 2) The water temperature at the heater outlet decreases ； 3) Rise in hydrophobic water level or heater filled with water ； 4) When leakage is severe, the pressure on the steam side increases, causing shock vibrations in the steam inlet pipe and the drain pipe. 103. What should be noted when adjusting the lubricating oil temperature after startup? After startup, special attention should be paid to adjusting the lubricating oil temperature. When adjusting the amount of cooling water, care must be taken to avoid excessive rises or falls in oil temperature; the change in oil temperature should be gradual. At the same time, it is necessary to contact the main control system promptly to inquire about the turbine speed, so as to have a reliable basis for adjusting the amount of cooling water and to ensure that the oil temperature and its fluctuations remain within normal ranges. 104. What are the reasons for low pressure at the condensate pump outlet during unit operation? 1) High load ； 2) Meter failure ； 3) The combined control of the deaerator and condenser water levels is inadequate ； Low condenser water level ； 4) Incorrect activation of the condensate pump recirculation ； 5) The check valve of the standby pump leaks heavily ； 6) Severe leakage in the low-pressure heater ； 7) Several control valves with a relatively large cooling water flow rate were accidentally opened. 105. What are the maintenance measures for the thickening pump? 1) Disengage pump interlock, power the motor ； 2) Outlet and inlet doors of the condensate pump ； 3) Shut off the condensate pump to the condenser air valve ； 4) Close the seal water valves of the condensate pumps, as well as all gauge doors ； 5) Open the water valve and inform the control room to be aware of the vacuum ； 6) Hang warning signs on each door and the motor body. 106. What factors affect the water level of hot water wells? 1) Operation status of the condensate pump ； 2) Combined control status of deaerator level and condenser level ； 3) Is the filter at the inlet of the condensate pump clogged? ； 4) Start the pump for draining water from the furnace to the condenser return water ； 5) Are there any leaks in the titanium tubes of the condenser? ； 6) Load variation ； 7) Status of the make-up water pump, make-up water valve, and make-up water bypass valve. 107. What are the reasons for the increased conductivity of condensed water? 1) Desalination unit trips, bypass valve opens, or manual bypass opening is too large ； 2) Resin failure in the desalination unit ； 3) Condenser titanium tube leakage ； 4) The water quality in the condensate make-up tank is substandard ； 108. What are the symptoms of leaks in the titanium tubes of a condenser? 1) Increase in supercooling ； 2) End difference decreases ； 3) High electrical conductivity ； 4) Rising water level in hot water wells (severe) ； 5) Vacuum drop. 109. What is condensate subcooling? What are the hazards of supercooling? The difference between the turbine exhaust temperature and the condensate water temperature. Harm: 1) Increases the oxygen content in the condensate water ； 2) It causes an additional amount of heat from the condensate itself to be carried away by the cooling water, which in turn results in the need for more steam extraction during the reheating of the condensate, thereby reducing efficiency. 110. What are the maintenance measures for the inlet filter of the thickening pump? What to pay attention to? 1) Shut off the inlet and outlet valves of the condensate pump ； 2) Shut off the air valve of the filter screen ； 3) Open the water gate ； 4) Close the condensate pump casing to the condenser exhaust valve ； 5) Close the seal water inlet valve of the condensate pump ； 6) Power off the condensate pump motor and hang a warning sign ； 7) Hang warning signs on each door. Note: The air valve on the filter screen must remain closed at all times. After draining water, the control room should be informed to pay attention to the vacuum level in the rewatering unit. 111. How to determine if an oil cooler is leaking? Since the pressure on the oil side is higher than that on the cooling water side, the air valve on the water side of the oil cooler should be opened; if oil is present in the water, it indicates a leak in the oil cooler. 112. What are the reasons for a sudden drop in the speed of the feedwater pump? 1) Load shedding ； 2) Motor failure ； 3) Malfunctionous closure of the small turbine inlet valve ； 4) Loss of EH oil pressure ； 5) Speed control failure. 113. What are the reasons for low inlet pressure of the pre-pump? 1) Fault on the steam side of the low-pressure heater, resulting in low deaerator pressure ； 2) Deaerator steam supply failure; heating cannot be activated ； 3) The inlet filter of the pre-pump is clogged ； 4) Low load. 114. What is the purpose of installing a pre-pump? Increase the net positive suction head and lower the deaerator elevation. 115. What are the advantages of the speed control method for feedwater pumps? With variable speed regulation, the hydraulic loss in the water supply system depends only on the flow rate; therefore, its resistance characteristics do not change. That is, there are no throttling losses, thereby improving the economic efficiency during off-design operation. 113. The feed water pump is used as a backup; what should be done if it reverses direction? The reversal is caused by a faulty check valve at the pump outlet, or by problems with the intermediate tap or the recirculation check valve. In such cases, the outlet valve and the intermediate tap should be closed manually, as well as the recirculation valve. 114. What are the reasons for low lubricating oil pressure in the feed water pump? 1) The output of the lubricating oil pump built into the hydraulic coupling is insufficient ； 2) The lubricating oil filter is severely clogged ； 3) Cool oil cooler leak ； 4) Low oil level ； 5) Clogged oil pipeline. 131. What are the reasons for high oil temperature in the feed water pump? 1) High cooling water temperature ； 2) Cooler scaling ； 3) The speed of the feed water pump is 4500–5000 rpm. 4) High load leads to increased heat dissipation in the bearing shells ； 5) Bearing wear leads to increased mechanical friction losses and greater heat dissipation ； 115. What phenomena occur when the air supply pipe of the high-pressure steam accident drain pneumatic valve breaks? The accident drain pneumatic valve opens. 116. What should be done if the air compressor trips during operation and the backup unit does not connect? 1) If it is found that the backup air compressor is not connected, immediately switch the interlock switch to the position corresponding to the backup air compressor, and check whether it starts running. If it does not start, switch the interlock switch back to the position of the currently operating air compressor, and then check whether that compressor can start running. If it still does not start, immediately investigate the reason for the shutdown of that compressor. At the same time, depending on the pressure drop in the large tank, contact the shift supervisor to open the compression connection valves for Units #1 and #2 ； 2) Once the interlock switch is set to the standby air compressor position and the compressor starts running, its operation condition should be carefully checked. At the same time, check the reason for the tripping of the originally operating air compressor, and notify the maintenance team to come and handle it ； 3) If the originally operating air compressor can be started by forced operation, its performance should be carefully checked at this time to analyze the reasons for the compressor tripping and the failure of the backup unit to engage. 4) Report the above situation to the captain and the shift supervisor, and keep a record. 117. What are the reasons for deaerator vibration during startup? 1) The steam flow velocity inside the deaerator is too high ； 2) Switching of the steam source or improper adjustment of the steam source leads to pressure fluctuations in the deaerator, which in turn causes fluctuations in water flow velocity and resulting vibrations ； 3) The condensate water temperature is too low, resulting in a large temperature difference between hot and cold fluids ； 4) Poor water level regulation leads to excessive water levels and uneven internal pressure ； 5) Low-temperature drain water entering the deaerator or high-temperature drain water entering the deaerator causes vibration in the pipelines connected to the deaerator, leading to vibration of the deaerator itself ； 118. What is water hammer? What are the symptoms of water hammer in pipelines? When water is delivered through long-distance water pipelines with large height differences, a sudden loss of power due to reasons such as power outages causes the flow velocity of the water inside the pipes to change abruptly, accompanied by changes in pressure within the pipelines. This leads to sudden increases or decreases in local pressure. Such sudden pressure changes exert a ‘hammering’ effect on the pipes; this phenomenon is known as ‘water hammer’. The phenomenon of water hammer occurs when pressure rises or falls suddenly; these pressure changes propagate rapidly through the piping system, causing pressure fluctuations that lead to pipe vibration and the production of a rumbling sound. The pressure fluctuations and vibrations caused by water hammer gradually diminish and disappear over time. 119. What are the reasons for increased bearing temperature during the operation of a centrifugal pump? 1) The oil level is too low, resulting in a reduced amount of lubricating oil reaching the bearings ； 2) The quality of the lubricating oil is unsatisfactory; water has entered the oil, there are impurities present, or the oil has emulsified and deteriorated ； 3) The oil ring does not rotate, resulting in a disruption in oil supply to the bearings ； 4) Those with bearing cooling water: insufficient amount of cooling water ； 5) Bearing damage ； 6) For rolling bearings, in addition to the reasons mentioned above, excessive tightening of the bearing cover can eliminate its radial clearance and result in a loss of flexibility. 120. How to reduce pressure loss in pipelines? 1) Keep the valves in the steam and water pipeline system fully open as much as possible, to minimize unnecessary valves and throttling elements ； 2) Reasonably select pipe diameter and pipe layout ； 3) Adopt appropriate technical measures to reduce local friction losses ； 4) Reduce leakage losses. 121. Causes and solutions for vibration in circulating water pumps? Causes: 1) Loose foundation bolts of the pump and motor ； 2) The pump and motor are not aligned centrally ； 3) Friction between the pump and motor thrust bearings increases, leading to higher resistance ； 4) Friction or damage occurs between the moving and stationary parts of the pump and motor ； 5) Increased clearance or damage to the bearing shells ； 6) Change in motor excitation center ； 7) Loose motor stator coils ； 8) Pump cavitation, 9) Foreign objects entering the pump. Handling: If an increase in vibration in the circulating water is detected, the cause of the vibration should be investigated immediately, and maintenance personnel should be notified. When the vibration becomes too severe to allow continued operation, the control room should be contacted to shut down the system. 122. What are the reasons for an increase in the outlet pressure of a circulation pump? 1) Two pumps are operating in parallel ； 2) Secondary filter clogged ； 3) Manually close the electric valves for the inlet and outlet of the condenser circulating water ； 4) Backwashing of the secondary filter screen ； 123. What should be done if the outlet valve does not open after the circulation pump starts? If the outlet valve fails to open after the circulation pump begins operating, the pump should be stopped immediately, and maintenance personnel should be notified to handle the issue. 124. Why is it necessary to close the outlet valve first before stopping the circulation pump? The circulation pump is an axial flow pump, and since the diameter of the outlet pipe is relatively large, no check valve is installed. In this way, if the outlet valve is not closed first when the pump stops, a large amount of water will flow back, causing the pump to rotate in reverse; in severe cases, the impellers of the circulation pump may be damaged. Therefore, when stopping the circulation pump, the outlet valve should be closed first before shutting down the pump. 125. What phenomena occur when a pump experiences cavitation? When cavitation occurs, noises of various frequencies are produced inside the pump. In severe cases of cavitation, a popping sound can be heard from within the pump, and the pump body vibrates as well. At the same time, the flow rate, head, and efficiency of the water pump decrease significantly, and the ammeter reading fluctuates. 126. What are the causes of increased temperature in the motor bearing shells of a circulation pump, and how to address it? Reason: 1) Degradation of oil quality, damage to the oil film ； 2) The oil level in the bearing bush is too low or there is no oil ； 3) Damage to the bearing bush oil ring ； 4) Cooling water interruption or filter clogging ； 5) Improper bearing clearance, issues with assembly ； 6) Severe vibration of the motor and pump leads to an increase in the temperature of the bearing shells ； Handling: Once it is detected that the bearing temperature is high, the cause of this increase should be identified immediately, the trend in the rise of the bearing shell temperature should be closely monitored, and the captain should be informed. When the tripping value is reached, contact the main controller to stop the operation of the motor. 127. What are the reasons why the pump doesn’t pump water? 1) The pump is not filled with water; there is air inside ； 2) Blockage of the water flow channel ； 3) The pump bottom valve has fallen off ； 4) The impeller or shaft key is damaged, preventing proper transfer of energy to the water ； 5) Incorrect motor wiring causes the water pump to rotate in reverse. 128. What factors might cause abnormal noises, changes in current, and changes in outlet pressure during pump operation? 1) The water pump experiences cavitation ； 2) Air enters the water pump or air is not completely expelled during startup ； 3) Low water level in the square well ； 4) Debris enters the water pump ； 5) Friction between the water pump impeller and the pump casing ； 6) Damage to the water pump shaft bearing or damage to the motor shaft bearing ； 7) Motor traction damage ； 8) The original center is not aligned, resulting in significant vibration. 129. How to handle smoking and burning of a circulation pump motor? If the pump motor starts smoking or catching fire while in operation, the pump should be stopped immediately, and the control room should be contacted to turn off the power supply. Dry chemical extinguishers and carbon tetrachloride fire extinguishing agents should be used to put out the fire; if necessary, foam extinguishers can also be used to extinguish the fire in the motor. If only one pump is in operation, the backup pump should be activated promptly. 130. How to handle automatic tripping during the startup of a circulation pump? 1) Check whether there is any jamming or tightness in the rotating parts of the water pump and motor ； 2) Check the stator coils ； 3) Check for any abnormalities in the switch operating mechanism ； 4) Check whether the relay operates. 131. Under what circumstances should the backup pump be started first and the faulty pump stopped later? 1) The motor makes abnormal noises or has a smell of burned insulation ； 2) The current exceeds the normal operating value ； 3) The vibration of the water pump motor is high, exceeding the allowable value ；