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Brief question: 1. Briefly describe the second law of thermodynamics. Answer: The second law of thermodynamics explains the direction, conditions, and extent of energy transfer and conversion. It has two ways of description: from the perspective of energy transfer, heat cannot spontaneously move from a colder object to a hotter object without paying a cost. From the perspective of energy conversion: it is impossible to create a heat engine that absorbs heat from a single heat source and converts all of it into work without any other changes occurring. 2. What is a reaction turbine? Answer: A reaction turbine is one in which the degree of expansion of steam occurs to roughly the same extent in the nozzle and the moving blades. At this time, the moving blades are subjected not only to the forces caused by the impact of the steam flow, but also to the reaction forces resulting from the expansion and acceleration of the steam within the blades. Due to the significant pressure difference between the steam at the inlet and outlet of the moving blades, the axial thrust in reaction turbines is greater compared to impulse turbines. Therefore, a balance disk is generally installed to balance the axial thrust. 3. Briefly describe how local flow losses are formed Answer: In a localized region of flow, due to sudden changes in boundaries—such as valves, elbows, or abrupt changes in the shape or cross-sectional area of pipes—the magnitude and direction of the fluid flow velocity change drastically. The intense collisions between fluid particles give rise to vortices, which consume energy; this results in flow losses. 4. Under what conditions does the differential expansion of the steam turbine take on a negative value? Answer: Due to the difference in the steel materials used for the cylinder and the rotor, the linear expansion coefficient of the rotor is generally higher than that of the cylinder. Additionally, since the rotor has a smaller mass but a larger surface area exposed to heat, during normal operation of the unit, the differential expansion is always positive. When the load drops rapidly or there is a load rejection, the main steam temperature and the reheat steam temperature decrease; water hammer in the turbine may occur; or improper use of the heating devices during unit startup and shutdown – all of these can result in a negative value for the differential expansion. 5. What is an isentropic process? A thermodynamic process in which entropy remains constant is called an isentropic process. A reversible adiabatic process, that is, an adiabatic process with no energy loss, is a isentropic process. In irreversible processes with energy loss, although no heat is added from the outside, the working fluid must absorb heat generated by losses such as friction and disturbances; this heat causes an increase in the entropy of the working fluid, and thus an adiabatic process is not an isentropic process. The expansion process of the turbine working fluid is an irreversible adiabatic process. 6. Briefly describe the content of the optimization analysis for the start-up and shutdown process of steam turbines. Answer: (1) Determine a reasonable temperature change rate based on the requirements regarding rotor life loss rate, thermal deformation, and thermal expansion differences ； (2) Ensure that the temperature change rate varies with the heat release coefficient ； (3) Monitor that the temperatures at various measurement points of the steam turbine, as well as differential expansion and vibration, remain within limits ； (4) Crankshaft preheating and positive temperature difference starting to achieve optimal temperature matching ； (5) Minimize the startup time while ensuring the safety of the equipment, in order to reduce power and fuel consumption, etc. 7. What are the types of steam turbines based on their working principle? How are they classified according to the characteristics of thermodynamic processes? Answer: ① Turbines are divided into two types based on their working principle: impulse turbines and reaction turbines. ②Turbines are classified according to the characteristics of their thermodynamic processes into: condensing turbines and back-pressure turbines, extraction turbines, and intermediate-reheat turbines. 8. What is the characteristic curve of a pump? Answer: The characteristic curve of a pump is a curve that shows the relationships between flow rate, head, required power, and efficiency at a certain rotational speed. That is: Q━H curve, Q━N curve, Q━η curve. 9. What are the mechanical properties of metals? Answer: The mechanical properties of metals are the characteristics exhibited by metal materials under external forces. Such as: elasticity, strength, toughness, and plasticity, etc. 10. What is a proper starting method for a turbine? Answer: A proper starting method for a turbine refers to an appropriate heating strategy that ensures that during the startup process, the thermal stresses, thermal deformations, differential expansion between the rotor and the cylinder, as well as the vibrations of the rotating parts remain within acceptable limits. This approach enables the metal temperature of the unit to rise evenly to the operating temperature required at rated load as quickly as possible. 11. Why is a slip pin system required in steam turbines? Answer: During startup and load application, the temperature of the steam turbine casing changes significantly; therefore, the thermal expansion value is relatively large. To ensure that the cylinder can expand freely in the prescribed direction when heated, and to keep the cylinder aligned with the center of the rotor. Similarly, to ensure that the cylinder can contract freely in the specified direction when the turbine is shut down, turbines are equipped with a pin system. 12. What are the main causes of damage to turbine bearing shells? Answer: ① Oil supply cut off to the bearing during operation ； ②The unit is experiencing severe vibration ； ③Manufacturing defects in bearing shells ； ④Excessively high bearing oil temperature ； ⑤The quality of the lubricating oil has deteriorated. 13. What are the factors that affect the slope and shape of the turbine coastdown curve? Answer: ① The degree of opening of the vacuum break door, and the timing of when it opens ； ②Is there friction in the rotating parts inside the unit? ； ③Are the main steam valve, throttle valve, and extraction check valve airtight? 14. What is the working principle of mechanical seals? Answer: A mechanical seal is a type of seal that does not require packing. Its working principle relies on the tight axial contact between two precisely machined end surfaces (the rotating ring and the stationary ring) to achieve sealing. The moving ring is mounted on the moving ring seat and rotates together with the shaft ； The stationary ring is mounted on the stationary ring seat of the pump body and constitutes the stationary part. There is a water film between the axial sealing surfaces of the rotating ring and the stationary ring, which serves to cool and lubricate these surfaces. When the pump is in operation, the friction between the two sealing surfaces causes the liquid inside the sealing chamber to heat up. To prevent vaporization, the system is designed with a circulating fluid that removes the heat generated by friction, thereby also protecting the two sealing surfaces from damage and extending their service life. The circulating fluid is designed to function as a pump on the rotating ring seat, generating pressure to maintain circulation inside; the liquid that has been discharged enters an external cooler and, after passing through a magnetic filter, returns to the mechanical seal. 15. What are the performance advantages of water ring vacuum pumps over jet ejectors? Answer: The performance of exhaust equipment can be divided into two main aspects: start-up performance and continuous operation performance. Starting performance refers to the pumping capacity of the exhaust equipment under starting conditions, and it directly affects the time required to create the vacuum necessary for starting the turbine in the condenser. The pumping capacity of water ring vacuum pumps at low vacuum levels is much greater than that of water jet ejectors and steam jet ejectors at the same pressure. The pumping capacity of water ring vacuum pumps at low vacuum levels is much greater than that of water jet ejectors under the same suction pressure. The continuous operation performance directly reflects the operating performance of the vacuuming equipment under rated conditions; the vacuuming capacity should not be too high, otherwise a large amount of steam in the condenser will be drawn away. The pumping capacity of a water ring vacuum pump is related to the inlet pressure; the lower the inlet pressure, the weaker the pumping capacity. Therefore, it can meet the requirements for steam extraction under low vacuum conditions during startup, as well as under high vacuum conditions. 16. How does the working fluid in a hydraulic coupling transmit power? Answer: In a hydraulic coupling, the chambers of the driving turbine and the driven turbine are filled with working fluid, creating a circulating flow path. If the main shaft rotates at a certain speed, the oil in the working chamber formed by the driving turbine and the driven turbine is introduced from the inside of the driving turbine; under the effect of centrifugal force, it is flung to the outside of the oil chamber, forming a high-speed oil flow that strikes the blades of the driven turbine, thereby causing those blades to rotate as well. Then, the working oil flows along the passive turbine blades toward the inside of the oil chamber and gradually slows down as it returns to the inside of the active turbine, thus forming a circular flow pattern for the oil. This cycle repeats, resulting in a natural circulation of the working oil between the impeller and the turbine. In this way, the working fluid gains energy within the driving turbine and releases energy within the driven turbine, thus completing the transfer of energy. 17. What are the hazards of air in the condenser? Answer: Air in the condenser poses three main hazards: (1) An increased amount of air entering the system raises the partial pressure of air, thereby reducing the vacuum level in the condenser. (2) Air hinders steam condensation, reducing the heat transfer coefficient and increasing the heat transfer temperature difference, thereby causing a decrease in vacuum. (3) It increases the subcooling of the condensate water, reducing the thermal cycle efficiency of the steam turbine. 18. Safety and economic analysis of main steam temperature. Answer: Abnormal changes in main steam temperature pose a significant threat to the operational safety of turbines. As the main steam temperature increases, the ideal enthalpy drop of the steam rises and the exhaust steam humidity decreases, which contributes to an improvement in the thermal efficiency of the turbine. However, a steam temperature higher than the allowable value has an impact on both the reliability and service life of the equipment ； Excessively high steam temperature reduces the strength of the materials and causes excessive expansion of the components, thereby leading to changes in the dynamic and static clearances as well as the assembly tension ； This will cause significant damage to the main steam valve, control valves, as well as the stationary and moving blades of the first few stages in the high-pressure inner cylinder. Under high-temperature conditions, the creep rate of metal materials increases, which can cause equipment damage or reduce its service life. Therefore, both the extent of over-temperature and the cumulative time must be strictly limited. A decrease in the main steam temperature during operation is detrimental to both the safety and economy of the steam turbine. On the one hand, as the steam temperature decreases, the ideal enthalpy drop of the steam is reduced, the moisture content in the exhaust steam increases, and efficiency declines. On the other hand, when the temperature decreases while maintaining the rated load, an increase in steam flow is extremely detrimental to the final stage blades. A decrease in steam temperature also increases the reaction degree at each stage of the turbine and raises the axial thrust. 19. Working principle of thermal deaeration: Answer: The principle of thermal deaeration is based on Henry’s law and Dalton’s law. Henry’s law states that when there is equilibrium between a liquid and a gas, at a given temperature, the amount of gas dissolved per unit volume of water is proportional to the partial pressure of that gas above the water surface. If the partial pressure of this gas at the water surface is greater than its actual partial pressure at that level, the gas will separate from the water due to this pressure difference until a new equilibrium is reached. If a certain gas can be completely removed from the surface of the liquid, then that gas can be entirely eliminated from the liquid. Dalton’s law states that the total pressure of a gas mixture is equal to the sum of the partial pressures of the individual gases that make up the mixture. For feed water, the total pressure of the gas mixture above the water surface equals the sum of the partial pressure of the gases dissolved in the water and the partial pressure of water vapor. In a deaerator, as water is heated at constant pressure, its evaporation increases, which raises the partial pressure of vapor above the water surface; correspondingly, the partial pressures of other gases above the water surface decrease. When the water is heated to its boiling point at the pressure in the deaerator, the partial pressure of water vapor approaches the total pressure of the gas mixture above the water surface. At this point, the partial pressures of the other gases above the water surface tend to zero, and as a result, the gases dissolved in the water escape from it due to this pressure imbalance, and are carried away through the deaerator’s exhaust pipe. 20. Impact of increased turbine exhaust pressure on turbine operation. Answer: When the exhaust pressure increases, the ideal enthalpy drop of the turbine decreases ； If the steam flow remains constant, the output of the turbine will decrease. After the exhaust pressure increases, the reduction in the total enthalpy drop of the turbine is primarily reflected in a decrease in the enthalpy drop across the last few stages, whereas the enthalpy drop across the high-pressure stages remains essentially unchanged. Therefore, at this time, the stresses in all levels of blades and diaphragms are within safe limits. When the exhaust pressure increases, it will cause the temperature on the exhaust side to rise. Excessively high exhaust temperature may cause the unit’s center to shift, leading to vibration ； Furthermore, excessively high exhaust temperature can also lead to uneven temperatures in the exhaust cylinder, resulting in deformation. It can also cause the flanges of the condenser copper tubes on the tube sheet to loosen, allowing circulating water to seep into the steam side and deteriorating the quality of the steam. It can also cause excessive thermal expansion in components such as the low-pressure cylinder and bearing housings, leading to changes in alignment, resulting in unit vibration or the disappearance of the radial clearance in the end shaft seals, thereby causing friction. 21. What is the function of the turbine’s slip pin system? Answer: The slip pin system is a device that ensures the cylinder can expand freely in a controlled manner while maintaining its axis intact. During startup and load increase, the temperature of the cylinder in the turbine rises gradually, causing it to expand. Since the temperature rise of the base plate is lower than that of the cylinder, if the cylinder and the base plate are fixedly connected, the cylinder will not be able to expand freely. Therefore, various sliding pins should be installed between the cylinder and the base plate as well as between the cylinder and the bearing housing, and appropriate gaps should be left in the bolts that fix the cylinder, thereby creating a complete sliding pin system that ensures both free expansion of the cylinder and maintenance of the unit’s center position. 22. What are the advantages and disadvantages of on-load starting using the main steam valve and starting using the control valve? During main steam valve run-up, the steam valves are fully opened during startup; the rotational speed is controlled by the main steam valve. Once the speed reaches a certain value or a small load is applied, the control shifts to the governing valves. With this starting method, the steam turbine receives steam from all around its circumference. Apart from the uniform temperature distribution along the circumference, the enthalpy drop across all nozzles is very small. The relatively high steam temperature at the regulating stage is its most notable advantage. The downside is that it may cause erosion of the main steam valve, leading to improper closure of the same. In modern units that use main steam valve stroking for startup, a pre-opening valve located beneath the main steam valve seat is generally used to control steam admission; this prevents direct erosion of the main steam valve. Throttle surge operation involves opening the main steam valve fully at startup, with the steam flow entering the turbine being controlled by the throttle valve. This method typically involves partial steam injection, resulting in uneven heating of the cylinder and large temperature differences across different parts ； However, there is no need for switching between the high-pressure main steam valve and the high-pressure control valve, making it easy to operate. Initially, single-valve control is applied during the barring-in process of units using valve-controlled barring-in, ensuring that the steam turbine continues to receive steam on its full circumference; this reduces the temperature difference between various parts of the cylinder. 23. What are the aspects of turbine life management? Answer: To make better use of turbines, it is necessary to carry out planned management of their lifespan. Turbine lifespan management involves two aspects: (1) Formulating a clear and practical plan for the turbine’s operational life over its entire service period, that is, determining a scheme for allocating the turbine’s lifespan by specifying in advance the types of startups, the number of starts and stops, changes in operating conditions, as well as the number of load shedding events throughout its service life. (2) Based on the life distribution scheme, the optimal starting procedures and operation plans under varying conditions for starting and stopping the turbine are developed, ensuring that the turbine starts as quickly as possible while maintaining economic efficiency, without exceeding the allowable limits on life wear. 24. How can one distinguish between critical resonance, oil whip, and clearance oscillation on-site based on test results? Answer: These three types of vibration can be distinguished based on the measurement results of speed, vibration frequency, and amplitude. At critical resonance, its vibration frequency matches the frequency corresponding to the then rotational speed; moreover, after the rotational speed exceeds the critical speed, the vibrations decrease rapidly. Oil whip typically occurs during the speed-up process; its resonant frequency is equal to half of the frequency corresponding to the current rotational speed (approximately the rotor’s first critical speed). As the rotational speed increases, the vibration frequency remains unchanged, and the amplitude does not decrease. Gap oscillation generally occurs during the loading process. It occurs when the load reaches a certain value and disappears as the load decreases; its vibration frequency is also close to the frequency corresponding to the rotor’s first critical speed. 25. Where does the maximum stress occur in the rotors of the N125 and N200 units during startup? What types of (tensile, compressive) thermal stresses act on the inner and outer walls of the cylinder during startup? Where are the high thermal stress values? What are the main factors affecting thermal stress? At startup, the minimum stress in the N125 and N200 rotors occurs at the elastic grooves on the outer surfaces of the high and medium pressure rotors (front shaft seals). During startup, the inner wall is subjected to compressive stress while the outer wall is subjected to tensile stress; the stress on the inner wall is twice that on the outer wall. The main factor affecting thermal stress is the temperature difference, which depends on the rate of temperature rise and the amount of temperature increase of the steam. 26. What are the measures for blade frequency modulation? What is the basis? (1) Add welds at the junction of the girth ring, lacing, and blade ； (2) Radial hole at the leaf tip ； (3) Grind the leaf root contact surface to improve connection stiffness ； (4) Change the number of stepped blades ； (5) Install girders or strapping, or change their dimensions. These frequency tuning measures are based on the principle that changing the mass and stiffness of the blade can alter its natural vibration frequency, thereby detuning it from the excitation force frequency. When the mass decreases and the stiffness increases, the natural frequency increases. 27. How many common control methods are there for steam turbines? What are their respective features? There are three common control methods for steam turbines. They are: nozzle regulation, throttling regulation, and sliding pressure regulation. The characteristic of nozzle regulation is that it achieves high efficiency at partial load, but not the highest efficiency at full load. Moreover, under varying operating conditions, the temperature of the high-pressure components (located after the regulation stage) changes significantly, which can lead to substantial thermal stresses in these components, resulting in poor load adaptability. The throttle regulates lower efficiency at part load, but the temperature changes across various stages remain relatively stable under varying operating conditions. Sliding pressure regulation eliminates throttling losses, thus achieving the highest efficiency within the turbine; however, as the ideal enthalpy drop decreases at low loads, the cycle efficiency drops, so the economic efficiency of the unit is not necessarily good. Sliding pressure regulation results in the smallest temperature changes at all stages under variable operating conditions. This is its prominent advantage. 29. What is the function of the turbine slip pin system? What type of support is generally used for the high-pressure cylinder in high-parameter units, and why? Its function is to guide the cylinder to expand in the specified direction when heated, thereby ensuring that the center of the cylinder and the bearing housing (i.e., the center of the rotor) are on the same straight line. High-parameter high-pressure cylinders generally use upper cat claw supports, as the cat claws of such cylinders are relatively thick. With upper cat claw supports, the load-bearing surface becomes the midline of the cylinder; this allows the height of the cylinder’s center line to remain consistent with the height of the bearing housing’s center line when the cylinder is heated. 30. Try to draw a typical coasting curve and provide a brief analysis; what is the purpose of this curve? The typical rotor coasting curve is shown in the figure. The coasting curve can be divided into three stages: (1) In section AB, the speed decreases rapidly, as the blower friction loss is proportional to the cube of the speed. (2) The speed in section BC decreases slowly; at this point the speed is already low, and the frictional losses due to blowing air are relatively small. The main energy consumption occurs due to the mechanical resistance of the main oil pump and bearings. (3) The CD speed drops rapidly; at this point the oil film has been broken, resulting in high resistance. Under normal circumstances, if the vacuum level decreases in a regular manner, the rotor’s coasting curve should not change; therefore, this curve can be used to identify certain faults. For example, if the coasting time decreases sharply, it may indicate wear of the bearing shells or friction between the moving and stationary components ； If the idle time increases, it may be due to poor valve sealing or faulty valves in the extraction pipeline. 31. What are the main factors that affect the dynamic characteristics of the control system? How do they have an impact? Regarding the object under consideration, two indicators are used to reflect its impact: one is the rotor rise time constant Ta. The smaller Ta is, the faster the acceleration when the load is removed, the greater the overshoot, and the less stable the dynamics become ； The second is the intermediate volume time constant TV; the larger TV is, the worse the dynamic stability. From the perspective of the control system, three indicators are used to reflect its impact: the first is the speed variation rate δ; the larger δ is, the better the dynamic stability (but a high value of δ results in a large increase in rotational speed) ； The second is the time constant Tm of the hydraulic actuator; the larger Tm is, the worse the dynamic stability ； Third is the delay rate ε; the larger ε, the worse the dynamic stability. 32. Describe the main methods for eliminating oil film oscillations What is its main starting point? Main measures to eliminate oil film oscillation: (1) Increase the bearing specific pressure. (Such as reducing the width of the bearing surface of the shaft bearings.) (2) Reducing the viscosity of the lubricating oil (by increasing the oil temperature). (3) Using shaft bearings with good stability (such as oval-shaped or tilting bearings). The main approach is to increase the eccentricity of the shaft journal (x=e/δ). 33. Why is the back arc at the top of the final stage blades in condensing steam turbines often eroded? What measures should be taken? The last stage of a condensing steam turbine is the stage with the highest steam humidity; the velocity of the condensed water droplets is low. As can be seen from the exit velocity triangle, these water droplets strike the back arc of the inlet edge of the moving blades, wetting it. Also, due to centrifugal force, water droplets are flung toward the top of the leaf. Therefore, the erosion is most severe at the back arc of the top of the final-stage moving blade. Measures: ① Employ a dehumidification device; ② Improve the erosion resistance of the inlet edge of the moving blades. 34. How is the axial thrust generated in an impulse multi-stage steam turbine? What are the hazards of excessive axial thrust? What measures can be taken to balance the axial thrust? Is it possible to balance the axial thrust to zero or a very low value in order to eliminate the thrust disc? Why? Causes of axial thrust: ① Change in the axial velocity of the steam flow, ② Pressure difference before and after the impeller and blades, ③ Action of steam pressure on the rotor shoulders. Excessive axial thrust can cause the thrust bearings to burn out and result in shaft misalignment. Balance measures: ① Provide balance holes on the impeller, ② Arrange the cylinders opposite to each other, ③ Install balance pistons, ④ Install thrust bearings. No. It is necessary to prevent the rotor from becoming out of alignment when the axial thrust changes. 35. What are the advantages of cold-state sliding parameter startup using pressure method compared to startup based on rated parameters? (1) The boiler can be started once its steam parameters reach a certain value, which reduces the startup time. (2) The temperature difference between the steam and the metal is small, resulting in low thermal stress; moreover, due to the high steam flow rate, the metal temperature rises rapidly. (3) There is no energy loss resulting from bypass temperature and pressure reduction. (4) After being under load, steam can be supplied throughout the entire circumference, ensuring uniform heating of the turbine. (5) Since the parameters are low but the flow rate is high during startup, the heat generated by the aerodynamic friction losses in the low-pressure section can be easily dissipated, preventing the exhaust temperature from rising too high. 36. Describe the causes, consequences of cylinder crown deformation, and the measures to be taken. The deformation of the cylinder crown is caused by the temperature difference between the upper and lower cylinders. The specific reasons are as follows: (1) The lower cylinder loses a large amount of heat due to the presence of steam extraction and drain pipes ； (2) The hot steam inside the cylinder flows upward and condenses, releasing heat ； (3) The insulation layer of the lower cylinder tends to fall off. As a result, when the deformation is large, the dynamic and static radial clearances may disappear, leading to collisions. Measures to control deformation include strictly controlling the temperature rise rate during startup, fully opening the water drainage valves, and making every effort to improve the maintenance of the protective layer on the lower cylinder. 37. A power plant consists of only two units, Unit A and Unit B. The speed variation rate of Unit A is δA = 5%, while that of Unit B is δB = 4%. The grid frequency is 50 Hz, and both units are operating at their rated load of 200 MW. Question: (1) If the external load decreases by 90 MW, what will be the grid frequency? (2) If the external total load remains unchanged at 310MW, and it is desired for Unit A to operate at full load while restoring the grid frequency to 50HZ, where should the static characteristics of Units A and B be shifted? (1) Suppose the grid frequency increases by Δf, causing the speed of the turbine to increase by Δn revolutions per minute; as a result, machine A reduces its load and machine B also reduces its load. Therefore, f = 0.5 Hz, meaning the grid frequency is 50.5 Hz. (2) The static characteristics of machine A remain unchanged, while the load on machine B is (310 – 200) = 110 MW. Hence, the static characteristics of machine B need to be adjusted to 38. Principle of operation of sliding bearings. What factors affect the formation of the oil film and its thickness? Since the diameter of the journal is definitely smaller than that of the bearing shell, the journal is supported within the bearing shell by a wedge-shaped gap. When the journal rotates and lubricating oil is added, due to the rotation of the journal and the viscosity of the oil, the oil flows from the wider area to the narrower area, forming an oil wedge that generates a certain amount of oil pressure. When this oil pressure is sufficient to support the load on the journal, the journal and the bearing shell are separated by an oil film, resulting in liquid lubrication (also known as wet friction). The angle of the oil wedge, the viscosity of the oil, and the speed of the shaft journal all affect the formation and thickness of the oil film. 39. What are state parameters? Answer: Physical quantities that characterize the state of a working fluid are called state parameters. The state parameters of a working fluid include pressure, temperature, specific volume, enthalpy, entropy, internal energy, etc. Among them, pressure, temperature, and specific volume are the basic state parameters of the working fluid. 40. How should cavitation in the speed-regulated feedwater pump be addressed? Answer: The cavitation in the speed-regulated feed water pump should be addressed as follows: (1) If there is mild cavitation in the feed water pump, the cause should be identified immediately and eliminated promptly. ⑵If cavitation is severe, the standby pump should be started immediately, and the feed water pump causing cavitation should be shut down. ⑶Open the feed pump recirculation valve. 41. What is the sequence of low oil pressure interlocks for each oil pump in the lubricating oil system of a steam turbine generator set? Answer: The low-voltage interlock sequence for the oil pump is that once the lubricating oil pressure drops to a certain level, the AC lubricating oil pump is activated ； Finally, engage the emergency oil pump (DC lubricating oil pump). 42. Why is it specified that the water pressure in the generator stator must not be higher than the hydrogen pressure? Answer: Because if the water pressure in the generator stator is higher than the hydrogen pressure, any leakage in the stator water system within the generator will allow water to enter the generator, resulting in grounding of the generator’s stator and posing a threat to the generator’s safety. Therefore, the water pressure in the generator stator should be kept below a certain value relative to the hydrogen pressure, and adjustments should be made immediately if such limits are exceeded. 43. What should be monitored when the heater is in operation? Answer: When operating a heater, it is necessary to monitor the following parameters: (1) the water parameters at the inlet and outlet of the heater; (2) the pressure and temperature of the heating steam, as well as the flow rate of the water being heated. ⑶Height of the drain water level on the steam side of the heater. ⑷End differential of the heater. 44. Explain the specific contents of the “three no-lets-go” principle in dealing with all accidents. Answer: The specific details of the “three no-lets-go” principle are: (1) Do not let go until the cause of the accident is clarified ； ⑵ Those responsible for accidents and those who should receive education are not let off without being educated. ⑶ No lapse in taking preventive measures will be tolerated. 45. What are the main technical parameters and economic indicators that affect the economic operation of steam turbine generator sets? Answer: The main technical parameters and economic indicators that affect the economic operation of steam turbine generators include steam pressure, steam temperature, vacuum level, feedwater temperature, steam consumption rate, power consumption of circulation water pumps, utilization rate of high-pressure heating, condenser terminal difference, supercooling degree of condensate water, and thermal efficiency of the turbine. 46. What is the circulation ratio of oil? What are the hazards of having a circulation ratio that is too high or too low? The oil circulation ratio is defined as the ratio of the hourly oil output of the main oil pump to the total volume of oil in the tank; it should generally be less than 10. An excessively high cycle rate reduces the service life of the oil ； If the tank’s capacity is insufficient, the oil stays in the tank for a shorter period of time, leaving no time to remove the water and air from it, which results in a rapid deterioration of the oil quality. 47. How to control and reduce thermal stress when starting a steam turbine using its rated parameters? Answer: When starting the turbine according to the rated parameters, at the moment when the rotor is impulsed, live steam at a temperature close to the rated value enters the cylinder whose metal temperature is relatively low. Similar to the initial stage of warming up new steam pipes, the steam undergoes intense condensation and releases heat, causing the temperature of the inner walls of the cylinders and the outer surface of the rotor to rise sharply. Excessive temperature rise can easily generate significant thermal stress; therefore, when performing a cold start under rated conditions, measures such as limiting the steam flow rate and prolonging the warm-up and load-application periods must be taken to control the rate at which the metal heats up. Reduce uneven heating. To avoid excessive thermal stress and thermal deformation. 48. Among the conditions for turbine barring-in, why is it stipulated that a certain level of vacuum must be maintained? Answer: A certain level of vacuum must be maintained before starting the steam turbine; typically, it is around 60 kPa. If the vacuum is too low, more live steam is required to rotate the rotor. The excessive amount of exhaust steam suddenly discharged into the condenser causes a significant and rapid rise in the pressure on the steam side of the condenser. This may result in positive pressure forming on the steam side, leading to damage to the safety membrane designed to vent to the atmosphere. Additionally, this situation can also cause considerable thermal shock to the cylinder and rotor. When using an impulse rotor, the vacuum level should not be too high. A high vacuum level not only prolongs the time required to establish vacuum, but also results in a lower heat release rate due to the reduced amount of steam passing through the turbine; this slows down the heating of the turbine and makes it difficult to stabilize its speed, thereby extending the startup time. 49. What are the three stages in the formation process of water vapor at constant pressure? What are the names of the heats absorbed in each stage? Answer: (1) The constant-pressure preheating process of unsaturated water: that is, heating water at any temperature to become saturated water. The heat added is called liquid heat or preheating heat. (2) The constant-pressure and constant-temperature vaporization process of saturated water: that is, the transformation of saturated water into dry saturated steam upon heating; the heat added in this process is called the latent heat of vaporization. (3) Superheating process of steam: that is, heating dry saturated steam to superheated steam at any temperature. The heat added is called superheat heat. 50. Describe the characteristics of hydrostatic pressure The direction of hydrostatic pressure is perpendicular to its acting surface and points toward it. The hydrostatic pressure in a static liquid is equal in all directions at any given point. 51. What is the impact of super-temperature and superheating of metals on the lifespan of boiler steel tubes? Over-temperature conditions can be categorized as short-term or long-term; in either case, over-temperature and overheating will reduce the lifespan of the boiler steel tubes. Short-term severe overheating or long-term overheating will exacerbate the damage to boiler steel tubes. 52. What is a distributed control system? It is a system that uses a microprocessor as its core, and employs data communication and CRT display technologies to enable centralized operation and management as well as decentralized control of the production process; it is a product of the integration of computer technology, control technology, data communication technology, and graphic display technology. 53. Why does the saturation pressure increase as the saturation temperature rises? Because the higher the temperature, the greater the average kinetic energy of the molecules, and the higher the molecules can rise out of the water, which increases the density of molecules on the vapor side. At the same time, as the temperature rises, the average speed of steam molecules also increases, which leads to more frequent collisions between these molecules and the container walls, thereby increasing the pressure. Therefore, the saturation pressure increases as the saturation temperature rises. 54. Why does the use of a regenerative cycle improve thermal efficiency? In a regenerative cycle, a portion of the steam that has done work and is extracted from the turbine is sent to a regenerative heater to heat the condensate water coming from the condenser. The temperature of the condensate water (or feedwater) is increased; this allows the boiler to absorb less heat from fuel combustion, thereby saving fuel. Furthermore, since the steam from the extraction section does not condense in the condenser, it reduces the heat loss carried away by the cooling water. Therefore, using a regenerative cycle can improve thermal efficiency. 55. What is a distributed control system? It is a system that uses a microprocessor as its core, and employs data communication and CRT display technologies to enable centralized operation and management as well as decentralized control of the production process; it is a product of the integration of computer technology, control technology, data communication technology, and graphic display technology. 56. What are the hazards of vaporization faults in water pumps? At worst, it can reduce water supply pressure and flow rate ； In severe cases, this can lead to pipeline shock and vibration, axial movement of the pump shaft, and friction between the moving and stationary parts, resulting in a disruption in water supply. 57. What are the physical properties of metal materials? The physical properties of metal materials include the density, specific heat, melting point, electrical conductivity, magnetism, thermal conductivity, thermal expansion, oxidation resistance, and wear resistance of metals. 58. Describe the characteristics of hydrostatic pressure The direction of hydrostatic pressure is perpendicular to its acting surface and points toward it. The hydrostatic pressure in a static liquid is equal in all directions at any given point. 59. Why is a certain level of vacuum specified as a condition for starting a steam turbine? Answer: A certain level of vacuum must be maintained before starting the steam turbine; typically, it is around 60 kPa. If the vacuum is too low, more live steam is required to rotate the rotor. The excessive amount of exhaust steam suddenly discharged into the condenser causes a significant and rapid rise in the pressure on the steam side of the condenser. This may result in positive pressure forming on the steam side, leading to damage to the safety membrane designed to vent to the atmosphere. Additionally, this situation can also cause considerable thermal shock to the cylinder and rotor. When using an impulse rotor, the vacuum level should not be too high. A high vacuum level not only prolongs the time required to establish vacuum, but also results in a lower heat release rate due to the reduced amount of steam passing through the turbine; this slows down the heating of the turbine and makes it difficult to stabilize its speed, thereby extending the startup time. 60. Among the conditions for turbine barring-in, why is it stipulated that a certain level of vacuum must be maintained? Answer: A certain level of vacuum must be maintained before starting the steam turbine; typically, it is around 60 kPa. If the vacuum is too low, more live steam is required to rotate the rotor. The excessive amount of exhaust steam suddenly discharged into the condenser causes a significant and rapid rise in the pressure on the steam side of the condenser. This may result in positive pressure forming on the steam side, leading to damage to the safety membrane designed to vent to the atmosphere. Additionally, this situation can also cause considerable thermal shock to the cylinder and rotor. When using an impulse rotor, the vacuum level should not be too high. A high vacuum level not only prolongs the time required to establish vacuum, but also results in a lower heat release rate due to the reduced amount of steam passing through the turbine; this slows down the heating of the turbine and makes it difficult to stabilize its speed, thereby extending the startup time. 61. What are the hazards of vaporization faults in water pumps? Answer: Its harm, at the least, results in a decrease in water supply pressure and flow rate ； In severe cases, this can lead to pipeline shock and vibration, axial movement of the pump shaft, and friction between the moving and stationary parts, resulting in a disruption in water supply. 62. Briefly describe the working principle of the oil injector in the turbine oil system. Answer: When the pressure oil is ejected at high speed through the nozzle, the suction effect of the free jet is utilized to draw the oil from the tank, passing through the filter screen into the diffuser tube. After slowing down and increasing pressure in the diffuser tube, the oil is discharged from it at a certain pressure. 63. What are some ways to reduce heat loss? Answer: The method to reduce heat dissipation losses is to increase the thickness of the insulation layer to raise the thermal resistance to heat conduction ； Try to reduce the overall heat transfer coefficient between the outer surface of the equipment and the air. 64. What is the relationship between over-temperature and overheating in metals? Answer: Over-temperature and overheating of metals are conceptually the same; the difference is that over-temperature refers to the situation in which, during operation, various factors cause the temperature of the metal tube wall to exceed its allowable level, while overheating occurs as a result of over-temperature, leading to varying degrees of damage to the metal. In other words, over-temperature is the cause of overheating, and overheating is the result of over-temperature. 65. What are the factors that affect heat transfer? Answer: As can be seen from the heat transfer equation Q = KFΔt, the amount of heat transferred is determined by three factors. That is: the average temperature difference △t for heat transfer between cold and hot fluids, the heat exchange area F, and the heat transfer coefficient K. 66. How to analyze the pressure in the monitoring section during operation? Answer: After installation or major repairs, it is necessary to conduct actual measurements of the turbine’s flow path under normal operating conditions, in order to determine the relationship between the unit load, main steam flow rate, and the pressure in the monitoring section. This information can then be used as a standard for monitoring operations on a regular basis. Except for the last stage and the second-to-last stage of the turbine, the pressure of the control stages and the extraction pressures at each stage vary proportionally to the main steam flow rate. Based on this relationship, by monitoring the regulation stage pressure and the extraction pressures at various stages during operation, it is possible to effectively oversee whether the flow path is functioning properly. At the same load (main steam flow rate), an increase in the pressure in the monitored section indicates that the flow area downstream of that section has decreased, or that the high-pressure heater is shut down and the extraction steam volume has reduced. In most cases, the reduced flow area is caused by fouling on the blades; sometimes, pressure increases in the monitoring section due to blade breakage or blockages by mechanical debris. If the extraction pressures of the regulating stage and stages I and II of the high-pressure cylinder increase simultaneously, it may be due to obstruction in the opening of the medium-pressure control valve or the shutdown of extraction from one of the stages of the medium-pressure cylinder. When monitoring the pressure in each section, it is necessary to check not only whether the absolute value of this pressure exceeds the specified limit, but also whether the pressure difference between different sections exceeds the specified limit. If the pressure difference in a certain stage is too high, it may cause damage to equipment such as blades. 67. What are the main factors affecting the expansion difference of a steam turbine? Answer: The main factors affecting the expansion difference of a turbine are as follows: (1) Whether the turbine’s slip system is unobstructed ； (2) Control the rate of steam temperature rise (fall) and flow rate changes ； (3) Influence of shaft seal steam supply temperature ； (4) Effect of cylinder flange and bolt heating devices ； (5) Influence of condenser vacuum ； The impact of cylinder insulation and water drainage. 68. What is the essence of the first law of thermodynamics? What problem does it illustrate? Answer: The essence of the first law of thermodynamics is a specific application in thermodynamics of the law of conservation and transformation of energy. It explains the possibility of mutual conversion between thermal energy and mechanical energy, as well as their quantitative relationship. 69. What is the function of a turbine nozzle? Answer: The function of a turbine nozzle is to convert the thermal energy of steam into kinetic energy; in other words, it causes the steam to expand and lose pressure, increasing its flow velocity so that it can be ejected in a certain direction to drive the rotor blades and generate power. 70. What are the causes of turbine blade damage? Answer: The main causes of damage to turbine blades are 1) mechanical damage such as the entry of foreign objects into the turbine or the detachment of internal fixed components, 2) water impact damage, 3) corrosion and rusting of the blades, 4) water erosion damage, 5) defects existing in the blades themselves, 6) improper operation and maintenance such as operating outside the rated frequency, operating under overload conditions, or having inadequate steam inlet parameters. 71. What aspects should be paid attention to in order to improve the operational economy of units? Answer: (1) Maintain the rated initial steam parameters ； (2) Maintain rated reheat steam parameters ； (3) Maintain the most favorable vacuum ； (4) Maintain the minimum condensate subcooling ； (5) Make full use of heating equipment to raise the feedwater temperature ； (6) Pay attention to reducing the plant power consumption rate ； (7) Reduce the pressure loss of new steam ； (8) Maintain optimal efficiency of the turbine ； (9) Determine a reasonable mode of operation ； (10) Pay attention to the economic distribution of the turbine load. 72. What should be monitored during the operation of a heater? Answer: When operating the heater, it is necessary to monitor the following parameters: (1) the water values entering and leaving the heater; (2) the pressure and temperature of the heating steam, as well as the flow rate of the water being heated. ⑶Height of the drain water level on the steam side of the heater. ⑷End differential of the heater. 73. Briefly answer: What could be the possible causes of water or cold steam entering the turbine after it is shut down? Answer: The reasons for water or cold steam entering the turbine stem from ① the boiler and the main steam system ； ②Reheat steam system ； ③Steam extraction system ； ④Shaft seal system ； ⑤condenser ； ⑥The steam turbine’s own drain system. 74. What is a proper startup method for a steam turbine? Answer: The startup of a turbine is restricted by factors such as thermal stress, thermal deformation, expansion, and vibration. The so-called reasonable startup method involves finding an appropriate heating approach, and selecting suitable startup parameters (steam parameters, rising rate, warm-up time, initial load rate) based on the actual condition of the equipment before startup. This ensures that thermal stress, thermal deformation, expansion, and vibration remain within acceptable limits during the startup process, allowing the metal temperature to rise evenly to the operating temperature as quickly as possible. Reduce startup consumption and increase the mobility of the unit. 75. What is the function of a turbine nozzle? Answer: The function of a turbine nozzle is to convert the thermal energy of steam into kinetic energy; in other words, it causes the steam to expand and lose pressure, increasing its flow velocity so that it can be ejected in a certain direction to drive the blades and generate power. 76. What components make up the turbine itself? Answer: The turbine itself consists of two main parts: the stationary part and the rotating part. The stationary parts include cylinders, diaphragms, nozzles, bearings, etc ； The rotating parts include shafts, impellers, blades, couplings, etc. There are also steam seals. 77. What are the causes of cavitation in feedwater pumps? Answer: (1) The pressure inside the deaerator decreases ； (2) Low deaerator water level ； (3) The feed water pump operates for extended periods at low flow rates or under no-load conditions ； (4) The feed pump recirculation valve closes accidentally or is opened too slightly, causing the feed pump to operate in a sealed condition. 78. What are the disadvantages of an elevated condenser water level? Answer: An elevated condenser water level causes the condensate to become supercooled. It affects the economic operation of the condenser. If the water level is too high and submerges the copper tubes (at the bottom), it will reduce the total cooling area of the condenser; in severe cases, it will submerge the air tubes, causing the pump to draw in water and resulting in a decrease in the vacuum level of the condenser. 1. What parameters should be monitored during the operation of a heater? Answer: The following parameters need to be monitored during heater operation: ① The water flow rate in and out of the heater ； ②Pressure and temperature of the heating steam, as well as the flow rate of the water being heated ； ③Height of the heater’s water level at the steam trap level ； ④End differential of the heater. 79. What equipment should be checked if the oil level in the main fuel tank drops during operation? Answer: The following equipment should be checked: ① Check whether the oil level in the oil purifier has risen ； ②Does the oil purifier’s automatic water pump have water? ； ③Has the oil level in the seal oil tank increased? ； ④Is oil being supplied to the generator? ； ⑤Are there any leaks in the pipes, valves, and other components of the system? ； ⑥Is the oil cooler leaking? 80. What conditions must be met before a load rejection test? Answer: The following conditions must be met: (1) The turbine generator set has undergone 72 hours of trial operation with all its components performing well ； (2) The control system operates properly under no-load and full-load conditions, with the speed variation rate and lag rate meeting the specified requirements ； (3) The closing times of the automatic main steam valve and control valve meet the requirements; the tightness tests have passed; the interlock device for the extraction steam check valve functions properly, ensuring rapid and secure closure ； (4) After the overspeed test, the emergency safety device operated normally, and the manual emergency safety device functioned well ； (5) The various electrical and boiler equipment have been inspected and are in good condition; the main and reheat steam safety valves have been adjusted to operate reliably ； (6) Verify that the interlock protection devices related to load shedding have been activated, and deactivate all unnecessary interlocks ； (7) Various tachometers have passed inspection ； (8) Obtain consent from the power grid dispatching authority. 81. How to determine if an electric motor is operating with one phase disconnected? Answer: (1) If the motor and the equipment it drives were originally at rest, they cannot rotate ； If the motor was originally in operation, its speed will decrease. (2) When operating in two-phase mode, the motor emits abnormal noises. (3) If the ammeter is connected to the open-circuited phase, the current reading will be “0”; otherwise, the ammeter reading will increase significantly. (4) The temperature of the motor housing rises significantly. (5) The flow rate and pressure of the driven auxiliary machine decrease. 82. In automatic mode operated by the operator, what do the DEH target load commands represent when the power circuit is activated or deactivated? Answer: Once the power circuit is activated, the power feedback loop in the DEH control system comes online; at this point, the DEH target load command indicates the power level that the operator wants to achieve. After the power circuit is disconnected, the power feedback loop in the DEH control system is severed; at this point, the DEH target load command actually represents the valve opening degree that the operator intends to achieve. 83. In what situations is it necessary to break the vacuum for an emergency shutdown? Answer: An emergency shutdown by breaking the vacuum is required in the following situations: (1) The turbine speeds up to 3330 rpm while the emergency shutdown device does not activate. (2) The unit experiences severe vibration or there is obvious friction inside it. (3) Water hammer occurs in the turbine. (4) Sparks are emerging from the shaft seal. (5) Oil starvation or smoking of the bearing bush. (6) The lubricating oil pressure drops to the shutdown threshold, and starting the backup pump is ineffective. (7) Axial displacement to trip value. (8) The generator or exciter is smoking or on fire. (9) In the event of an explosion in the generator hydrogen system. (10) The turbine oil system catches fire and cannot be extinguished quickly. (11) By reducing the idling time, other conditions that lead to damage to turbine equipment can be minimized. 84. What is the starting method for the medium-pressure cylinder? What are the advantages? Answer: The starting method for the intermediate-pressure cylinder is to pre-heat the high-pressure cylinder during the startup of large intermediate-reheat units, but no steam is supplied to the high-pressure cylinder at the beginning of startup. The unit is started up by steam supplied to the intermediate-pressure cylinder; once it reaches a certain load, it switches to the normal mode of steam supply from both the high-pressure and intermediate-pressure cylinders. Up to the startup method with the unit at full load. The startup of the medium-pressure cylinder has the following advantages: (1) It reduces the startup time ； (2) Even cylinder heating ； (3) Crossing the brittle transition temperature in advance ； (4) Good adaptability to special operating conditions ； (5) Suppress the increase in temperature at the rear of the low-pressure cylinder. 85. Why is an air release valve installed on boilers? Answer: When water is introduced into the boiler, the space occupied by air in the water volume of the heating surfaces is gradually replaced by water. Driven by the incoming water, the air moves upward and accumulates there, occupying less and less space; its volume is compressed, resulting in a pressure higher than atmospheric pressure. Eventually, this air is discharged into the atmosphere through an air valve. It prevents the adverse effects of air retention on the quality of the working fluid and on the boiler tube walls due to heating. When the boiler is shut down, the air valve is opened before the pressure is reduced to zero in order to prevent a vacuum from forming inside the boiler’s pressure-bearing components due to the cooling of the working fluid and resulting volume contraction ； The pressure of the atmosphere can be used to release the boiler water. 86. What are the main technical parameters and economic indicators that affect the economic operation of steam turbine generator sets? Answer: The main technical parameters and economic indicators that affect the economic operation of steam turbine generators include steam pressure, steam temperature, vacuum level, feedwater temperature, steam consumption rate, power consumption of circulation water pumps, utilization rate of high-pressure heating, condenser terminal difference, supercooling degree of condensate water, and thermal efficiency of the turbine. 87. What components make up the steam turbine proper? Answer: The steam turbine proper consists of two main parts: stationary and rotating components. The stationary parts include cylinders, partitions, nozzles, and bearings, etc.; the rotating parts include shafts, impellers, blades, and couplings, etc. In addition, there’s also steam sealing. 88. The tasks of the turbine control system. Answer: The task of the turbine control system is to maintain balance between the turbine’s output power and the external load. That is, when the external load changes or the grid frequency (or the speed of the turbine units) changes, the control system of the turbine adjusts its power accordingly so as to match the external load, establish a new balance, and keep the speed deviation within specified limits. Additionally, it maintains the stable operation of the turbine when the external load is matched to the turbine’s output power. When an external fault (in the power grid) causes the turbo-generator to lose its load, the control system reduces the throttle valve opening of the turbine, ensuring that the increase in the turbine’s speed remains below the \"critical safety device activation value\", thus keeping the turbine running at no load. 89. What are the main reasons for supercooling of condensate? Answer: The main reasons for supercooling of condensate are: (1) Air accumulates on the steam side of the condenser. (2) The condensate water level is too high during operation. (3) The cooling water pipes of the condenser are poorly arranged or too densely packed. (4) Excessive circulating water volume, resulting in too low water level. 90. What is the function of a deaerator? Answer: The function of the deaerator is to remove oxygen and other gases from the boiler feedwater, thereby ensuring the quality of the feedwater. It also acts as a mixed heater in the heat recovery system, serving to heat the feedwater. 91. What is the function of a turbine nozzle? Answer: The function of a turbine nozzle is to convert the thermal energy of steam into kinetic energy; in other words, it causes the steam to expand and lose pressure, increasing its flow velocity so that it can be ejected in a certain direction to drive the rotor blades and generate power. 92. What are the causes of cavitation in feed water pumps? Answer: (1) The pressure inside the deaerator decreases. ⑵The water level in the deaeration tank is too low. ⑶The feed water pump operates for extended periods at low flow rates or under no-load conditions. ⑷If the feed pump recirculation valve closes accidentally or is opened too slightly, the feed pump will operate in a sealed condition. 93. What are the operating characteristics of the feed water pump? Answer: Since the feedwater temperature is generally quite high (the saturated temperature at the pressure of the deaerator), vaporization of the water occurs easily at the inlet of the feedwater pump, resulting in cavitation and thus a disruption in the water supply. Therefore, the feed water pump is generally installed below the deaerator tank in order to increase the static pressure at the pump’s inlet, prevent vaporization, and ensure the proper operation of the pump. Additionally, large-parameter units are equipped with pre-pumps before the feed water supply, in order to increase the inlet pressure of the feed water pump and improve its operating conditions. 94. What is the main reason for the positive increase in the expansion difference during the coasting phase after the turbine is stopped? Answer: (1) After stopping, the control valves close, preventing steam from entering the flow path; the heat generated by friction due to rotor expansion cannot be carried away by steam, resulting in an increase in the rotor temperature. (2) Poisson effect: As the centrifugal force decreases, the rotor elongates axially, resulting in an increase in the expansion difference. 95. What are the methods to reduce flow losses in soda water systems? Answer: (1) Keep the valves in the soda water pipeline system fully open as much as possible, and minimize the use of unnecessary valves and throttling elements. (2) Reasonably select the pipe diameter and arrange the pipes. (3) Adopt appropriate technical measures to reduce local resistance. (4) Reduce eddy current losses. 96. What are the boundary conditions for solving the heat conduction differential equation? What are the different types of boundary conditions? Answer: 1) Geometric conditions: These describe the geometric shape and size of the objects involved in the process. 2) Physical conditions: These describe the physical properties of the system, including the values and characteristics of the system’s parameters. 3) Time condition: Describes the characteristics of the process over time, usually providing the material property parameters at the beginning of the process. 4) Boundary conditions: a) Temperature values at the boundaries; b) Heat flux density values at the boundaries; c) Heat transfer coefficient α between the object’s boundary and the surrounding medium, as well as the temperature t1 of the surrounding medium. (Four of these conditions are sufficient.) 97. What types of feedback signals does the DEH system receive? Answer: The DEH system receives three types of feedback signals: the turbine speed, the generator power, and the pressure after the first stage of the high-pressure and medium-pressure cylinders. 98. What are the various types of losses in pumps? What components do they consist of? Answer: (1) Mechanical losses: include friction losses due to bearings and shaft seals, as well as disk friction losses. (2) Volumetric losses: include leakage losses from sealing rings, leakage losses from balancing devices, inter-stage leakage losses, and shaft seal leakage losses. (III) Flow losses: include frictional resistance losses, vortex resistance losses, and shock losses. 99. Why cannot the throttling process be considered an isenthalpic process? Answer: The enthalpy value of the steam remains constant before and after throttling, but it cannot be said that the throttling process is isenthalpic, because at the throttling orifice the enthalpy value decreases. This decrease in enthalpy is used to increase the kinetic energy of the steam, thereby creating vortices and disturbances; the kinetic energy of these vortices and disturbances is then converted into thermal energy, which is absorbed by the steam again, allowing its enthalpy value to return to its value before throttling. 100. What are the heat losses of a boiler? Answer: (1) Heat loss due to flue gas exhaust ； (2) Heat loss due to incomplete chemical combustion ； (3) Heat loss due to incomplete mechanical combustion ； (4) Boiler heat loss ； (5) Physical heat loss of ash.