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I. Fill-in-the-blank questions 1. When the vacuum drops to zero during the rotor’s free rotation, steam supply to the shaft seal should be stopped immediately. It is not advisable to stop it too early nor too late; the reason is that stopping it too early will allow cold air to enter, causing the rotor shaft seal to cool down and resulting in an excessive expansion difference； Stopping too late will lead to an increased temperature difference between the upper and lower cylinders, uneven heating of the rotor, and as a result, bending of the main shaft and deformation of the cylinders. 2. The steam consumption rate refers to the amount of steam used per unit of electricity generated__, and its expression is d= . If the steam consumption rate d increases after the unit has been operating for a period of time, it indicates that the economic efficiency of the unit has deteriorated.___ 3. Common measures for balancing axial thrust include: 1) __Opposition of high and medium pressure cylinders___ ； 2) Low-pressure cylinder shunting ； 3) __Set the balance piston ； Install the thrust bearing. 4. The physical meaning of the optimal speed ratio is __axial exhaust, minimal residual velocity loss, and the highest peripheral efficiency (or highest internal efficiency). The optimal speed ratio expression for a pure impulse stage is (X1)OP=_（x1）op=cosα1/2. . 5. The optimal vacuum for the condenser refers to __ at power and tw! The vacuum level at which the net benefit resulting from increased vacuum is maximized, under certain conditions. 6. In multi-stage steam turbines, those losses that _directly affect the steam conditions are collectively referred to as internal losses, while others are called external losses. For example, the steam leakage loss from the shaft seal and the losses in the intermediate reheating circuits belong to __external losses and internal losses respectively. 7. Oil film oscillation generally occurs when the rotor speeds up to twice its first critical speed. The main approach to eliminating oil film oscillation is to increase the eccentricity; specific measures include increasing the pressure ratio of the bearings and reducing the viscosity of the lubricating oil. 8. The speed regulation system lag rate refers to the ratio of the difference between the maximum and minimum speeds determined by the static characteristics under the same load to the rated speed n0 ； . The presence of inertia causes the units operating in single-unit mode to experience spontaneous speed fluctuations ； Units operating in grid connection can experience spontaneous load fluctuations. 9. During hot start-up, steam should be supplied to the shaft seal first before vacuuming is applied; this is to prevent cold air from coming into contact with the metal, which could lead to rapid cooling and excessive local negative differential expansion. 10. The function of the static feedback in the speed control system is to stabilize the control system. The role of dynamic feedback is to increase the dynamic stability of the control system. 11. The two important technical parameters of an oil-driven motor are: ① Lift coefficient ； ② Hydraulic actuator time constant. The requirements for them are to ensure smooth opening of the valve under any circumstances and rapid closing of the valve, as well as to prevent overspeeding. 12. Impeller-type rotors are used in impulse steam turbines, and their structure can be divided into four types: monoblock type, assembled type, combined type, and welded type. High-pressure rotors of high-power steam turbines all use the monoblock type rotor. 13. Units with intermediate reheat must operate in a unitized mode. Compared to units operating in a master-tube configuration, the unitized operation mode presents two problems: 1) Mismatch between the flow rates of the turbine and the boiler ； 2) The dynamic response time of the machine and boiler does not match. 14. A closed-loop turbine automatic control system can be divided into four components: 1) the speed sensing mechanism ； 2) Transmission amplification mechanism ； 3) Valve train ； 4) Adjustment object. 15. The indicators for evaluating the dynamic quality of the control system are as follows: 1) Stability, which requires the ability to transition steadily from one state to another equilibrium state, with the number of oscillations being ≤ 3–5 times. 2) Overshoot, which requires that the maximum control speed remain within the specified range ； 3) Transition time: required to be no more than 5–50 seconds. 16. The concept of reaction degree is the ratio of the ideal enthalpy drop in the moving blades to the total stagnation enthalpy drop of the stage. To achieve a higher stage efficiency, the appropriate root reaction degree should be 3%–5%, so as to keep the root free from suction and leakage. 17. The quality of the operation status of condensing equipment is reflected in the following three aspects: 1) Whether an optimal vacuum is maintained inside the condenser ； 2) ___Is the subcooling of the condensate at its minimum? ； 3) ____Is the quality of the condensate water satisfactory? 18. The common control methods for steam turbines include: _____nozzle control, throttling control, and __throttled pressure control. 19. The maximum axial thrust of a condensing steam turbine occurs under ___maximum load ； The maximum axial thrust in a back-pressure turbine occurs at a certain load ___ in the middle range of loads ； Under variable conditions, the variation in axial thrust of reaction turbines is ___ smaller_ (larger or smaller) than that of impulse turbines. 20. If the rotor’s coasting time decreases sharply, it may be due to worn bearing shells or friction between the moving and stationary parts ； If the rotor coasting time increases, it may be due to a leaky valve in the new steam pipeline, allowing steam to leak into the turbine. 21. The quality of thrust bearing lubrication is indicated by the temperature of the thrust bearings; the thickness of the tungsten layer in these bearings should not exceed the minimum axial clearance in the flow-through area. This is done to prevent axial friction between the moving and stationary parts in the event of alloy melting. 22. Couplings are of three types: rigid couplings, semi-flexible couplings, and flexible couplings. The rotors of steam turbines and generators are generally connected using semi-flexible couplings. 23. The main factors affecting the dynamic characteristics of the control system are: ① Delay rate ； ② Rotor rise time constant ； ③ Intermediate volume time constant ； ④ Rate of speed change ； ⑤ Hydraulic actuator time constant. 24. The purpose of the balance holes on the impeller is: 1) To vent the steam that leaks past the partition, thereby reducing the air leakage loss caused by the partition ； 2) Balance the steam pressure on both sides of the impeller to reduce the axial thrust of the turbine. 25. The thermal expansion dead center of the steam turbine is located near the center of the exhaust port of the low-pressure cylinder; this is mainly because the low-pressure cylinder and the condenser connected to it are quite heavy and bulky, making it difficult for them to move together. 26. The “starting load point” for hot start refers to the load on the unit’s cold start curve that corresponds to the metal temperature of the inner upper cylinder wall before startup. 27. Shrouds are typically used in the high and medium pressure stages of turbines; their function is to increase rigidity, reduce bending stresses caused by steam flow, form a vapor seal at the tip of the blades, and minimize steam leakage. 28. The wear and degradation of a steam turbine mainly include creep wear resulting from long-term operation at high temperatures, as well as thermal fatigue wear caused by operations such as starting and stopping, and changes in load. 29. To address the power lag issue in the intermediate and low-pressure cylinders of units with intermediate reheating, methods such as dynamic over-adjustment of the high-pressure control valve, dynamic over-adjustment of the medium-pressure control valve, shutting down the high-pressure heater, and injecting water into the reheater can be employed. 30. Oil film oscillation occurs when the rotor speeds up to twice its first critical speed. The main approach to eliminating this phenomenon is to increase the eccentricity; specific measures include raising the pressure ratio of the bearings and reducing the viscosity of the lubricating oil.