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1. Why cannot the vacuum be destroyed immediately after shutting down the machine under normal conditions? If the vacuum is disrupted immediately after shutting down the machine under normal conditions, a large amount of cold air will enter the condenser, causing it and the low-pressure cylinder to cool down rapidly. This results in a significant \"cold shock,\" which can lead to rapid contraction of the copper tubes in the condenser; this may cause the joints between these tubes to loosen and lead to leaks. The thermal stress on the low-pressure cylinder and rotor increases, and this can sometimes also result in increased vibration in the machine. At the same time, breaking the vacuum at higher speeds allows air to enter the low-pressure cylinder, which exerts a significant braking effect on the rotor blades and causes heating, especially in the case of long blades; therefore, the vacuum should not be broken prematurely when there is no fault. 2. Why can breaking the vacuum cause the unit to stop quickly? When the unit breaks the vacuum, it causes the pressure on the exhaust side of the low-pressure cylinder to rise rapidly, thereby reducing the enthalpy drop of the unit; in other words, its power generation capacity decreases, which has a braking effect ； Secondly, when the vacuum is disrupted, the last-stage blades of the turbine are subjected to significant frictional forces and torsional stresses, causing the turbine’s speed to drop rapidly. In other words, it’s like applying a sudden brake, which reduces the time during which the unit operates without control, thereby decreasing the likelihood of severe damage to the equipment due to accidents such as static and dynamic friction, water impact, overspeed, or failures in the oil system. 3. Why is it necessary to disrupt the vacuum at around 300–400 r/min during normal shutdown? One reason is that, as mentioned above, high rotational speeds should be avoided when disrupting the vacuum in order to prevent damage to the equipment due to shocks. Secondly, as the speed of the turbine unit decreases, the oil film in the turbine bearings becomes unstable; to prevent rubbing between the rotating and stationary parts, it is necessary to stop the rotor as quickly as possible ； Thirdly, specifying the rotational speed that disrupts the vacuum facilitates accurate calculation of the turbine’s coasting time, providing a more precise indication of the tightness of the turbine valves as well as the presence of static or dynamic friction ； Fourth, stop the main engine as soon as possible without compromising its safety, engage the barring gear, shut down the shaft seals, and cut off all heat supply sources to the turbine, allowing it to enter a phase of natural cooling. What is the difference between an emergency shutdown due to a loss of vacuum in the turbine and one that does not involve a loss of vacuum? First, the conditions under which such emergency shutdowns occur are different for each case. In simple terms, the condition that triggers a vacuum breakdown emergency shutdown is when our turbine can no longer rotate; continuing to do so would cause damage to the equipment, so it must be stopped immediately. Therefore, we employ a vacuum-breaking emergency shutdown to reduce the turbine’s coasting time, allowing the turbine to stop as quickly as possible in order to minimize the impact of the fault. A shutdown due to a vacuum loss without damage refers to a failure in the turbine and its associated systems that prevents the unit from operating properly, but there is no significant safety threat to the main engine; in other words, the turbine can still rotate. Therefore, it is possible to reduce the load rapidly and then shut down the machine following the normal shutdown procedures for vacuum loss. Second: the two differ in their approach to handling the condenser vacuum. One is to forcibly break the vacuum, and the other is for the vacuum to dissipate naturally. Methods to break vacuum: 1. Shut off the main steam extraction valve and open the auxiliary air extraction valve, allowing the condenser to be directly connected to the atmosphere in order to break the vacuum ； 2. There is a reverse drainage mechanism for breaking the vacuum in the gas phase space of the surface cooler; activating it can also quickly reduce the vacuum level in the surface cooler ； Third: the results produced by the two are different. One causes significant damage to the equipment (stops operation by breaking the vacuum), while the other causes less damage (stops operation without breaking the vacuum). In the event of a minor fault that causes tripping, increase the steam supply to the shaft seal, open the make-up water valve to maintain the liquid level, and activate the turning gear system 30 seconds after the speed drops to zero ； The goal in both cases is to maintain the vacuum in the surface cooler in order to prevent the rotor from deforming. In an emergency, however, it is necessary to stop the rotor quickly to prevent the situation from worsening; therefore, breaking the vacuum is the only way to achieve a rapid stop. Fourth: The two result in different rotor coasting times. The time for vacuum breakdown during idle operation is short, while the time for no vacuum breakdown during idle operation is long. Finally: the two create different feelings among leaders. If a manager hears that their turbine has stopped running due to a vacuum loss, it will definitely cause them great concern and make them sweat. The latter is much better. I. The principle of rapid shutdown by disrupting the vacuum: By disrupting the vacuum, the pressure on the exhaust side of the low-pressure cylinder rises rapidly, which reduces the enthalpy drop of the turbine unit; in other words, its power generation capacity decreases, thereby serving as a braking effect. In other words, it’s like applying a sudden brake, which reduces the time during which the unit operates without control, thereby decreasing the likelihood of severe damage to the equipment due to accidents such as static and dynamic friction, water impact, overspeed, or failures in the oil system. Generally, in order to reduce the high torsional stresses and the heat generated by frictional blowdown that act on the last-stage blades of the low-pressure turbine when the vacuum is broken, it is safer to break the vacuum at speeds below 2000 revolutions per minute. II. Is there a speed limit when activating the vacuum break valve on the host? In emergency situations, after the turbine trips, the vacuum break valve is opened to destroy the vacuum in the condenser, thereby causing the turbine rotor to stop rotating more rapidly. This will allow cold air to enter the cylinder, increasing the blowdown friction loss; this in turn increases the braking torque on the rotor, allowing the rotor’s coasting time to be reduced and thus accelerating the shutdown process. However, the rotor is also subjected to a large braking force, which in severe cases can cause the final stage blades to break. This braking force is related to both the rotor speed and the gas density, or rather, the gas pressure; the higher the speed and the greater the pressure, the greater the braking force and the more heat is generated. To limit the stress on the blades, an upper limit on the rotation speed when the vacuum break valve is opened is established to ensure the safety of the blades. Shanghai’s steam turbine manufacturers require that the turbine speed remain below 400 rpm without any adverse effects; once the speed drops below 2000 rpm, the damage caused by a loss of vacuum to the turbine is minimal. III. In the event that a steam turbine generator set encounters any of the following conditions, it shall be shut down urgently and the boiler stopped, as the turbine will lose its vacuum. 1. When the protection against a turbine speed exceeding 3300 r/min fails to activate. 2. When the steam turbine generator set experiences sudden severe vibration exceeding 0.25 mm and the protection fails to activate. 3. When there are clear sounds of metal friction or impact inside the turbine. 4. The axial displacement reaches the limit value (+1.0mm or –1.0mm). ) or the thrust bearing metal temperature is out of limit. 5. The lubricating oil supply is interrupted or the oil pressure drops to the limit value (0.06 MPa), and starting the backup oil pump is ineffective. 6. The oil level in the lubricating oil tank has dropped to the limit value (-300mm), and refilling the oil does not work. 7. Oil supply is interrupted to any bearing of the steam turbine generator set, smoking occurs, or the metal temperature of any radial bearing reaches 113°C, or the metal temperature of the thrust bearing reaches 107°C. (Apart from abnormal measurement points). 8. Water hammer occurs in the turbine, and the temperature difference between the upper and lower casings exceeds 56°C. Within 10 minutes, the main and reheat steam temperatures dropped sharply by 50°C; an alarm was triggered due to water ingress in the extraction steam pipeline, and the value exceeded the tripping threshold. 9. Abnormal friction and sparking at the turbine shaft seal. 10. A fire broke out in the turbine oil system and could not be extinguished quickly, posing a serious threat to the safety of the unit. 11. The generator smokes, catches fire, or explodes. 12. All plant power is lost. IV. In the event that a steam turbine generator set encounters any of the following conditions, it should be shut down urgently without breaking the vacuum. 1. The operation of the unit poses a threat to the safety of personnel and equipment; it is necessary to shut down the unit in order to prevent accidents involving personnel or equipment. 2. A fire poses a direct threat to the safe operation of the crew. 3. Important operational monitoring meters or devices of the turbine are showing incorrect readings or are non-functional, leaving no means of monitoring available. 4. The EH oil pressure of the turbine drops to 8.5 MPa, yet the protection system does not activate, or there is a leak in the oil circuit that cannot be sealed off. 5. The back pressure of the exhaust device is greater than 65 kPa. 6. When the generator is leaking severely, posing a threat to safe operation. 7. When there is a failure in the generator seal oil system and it is unable to maintain operation. 8. When the temperature difference of the generator stator bars is 14°C, or the temperature difference of the water exiting the stator water inlet pipe is 12°C, or the temperature of the temperature sensing element in any stator slot exceeds 90°C, or the temperature of the exiting water exceeds 85°C. 9. When the hydrogen purity inside the generator drops sharply below 92%, or when the hydrogen pressure drops sharply below the lower limit and cannot be maintained. 10. When the generator slip rings are causing severe arcing, posing a threat to the safety of the equipment. 11. During normal operation of the unit, the temperatures of the main and reheat steam drop by 50°C within 10 minutes. 12. When all operator stations of the thermal control DCS system fail (all operator stations experience a ‘black screen’ or ‘freeze’), and there are no reliable backup means for operation monitoring, making it impossible to restore normal operation in the short term. 13. In the event of serious failures in the main transformer, excitation transformer, or high-voltage transformer. 14. When the unit trip conditions are met but the protection fails to operate.