Check by reducing the vacuum

It’s the air extraction issue; could it be that the air extraction capacity is insufficient? Check whether the cooling water you are using is normal; is the cooling water used for gas extraction condensate? If so, it might be a problem with insufficient cooling of the gas extraction process.

As you said, when the speed increases and this situation occurs, it is generally due to insufficient condensation by the condenser (since the turbine is of the condensing type). Properly adjusting the cooling water is also related to pumping; insufficient pumping capacity can lead to a decrease in vacuum level. My personal opinion may not be accurate, but I hope it helps you!

It’s most likely that the temperature of the condensate inside the cooler is too high. Adding more soft water while the machine is running might help. Check as well whether there are any leaks in your vacuum pump. Also, make sure that the vacuum level is monitored; the vacuum pump should be activated in emergency situations. If there are leaks, there are many possible locations – have you checked them all? Additionally, verify that the temperature and pressure of the main steam are within normal ranges, and that the superheat level is sufficient. It’s normal for the vacuum level to drop as the speed increases, but it shouldn’t drop to the point that the machine shuts down

It wasn’t until the pressure was reduced to 1500 that the vacuum level reached 0.080 KP; the gauge pressure was therefore -20 kPa. This vacuum level is not acceptable. What should the vacuum level be before driving? The estimate is already quite low – -20 Kpa. Generally, this level of vacuum is overestimated; how is it still possible to drive in such conditions? ? At such a vacuum level, it is highly likely that the vacuum will be insufficient at the transcritical point, leading to a cascade shutdown. Is the vacuum level good before driving? ? ? First, check whether the injector is working properly? Is there a possibility that the valve is being switched on and off incorrectly? ? ? I think the possibility of a flange leak is not as high as those of the previous options.

If it is not due to issues such as the structure of the condenser copper tubes, insufficient circulating water or high temperatures, inadequate efficiency of the exhaust pump, or leaks, then this is likely the cause. When the turbine starts rotating, the vacuum level is usually still low, and some air remains in the cylinders and pipes; this air is carried towards the condenser along with the steam flow during rotation. During startup, the steam does not immediately exchange heat with the copper tubes of the condenser and thus does not condense right away; therefore, the vacuum level in the condenser always decreases during startup. When the steam entering the condenser after starting up begins to condense, and the exhaust pump continues to remove air, the vacuum can be restored to its original value quite quickly. This allows the vacuuming time to be appropriately extended, or the interlock value can be adjusted (though this method is not very advisable). For reference only, ya

Another thing is that I don’t know what the operating speed of your turbines is. Is the turbine’s speed of 4000 revolutions per minute within the normal operating range? At this point, is it necessary to switch the steam source for the steam seals on site, by shutting off the external steam supply? Or should the external steam supply for the steam seals be shut off too early, when the turbine is still far from reaching its normal speed, for example after it has reached 1500 revolutions per minute? Additionally: 1. In general steam turbines, there is also a valve called the vacuum break valve; check whether this valve has been accidentally activated 2. Before starting the turbine and after warming up the pipes, it is necessary to ensure that there is sufficient steam available for the steam seal. Once the pipe warming is complete, the inlet steam valve should be opened fully, followed by the exhaust valve. During the process of opening the exhaust valve, especially when it is first opened or up to halfway open, the negative pressure in the surface cooler reaches its peak. Did the person in question notice how low the negative pressure in the surface cooler became at that time? During the low-speed startup process, the exhaust temperature is relatively high due to the blowing effect of the last stages of the turbine, and the negative pressure also drops slightly for a while; however, things improve after about 1,000 revolutions. Once the turbine enters the transcritical regime and the TTVs are fully open, the lowest continuous rotational speed of the turbine is reached at this point, at which the throttling effect of the TTVs is at its maximum, and the amount of steam consumed during throttling startup is also high. The vacuum level in the surface cooler decreases further at this stage. After overcoming this issue, the turbine switches to nozzle-driven operation, and the steam consumption drops significantly; at this time, the vacuum level begins to improve. For turbines equipped with extraction systems, extraction starts to be used once the lowest continuous rotational speed is reached, resulting in further reduction in the condensate volume and another improvement in the vacuum level. As the rotational speed continues to increase and the compressor load rises, the negative pressure becomes somewhat higher again; but at a rotational speed of 1,500 revolutions, the negative pressure is only -20 KPa. Is it possible that the main extractor in the surface cooler isn’t activated?