Should the brake be tripped and the machine stopped when the steam temperature drops by 50 ° C within 10 minutes?
Date: 2023-08-17Read: 46
Twenty five countermeasures to prevent the bending accident of the main shaft of the steam turbine: If any of the following situations occur in the steam turbine, the brake should be immediately shut down. One of the requirements is that when the main and reheat steam temperatures suddenly drop by 50 ℃ within 10 minutes during normal operation of the unit, the brake should be immediately shut down. The peak shaving single-layer cylinder can be executed according to the manufacturer's relevant regulations.
Nowadays, many power plants have implemented this protection logic in DCS, but some people believe based on unit operating experience that this protection should be judged based on the current main steam superheat of the unit to determine whether to activate. If the main and reheat steam superheat is greater than 100 ℃, and even if it drops by 50 ℃ after 10 minutes, the main and reheat steam superheat still exceeds 50 ℃, then there is no need to trip the unit; If the superheat of the main and reheated steam is less than 100 ℃ and drops by 50 ℃ after 10 minutes, it is necessary to trip the machine.Actually, this consideration is one-sided, because in normal operation, based on steam pressure conversion, the main steam superheat is above 150 ℃, and the reheated steam superheat is even above 200 ℃. If the statement that overheating is safe as long as it is greater than 50 ℃ is followed, it is clearly incorrect. Because at this momentThe steam is approaching a wet saturation state, and the humidity will continue to increase. If the turbine is not shut down or depressurized and heated up as soon as possible, it is likely to be subjected to significant water impact, resulting in serious damage.In fact, the consequences of a sudden drop in steam temperature during normal operation are not just about considering the water entering the turbine. The significant temperature drop process is actuallyThe rapid cooling process of the metal components of the steam turbine generates considerable thermal stress, especially at the regulating stage and the intermediate pressure inlet holding ring.At this time, the expansion difference, axial displacement, temperature difference between the upper and lower cylinders, and vibration of the unit will all undergo changes, posing a serious threat to the safe operation of the unit.So, regardless of whether the unit is equipped with this protection, in order to ensure the safety of the steam turbine, when a significant drop in steam temperature occurs during operation and its downward trend cannot be controlled in a short period of time, we shouldResolutely trip and stop the machine.(Source: Steam Turbine Debugging)