Since the front-end difference of the working water cooler and the temperature rise of the working water in the vacuum pump do not change with the turbine load, when the turbine load decreases, the vacuum pump evaporating headroom decreases, and the possibility of vacuum pump cavitation increases. Moreover, the lower the turbine load, the greater the potential for vacuum pump cavitation. Under the condition that the turbine load is fixed, the lower the cooling water temperature is, the smaller the NPSH of the water ring vacuum pump is; the lower the turbine load is, the lower the NPSH of the water ring vacuum pump is. The greater the possibility of cavitation. Since the minimum suction pressure of the water ring vacuum pump is limited by cavitation, the condenser vacuum is limited. Although the condenser itself can achieve lower pressure, due to the minimum suction pressure of the vacuum pump, the condenser pressure can only reach the minimum suction pressure of the vacuum pump (ignoring the resistance between the condenser and the vacuum pump). .
Under the condition that the turbine load and the cooling water temperature are low, considering the different factors, the obtained condenser pressure is different. In the conventional condenser characteristic curve, the condenser is considered to be in an ideal condition, that is, regardless of the influence of the turbine load and the cooling water temperature, the leakage of air into the vacuum system affects the condenser pressure, and the condenser is considered Pressure is always determined by its own operating parameters. Under the condition of low load of steam turbine, due to the increase of air quantity leaked into the vacuum system, the condenser end difference is approximately constant, and the pressure change of the condenser is obtained as the cavitation characteristics of the pump. In fact, when the turbine load is low to a certain extent, vacuum pump cavitation occurs. At this time, because the vacuum pump suction pressure is limited by cavitation, it can only maintain its minimum suction pressure.
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