What are the hazards of a drop in steam pressure in a turbine?
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Today’s daily question is about a drop in the steam pressure of a turbine; it is necessary to increase the load promptly, otherwise it will affect the operation of the unit.
The main effects of a decrease in main steam pressure on operation are as follows: (1) When the main steam temperature remains constant, a decrease in main steam pressure results in a reduced enthalpy drop across the entire unit, thereby lowering its operational efficiency. (2) After the main steam pressure decreases, if the opening degree of the control valve remains unchanged, the steam intake to the turbine will decrease; as a result, the stress on each stage of the blades will reduce, and the axial thrust will also decrease. The power output of the unit will decline as the flow rate decreases. It has no impact on the safety of the unit. (3) If the power generated by the unit does not decrease after the main steam pressure drops, or if it still has to generate the rated power, then the total steam flow rate in the unit will inevitably exceed the rated value. In such a case, if the pressures in various monitoring sections exceed the maximum allowable values, it will result in excessive axial thrust, which is dangerous and not permissible.
Under the same load, a decrease in steam pressure requires an increase in flow rate, which can cause overload of the turbine; in particular, the last few stages of the blades are severely eroded by water. Therefore, the load must be reduced when the steam pressure drops.