Answer:
The moisture content at the exit of the turbine increases which can decrease the efficiency of the turbine and can erode the turbine blades
There is always a chance of air leakage in the condenser if the condenser is operated at a lower pressure than the atmosphere. Reason: The pressure outside the condenser will be more than the pressure inside the condenser which may push the air inside the condenser from outside.
There is a limit to how much pressure can be reduced. This limit is imposed by the outside temperature of the cooling medium. The cooling medium temperature is fixed and there is fixed saturation pressure at that temperature. To have heat flow from steam inside the condenser to the outside cooling medium there must be some temperature difference and hence the saturation pressure of the steam should be more than the outside saturation pressure of the cooling medium.
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