What are the factors affecting the selection of condensing pressure?

The answer below is correct but it is important to keep in mind that the condeser vacuum is imposed by the operating conditions. The minimum condeser pressure corresponds to the vapour pressure at the cooling water inlet temperature, generally steam turbine operating in cold enviromnet operate at a lower condenser pressure than steam turbine operating in hot enviroment. it is also worthy of note to know that at lower condeser pressure the turbine has higher output

1-cooling water inlet temprature

2-loading on turbine

3- amount of air leakage