A steam turbine installation that has a steam turbine, a steam generator and a feed water pre-heating unit operated by process steam is provided. The steam turbine has an overload bypass line with which main steam can be fed to the feed water pre-heating unit between the steam turbine input and the extraction point during overload operation of the steam turbine, wherein the feed water pre-heating unit has an auxiliary extraction line that is connected to the overload bypass line in such a way that process steam can be extracted from the steam turbine during partial load operation of the steam turbine and added to the feed water pre-heating unit for the additional pre-heating of feed water.