The paper considers a steam turbine cogeneration plant that includes a back-pressure steam turbine and a natural gas-fired steam boiler that enables exhaust gas heat recovery, which is rather promising for the isolated heat and electricity consumers. A design and verification mathematical model of the steam turbine plant was developed. The focus is made on the optimization studies into the effect of the relative efficiency of turbine compartments on the performance indices of the steam turbine cogeneration plant with an installed electric capacity of 50 MW that uses the heat of steam contained in the combustion products of the boiler for heating the feed-water of the heat network