The authors carried out the circuit-parametric optimization studies of a promising cogeneration STU, which includes a backpressure steam turbine and a gas-fired steam boiler capable of heat recovery from flue gases. A mathematical model was employed to analyze how the internal relative efficiency of the steam turbine compartments in such an STU could affect the core operating parameters and the design characteristics of the heat exchange equipment of the unit. Mathematical modeling and circuit-parametric optimizations were run in the Machine Programming System, a software package developed by the Department of Heat and Power Systems, Melentiev Energy Systems Institute, Siberian Branch of the Russian Academy of Sciences. The optimization criterion was the price of STU-supplied electricity at the given prices of supplied heat and fuel with the adjustment for the internal rate of return on investment. Circuit-parametric optimizations show that the price of electric energy from a cogeneration STU linearly depends on the internal relative efficiency of the turbine compartments, and when it changes from 0.82 to 0.9, the price of electric energy decreases by 0.03 cents/kW. The cost effect of the increase in efficiency can be up to 98.79 thous. USD/year given the quantitative supply of electricity from the STU. The methodological approach used in this work enables feasibility testing of the attempts to improve the internal relative efficiency of the steam turbine compartments and can be useful both in the design and operation of thermal power plants. The estimated effects of internal relative efficiency of the turbine compartments on the core operating parameters and the characteristics of the unit will help determine the reliability and efficiency of its operation.