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This paper presents a new approach in mathematical modeling of thermodynamic cycles and electric power of utility district-heating and co-generation steam turbines. The approach is based on the application of the dimensionless mass flows, which describe the thermodynamic cycle of a combined heat and power steam turbine. The mass flows are calculated relative to the mass flow to low pressure turbine. The procedure introduces the extraction mass flow load parameter vh which clearly indicates the energy transformation process, as well as the co-generation turbine design features, but also its fitness for the electrical energy system requirements. The presented approach allows fast computations, as well as direct calculation of the selected energy efficiency indicators. The approach is exemplified with the calculation results of the district heat power to electric power ratio, as well as the cycle efficiency, vs. vh. The influence of vh on the conformity of a combined heat and power turbine to the grid requirements is also analyzed and discussed. [ABSTRACT FROM AUTHOR]