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26The iterative process of constricting a new steam turbine unit or of its new version commences with development of the thermal process circuit. It is exactly at this stage that the composition of steam turbine unit (STU) equipment is determined, the operating condi tions of each of its components that are required for designing the equipment are evaluated, and the techni cal-economic indicators are estimated. Naturally, a turbine is the STU main component. The effectiveness with which the steam supplied to the turbine is con verted into mechanical energy has a direct influence on the STU thermal efficiency indicators. As A.A. Palagin pointed out in his work [1], uncertainty in the results of designing the STU thermal process circuit will persist until the turbine has been constructed and tested and until the relative internal efficiencies of its cylinders have been determined. Nonetheless, assessment of the steam energy conversion efficiency in the turbine is necessary at all development stages of a new STU, and the relevant recommendations were elaborated by well known scientists specializing in turbines, in particular, by Shcheglyaev [2].At the first stage of work on developing the STU thermal process circuit, the values of relative internal efficiencies (η ri ) of the turbine cylinders are required for constructing the hs diagram of the steam expansion process and for determining the steam parameters in the extractions and in the turbine last stages. Without knowing this information the designer will not be able to calculate the thermal process cir cuit. In turn, without having the thermal process cir cuit calculation results, it is impossible to carry out a stage wise thermal calculation of the turbine, from which refined values of relative internal efficiencies can be obtained.The results obtained from experimental investiga tions and tests of manufactured turbines are the basis for determining η ri .In [2], the following dependence for calculating the internal relative efficiency of single shaft turbines without steam reheating is presented, which was obtained from the results of thermal tests carried out on US turbines:(1)where k = 0.92-1.04 is the correction coefficient that depends on superheated steam's initial pressure and temperature, F = 40-220 cm 2 is the critical nozzle section equivalent to the nozzle cascade flow section and determined from the steam flow rate in the tur bine.The value of η ri calculated from (1) takes into account the losses due to steam wetness at the end of its expansion process and the residual velocity loss.In [2], a graph of the relative internal efficiency η ri is given for the group of turbine uncontrolled stages operating on superheated steam (at zero moistureAbstract-Formulas for evaluating the relative internal efficiencies of turbines that have not been designed as yet are given in many publications. Such assessments are required at the first stages of development and cal culation of the thermal process circuit of a new steam turbine unit. The above mentioned formul...

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