POWER EXPENSES TO DRIVE A TURBINE STAGE UNDER LOW-FLOW MODES

Abstract

The task of determining the power consumption during the operation of the turbine stage in the low-cost mode is considered. To solve it, a theoreticalexperimental approach was used, based on the one-dimensional theory of the movement of a incompressible working medium and the results of an experimental study of a number of models of large fanning degrees, in which the working medium is air. When operating heating turbines, the lowpressure cylinders work in the area of low-cost modes up to 85 % of the time, both with a partially and completely closed rotary diaphragm of the regulating stage. When the volumetric flow rate of steam in the flow part of the low-pressure cylinder at low-flow modes is reduced, a sleeve separation of the flow develops and a vortex is formed in the inter-crown gap of the stage. The mode in which the power supplied to the impeller is spent on maintaining these currents corresponds to the "pure" ventilation mode. In contrast to the existing methods for determining the ventilation power losses in the stages of large fanning, the paper proposes a dependence based on the geometric configuration of the stages of the low-pressure cylinder of the heating turbines and their operating conditions. Taking into account the processes in the stage and the data obtained on the experimental stand, formulas were determined account the components of power losses - the function of the influence of the flow exit angles from the guide apparatus of the stage; influence of fanning l/Dmid; influence of the relative width of the working blade B/Dmid and the angle of inclination of the peripheral meridional circuit γm. The obtained dependences, which allow determining the coefficients of power consumption for the stage in the ventilation mode and the operation mode before idling, make it possible to calculate power consumption in the entire range of changes in low-flow modes. On the example of the last stage of the T-250/300-240 turbine, a comparison of the results of calculation studies according to the proposed dependence with the results obtained in real conditions of full-scale experiments was performed, which showed that their difference does not exceed 5 %.