Effect of Steam Turbine Input on Overall Efficiency at Constant Power Output

Abstract

This study aims to evaluate the effect of change of steam turbine input, which is characterized by steam mass flow rate and the isentropic enthalpy drop, on the overall efficiency of steam turbine at constant power out put. Steam turbine unit one in Garri power plant one has been selected for this study. It has been concluded that for a constant output power the overall efficiency is not constant due to fluctuation of the product of steam mass rate of flow and the isentropic enthalpy drop values. For constant power output the steam mass rate of flow values are changed to compensate for the change in the values of the isentropic enthalpy drop and the internal losses. So the overall efficiency value is not constant at constant power output due to the change in the condition of steam at inlet and outlet to the turbine, which affect the internal losses and the required mass flow rate, and the changes in the internal losses caused by change in steam mass flow rate. Also it has been concluded that the best overall efficiency values were obtained during the highest load condition and the worst efficiency values were obtained during the lowest load condition.