Development and application of a thermodynamic-cycle performance analysis method of a three-shaft gas turbine

Based on the calculation method, further investigation of the characteristics of the gas turbine is performed on a wide load range when the power turbine operates at a fixed physical speed. The results show that a variable-angle nozzle significantly affects the performance of the gas turbine. The surge margin of the low-pressure compressor is also shown to be particularly important when the gas turbine operates at a high gas temperature with a more open variable-angle nozzle; also, due to the limitations imposed by the temperature control line, the high-pressure compressor always have an adequate surge margin. Throughout the operation range, the low-pressure and high-pressure turbines have high isentropic efficiencies; however, opening or closing the nozzle would decrease the isentropic efficiency of the power turbine compared with the ideal design condition. When the power output is constant, closing the nozzle causes the turbine inlet temperature to increase, thus increasing the efficiency of the gas turbine. Therefore, the optimal operating line under a wide range of loads is obtained by combining the adjustment of the variable-angle nozzle and the gas temperature.