In this work, component characteristics of a reheat cycle gas turbine in a commercial combined cycle power plant were evaluated. An inverse performance analysis, in which component characteristic parameters were estimated based on measured performance data, was carried out. The measured parameters were the power, the fuel flow rates of two combustors, and the temperatures and pressures at various locations such as the compressor discharge, exits of both the high-and low-pressure turbines. The estimated parameters from the analysis include the compressor and turbine efficiencies and the inlet air flow rate. The analysis was performed for a wide operation range in terms of the ambient temperature and load, providing a database for the variations of the characteristic parameters with changes in the operating condition. In addition, a sensitivity analysis was performed to examine the influence of the uncertainties of the measured parameters on the estimated parameters. The analysis program can be further developed into a performance diagnosis tool and the obtained component characteristic data can be used as reference database.

In order to fully address the characteristics of the alternative recuperated cycle with divided turbine expansion, both the design and off-design analyses have been performed. Two types of mechanical design are assumed: two-shaft and single-shaft. In particular, optimal pressure ratio division between the high and low pressure turbines is evaluated for the single shaft configuration. It is predicted that the alternative recuperated cycle hardly exhibits sensible design efficiency advantage over the conventional recuperated cycle for moderate turbine inlet conditions and with usual component performances. An advantage of the alternative cycle with single shaft design is that thermal efficiency is less sensitive to compressor pressure ratio compared with other configurations and we can also have flexibility in the turbine division without much efficiency loss. The part load analyses have been carried out with the aid of realistic component maps and models for off-design operation. In addition to the general fuel only control, a variable speed control is assumed as the part load operating strategy of the single shaft configuration. Obvious advantage with the alternative cycle is observed in the variable speed operation of the single shaft design. With this strategy, the part load efficiency of the alternative cycle is far superior to the conventional cycle. Almost constant efficiency is predicted for a wide power range.