In this study, air preheating, air-fuel preheating and simple cycles where steam injected in to combustion chamber are analyzed. The effects of steam injection on thermodynamic performance are calculated and obtained for the three different gas turbine cogeneration systems. Simulation programs written by the authors in FORTRAN code are obtained for the analyses by applying the first law of thermodynamics and the exergy analysis method. Thermodynamic performance of these three different cycles for variable mass of injected steam and different stages are obtained and compared with the results of the literature. The effects of injection steam into combustion chambers of those three cycles for variable compressing ratios, on power, efficiencies and performance are obtained. Consequently, the advantages and the disadvantages of injection steam are evaluated and all results of this study are compared with the literature. Injection steam into combustion chamber increases the electricity power and the electricity efficiency but decreases the heat power of the cycles
