The effectiveness of the primary link of a conventional gas turbine set has been expressed by means of the incremental energy efficiency, defined as the ratio of the attained increase of power to the increase of chemical energy consumption. The calculations performed for the humid air turbine (HAT) applied as a primary link indicate a high effectiveness of the utilization of the additionally consumed fuel. The compression ratio in both parts of the considered gas turbine set has been optimized in order to attain maximum energy efficiency.