A method of operating a steam turbine in a combined-cycle power system is provided. The method includes channeling a first amount of steam from a first steam generator to the steam turbine to facilitate powering the steam turbine, generating a second amount of steam within a second steam generator that is coupled in flow communication with the steam turbine, and calculating a predicted stress level within the steam turbine in the event the second amount of steam is channeled from the second steam generator into the steam turbine. An initiation time at which to channel the second amount of steam into the steam turbine is determined such that the calculated predicted stress level will not exceed a predetermined stress limit of the steam turbine. The second amount of steam is automatically channeled from the second steam generator to the steam turbine at the determined initiation time.