This paper provides simplified mathematical representations of heavy-duty gas turbines that are suitable for use in dynamic power system studies and in dynamic analyses of connected equipment. The full range of heavy-duty, single-shaft gas turbines, from 18 MW (24,000 HP) and 106 MW (142,000 HP), is covered, as well as both liquid and gas fuel systems, parallel and isolated operation, droop and isochronous governors, and the impact of both air- and hydrogen-cooled generators on the characteristics of the model. Alterations to the models, for the purpose of further simplification, are also discussed.

There have been several recent applications of large single shaft, heavy duty gas turbines in mechanical drive service, powering high horsepower, multi-casing compressors. This variable speed application of a traditional constant speed driver, with a more limited operating speed range, has created a need for simplified but accurate mathematical representations that can be incorporated into overall process simulations to allow interactive dynamic evaluation of the complete system.

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Gas turbines furnished with heat recovery equipment generally have maximum cycle efficiency when the gas turbine is operated at its ambient capability. At reduced gas turbine output the cycle performance can fall off rapidly as gas turbine exhaust temperature drops, which reduces the heat recovery equipment performance. This paper reviews the economic gains which can be realized through use of several control modes which are currently available to optimize the cycle efficiency at part load operation. These include variable inlet guide vane (VIGV) control for single-shaft units, and combined VIGV and variable high-pressure set (compressor) speed control for two-shaft units. In addition to the normal control optimization mode to maintain the maximum exhaust temperature, a new control mode is discussed which allows airflow to be modulated in response to a process signal while at constant part load. This control feature is desirable for gas turbines which supply preheated combustion air to fired process heaters.

With the increasing utilization of gas turbines in industrial and cogeneration applications, they are taking on a greater role in base load service. Because of their inherent responsiveness, they also offer operating characteristics that can enhance their contribution to utility systems as a generator prime mover. This paper will describe these characteristics, particularly as they relate to the interaction of the gas turbine, the governor, and the temperature control system. Additional features, such as load control, variable inlet guide vanes, peaking operation and other unique characteristics are also discussed from this point of view.