Modelling of the long term dynamic performance of a gas turbo generator set

The paper introduces the long term dynamics model for stationary gas turbines, including the turbogenerator, with especial attention for use in combined gas and steam (CGS) power plants. The gas turbine model is devoted to large rated power gas turbines, whose fluid mechanical time response is much larger than that for the fluid gas flow in its three compartments: compressor, combustion chamber and turbine. The complete set of equations governing the pressure, temperature, mass flow and energy flow of the different sections within the gas turbine cycle are derived. The thermodynamic equations of the three fluid dynamic sections are complemented with the fluid mechanical equations of the three shaft sections of turbine, compressor and electrical generator. For torsion free operation, the resulting long term dynamic model of the gas turbine is deduced and simulation results showing its open loop dynamic behaviour, especially the tendency to expose nonminimum phase dynamics or back swings are demonstrated