Transient Performance of Siemens SGT-750 and SGT-800 : Modeling and Simulations of Industrial Gas Turbines on Island Grids

Abstract: Distributed energy production in the form of renewable energy sources are expected to increase in the coming years, a consequence of this is instability of the power grids due to the stochastic nature and lack of inertia of renewable energy sources. In addition, small and local, so called island grids, are on the rise and these system may present an even higher sensitivity to frequency fluctuations. In these applications gas turbines are an attractive option owing to the quick start capabilities, flexible fuel options and reliable operation. The aim of this thesis is to evaluate the transient capabilities of the Siemens SGT-750 double shaft and SGT-800 single shaft industrial gas turbines in island grid settings, through simulations of substantial load increases in varying ambient settings. Furthermore the possibility of using hydrogen fuel as a renewable option to the standard natural gas will be evaluated. This thesis provides a model of a simple island grid for load sharing between two or three turbines. The model was tuned to real life test data for the two gas turbines considered. In order to evaluate the capabilities of the turbines simulations were run in cold (-30 oC), hot (30 oC) and ISO (15 oC) conditions, evaluating the maximum instant load increase capabilities. Case studies were also run on island grids containing two or three turbines in order to determine the frequency response in case of an event. Case A regarded a scenario in which two turbines ran on 50% of rated power and one tripped, case B regarded three turbines working on 33% of rated power and one tripped out. Lastly, the maximum load increase cases with hydrogen fuel mixes (25, 50, 75 and 100% hydrogen by volume) were considered. The results suggest that the SGT-750 and SGT-800 gas turbines are capable of handling scenarios on reasonably dimensioned power systems, with both machines capable of recovering instant load increases of over 50% of the rated power. The findings shows thats hort periods (<10 s.) of allowed overfiring temperatures are necessary for the transient performance for the most extreme scenarios of high ambient temperatures and large loadincreases (around 50% of rated power). Furthermore an empirical κ-parameter, related to inertia and operational stability is discussed in order to compare GT load increase capability. The relevance of inertia and dynamic response is discussed and conceptually simulated to highlight the their role in gas turbine transient response. The hydrogen simulations, aside from the 75% case, showed little difference from natural gas in transient scenarios. The 75% hydrogen fuel consisting of high amounts ofinert gas however, rendered the turbine unable to withstand substantial load increases. The hydrogen simulation results are suggested to be accounted for by the rather simple combustion system and the energy densities of the gases.