Abstract
Single-shaft gas turbine and its cycles are sensitive to frequency drops and, therefore, sudden change loads or large frequency dips might affect their stability. This phenomenon is related to the reduction of the air mass flow passing through the machine during the frequency dips, which might lead to an interaction between governor and temperature control loop. In this paper, the performance of the combined cycle and steam-injected gas turbine are studied during frequency dips and transient maneuvers. For this purpose, two similar units are developed based on these cycles and their performances are studied in different scenarios. The simulation results show that the steam injected gas turbine has a better performance during frequency drops and it can handle relatively larger change loads.
Highlights
The behavior of the gas turbine and its related cycles during frequency drops differs from other popular prime movers, such as steam turbines and hydroelectric units
To compare the performance of the combined cycle and the steam-injected gas turbine (STIG) cycle during frequency dips, two similar units with the same output power are considered in this work
Sudden change loads and large frequency drops may affect the stability of a gas turbine and the cycles based on it
Summary
The behavior of the gas turbine and its related cycles during frequency drops differs from other popular prime movers, such as steam turbines and hydroelectric units. This reduction in the gas turbine output power will lead to larger frequency drops and, will affect the grid stability [1]. This issue is more important when the gas turbine is running in island mode or in smart grids with a large capacity of renewable energy, as, in these grids, there is no control over the amount of generated power by solar or wind power units and the grid frequency control would rely on fossil fuels units [2]. In the STIG cycle, the produced steam in the HRSG is injected into the combustion chamber of the gas turbine to increase the cycle efficiency and output power (Figure 1). All of the simulation has been done when the units are running in island mode, which is known as the most difficult case in grid frequency control
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