Model-Based Control Strategy to Reduce the Fault Current of a Gas Turbine Synchronous Generator under Short-Circuit in Isolated Networks

The fault protection devices that are used in high power isolated power systems require attention because of the high current levels. Such installations might benefit if their short-circuit current levels are reduced by control, rather than by inserting series impedance to the generators that would otherwise worsen regulation and increase size. This work proposes a strategy for controlling the fault current by actuating on the excitation system of a synchronous generator. The aim is to reduce fault levels during, both, transient and steady-state. The proposed strategy utilizes an adaptive algorithm working as an optimal model-based controller with current feedback, whenever a fault is detected and until its clearance. The used methodology comprises the modeling of the synchronous generator, as well as of the main sub-elements that are dynamically involved in the system, namely the exciter and the gas turbine models. The analyzes and simulations results are obtained for a round-rotor synchronous generator with a nominal power of 31.25 MVA. The proposed strategy effectively reduces the fault current amplitudes during transient dynamics compared to the system operating with a typical automatic voltage regulator (AVR).