Short-circuit current of a doubly-fed induction generator: Analytical solution and insights

Variable-speed turbines have gained increasing importance in pump-storage power stations since they present big advantages compared to the classical topology with a synchronous generator. Within the variable-speed solutions, the one employing a doubly-fed induction generator (DFIG) has become the preferred solution for large installations since it provides the advantages of variable-speed operation and four-quadrant active and reactive power capabilities using converters rated only a small fraction of the rated power. A deep understanding of the characteristics of the fault current fed by a DFIG after a three-phase short-circuit at its terminals is of utmost importance to define the requirements of the generator circuit-breaker (GenCB) to be installed between the generator and the step-up transformer. This paper analyses in detail the characteristics of the current fed by a DFIG after such a fault. A mathematical model is presented and deep insights into the impacts of the machine´s operating parameters on the fault current waveform are given. Results are compared with simulations performed with the Electromagnetic Transients Program (EMTP).