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).