Investigation on the application of generator circuit-breakers in power plants employing doubly-fed induction generators

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. The only standard which covers the requirements for GenCBs is IEEE Std C37.013-1997 (R2008) with its amendment IEEE Std C37.013a-2007; which will be soon replaced by the IEC/IEEE Joint Development IEC/IEEE 62271-37-013. The question whether these requirements are adequate for the application of GenCBs in pump-storage power stations employing DFIGs is considered in the present work. A detailed analysis of the characteristics of the current fed by a DFIG after such a fault is provided and the consequent challenges for GenCBs are outlined.