Assessment of Requirements for Application of Generator Circuit-Breakers in Synchronous Compensator Plants

The purpose this paper is to assess the requirements of application of generator circuit-breaker (GCB) in synchronous compensator plants. Currently, there is increasing demand of synchronous compensators to provide system stability in a grid with high share of converter-based renewable generation. To define the requirements of GCB to be installed between the synchronous compensator and the step-up transformer, it is utmost important to understand the characteristics of the current fed by a synchronous compensator after a three-phase short-circuit at its terminals. The main difference between synchronous generator and synchronous compensator, in this respect, is the loading conditions. This paper compares the effect of pre-fault loading of synchronous generator and synchronous compensator on the short-circuit current characteristics over their complete operating range and emphasizes the importance of zero power factor loading at overexcited and underexcited operating point in defining the requirements of GCB. Furthermore, analytical equations are described for the calculation of short-circuit current fed by synchronous compensator under pre-fault loading conditions. A case study is presented to demonstrate the capability of the GCB to interrupt fault currents which show delayed current zeros (DCZ) taking into account SF6 and vacuum extinguishing technologies.