Synchronous generator modelling and excitation voltage control for GIC studies

Geomagnetically Induced Currents (GIC) have very low-frequency characteristics and can disturb power system dynamics. The steady-state responses of transformers to GIC modelled as dc equivalent currents are well documented, but the dc simplification may not be representative. In this study, we use a more realistic 20 mHz ac GIC. We have not found any studies focusing on the dynamic response of synchronous generators with GIC. Generator models are complex having several parameters but are often simplified as ac equivalent sources without any representation of their field flux. We present a methodology for including synchronous generator models in dynamic GIC studies. A 4-bus power system was modelled in MATLAB/Simulink and the responses of an ideal and non-ideal ac electrical equivalent generator model are compared against full synchronous machine models having excitation and turbine/governor systems. The results imply that careful considerations are needed when modelling the source generators and that volt drop mitigation may be possible during geomagnetic disturbances when excitation system controls are optimized.