Solar Farm Harmonic Analysis and Operation under DC currents

The DC currents might flow in a power system due to Geomagnetic Disturbances (GMDs) that result from either a solar storm or a high-altitude nuclear detonation. The increasing inverter-based generation is also injecting small DC currents into the power systems. These currents could have serious implications for the power systems as they drive the transformers towards saturation, cause massive draw of reactive power, cause transformers internal heating and maloperation of protection equipment. This paper studies the impact of the DC currents flowing in a power transmission network on a 50MVA grid-tied solar farm. A variety of loading conditions that include both local and remote loads have been considered. A detailed harmonic analysis is performed and evaluated against IEEE-519. Also, the limitations imposed by the DC current flow in a power grid on the solar farm capabilities have been highlighted. Finally, the effectiveness of a Neutral Blocking Device (NBD) in restoring the normal operation of a solar farm has been evaluated. The PSCAD/EMTDC has been utilized as the simulation platform and the associated results are presented.