Stability analysis of the Namibian power grid with integration of large offshore wind farms using a VSC-HVDC scheme

Abstract

The use of the wind for electrical power production has seen a meteoric increase due to the wind being a free and abundantly available resource, especially when the site is offshore. The wind resource along the Namibian coastline could therefore be implemented to develop offshore wind farms that would enable Namibia to meet its steadily increasing power demand. The efficient transmission of bulk power from offshore sites to the onshore AC grid is widely achieved through voltage source converter-based high voltage direct current (VSC-HVDC) schemes. This study aims to investigate the power system stability response of the Namibian network, particularly in terms of rotor angle stability, to the integration of large offshore wind farms. A single machine infinite bus (SMIB) model developed in DIgSILENT PowerFactory was used as a test bed for the study. Transient and small-signal stability analysis in relation to different fault scenarios on the main transmission lines were then carried out after doubly-fed induction generators (DFIGs) representing offshore wind farms were integrated into the SMIB model. The same methodology was applied on a reduced model of the NamPower network. DigSILENT PowerFactory’s VSC-HVDC offshore wind farm template model was integrated to a reduced model of the NamPower network. The entire network was then subjected to different fault scenarios along backbone transmission lines, major busbars and the HVDC link at different penetration levels of offshore wind power. The study established that the integration of large offshore wind farms using a VSC-HVDC scheme to the reduced NamPower network negatively affected the network's transient and small-signal stability. However, there was a positive impact on the voltage levels of the network due to the reactive power compensation supplied by the VSC-HVDC link. The VSC-HVDC link also maintained low-voltage ride-through of the offshore wind farms during faults that comply with the Namibian transmission grid code.