Power Tapping from HVDC Link: Utilization of Tap Point Information and Voltage Margin to Ascertain Proximity to Voltage Collapse

Long distance point-to-point HVDC link which traverse rural dwelling places can be utilized for tapping power to feed those areas. However, the extent of power tapped if not curtailed can lead to voltage collapse of the system. In this paper, analysis of Voltage stability index (VSI) to ascertain the nearness of HVDC link to voltage collapse is presented. However, this VSI method needs constantly measuring the tap voltage and current to ascertain nearness to voltage collapse. Therefore, power tap limit as a function of tap point information such as the length of the link, tap point distance from the main converter station and voltage margin at any point along the HVDC link and optimum tap limit is proposed. Simulation of the proposed technique is carried out in Matlab/Simulink environment with a case study of Namibia/Zambia Caprivi link VSC HVDC system. The simulation results depict that when power tapped is above the derived limit, the DC-link bus voltage collapses. More so, Small and large disturbance voltage stability was also studied. Results also show that when power tapping is below tap limit, small and large disturbances do not have effect on the DC-link voltages, however, when power tapped is above limit, the disturbances lead to voltage instability.