Enhancing the Performance of Eskom's Cahora Bassa HVDC Scheme and Harmonic Distortion Minimization of LCC-HVDC Scheme Using the VSC-HVDC Link

Cahora Bassa, a thyristor-based High Voltage Direct (HVDC) link, transmits 1920 MW of power from a hydro-power plant in Zambezi River, north of Mozambique, to Apollo Substation in Johannesburg, South Africa. The high degree of harmonics distortion that is transferred into the AC side of the transmission network and the continuous increase in the rate at which commutation failure occurs during systems disturbance are both flaws in the utilization of this HVDC converter technology. AC and DC filters with rugged controllers are often used to minimize this effect but are limited in scope. Modern converter technology, such as the Voltage Source Converter (VSC), was proposed in this study to reduce harmonics content level, increase power transfer capabilities, enhance network stability, and reduce the rate of commutation failure occurrence. This paper, therefore, evaluates the performance analysis of the Cahora Bassa HVDC link and its level of harmonic distortion in the line commutated converters. A proposed method of utilizing VSC HVDC is provided as a suitable solution using three modular-level voltage source converter technology. Current and voltage waveform characteristics during a three-phase short circuits fault were analyzed, and the latest developments in the area of VSC HVDC were discussed. The results show a lower total harmonics distortion with the usage of VSC HVDC converter technology at the inverter station. The continuous occurrence of commutation failure was minimized by implementing a new converter architecture. The network simulation and analysis were carried out using the DIgSILENT PowerFactory engineering software tool.

Automated summary

This study evaluates the performance and harmonic distortion level of the Cahora Bassa HVDC link, and proposes the usage of Voltage Source Converter (VSC) HVDC technology as a solution to reduce harmonics content, increase power transfer capabilities, and enhance network stability. By analyzing the current and voltage waveform characteristics, it is found that the usage of VSC HVDC converter technology at the inverter station leads to lower total harmonics distortion, and the continuous occurrence of commutation failure is minimized by implementing a new converter architecture.