Voltage quality improvements through capacitor bank tuning in the Eskom transmission network

Eskom has developed a power system engineering approach which considers power quality issues at every phase from planning onwards. The approach was used during the recent expansion to the Eastern KwaZulu-Natal transmission network, which was dominated by the integration of the 800 MW Alusaf aluminium smelter. Customer filters to reduce harmonic voltage distortion were impractical in this case, and the tuning of transmission capacitors was found to be a better solution. The paper describes the selection of a flexible harmonic filter configuration against the background of possible future improvements, which could include active power filters when the technology becomes commercially available. It then discusses the determination of filter component ratings from the results of transient simulations and harmonic loading calculations. Transient simulations with the Alternative Transients Program were used to determine appropriate short-time overvoltage and overcurrent ratings for the filter components. Included in the discussion on transient simulations is the development of frequency dependent network equivalents for various transmission system configurations of concern. The discussion on harmonic loading calculations shows how current injection simulations were used to characterise the network and the load, how the interaction between these characteristics was assessed and how IEC and Eskom specifications were applied to determine the steady-state ratings of the filter components. Finally, the paper presents some measurements conducted following installation of the plant, in order to demonstrate the effectiveness of the solution.