Optimal shunt capacitor bank design for limiting voltage dip severity on Wabigalo feeder

Abstract

Uganda’s vision 2040 strategically focuses on promoting industrialization as a tool for national socioeconomic transformation through job creation and value addition. Industrialization also increases local consumption of the national grid electricity. However, the Uganda medium voltage grid through which all industries are supplied is susceptible to power quality disturbances such as voltage dips yet many industries are adopting sensitive digital equipment for production efficiency. Past efforts to mitigate effects of voltage dips on industrial consumers in Uganda have proved costly for example the five million United States Dollars tariff funded quality of supply investment for the Namanve Roofings factory in 2017. Hence the purpose of the study was to establish an optimal shunt capacitor bank design as a cost-effective approach for limiting voltage dip severity on radial industrial supply grids using Wabigalo 33 kV feeder supplying industries in the Luweero service region as a case study. The power system hypothesis that; “the stability of a given grid is dependent on the initial operating condition and the type of disturbance,” provided the basis for the optimal capacitor bank design solution as voltage dips represent a short-term voltage stability problem. The study employed the experimental design using the quantitative approach and power system simulation methods. Voltage dip propagation was determined using the method of fault positions while the optimal shunt capacitor bank design was developed using the Tabu Search Metaheuristic Algorithm in combination with the loss sensitivity factor modelled in the DIgSILENT software. The performance and cost benefit of the optimal shunt capacitor bank design as the intervention was compared with that of the Static VAR Compensator (SVC) as the standard method. The findings obtained showed that the developed optimal shunt capacitor bank (SCB) design yielded a 76.5 % saving on the initial cost of investment compared to SVC. The optimal SCB design provides superior performance benefits in terms of improving pre-disturbance voltage profile thereby limiting voltage dip severity as such, the residual voltage magnitude was improved by 0.1 pu compared to 0.05 pu when the SVC was applied. Furthermore, the optimal SCB design reduced voltage dip propagation index from 87% to 0% for Kakiri fault position while the SVC only reduced from 87% to 22% implying a better performance of optimal capacitor bank design. Therefore, the study findings showed that the optimal SCB design approach is better suited for limiting voltage dip severity on long radial feeders due to its cost effectiveness.