Evaluating the impact of lightning strikes on medium voltage lines in Uganda.

Abstract

Lightning strikes are a major cause of power outages on medium voltage lines in tropical countries like Uganda. Many medium voltage lines are still vulnerable due to the limited protection systems and the absence of detection systems. The main objective of the study was to evaluate the impact of lightning strikes on medium voltage lines in Uganda. Specific objectives included modelling line configurations under direct and indirect strikes, assessing flashover rates, and studying non-structural factors. This study evaluated the impact of lightning strikes on medium voltage lines in Uganda by studying four configurations (horizontal, wishbone-wye, wishbone-delta, and wishbone-vertical), and nine lines selected from West Nile, Eastern Uganda, and Northern Uganda using software tools EMTP for direct strikes, LIOV-EMTP for nearby strikes, and the statistical methods such as the IEEE standard 1410-2010, and the IEEE standard 1243-1997. Additionally, four insulator types (suspension, line-post, porcelain pin, and composite pin) were studied in COMSOL Multiphysics. The results in EMTP reveal that configurations without an overhead ground wire experience higher induced voltages and currents whereas adding an OHGW reduces these values by 82.24% and 49.36% respectively. Further studies in EMTP reveal that widely spaced surge arresters (5 km or more) are less effective for lines without an OHGW. Further analysis in LIOV-EMTP and the three statistical methods reveal that grounding resistances of above 10 Ohms reduce arrester performance and insulators rated 170 kV peak fail to protect medium voltage lines in areas with high soil resistivity values and struggle to safeguard lines in regions with high lightning ground flash densities where flashover rates are high. COMSOL Multiphysics simulations indicate that composite insulators exhibit lower electric field stress while porcelain insulators show sharper peaks increasing their vulnerability. The study concludes that medium voltage lines in high lightning activity regions should be constructed with an OHGW, use the wishbone-vertical configuration, and the line-post insulator for better performance. Furthermore, increasing the insulator lightning impulse voltage rating to 250 kV peak and maintaining a surge arrester spacing of 3 km or less with an arrester grounding resistance of 5 Ohms or lower are essential measures for better protection against lightning strikes.