Study and design of lightning protection for H.V. transmission lines in the Egyptian Unified Network

Abstract

High and Extra high voltages (H.V. and E.H.V.) overhead transmission lines and the associated substations have been subjected to surge overvoltages due to atmospheric lightning storms and switching operations. Overvoltages produced by surges on transmission lines may cause flashover of line insulation and can reach substations, in the form of travelling waves, and may damage its equipment apart from the economic losses due to power outages. Protection of transmission lines against the effects of lightning is secured by a combination of ground wires to minimize the possibility of insulator flashovers, and various types of protective devices. The objective of this research is to reduce the number of interruptions due to lightning to a minimum acceptable amount according to the international standards and codes. This study, at certain level of voltage, concentrates on the design of different types of arresters needed for certain level of protection according to its internal material, characteristics and advantages. Our study showed that Zinc Oxide (ZnO) arresters are the most perfect for this purpose. In this research measures were taken to protect H.V. and E.H.V. lines and substations of the Egyptian Unified Network (E.U.N). Great attention was paid to the sections of lines that are in immediate vicinity to the substations, which are normally called 'Approaches'. A safe, reliable and economical lightning protective system using Metal-Gapless Arresters (MOA) was developed and tried in the Egyptian Unified Network for different system of voltages at power frequency. This new technique was developed using a Matlab computer program. Optimization was done to select the best arrester for certain industrial application with the minimum cost based on rated voltage, discharge current and location of these arresters with respect to the selected substation. A reduced insulation withstand voltage level for substation was achieved using this novel technique. This new developed technique showed to be an effective tool and useful method to design engineers to select the optimum arrester type with the minimum cost and the safest location.