Getachew, Biru (PhD)Adugna, Edosa2019-05-312023-11-282019-05-312023-11-282017-12http://etd.aau.edu.et/handle/12345678/18360Lightning is one of the most significant sources of over voltages in overhead transmission lines. The lightning over voltages could lead to failure of the devices connected to the transmission line. A fundamental constraint on the reliability of an electrical power transmission system is the effectiveness of its protective system. The role of the protective system is to safeguard transmission system components from the effects of electrical overstress. Shield wire and surge arresters are an important means of lightning protection in transmission and distribution systems. Therefore, it is necessary to analyze the influence of over voltages caused due to lighting. This research is aimed at study and evaluation of the protection level of transmission line by using shield wire and line surge arresters against lightning overvoltage. The increase in voltage due to lightning is in investigated by using the MATLAB software. Direct and induced, types of lightning strokes are considered. The model of a 500kV three-phase overhead power transmission line is developed considering the RL circuit. The simulations are performed based on a time domain analysis. Also numerical analysis is made for 500kV tower structure transmitting power over 620km from GERD to Dedesa and then to Holeta being protected by shield wire. Probability of lightning stroke going to shield wire and phase conductor is analytically determined in each cases. Accordingly the effective area of the lightning stroke that goes to phase conductor per 100km per year is 0.0301m2and that goes to shield wire per 100km per year is0.399m2. Probability of failure and failure rate is obtained to be 31% and 0.0024respectively which means it takes 413.18failures per year years between.en-USlightning, Modelingtransmission lineprotectionThesis