Title	Effect of tower footing resistance on the effectiveness of externally gapped line arrester in providing overhead line protection against lightning strokes
Authors	Lo, Pak Ngai Edmond
Advisors	Bu, Siqi
Degree	Undergraduate
Issue Date	2018
Absctract	Lightning is considered one of the important problems for insulation design of transmission line system, which will adversely affect the performance of overhead lines for power transmission. Therefore, a study of lightning overvoltage is vitally important when considering the design of insulation requirement of electric power system, especially for transmission tower. Different methods of reducing lightning flashover rates (in terms of two main categories: shielding failure and back flashover) are suggested around the globe, for example, tower footing resistance reduction, installation of additional ground wires, smaller shielding angle, etc. However, some of the above methods are impractical due to high cost or difficulties in implementation. Installation of line arresters is considered to be the most effective method among existing solutions and hence, installation of line arresters in the most cost-effective way deserves investigation. This project examines the correlation between the lightning flashover rate in terms of shielding failure and different phases of line arresters, namely shielding failure analysis. Electrogeometric Model (EGM) will be used for the shielding failure analysis by comparing critical current (Ic ) and maximum penerating lightning current (Im). Additionally, the correlation between the lightning flashover rate in terms of back flashover and various phases of line arrester(s) under the effect of varying tower footing resistance will be conducted, namely back flashover analysis. Simulation has been conducted in EMTP-RV software and simulation results of the application of externally gapped line arrester on the 400kV double circuit transmission line have been studied and compared. Regarding the results, it was found that top phase and bottom phase of tower suffered from the highest shielding failure rate and back flashover rate respectively. There are two approaches for determining installation configuration of line arresters, with the past lightning record of power company being the first. Line arrester should be installed at top phase since occurrence of shielding failure is more frequent than that of back flashover. Another aspect is the consequence of lightning flashover. Installing line arrester at bottom phase is the most cost-effective option in this case because the consequence of back flashover is far severe than that of shielding failure.
Subjects	Lightning protection Lightning-arresters Electric lines
Award	Outstanding Final Year Project Award
Publisher	Hong Kong Polytechnic University
Rights	All rights reserved.