Study of probable effects of building structure and lightning protection system on lightning current

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Study of probable effects of building structure and lightning protection system on lightning current


Author: Man, Kai-yuen
Title: Study of probable effects of building structure and lightning protection system on lightning current
Degree: M.Eng.
Year: 2005
Subject: Hong Kong Polytechnic University -- Dissertations
Lightning protection
Department: Dept. of Building Services Engineering
Pages: iv, 101, 3, 11 leaves : ill. ; 30 cm
Language: English
InnoPac Record:
Abstract: Traditional lightning research on lightning current focuses on the dispersion of lightning currents in a building. The effects of building structure and the lightning protection system (LPS) on lightning current are seldom considered. The absence of research in this area is the main motivation behind the study. The purpose of this project is to evaluate the possible effects of a building and its LPS on the current of a lightning stroke to it by computer simulation, so as to make suggestions on improvements to the design of a building LPS. Lightning channel models were developed in the study. Distributed-circuit models were chosen for the study of lightning current behaviours. The results showed that both current and the rate of change of current can be reasonably simulated by the proposed basic lightning channel model. The simulation was successful and the proposed lightning channel model is consistent. All LPS can be represented by inductance, resistance and capacitance. Different values of resistance were integrated in the channel base. Peak current is reduced significantly if a larger value of resistance is used while the rising rate does not change with base resistance. Peak voltage increases with resistance values. The simulations concerning upward leader were also performed. Lightning current, rising rate of current and voltage across the building decrease if upward leader exists. The effect of inductance was investigated by changing the values of base inductance. Peak current and the rising rate of current decreases with increasing inductance, while peak voltage increases with inductance. Inductance can lengthen the stroke duration and reduce the rising rate of current. Different LRC combinations were also investigated. The effectiveness of integrating capacitance to reduce peak current is not as significant as the effect of inductance. Among the 4 different cases of LRC combinations, lightning current and rising time are smaller if the value of inductance matches the value of capacitance. Increasing base resistance is not recommended as the risk of flashover is large. Increasing base inductance can reduce peak current and rising rate of current. Adding capacitance may help to further decrease the rising rate of current providing that the value of capacitance matches with the value of capacitance. The design of an LPS can be improved if an LPS or a lightning rod can simulate the function of upward leader in terms of its LRC. The study provided a new concept of reducing lightning current by building or its LPS. The study gave theoretical support to improve LPS as the new concept is in preliminary stage.

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