Lightning overvoltage studies in medium voltage distribution lines

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Helsinki University of Technology | Diplomityö
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Date

2008

Department

Elektroniikan laitos

Major/Subject

Sähköverkot ja suurjännitetekniikka

Mcode

S-18

Degree programme

Language

en

Pages

78 + (13)

Series

Abstract

This research work involves simulations, laboratory experiments and statistical analyses of lightning overvoltages in MV distribution lines. The present understanding of lightning models and the nature of lightning overvoltages are also critically investigated and evaluated. All simulations are carried out with reference to fast transient simulation guidelines as specified in the lightning literature. In the experimental work, the electrical breakdown characteristics of lightning impulse voltages are observed on both the tree and the grounded conductor with variations in the striking distances from the lightning electrode to the two objects. This is used to determine the attractiveness of the tree on direct strokes to the grounded conductor. A calibration constant is extracted, which corresponds to the probability of occurrence of direct strokes to both the tree and the grounded conductor being equal. This constant is then incorporated in the electro geometric model to determine the influence of tree height on the exposure arc of a grounded conductor. The experimental result is compared with similar work available in the literature. Finally, the statistical analyses are performed in order to estimate the lightning performance level of the two existing distribution line designs in Finland, which are overhead lines and covered conductors, and also investigate improvements.

Description

Supervisor

Lehtonen, Matti

Thesis advisor

Lehtonen, Matti

Keywords

lightning strokes, lightning overvoltages, MOV arresters, ATP/EMTP, test feeder, distribution line, exposure-arc (EA), electro-geometric model, tree

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Citation

Permanent link to this item

https://urn.fi/URN:NBN:fi:aalto-2020120554198

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[dipl] Teknillinen korkeakoulu / TKK