Lightning Protection according to IEC 62305 Electrical and Computer Engineering

119 Pages·2015·2.47 MB·English

Lightning Protection according to IEC 62305
Diogo Filipe da Silva Santos
Thesis to obtain the Master of Science Degree in
Electrical and Computer Engineering
Supervisor: Profª. Maria Teresa Nunes Padilha de Castro Correia de Barros
Examination Committee
Chairperson: Prof. Rui Manuel Gameiro de Castro
Supervisor: Profª. Maria Teresa Nunes Padilha de Castro Correia de Barros
Members of the Committee: Profª. Maria Eduarda de Sampaio Pinto de Almeida
Pedro
November 2015
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Abstract

Protection of structures against lightning has been an area of study for a very long time. Since the
middle of the 18th century it began with the work of Benjamin Franklin by protecting structures against
the effects of direct lightning discharges with his famous invention, the lightning rod, which it is still
used today as an air-termination system.

More recently, with the increasing in technology and maintenance of electrical and electronic
equipment, the low operating voltage of that equipment and the increasing height of structures, the
necessity for better lightning protection risk evaluation and measures became a very urgent matter.
That is where the IEC 62305 enters.

The objectives of this thesis are to understand the Risk Management methodology created by the
international committee of IEC, translated in the standard IEC 62305 – Lightning Protection, and apply
it to a computer program.

In order to accomplish that, it is crucial to dominate two subjects: (1) the characterization of the
lightning discharge, including the explanation of the phenomenon itself, which was very difficult to
describe until the 1950s, and the definition of the several current parameters; and (2) the lightning
incidence models adopted by the standard, including the description of the Electrogeometric Model
(EGM) and the Electrical Shadow Model.

Only when these subjects are fully understood, it is possible to take the standard’s risk management
methodology and create a user-friendly computer program, capable of supporting risk assessment and
elaborate effective solutions, according to IEC 62305.

Keywords
Lightning discharge, risk assessment, lightning protection system, IEC 62305
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Resumo

A proteção de estruturas contra descargas atmosféricas tem sido uma área de estudo há já muito
tempo. Desde meados do século 18 que começou com o trabalho de Benjamin Franklin na proteção
de estruturas contra os efeitos de descargas atmosféricas diretas, usando a sua famosa invenção, o
para-raios, que ainda hoje é utilizado como sistema de proteção aéreo.

Mais recentemente, com o aumento da tecnologia e manutenção de equipamentos elétricos e
eletrónicos, a baixa tensão a que estes operam e o aumento da altura média das estruturas, tornou a
necessidade de melhores avaliações de risco e de medidas de proteção contra descargas
atmosféricas um assunto urgente.

Os objectivos desta dissertação são perceber a metodologia de Gestão do Risco criada pelo comité
internacional CEI, traduzida na norma CEI 62305 – Proteção contra descargas atmosféricas, e aplicá-
la a um programa computacional.

Para atingir isso, é crucial dominar dois assuntos: (1) a caracterização da descarga atmosférica,
incluindo a descrição do fenómeno em si, o que foi em si bastante difícil de descrever até à década
de 1950, e a definição dos vários parâmetros que compõem a corrente da descarga; e (2) os modelos
de incidência adotados pela norma, incluindo a explicação do Modelo Eletrogeométrico e o Modelo de
Sombra Elétrica.

Apenas quando estas matérias estão completamente compreendidas é possível pegar na
metodologia de gestão do risco presente na norma e criar um programa computacional de utilização
amigável, capaz de servir de avaliação do risco e elaborar soluções eficazes, segundo a norma CEI
62305.

Palavras Chave
Descarga atmosférica, avaliação do risco, proteção contra descargas atmosféricas, CEI 62305
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Index

Abstract .................................................................................................................................................... iii
Resumo .................................................................................................................................................... v
List of Figures .......................................................................................................................................... ix
List of Tables ........................................................................................................................................... xi
Terms, definitions, symbols and abbreviations ..................................................................................... xiii
1. Introduction .......................................................................................................................................... 1
1.1. Overview ....................................................................................................................................... 1
1.2. Objectives ..................................................................................................................................... 3
1.3. Outline ........................................................................................................................................... 3
2. Overview of international lightning protection standards ..................................................................... 5
2.1. IEC standard 62305 ...................................................................................................................... 5
2.1.1. Before IEC 62305 ................................................................................................................... 5
2.1.2. New approach with IEC 62305 ............................................................................................... 7
2.2. Different approaches by national lightning protection standards .................................................. 8
2.2.1. Differences between national lightning protection standards and the IEC 62305 ................. 8
2.2.2. Conventional and un-conventional lightning air-termination systems .................................... 9
3. General characterization of lightning discharges .............................................................................. 11
3.1. The lightning discharge phenomenon......................................................................................... 11
3.2. Current parameters ..................................................................................................................... 13
3.2.1. Peak current, ..................................................................................................................... 13
3.2.2. Maximum current steepness ................................................................................................ 14
𝐼
3.2.3. Charge, ............................................................................................................................. 14
3.2.4. Specific e𝑄nergy, ........................................................................................................... 14
3.3. Cumulative statistical distributions of lightning peak currents .................................................... 16
𝑊/𝑅
3.4. Recent work in direct peak current measurements .................................................................... 18
3.5. Other parameters derived from current measurements ............................................................. 19
4. Lightning incidence models adopted by IEC 62305 .......................................................................... 23
4.1. Historical overview ...................................................................................................................... 23
4.2. The Electrogeometric Model (EGM) ........................................................................................... 24
4.2.1. Model description ................................................................................................................. 24
4.2.2. The Rolling sphere method (RSM) ....................................................................................... 26
4.3. The Electric Shadow Model ........................................................................................................ 28
4.4. Lightning protection level (LPL) according to IEC 62305 ........................................................... 29
4.5. Final considerations and comparison between EGM and other lightning incidence models ..... 30
5. Risk Management .............................................................................................................................. 35
5.1. Basic Concepts and Methodology .............................................................................................. 35
5.2. Risk Evaluation ........................................................................................................................... 39
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5.2.1. Number of dangerous events, ......................................................................................... 40
5.2.2. Probability of damage to a stru𝑁𝑁ct𝑋ure, ............................................................................... 43
5.2.3. Consequent loss from damage into th𝑃e𝑋 structure and/or its contents, ............................ 48
5.3. Risk mitigation measures ............................................................................𝐿..𝑋.............................. 52
5.3.1. M1: Installing an LPS of an appropriate class ...................................................................... 53
5.3.2. M2: Installing SPDs of an appropriate LPL at the line entrance point ................................. 55
5.3.3. M3: Protection measures against the consequences of fire ................................................ 56
5.3.4. M4: Providing zone(s) with a coordinated SPD system for the internal power and telecom
systems .......................................................................................................................................... 56
5.3.5. M5: Providing zone(s) with an adequate spatial grid-like shield. ......................................... 56
6. Application of the computer program – L.R.A. .................................................................................. 61
6.1. L.R.A. structure ........................................................................................................................... 61
6.2. Example 1: Hospital .................................................................................................................... 63
6.2.1. Structure: geometric and environmental characteristics ...................................................... 64
6.2.2. Connected lines: geometric and environmental characteristics ........................................... 65
6.2.3. Type of loss .......................................................................................................................... 68
6.2.4. Lightning protection zones ................................................................................................... 69
6.2.5. Results ................................................................................................................................. 72
6.2.6. Lightning protection measures ............................................................................................. 74
6.3. Example 2: South Tower in Instituto Superior Técnico (IST), Alameda Campus ....................... 80
6.3.1. Evaluation , assuming a no risk of explosion ...................................................... 85
6.3.2. Evaluation 1: a𝐿s𝑂su=m0in−g risk of explosion ........................................................... 88
7. Conclusions ...........2....𝐿..𝑂...=....0....1...−......................................................................................................... 91
7.1. Summary ..................................................................................................................................... 91
7.2. Achievements ............................................................................................................................. 91
7.3. Future work ................................................................................................................................. 92
Appendices ............................................................................................................................................ 97
Appendix A: Informative tables .......................................................................................................... 97
Bibliography ........................................................................................................................................... 93

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List of Figures

Figure 1: Organization of the four parts of IEC 62305 – Protection against lightning (from IEC 62305-1
[1]) ........................................................................................................................................................... 2
Figure 2: (a) Types of cloud flashes: (i) intracloud; (ii) air discharges; (iii) intercloud; (b) Types of
ground flashes: (i) downward negative ground flashes; (ii) downward positive ground flashes; (iii)
upward positive ground flashes; (iv) upward negative ground flashes, from [19] ................................. 12
Figure 3: Impulse lightning current parameters (typically ) from IEC 62305-1 [1] ................. 15
Figure 4: Cumulative statistical distributions of lightn𝑇in2g< p2e 𝑚𝑚ak𝑠 currents, giving percent of cases
exceeding abscissa value (from [22]) ................................................................................................... 17
Figure 5: Cumulative frequency of the current peak of the negative first stroke according to CIGRE .. 18
Figure 6: Design of an air-termination system according to the rolling sphere method (from [3]) ........ 27
Figure 8: Cumulative frequency of the current peak of the negative first stroke according to CIGRE .. 31
Figure 9: Lightning attractive radii as predicted by EGM (crosses), SLIM (solid line) and CVM (dashed
line) as a function of return stroke peak current for several structure heights (from [41]) .................... 33
Figure 10: Types of damage and types of loss according to the striking point – Source of damage .... 36
Figure 11: Types of loss and corresponding risks resulting from different types of damage ................ 37
Figure 12: Collection areas introduced in IEC 62305 [47] .................................................................... 42
Figure 13: Probabilities that a flash to or near a structure cause damage in the structure and/or its
contents ................................................................................................................................................. 44
Figure 14: Probabilities that a flash to or near a connected line cause damage in the structure and/or
its contents ............................................................................................................................................ 45
Figure 15: M1 measure organization chart of the probabilities and parameters influenced by upgrading
the LPL of the LPS, ........................................................................................................................... 54
Figure 16: M2 measu𝑃r𝐵e organization chart of the probabilities and parameters influenced by ...... 55
Figure 17: M4 measure organization chart of the probabilities and parameters influenced by 𝑃𝐸𝐵 ..... 57
Figure 18: M5 measure organization chart of the probabilities and parameters influenced by𝑃 𝑆th𝑃𝐷e mesh
widths, .............................................................................................................................................. 58
Figure 1𝑤9𝑚: Flowchart of the L.R.A. structure .......................................................................................... 63
Figure 20: Inputs related to the geometric and environmental characteristics of the structure ............ 65
Figure 22: Number of lines (power + telecommunications) connected to the structure to be protected65
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Figure 21: Lightning ground flash density computation by the keraunic number and the world
map distribution [49] ..................................................................................................𝑇..𝑑.................𝑁𝑁..𝐺....... 66
Figure 23: Inputs related to characteristics of the connected lines to the structure .............................. 67
Figure 24: Type of loss in analysis ........................................................................................................ 69
Figure 25: Definition of the lightning protection zones .......................................................................... 70
Figure 26: Unlocking the buttons to enable the characterization of each zone .................................... 70
Figure 27: Parameters that describe the zone “”Rooms Block” for the Hospital example .................... 72
Figure 28: Risk result – risk of loss of human life, for each zone, by risk component ...................... 73
Figure 29: Sele𝑅c1tion of appropriate lightning protection measures according with the three most
influential risk components for the overall risk....................................................................................... 74
Figure 30: Re-calculated risk after taking the lightning protection measures of Solution 1 .................. 75
Figure 31: Re-calculated risk after taking the lightning protection measures of Solution 2 .................. 76
Figure 32: Calculated risk after taking the lightning protection measures of Solution 3 ....................... 77
Figure 33: Parameters that describe the zone “”Intensive Care Unit” from the Hospital example ........ 78
Figure 34: Calculated risk, – risk of loss of economic value, for each zone, by type of risk ............ 78
Figure 35: Simplified econo𝑅m4ic evaluation based on risk analysis ....................................................... 79
Figure 36: Annual savings, , for the three solutions presented ......................................................... 80
Figure 37: South tower in In𝑆s𝑀tituto Superior Técnico ............................................................................ 80
Figure 38: Parameters that describe the laboratory zones of the South Tower in IST ......................... 83
Figure 39: Calculated risk for evaluation ................................................................................ 84
Figure 40: Calculated risk for evaluation 1: 𝐿𝑂 =0 ............................................................................. 84
Figure 41: Data given by the “Information2”: b𝐿u𝑂tt=on0 ...1............................................................................... 86
Figure 42: Approximately collection area of the structure to be protected: South Tower in IST ........... 86
Figure 43: Calculated risk when protection measure against fire is applied: ....... 87
Figure 44: Calculated risk when a lightning protection system of LPL III is 𝑟i𝑝ns=ta0lle.5d→ in 𝑟t𝑝he= s0tr.u2cture to
be protected ........................................................................................................................................... 87
Figure 45: Calculated risk when a coordinated SPD system is installed in zone 3, “Laboratories” ...... 89
Figure 46: Calculated risk of a structure with a lightning protection system LPL II and the preventing
fire measures implemented ................................................................................................................... 89

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