lighting and earthing design according to ieee80_2000 and iec 62305-2 by aya emad mahmoud

LIGHTING AND EARTHING DESIGN ACCORDING TO

IEEE80_2000 AND IEC 62305-2

BY

AYA EMAD MAHMOUD HAMID

INDEX NO. 074015

Supervisor

Dr. ABDULL ALRAHMAN ALI KARRAR

REPORT SUBMITTED TO

University of Khartoum

In partial fulfillment of the requirement for the degree of

B.Sc. (HONS) Electrical and Electronic Engineering

(CONTROL ENGINEERING)

Faculty of Engineering

Department of Electrical and Electronic Engineering

September 2012

ii

DECLARATION OF ORIGINALITY

I declare that this thesis entitled “LIGHTING AND EARTHING

DESIGN ACCORDING TO IEC 62305-2 AND IEEE80_2000” is my

own work except as cited in the references. The report has not been

accepted for any degree and is not being submitted concurrently in

candidature for any degree or other award.

Signature : _________________________

Name : ____________________________

Date : _____________________________

iii

DEDICATION

To my parents, without whom this thesis would not have seen

light,

To my brother and sisters,

To my colleagues and friends,

To all who taught me a letter

To you all I dedicate this work with all my love and respect;

hoping that it will be of some benefits and use...

Aya

iv

ACKNOWLEDGEMENT

Without the contribution of many people this thesis would not have been

accomplished, I regret it is not possible to name these people in this

acknowledgement.

In particular I am extremely indebted to Dr. Abdull Alrahman Ali Karrar for his

sustained support and fruitful supervision.

Above and before all I thank God who gave me the will and ability to do this work

and put this humble effort between your hands

v

ABSTRACT

. Lightning is one of the most beautiful displays in nature but it can have

devastating results. Lightning can kill people, destroy properties and cause millions of

dollars of damage. Thus protection against this phenomenon is crucial for avoiding

such loss.

Absolute protection against lightning is impossible but through deployment

of a judicious combination of defenses, the lightning protection engineer can attempt

to mitigate the lightning consequences. The need for protection, the economic benefits

of installing protection measures and the selection of adequate protection measures

should be determined in terms of risk management.

The IEC 62305-2 standard presents a procedure to assess the risk due to all

possible effects of lightning flashes to structures. The risk management procedure

described in IEC 62305-2 is rather complicated. It would be useful for lightning

protection engineers to have a software tool to carry out this risk assessment.

The purpose of substation grounding/earthing is to protect the equipment from

efeect of short circite and surges and lightning strikes and to protect the operating

persons in the substation. The substation earthing system is necessary for connecting

neutral points of transformers and generators to ground and also for connecting the

non current carrying metal parts such as structures, overhead shielding wires, tanks,

frames, etc. to earth. Earthing of surge is through the earthing system.

In this project we developed two software tools. One to perform the tedious

risk assessment as described in IEC 62305-2. The other is to assess the safety of the

ground grid design as described in IEEE80-2000 standard. Both of them were

developed using visual basic and they were proved to be reliable and intuitive

vi

المستخلص

انبزق يؼخبز ي اجم انشاذ ف انطبيؼ . نك خائج يذيز. يك نهبزق ا يمخم الاسا.يذيز

يايسب خسائز ححسب بانلاي . نذا ظغ حاي ظذ ذ انظاز ي جذا نخفاد يثم ذ انخهكاث

انخسائز.

باسطت انصت انحاي انطهم ظذ انبزق يسخحيه نك ي خلال شز يجػ ي اناغ انجيذ

انحاي انفائذ الالخصادي ي حزكيب يذس انحاي ي انبزق يك ا يحذ ي أثار انبزق .انحج ان

انحاي اخخيار حذابيز انحاي انكافي يجب ا ححذد ي حيث ادار انخاغز.

IEC 62305-2

يمياس يؼزض إجزاء نخميى انخاغز نجيغ الاثار انحخه ي انبزق ػه انشاءاث ، إجزاء إدارة

،سيك ي انفيذ نذسانؼمذIEC 62305-2انصف ف انمياس انخاغز

انحاي ي انصاػك ا يك نذيى بزايج نخميى ذ انخاغز.

حاثيزاث ي حأريط انحطاث حاي انؼذاث الاشخاص انؼايهي ف انحط ي ضانغز

انحايذ ي انحلاث انؼاصف،ظاو حأريط انحطاث ظزر جذا نزبػ انماغ رانمصانصاػك

اننذاث ان الارض ايعا ربػ الاجزاء انؼذي انخ لاححم حيار يثم انشأث ان الارض.

.IEC 62305لذ لا ف ذا انشزع بخصيى بزايجي الأل نخميى انخاغز كا يظح ف يمياس

Visualلذ حى اسخخذاو نفت .IEEE80-2000انثاي نخميى سلايتانخصيى انشبك نلأرض كا يظح ف

Basic . لذ اثبج ا يك اػخاد انبزايجي يغ سن اسخخذايا. نخصيى انبزايجي

vii

TABLE OF CONTENTS

DECLARATION OF ORIGINALITY .................................................................................... I

DEDICATION …………………………………………………………………………………………...…II

ACKNOWLEDGEMENT ...................................................................................................... IV

ABSTRACT ............................................................................................................................. V

VI ............................................................................................................................... المستخلص

LIST OF FIGURES ................................................................................................................ XI

LIST OF TABLES ................................................................................................................ XII

LIST OF ABBREVIATIONS ............................................................................................. XIII

CHAPTER ONE ...................................................................................................................... 1

1.1. Overview .............................................................................................................................. 1

1.2. Problem statement............................................................................................................... 3

1.3. Motivation ........................................................................................................................... 3

1.4. Objectives ............................................................................................................................ 4

1.5. Thesis Layout ........................................................................................................................ 4

2. .......................................................................................................... CHAPTER TWO

.................................................................................................................................................. 5

2.1. Introduction ......................................................................................................................... 5

2.2. History of lightning ............................................................................................................... 6

2.3. Lightning Damage ................................................................................................................. 8

2.3.2 Human injury .............................................................................................................................. 8

2.3.3 Physical Damage .................................................................................................................... 9

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2.4. Loss ...................................................................................................................................... 9

2.5. Risk ....................................................................................................................................... 9

2.5.1. Tolerable Risk ...................................................................................................................... 10

2.5.2. Risk components ................................................................................................................. 10

2.5.2.1. Risk components for a structure due to flashes to the structure .............................. 10

2.5.2.2. Risk component for a structure due to flashes near the structure ........................... 11

2.5.2.3. Risk components for a structure due to flashes to a service connected to the

structure 11

2.5.2.4. Risk component for a structure due to flashes near a service connected to the

structure 12

2.5.3. Composition of risk components related to a structure ..................................................... 12

2.5.3.1. Composition of risk components with reference to the source of ............................ 13

damage ......................................................................................................................................... 13

2.5.3.2. Composition of risk components with reference to the type of damage .................. 13

2.5.4. Assessment of risk components for a structure .................................................................. 14

2.6. OBJECTIVE OF EARTHING .................................................................................................... 15

2.7. REQUIREMENT OF GOOD EARTHING .................................................................................. 16

2.8. Earthing conductor ............................................................................................................. 16

2.9. Earth Resistance ................................................................................................................. 16

2.10. Earth grid ............................................................................................................................ 16

2.11. Step Potential and Touch Potential .................................................................................... 17

2.11.1. Step Potential ................................................................................................................. 17

2.11.2. Touch Potential............................................................................................................... 17

2.12. Permissible Current through a Human Body during the Fault ............................................. 18

2.13. Common Shock Situations .................................................................................................. 18

2.14. Protective Surface Material ................................................................................................ 19

2.15. Design Procedures of a Grounding System ......................................................................... 19

2.16. Design Modifications .......................................................................................................... 21

2.17. Tolerable Body Current Limits ............................................................................................ 21

2.18. Circuit Equivalents for Common Shock Situations .............................................................. 23

2.18.1. Resistance of the Human Body ....................................................................................... 23

2.18.2. Touch and Step Voltage .................................................................................................. 23

2.19. Addition of Surface Layer ................................................................................................... 26

2.19.1. Tolerable Step and Touch Voltage .................................................................................. 27

2.19.2. Conductor Sizing ............................................................................................................. 28

2.19.3. Asymmetrical Currents ................................................................................................... 29

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2.20. Ground Resistance.............................................................................................................. 29

2.21. Maximum Grid Current....................................................................................................... 31

2.22. Ground Potential Rise (GPR) ............................................................................................... 32

2.23. Computing Maximum Step and Mesh Voltages .................................................................. 32

2.23.1. Mesh Voltage (Em) ......................................................................................................... 32

2.23.2. Step Voltage (Es) ............................................................................................................. 36

3. ...................................................................................................... CHAPTER THREE

................................................................................................................................................ 38

3.1. Requirement Analysis and Software Definition .................................................................. 38

3.2. Tools ................................................................................................................................... 39

3.2.1. Microsoft Visual Studio ....................................................................................................... 39

3.2.2. Visual Basic (VB) .................................................................................................................. 39

3.2.3. Word Cleaner 5.0 ................................................................................................................ 41

3.2.4. HTML Help Workshop ......................................................................................................... 41

3.3. Development Plan .............................................................................................................. 42

3.4. Lightning risk assessment ................................................................................................... 42

3.4.1. Structure page ..................................................................................................................... 42

3.4.2. Service lines ......................................................................................................................... 45

3.4.3. Zones ................................................................................................................................... 46

3.4.4. Losses .................................................................................................................................. 48

3.4.4.1. Loss of service to the public:...................................................................................... 50

3.4.4.2. Loss of cultural heritage............................................................................................. 52

3.4.4.3. Loss of Human Life ..................................................................................................... 55

3.4.4.4. Loss of service to the public ....................................................................................... 55

3.4.4.5. Loss of cultural heritage............................................................................................. 55

3.4.5. Risk calculations .................................................................................................................. 56

3.4.6. Risk composition ................................................................................................................. 57

3.4.7. Protection measures ........................................................................................................... 57

3.4.7.1. Reducing RA ............................................................................................................... 59

3.4.7.2. Reducing RB ............................................................................................................... 59

3.4.7.3. Reducing RC ............................................................................................................... 60

3.4.7.4. Reducing RM .............................................................................................................. 61

3.4.7.5. Reducing RU and RV .................................................................................................. 61

3.4.7.6. Reducing RW and RZ .................................................................................................. 62

3.5. Design ................................................................................................................................ 63

3.5.1. GRID DESIGN ....................................................................................................................... 65

3.5.2. Soil Editor ............................................................................................................................ 65

3.5.3. General Design Data ............................................................................................................ 66

3.5.4. Drawing the Grid ................................................................................................................. 68

3.5.5. Earthing grid graphical tool ................................................................................................. 68

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3.6. File ..................................................................................................................................... 69

3.6.1. New ..................................................................................................................................... 69

3.6.2. Open .................................................................................................................................... 69

3.6.3. Save and Save As ................................................................................................................. 69

3.7. Help .................................................................................................................................... 69

3.8. Implementation ................................................................................................................. 70

3.9. Deployment ........................................................................................................................ 70

4. ......................................................................................................... CHAPTER FOUR

................................................................................................................................................ 71

4.1. Lightning Risk Assessment Software Testing ...................................................................... 71

4.1.1. About NTC Tower ................................................................................................................ 71

4.1.2. Relevant data and characteristics ....................................................................................... 73

4.1.3. Calculations ......................................................................................................................... 79

4.1.4. Result Discussion ................................................................................................................. 84

4.2. GRID DESIGN Testing .......................................................................................................... 87

4.3. Results ................................................................................................................................ 88

5. ....................................................................................................... 5 CHAPTER FIVE

................................................................................................................................................ 91

5.1. Conclusion .......................................................................................................................... 91

5.2. Future work ........................................................................................................................ 92

BIBLIOGRAPHY ................................................................................................................. 93

APPENDIX A: ASSESMENT OF NX ................................................................................. A1

APPENDIX B: ASSESMENT OF PX .................................................................................. B1

APPENDIX C: ASSESMENT OF LX .................................................................................. C1

APPENDIX D: MATERIAL CONSTANTS AND EQUIVALENT SUBSTATION

IMPEDANCES ..................................................................................................................... D1

APPENDIX E: LIGHTNING RISK ASSESSMENT SOFTWARE AND GDID DESIGN

SOFTWARE HELP FILES .................................................................................................. E1

xi

LIST OF FIGURES

Figure( ‎2.1) Step Potential and Touch Potential .................................................... 17

Figure( ‎2.2) Exposure to touch voltage .................................................................... 23

Figure( ‎2.3 )Touch voltage circuit ............................................................................ 24

Figure( ‎2.4) Exposure to step voltage ....................................................................... 24

Figure( ‎2.5) Step voltage circuit ................................................................................ 25

Figure ‎(3.1) development plan .................................................................................. 42

Figure (‎3.2) Structure page design sketch ............................................................... 43

Figure ‎(3.3) Collection area graphical tool design sketch ...................................... 44

Figure ‎(3.4) Design sketch for Service Lines page .................................................. 45

Figure (‎3.5) Design sketch for Zones page ............................................................... 46

Figure ‎(3.6)‎Design‎sketch‎for‎Zones’‎internal‎systems‎page ................................. 48

Figure (‎3.7) Design sketch for Losses page .............................................................. 49

Figure ‎(3.8 )Design sketch for Guided Loss of Human Life window .................... 49

Figure (‎3.9) Design sketch for Typical Loss of Human Life window .................... 50

Figure ‎(3.10) Design sketch for Guided Loss of Service window .......................... 51

Figure (‎3.11) Design sketch for Typical Loss of Service window .......................... 51

Figure ‎(3.12) Design sketch for Guided Loss of Cultural Heritage window ........ 52

Figure (‎3.13) Design sketch for Typical Loss of Cultural Heritage window ........ 52

Figure (‎3.14) Design sketch for Guided Economic Loss window .......................... 53

Figure (‎3.15) Design sketch for Typical Economic Loss window .......................... 54

Figure (‎3.16) Design sketch for Manual Loss of Human Life, Loss of service, Loss

of cultural Heritage and Economic Loss window ................................................... 55

Figure (‎3.17) Design sketch for Calculation page ................................................... 56

Figure ‎(3.18) Design sketch for Risk composition window .................................... 57

Figure ‎(3.19) Design sketch for Protection measure page ...................................... 58

Figure (‎3.20) Design sketch for reducing RA window ............................................ 59

Figure( ‎4.1) Structure and service lines data for the NTC Tower......................... 78

Figure( ‎4.2) Zones and internal systems data for the NTC Tower ........................ 79

Figure( ‎4.3) Losses data for the NTC Tower ........................................................... 79

Figure( ‎4.4) The NTC Tower enlarged with a scale factor of 4 ............................. 80

Figure (‎4.5) Collection area for direct strikes to the NTC Tower ......................... 81

Figure( ‎4.6) Collection area for strikes near the NTC Tower ................................ 81

Figure ‎(4.7) Lightning risk assessment calculations for the NTC Tower ............. 82

Figure (‎4.8) Risk assessment results (R1) when assuming that the NTC Tower is

surrounded by objects smaller or of the same height ............................................. 85

Figure (4.9) Risk assessment results (R1) when loss of human life due to failure

of internal systems is not considered ........................................................................ 86

Figure (4.10)................................................................................................................ 88

xii

LIST OF TABLES

Table (2.1) Tolerable Risk ......................................................................................... 10

Table (‎4.1) Structure characteristics ........................................................................ 73

Table (‎4.2) Internal power system and relevant incoming power line

characteristics ............................................................................................................. 73

Table (4.3) Internal power system and relevant incoming power line

characteristics ............................................................................................................. 74

Table (‎4.4) Internal telecom system and relevant incoming line characteristics . 74

Table (‎4.5) Zone Z1 characteristics .......................................................................... 75



Table (4.8) Zone Z4 characteristics .......................................................................... 76

Table (4.9) Zone Z5 characteristics .......................................................................... 77

Table (4.10) Loss Factors relevant to R1 ................................................................. 77

Table (4.11) Factors relevant to R2 .......................................................................... 77

Table (4.12) Loss Factors relevant to R4 ................................................................. 78

Table(4.13) Collection areas Ad and Am ................................................................. 81

Table (‎4.14) Risk components relevant to R1 .......................................................... 82

Table (‎4.15) Risk components relevant to R2 .......................................................... 83

Table(4.16) Risk components relevant to R4 ........................................................... 83

Table (4.17) Risk Totals ............................................................................................. 84

Table (4.18) Soil model parameters .......................................................................... 87

Table )4.19) System data ........................................................................................... 87

Table(4.20) Ground grid parameters ....................................................................... 87

Table(4.21) Results according to GRID DESIGN and ETAP................................ 88

xiii

LIST OF ABBREVIATIONS

A Area occupied by the ground grid

Ad Collection area for flashes to an isolated structure

Ai Collection area for flashes near a service

Al Collection area for flashes to a service.

Am Area of influence for flashes near a structure

B Radius of a foot taken as a metallic disk

Cd Location factor

Ce Environmental factor

Ct Correction factor for a HV/LV transformer on the service

ct Total value of the structure, in currency

D Spacing between parallel conductors

D Diameter of grid conductors

D1 Injury to living beings

D2 Physical damage

D3 Failure of electrical and electronic systems

Df Decrement factor for the duration of the fault

DLL Dynamic link library

Dm Is the maximum distance between any two points on the grid

GPR Ground Potential Rise

GUI Graphical user interface

H Height of the structure

H Depth of the grid

Ha Height‎of‎the‎structure‎connected‎at‎end‎“a”‎of‎a‎service

Hb Height‎of‎the‎structure‎connected‎at‎end‎“b”‎of‎a‎service.

Hc Height of the service conductors above ground

hs Thickness of surface material

Hz Factor increasing the loss when a special hazard is present

I rms magnitude of the current through the body

IDE Integrate Development Environment

IEC International Electrotechnical Committee

IEEE Institute of Electrical and Electronics Engineers

xiv

Ig rms symmetrical grid current

K Constant related to electric shock energy

KMS Factor relevant to the performance of protection measures against LEMP

KS1 Factor relevant to the screening effectiveness of the structure

KS2 Factor relevant to the screening effectiveness of shields internal to the

structure

KS3 Factor relevant to the characteristics of internal wiring

KS4 Factor relevant to the impulse withstand voltage of a system

L Length of structure

L1 Loss of human life in a structure

L2 Loss of service to the public in a structure

L3 Loss of cultural heritage in a structure

L4 Loss of economic value in a structure

La Length of the structure connected‎at‎end‎“a”‎of‎a‎service

LA Loss related to injury to living beings

Lc Length of service section

LC Loss related to failure of internal systems (flashes to structure)

Lc Total length of grid conductor

LEMP Lightning Electomagnetic Impulse

Lf Loss in a structure due to physical damage

LM Loss related to failure of internal systems (flashes near structure)

Lo Loss in a structure due to failure of internal systems

Lp Peripheral length of grid

LPS Lightning Protection System

LR Total length of ground rods

Lr Spacing between parallel conductors

Lt Loss due to injury by touch and step voltages

LT Total burial length of conductors

LX Consequent loss in a structure

Lx Maximum length of grid in the x-direction

Ly Maximum length of grid in the y-direction

MS Microsoft

N Grid Geometric factor

xv

ND Number of dangerous events due to flashes to a structure

NDa Number‎of‎dangerous‎events‎due‎to‎flashes‎to‎a‎structure‎at‎“a”‎end‎of‎line

Ng Lightning ground flash density

NI Number of dangerous events due to flashes near a service

NL Number of dangerous events due to flashes to a service

NM Number of dangerous events due to flashes near a structure

Np Number of possible endangered persons (victims or users not served).

Nt Expected total number of persons (or users served)in the structure

NTC International Telecommunication Corporation

NX Number of dangerous events per annum

Px Probability of damage

PA Probability of injury to living beings (flashes to a structure)

PB Probability of physical damage to a structure (flashes to a structure)

PLI Probability of failure of internal systems (flashes near a connected service)

PLD Probability of failure of internal systems (flashes to a connected service)

LPL Lightning Protection Level

PM Probability of failure of internal systems (flashes near a structure)

PMS Probability of failure of internal systems (with protection measures)

PSPD Probability of failure of internal systems or a service when SPDs are

installed.

PX Probability of damage to a structure

R1 Risk of loss of human life in a structure

R2 Risk of loss of service to the public in a structure

R3 Risk of loss of cultural heritage in a structure

R4 Risk of loss of economic value in a structure

Ra Reduction factor associated with the type of surface of soil.

RA Risk component (injury to living beings – flashes to a structure)

RAD Rapid Application Development

RB Risk component (physical damage to a structure – flashes to a structure)

Rb Body Resistance

RC Risk component (failure of internal systems -flashes to a structure)

RD Risk for a structure due to flashes to the structure

Rf Factor reducing loss depending on risk of fire

xvi

RF Risk due to physical damage to a structure.

Rf: Ground resistance of one foot

Rg Is the substation ground resistance

RI Risk for a structure due to flashes not striking the structure

RM Risk component (failure of internal systems – flashes near a structure)

RO Risk due to failure of internal systems

Rp Factor reducing the loss due to provisions against

Rs Shield resistance per unit length of a cable

RS Risk due to injury to living beings

RT Tolerable risk

Ru Reduction factor associated with the type of surface of floor

RX Risk component for a structure

S1 Flashes to a structure

S2 Flashes near a structure

SB Shock energy

Ta Ambient temperature

tc Duration of current

TCAP Thermal capacity per unit volume

TC81 Technical Committee of the International Electrotechnical Committee

Td Thunderstorm days per year

tf Is the time duration of the fault

Tm Is the maximum allowable temperature

tp Time in hours per year that persons are present in a dangerous place

UW Rated impulse withstand voltage of a system

VB Visual Basic

VS Visual Studio

W Width of structure

ZS Zones of a structure

ZTh Theveninimpedance

αr Thermal coefficient of resistivity at reference temperature Tr

Ρ Soil resistivity

ρr Resistivity of the ground conductor at reference temperature Tr

ρs Resistivity of surface layer material

INTRODUCTION CHAPTER 1

1

CHAPTER ONE

INTRODUCTION

1.1. Overview

Lightning is one of the natural phenomena that can be observed by every human

being, it is also known that Lightning is a massive electrostatic discharge caused by

unbalanced electric charge in the atmosphere, and for that, it has devastating results.

Lightning can kill people, destroy properties and cause millions of dollars of damage.

Thus protection against this phenomenon is crucial for avoiding such loss. The need

for protection, the economic benefits of installing protection measures and the

selection of adequate protection measures should be determined in terms of risk

management.

Risk assessment as applied to Lightning Safety for Buildings and Facilities first was

conceived in 1993 at Kennedy Space Center by the US Air Force [1]

. This risk

assessment process is a tool for establishing priorities to upgrade operational

procedures and structures.

Following a world-wide scientific and technical work, IEC standards are based on

scientifically proven theories and experimentation taking into account the

international expertise in the matter. They lay down requirements for the design and

installation of LPS (Lightning Protection Systems) for structures and buildings, the

protection against lightning of services entering the buildings and the protection of

electrical and electronic systems.

TC81 has achieved its first cycle of work when issuing a standard (IEC 62305) in four

parts (IEC 62305-1 to 4). The complete standard provides the general principles to be

followed in the protection against lightning of structures (including their installations

and contents as well as persons).

http://en.wikipedia.org/wiki/Electrostatic_discharge

http://en.wikipedia.org/wiki/Electric_charge

http://en.wikipedia.org/wiki/Earth%27s_atmosphere


2

The risk management method which is reported in IEC 62305-2 provides a procedure

for the evaluation of the total risk to be compared with an upper limit of tolerable risk;

this procedure allows the selection of appropriate protection measures to be adopted

to reduce the risk below the tolerable limit.

The risk R of lightning on the structure according to IEC 62305-2 is the sum of

different‎ components‎ RX‎ (X‎ =‎A,‎B,…);‎ each‎ risk‎ component‎ RX‎ depends‎ on‎ the‎

point of strike; it also depends on the number of dangerous events N, the probability

of damage PX and the consequent loss LX so that RX = N PX LX .

Saying that an electrical power system is protected means that it is safe and reliable,

and these are two major concerns in the operation and design of an electrical power

system. To ensure that substations are safe and reliable, the substation must have a

properly designed grounding system.

The sole purpose of substation grounding/earthing is to protect the equipment from

surges and lightning strikes and to protect the operating persons in the substation. The

substation earthing system is necessary for connecting neutral points of transformers

and generators to ground and also for connecting the noncurrent carrying metal parts

such as structures, overhead shielding wires, tanks, frames, etc. to earth. Earthing of

surge is through the earthing system. The function of substation earthing system is to

provide a grounding mat below the earth surface in and around the substation which

will have uniformly zero potential with respect to ground and lower earth resistance to

Provide discharge path for lightning over voltages coming via rod-gaps, surge

arresters, and shielding wires etc.

Ensure safety of the operating staff by limiting voltage gradient at ground level in

the substation

Provide low resistance path to the earthing switch earthed terminals, so as to

discharge the trapped charge (Due to charging currents even the line is dead still

charge remains which causes dangerous shocks) to earth prior to maintenance and

repairs.

IEEE Std.80 has been widely revised for more than ten years and is generally

followed as a standard for the grounding systems. In this work, a GUI computer


3

program has been developed. The calculations of the step voltage, touch voltage,

GPR, and grounding resistance, are based on IEEE Std. 80 - 2000. The results of

proposed Grid Design tool compared and verified with the results of ETAP.

1.2. Problem statement

The purpose of a lightning protection system is to protect buildings from direct

lightning strikes and possible fire, or from the consequences of the load-independent

active lightning current. Lightning strikes to a structure cannot be prevented, yet the

damage caused can be avoided through the implementation of a lightning protection

system. The decision on providing the most adequate lightning protection is not an

easy task. So that we need to use reliable software to facilitate the risk assessment

process and decide on the best protection scheme.

Substations as a whole being an important part of the complete power system,

grounding system of substations plays a vital role in overall performance of reliable

power system. To Design a proper substation grounding system it is not easy. There

are many parameters that affect its design. In order to properly plan and design the

grounding grid, calculations of the following must be done: maximum fault current,

grid resistance, grid current, safe touch and step voltages, ground potential rise, as

well as expected touch and step voltage levels.

1.3. Motivation

To help lightning protection engineers with the numerous calculation of the risk

management procedure described in IEC 62305-2 that could take hours and hours, we

developed a software tool not only to assess the risk on the structure but also guide

them to arrive at an effective protection scheme.

Designing a ground grid requires the calculation of mesh and step voltages to see

whether they exceed the tolerable limit or not. The designer would try different grid

layout until they arrive at a safe design. To help them with this process we developed

a suitable software tool based on the procedure given in IEEE 80-2000 standard.


4

1.4. Objectives

This work has two objectives

1. Developing lightning risk assessment software to help the user assess the risk due

to all possible effects of lightning strikes to structures according to the risk

management method reported in IEC 62305-2.

2. Developing an effective design tool according to IEEE 80-2000 standard to help

designers model and build grounding systems that will ensure the performance of

power systems and safety of personnel.

1.5. Thesis Layout

This report is organized into five chapters:

Chapter 2 (Literature review): This chapter goes through the demanding issues of

providing protection against lightning and of assuring safety in AC substations. Also

in this chapter the lightning risk assessment process is presented along with the

concepts and various calculations needed to assure the safety of the substation ground

grid.

Chapter 3 (System design and implementation): This chapter details the objectives

of this project, and focus on how these objectives were achieved. Also it presents the

tools, design methodology and implementation of the Lightning Risk Assessment

software and the GRID DESIGN software.

Chapter 4 (Testing and results discussion): This chapter contains the results of the

testing of the two software tools and the discussion on these results testing procedure

and the validation of the performance for the two programs.

Chapter 5 (Conclusions and recommendations): this chapter contains a conclusion

about the developed software tools performance and recommended future work

LITERATURE REVIEW CHAPTER 2

5

2.

CHAPTER TWO

LITERATURE REVIEW

2.1. Introduction

Lightning is an atmospheric discharge of electricity, which typically occurs during

thunderstorms, and sometimes during volcanic eruptions or dust storms. The leader of

lightning can travel at speeds of 60,000 mis, and can reach temperatures approaching

30,000 ᵒ C (54,000ᵒF) [2]

, hot enough to fuse soil or san year d into glass channels.

There are over 16 million lightning storms every year [2].

Lightning is a major cause of

building fires, even though highly effective protection against this threat has long

been available.

Most lightning occurs within the clouds. Only about 20% strike the surface [2]

.

Because air is a good insulator, the lightning tends to take the shortest route towards a

high object on the surface or a path with least resistance.

Nothing is quite common or abundantly available throughout world in the Earthing

soil. Most of us think earth as something to be used for planting or to be excavated

for a building foundation. Yet, it also has an electrical property-conductivity that is

put to practical use every day in individual plants and Electrical utilities. Broadly

speaking earth resistance is the resistance of the soil to the passage of electrical

current. Actually earth is a poor conductor compared with normal conductor

like copper. But if the area of path for the current is large enough, the resistance can

be quite low and earth can be a conductor. Earthing is foremost important for the

safety of human beings, animals, and consumer property and utilities equipment.


6

2.2. History of lightning

In the 1700s Benjamin Franklin proposed a method of protecting structures from the

effects of Lightning [3]

. His method was based on observations that suggested

lightning prudentially strikes elevated object and lightning currents can be carried to

and dissipated in earth by a suitable network of conductors and grounding electrodes.

Various approaches aimed at providing protection against lightning , similar to

Franklin‟s‎method‎ of‎ elevated‎ rods‎ and‎ down-conductors, have been tried over the

past 250 years; the more successful designs have been described and published as

standards for guidance and protection of the public.

In 1904, The National Fire Protection Association of Quincy, MA, established the

American standard for installation of lightning protection systems. Now known as

NFBA 780, the standard for the installation of lightning protection systems is revised

periodically by an NFBA technical committee to incorporate new knowledge about

the physics of lightning and advances in technology.

It is well established that properly installed and maintained conventional structural

lightning‎protection‎systems‎(LPS)‎based‎on‎franklin‟s‎methods‎significantly‎decrease‎

lightning damage. Several different types of devices, including lightning rods and

electrical charge dissipaters, are used to prevent lightning damage and safely redirect

lightning strikes.

The installation of such system in conformance with NFPA 780 is not simple matter.

A lightning rod (or lightning protector) is a metal strip or rod, usually of copper or

similar conductive material , used as part of lightning safety to protect tall or isolated

structures (such as the roof of a building or the mast of a vessel) from lightning

damage. Its formal name is lightning finial or air terminal. Sometimes , the systems is

informally referred to as a lightning conductor, arrester, or discharger, however, these

terms actually refer to lightning protection systems in general or specific components

within them .

Lightning protection systems after lightning streamer behavior. Proper producers

followed for the protection must be followed for the protection to be effective.


7

To provide effective protection for structures, alighting protection system must

include:

- A sufficient number or rods must extend above the upper potions of the structure

to be protected and their tips must be so exposed that one of them becomes the

locally-preferred strike receptor upon the close approach of a leader, descending

from a thundercloud.

- The‎ connection‎ between‎ the‎ strike‎ receptor‎ and‎ the‎ earth,‎ namely‎ the‎ “main‎

conductors”‎and‎the‎“down‎conductor‎system”‎must‎be‎able‎to‎carry‎the‎rapidly-

varying lightning current without significant heating and without dislodging.

- The impedance to the flow of current in the down conductor must be sufficiently

low‎that‎“side‎flashes”‎ to‎objects‎ in‎ the‎vicinity‎do‎not‎occur‎as‎a‎ result‎of‎high‎

voltage developed by the passage of the current.

- The connection from the down conductors to the earth must allow the lightning

current to flow into the ground without the development of large electrical

potential‎ differences‎ on‎ the‎ earth‟s‎ surface‎ and‎ without‎ creating‎ hazards‎ to‎

personal or structures nearby.

- All nearby metal components of the structure must be electrically bonded to its

down-conductor‎ system‎ to‎minimize‎ the‎ probability‎ of‎ “side‎ flashes.‎Given‎ this‎

complexity in designing effective lightning protection systems, standards that

specify the requirements which must be met to ensure the adequacy of each

lightning protection installation are essential by most industrialized nations.

The American standard represents nearly 250 years of practical experience and about

100 years of consensus among specialists in the physics of lightning, of manufacturers

of lightning protection equipment and of lightning protection installers.

The members of the AMS committee on atmospheric electricity have reviewed the

modern practices of lightning protection and have concluded that NFPA 780 is useful

standard with a sound scientific basis. The Society recognizes the need for lightning

protection standard and supports the current American edition specifying the

installation of lightning protection systems.


8

2.3. Lightning Damage

2.3.1 Failure of internal system

Part of the lightning current can be carried inside a building by electric power,

telephone,

Analog or digital data lines (e.g., closed circuit television cameras, sensors in an

industrial plant, etc.). This direct injection of lightning current inside a building can

cause immense damage to electrical – and especially electronic – circuits and

equipment [4]

.

Examples of lightning damage to electrical equipment include flashover of insulation

inside motors or transformers, so that the equipment is no longer functional. Examples

of lightning damage to electronic equipment includes vaporized traces on printed

circuit boards, vaporized transistors and integrated circuits, blown fuses, etc.

Aside from surge currents that are conducted on wires or cables, there can also be

damage from magnetic fields associated with lightning currents [4]

. For example,

lightning current that travels to earth along reinforcing steel inside a concrete wall or

column can produce a rapidly changing magnetic field that can erase floppy disks or

computer tapes inside a storage cabinet. Further, this rapidly changing magnetic field

can induce a surge current in loops of wire or cable that are common in computer

systems, and such surge currents can cause damage or upset in the same way as direct

injection of lightning current into wires and cables.

Lightning current can travel for long distances on overhead power lines, or in

underground pipes and cables, so that a user who experiences upset or damage may

not recognize that it coincided with a lightning strike some distance from the user.

2.3.2 Human injury

Lightning strikes injure humans in several different ways [5]

:

Direct strike, which is usually fatal.

Contact injury, when the person was touching an object that was struck


9

Side splash, when current jumped from a nearby object to the victim

Ground strike, current passing from a strike through the ground into a nearby

victim. A strike can cause a difference of potential in the ground (due to resistance

to current in the Earth), amounting to several thousand volts per foot.

Blast injuries, including hearing damage or blunt trauma by being thrown to the

ground.

2.3.3 Physical Damage

At the point of impact there would be a major release of heat that would result in

severe physical damage to the structure. This damage can include vaporization of

masonry, melting of structural materials, explosion and destruction of structure and

setting a building on fire.

Fire could also‎ be‎ triggered‎ by‎ sparks‎ caused‎ by‎ overvoltage‟s coming through the

service lines or those resulting from resistive and inductive coupling.

2.4. Loss

Each type of damage, alone or in combination with others, may produce a different

consequential loss in the object to be protected. The type of loss that may appear

depends on the characteristics of the object itself and its content. The following types

of loss shall be taken into account:

L1 Loss of human life

L2 Loss of service to the public

L3 Loss of cultural heritage

L4 Loss of economic value

2.5. Risk

The risk R is the value of a probable average annual loss. For each type of loss which

may appear in a structure, the relevant risk shall be evaluated. The risks to be

evaluated in a structure may be as follows:

R1 Risk of loss of human life

http://en.wikipedia.org/wiki/Hearing_damage#Physical_trauma


10

R2 Risk of loss of service to the public

R3 Risk of loss of cultural heritage

R4 Risk of loss of economic value

2.5.1. Tolerable Risk

Representative values of acceptable risk RT, where lightning flashes involve loss of

human life or loss of social or cultural values, are given under the responsibility of

IEC as in Table (2.1).

.

Table (‎2.1) Tolerable Risk

Types of loss RT

Loss of human life or permanent injuries 10–5

Loss of service to the public 10–3

Loss of cultural heritage 10–3

For the loss of the economic value a private decision will be taken by the owner or the

designer of the structure under their own responsibility.

Protection against lightning is required if the risk R (whether this be R1, R2 or R3) is

greater than the tolerable risk RT. Conversely if R is lower than RT then no protection

measures are required.

2.5.2. Risk components

To evaluate risks, R, the relevant risk components (partial risks depending on the

source and type of damage) shall be defined and calculated.

Each risk, R, is the sum of its risk components. When calculating a risk, the risk

components may be grouped according to the source of damage and the type of

damage.

2.5.2.1. Risk components for a structure due to flashes to the structure

RA: Component related to injury to living beings caused by touch and step

voltages in the zones up to 3 m outside the structure. Loss of type L1 and, in the


11

case of structures holding livestock, loss of type L4 with possible loss of animals

may also arise [6]

.

RB: Component related to physical damage caused by dangerous sparking inside

the structure triggering fire or explosion, which may also endanger the

environment. All types of loss (L1, L2, L3 and L4) may arise [6]

.

RC: Component related to failure of internal systems caused by LEMP. Loss of

type L2 and L4 could occur in all cases along with type L1 in the case of

structures with risk of explosion and hospitals or other structures where failure of

internal systems immediately endangers human life [6].

2.5.2.2. Risk component for a structure due to flashes near the structure

RM: Component related to failure of internal systems caused by LEMP. Loss of

type L2 and L4 could occur in all cases, along with type L1 in the case of

structures with risk of explosion and hospitals or other structures where failure of

internal systems immediately endangers human life [6]

.

2.5.2.3. Risk components for a structure due to flashes to a service connected to

the structure

RU: Component related to injury to living beings caused by touch voltage inside

the structure, due to lightning current injected in a line entering the structure. Loss

of type L1 and, in the case of agricultural properties, losses of type L4 with

possible loss of animals could also occur [6]

.

RV: Component related to physical damage (fire or explosion triggered by

dangerous sparking between external installation and metallic parts generally at

the entrance point of the line into the structure) due to lightning current

transmitted through or along incoming services. All types of loss (L1, L2, L3 and

L4) may occur [6]

.

RW: Component related to failure of internal systems caused by over-voltages

induced on incoming lines and transmitted to the structure. Loss of type L2 and

L4 could occur in all cases; along with type L1 in the case of structures with risk

of explosion and hospitals or other structures where failure of internal systems

immediately endangers human life [6]

.


12

2.5.2.4. Risk component for a structure due to flashes near a service connected

to the structure

RZ: Component related to failure of internal systems caused by over-voltages

induced on incoming lines and transmitted to the structure. Loss of type L2 and L4

could occur in all cases; along with type L1 in the case of structures with risk of

explosion and hospitals or other structures where failure of internal systems

immediately endanger human life [6]

.

2.5.3. Composition of risk components related to a structure

Risk components to be considered for each type of loss in a structure [6]

are listed

below:

R1: Risk of loss of human life:

(2.1)

R2: Risk of loss of service to the public:

(2.2)

R3: Risk of loss of cultural heritage:

(2.3)

R4: Risk of loss of economic value:

(2.4)


13

2.5.3.1. Composition of risk components with reference to the source of

damage

(2.5)

where:

RD is the risk due to flashes striking the structure (source S1) which is defined as the

sum:

(2.6)

where

RI is the risk due to flashes influencing it but not striking the structure (sources: S2,

S3 and S4). It is defined as the sum:

(2.7)

2.5.3.2. Composition of risk components with reference to the type of damage

(2.8)

where:

RS is the risk due to injury to living beings (D1) which is defined as the sum:

(2.9)

RF is the risk due to physical damage (D2) which is defined as the sum:

(2.10)


14

RO is the risk due to failure of internal systems (D3) which is defined as the sum:

(2.11)

1) Only for structures with risk of explosion and for hospitals with life-saving

electrical equipment or other structures when failure of internal systems immediately

endangers human life.

2) Only for properties where animals may be lost.

2.5.4. Assessment of risk components for a structure

Each risk component RA, RB, RC, RM, RU, RV, RW and RZ, may be expressed by

the following general equation:

(2.12)

where:

NX is the number of dangerous events per annum

PX is the probability of damage to a structure

LX is the consequent loss

The number NX of dangerous events is affected by lightning ground flash density (Ng)

and by the physical characteristics of the object to be protected, its surroundings and

the soil [6]

.

The probability of damage PX is affected by characteristics of the object to be

protected and the protection measures provided [6]

.

The consequent loss LX is affected by the use to which the object is assigned, the

attendance of persons, the type of service provided to public, the value of goods

affected by the damage and the measures provided to limit the amount of loss [6]

.


15

According to IEC 62305-2 the risk components are calculated as follows:

(2.13)

(2.14)

(2.15)

(2.16)

( (2.17)

( (2.18)

( (2.19)

( (2.20)

Assessment of ND, NM, NDa, NL and NI is found in Annex A while the assessment of

PA, PB, PC, PM, PU, PV, PW and PZ is found in Annex B. Assessment of

LA,LB,LC,LM,LU,LV, LW and LZ is given in Annex C

2.6. OBJECTIVE OF EARTHING

Prime Objective of Earthing is to provide a Zero potential surface in an around and

under the area where the electrical equipment is installed or erected. To achieve this

objective the non-current carrying parts of the electrical equipment is connected to the

general mass of the earth which prevents the appearance of dangerous voltage on the

enclosures and helps to provide safety to working staff and public [7]

.


16

2.7. REQUIREMENT OF GOOD EARTHING

a) Good earth should have low resistance.

b) It should stabilize circuit potential with respect to ground and limit overall potential

rise.

c) It should protect people and material from injury or damage due to over voltage.

d) It should provide low impedance path to fault currents to ensure prompt and

consistent operation of protective relays, Surge arrester etc...

e) It should keep maximum potential gradient along the surface of the sub-station

within safe limits during ground fault.

2.8. Earthing conductor

The‎metal‎parts‎of‎equipment‟s‎are‎connected‎to‎the‎low‎resistance‎electrodes‎by‎the‎

„earth‎conductors‎of‎suitable size.

2.9. Earth Resistance

Earth Resistance is the resistance offered by the earth electrode to the flow of current

in to the ground [8]

. To provide a sufficiently low resistance path to the earth to

minimize the rise in earth potential with respect to a remote earth fault. Persons

touching any of the non current carrying grounded parts shall not receive a dangerous

shock during an earth fault. Each structure, transformer tank, body of equipment, etc.,

should be connected to earthing mat by their own earth connection.

2.10. Earth grid

Bonding all metal parts of the system to be earthed, the earth conductor and the earth

electrodes put all together form an Earth Grid.


17

2.11. Step Potential and Touch Potential

Grounding system in an electrical system is designed to achieve low earth resistance

and‎also‎to‎achieve‎safe‎„Step‎Potential‎„and‎„Touch‎Potential‟.

2.11.1. Step Potential

Step potential is the potential difference between the feet of a person standing on the

floor of the substation, with 0.5 m spacing between the feet (one step), through the

flow of earth fault current through the grounding system [8] .

2.11.2. Touch Potential

Touch potential is a potential difference between the fingers of raised hand touching

the faulted structure and the feet of the person standing on the substation floor. The

person should not get a shock even if the grounded structure is carrying fault current,

i.e, The Touch Potential should be limited to a tolerable value [8].

Figure (‎2.1) Step Potential and Touch Potential

http://kiran111.hubpages.com/hub/Power-Substation-Types


18

2.12. Permissible Current through a Human Body during

the Fault

Permissible Current through a Human Body during the Fault is quite sensitive to AC

currents ranging from 50-60 Hz. The effects of the AC current going through a human

body depend on the magnitude, duration, and also frequency [9]

. The threshold of

perception for the human body is about 1mA. Currents between 1-6 mA, often called

let-go currents, usually do not impair a person from controlling his muscles and

releasing the energized object they were holding. Higher currents ranging from 9-25

mA can cause pain and affect the muscle control so that the energized object is hard if

not impossible to release. Still higher currents between 25-75 mA can affect breathing

and may cause fatality. If current is even higher, it could result in ventricular

fibrillation of the heart, which if not treated quickly, can result in death [9]

. When

currents reach 100 mA and higher, above the ventricular fibrillation level, it can cause

burns, heart paralysis, and inhibition of breathing.

2.13. Common Shock Situations

There are three main electrical shock situations that can occur when a person is

around a substation. The first is a foot-to-foot shock which would involve the current

going through one foot and then out the other. This is typically caused by an increase

in ground potential rise which allows current to build up on the soil surface and then

through objects on the surface. The foot-to-foot shock is the least dangerous of the

three because the current does not go through vital organs such as the heart [10]

. The

second is hand-to feet which involves touching something that is electrified with the

hand and having the current pass into the ground through the feet. The final shock

situation is a hand-to-hand or metal-to-metal contact which would be touching

something electrified with one hand and having the current go through the other hand

that is touching something else. These shocks can usually be eliminated by connecting

all the objects in the substation to the grounding grid [10]

. The use of a thin layer of

surface material such as gravel around the substation can greatly reduce the chance

and strength of electric shocks. The gravel can increase the resistance between the

ground and a person thus making currents less likely to pass through them. Figure

(2.2) shows the different shock situations.


19

2.14. Protective Surface Material

In order to greatly reduce the shock current and increase the contact resistance

between the soil and the feet of people in a substation, a thin layer of a highly resistive

protective surface material just as crushed rock (gravel) is spread above the earth

grade at a substation. Generally a layer of the surface material is 3-6 inches and it

extends 3-4 feet outside the substation fence. If it is not extended beyond the

substation fence, the touch voltages become dangerously high.

Ground Resistance :

The ground resistance for a substation needs to be very low to minimize the ground

potential rise and increase the safety of the substation [9].

The ground resistance is

usually‎ 1‎Ω‎or‎ less‎ for‎ transmission‎ and‎other‎ large‎ substations‎[10] .

In distribution

substations, the usual acceptable range is 1-5Ω‎[10]

. Resistance primarily depends on

the area to be occupied. Also resistance can be decreased for a given area by using

ground rods and adding more grid conductors. If it is impossible to reach a desired

ground resistance by adding more grid conductors and/or ground rods, the soil

surrounding the electrode can be modified. Sodium chloride, magnesium, and copper

sulfates, or calcium chloride can be used to increase the conductivity of the soil

immediately surround the electrodes. Another method is to place a ground

enhancement material around the rod. Other methods are mentioned in IEEE Std. 80-

2000 [10]

.

2.15. Design Procedures of a Grounding System

The design process of a substation grounding system requires many steps. The

following steps were established by the IEEE Standard 80-2000 for the design of the

ground grid:

Step 1: The property map and general location plan of the substation should

provide good estimates of the area to be grounded. A soil resistivity test will

determine the soil resistivity profile and the soil model needed.

Step 2: The conductor size is determined. The fault current 3I0 should be the

maximum expected future fault current that will be conducted by any conductor in

the grounding system, and the time, tc, should reflect the maximum possible

clearing time (including backup).


20

Step 3: The tolerable touch and step voltages are [to be] determined. The choice of

time, ts, is based on the judgment of the design engineer.

Step 4: The preliminary design should include a conductor loop surrounding the

entire grounded area, plus adequate cross conductors to provide convenient access

for equipment grounds, etc. The initial estimates of conductor spacing and ground

rod locations should be based on the current, IG, and the area being grounded.

Step 5: Estimates of the preliminary resistance of the grounding system in uniform

soil can be determined. For the final design, more accurate estimates of the

resistance may be desired. Computer analysis based on modeling the components

of the grounding system in detail can compute the resistance with a high degree of

accuracy, assuming the soil model is chosen correctly.

Step 6: The current, IG, is determined. To prevent overdesign of the grounding

system, only that portion of the total fault current, 3I0, that flows through the grid

to remote earth should be used in designing the grid. The current, IG, should,

however, reflect the worst fault type and location, the decrement factor, and any

future system expansion.

Step 7: If the GPR of the preliminary design is below the tolerable touch voltage,

no further analysis is necessary. Only additional conductor required to provide

access to equipment grounds is necessary.

Step 8: The calculation of the mesh and step voltages for the grid as designed can

be done by the approximate analysis techniques for uniform soil, or by the more

accurate computer analysis techniques.

Step 9: If the computed mesh voltage is below the tolerable touch voltage, the

design may be complete (see Step 10). If the computed mesh voltage is greater

than the tolerable touch voltage, the preliminary design should be revised (see

Step 11).

Step 10: If both the computed touch and step voltages are below the tolerable

voltages, the design needs only the refinements required to provide access to

equipment grounds. If not, the preliminary design must be revised (see Step 11).

Step 11: If either the step or touch tolerable limits are exceeded, revision of the

grid design is required. These revisions may include smaller conductor spacing,

additional ground rods, etc. More discussion on the revision of the grid design to

satisfy the step and touch voltage limits is given in [Section 2.12]


21

Step 12: After satisfying the step and touch voltage requirements, additional grid

and ground rods may be required. The additional grid conductors may be required

if the grid design does not include conductors near equipment to be grounded.

17Additional ground rods may be required at the base of surge arresters,

transformer neutrals, etc. The final design should also be reviewed to eliminate

hazards due to transferred potential and hazards associated with special areas of

concern [10].

2.16. Design Modifications

If the calculated grid mesh and step voltages are greater than the tolerable touch and

step voltages, then the preliminary design needs to be modified. The following are

possible remedies:

i. Decrease total grid resistance: If the total grid resistance is decreased, the

maximum GPR is decreased; hence the maximum transferred voltage is

decreased. An effective way to decrease the grid resistance is to increase the area

occupied by the grid. Deepdriven rods or wells can be used also if area is limited.

ii. Decrease grid spacings: Decrease the mesh size by increasing the number of

parallel conductors in each direction. Dangerous potentials within the substation

can be eliminated. For the perimeter, a ground conductor can be buried outside

the fence, or increase the density of ground rods at the perimeter.

iii. Increase the thickness of the surface layer: a practical limit may be 6 inches.

iv. Limit total fault current: If feasible, limiting the total fault current will decrease

the GPR and gradients in proportion.

v. Diverting greater part of the fault current to other paths

vi. Barring access to limited areas: if practical, can reduce the probability of hazards

to personnel [10].

2.17. Tolerable Body Current Limits

In order to design a proper and safe substation grounding system, various safety

parameters must be found such as the touch and step voltage levels. Each grounding

system must be uniquely designed in order to have the mesh and step voltages below


22

the tolerable touch and step voltages of the personnel that might be working at the site

when a fault occurs.

A human body at 50Hz or 60Hz can gave duration of the current less than the value

that can cause ventricular fibrillation of the heart. Ventricular fibrillation is caused

when the body current replaces the normal rhythmic contraction of the heart and may

cause a lack of circulation and pulse [10] [9]

.

Dalziel‟s‎ studies‎ show‎ that‎ the‎ no‎ fibrillation‎ current‎ of‎magnitude,‎ IB,‎ at‎ duration‎

ranging from 0.03-3.0 s can be simply expressed as [11]

:

√

(2.21)

Where

√ (2.22)

and

I is the rms magnitude of the current through the body (A)

ts is the duration of the current exposure (s)

SB is the shock energy

k is the constant related to electric shock energy

Based‎on‎Dalziel‟s‎studies,‎99.5%‎of‎people‎can‎safely‎withstand‎the‎magnitude‎of‎the‎

current without ventricular fibrillation [11]

. Dalziel also found that the shock energy

constant to vary with weight. For a person weighing approximately 50 kg k50=0.116,

thus the formula for allowable body current becomes:

√

(2.23)

For a person weighing approximately 70 kg k70 = 0.157, thus the formula for

allowable body current becomes:


23

√

(2.24)

2.18. Circuit Equivalents for Common Shock Situations

2.18.1. Resistance of the Human Body

The human body can be approximated as a resistance for DC and 50 Hz or 60 Hz AC

currents. The current path is considered from one had to both feet or from one foot to

the‎other.‎The‎internal‎resistance‎of‎a‎human‎body‎is‎approximately‎300‎Ω.‎The‎body‎

resistance including skin ranges from 500-3000‎Ω‎[10]

. For simplicity, IEEE Std 80-

2000 represents the resistance of a human body from hand-to-feet and also from hand-

to-hand, or from one foot to the other as

2.18.2. Touch and Step Voltage

The accidental circuit in Figure 6 is the result of hand-to-feet contact. The voltage

found in this circuit is referred to as touch voltage because it results from someone

touching an electrified object while the feet are in contact with the ground. In most

cases the limiting factor for a grounding design is the tolerable touch voltage. Figure

(2.2) serves as a visual aid in displaying a typical hand-to-feet circuit through a

person.

Figure ( ‎2.2) Exposure to touch voltage


24

Figure (‎2.3 ) Touch voltage circuit

Another accidental circuit occurs as a result of foot-to-foot contact as seen in Figure

(2.4). The voltage found in this circuit can be referred to as the step voltage because it

would result from someone standing on soil which has current build up on its surface

due to a ground potential rise [10]

. Figure (2.4) serves as a visual aid in displaying a

typical foot-to foot circuit through a person.

Figure ( ‎2.4) Exposure to step voltage


25

Figure( ‎2.5) Step voltage circuit

Using Figure (2.3) or Figure (2.5), the Thvenin equivalent circuit for the current

through the body, Ib, of a person is:

(2.25)

where

VTh is the Thevenin voltage between terminal H and F (V)

ZTh is‎the‎Thevenin‎impedance‎from‎point‎H‎and‎F‎(Ω)

RB is‎the‎body‎Resistance‎‎‎(Ω)

The Thevenin equivalent impedance for the touch voltage accidental circuit is:

(2.26)

The Thevinin equivalent impedance for the step voltage accidental circuit is:

(2.27)

where

Rf: is the ground resistance of one foot


26

In circuit analysis, a human foot is represented as a conducting metallic disc and

resistance of the shoes and socks are neglected.

The equation to calculate the ground resistance Rf is:

(2.28)

where

ρ is‎the‎earth‟s‎resistivity‎‎(Ω·m)

b is the radius of a foot taken as a metallic disk (typically 0.08m)

Using a circular plate of approximately 0.08m, the equations for ZTh are:

For touch voltage accidental circuit

(2.29)

And for step voltage accidental circuit

(2.30)

2.19. Addition of Surface Layer

When possible, substations place a layer of highly resistive material such as crushed

rock. The addition of a surface layer changes the ground resistance, Rf. The new

ground resistance becomes(as proposed by Thaper, Gerez and Kerjriwal in [12]

:

(

)

(2.31)

The surface layer derating factor, Cs, can be calculated as [10]

:


27

(

)

(2.32)

where

ρ is the resistivity‎of‎the‎earth‎(Ω·m)

ρs is‎the‎resistivity‎of‎surface‎layer‎material‎‎(Ω·m)

hs is the thickness of surface material (m)

2.19.1. Tolerable Step and Touch Voltage

When designing a substation grounding system, the maximum tolerable voltages must

be calculated in order to create a proper ground grid. These voltages depend on the

soil resistivity, soil layer and the duration of the shock current. The maximum driving

voltage‎of‎any‎accidental‎circuit‎shouldn‟t‎exceed‎the‎step‎voltage‎and‎touch‎voltage‎

limits.

For step voltage the limit is:

(

(2.33)

For a body weighing 50 kg

(

√

(2.34)


(

√

(2.35)

For touch voltage, the limit is

(

)

(2.36)


28


(

√

(2.37)


(

√

(2.38)

If‎no‎protective‎surface‎layer‎is‎used‎in‎the‎substation,‎Cs‎=‎1‎and‎ρs=ρ.

2.19.2. Conductor Sizing

The symmetrical current can be calculated based on the material and the size of the

conductor used as the following equation which is taken from the derivation by

Sverak [13]

√(

) (

)

(2.39)

where

Tm is the maximum allowable temperature (ºC)

Ta is the ambient temperature (ºC)

αr is the thermal coefficient of resistivity at reference temperature Tr (1/ºC)

ρr is‎ the‎ resistivity‎ of‎ the‎ ground‎ conductor‎ at‎ reference‎ temperature‎Tr‎ (µΩ-

cm)

tc is the duration of current (s)

Ko Equals‎to‎(1/‎αo)

TCAP is the thermal capacity per unit volume (J/ (cm 3. ºC))


29

Common‎values‎of‎αr,‎K0,‎Tm,‎ρr,‎and‎TCAP‎values‎can‎be‎found‎in‎Annex D.

2.19.3. Asymmetrical Currents

If the effect of the dc offset is needed to be included in the fault current, the values of

the symmetrical current is found by:

(2.40)

√

(

)

(2.41)

Where

tf is the time duration of the fault (s)

(2.42)

2.20. Ground Resistance

One of the first steps in determining the size and layout of the grounding system is the

estimation of the total resistance to remote earth. Resistance primarily depends on the

area of the grounding system. In early stages of the design, the area to be occupied is

usually known [4,6]. As an approximation, the minimum value of the substation

grounding resistance in uniform soil can be estimated as:

√

(2.43)

where


30

Rg is‎the‎substation‎ground‎resistance‎(Ω)

ρ is the soil resistivity‎(Ω-m)

A is the area occupied by the ground grid (𝑚2)

Laurent and Niemann proposed a method of calculating the substation ground

resistance by adding a second term [14] [15]

. This equation gives an upper limit of the

substation ground resistance. This proposed equation is:

√

(2.44)

Where

LT is the total burial length of conductors (m)

The total burial length is the combination of the horizontal and vertical conductors in

the grid as well as the ground rods. LT can be calculated as:

(2.45)

Where

LC is the total length of grid conductor (m)

LR is the total length of ground rods (m)

A better approximation was determined by Sverak to take into account the effect of

grid depth [16]

to include the grid depth

[

√ (

√ ⁄ )

]

(2.46)

where

h is the depth of the grid (m)

This equations shows that a larger the area and the greater the total length of the

grounding conductor used would resulting a lower ground grid resistance.


31

2.21. Maximum Grid Current

A portion of the fault current will flow through the grounding grid to the earth. This is

called the grid current and must be calculated. The maximum grid current, IG, can be

calculated as:

(2.47)

Where

IG is the maximum grid current (A)

Df is the decrement factor for the duration of the fault

Ig is the rms symmetrical grid current (A)

The symmetrical grid current, Ig, is the portion of the symmetrical ground fault

current that flows between the grid and surrounding earth. It is expressed as

(2.48)

Where

Ig is the rms symmetrical grid current (A)

If is the rms symmetrical grid fault current (A)

Sf is the fault current division factor

Current Division Factor

It is a factor representing the inverse of a ratio of the symmetrical fault current to that

portion of the current that flows between the grounding grid and surrounding earth.

The process of computing Sf consists of deriving an equivalent representation of the

overhead ground wires, neutrals, etc., connected to the grid and then solving the

equivalent to determine what fraction of the total fault current flows between the grid

and earth, and what fraction flows through the ground wires or neutrals.

Garett and Patel developed a graphical method for determining the maximum grid

current, based on results obtained using a computer program of EPRI TR-100622


32

[B63]. They develop a set of curves of Sf vs. grid resistance to provide a quick and

simple method to estimate the current division factor.

Table (D.2) shows the equivalent transmission and distribution ground system

impedance at 1Ω for 100% remote contribution with X transmission lines and Y

distribution feeders. To determine Sf, parallel the grid resistance with the appropriate

impedance from the table.

2.22. Ground Potential Rise (GPR)

Ground‎potential‎ rise‎ (GPR)‎ is‎ defined‎as:‎ “the‎maximum‎electrical‎ potential‎ that‎ a‎

substation grounding grid may attain relative to a distant grounding point assumed to

be‎at‎the‎potential‎of‎remote‎earth.”‎The‎GPR‎is‎calculated‎as:

(2.49)

Where

Rg is‎the‎substation‎ground‎resistance‎(Ω)

IG is the maximum grid current (A)

2.23. Computing Maximum Step and Mesh Voltages

IEEEE Std. 80-2000 compiled a set of equations that can be used to calculate

maximum step and mesh voltage [10]

.

2.23.1. Mesh Voltage (Em)

Mesh voltage is a form of touch voltage. Mesh voltages represent the highest possible

touch‎voltages‎that‎may‎be‎encountered‎within‎a‎substation‟s‎grounding‎system.‎Mesh‎

voltage is the basis for designing a safe grounding system, both inside the substation

and immediately outside. In order for the grounding system to be safe, the mesh


33

voltage has to be less than the tolerable touch voltage. Otherwise the substation

ground grid design needs modification [10]

.

The mesh voltage can be calculated as:

(2.50)

Where

ρ is‎the‎resistivity‎of‎the‎earth‎(Ωˑm)

LM is the effective burial length (m)

Km is the geometrical spacing factor

Ki is the irregularity factor

The geometrical spacing factor (as proposed by Sverak in [16]

), Km, for mesh voltage

is:

* *

(

+

[

( ]+

(2.51)

Where

D is the spacing between parallel conductors (m)

d is the diameter of grid conductors (m)

h is the depth of ground grid conductors (m)

Kii is the corrective weighting factor adjusting for the effects of inner conductors on

the corner mesh

Kh is the corrective weighting factor adjusting for the effects of grid depth

The corrective weighted factor, Kh is:

√

(2.52)


34

Where

h0 is the grid reference depth (h0 =1)

For ground grids with ground rods along the perimeter and throughout the grid, as

well as in the corners, the corrective weighting factor, Kii, is:

For grids with no ground rods, or few ground rods scattered throughout the gird, but

none located along the perimeter or in the corners, the corrective weighting factor, Kii,

is

(

(2.53)

where the geometric factor, n, is composed of factors na, nb, nc, and nd. These factors

are developed by Thapar, Gerez, Balakrishnan, and Blank, [17]

the geometric factor, n,

is:

(2.54 )

where

(2.55)

nb = 1 for square grids

nc = 1 for square and rectangular grids

nd = 1 for square, rectangular, and L-shaped grids

Otherwise:

√

√

(2.56)


35

√

(2.57)

√

(2.58)

Where

LC is the total length of conductor in the horizontal grid (m)

Lp is the peripheral length of grid (m)


d is the diameter of grid conductors (m)


A is the area of grid (m2)

Lx is the maximum length of grid in the x-direction (m)

Ly is the maximum length of grid in the y-direction (m)

Dm is the maximum distance between any two points on the grid (m)

The irregularity factor, Ki, is used in conjunction with n. It is calculated as:

(2.59)

For grids with no ground rods, or few ground rods scattered throughout the gird, but

none located along the perimeter or in the corners, the effective buried length, LM, is:

(2.60)

where


36

LR is the total length of all ground rods (m)

For ground grids with ground rods along the perimeter and throughout the grid, as

well as in the corners, the effective buried length, LM, is [10]

:

(

(

√

)

)

(2.61)

Where

Lr is the total length of each ground rods (m)

2.23.2. Step Voltage (Es)

If a grid system is designed for safe mesh voltages, the step voltages will be within

tolerable limits. Step voltages are usually smaller than touch voltages because both

feet are in series rather than parallel. Also, the body can tolerate higher currents

through afoot-to-foot‎ path‎ because‎ it‎ doesn‟t‎ pass‎ through‎ vital‎ organs‎ such‎ as‎ the‎

heart. For the ground system to be safe, the step voltage has to be less than the

tolerable step voltage

The step voltage can be calculated as follows [10]

(2.62)

The effective buried conductor length LS is:

(2.63)

The step factor KS (as proposed by Sverak [18])

for the step voltage is given by


37

[

( ]

(2.64)



n is the geometric factor composed of factors na, nb, nc, and nd

DESIGN CHAPTER 3

38

3.

CHAPTER THREE

DESIGN

3.1. Requirement Analysis and Software Definition

The idea is to design GUI software that is able to evaluate the risk due to all possible

effects of lightning flashes to structures in accordance to EN 62305-2. It helps the

designer decide on how to select the most suitable protection measures in order to

reduce the risk to or below a tolerable limit.

GRID DESIGN has been developed using Visual basic based on the IEEE 80 2000

standard guidelines for designing grounding system. This software analyzes

performance of any grounding system by taking data related to grid geometry, general

system parameters and soil characteristics

Requirements

The lightning risk assessment software is to have the following features:

Calculate the collection areas for any type of structures

Consider multiple incoming lines to the structure

Consider multiple remotely connected structures

Split the structure under consideration into multiple zones in order to define high

risk areas

Perform the risk assessment and display the risk factors in colors to ease the

identification of those requiring attention

Provide protection measures and evaluate their effect on reducing the risk

Full detailed reporting facility

Detailed help

The GRID DESIGN software calculates the following:

The tolerable Step and Touch potentials

DESIGN CHAPTER 3

39

The actual Step and Touch potentials

Ground system resistance

Ground potential rise

Maximum ground grid current

The size of the ground grid conductors

3.2. Tools

3.2.1. Microsoft Visual Studio

MS Visual Studio is an integrated development environment (IDE) from Microsoft. It

is used to develop console and graphical user interface (GUI) applications along with

Windows Forms applications, web sites, web applications, and web services in both

native code together with managed code for all platforms supported by Microsoft

Windows, Windows Mobile, Windows CE, .NET Framework, .NET Compact

Framework and Microsoft Silverlight.

Visual Studio includes a code editor supporting IntelliSense as well as code

refactoring. The integrated debugger works both as a source-level debugger and a

machine-level debugger. Other built-in tools include a forms designer for building

GUI applications, web designer, class designer, and database schema designer. It

accepts plug-ins those enhance the functionality at almost every level.

Visual Studio supports different programming languages. Built-in languages

include C/C++ (via Visual C++), VB.NET (via Visual Basic .NET), C# (via Visual

C#), and F#. Support for other languages such as M, Python, and Ruby among others

is available via language services installed separately. It also

supports XML/XSLT, HTML/XHTML, JavaScript and CSS.

3.2.2. Visual Basic (VB)

Visual Basic is a third-generation event-driven programming language and integrated

development environment (IDE) from Microsoft for its COM programming model

first released in 1991. Visual Basic is designed to be relatively easy to learn and use.

DESIGN CHAPTER 3

40

Visual Basic was derived from BASIC and enables the rapid application development

(RAD) of graphical user interface (GUI) applications, access to databases.

A programmer can put together an application using the components provided with

Visual Basic itself. Though the program has received criticism for its perceived faults

from version 3 Visual Basic was a runaway commercial success and many companies

offered third party controls greatly extending its functionality [19].

Language feature

Like the BASIC programming language, Visual Basic was designed to be easily

learned and used by beginner programmers. The language not only allows

programmers to create simple GUI applications, but to also develop complex

applications. Programming in VB is a combination of visually arranging components

or controls on a form, specifying attributes and actions of those components, and

writing additional lines of code for more functionality. Since default attributes and

actions are defined for the components, a simple program can be created without the

programmer having to write many lines of code. Performance problems were

experienced by earlier versions, but with faster computers and native code

compilation this has become less of an issue.

The Visual Basic compiler is shared with other Visual Studio languages (C, C++), but

restrictions in the IDE do not allow the creation of some targets (Windows model

DLLs) and threading models.

Visual Basic provides a fast and easy way to create .NET Framework-based Windows

applications. As with all programs that target the .NET Framework programs written

in Visual Basic benefit from security and language interoperability.

Although VB programs can be compiled into native code executables from version 5

onwards, they still require the presence of runtime libraries of approximately 1 MB in

size. Runtime libraries are included by default in Windows 2000 and later, however

for earlier versions of Windows runtime libraries must be distributed together with the

executable.

DESIGN CHAPTER 3

41

Visual Basic can create executables (EXE files), ActiveX controls, or Dynamic Link

Library (DLL) files, but is primarily used to develop Windows applications and to

interface database systems. Dialog boxes with less functionality can be used to

provide pop-up capabilities. Controls provide the basic functionality of the

application, while programmers can insert additional logic within the appropriate

event handlers.

There is a large library of utility objects, and the language provides basic object

oriented support. Unlike many other programming languages, Visual Basic is

generally not case sensitive, although it will transform keywords into a standard case

configuration and force the case of variable names to conform to the case of the entry

within the symbol table. String comparisons are case sensitive by default.

Forms are created using drag-and-drop techniques. A tool is used to place controls

(e.g., text boxes, buttons, etc.) on the form (window). Controls have attributes and

event handlers associated with them. Default values are provided when the control is

created, but may be changed by the programmer. Many attribute values can be

modified during run time based on user actions or changes in the environment,

providing a dynamic application [19].

3.2.3. Word Cleaner 5.0

Word Cleaner enables you to batch convert Word files (and .odt, .rtf & .txt files) to

HTML/XHTML/TXT files and clean out all the unnecessary tags, reducing the size of

your files.

3.2.4. HTML Help Workshop

Microsoft® HTML Help consists of an online Help Viewer, related help components,

and help authoring tools from Microsoft Corporation. The Help Viewer uses the

underlying components of Microsoft Internet Explorer to display help content. It

supports‎ HTML,‎ ActiveX®,‎ Java™,‎ scripting‎ languages‎ (JScript®,‎ and‎ Microsoft‎

Visual Basic® Scripting Edition), and HTML image formats (.jpeg, .gif, and .png

files). The help authoring tool, HTML Help Workshop, provides an easy-to-use

system for creating and managing help projects and their related files.

DESIGN CHAPTER 3

42

3.3. Development Plan

The methods were implemented by the plan of Waterfall - Model. The Waterfall-

Model is basically a development approach which follows a 'top down' mechanism.

The development process goes through several phases to meet the customer's

specifications and requirements. The development plan is shown in Figure (3.1).

Figure ‎3.1) Development plan

.

3.4. Lightning risk assessment

The risk assessment process according to EN 62305-2 requires data considering the

structure, its surroundings and its contents along with the data for the various lines

connected to it.

To make the lightning risk assessment software elegant and intuitive we grouped the

data into four groups.

Structure data

Incoming lines data

Zones data

Losses data

3.4.1. Structure page

Through the data provided in this page the software will be able to assess the

collection area of direct strikes to the structure, collection area for strikes near the

structure, Probability of physical damage due to direct strikes and Ks1.

DESIGN CHAPTER 3

43

Figure (‎3.2) Structure page design sketch

In this page the user is to:

Specify the structure type whether it is a rectangle structure, structure with pitch

roof or a complex shaped structure.

Enter the structure dimensions: length, width and height. For structures with pitch

roof the user is to enter the roof protrusion height.

Specify the location factor of the structure to determine the value of Cd.

Specify the location factor of the structure to determine the value of Ce.

Specify the location factor of the structure to determine the value of Ng. The

software is designed to provide a world thunder-days map to help the user specify

the thunder-days of the regions under consideration.

Specify the level of LPS installed on the structure. We wrote the code with the

assumption that the installed LPS conform with the requirements of EN 62305-3

thus the software will automatically provide SPD protection at the line entrance.

Specify the type of external shielding to determine the value of Ks1.

DESIGN CHAPTER 3

44

Figure ‎3.3) Collection area graphical tool design sketch

Collection area graphical tool:

The graphical tool for estimating the collection area provides a user interface for

drawing the structure using two basic building blocks; polygons and ellipses (or

circles).

The polygon structure is drawn by defining is corner points (coordinates), and the

structure height. For circular structures the user needs to specify the containing

rectangle and the structure height.

After defining the structure it may be displayed. If the size on the display window is

two small, it may be enlarged by selecting an appropriate scale (up to 4 times).

The collection area is drawn in accordance with the IEC 62305 standard, by drawing

the surrounding area using a combination of polygon and circular or semicircular

shapes. The whole collection area, including the structure boundaries is then painted

in black. This is useful for estimating the area.

The area is then simply estimated by counting the number of black pixels in contrast

to the background color of the drawing canvas (each pixel approximating 1 square

meter). When testing systems using this method it was found that the actual number

of pixels was larger than the actual area, probably due to that boundary pixels are

represented by full pixels in cases where they should have been half pixels. In any

case, and appropriate adjustment was introduced where about half of the perimeter

length was subtracted. This offered an exact estimate in cases where the structure was

DESIGN CHAPTER 3

45

a regular square or triangular shape, but for more complex cases it only improved the

accuracy.

3.4.2. Service lines

The software is designed to consider the characteristics of incoming lines (energy

and/or signal) connected to the internal systems of the structure. We designed it to

have no limits in considering the number of connected lines.

Through the data provided in this page the software will be able to assess: collection

area of direct strikes to the line, Collection area for strikes near the line PLD, PLI and

PSPD.

Figure ‎3.4) Design sketch for Service Lines page

In this window the user is to:

Specify the line type whether it is overhead or underground

o For overhead lines specify the length and height of the line.

o For underground cables specify the line length and soil-resistivity.

Specify the location factor of the line to determine the value of cd.

Specify the environmental factor of the line to determine the value of cd.

Specify the line shielding. According to the type of line shielding the software will

assign a value to PLD and PLI.

Select the surge protection level at the entrance of the line to determine the value

of PSPDL.

DESIGN CHAPTER 3

46

For the structure at the other end of the service line the user is to specify its height,

length width and its location factor.

Add, Rename and Delete

By clicking on the Add button the user will be able to add a new line. The program

creates the new line using default values. Clicking on the Rename button will enable

the user to change the name of the selected line. Clicking on the Delete button will

enable the user to delete the line and its data .

3.4.3. Zones

The software allow for the division of the structure into several zones in order to

define high risk areas. The software has no limits in considering the number of zones

and their internal systems. Through the data provided in this page the software will be

able to assess: ra, PA, hz, rf, rp and Ks2.

Figure (‎3.5) Design sketch for Zones page


Select zone type. For external zones we would only consider the risk of injury to

living beings due to direct flashes so we wrote the code to only enable the

selection of ground surface type and protection measures against touch and step

voltages. For internal zones all types of risk are to be considered.

Select the floor type to determine the value of ra.

DESIGN CHAPTER 3

47

Specify protection measures against touch and step voltages. In order to assess the

probability of injury to living beings we provided five checkboxes so that the user

is able to specify any combination of protection measures against touch and step

voltages.‎ In‎ the‎ code‎ we‎made‎ sure‎ that‎ if‎ the‎ user‎ checks‎ the‎ “No‎ protection‎

measures”‎option‎then‎no‎other option is to stay checked.

Select the level of fire risk to determine the value of rf.

Select the type of fire protection system to determine the value of rp.

Select the type of existing hazard to determine the value of hz.

Select the type of existing economic hazard to determine the value of hz.

Specify the type of internal zone shielding to determine the value of KS2. If the

shield is a mesh then the user is to enter the mesh size.


By clicking on the Add button the user will be able to add a new zone. The program

creates the new zone using default values. Clicking on the Rename button will enable

the user to change the name of the selected zone. Clicking on the Delete button will

enable the user to delete the zone and its data.

Internal systems:

The software let the description of internal energy and/or of signals systems for each

zone. Through the data provided in this page the software will be able to assess: KS3,

KS4, PSPDC, Pu, Pv, Pw and Pz.

DESIGN CHAPTER 3

48

Figure ‎3.6) Design‎sketch‎for‎Zones’‎internal‎systems‎page


Select the line to which the internal system is connected to. Through this selection

the program will be able to relate the data of the internal system to that of the line

supplying it.

Select the type of wiring to determine a value of KS3.

Select the protection level of protection of Coordinated SPD installed to determine

a value of PSPDC.


By clicking on the Add button the user will be able to add a new internal system. The

program creates the new system using default values. Clicking on the Rename button

will enable the user to change the name of the selected internal system. Clicking on

the Delete button will enable the user to delete the internal system and its data.

3.4.4. Losses

To assess the loss factors Lf, Lo and Lt for each type of risk the software is designed

to provide the user with three options:

Guided.

Typical.

DESIGN CHAPTER 3

49

Manual.

Figure (‎3.7) Design sketch for Losses page

Loss of human life:

Guided:

If the information required for calculating the loss factors according to the equations

provided in the standard is available, the user can choose guided and enter the data for

each zone.

Figure ‎3.8 ) Design sketch for Guided Loss of Human Life window


Enter the total number of people present in the structure.

Enter the number of possible endangered people due to:

o Physical damage.

DESIGN CHAPTER 3

50

o Failure of internal systems.

o Touch and Step voltages.

Enter the time in hours per year for which people are present in the zone.

Typical:

We designed the software to provide the user with typical values for the loss factors

according to EN 62305-2.

Figure (‎3.9) Design sketch for Typical Loss of Human Life window


Select the type of the structure from the drop-down list.

Check this option if there is a risk of explosion on the structure.

Enter the total number of people present in the structure.


o Physical damage.

o Failure of internal system.


3.4.4.1. Loss of service to the public:

Guided:

If the information required for calculating the loss factors are available the user can

choose guided and enter the data for each zone.

DESIGN CHAPTER 3

51

Figure ‎3.10) Design sketch for Guided Loss of Service window


Enter the total number of users served.

Enter the annual period of loss of service in hours.

Enter the number of possible endangered people in each zone due to:

o Physical damage.

o Failure of internal system.


Typical:

The software provides the user with typical values for the loss factors according to EN

62305-2.

Figure (‎3.11) Design sketch for Typical Loss of Service window


Select the service that will be lost due to physical damage.

Select the service that is lost due to failure of internal systems.

DESIGN CHAPTER 3

52

Specify the loss percentage for each zone. The user can either select the Default

option and the software will divide the typical loss values equally among the

structure‟s‎ zones,‎ or‎ they‎ can‎ select‎ the‎ User‎ defined‎ option‎ to‎ enter‎ the‎

percentage contribution of each zone in the total loss value.

3.4.4.2. Loss of cultural heritage

Guided:



Figure ‎3.12) Design sketch for Guided Loss of Cultural Heritage window


Enter the total insured value of the structure in currency.

Enter the insurable value of possible loss of goods for each zone in currency.

Typical:


62305-2.

Figure (‎3.13) Design sketch for Typical Loss of Cultural Heritage window

DESIGN CHAPTER 3

53

In this window the user is to specify the cultural heritage loss percentage for each

zone. The user can either select the Default option and the software will divide the

typical‎ loss‎ value‎ equally‎ among‎ the‎ structure‟s‎ zones,‎ or‎ they‎ can‎ select‎ the‎User‎

defined option to enter the percentage contribution of each zone in the total loss value

Economic loss:

Guided:



Figure (‎3.14) Design sketch for Guided Economic Loss window


Enter the total value of the structure in currency.

Enter the value of possible loss due to

o Physical damage.

o Failure of internal systems.


Typical:


62305-2.

DESIGN CHAPTER 3

54

Figure (‎3.15) Design sketch for Typical Economic Loss window


Select the type of the structure from the drop-down list.

Select the type of your structure from the drop-down list.

Specify the Economic loss percentage for each zone. The user can either select the

Default option and the software will divide the typical loss value equally among

the‎ structure‟s‎ zones,‎ or‎ they‎ can‎ select‎ the‎ User‎ defined‎ option‎ to‎ enter‎ the‎

percentage contribution of each zone in the total loss value.

Specify if the loss of animals is considered.

Manual:

The software provides the with the option of entering the loss factors for each zone

directly

DESIGN CHAPTER 3

55

Figure (‎3.16) Design sketch for Manual Loss of Human Life, Loss of service, Loss

of cultural Heritage and Economic Loss window

3.4.4.3. Loss of Human Life

The user is to enter the three loss factors for each zone

Loss due to physical damage.

Loss due to failure of internal systems.

Loss due to Touch and Step voltages.

3.4.4.4. Loss of service to the public

The user is to enter the two loss factors for each zone.



3.4.4.5. Loss of cultural heritage

For each zone the user is to enter the loss factor due to physical damage.

Economic Loss

The user is to enter the three loss factors for each zone



Loss due to Touch and Step voltages.

DESIGN CHAPTER 3

56

3.4.5. Risk calculations

The risk evaluation is made simultaneously in all zones; the software shows in just a

few seconds where in the structure and why it is so important to arrange protection

measures. The risk components greater than the tolerable value are displayed in RED

while the risk components less than the tolerable value are displayed in GREEN.

Figure (‎3.17) Design sketch for Calculation page

When the user click on any zone –anywhere on the zone column- in the risk

assessment list the software will provide them with a deeper insight into the specified

zone through the information displayed in:

Internal system list. In this list the risk components RU, RV, RW and RZ

associated with each internal system are displayed.

Risk assessment chart. In this chart the contribution of each risk component in the

overall risk of lightning on the specified zone is displayed.

Existing protection measures:

Display the protection measures that are already installed in the structure

DESIGN CHAPTER 3

57

3.4.6. Risk composition

The user is to click on this button to display the contribution of risk components on

the total risk of loss of human life, loss of service o people in the structure, loss of

cultural heritage and Economic loss according to the type of damage or source of

damage.

Figure ‎3.18) Design sketch for Risk composition window

3.4.7. Protection measures

After assessing the risk on the structure the software will help the user to evaluate the

effect of different protection measures to mitigate such a risk.

We provided the user with three solution cases, each case being a separate risk

assessment in its own right. In each case the user can try different protection measures

to reduce the risk to the tolerable limit. The purpose of this is to allow the designer to

obtain different solutions and then decide which one is to be the most technical and

economical solution.

DESIGN CHAPTER 3

58

Figure ‎3.19) Design sketch for Protection measure page

By clicking on any zone in the risk assessment list the software will provide the user

with a deeper insight into the specified zone through the information displayed in:

Internal system list. In this list the risk components RU, RV, RW and RZ

associated with each internal system are displayed.

Risk assessment chart. In this chart the contribution of each risk component in the

overall risk of lightning on the specified zone is displayed.

With this information the user can easily identify the most critical risk components.

Double click to select protection measures:

Double click on the risk component you want to reduce and the software will provide

you with the protection measures necessary to reduce this component to the tolerable

limit.

Recommended protection measures:

Display the combination of protection measures adopted to reduce the risks R1, R2

and R3 to the tolerable value.

DESIGN CHAPTER 3

59

3.4.7.1. Reducing RA

Figure (‎3.20) Design sketch for reducing RA window

To reduce RA the software provides the following protection measures

Ground surface type. the user is to select the appropriate surface type to:

o Increase the surface resistivity of the soil around the structure (Outside

zone).

o Increase the surface resistivity of internal floors ( Inside zone),

Protection measures against touch and step voltages. The user is to check one

or more of these options to reduce the probability of injury to living beings due to

flashes to a structure.

o Electrical insulation. Provide adequate insulation of exposed conductive

parts that could come in contact with the person.

o Soil equipotentialization. Create an equipotential plane by means of a

meshed conductor earthing arrangement to reduce the step voltage threat.

o Physical restriction and warning notices. Provide warning notices and

physical restrictions where possible to avoid contact with external

dangerous parts.

3.4.7.2. Reducing RB

Figure (3.21) Reducing RB

DESIGN CHAPTER 3

60

To reduce RB the software provides the following protection measures

Install LPS. The user is to select the level of LPS to install on the structure to

reduce the probability of physical damage to the structure due to direct flashes.

According to BN 62305-3 the software automatically provides SPD at line

entrance thus reducing:

o The Probability of injury to living beings due to flashes striking a

connected service.

o The Probability of physical damage to the structure due to flashes striking

a connected service.

Fire protection. Provide fire protection as a measure to limit fire propagation thus

reducing the amount of loss due to physical damage.

3.4.7.3. Reducing RC

Figure (3.22) Reducing RC

To reduce RC the software provides the following protection measures

Coordinated SPD. Installing coordinated SPD on internal systems reduces:

o The probability that a flash to a structure will cause a failure of internal

systems.

o The Probability that a flash to a service will cause failure of internal

systems.

o The Probability that a lightning flash near an incoming service will cause

failure of internal systems.

DESIGN CHAPTER 3

61

3.4.7.4. Reducing RM

Figure (3.23) Reducing RM

To reduce RM the software provides the following protection measures

Zone shielding. Provide effective shielding against induced Lightning

Electromagnetic Impulse (LEMP) effects.

Internal wiring. The user is to select the appropriate type of line routing and

shielding to minimize voltages and currents induced into electrical and electronic

system.

Coordinated SPD. The user is to select the level of coordinated SPD to be

installed on internal system.

Withstand voltage. The user can select equipments with a higher impulse

withstand voltage level .

3.4.7.5. Reducing RU and RV

SPD at line entrance and equipments with better withstand voltage will reduce both

RU and RV while fire protection measures will reduce RB and RV

DESIGN CHAPTER 3

62

Figure (3.24) Reducing RU and RV

To reduce RU and RV the software provides the following protection measures

SPD at line entrance. Provide SPD at the line Entrance to reduce:

o The Probability of injury to living beings due to flashes striking a

connected service.

o The Probability of physical damage to the structure due to flashes striking

a connected service.

Withstand voltage. The user can select equipments with higher capabilities of

withstanding high voltage.

To reduce RV the software provides the following protection measures

Fire protection. Provide fire protection as a measure to limit fire propagation thus

reducing the amount of loss due to physical damage.

3.4.7.6. Reducing RW and RZ

Figure (3.25) Reducing RW and RZ

To reduce RW and RZ the software provides the following protection measures

DESIGN CHAPTER 3

63

Coordinated SPD. The user is to select the level of coordinated SPD to be

installed on internal system.

Withstand voltage. The user can select equipments with higher capabilities of

withstanding high voltage.

3.5. Design

The software asks for data related to ground grid geometry, No. of ground rods, data

regarding substation soil, generalized data related to power system for safety criteria

establishment, conductor size and material etc. Then it calculates tolerable voltages as

per safety criteria, actual mesh and step voltages, grounding system resistance (Rg),

ground potential rise (GPR) and safety of the proposed grounding system. After

calculation results are displayed in a Textbox. Algorithm of working of this software

is shown in fig. 4 as shown below.

DESIGN CHAPTER 3

64

Figure (3.26) flow chart of GRID DESIGN software

DESIGN CHAPTER 3

65

3.5.1. GRID DESIGN

Figure (3.27) GRID DESIGN


Click on the Soil Editor button to open the soil editor and enter the soil

model parameters.

Click on the General Design Data button to open the general design

window

Click on the Result button to display the following results:

o The tolerable Step and Touch potentials.

o The actual Step and Touch potentials.

o Ground system resistance.

o Ground potential rise.

o Maximum Ground Grid current.

o The size of the ground grid conductors.

Click on the Report button to view the final report.

3.5.2. Soil Editor

The software allows for the following soil resistivity models to be used:

1. Two-layer, horizontally stratified.

2. Uniform (homogeneous).

DESIGN CHAPTER 3

66

Figure (3.28 ) Soil Editor

In this window the software will ask the user to specify the soil model parameters.

Resistivity of the soil in ohm-m.

The Surface Material depth in meters.

Material resistivity of the Surface Layer soil in ohm-m.

To specify a uniform soil model then the user is to enter the top and bottom layer

resistivity as the same value.

3.5.3. General Design Data

Figure (3.29) General Design Data


Select the conductor material type from the drop-down list

DESIGN CHAPTER 3

67

Enter the r.m.s value of the maximum fault current expected to flow to ground in

kA, with no dc offset included. The effect of the dc offset is introduced by

specifying the Decrement factor.

Enter the maximum duration of fault current in seconds

Enter the soil ambient temperature in ºC.

Specify the maximum allowable temperature. This temperature limit can be the

fusing temperature of the conductor or a limit based on the type of connections

made between conductors or a limit imposed by the presence of nearby flammable

materials. The software provides the user with two options for determining this

temperature:

o User specified. The user is to click on this option to specify the

maximum allowable temperature.

o Fusing temperature. The user is to click on this option and the

software will set the allowable temperature limit equal to the fusing

temperature of the specified conductor material.

Specify the Decrement factor by which the symmetrical RMS fault current

magnitude must be increased in order to obtain an equivalent RMS current

magnitude. This component accounts for the dc component of the fault current

waveform There software provides the user with two options for determining this

factor:

o User specified. The user is to click on this option to enter the current

division factor.

o Computed. The user is to click on this option and the software will

calculate the division factor according to X/R ratio and system frequency.

Specify the current division factor Sf which is the fraction of the total fault current

that flows through the earth. The software provides the user with two options for

determining this factor:

o User specified. The user is to click on this option to enter the current

division factor.

o Computed. The user is to click on this option and the software will

calculate this factor according to: Number of transmission lines, Number

of distribution feeders and Rg and Rtg values.

DESIGN CHAPTER 3

68

3.5.4. Drawing the Grid

Drawing the grid will be done in four steps

1. Draw grid periphery.

2. Draw the X-axis (horizontal) conductors.

3. Draw the Y-axis (vertical) conductors.

4. Draw grid rods.

Figure (3.30) Grid periphery

3.5.5. Earthing grid graphical tool

The graphical tool for drawing the earthing grid provides a flexible approach for

completing the grounding mesh in four stages. The user starts by defining and

drawing the grid perimeter. The drawing scale and hence all subsequent displays are

affected by the maximum dimensions entered in the grid perimeter. Next the user

enters all horizontal (x-axis) conductors. To facilitate repetition of similar parallel

conductors, it is possible to define the spacing between them and then only one click

operation is necessary to add a new conductor. Addition of vertical (y-axis)

conductors follows the same approach for the horizontal conductors. All along these

operations, the important dimensions required in the analysis are computed and

updated; namely these are the grid perimeter Lp, total conductor length Lc, maximum

dimension in both directions Lx and Ly, and total mesh area A.

The last stage involved is the definition of number, position and dimensions of

grounding rods. This is facilitated through an interface which allows the placement of

DESIGN CHAPTER 3

69

rods in virtually any desired position on the mesh. Furthermore it is possible to define

rods which are in a regular matrix format by simply specifying the number and

spacing of rods in each direction. The parameter LT which defines the total number of

grid conductors including ground rods is affected and updated whenever a rod is

entered in that data.

3.6. File

3.6.1. New

If the user has made any changes in the data then the software will first ask the user if

they want to save these changes and then it will rest the program into its default form.

3.6.2. Open

This function will display an open file dialog which asks the user to specify the text

file to open, and then the software will read the contents of the file.

3.6.3. Save and Save As

The save function saves the data entered by the user in a fixed text file. For each save

request from the user, the save function will rewrite the whole file. On the other hand,

the save As function will display a save file dialog which asks the user to choose a

directory to save the text file in it and a file name. The function creates a text file in

the specified directory with the entered name, and then the data is saved to this text

file.

3.7. Help

The software provides the user with a detailed help to guide them and to explain how

to use this software. We used a free trial of Word Cleaner 5.0 to convert the help files

that we wrote in Microsoft word 2007 into .html files. These files were compiled

using the HTML Help Workshop which has a built-in compiler into a small CHM

format file, and then we include this CHM file to our software.

DESIGN CHAPTER 3

70

3.8. Implementation

The two programs were implemented using visual basic. All implementation code can

be found on the accompanying CD. For detailed discretion of the two programs refer

to Annex (E).

3.9. Deployment

The final thing to do was to deploy our software. We created an executable file which

could be installed on any machine. We used the built-in deployment feature that

comes with Visual Basic to create a Windows Installer file - a .msi file for the purpose

of deploying applications.

TESTING CHAPTER 4

71

4. CHAPTER FOUR

TESTING

4.1. Lightning Risk Assessment Software Testing

In order to validate the results given by Lightning Risk Assessment Software we used

it to assess the risk of lightning strikes on the NTC Tower, and then we compared its

results against those obtained with the help of StrikeRisk vs 5.0 software.

The NTC required a risk assessment to be performed to review the installed lightning

protection system of the NTC Tower and report on its adequacy to serve the purpose

intended, and whether it would be required to supplement or replace the existing

system. Sorouh ADVANCE ENGINEERING WORKS performed a risk assessment

using StrikeRisk v5.0 Risk Management Software. This software is developed by

Furse technical team. Furse is a world leader in the design, manufacture and supply of

earthing and lightning protection systems. Having provided lightning protection

schemes for many developments in the Middle East and Far East, including the Burj

Khalifa 7 star hotel in Dubai and the Petronas Towers in Malaysia.

4.1.1. About NTC Tower

This Tower is the head quarter for the NTC and all related regulatory and monitoring

activities necessary to fulfill the requirements of the global information society.

It is a multi-storey intelligent tower which utilizes advanced building management

technologies. The tower is located in the eastern region of Khartoum on the Blue Nile

beside the Manshiyya Bridge. Land area of the tower is 5000 square meters. The

tower is designed of 29 storeys and a total height of 110 meters with a top 30 meter

mast. The tower is considered the highest in the country.

TESTING CHAPTER 4

72

The NTC Tower has the following features and privileges:

Facades with solar energy generation cells providing 20% of building needed

energy.

6 lifts; 4 interior and two panoramic. Main and sideway staircases. A movable

staircase‎for‎VIP‟s.

Information data control for the lifts intelligence.

Complementary control range of management, inside-outside security and

monitoring.

Major conference hall with capacity of 280 persons. Minor meeting halls in

relevant administrative wings.

Underground garage.

Three public gardens facing the Blue Nile.

Locations for data centre, labs for metrology and type approvals, research and

studies.

In NTC Tower due to lightning strikes it is possible to distinguish the following

typical damages:

A loss of electrical power and loss of fire protection.

Failure‎of‎labs‟‎equipment‎and‎loss‎of‎important‎data.‎

Physical damage of antenna, solar cells and other outdoor equipment due to direct

strikes.

Fire initiated by sparks caused by overvoltages resulting from resistive and

inductive coupling;

Injuries to people by step and touch voltages resulting from resistive and inductive

coupling and due to overcurrents and to overvoltages in the line.

Each type of damage, alone or in combination with others, may produce different

consequential loss in the Tower. It is possible to distinguish loss of human life, loss of

service to the public and loss of economic value. Thus it is crucial to insure the

effectiveness of the lightning protection system of the NTC.

TESTING CHAPTER 4

73

4.1.2. Relevant data and characteristics

Data and characteristics of:

1) The building itself and its surroundings are given in Table (4.1).

2) Internal electrical systems and relevant incoming power line are given in Table

(4.2).

3) Internal electronic systems and relevant incoming telecom line are given in Table

(4.3).

4) Internal electronic systems and relevant incoming antenna line are given in Table

(4.4).

Table (‎4.1) Structure characteristics

Parameter Description Symbol Valu

e

Length - Lb 50

Width - Wb 50

Height - Hb 136

Location factor Isolated structure Cd 1

LPS Level I Pb 0.02

Structure shield None conducting KS1 1

Lightning flash density 1/km2/year Ng 2


characteristics


e

Length - L 1000

Soil resistivity - Ρ 300

Transformer correction factor Line without transformer Ct 1

Line location factor Isolated Structure Cd 1

Line environment factor rural Ce 1

TESTING CHAPTER 4

74

Line shield: not bonded to

equipotential bonding bar

Shielded cable 5<Rs <20

Ohms/km

PLD 0.9

PLI 0.1

Internal wiring precaution Shielded cable 5<Rs <20

Ohms/km

KS3 0.001

Equipment withstand voltage Uw Uw = 4 kV KS4 1

Coordinated SPD protection None PSPDC 1

End (a) line structure dimensions

(m)

- La×Wa×Ha 0×0×

0


characteristics

Parameter Description Symbol Value

Length - L 1000





Line shield: None PLD 1

PLI 1

Internal wiring precaution Shielded cable 1<Rs <5

Ohms/km

KS3 0.0002

Equipment withstand voltage Uw Uw = 1.5 kV KS4 1



(m)

- La×Wa×

Ha

0×0×0

Table (‎4.4) Internal telecom system and relevant incoming line characteristics


Length - L 1000


TESTING CHAPTER 4

75




Line shield: not bonded to

equipotential bonding bar

Shielded cable 5<Rs <20

Ohms/km

PLD 1

PLI 0.5

Internal wiring precaution Shielded cable Rs <1

Ohms/km

KS3 0.0001

Equipment withstand voltage Uw Uw = 1.5 kV KS4 1



(m)

- La×Wa×H

a

0*0*0

For the NTC Tower five zones are defined. Characteristics of these zones are given in

Table (4.5) for zone Z1, in Table (4.6) for zone Z2, in Table (4.7) for zone Z3, in

Table (4.8) for zone Z4 and in Table (4.9) for zone Z5.

Table (‎4.5) Zone Z1 characteristics


e

Ground surface type Agricultural, concrete Ru 0.01

Shock protection No protection measures PA 1

Risk of fire High Rf 0.1

Fire protection Automatic distinguisher Rp 0.2

Zone shield None conducting KS2 1

Life hazard Difficulty of evacuation Hz 5

Economic hazard Contamination of surroundings

or environment

Hz 50





TESTING CHAPTER 4

76


Fire protection Automatic distinguisher Rp 0.2

Zone shield None conducting Ks2 1

Life hazard Low level of panic Hz 2

Economic hazard Hazard for surroundings or

environment

Hz 20




Shock protection Electrical insulations

Soil equipotentialization

Warning notices

PA 1.0E-

05

Risk of fire None Rf 0

Fire protection No provision Rp 1


Life hazard Hazard for surroundings or

environment

Hz 20


environment

Hz 20




Shock protection Electrical insulations

Soil equipotentialization

Warning notices

PA 1.0E-

05


TESTING CHAPTER 4

77

Fire protection Manuel distinguisher Rp 0.5


Life hazard High level of panic Hz 10

Economic hazard Contamination of surroundings

or environment

Hz 50





Risk of fire None Rf 0

Fire protection No provision Rp 1


Life hazard No special hazard Hz 1


environment

Hz 20

Table (‎4.10) Loss Factors relevant to R1

Zone1 Zone2 Zone3 Zone4 Zone5

Loss due to physical damage 0.42 0.42 0.0 0.33 0.0

Loss due to failure of internal

systems

0.01 0.01 0.0 0.1 0.0

Loss due to touch and step

voltages

0.0 0.0 0.01 0.0 0.0

Table (‎4.11) Factors relevant to R2

Zone1 Zone2 Zone3 Zone4 Zone5



systems

0.01 0.01 0.0 0.01 0.01

TESTING CHAPTER 4

78

Table (4.12) Loss Factors relevant to R4

‎4 Zone1 Zone2 Zone3 Zone4 Zone5



systems

0.01 0.0 0.01 0.01 0.01

Loss due to touch and step

voltages

0.0 0.0 0.01 0.01 0.01

This data was input to Lightning Risk Assessment Software. The following figures

are snap shots of the program showing the data for the NTC Tower, service lines,

zones and losses.

Figure (‎4.1) Structure and service lines data for the NTC Tower

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79

Figure (‎4.2) Zones and internal systems data for the NTC Tower

Figure (‎4.3) Losses data for the NTC Tower

4.1.3. Calculations

TESTING CHAPTER 4

80

Collection area for direct strikes to the structure and collection area for events

near the structure

The graphical tool was used to determine collection areas Ad and Am as follows:

The structure was represented with a polygon of 16 points and a height of 98 m

The antenna on the roof was represented by a circular structure with a radius of

0.875 m and a height of 136 m

The structure drawn by the graphical tool is shown in Figure (4.4). Figure (4.5) shows

the estimation of collection area for direct strikes while Figure (4.6) shows the

estimation of collection area for events near the structure.

Figure (‎4.4) The NTC Tower enlarged with a scale factor of 4

TESTING CHAPTER 4

81

Figure (‎4.5) Collection area for direct strikes to the NTC Tower

Figure (4.6) Collection area for strikes near the NTC Tower

The values of Ad and Am estimated by the graphical tool are given in table (4.13)

Table (4.13) Collection areas Ad and Am

Collection area for direct strikes to structure 524329.00006 m2

Collection area for strikes near the structure 229669.09997m2

The lightning risk assessment software performed a full risk assessment using the data

given in tables (4.1) to (4.12). The results are:

TESTING CHAPTER 4

82

Assessment of R1 given in Table (4.14).



The following figure is a snap shot showing the results of lightning risk assessment of

the NTC Tower.

Figure ‎4.6) Lightning risk assessment calculations for the NTC Tower

Table (‎4.14) Risk components relevant to R1

Risk

compone

nt

Zone1 Zone2 Zone3 Zone4 Zone5 Structure

RA 0.000E00 0.000E00 1.049E-09 0.000E00 0.000E00 1.049E-09

RB 4.404E-03 1.762E-03 0.000E00 3.461E-05 0.000E00 6.201E-03

RC 1.049E-02 1.049E-02 0.000E00 0.000E00 0.000E00 2.098E-02

RM 0.000E00 0.000E00 0.000E00 0.000E00 0.000E00 0.000E00

RU 0.000E00 0.000E00 0.000E00 0.000E00 0.000E00 0.000E00

RV 8.613E-05 3.445E-05 0.000E00 0.000E00 0.000E00 1.206E-04

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83

RW 3.896E-04 3.896E-04 0.000E00 0.000E00 0.000E00 7.792E-04

RZ 1.330E-02 1.330E-02 0.000E00 0.000E00 0.000E00 2.660E-02

Total 2.867E-02 2.598E-02 1.049E-09 3.461E-05 0.000E00 5.468E-02

Table (‎4.15) Risk components relevant to R2

Risk

compone

nt


RB 2.097E-04 2.097E-04 0.000E00 1.049E-06 2.097E-04 6.301E-04

RC 1.049E-02 1.049E-02 0.000E00 0.000E00 1.049E-02 3.147E-02

RM 0.000E00 0.000E00 0.000E00 0.000E00 0.000E00 0.000E00

RV 4.101E-06 4.101E-06 0.000E00 0.000E00 4.101E-06 1.230E-05

RW 3.896E-04 3.896E-04 0.000E00 0.000E00 3.896E-04 1.169E-03

RZ 1.330E-02 1.330E-02 0.000E00 0.000E00 1.330E-02 3.990E-02

Total 2.439E-02 2.439E-02 0.000E00 1.049E-06 2.439E-02 7.317E-02

Table (4.16) Risk components relevant to R4

Risk

compone

nt


RA 0.000E00 0.000E00 1.049E-09 1.049E-09 1.049E-05 1.049E-05

RB 2.097E-02 0.000E00 8.389E-05 1.049E-04 8.389E-03 2.955E-02

RC 1.049E-02 0.000E00 0.000E00 0.000E00 1.049E-02 2.098E-02

RM 0.000E00 0.000E00 0.000E00 0.000E00 0.000E00 0.000E00

RU 0.000E00 0.000E00 0.000E00 0.000E00 4.101E-09 4.101E-09

RV 4.101E-04 0.000E00 0.000E00 0.000E00 1.641E-04 5.742E-04

RW 3.896E-04 0.000E00 0.000E00 0.000E00 3.896E-04 7.792E-04

RZ 1.330E-02 0.000E00 0.000E00 0.000E00 1.330E-02 2.660E-02

Total 4.556E-02 0.000E00 8.389E-05 1.049E-04 3.274E-02 7.849E-02

TESTING CHAPTER 4

84

Table (4.16) Risk Totals

Lightning Risk

Assessment

StrikeRisk vs4.0 IEC 62305-2

Risk of Loss of Human

Life

5.468E-02 5.4597E-02 5.468E-02

Risk of Loss of Service 7.317E-02 7.3134E-02 7.317E-02

Risk of Economic Loss 7.849E-02 7.8175E-02 7.849E-02

4.1.4. Result Discussion

Performing a complete analysis on the calculations made by the two programs and

comparing the various parameters against the IEC 62305-2 we concluded that the

differences between their results are due to three factors:

Assessment of collection area for events near the structure.

Assessment of rf factor reducing the loss depending on risk of fire.

Assessment of PLD probability of failure of internal systems due to flashes to

power lines.

Assessment of collection area for events near the structure

According to Strike Risk vs5.0 this area is equal to 180000m2 which is impossible

since hypothetically a single point will result in an area of 196349.54m2 thus for any

structure this area should be greater than this.

Assessment of rf factor reducing the loss depending on risk of fire

For Zone1, Zone2, Zone4 and Zone5 Direct Strike assigned a value of 0.5 to this

parameter which does not exist in the standard - refer to Annex C, Table (C.3).

Assessment of PLD probability of failure of internal systems due to flashes to

power lines

For the power line Strike Risk assigned a value of 1 to this parameter while according

to the characteristics of the line it should have been 0.9.

TESTING CHAPTER 4

85

It can be seen that there is no major difference between the results of StrikeRisk and

those of Lightning Risk Assessment, yet comparing both of them to IEC reveal that

our program is more accurate, the results are almost a complete match to those

obtained by hand calculations.

Comments on the results of the risk assessment performed on the NTC tower

Risk components RB and RV

Even with the use of the most stringent lightning protection system specified in IEC

62305 (LPS Class I), the computed risk RB (6.201 x 10-3) is higher than the tolerable

risk (10-5), as can be seen in Figure ( 2. 7). This is because:

The NTC tower is a tall structure located in a rural area with no other buildings

surrounding it.

The risk of fire in the structure is assumed to be high.

Due to the fact that the NTC tower is a tall structure the resulting collection area for

direct strikes is very high thus there is a high possibility of it being struck by

lightning. Along with the fact that there are no other buildings surrounding it, this

possibility is even more increased in fact it would be doubled.

Assessing the lightning risk on the NTC Tower with the assumption of it being

surrounded by other structures of the same height or smaller resulted in a total risk of

loss of human life of 1.640×10-2

which is still greater that the tolerable limit. The

main reason for that is the fact that the structure has a high risk of fire.

Figure (4.8) Risk assessment results (R1) when assuming that the NTC Tower is

surrounded by objects smaller or of the same height

TESTING CHAPTER 4

86

For the designer who performed the risk assessment on the NTC tower they suggested

that the risk of fire is high in all zones. This resulted in a high risk value for the two

components RB and RV. Is it true that the risk of fire is high? Did they really assess

this risk based on a scientific method or did they just go for the worst case scenario.

We will need to find other ways to reduce the threat. A suggestion would be to

implement a lightning warning system to minimize the exposure of personnel in the

Zone1, Zone2 and Zone4 during thunderstorms.

Risk components RC, RM, RW and RZ

According to the IEC 62305-2 standard RC, RM, RW and RZ are considered only in

the case of hospitals, structures with risk of explosion or structures where failure of

internal system immediately endanger human lives. For the NTC tower none of the

above is true, there should be no loss of human life due to failure of internal systems.

Thus these risk components should have not been considered for the risk of loss of

human life. If these components are not considered the overall risk of loss of human

life reduces to 6.321×10-3

.

Figure ‎4.7) Risk assessment results (R1) when loss of human life due to failure of

internal systems is not considered

As shown in the previous discussion, Lightning Risk Assessment software is proven

to be a powerful tool to define what needs to be protected and at which level of

protection. But it must be noted that very often the data required for the risk

assessment are not easily available and to get them is the hardest part for the

protection engineer. Some of the data are determined in a subjective manner and

could easily result in under or over estimating the risk on the structure thus it is

TESTING CHAPTER 4

87

strongly recommended to acquire the knowledge and experience in order to use this

software with the best efficiency.

4.2. GRID DESIGN Testing In order to validate the results given by GRID DESIGN software; rectangle grid have

been analyzed by it and with the help of Ground Grid Systems (GGS) module of

ETAP – professional software.

The grounding system has a rectangular shape grid supplemented by vertical ground

rods. The data required for performance analysis is:

Soil model parameters given in Table (4.18).

Ground grid parameters given in Table (4.19).

System data given in Table (4.20).

Table (4.17) Soil model parameters

Soil resistivity 400

Surface layer resistivity 2500

Surface layer depth 0.102

Table (4.19) System data

Conductor type hard-drawn copper

Symmetrical short circuit current 3180

Maximum fault duration 0.5

Ambient temperature 40

Maximum allowable temperature Fusing temperature

Decrement factor 1

Current division factor 0.6

Table (4.20) Ground grid parameters

Depth of burial of grid 0.5

Length in X direction 84

TESTING CHAPTER 4

88

Length in Y direction 63

Spacing between conductors 7

No. of ground rods 38

Length of ground rod 10

4.3. Results

Figure (4.10)

After analyzing the performance of the grounding system described in tables (4.18) to

tables (4.20), GRID DESIGN gives results as shown in Table (4.21).

Table (4.21) Results according to GRID DESIGN and ETAP

GRID DESIGN ETAP

Touch and Step criteria

Touch Voltage for body weight of 50

kg

621.04 621.2

Step Voltage for body weight of 50 kg 1992.02 1992.5

Designed Mesh and Step voltages

Calculated Mesh voltage 593.61 581.3

TESTING CHAPTER 4

89

Calculated Step voltage 459.44 455.7

Grid parameters

Grid resistance 2.62 2.61

Grid potential rise 4996.19 4998.2

As seen from the Table (4.21), the maximum difference between the results obtained

from GD and those obtained from ETAP is in the calculation of mesh voltage. It is

about 2% but for the rest of the results the error is about 0.04%. Thus we can say that

GD is accurate and reliable as a tool for designing grounding systems.

.

CONCLUSION AND FUTURE WORK CHAPTER 5

91

5. 5 CHAPTER FIVE

CONCLUSION AND FUTURE WORK

5.1. Conclusion

In this project, the lightning risk assessment software and GRID design software was

successfully implemented. It has been validated and proven as a reliable, efficient and

easy to use tool.

As a computer aided design tool, this software is of much importance to the lightning

protection engineers. It can carry out lightning risk assessment successfully on any

kind of structures with any number of incoming lines. It allows for the division of the

structure under consideration to various areas in order to identify high-risk areas.

After that performs a careful assessment of the risks and results appear in a few

seconds analyzing the structure and why it is very important to arrange for protection.

Finally it guides the designer and provides him with adequate protection measures to

reduce some of the risks to or less the allowable limit.

The grounding network design software has proven to handle grounding system in

uniform as well as a two layer soil style in all forms of the networks. The program can

design the network successfully and calculate the actual step and touch potentials,

compare them to the accepted values and thus decide whether terrestrial network

design is safe or not.

CONCLUSION AND FUTURE WORK CHAPTER 5

92

5.2. Future work

For the lightning risk software, and there are some features that can be added to

increase its effectiveness. These are:

Economic evaluation:

Since the program can provide as many as three combinations of protection programs

as a solution to reduce the risk to under the limit, the designer should adopt the most

economical solution. And therefore it is recommended to add feature-economic

evaluation of the program to assist in evaluating the cost-effectiveness of any

protection measures.

For the GRID software design, and there are also some features that can be added to

increase its effectiveness. These are:

Ground Grid optimization

The terrestrial network should be designed to be optimized. The design should be

most appropriate, safe and cost-effective under given network conditions, and

safety constraints. And therefore it is recommended to add a feature improvement

to the program to help improve the design. This may proceed by varying the

number, dimension, spacing and general layout of conductors in the terrestrial

network. Additionally, the number of ground rods can be modified to get the most

appropriate design at the lowest possible cost.

93

Bibliography

[1] lightningsafety. [Online]. http://www.ligthningsaftey.com

[2] Manfred Kaiser, How the weather affects your health. Australia: Michelle

Anderson, 2010.

[3] oceanelectric. [Online]. http://www.oceanelectric.net

[4] perfectcomputersolutions. [Online]. http://www.perfectcomputersolutions.com

[5] Morton MJ, McManus JG, Barillo DJ, Cancio LC Ritenour AE, "Lightning

injury: a review," U.S. Army Institute of Surgical Research, Fort Sam Houston,

paper 2008.

[6] "IEC 62305-2 protection against lightning - Part 2: Risk management for

structures and services," 2006.

[7] scribd. [Online]. http://www.scribd.com

[8] kiran111.hubpages. [Online]. http://www.kiran111.hubpages.com

[9] D. Miroslav Markovic, "Grounding Grid Design In Electric Power Systems,"

TESLA Institute, 1994.

[10] "IEEE 80-2000 IEEE Guide for Safety in AC Substation ,".

[11] C.F. Dalziel, "Dangerous electric currents," 1946.

[12] B. Thapar, V. Gerez, and H. Kejriwal, "B. Thapar, V. Gerez, and H.Reduction

factor for the ground resistance of the foot in substation yards," 1994.

[13] J.G. Sverak, "Sizing of ground conductors against fusing ," 1981.

[14] P.G Laurent, "Les Bases Generales de la Technique des Mises a la Terre dems

les Installations Electriques," 1951.

[15] J. Nieman, "Unstellung von Hochstspannungs - Erdungsalagen Aufden Betrieb

mit Starr Geerdeten Sternpunkt," 1952.

[16] J.G Sverak, "Simplified analysis of electrical gradients above a ground grid; Part

I - How good is the present IEEE," 1984.

[17] B. Thaper, V. Gerez, and D. Blank, "Simplified equations for mesh and step

http://www.ligthningsaftey.com/

http://www.oceanelectric.net/

http://www.perfectcomputersolutions.com/

http://www.scribd.com/

http://www.kiran111.hubpages.com/

94

voltages in an AC substation," 1991.

[18] J. G. Sverak, "Sizing of ground conductors against fusing ," 1981.

[19] Wikipedia. [Online]. http://www.wikipedia.org

http://www.wikipedia.org/

APPENDIX A

A1

APPENDIX A : ASSESSMENT OF Nx

A.1 Assessment of Nx The probable number of strikes per year to or near the structure/service; is the product

of the annual number of flashes per 1 km2 of ground surface in the region where the

structure is placed, multiplied by an equivalent collection area (in km2) relevant to the

structure/service

N=Ng×A (A.1)

A.1.1 Determination of the collection area Ad

For isolated structures on flat ground, the collection area Ad is the area defined by the

intersection between the ground surface and a straight line with 1/3 slope which

passes from the upper parts of the structure (touching it there) and rotating around it [

1 ]. Determination of the value of Ad may be performed graphically or

mathematically.

Rectangular structure

For an isolated rectangular structure with length L, width W, and height H on a flat

ground, the collection area is then equal to:

Ad = L × W + 6 × H × (L + W) + 9 × × (H)2 (A.2)

Factors Cd, Ce and Ct modifying the collection area are introduced to take into

account the location of the structure and incoming lines, the environmental conditions

and the presence of transformer on the HV supply line.

APPENDIX A

A2

Table (A.1) Shows location Factor Cd:

Table (A.1) Location factor Cd

Relative location Cd

Object surrounded by higher

objects or trees

0.25

Object surrounded by objects or

trees of the same heights or

smaller

0.5

Isolated object: no other objects in

the vicinity

1

Isolated object on a hilltop or a

knoll

2

Table (A.2) Shows transformer Factor Ct:

Table (A.2) Transformer Factor Ct

No transformer on site, service only. 1

Service with two winding transformer. 0.2

Table (A.3) Shows environmental Factor Ce

Table (A.3) Ce Environment

Environment Ce

Urban with tall buildings 0

Urban 0.1

Suburban 0.5

Rural 1

APPENDIX A

A3

A.1.2 Number of dangerous events ND for a structure:

ND may be evaluated as the product:

ND = Ng ×Ad ×Cd/b ×10–6

(A.4)

Where

Ng is the lightning ground flash density (1/km2/year);

Ad is the collection area of the isolated structure (m2)

Cd/b is the location factor of the structure (see Table A.2).

A.1.3 Number of dangerous events NDa for an adjacent structure:

The average annual number of dangerous events due to flashes to a structure at “a”

end of a line NDa may be evaluated as the product:

NDa = Ng × Ad/a × Cd/a × Ct × 10–6

(A.5)

Where

Ng is the lightning ground flash density (1/km2/year);

Ad is the collection area of the isolated adjacent structure (m2)

Cd is the location factor of the adjacent structure

Ct is the correction factor for the presence of a HV/LV transformer on the service

to which the structure is connected, located between the point of strike and the

structure. This factor applies to line sections upstream from the transformer

with respect to the structure.

A.2 Assessment of the average annual number of dangerous

events due to flashes near a structure NM NM may be evaluated as the product:

NM = Ng × (Am – Ad/b Cd/b) ×10–6

(A.6)

Where

Ng is the lightning ground flash density (flash/km2year);

APPENDIX A

A4

Am is the collection area of flashes striking near the structure (m2).

The collection area Am extends to a line located at a distance of 250 m from the

perimeter of the structure.

If NM < 0, NM = 0 shall be used in the assessment.

A.3 Assessment of the average annual number of dangerous

events due to flashes to a service NL For a one-section service, NL may be evaluated by:

NL = Ng × Al × Cd × Ct × 10–6

(A.7)

Where

Ng is the lightning ground flash density (flash/km2/year);

Al is the collection area of flashes striking the service (m2)

Cd is the location factor of service

Ct is the correction factor for the presence of a HV/LV transformer located between

the point of strike and the structure. This factor applies to line sections upstream from

the transformer with respect to the structure.

Table A.4 Collection areas Al and Ai depending on the service characteristics

Aerial Buried

Al (Lc – 3(Ha+ Hb)) 6 Hc (Lc – 3(Ha+ Hb))

Ai 1 000 Lc 25 Lc

A.4 Assessment of average annual number of dangerous

events due to flashes near a service NI For a one-section (overhead, underground, screened, unscreened, etc.) service, the

value of NI may be evaluated by

NI = Ng × Ai × Ce × Ct × 10–6

(A.8)

APPENDIX B

B1

APPENDIX B ASSESSMENT OF Px :

The probability of damage, P, depends on the protection means provided whether they are

ingrained in the construction of the structure or intentionally provided

B.1 Probability PA that a flash to a structure will cause

injury to living beings The values of probability PA of shock to living beings due to touch and step voltage by a

lightning flash to the structure, as a function of typical protection measures, are given in Table

B.1.

Table (B.1) shows values of PA:

Table (B.1) Values of probability PA that a flash to a structure will cause shock to living

beings due to dangerous touch and step voltages

Protection measure PA

No protection measures 1

Electrical insulation of exposed down-conductor 10-2

Effective soil equipotentialization 10-2

Warning notices 10-1

If more than one provision has been taken, the value of PA is the product of the

corresponding PA values.

B.2 Probability PB that a flash to a structure will cause

physical damage The values of probability PB of physical damage by a flash to a structure, as a function of

lightning protection level (LPL), is given in Table B.2:

APPENDIX B

B2

Table (B.2.) Values of PB depending on the protection measuresto reduce physical damage

Characteristics of structure Class of LPS PB

Structure not protected by LPS 1

Structure protected by LPS IV 0.2

III 0.1

II 0.05

I 0.02

Structure with an air-termination system conforming to LPS I and a

continuous metal or reinforced concrete framework acting as a natural

down-conductor system

0.1

Structure with a metal roof or an air-termination system, possibly including

natural

components, with complete protection of any roof installations against direct

lightning strikes and a continuous metal or reinforced concrete framework

acting as a natural down-conductor system

0.001

B.3 Probability PC that a flash to a structure will cause

failure of internal systems The probability PC that a flash to a structure will cause a failure of internal systems depends

on the adopted coordinated SPD protection:

PC = PSPD (B,1)

Values of PSPD depend on lightning protection level (LPL) for which SPD are designed, as

shown in Table B.3:

APPENDIX B

B3

Table (B.3) Value of the probability PSPD as a functionof for which SPDs are designed

LPL PSPD

No coordinated SPD protection 1

III-IV 0.03

II 0.02

I 0.01

B.4 Probability PM that a flash near a structure will cause

failure of internal systems The probability PM that a lightning flash near a structure will cause failure of internal systems

depends on the adopted protection measures reducing the penetration of the lightning

electromagnetic impulsive field (LEMP) into the building and its coupling with internal

systems and devices, according to a factor KMS.

Factor KMS can be expressed by the product as follows:

KMS = KS1 KS2 KS3 KS4 (B.2)

Where

KS1, KS2 are the factors which take into account the effect of external and internal

screens adequately.

KS3 is the factor due to wiring screening and routing precautions.

KS4 is the factor related to the impulse withstand voltage level of the system to be

protected.

When coordinated SPD protection meeting the requirements of IEC 62305-4 is not provided,

the value of PM is equal to the value of PMS. The values of PMS.as a function of KMS are

given in Table B.4

When coordinated SPD protection according to IEC 62305-4 is provided, the value of PM is

the lower value between PSPD and PMS.

Table (B.4) shows Value of the probability PMS as a function of factor KMS:

APPENDIX B

B4

Table B.4 Value of the probability PMS as a function of factor KMS

KMS PMS

≥0.4 1

0.15 0.9

0.07 0.5

0.035 0.1

0.021 0.01

0.016 0.005

0.015 0.003

0.014 0.001

≤0.013 0.0001

Table (B.5) Shows value of factor KS3 depending on internal wiring:

Table (B.5) Value of factor KS3 depending on internal wiring

Type of internal wiring KS3

Unshielded cable – no routing precautions in order to avoid loops 1

Unshielded cable – with routing precautions in order to avoid large

loops

0.2

Unshielded cable – with routing precautions in order to avoid small

loops

0.02

Shielded cable 5 <Rs<= 20 Ohms/km 0.001

Shielded cable 1 <Rs<= 5 Ohms/km 0.0002

Shielded cable Rs<= 1 Ohms/km 0.0001

APPENDIX B

B5

B.5 Probability PU that a flash to a service will cause injury

to living beings The values of probability PU of injury to living beings due to touch voltage by a flash to a

service entering the structure depends on the characteristics of the service shield, the impulse

withstand voltage of internal systems connected to the service, the typical protection measures

(physical restrictions, warning notices, etc. (see Table B.1) and the SPD(s) provided at the

entrance of the service.

When SPD(s) are not provided for equipotential bonding in accordance with IEC 62305-3, the

value of PU is equal to the value of PLD, where PLD is the probability of failure of internal

systems due to a flash to the connected service. Values of PLD are given in Table B.6.

When SPD(s) are provided for equipotential bonding in accordance with IEC 62305-3, the

value of PU is the lower value between PSPD (Table B.3) and PLD.

Table (B.6) Shows values of the probability PLD depending on the resistance RS of the cable

screen and the impulse withstand voltage Uw of the equipment:

Table (B.6) Values of the probability PLD depending on the resistance RS of the cable screen and

the impulse withstand voltage Uw of the equipment

Uw ( kV ) 5 < RS < 20

Ω/km

1 < RS < 5

Ω/km

RS < 1

Ω/km

1.5 1 0.8 0.4

2.5 0.95 0.6 0.2

4 0.9 0.3 0.04

6 0.8 0.1 0.02

For unshielded service PLD = 1 shall be taken.

APPENDIX B

B6

B.6 Probability PV that a flash to a service will cause

physical damage The values of probability PV of physical damage by a flash to a service entering the structure

depend on the characteristics of service shield, the impulse withstand voltage of internal

systems connected to the service and the SPDs provided.

When SPD(s) are not provided for equipotential bonding according to IEC 62305-3, the value

of PV is equal to the value of PLD, where PLD is the probability of failure of internal systems

due to a flash to the connected service. Values of PLD are given in Table B.6.

When SPD(s) are provided for equipotential bonding in accordance with IEC 62305-3, the

value of PV is the lower value between PSPD (see Table B.3) and PLD.

Probability PW that a flash to a service will cause failure of internal systems

The values of probability PW that a flash to a service entering the structure will cause a

failure of internal systems depend on the characteristics of service shielding, the impulse

withstand voltage of internal systems connected to the service and the SPDs installed .

When coordinated SPD protection conforming to IEC 62305-4 is not provided, the value of

PW is equal to the value of PLD, where PLD is the probability of failure of internal systems

due to a flash to the connected service. Values of PLD are given in Table B.6.

When coordinated SPD protection conforming to IEC 62305-4 is provided, the value of PW is

the lower value between PSPD (see Table B.3) and PLD.

B.7 Probability PZ that a lightning flash near an incoming

service will cause failure of internal systems The values of probability PZ that a lightning flash near a service entering the structure will

cause a failure of internal systems depend on the characteristics of the service shield, the

impulse withstand voltage of the system connected to the service and protection measures

provided.

When coordinated SPD protection conforming to IEC 62305-4 is not provided, the value of PZ

is equal to the value of PLI, where PLI is the probability of failure of internal systems due to

flash to the connected service. Values of PLI are given in Table B.7.

APPENDIX B

B7

When coordinated SPD protection conforming to IEC 62305-4 is provided, the value of PZ is

the lower value between PSPD (see Table B.3) and PLI.

Table (B.7) Shows values of the probability PLI depending on the resistance RS of the cable

screen and the impulse withstand voltage Uw of the equipment:

Table (B.7) Values of the probability PLI depending on the resistance RS ofthe cable screen and

the impulse withstand voltage Uw of the equipment

Uw

kV

No shield

Shield not bonded to

Equipotential bonding

bar to which

equipment is

connected

Shield bonded to equipotential

bonding bar and equipment

connected to the same bonding bar

5 < RS < 20

Ω/km

1 < RS < 5

Ω/km

RS < 1

Ω/km

1.5 1 0.5 0.15 0.04 0.02

2.5 0.4 0.2 0.06 0.02 0.008

4 0.2 0.1 0.03 0.008 0.004

6 0.1 0.05 0.02 0.004 0.002

APPENDIX C

C1

APPENDIX C ASSESSMENT OF Lx :

The consequence of the loss, L is a function of the use of the structure and its

contents, the exposure of humans during lightning events, the value of the goods

affected by the damage and the measures provided to limit the amount of loss

The loss LX varies with the type of loss (L1, L2, L3 and L4) considered and, for each

type of loss, with the type of damage (D1, D2 and D3) causing the loss. The following

symbols are used:

Lt is the loss due to injury by touch and step voltages;

Lf is the loss due to physical damage;

Lo is the loss due to failure of internal systems.

C.1 Loss of human life The value of Lt, Lf and Lo may be determined in terms of the relative number of

victims from the following approximate relationship:

LX = (np / nt) × (tp / 8 760) (C.1)

Where

np is the number of possible endangered persons (victims).

nt is the expected total number of persons (in the structure).

tp is the time in hours per year for which the persons are present in a dangerous

place, outside of the structure (Lt only) or inside the structure (Lt , Lf and Lo).

Table (C.1) Shows typical mean values of Lt, Lf and Lo:

APPENDIX C

C2

Table C.1 Typical mean values of Lt, Lf and Lo

Type of structure Lt

With people inside 10-4

With people outside 10-2

Type of structure Lf

Hospitals, hotels, civil buildings 10-1

Industrial, commercial, school 5*10-2

Public entertainment, churches, museum 2*10-2

Others 10-2

Type of structure Lo

Structure with risk of explosion 10-1

Hospital or other structure where loss of a service would

immediately endanger life.

10-3

Table (C.2) Shows values of factor hz increasing the relative amount of loss in

presence of a special hazard:

Table C.2 Values of factor hz increasing the relative amount of loss

in presence of a special hazard

Special hazard Hz

No special hazard 1

Low level of panic, structure limited to two floors and <100 occupants 2

Average level of panic, occupants >100 but <1000 5

Difficulty in evacuation, immobilized persons, hospitals...etc. 5

High level of panic, occupants >1000 10

Hazard for surroundings or environment 20

Contamination of surroundings or environment 50

APPENDIX C

C3

Table (C.3) Shows values of reduction factor rf as a function of risk of fire of

structure:

Table C.3 Values of reduction factor rf as a function of risk of fire of structure

Risk of fire Rf

None 0

Low 10-3

Ordinary 10-2

High 10-1

Risk of explosion 1

Table (C.4) Shows values of reduction factor rp as a function of provisions taken to

reduce the consequences of fire:

Table C.4 Values of factor hz increasing the relative amount of loss in presence of a special

hazard

Provision rp

No provisions 1

Manual fire extinguishers or systems, manual alarm, Hydrants or

protected escape routes.

0.5

Automatic fire extinguishers or automatic alarm installations 0.2

C.2 Loss of service to the public The values of Lf and Lo can be determined in term of the relative amount of possible

loss from the following approximate relationship:

Lx = np / nt × t / 8 760 (C.2)

Where:

np is the mean number of possible endangered persons (users not served).

nt is the total number of persons (users served).

APPENDIX C

C4

t is the annual period of loss of service (in hours).

Table (C.5) Shows typical mean values of Lf and Lo;

Table C.5 Typical mean values of Lf and Lo

Type of service Lf Lo

Gas supply, Water supply 10-1

10-2

Radio, TV, Telecommunications, Power supply,

Railway

10-2

10-3

C.3 Loss of cultural heritage The value of Lf can be determined in terms of the relative amount of possible loss

from the following approximate relationship:

Lx = c / ct (C.3)

Where

c is the insurable value of possible loss of goods in currency.

ct is the total insured value of all goods present in the structure in currency.

A typical mean value of Lf, when the determination of c and ct is uncertain or

difficult, is:

Lf = 10–1

C.4 Economic loss The value of Lt, Lf and Lo can be determined in terms of the relative amount of

possible loss from the following approximate relationship:

Lx = c / ct (C.4)

Where

APPENDIX C

C5

c is the mean value of possible loss of the structure (including its content and

relevant activities and its consequences) in currency;

ct is the total value of the structure (including its content and relevant activities) in

currency

Table (C.6) Shows typical mean values of Lt, Lf and Lo:

Table C.6 – Typical mean values of Lt, Lf and Lo

Type of structure Lt

All types – Inside buildings 10-4

All types – Outside buildings 10-2

Type of structure Lo

Hospital, Hotel, Industrial, Museum or Agricultural 0.5

Schools, Office/Commercial/Economic, Church, Public, Entertainment 0.2

Others 0.1

Type of structure Lf

Risk of explosion 10-1

Hospitals, Industrial or Commercial complexes, Offices, Hotels 10-2

Museums, Agricultural, Schools, Churches, Publicbuildings 10-3

Others 10-4

APPENDIX D

D1

APPENDIX D MATERIAL CONSTANTS AND

EQUIVALENT SUBSTATION IMPEADANSE :

Table (D.1) Material constants

Material

αr factor at20

ºC

Koat 0°C (0

°C) Fusinga ρr 20 °C

TCAP

thermal

Description conductivity (1/ºC)

temperature (μΩ·cm) capacity

(%)

Tm (°C)

[J/(cm3·°C)]

Copper,

annealed,

soft-drawn,

Copper,

100 0.003 93 234 1083 1.72 3.42

commercial,

hard-drawn,

Copper-clad

97 0.003 81 242 1084 1.78 3.42

steel wire 40 0.003 78 245 1084 4.4 3.85

Copper-clad,

steel wire 30 0.003 78 245 1084 5.86 3.85

Copper-clad,

steel rodᵇ 20 0.003 78 245 1084 8.62 3.85

Aluminum,

EC grade 61 0.004 03 228 657 2.86 53.5

Aluminum,

5005 alloy 53.5 0.003 53 263 652 3.22 2.6

Aluminum,

6201 alloy 52.5 0.003 47 268 654 3.28 2.6

Aluminum-

clad, steel

wire

20.3 0.003 60 258 657 8.48 3.58

Steel, 1020 10.8 0.001 60 605 1510 15.9 3.28

Stainless-

clad, steel

rodᶜ 9.8 0.001 60 605 1400 17.5 4.44

Zinc-coated,

steel rod 8.6 0.003 20 293 419 20.1 3.93

Stainless

steel, 304 2.4 0.001 30 749 1400 72 4.03

APPENDIX D

D2

Table D.2 Approximate equivalent impedances of transmission line overhead shield wires and

distribution feeder neutrals

Number of

transmission lines

Number of

distribution

neutrals

Rtg= 15;

Rdg= 25;

R+jx(Ω)

Rtg= 100;

Rdg= 200;

R+jx(Ω)

1 1 0.91 +j.485 3.27 +j.652

1 2 0.54 +j0.33 2.18 +j.412

1 4 0.295 +j0.20 1.32 +j.224

1 8 0.15 +j.11 0.732 +j.133

1 12 0.10 +j.076 0.507+j.091

1 16 0.079+j.057 0.387 +j.069

2 1 0.685 +j.302 2.18 +j.442

2 2 0.455 +j.241 1.63 +j.324

2 4 0.27 +j.165 1.09 +j.208

2 8 0.15 +j0.10 0.685 +j.122

2 12 0.10 +j0.07 0.47 +j.087

2 16 0.08 + j.055 0.366 + j.067

4 1 0.45 +j0.16 1.30 +j.273

4 2 0.34 +j0.15 1.09 +j0.22

4 4 0.23 +j0.12 0.817 +j0.16

4 8 0.134 +j.083 0.546 +j.103

4 12 0.095 +j.061 0.41 +j.077

4 16 0.073 +j0.05 0.329 +j0.06

8 1 0.27 +j0.08 0.72 +j.152

8 2 0.23 +j0.08 0.65 +j.134

8 4 0.17 +j.076 0.543 +j0.11

8 8 0.114 +j.061 0.408 +j.079

8 12 0.085 +j.049 0.327 +j.064

8 16 0.067 +j.041 0.273 +j.052

12 1 0.191 +j.054 0.498 +j.106

12 2 0.17 +j.055 0.462 +j.097

12 4 0.14 +j.053 0.406 +j.083

12 8 0.098 +j.047 0.326 +j.066

12 12 0.077 +j.041 0.272 +j.053

APPENDIX D

D3

12 16 0.062 +j.035 0.234 +j.046

16 1 0.148 +j0.04 0.380 +j.082

16 2 0.135 +j.041 0.360 +j.076

16 4 0.113 +j.041 0.325 +j.067

16 8 0.086 +j.038 0.272 +j.055

16 12 0.068 +j.034 0.233 +j.047

16 16 0.057 +j0.03 0.203 +j.040

1 0 2.64 +j0.60 6.44 +j1.37

1 0 2.64 +j0.60 6.44 +j1.37

2 0 1.30 +j0.29 3.23 +j0.70

4 0 0.65 +j.15 1.61 +j.348

8 0 0.327 +j.074 0.808 +j.175

12 0 0.22 +j.049 0.539 +j.117

16 0 0.163 +j.037 0.403 +j.087

0 1 1.29 +j.967 6.57 +j1.17

0 2 0.643 +j.484 3.29 +j0.58

0 4 0.322 +j.242 1.65 +j.291

0 8 0.161 +j.121 0.826 +j.148

0 12 0.108 +j.081 0.549 +j.099

0 16 0.080 +j.061 0.412 +j.074

APPENDIX E

E1

APPENDIX E : LIGHTNING RISK

ASSESSMENT SOFTWARE AND GRID

DISGN SOFTWARE HELP FILES

Lightning Risk

Assessment

Software Lightning risk assessment software evaluates the risk due to all possible effects of

lightning flashes to structures in accordance to EN 62305. It helps you decide on how

to select the most suitable protection measures in order to reduce the risk to or below

a tolerable limit.

Structure: In this page you will specify:

Structure dimensions

Structure type

Environmental influences

Structure characteristics

APPENDIX E

E2

Structure type:

Select the type of the structure from the drop down list

Structure dimensions:

Specify the structure dimensions in order to calculate the collection area of direct and

indirect flashes.

Height:

Enter the structure height in meters

Length:

Enter the structure length in meters

Width:

Enter the structure width in meters

APPENDIX E

E3

For complex structures, the software provides you with two options.

User Defined

Graphical Calculation

User Defined

Select this option to enter the collection area for direct strikes and the collection

area for events near the structure

Graphical calculation

Select this and click Draw. The software will allow you to use the collection area

graphical tool to draw the structure and then it will estimate the collection areas.

APPENDIX E

E4

Collection Area Graphical Tool

In the polygon data box define the polygon points and the structure height.

Click on Show Structure and the structure plan is will be shown on the right hand

pane

You may enlarge the structure by typing any positive number from 0 to 4.

APPENDIX E

E5

Show Collection Area

Click on show collection area and the program will estimate the collection area

and display it in m2.

APPENDIX E

E6

Show Collection Area for Events Near Structure

Click this button and the program will estimate the collection area for events near

the structure

Environmental influence:

Location factor:

Select the location factor for your structure from the drop-down list

Environmental factor:

Select the environmental factor for your structure from the drop-down list

Thunder-days number:

If known, enter the number of Thunder-days else, the software provides a

world thunder-days map to help you specify the thunder-days of the regions

under consideration.

Structure characteristics:

Structure LPS:

Select the protection level for the lightning protection system -LPS- installed

on your structure

*Your LPS must conform to the requirements of EN 62305-3

APPENDIX E

E7

Structure shield:

Select the type of external shield of the structure

Service lines: The software considers the characteristics of incoming lines (energy and/or signal)

connected to the internal systems of the structure.

In this page you will specify:

Line characteristics

Nearby structure characteristics

Line characteristics:

Line type:

Select the line type (overhead or underground).

For overhead lines specify the length and height of the line

For underground cables specify the line length and soil-resistivity

APPENDIX E

E8

Location factor:

Select the line location factor from the drop-down list

Environmental factor:

Select the line environmental factor from the drop-down list

Line shielding:

Select the line shielding from the drop-down list

SPD at line entrance:

Select the surge protection level at the entrance of the line from the drop-down list

Nearby structure characteristics:

Height:

Enter the structure height in meters

Length:

Enter the structure length in meters

Width:

Enter the structure width in meters

Location factor:

Select the location factor for the structure from the drop-down list

Add:

Click on the add button o add a new line. The program creates the new line using

default values

Rename:

Click on the rename button to change the name of the selected line

Delete:

Click on this button to delete he line and its data

*The software has no limits in considering the number of connected lines.

APPENDIX E

E9

Zones: The software allow for the division of the structure into several zones, having each

zone a different risk value, and allows the selection of the most suitable protection

measures needed for each zone.

In this page you will specify:

Zone characteristics

Zone’s internal system characteristics

Zone characteristics:

Zone type:

Select zone type

For external zones:

Ground surface type:

Select the floor type

APPENDIX E

E10

Protection against touch voltage

Check on the protection measures adopted against touch and step voltages

For internal zones:

Ground surface type

Select the floor type

Protection against touch voltage

Check on the protection measures adopted against touch and step voltages

Risk of fire:

Select fire risk

Fire protection:

Select the type of fire protection system

Life hazard:

Select life and economic hazard

Zone shielding:

Select zone shielding

Add:

Click on the add button to add a new zone. The program creates the new zone using

default values

Rename:

Select the zone then click on the rename button to change the name of the selected

zone

Delete:

Click on his button to delete he zone and is data

APPENDIX E

E11

Internal systems:

The software let the description of internal energy and/or of signals systems for each

zone and it allows the evaluation of the risk due to surges.

Connected to:

Select the line to which the internal system is connected to

Internal wiring type:

Select the type of wiring

Coordinated SPD:

Select the protection level of Coordinated SPD installed

Add:

Click on the add button to add a new internal system.

APPENDIX E

E12

Rename:

Click on the rename button to change the name of the selected internal system

Delete:

Click on the delete button to delete the internal system and its data

*The software has no limits in considering the number of zones and their internal

systems.

Losses: The values of amount of loss LX should be evaluated and fixed by the lightning

protection designer (or the owner of the structure). It is recommended that the

equations given in EN 62305-2 are to be used as the primary source of values for LX.

Loss of human life

Loss of service

Loss of cultural heritage

Economic loss

APPENDIX E

E13

Loss of human life: The software provides you with three options:

Guided

Typical

Manual

Typical:

The software provides you with typical values for the loss factors according to EN

62305-2.

Type of structure:

Select the type of your structure from the drop-down list

Structure with risk of explosion:

Check this option if there is a risk of explosion on your structure

Number of possible endangered people due to:


Physical damage

Failure of internal system

APPENDIX E

E14

Touch and Step voltages

Guided:

If the information required for calculating the loss factors are available then choose

guided and enter the data for each zone

People present inside/outside the structure:

Enter the total number of people present in the structure

Number of possible endangered people due to:


Physical damage

Failure of internal systems


Time in hours per year for which people are present in the zone:

Enter the time in hours per year for which people are present in the zone

APPENDIX E

E15

Manual:

The software provides you with the option of entering the loss factors for each zone

directly.

Enter the three loss factors for each zone

Loss due to physical damage

Loss due to failure of internal systems

Loss due to Touch and Step voltages

APPENDIX E

E16

Loss of service to the public: The software provides you with three options:

Guided

Typical

Manual

Typical:


62305-2.

Service loss due to:

Physical damage:

Select the service that will be lost due to physical damage

Failure of internal system:

Select the service that is lost due to failure of internal systems

APPENDIX E

E17

Service loss percentage for each zone: Default:

Select this option and the software will divide the typical loss values equally

among the structure’s zones

User defined:

Select this option and you will be able to enter the percentage contribution of

each zone in the total loss value

Guided:



Total number of users served:

Enter the total number of users served

Annual period of loss of service-in hours:

Enter the annual period of loss of service in hours

Number of possible users not served due to:


Physical damage

APPENDIX E

E18

Failure of internal system


Manual:


directly.

Enter the two loss factors for each zone




APPENDIX E

E19

Loss of cultural heritage: The software provides you with three options:

Guided

Typical

Manual

Typical:


62305-2.

Cultural Heritage loss percentage for each zone:

Default:

Select this option and the software will divide the typical loss value equally


User defined:



Guided:



APPENDIX E

E20

Total insured value of the structure (in currency):

Enter the total insured value of the structure in currency.

Insurable value of possible loss of goods (in currency)

For each zone enter the insurable value of possible loss of goods in currency.

Manual:


directly.

For each zone enter the loss factor due to physical damage.

APPENDIX E

E21

Economic loss: The software provides you with three options:

Guided

Typical

Manual

Typical:


62305-2.

Economic loss due to:

Physical damage:


Failure of internal system:


Economic loss percentage for each zone:

Default:

Select this option and the software will divide the typical loss values equally


APPENDIX E

E22

User defined:



Animals present in the zone:

Check this option if the loss of animals is considered

Guided:



Total value of the structure (in currency)

Enter the total value of the structure in currency

Value of possible loss of the zone due to:

Enter the value of possible loss due to

Physical damage

Failure of internal systems


APPENDIX E

E23

Manual:


directly.

Enter the three loss factors for each zone




APPENDIX E

E24

Risk calculations: The risk evaluation is made simultaneously in all zones; it shows in just a few seconds

where in the structure and why it is so important to arrange protection

measures. Please refer to the Calculation Methods section for more information on

how to calculate the risks

The risk components greater than the tolerable value are displayed in RED while the

risk components less than the tolerable value are displayed in GREEN

Select the risk R1, R2, R3 or R4 to display its components

Click on any zone –anywhere on the zone column- in the risk assessment list and the

software will provide you with a deeper insight into the specified zone through the

information displayed in:

Internal system list

Risk assessment chart

Internal Systems:

Display the risk components RU, RV, RW and RZ associated with each internal system

APPENDIX E

E25

Risk assessment chart:

Display the contribution of each risk component in the overall risk of lightning on the

specified zone

Existing protection measures:

Display the protection measures that are already installed in the structure

Risk composition:

Click on this button to display the contribution of risk components on the total risk of:

Loss of human life

Loss of service o people in the structure

Loss of cultural heritage

Economic loss

According to the type of damage or source of damage

APPENDIX E

E26

Protection measures: After assessing the risk on your structure the software will help you to evaluate the

effect of different protection measures to mitigate such a risk.

Click on any zone in the risk assessment list and the software will provide you

with a deeper insight into the specified zone through the information displayed in:

Internal system list

Risk assessment chart

Internal Systems:

View the risk components RU, RV, RW and RZ associated with each internal

system.

Risk assessment chart:

Display the contribution of each risk component in the overall risk of lightning on

the specified zone.

With this information you can easily identify the most critical risk components.

APPENDIX E

E27

Double click to select protection measures:

Double click on the risk component you want to reduce and the software will provide

you with the protection measures necessary to reduce this component to the tolerable

limit

Recommended protection measures:

Display the combination of protection measures adopted to reduce the risks R1, R2

and R3 to the tolerable value

Reducing RA:

Type of surface:

Select the appropriate surface type to:

Increase the surface resistivity of the soil around the structure ( Outside zone)

Increase the surface resistivity of internal floors ( Inside zone)

Protection measures against touch and step voltages:

Check one or more of these options to reduce the probability of injury to living beings

due to flashes to a structure.

Electrical insulation:

Provide adequate insulation of exposed conductive parts that could come in

contact with the person.

Soil equipotentialization:

Create an equipotential plane by means of a meshed conductor earthing

arrangement to reduce the step voltage threat.

APPENDIX E

E28

Physical restriction and warning notices:

Provide warning notices and physical restrictions where possible to avoid contact

with external dangerous parts

Reducing RB:

Install LPS:

Select the level of LPS to install on your structure to reduce the probability of

physical damage to the structure due to direct flashes

According to BN 62305-3 the software automatically provides SPD at line entrance

thus reducing:

The Probability of injury to living beings due to flashes striking a connected

service

The Probability of physical damage to the structure due to flashes striking a

connected service

Fire protection:

Provide fire protection as a measure to limit fire propagation thus reducing the

amount of loss due to physical damage

Reducing RC:

APPENDIX E

E29

Coordinated SPD:

Install coordinated SPD on your system to reduce:

The probability PC that a flash to a structure will cause a failure of internal

systems

The Probability PW that a flash to a service will cause failure of internal

Systems

The Probability PZ that a lightning flash near an incoming service will cause

failure of internal systems

*Coordinated SPD protection is effective to reduce PC only in structures protected by

an LPS or structures with continuous metal or reinforced concrete framework acting

as a natural LPS, where bonding and earthing requirements of IEC 62305-3 are

satisfied.

Reducing RM:

Zone shielding:

Provide effective shielding against induced Lightning Electromagnetic Impulse

(LEMP) effects

APPENDIX E

E30

Internal wiring:

Select the appropriate type of line routing and shielding to minimize voltages and

currents induced into electrical and electronic system.

Coordinated SPD:


The probability PM that a flash near a structure will cause a failure of internal

systems


systems


Systems



Withstand voltage:

Select equipments with a higher impulse withstand voltage level

Reducing RU:


Provide SPD at the line Entrance to reduce:


service

APPENDIX E

E31


connected service

Withstand voltage:

Select equipments with higher capabilities of withstanding high voltage

Reducing RV:


Provide SPD at line Entrance o reduce:


service


connected service

Withstand voltage:


Fire protection:

Provide fire protection as a measure to limit fire propagation thus reducing the

amount of loss due to physical damage

APPENDIX E

E32

Reducing RW:

Coordinated SPD:


The probability PM that a flash near a structure will cause a failure of internal

systems


systems


Systems



Withstand voltage:


APPENDIX E

E33

GRID

DESIGN

The grid design software helps you model and build your electrical grounding system

according to IEEE 80-2000 standard that will ensure the performance of power

systems and safety of personnel.

The grid design software calculates the following:






APPENDIX E

E34

Soil Editor

Click on this button to open the Soil Editor window

General Design Data

Click on this button to open the General Design Data window

Results

Click on this button to display the following results






Report

Click on this button to view a detailed report in Microsoft Word.

Drawing the Grid: Drawing the grid will be done in four steps

1. Draw grid periphery

2. Draw the X-axis (horizontal) conductors

3. Draw the Y-axis (vertical) conductors.

4. Draw grid rods

APPENDIX E

E35

Grid periphery:

To draw the grid periphery the user just has to enter the corners of the grid

Grid depth:

The user is to enter the depth of the grid

Draw periphery:

Click this button to draw the grid

X-axis (horizontal) conductors:

To draw these conductors you must specify the start and the end of the conductor line

and the vertical spacing between the conductors

APPENDIX E

E36

Repeat line:

Click on this button to create an exact replica of the horizontal conductor

Draw line:

Click on this button to draw the horizontal conductors

Erase lines:

Clicks on this button to erase all the horizontal conductors

Y-axis (vertical) conductors:

To draw these conductors you must specify the start and the end of the vertical

conductor and the horizontal spacing between the conductors

Repeat line:

Click on this button to create an exact replica of the conductor

Draw line:

Click on this button to draw the conductors

Erase lines:

Clicks on this button to erase all the vertical conductors

Grid rods:

The software allows the user to draw individual rods or they can define a pattern for

the rods

APPENDIX E

E37

Draw Rods:

Click on this button to draw the rods

Erase Rods:

Clicks on this button to erase all rods

Soil Editor:

The following soil resistivity models can be used:

1. Two-layer, horizontally stratified

2. Uniform (homogeneous)

In this window you will specify your soil model parameters.

APPENDIX E

E38

Soil Resistivity:

Enter the Resistivity of the soil in ohm-m in this field.

Thickness of surface layer:

Enter the Surface Material depth in meters.

Surface Layer Resistivity:

Enter the material resistivity of the Surface Layer soil in ohm-m.

*To specify a uniform soil model then enter the top and bottom layer resistivity as the

same value.

General Design Data:

APPENDIX E

E39

Conductor material:

Select the conductor material type from the drop-down list

Symmetrical short circuit current:

Enter the r.m.s value of the maximum fault current expected to flow to ground in kA,

with no dc offset included. The effect of the dc offset is introduced by specifying the

Decrement factor.

Duration of current in s:

Enter the maximum duration of fault current in seconds

Design Ambient Temperature:

Enter the soil ambient temperature in ºC.

Maximum Allowable Temperature:

This is the allowable temperature limit: it can be the fusing temperature of the

conductor or a limit based on the type of connections made between conductors or a

limit imposed by the presence of nearby flammable materials. There are two options

for determining this temperature:

User specified

Fusing temperature

User specified:

Click on this option to specify the maximum allowable temperature

Fusing temperature:

Click on this option and the software will set the allowable temperature limit equal to

the fusing temperature of the specified conductor material.

Decrement factor:

Specifies the multiplicative constant by which the symmetrical RMS fault current

magnitude must be increased in order to obtain an equivalent RMS current magnitude

which accounts for the dc component of the fault current waveform. There are two

options for determining this factor:

User specified

Computed

User specified:

Click on this option to enter the current division factor

Computed:

Click on this option and the software will calculate the division factor according to:

APPENDIX E

E40

X/R ratio

Frequency

X/R ratio:

Enter the x/r ratio of your system

Frequency:

Select your system frequency from the drop-down list

Current division factor:

The current division factor Sf is the fraction of the total fault current that flows

through the earth. There are two options for determining this factor:

User specified

Computed

User specified:

Click on this option to enter the current division factor

Computed:

Click on this option and the software will calculate this factor according to:

Number of transmission lines

Number of distribution feeders

Rg and Rtg

Number of transmission lines:

Enter the number of transmission lines entering your station

Number of distribution feeders:

Enter the number of distribution feeders leaving your station

Rtg and Rdg:

Select the value of Rtg and Rdg from the drop-down list.

*Rtg is the impedance to remote earth of each transmission ground electrode in Ω

while Rdg is the impedance to remote earth of each distribution ground electrode in Ω

Documents

lighting and earthing design according to ieee80_2000 and iec 62305-2 by aya emad mahmoud