ALI AHMED ALI SALEM -...

STUDY OF LIGHTNING GROUND FLASHES INTERACTION

WITH RAILWAY LINES

ALI AHMED ALI SALEM

UNIVERSITI TUN HUSSEIN ONN MALAYSIA

STUDY OF LIGHTNING GROUND FLASHES INTERACTION WITH RAILWAY

LINES

ALI AHMED ALI SALEM

This project report presented in partial

fulfillment of the requirements for the award of the

Degree of Master of Electrical Engineering

Faculty of Electrical and Electronic Engineering

Universiti Tun Hussein Onn Malaysia

January 2016

ii

Special dedication

I dedicate this work to my beloved mother, father,wife,brother and son.

.

iii

ACKNOWLEDGEMENT

All praises is to ALLAH Subhanahu wa ta’ala for bestowing me with health,

opportunity, patience, and knowledge to complete this research. May the peace and

blessings of ALLAH Subhanahu wa Ta’aala be upon Prophet Muhammad (Sallallahu

alayhi wa sallam).

My profound gratitude goes to my supervisor Prof. Dr.Hussein Bin Ahmed ,

for his invaluable guidance, excellent supervision, continuous encouragement and

constant support in making this research possible. His cooperation, tolerance,

constructive criticism and useful suggestions have been of immense encouragement

to me and enabled me to develop a deeper understanding of this research. I sincerely

thank him for the time spent in proofreading and correcting my mistakes.

I am especially indebted to my parents and my brother, who were my first

teachers in this world by setting a good example for me about how to live, study, work

and for their love, sacrifices, and support. I also acknowledge with thanks and humility

my wife and daughter who have remained my anchor in terms of love, support,

encouragement and prayers. I will forever remain grateful to them.

Finally, I extend my gratitude to all those who were directly or indirectly

involved by either encouraging, praying and offering constructive advice in this

project work.

Thank you.

iv

ABSTRACT

Railway signaling systems on conventional lines of Malaysian railway companies

have been damaged from lightning, especially in 2010. Therefore, effective and

economical lightning protection measures are necessary for railway signaling systems

because suspended operation or train delays due to lightning damage may cause social

disruption. For analyzing lightning risk and making study for countermeasures against

lightning damage, must measure the lightning overvoltage on railway signaling

cables, which were laid at the ground surface and overhead, and rails in the field to

enable quantitative analysis of the frequency of lightning overvoltage occurrence.

Moreover, we investigated the correlation of lightning overvoltage (V) on signaling

cables and rails with lightning conditions, such as the strike current (I) and the strike

position ( distance from the measuring position). From this we deduced the correlation

between the lightning overvoltage (V) and (I), expressed as a linear expression. From

this correlation, the lightning risk for railway signaling systems against lightning

conditions can be estimated. In addition, it is possible to calculate the possibility of

lightning damage to railway signaling equipment.

v

ABSTRAK

Railway sistem pada talian konvensional syarikat keretapi di Malaysia isyarat telah

rosak dari kilat, terutamanya pada tahun 2010. Oleh itu, langkah-langkah

perlindungan kilat berkesan dan ekonomi yang perlu untuk sistem isyarat kereta api

kerana operasi atau kereta api digantung kelewatan akibat kerosakan kilat boleh

menyebabkan gangguan sosial. Untuk menganalisis risiko kilat dan membuat kajian

untuk langkah balas terhadap kerosakan kilat, mesti mengukur voltan lampau kilat di

kereta api isyarat kabel, yang telah dibentangkan di permukaan tanah dan overhed,

dan landasan keretapi di lapangan untuk membolehkan analisis kuantitatif kekerapan

berlakunya kilat voltan. Selain itu, kami mengkaji korelasi voltan lampau kilat (V)

pada isyarat kabel dan landasan dengan keadaan kilat, seperti mogok semasa (I) dan

kedudukan mogok (jarak dari kedudukan pengukur). Dari sini kita disimpulkan

hubungan antara voltan lampau kilat (V) dan (I), dinyatakan sebagai ungkapan linear.

Dari korelasi ini, risiko kilat untuk sistem isyarat kereta api terhadap keadaan kilat

boleh dianggarkan. Di samping itu, ia adalah mungkin untuk mengira kemungkinan

kerosakan kilat untuk peralatan kereta api isyarat.

vi

TABLE OF CONTENTS

CONTENTS PAGE

TITLE

APPROVAL i

DECLARATION ii

ACKNOWLEDGEMENT iii

ABSTRACT iv

ABSTRAK v

TABLE OF CONTENTS vi

LIST OF FIGURES x

LIST OF TABLES xvi

LIST OF SYMBOLS AND ABBREVIATIONS xix

CHAPTER 1 INTRODUCTION 1

1.1 Project background 1

1.2 Problem statements 2

1.3 Project objectives 2

1.4 Project scopes 3

1.5 Thesis outline 3

CHAPTER 2 LITERATURE REVIEW 4

2.1 Introduction 4

2.2 Mechanism of Lightning to railway 5

2.3 Effects of Lightning Discharges in the railway 6

2.3.1 Direct strokes 7

2.3.2 Indirect effects. 7

2.4 Railway system 7

vii

2.4.1 Lightning Surge parameters of the rail 8

2.4.2 Surge attenuation ratio in the rail 8

2.9.3 Electric circuit for the railway 9

2.5 Kluang double -track railway system 9

2.6 Modeling Indirect Lightning Strikes for Railway Systems 11

With Lumped Components 11

2.6.1 Induced voltages across lumped devices along the track

System in railway and transmissions lines. 11

2.6.2 The Electrified Railway System. 14

2.7 Pole insulator flashover and ionization at the pole footing. 16

2.7.1. Interconnection between the conductors 16

2.7.2. Pole insulator flashover and soil ionization at the pole

footing.

16

2.8 Waves on Railway Lines. 18

2.8.1 Reflection and Refraction of Travelling Waves

(bewley lattice diagram) 20

2.8.2 Propagation the waves in bewley lattice diagram method. 21

2.9 Lightning risk evaluation for railway signalling systems 22

2.10 Devices along Electrified Railway Systems. 24

2.10.1 Trackside Transformers. 24

2.10.2 Track Circuit. 25

2.10.3 The effect in interlocking relay railroad crossing work 26

CHAPTER 3 METHODOLOGY 29

3.1 Introduction 29

3.2 Flow chart of project 30

3.3 Lightning parameters and equivalent attractive area in kluang 31

train station.

3.4 Railway study Overview. 32

3.5 Railway model. 32

3.6 Analysis of the lightning stroke to railway tracks. 33

3.6.1 Simultaneous and multiple Direct lightning strike. 33

3.6.2 Simultaneous and single direct lightning strike 34

3.6.3 Direct multiple lightning strike in the different time. 34

viii

3.6.4 Simultaneous and multiple Indirect lightning strike 35

3.6.5 Indirect multiple lightning strike in the different time 37

3.7 Measurement kluang railway tracks. 37

3.8 Calculation voltages and currents values in kluang railway tracks. 38

3.9 Simulink Of the interaction of lightning strike to railway tracks. 40

3.10 Graphic User Interface Simulation For direct and indirect

lightning strike with railway according to bweley lattice diagram. 41

3.11 Study Voltages Waves in Railway by GUI. 42

3.12 Laboratory tests of induced overvoltage at railway tracks. 43

3.12.1 Railway tracks model and resistor voltage divider. 43

3.12.2 Laboratory tests of induced overvoltage in railway track for

AC voltage.

45

3.12.3 Laboratory tests of induced overvoltage in railway track for

a lightning impulse voltage.

45

3.12.4 Calculation of overvoltage values. 47

CHAPTER 4 RESULTS AND ANALYSIS 49

4.1 Introduction 49

4.2 Generation Voltage and Current Impulses. 50

4.3 Results Simulink Interaction Lightning With Railway System

(direct stroke). 51

4.3.1 results the voltages and currents when intraction

Single Lightning Strike In Railway. 51

4.3.1.1 Overvoltages at railway track S with SRG and SG strike. 51

4.3.1.2 The overvoltages at raialway track R when SRG strike. 52

4.3.1.3 Overvoltage at railway track R where SG strike. 54

4.3.1.4 The overcurrent waves at railway track -S. 55

4.3.1.5 The overcurrents waves at railway track R where

SG strike.

56

4.3.1.6 Overcurrent waves at railway track R where SRG

strike.

57

4.3.2 Multiple Lightning strike to the railway track

for the simultaneous case.

58

4.3.2.1 Voltages at railway track S. 59

ix

4.3.2.2 Overcurrent waves at railway track S . 60

4.3.2.3 Overvoltage wave at railway track R where

SG strike of multiple srike.

61

4.3.2.4 Overurrent wave at railway track R where

SG strike -multiple.

62

4.3.2.5 Overvoltage and overcurrent wave at railway

track R where SRG strike –multiple strikes.

63

4.3.3 Multiple Lightning Strike at Railway track R

at the different time of occurrenc.

65

4.4 Results Simulink Interaction Lightning With Railway System

(indirect stroke). 66

4.4.1 The Overvoltages and overcurrents waves for a single

strike at railway track- S and railway track R.

66

4.4.2 The overvoltage and overcurrent waves for multiple

strikes occure simultaneously.

69

4.4.3 Overvoltage and overcurrent waves for amultiple

strikes in the different time.

71

4.5 Results of voltage impulses using graphic user interface. 72

4.6 Results of the value peak voltages and current for four point

using graphic user interface based to Bewley Lattice diagram.

73

. 4.7 Results of the Travelling waves for Lightning strike

at railway track.

75

4.8 Result voltages at MTLs in railway system. 76

4.9 Result of Laboratory tests of induced overvoltage

at railway track for AC voltage.

77

4.10 Result of Laboratory tests of induced overvoltage

at railway tracks for lightning impulse voltage.

79

4.11 Comparison result of voltage at railway track in laboratory

test with simulation.

81

CHAPTER 5 83

5.1 Conclusion 83

5.2 Future work 84

RRERENCES

APPENDIX

x

LIST OF FIGURES

Figure Page

2.1 Induced charges on railway 5

2.2 Categories of Lightning discharges 6

2.3 Railway track joint. 7

2.4 Profile of the railway track 8

2.5 Outline of measuring surge parameters of railway track 8

2.6 Railway tracks electric model propagation of surges 9

2.7 Railway tracks in Kluang station 10

2.8 Schematic of double-track railway system (axes are in metres). 10

2.9 MTL system representative of a typical railway traction

conductor feeding system 12

2.10 Railway track showing the complexity of MTLs 13

2.11 Railway track showing of MTLs in Malaysia 13

2.12 Schematic of single-track railway system (axes are in meters) 14

2.13 Ericsson BV-ECLALPLE 1S1.2 + 28P 0.9 cable, a typical

communication cable used in the railway systems 16

2.14 Interconnection between R5, R6 and R1 17

2.15 Insulators, connections and pole footing resistance in a single

track railway system 18

2.16 Travelling wave in railway Line model 18

2.17 Bewley Lattice diagram that illustrates the injected voltage

traveling back and forth in railway line 21

2.18 Bewley Lattice diagram for one section in railway line 22

2.19 Evaluation flow of lightning risk for railway signalling systems 23

2.20 Transformer connections in BT feeding systems 24

xi

2.21 Transformer connections in AT feeding systems 25

2.22 A typical track circuit configuration used in railway system 26

2.23 The JRK 10470 and BML 301053, a typical relay unit used in the

railway systems respectively. Adopted from 27

2.24 GRS Type-K interlocking relay 27

2.25 Cross railway with road in the Kluang 28

2.26 light signal closed When the train far from the road 28

2.27 light signal open. When the train near from the road (before cross

the road) 28

3.1 Flow chart of project. 30

3.2 A pictorial view of a section at Kluang railway track 31

3.4 System study overview. 32

3.5 Railway track Stricture 32

3.6 Railway track electric model 33

3.7 System study overview direct strike (∆t = 0) 33

3.8 Model railway in the direct strike 33

3.9 Single lightning strike to railway track 34

3.10 (a) Voltage waveforms on terminal “Rail (S). (b) Voltage

waveforms on “Rail (R) 34

3.11 System study overview direct strike (∆t ≠ 0) 34

3.12 System study overview indirect strike (∆t = 0) 35

3.13 Model of railway tracks subjected to indirect strikes 35

3.14 3-D representation of a lightning location strike the ground 50m

away from the test object railway tracks 36

3.15 System study overview indirect strike (∆t ≠ 0) 37

3.16 Measurement of R and L based on per meter 37

3.17 Measurement of C1 and C2 37

3.18 Tracks at the Kluang railway station 38

3.19 Three tracks with two tracks junction 39

3.20 Simulink circuit of lightning strike at railway tracks 41

3.21 GUI lightning strike at railway 42

3.22 The example railway tracks systems 42

3.23 Calculation of 4 railway tracks using GUI 43

3.24 Railway tracks model 43

xii

3.25 Resistor voltage divider 44

3.26 Connection of resistor voltage divider 44

3.27 Laboratory testing of induced overvoltage with single-stage AC

Voltage 45

3.28 Experimental setup for Generation of Lightning Impulse

Voltages 46

3.29 Schematic diagram of the lightning impulse voltages

component 46

3.30 Schematic diagram of laboratory tests for lightning impulse

voltage 47

3.31 Schematic diagram of railway track test circuit for AC voltage 47

3.32 Schematic diagram of railway track test circuit for lightning

impulse voltage 48

4.1 Voltage wave 50

4.2 Current wave 50

4.3 Overvoltage wave at point 1 at railway track S where SG strike

(V1) 51


(V3) 52


(V7) 52

4.6 Overvoltage wave at point 1 at railway track R where SRG

strike (V1’) 53

4.7 Overvoltage wave at point 3 in railway track R where SRG

strike (V3’) 53

4.8 Overvoltage wave at point 7 at railway track where SRG strike

(V7’) 53

4.9 Overvoltage wave at point 1 at railway track R where SG strike 54

4.10 Overvoltage waveform at point 3 at railway track R where SG

strike 54

4.11 Overvoltage waveform at point 7 at railway track R where SG

strike 55

4.12 Overcurrent wave at point 1 at railway track S (I1) 55


xiii


4.15 Overcurrent wave at point 1 at railway track R where SG strike

(I1’) 57

4.16 Overcurrent wave at point 7 at railway track R where SG strike

(I7’) 57

4.17 Overcurrent wave at point 1 at railway track R where SRG

strike 58

4.18 Overcurrent wave at point 7 at railway track R where SRG

strike 58

4.19 Overvoltage wave at point 1 at railway track S of multiple

strike 59


strike 59


strike 59

4.22 Overcurrent waves at points 1, 3 and 7 at railway track S of

multiple strike (I1, I3 and I7) 60

4.23 Overvoltage wave at point 1 at railway track R where SG strike

of a multiple strike (V1’) 61


of a multiple (V3’) 61


of a multiple strike (V7’) 62

4.26 Overcurrent waves at point 1, 3 and 7 at railway track R with

SG strike of multiple strike (I1, I3 and I7’) 62


strike of a multiple strike (V1’’) 63



4.29 Overvoltage wave at point 7at railway track R where SRG


4.30 Over currents waves at points 1, 3 and 7 at railway track R

where SRG strike of a multiple strike (I1’’, I3’’ and I7’’) 64

xiv

4.31 Overvoltage waves at points 1, 3 and 7 at railway track of a

multiple strike (V1, V3 and V7) 65

4.32 Overcurrent waves at points 1, 3 and 7 at railway track of a

multiple strike (I1, I3 and I7) 66

4.33 Overvoltage waves at points 3, 6 and 8 at railway track for a

single strike (V3, V6 and V8) 67

4.34 Overcurrent waves at points 3, 6 and 8 at railway track for a

single strike (I3, I6 and I8) 67

4.35 Overvoltage waves at points 3, 6 and 8 at railway track R for a

single strike (V3’, V6’ and V8’) 68

4.36 Overcurrent waves at points 3, 6 and 8 at railway track for a

single strike (I3’, I6’ and I8’) 69

4.37 Overvoltage waves at points 2, 4’ and 6 at railway tracks for a

multiple strikes (V2, V4’and V6). 70

4.38 Overcurrent waves at points 2, 4’ and 6 at railway tracks for a

multiple strikes (I2, I4’and I6 70

4.39 Overvoltage waves at points 2, 4’ and 6 at railway tracks for a

multiple strikes (V2, V4’and V6) 71

4.40 Overcurrent waves at points 2, 4’ and 6 at railway tracks for a

multiple strikes (I2, I4’and I6) 72

4.41 Overvoltage impulse when ΔT=1 when time frame is 2T 72

4.42 Overvoltage impulse when ΔT=2 and time frame is 4T 73

4.43 Voltage impulse when ΔT=3 and time frame is 6T 73

4.44 Peak voltages for 4 points using Bweley Lattice diagram 73

4.45 Peak voltages for 4 points using Bweley Lattice diagram 74

4.46 Waves of the voltages at end sending and receiving for a single

strike for one railway track using Bweley Lattice diagram 74

4.47 Wave of the voltages at end sending for a multiple strike at one

railway track using Bweley Lattice diagram 74

4.48 Transmitted waves at junction A 75

4.49 Transmitted waves at junction B 75

4.50 Transmitted waves at junction C 76

4.51 Transmitted waves at junction D 76

4.52 Overvoltage waves at MTLs and railway tracks 77

xv

4.53 Oscilloscope reading for AC voltage test 79

4.54 Output railway track overvoltage impulse for 1 µs 80

4.55 Output railway track overvoltage impulse for 10 µs 80

4.56 Input railway track overvoltage impulse for 5 µs 80

4.57 Input railway track overvoltage impulse for 1 µs 81

4.58 Laboratory tests of induced overvoltage at railway track for

lightning impulse voltage connection 81

4.59 Overvoltage wave at point 1 at railway track S and R. 82

xvi

LIST OF TABLES

Table Page

2.1 Conductor nomenclature of Kluang tracks 10

2.2 Material properties of MTLs 11

2.3 Base-current parameter values. 12

2.4 Conductor radii and characteristic impedances for Figure 2.16 12

2.5 Conductor nomenclature 14

2.6 Conductor nomenclatures and properties in a typical single-track

electrified railway system 15

2.7 Impulse withstand levels for the insulators 17

3.1 Parameter pertaining location of study 32

3.2 R, L, C1, C2, Z and Y of the Kluang railway tracks 38

3.3 The Reflection coefficient and refraction coefficient in points

along railway tracks 39

3.4 Magnitude of over voltages at various points on the track 40

3.5 Magnitude of overvoltage at the junctions A and B 40

3.6 Parameters of simulink railway model 40

3.7 Parameter of railway tracks systems 42

3.8 Railway tracks model specifications 44

3.9 Single-stage AC Voltage technical Specification 45

4.1 Overvoltage values in tracks S in point 1, 3 and 7 single lightning

directly 52

4.2 Overvoltage values in tracks R in point 1, 3 and 7 single

lightning directly 54

4.3 Overvoltage values in tracks R in point 1, 3 and 7 where SG

strike single 55

xvii

4.4 Overcurrent values in tracks S in point 1, 3 and 7 56

4.5 Overcurrent values in tracks R in point 1, 3 and 7 when SG strike 57

4.6 Overcurrent values in tracks R in point 1 and 7 when SRG strike 58

4.7 Overvoltage values in tracks S in point 1, 3 and 7-multiple

strikes 60

4.8 Overcurrent values in tracks S in point 1, 3 and 7-multiple strike 61


strikes 62

4.10 Overvoltage values in tracks S in point 1, 3 and 7 63


strikes 64

4.12 Overcurrent values in tracks R in point 1, 3 and 7 where SRG

strike 65

4.13 Overvoltage values in tracks R in point 1, 3 and 7-multiple

strikes 66

4.14 Overcurrent values in tracks R in point 1, 3 and 7-multiple strike 66

4.15 Overvoltage values in tracks R in point 3, 6 and 8 –indirect 67

4.16 Overcurrent values in tracks R in point 3, 6 and 8-indirect 68

4.17 Overvoltage values in tracks R in point 3, 6 and 8-indirect 68

4.18 Overcurrent values in tracks R in point 3, 6 and 8 69

4.19 Overvoltage values in tracks S and R in point 2, 4 and 6 69



4.22 Overcurrent values in tracks S and R in point 2, 4 and 6 72

4.23 Input voltage and current and Oscilloscope reading output

voltage 77

4.24 New overvoltage value that induced in railway track R model for

all the experience 78

4.25 Results of Laboratory tests of induced overvoltage at railway

track for lightning impulse voltage 79

4.26 Percentage output values to input values for lightning impulse

voltage 79

xviii

4.27 Induced overvoltage at railway track for lightning impulse

voltage 82

xix

LIST OF SYMBOLS AND ABBREVIATIONS

MLS Multiple lightning stroke

FLF Flash Lightning Flatlands

MV Mega voltage

LF Leader Formation

CC Cloud-to-cloud

BL Ball lightning

GC Ground-to-cloud

E Electrical fields

V Propagation speed

RS Railway System

R Resistance

L IInductance

G Conductance

Γ Propagation constant

RLs Railway lines

BTs Booster transformers

ATs Autotransformers

EMI Electromagnetic interferenc

𝜶 Refection Coefficient

𝜷 Transmission Coefficients

A Equivalent Attractive area

b Effective width

Ra Equivalent Attractive distance

BLD Bewley lattice diagram

Z Impedance

xx

Y Admittance

SG Railway track S and ground

SRG Railway track S and Railwaytrack R and ground

MTLs Multiple transmission lines

1

CHAPTER 1

INTRODUCTION

1.1 Project Background

Lightning is an important meteorological process, it is a dangerous natural

phenomenon which causes disturbances in our life, and it has a bad effect on mankind.

So a great attention has been taken towards this phenomenon. From railway point of

view, these rails should be protected against this phenomenon, where large parts of

the railway exposed to lightning. System components can be exposed to lightning-

induced overvoltage's; this overvoltage have high magnitude comparing with any

voltage level of the distribution network, so flashover is generated causing damage to

the equipment when insufficient protection against this phenomenon is used. This

directly effects on system reliability for railways. Of all lightning discharges only

around 25% of the lightning bolt reaches the ground. Lightning being an intense

power source (although of short duration), has the potential to cause significant

damage to life and property [1].

Attempts to understand the phenomena (being most spectacular in nature but

destructive), has been a great challenge and forms one of the well-researched area. In

spite of enormous research efforts, when it comes to the question of “how likely is it

that lightning will strike an object and cause damage?” deterministic answers are not

possible yet [2]. For such questions one needs to heavily depend upon the lightning

statistics. The other variables on which the CG discharges depend are terrain, tall

structures & trees, their relative spatial spread, shape and composition of the

structures, and soil resistivity (which has bearing on dampness and its type), to name

a few important ones [3]. Lightning CG discharges have many destructive effects, as

is widely known. The more damaging effects have come to the fore due to its indirect

2

effects on modern electronic gadgets, which are susceptible to surge voltages and

currents. The effort here is to bring out the salient features of lightning with specific

reference to indirect effects. The lightning is the main cause of problems in railway

in the world [4] [5].

1.2 Problem Statement

Lightning strikes are atmospheric phenomena which have adverse effects on railway.

Lightning strikes damaged rail infrastructure an average of 192 times each year

between 2010 and 2013, with each strike leading to 361 minutes of delays. In addition,

58 trains schedules a year were cancelled due to lightning related faults. Predicting

the geographical and temporal distribution of the lightning strike densities through

modeling can help railway designers to improve the protection of the existing and new

railway. When lightning strikes a rail, the high voltage can damage this sensitive

electronic signaling equipment. As our signaling system fails safe, when a component

is damaged all signals in the area turn red and trains must stop. In order to compare

the results of the model simulations to the physical data, characterization is required.

The distribution of the lightning strike densities generates patterns which are highly

nonlinear and no stationary. Nowadays simulation technique is implemented to

improve traditional techniques, where the results can be obtained instantaneously after

it analyzes the input data of the railway such as currents (i) and voltages (v). In this

project MATLAB SIMULINK is used to simulate railway system and analyze the

result.

1.3 Project Objectives

This project proposes the analysis simulation of lightning strike in railway using

MATLAB program, the objectives of the work are:

i) To design railway model through direct and indirect lightning strike using

MATLAB tools and analyze the step by step the voltage and current

curves.

ii) To analyze the scenario of propagation currents and voltages and the

travel waves that cause the system instability in railway according to

Bewley Lattice diagram after the lightning stroke.

3

iii) To test of railway track model with a single lightning impulse voltage and

AC voltage in the laboratory.

1.4 Project Scope

The project primarily concerned with lightning ground flashes interaction with

railway lines .the scope of this project are:

(i) The Malaysian railway transport system will be studied and the case study

is based on Kluang railway station.

(ii) Simulation of the lightning-induced surge propagation along the railway

lines will be done using Bewley Lattice method of analysis.

(iii) Modeling and simulation analysis study will be also involve with the use

of MATLAB software and laboratory test.

(iv) In the project simulation execution ,the flashing lightning strike modes be

focused :

a) Single lightning stroke.

b) Multiple lightning stroke (multiplicity level up to 2).

c) Multiple and Simultaneous lightning stroke (multiplicity level up to

2).

(v) In the laboratory test the lightning impulse voltage is more than 2 kV.

1.5 Thesis Outline

This thesis is separated into 5 chapters. In the first chapter focuses on outlines the

main idea of this project. The would explained about lightning phenomenon,

motivation methods and principals locating of lightning strikes, and literature reviews

of previous researchers this in the second chapter. The following describe the

methodology of the project, including the tools and equipment's, procedure and

processes involved for the hardware and software development of the entire project.

And in forth chapter discussed on the results obtained from the lightning detection

system. Finally in chapter 5 is about conclusion and recommendations that can be

used for further research related to this topic in future would be included.

4

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

Lightning is a sudden high-voltage discharge of electricity that occurs within a cloud,

between clouds, or between a cloud and the ground and external of the cloud. Globally,

there are about 40 to 50 flashes of lightning every second or nearly 1.4 billion flashes

per year. These electrical discharges are extreme deadly and devastative. Lightning is

a giant spark of electricity in the atmosphere between clouds, the air, or the ground. In

the early stages of development, air acts as an insulator between the positive and

negative charges in the cloud and between the cloud and the ground. When the

opposite charges builds up enough, this insulating capacity of the air breaks down and

there is a rapid discharge of electricity that we know as lightning. The flash of lightning

temporarily equalizes the charged regions in the atmosphere until the opposite charges

build up again [6].Lightning can occur between opposite charges within the

thunderstorm cloud (intra-cloud lightning) or between opposite charges in the cloud

and on the ground (cloud-to-ground lightning).Lightning is one of the oldest observed

natural phenomena on earth. It can be seen in volcanic eruptions, extremely intense

forest fires, surface nuclear detonations, heavy snow storms, in large hurricanes, and

obviously, thunderstorms. Lightning strike comes about every day in the world. The

lightning strike towards the surface on earth has been estimated at 100 times every

second. Thus, almost every governments suffer major loses because of this

phenomenon every year. It also would cause horrific injury and fatality to humans and

5

animals. The lightning may affect almost every organ system as the current passes

through the human body taking the shortest pathways between the contact points.

There are 25.9% of lightning strike occurrences for victims who took sheltered under

trees or shades, whereas 37% at open space area. Head and neck injury are two

common areas which have an effect on the lightning strike victims with 77.78% and

74% respectively. Only 29.63% of the cases presented with ear bleeding [7].United

State National Lightning Safety Institution reported that Malaysia has highest

lightning activities in the world whilst the average-thunder day level for Malaysia’s

capital Kuala Lumpur within 180 - 260 days per annum [8, 9]. The isokeraunic level

is approximately 200 thunderstorm days a year. The lightning ground flash density is

2.2 Mechanism of Lightning to railway.

Lightning is an electric discharge in the form of a spark or flash originating in a

charged cloud. It has now been known for a long time that thunder clouds are charged,

and that the negative charge center is located in the lower part of the cloud where the

temperature is about - 50 C, and that the main positive charge center is located several

kilometers higher up, where the temperature is usually below - 200 C. In the majority

of storm clouds, there is also a localized positively charged region near the base of

the cloud where the temperature is 00 C. Figure 2.1 shows such a cloud located above

an overhead transmission line.

Figure 2.1: Induced charges on railway.

Fields of about 1000 V/m exist near the Centre of a single bipolar cloud in

which charges of about 20 C are separated by distances of about 3 km, and indicate

the total potential difference between the main charge centres to be between 100 and

6

1000 MV. The energy dissipated in a lightning flash is therefore of the order of 1000

to 10,000 MJ, much of which is spent in heating up a narrow air column surrounding

the discharge, the temperature rising to about 15,000 0 C in a few tens of

microseconds. Vertical separation of the positive and negative charge centres is about

2 - 5 km, and the charges involved are 10 - 30 C [10]. The average current dissipated

by lightning is of the order of kilo-amperes. During an average lightning storm, a total

of the order of kilo-coulombs of charge would be generated, between the 00 C and

the -40 0 C levels, in a volume of about 50 km3 [11].

2.3 Effects of lightning discharges in the railway.

The physics of lightning is still a mystery. CG discharges can be quite destructive,

particularly when grounded objects are not protected. The number of lightning related

deaths in humans is small when compared to other causes of accidents. Livestock on

the farms is most susceptible, particularly four legged animals with large spans

between legs; e.g. cattle’s. Lightning plays an important role in forest fires and

associated damages. Interaction of CG discharges with railway can disrupt power

lines can causing power failures [12]. The effects of CG discharges can be broadly

classified into two categories, namely: (i) direct (direct strokes), and (ii) indirect

(indirect strokes). Indirect effects can be further viewed as those due to: (a)

conductive, inductive and capacitive coupling, and (b) radioactive coupling [13].

Figure 2.2: Categories of Lightning discharges.

7

2.3.1 Direct strokes.

A lightning CG discharge, strikes an object directly, such as power-line or building,

and it can result in significant damage. Direct effects generally result in physical

damage and have associated fire hazards. In the case of buildings it can result in cracks

in the masonry work. The injected voltages and currents associated with direct strokes

being much higher compared to indirect strokes, will have the ability even to damage

power and distribution equipment and cut railway [14]. Most often the electrical

motor insulations associated with the irrigation pump becomes the victim of a direct

stroke. Other common examples are welding of contactors of the motors starters and

explosion of power distribution transformers. The protections in the form of lightning

rods and ground overhead wires can significantly reduce the chances of direct strokes.

Having averted the direct strokes if one has to successfully reduce the probable

secondary effects an appropriate grounding and bonding system is a must [15].

2.3.2 Indirect effects.

Even if the lightning rods and ground overhead wires effectively shield the buildings,

power lines, railways, and other objects, Once the lightning CG discharges are to the

ground rod and railway lines, the charges tend to flow to the ground through the

associated grounding system., the system needs grounding with zero ground

impedance, ideally. In actuality the ground impedances are neither zero nor stable due

to many of the soil properties and its associated parameters. There are guidelines

related to the threshold permissible values of earth resistances depending on the

criticality of the system being protected [16].

2.4 Railway system.

As show the figure 2.3 Rail composed of a set of sections connected by junctions long

the section about 100m.

Figure 2.3: Railway track joint.

8

The line profile of the rail track at the test section is shown in Figure. 2.13 a

rail track consists of rails, cross ties, a rail bed, and a track bed.

Figure 2.4: Profile of the railway track.

2.4.1 Lightning surge parameters of railway track [17].

The surge impedance and the surge propagation velocity are important parameters as

the surge characteristics of a rail. We investigated the surge impedance and the surge

propagation velocity between the rail and the ground due to measuring the injection

current to the rail and the induced voltage on the rail when the steep-front current was

injected into the rail. The outline of measuring method is shown in Figure2.5.

Figure 2.5: Outline of measuring surge parameters of railway track.

2.4.2 Surge attenuation ratio in the railway track.

The surge attenuation caused by traveling along the rail is important parameters as the

surge characteristics of a rail. We investigated the lightning surge attenuation ratio

due to measure the voltage waveforms between the rail and the ground at the Sending

end and the receiving end Surge.

9

2.4.3 Electric circuit for the railway.

The electric circuit, which is formed between sending end and receiving end of rail

showing in Figure 2.6 can be considered a two-port circuit composed from the

distributed-parameter line such as rails. We investigated the frequency-dependent

four-terminal parameters (resistance R, inductance L, conductance G and capacitance

C) of the rails to estimate the distributed parameter adopted in the calculation model

due to measure the open circuit impedance and the short circuit impedance by non-

grounding or grounding at the receiving end of rail, respectively. In the same way,

open/short circuit impedance between rails [18].

Figure 2.6: Railway tracks electric model propagation of surges.

2.5 Kluang single-track railway.

A photograph of the railway line in Kluang station is shown in Figure 2.7 it shows the

distribution of MRLs. Both the tracks and ground conductors are considered as MRLs

under the ground and are assumed to be infinite in either direction, which makes the

problem two-dimensional. The schematic of MRLs model for double -track electrified

railway system commonly found in Kluang is shown in Figure 2.15, the associated

conductor systems are described in Table 2.1. The different mediums that would be

of interest for the wave propagation studies are shown in Table 2.2. The typical values

shown in Table 2.2 are taken; further, they are nominal and do not correspond to some

extreme conditions of climate or temperature.

(2.6)

11

Figure 2.7: Railway tracks in Kluang station.

Figure 2.8: Schematic of double-track railway system (axes are in metres).

Table 2.1: Conductor nomenclature of Kluang tracks.

Conductor nomenclature Conductor with bundle

S1-rail Z1

R1-rail Z2

S2-rail Z3

R2-rail Z4

Cable Z5

Rail and ballast .include the conductor’s Z1 and Z2 are the rail1. Z3and Z4 are

the rail2. Z1 and Z3 are called the S-rail and is continuous and forms one of the

reference/return conductors.Z2 and Z4 are the I-rail, which is broken every 1.02 km

and is used for the signaling purpose. The track circuits are connected across the S-

rail and I-rail and across which a constant potential of 7V exists. This voltage

collapses to zero once the locomotive is on this section of the rails in the normal case.

Groun

d

11

Then relay units are also connected across the tracks. These serve the purpose of train

positioning and signaling systems. Z5 is the cable underground, which feeds the light.

The Kluang railway system works at 10 kV and 16(2/3) Hz [19].

Table 2.2: Material properties of MTLs.

Mediums/conductor

Systems

Relative

permittivity

Relative

permeability

Conductivity

(S/m)

Air 1.0 1.0 1.0e-11

Ballast 10.0 1.0 1.0e-5

Ground 10.0 1.0 4.0e-4

Z1,Z2,Z3and Z4 1.0 20.0 4.40e-6

2.6 Modeling direct Lightning Strikes for Railway Systems with Lumped

Components.

A model with most common devices connected along the multiconductor

transmission line (MTL) system of railway, i.e., booster transformers (BTs),

autotransformers (ATs), and track circuits, for evaluating the voltage and current

propagation due to lightning and switching transient sources was developed by the

authors [20]. As the potential between above ground wires and poles may exceed the

insulator impulse withstand voltage levels, flashovers occur and hence needs to be

implemented in the model [21].

2.6.1 Induced Voltages Across Lumped Devices Along The Track System in

Railway And Transmissions Lines.

The electromagnetic interference (EMI) source used in the calculations is

representative of a subsequent lightning return stroke. The lightning is simulated to

strike at a 50-m perpendicular distance from the midpoint of the system. The lightning

channel base-current wave shape, at time t, is expressed by the sum of two functions

expressed as (1), with the parameters as stated in Table 2.3 [22].With these parameter

values, the base current peak is about 12 kA. This current is assumed to propagate

upward in the lightning channel in accordance with the modified transmission-line

model with linear decay [23]. The field-to-line coupling model adopted in the

calculations is the Agrawal et al. model. In this model, the electromagnetic fields are

12

represented as series- and shunt-connected voltage sources along the lines of the MTL

system [24]. In the analysis, an MTL system, representative of the catenary track

system of electrified single-track railway system, as shown in Figure. 2.9, is

considered. As seen, this 6-km long MTL system consists of five overhead wires, S-

rail, I-rail, catenary, return conductor/negative feeder (called as return conductor), and

auxiliary wire. All lines are terminated to the finitely conducting ground (ground

resistivity 1000 Ω/m) by their self-characteristic impedance. The conductor radii and

characteristic impedances are given in Table 2.4. Characteristic impedances are

calculated for ideal ground, and are only approximate for finitely conducting ground.

The telegraphers’ equation for the 5-conductor transmission line system above finitely

conducting ground is given as follows [25]:

Table 2.3: Base-current parameter values.

I01 τ11 τ21 n1 I02 τ12 τ22 n2

(kA) (µs) (µs) (kA) (µs) (µs)

10.7 0.25 2.5 2 6.5 2.1 230 2

' Figure. 2.9: MTL system representative of a typical railway traction conductor

feeding system.

Table 2.4: Conductor radii and characteristic impedances for Figure 2.16.

S-Rail R-Rail Catenary Return/ Auxiliary

Neg.feeder wire

Radii(mm) 49.5 49.5 50.6 8.2 5.6

Zc(Ω) 186 186 331 442 490

13

In Figure 2.17. It shows the complex distribution of MTLs. In the simulation,

we have taken only a single-track system. However, an analysis with the double-track

system would be similar as described here but with more conductors. Both the tracks

and overhead conductors are considered as MTLs above the ground and are assumed

to be infinite in either direction [26].

Figure 2.10: Railway track showing the complexity of MTLs.

Figure 2.11: Railway track showing of MTLs in Malaysia

14

Figure 2.12: Schematic of single-track railway system (axes are in meters).

Table 2.5: Conductor nomenclature.

Conductor nomenclature Conductor with bundle

S-Rail R1

R-Rail R2

Contact and messenger R3

Reinforcement R4

Return R5 and R6

help R7-R9

2.6.2 The electrified railway system.

A normal single-track electrified railway system can consist of as many as ten above

ground conductors, and one buried communication cable along the track, not shown

in the cross sectional view of the MTL system. The contact and messenger cables,

both noted as R3 in the cross-sectional view of Figure. 2.17, are interconnected at

every 7-10 m and these conductors can, in accordance with the principle of bundled

conductors [27], be combined into a single conductor.

Railway

Tracks

15

Table 2.6: Conductor nomenclatures and properties in a typical single-track electrified

railway system.

Conductor nomenclature Conductor notation Conductivity (S/m)

S-Rail R1 4.4×10-6

R-Rail R2 4.4×10-6

Contact and messenger R3 5.8×10-7

Reinforcement R4 3.5×10-7

Return R5 and R6 3.5×10-7

help R7-R9 3.5×10-7

Names, notations and conductivities of the overhead conductors of Figure 1.1 are

presented in Table 2.6. The conductors forming the MTL system consist of the

following:

• Two rails; the S-rail, R1, is continuous though out the entire railway system and used

as a return path for the traction current and the I-rail, R2, has 45 insulated gaps at

regular intervals and is used for signaling purposes.

• The bundled R3 conductor, also known as the catenary wire, is used for feeding

power to the locomotive through the pantograph located on the locomotive roof with

15 kV, 16.67 Hz.

• An electrical reinforcement wire, R4, is running in parallel with the catenary and it

is connected to it every 200-300 m. This wire is present for reducing the catenary

system impedance.

• Return conductors, R5 and R6, are used for returning the traction currents to the

feeding stations.

• Auxiliary power wires, R7, R8 and R9, operating at 22 kV, 50 Hz are used to supply

power to trackside equipment after a step down to 400/230 V. The communication

cables used in the Swedish railway systems are buried or put in trenches at a depth of

0.5-0.75 m and about 1-2 m away from the tracks on the pole side. There are different

kinds of communication cables used on different track sections based on current

demand and future planning. A communication cable frequently used by Banverket is

the Ericsson made BV ECLALPLE 1S1.2 + 28P 0.9 [28], a cross sectional view of

this cable is shown in Figure 2.13. This multiconductor communication cable consists

of 60 copper conductors split in three layers, pair-wise twisted arrangement, enclosed

by a stranded aluminum shield and a steel armor [29].

16

Figure 2.13: Ericsson BV-ECLALPLE 1S1.2 + 28P 0.9 cable, a typical

communication cable used in the railway systems.

In double-track railway systems the tracks run in parallel and the overhead

conductors are mirrored, with a distance of 4.4-10 m between the centers of the lines,

with auxiliary wires only present at one side of the track [30].

2.7 Pole insulator flashover and ionization at the pole footing.

2.7.1 The interconnection between the conductors.

Interconnections between conductors play an important role in surge current

distribution. The return conductors (R5 and R6) and S-rail (R1) are connected together

at every 5 km. This situation is shown in Figure. 2.21 (dashed line). The

interconnection is assumed to be at the middle of the line being simulated, where the

lightning is assumed to strike at the top of conductor R7. The termination matrix at

this junction point on the middle of the line is a sparse conductance matrix with its

elements corresponding to short and open circuit resistances. Note that in all the

simulations, this junction is assumed to be in the middle of the two pole locations.

The distance between the two poles is 60 m.

2.7.2 Pole insulator flashover and soil ionization at the pole footing.

The poles support the conductors through insulators, which have different impulse

with stand voltages as shown in Table 2.7.

17

Figure 2.14: Interconnection between R5, R6 and R1.

The other terminations to the ground from the conductors are due to the

insulator flashovers on the poles and pole’s footing ionization/static resistance as the

case may be. Determining the equivalent termination resistance at the pole is a bit

complex and depends on the ionization characteristics at the pole footing and insulator

flashover behavior. The S-rail (R1) is connected to the pole footing directly and all

the other conductors excepting I-rail (R2) are connected to the pole through the

insulators, the schematic of which is shown in Fig. 2.22 The resistance (Rg) due to

soil ionization at the pole footing is calculated using the method proposed by the IEEE

standard [31],R0 is the footing resistance measured with low current (dc), IR the

lighting current through the footing resistance and Ig is the current required to produce

a voltage gradient, E0, at which soil breakdown occurs which is about 400 kV/m. The

termination resistance is calculated using the equivalent circuit based on the schematic

diagram shown Figure 2.15.

Table 2.7: Impulse withstand levels for the insulators.

Conductor

nomenclature

Ceramic insulator type Impulse withstand

voltage (kV)

R3 Rod or composite 225

R4 Lie post 170

R5 and R6 Spool 60

R7–R9 Pin 140

18

Figure 2.15: Insulators, connections and pole footing resistance in a single track

railway system.

At every 60 m along the MTL system there are poles. These are not only used

for grounding points for the S-rail, but also to hold the overhead wires in the air along

the system, as shown in Figure. 2.22. The above ground wires are connected onto this

pole by insulators of different materials and impulse withstand over voltages, as

shown in Table 2.7.

2.8 Waves on railway lines.

Figure 2.16: Travelling wave in railway Line model.

19

Considering the above railway line in the sinusoidal steady state. Assuming

series impedance per meter and shunt admittance per meter to neutral are:

𝑍 = 𝑟 + 𝑗𝜔𝑙 (2.1)

𝑦 = 𝑔 + 𝑗𝜔𝑐 (2.2)

From figure 2.16 V1 and I1 are per phase terminal voltages and currents at left

and V2, I2 are per phase terminal voltage and current at right. Considering a small

section of line length dx .Taking the series impedance and the shunt admittance of dx

are zdx and ydx respectively. The receiving end at the right side is located at x=0 and

the sending end at the left side is at x=L. Applying Kirchhoff’s voltage law and

Kirchhoff’s current law to dx.

𝛾 = √𝑍𝑌 = 𝛼 + 𝑗𝛽 (2.3)

𝛾 is a complex quantity which is known as the propagation constant. Where

Z is the characteristic impedance of the line and is given by:

𝑍 = √𝑅+𝐿

𝜕

𝜕𝑡

𝐺+𝐶𝜕

𝜕𝑡

(2.4)

𝑍 = √𝐿

𝐶 (2.5)

This is the characteristic impedance of the line. This implies that the voltage

and current waves travel down the line without changing their shapes.

𝜕2𝑢

𝜕2𝑥2= 𝐿𝑐𝑢 (2.6)

Equation (2.6) is the so called travelling wave equation of a loss less railway

line. The solutions of voltage and current equations reduce to

𝑢(𝑥, 𝑡) = 𝐴1(𝑡)𝑒𝑥

𝑣 + 𝐴2(𝑡)𝑒−𝑥

𝑣 (2.7)

𝑖(𝑥, 𝑡) = −1

𝑍0[𝐴1(𝑡)𝑒

𝑥

𝑣 − 𝐴2(𝑡)𝑒−𝑥

𝑣 ] (2.8)

Where v is the travelling wave propagation speed defined as:

21

V = 1

√𝐿𝐶 (2.9)

2.8.1 Reflection and refraction of travelling waves (Bewley Lattice diagram)

When the wave propagates along a railway line with certain characteristic impedance,

there is a fixed relation between the voltage and current waves. The line is defined as:

𝛼 =𝑍𝑅 − 𝑍0

𝑍𝑅 + 𝑍0

Where Z0 is a characteristic impedance of the line and ZR is the railway impedance

[32]. Similar coefficients can be obtained for the currents, but the current reflection

coefficient equals the negative of the voltage reflection coefficient value.

𝛽 = 𝑍0−𝑍𝑅

𝑍𝑅+𝑍0 (2.11)

As a special case, termination in a short circuit results in 𝛼 = -1 for the voltage

signals and 𝛽 = 1 for current signals. If the termination is an open circuit, ZR is infinite

and 𝛼 = 1 in the limit for the voltage signal and 𝛽 = -1 for the current signal. For a

travelling wave while propagating through the railway, the railway (refraction)

coefficient can be calculated as:

𝛽 = 2𝑍𝑅

𝑍𝑅+𝑍0 = 𝛼 + 1 (2.12)

Therefore, for a line terminated in a short circuit, the voltage of the backward

(or reflected) wave is equal and opposite to the voltage of the forward (or incident)

wave. The bounce diagram, also known as the lattice diagram, provides a systematic

way of tracing the wave propagation on a railway line in a graphical manner. This

methodology is called the bounce diagram since it represents the travel waves that

bounce back and forth at the impedance discontinuities of the railway line. Figure

2.17 shows the typical voltage bounce diagram [33] that represents the transient

voltage at the total railway length with an incidental voltage signal of V+.

(2.10)

21

Figure 2.17: Bewley Lattice diagram that illustrates the injected voltage traveling

back and forth in railway line.

𝑉𝑖,𝑗𝐿 = 𝛽𝑖−2,𝑖−1𝑉𝑖−1,𝑗

𝐿 + 𝛼𝑖−1,𝑖−2𝑉𝑖−1,𝑗𝑅 (2.13)

𝑉𝑖,𝑗𝑅 = 𝛼𝑖,𝑖+1𝑉𝑖+1,𝑗−1

𝐿 + 𝛽𝑖+1,𝑖𝑉𝑖+1,𝑗−1𝑅 (2.14)

Where Ti;i+1 and Ti+1;i are the transmission coefficients 𝛼𝑖,𝑖+1 and 𝛼𝑖+1,𝑖are the

refection coefficients between Zi and Zi+1. 𝛽𝑖,𝑖+1, 𝛽𝑖+1,𝑖 , 𝛼𝑖,𝑖+1 and 𝛼𝑖+1,𝑖 are

defined as follows [34].

𝛼𝑖,𝑖+1 =𝑍𝑖+1 − 𝑍𝑖

𝑍𝑖+1 + 𝑍𝑖

𝛼𝑖+1,𝑖 =𝑍𝑖 − 𝑍𝑖+1

𝑍𝑖+1 + 𝑍𝑖

𝛽𝑖,𝑖+1 = 1 + 𝛼𝑖,𝑖+1

𝛽𝑖+1,𝑖 = 1 + 𝛼𝑖+1,𝑖

2.8.2 Propagation the waves in Bewley Lattice diagram method.

Figure 2.18 show how the voltage propagation in one section and determined peak

voltage in end the line.

(2.15)

(2.16)

(2.17)

(2.18)

22

Figure 2.18: Bewley Lattice diagram for one section in railway line.

The following equations explain how to get the peak voltage in the strike point.

V1=u (t) t=0

V2= (α+ βα) t=2TT

V3= (α2β+α2β2) u (t) t=4TT

V4= (α3β2+α3β3) u (t) t=6TT

UTT=V1+V2+V3+V4 (2.23)

UTT (t) = ut(t)+ αut(1- β) (t-2TT) +α2 βu(t-4TT) +α2 β2 u(t-4TT) +α3 β2 u(t-6TT)

+ α3 β3 u(t-6TT) . (2.24)

= ut(t) +α (1- β) +ut (t-2TT) +α2 β3 (1-β) u(t-4TT) +α3 β2 (1-β) u(t-6TT)

= ut(t) +α (1+β)[ ut (t-2TT) +α β u(t-4TT)+ (α+β)2 u(t-6TT)]. (2.25)

2.9 Lightning risk evaluation for railway signalling systems.

The lightning overvoltage on signalling cables

V = 0.0145 × (I / r) + 0.17 (2.26)

The lightning overvoltage on rails

V = 0.0134 × (I / r) + 0.19 (2.27)

We can estimate the lightning conditions at the case of lightning damage occurrence

caused by exceeding the withstand voltages of railway signalling systems according

to (2.25) – (2.26). We can evaluate the occurrence frequency of lightning risk for

(2.19)

(2.20)

(2.21)

(2.22)

23

railway signalling systems to the occurrence probability of lightning conditions as

shown in Figure 2.19. If the railway signalling systems leading overhead power lines

have a withstand voltage of approximately 30 kV where countermeasures for

protection against lightning are taken, These lightning conditions correspond to the

case that 31 kA of lightning strikes within a 0.155-km radius. 31 kA of lightning

stroke current is 50 % value of cumulative occurrence frequency distribution of the

peak value of lightning current. [35].

𝑃(𝐼) =1

1+(𝐼

31)2.6

(2.28)

Where P (I) is the cumulative occurrence frequency distribution of the peak

value of lightning current [%]. Iis the lightning stroke current [kA]. At the region

where is N [times/year] of lightning stroke within a 10-km radius, the number of

lightning stroke within r/km radius can be calculated by (2.28).

𝑁(𝑟) = 𝑁 ×𝜋𝑟2

𝜋×102

Where N(r) is the number of lightning stroke within a r-km radius [times/year]

[36]. R is the radius [km]. N is the number of lightning stroke within a 10-km radius

[times/year]. for example of the region where is N = 1,000 times/year, we can evaluate

that occurrence frequency of lightning damages of railway signalling systems leading

overhead power lines is 0.36 times/year/equipment.

Figure 2.19: Evaluation flow of lightning risk for railway signaling systems.

(2.29)

24

2.10 Devices along Electrified Railway Systems.

The most common devices connected along electrified railway systems consist of

trackside transformers; BT and AT, and track circuits; relay and rectifier units. There

are also interconnections between the overhead conductors in the railway system,

depending on which feeding system that is used. In the single-track electrified railway

system with ten overhead conductors there are not only the contact, messenger and

reinforcement wires that are interconnected as explained before. The return

conductors are also interconnected, and for BT systems these are also connected to

the S-rail at the midpoint between two consecutive transformers. In double track

railway systems the S-rails of the different tracks are interconnected at every 300 m.

At every pole position the S-rail is shorted to the pole footing. The pole footing is in

turn grounded, but due to the phenomenon of soil ionization [37] not to ideal ground.

This can be accounted for by connecting series non-linear resistors between every

pole footing and the reference ground.

Components and devices connected to the auxiliary wires are not considered in this

work.

Figure 2.20: Transformer connections in BT feeding systems.

2.10.1 Trackside Transformers.

There are mainly two types of trackside transformer used in the Swedish electrified

railway system, BT and AT. Both these are 1:1 transformers with the same purpose,

i.e. to force the traction current to return through the designated return conductors (or

negative feeder) to the traction supply to reduce stray currents which may cause EMI

with electrical systems in the vicinity of the railway system. There are differences

between the transformers, the primary and secondary coils of a BT are connected in

series with the catenary and return conductor, and the coil of an AT is connected as

shunt between the catenary and negative feeder and the midpoint of this coil is

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