penjelasanatp

i

LIGHTNING SIMULATION STUDY ON LINE SURGE ARRESTERS AND

PROTECTION DESIGN OF SIMPLE STRUCTURES

NOOR SHAHIDA BT JAMOSHID

A project report submitted in fulfillment in partial fulfillment of the

requirements for the award of the degree of

Master of Engineering (Electrical - Power)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

MAY 2008

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To my beloved mother and father

iv

ACKNOWLEDGEMENT

Praise be to Allah s.w.t. to Whom we seek help and guidance and under His benevolence we exist and without His help this project could not have been accomplished. I would like to acknowledge the contributions of my respectful supervisor, Associate Professor Dr. Zulkarnain Bin Abdul Malek for his time, support and advice throughout this project. Without his support this proposal may not have come to fruition. I also would like to thank all my friends for the numerous ideas and helpful hands throughout this project. I wish to thank the grateful individuals from TNB Transmission Line group. Lastly, I am deeply grateful to my parents Jamoshid Bin Paramuthullah and Leha Binti Bahadur Khan, as well as to my sister and brothers for a support and care throughout my journey of education.

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ABSTRACT

There was a recent incidence where a direct lightning strike on the earth

shielding conductor of a 275/132kV quadruple circuit transmission line had caused the

breakage of the conductor at four points. Three short conductors connecting the line

arrester installed on the 132kV line were not affected. The location of the affected

arrester was not at the nearest tower to the point of strike but at the adjacent tower. The

arresters at the nearest tower were not affected. This phenomenon was studied using

ATP-EMTP simulation. Transmission tower is modeled according to the multi storey

tower proposed by Masaru Ishii which was validated through theory and calculation.

Simulation results show that the phenomenon cannot be conclusively reproduced within

the ATP-EMTP simulation. Study indicating the fact that the phenomenon may be a

one-off special case event. Overhead line is modeled by applying the PI subroutine file.

This project also study the protection of simple structures from lightning strikes. The

most common and simplest form of lightning protection is by using a vertical rod which

has the function of intercepting a lightning stroke before it can strike a nearby object it is

protecting, and then discharging the current to ground. In this simulation study, 1500

strokes were applied in a square plot ground area of 1km² and the number of flashes to

ground per square kilometer per year (Ng) is 15 strokes/ km²/year. A Monte-Carlo

technique is used to manipulate the statistical distribution of lightning strokes. The

program is written in C-language using MATLAB simulation.

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ABSTRAK

Baru-baru ini, satu kejadian telah berlaku di mana panahan petir pada

talian bumi, talian penghantaran atas 275/132kV litar berkembar empat (quadruple

circuit) telah menyebabkan talian bumi terputus kepada empat bahagian. Penangkap

kilat pada bahagian bawah talian 132kV pada menara talian penghantaran yang

berdekatan tidak berfungsi, sebaliknya penangkap kilat pada menara bersebelah yang

berfungsi. Menara penghantaran dimodel berdasarkan kepada model bertingkat yang

dicadangkan oleh Masaru Ishii. Model disahkan melalui kiraan dan teori. Keputusan

daripada simulasi kajian yang dijalankan tidak dapat membuktikan kejadian ini berlaku

melalui ATP-EMTP. Aturcara Simulasi ATP-EMTP telah digunakan dalam mengkaji

panahan petir terhadap litar berkembar empat. Talian atas dimodelkan dengan

menggunakan model PI yang sedia ada dalam EMTP. Simulasi menunjukkan fenomena

di atas tidal dapat ditunjukkan melalui simulasi dan ia mungkin merupakan kes terpencil.

Projek ini juga mengkaji perlindungan daripada struktur yang mudah terhadap panahan

kilat. Struktur yang asas dan mudah untuk perlindungan petir ialah dengan

menggunakan rod tegak dimana ia berfungsi memintas penahan petir sebelum ia

memanah kawasan sekitar yang dilindungi dan kemudian menyahcas arus ke bumi.

Untuk kajian simulasi ini, 1500 panahan telah dikenakan pada segiempat sama yang

berukuran 1 panjang dan lebar kawasan bumi. Bilangan panahan ke bumi per

per tahun (Ng) adalah sebanyak 15 panahan. Teknik Monte-Carlo telah digunakan untuk

manipulasi statistik taburan panahan petir. Program ini menggunakan bahasa C dalam

Simulasi MATLAB.

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF ABBREVIATIONS xiv

LIST OF SYMBOLS xv

LIST OF APPENDICES xvii

1 INTRODUCTION 1

1.1 Introduction 1

1.2 Problem Statement 2

1.3 Objective 4

1.4 Scope of Project 5

1.5 Organization of Thesis 5

2 LITERATURE REVIEW 6

2.1 Lightning Problem for Transmission Line 6

2.2 Effects on Transmission Line Protection 7

2.2.1 Backflashover 7

2.3 Travelling Wave

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2.4 Lightning Current 8

2.4.1 Characterization of the lightning discharge 9

2.5 Line Insulation Flashovers Model 11

2.6 Ground Flash Density 16

2.7 Tower Footing Resistance 16

2.8 Transmission Line Tower 17

2.8.1 Development of Tower Model 17

2.8.2 Tower model 18

2.9 Surge arrester 21

2.10 Transmission Line Model 24

2.11 Monte Carlo Simulation 25

2.11.1 The 3-Dimensional Electrogeometric Model 26

2.11.2 3-Dimensional Simulation of Fields of Influence 26

2.11.3 3-Dimensional Modeling of The Lightning Stroke 27

2.11.4 Ground Flash Density 30

2.11.5 Shielding Effect of a Vertical Rod 30

3 METHODOLOGY 31

3.1 ATP-EMTP Simulation 31

3.2 Typical EMTP Applications 32

3.3 Creating Simulation File 33

3.4 Creating Punch File 35

3.5 Simulation 36

3.6 Plot File 37

3.7 Transmission line 37

3.8 Transmission tower 38

3.9 Insulator String 44

3.10 Lightning source selection 44

3.11 Monte Carlo Simulation 47

3.12 Project Flow 50

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4 SIMULATION RESULT AND DISCUSSION 53

4.1 Introduction 53

4.2 Line Surge Arrester Study 54

4.2.1 Transmission tower 54

4.2.2 Transmission Line and Tower Circuit Model on 55

EMTP Simulation

4.3 Lightning Protection of Structures 64

4.3.1 Simple Structure Protection Result 64

5 CONCLUSIONS AND RECOMMENDATIONS 74

5.1 Conclusions 73

5.2 Recommendations 75

REFERENCES 76

Appendix A 80

x

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Flashover rate for different circuit without line surge arrester 23

2.2 Flashover rate for different circuit with line surge arrester 23

3.1 Parameter of the 275/132kV quadruple tower model 42

4.1 Voltage between each phase and insulator string at tower 3 63

4.2 Voltage between each phase and insulator string at tower 4 63

4.3 Lightning stroke with effective striking distance 71

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 Transmission line had caused the breakage of the conductor 3

at four portions

1.2 The direct stroke on shield wire between T70-T71 affected 3

Three TLAs installed at T69 and T68

2.1 Reflection and refraction at tower after lightning strike 8

2.2 Lightning current shape, according to IEEE guidelines 10

2.3 Peak current magnitude (kA) versus flashover rate 10

2.4 Rise time lightning current versus flashover rate 11

2.5 Critical flashover voltage for 275/132kV transmission line 12

2.6 The back flashover mechanism. 14

2.7 Model used for string of insulator up 275/132kV. 14

2.8 Kawai tower model 18

2.9 Mathematical calculation for multistory tower model 20

2.10 Multiconductor vertical line model 20

2.11 Line arrester installed on 275/132kV 22

2.12 Transmission line model 23

2.13 Fields of influence of a vertical rod and ground. Rs and rsg 28

are the effective striking distances of the vertical rod and ground

2.14 Fields of influence of horizontal wire and ground 28

2.15 Fields of influence of rectangular block and ground 29

2.16 Display of lightning strokes (represented by dots) terminating 30

on structure (vertical rod) and surrounding ground - plan view

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3.1 Overview of ATPDraw commands and function 32

3.2 Data window for simulation setting 34

3.3 Data window for inserting the parameter 35

3.4 Data window for transmission line 36

3.5 Transmission line model 39

3.6 Multistorey transmission tower 39

3.7 M.Ishii’s tower model for a double line tower 40

3.8 Tower equivalent radius 41

3.9 Modified M.Ishii’s tower model for a quadruple circuit line 43

tower modeling

3.10 Insulation string model 44

3.11 Waveform of fast front voltage surge using Heidler model, 45

20kV with 0.5µs fast front time

3.12 Waveform of voltage using DC model, 20kV with 0.5µs fast 46

front time

3.13 Voltage at tower top by using a DC source as input 47

3.14 Flow chart of Monte Carlo simulation on transmission line 49

3.15 Project flow chart 51

3.16 Protection of simple structures due to lightning strikes 52

4.1 Complete multistorey model 54

4.2 Voltage at tower top, tower base and each crossarm of the tower 55

4.3 The simulation circuit of 275/132kV multistory quadruple 56

transmission line, transmission tower with EMTP

4.4 Voltage at red phase and insulator string tower 3 (275kV) 57

4.5 Voltage at blue phase and insulator string tower 3 (275kV) 57

4.6 Voltage at yellow phase and insulator string tower 3 (275kV) 58


4.8 Voltage at blue phase and insulator string tower 3(132kV) 59

4.9 Voltage at yellow phase and insulator string tower 3(132kV) 59



xiii





4.16 Lightning Surge Arrester Configuration L-Arrangement 64

4.17 Display of lighting strokes at surrounding ground-plan view 65

4.18 Display of lightning strokes (represented by dots) 66

terminating on structure (vertical rod), and surrounding

ground-plan view with current 2.5kA and 5kA.

4.19 Vertical rod and its effective striking with current 2.5kA 69

4.20 Vertical rod and its effective striking with current 5kA 69



4.23 Field of influence of a rectangular block above ground which 72

can be used to represent a building structure or a patch of trees

with current 2.5kA with 2 dimensional electrogeomatric model.

4.24 Field of influence of vertical cylinder can be used to represent a 72

building structure or a patch of trees with current 2.5kA

(3 dimensional electrogeomatric model).

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LIST OF ABBREVIATIONS

ATP - Alternative Transient Program

EMTP - Electromagnetic Transient Program

TLA - Transmission Line Arrester

TD - Thunder Days

CIGRE - International Conference on Large High-Voltage Electric

System

IEEE - Institute Electrical and Electronics Engineers

LCC - Line Cable Constant

R-L - Resistance and Inductance

SiC - Silicon Carbide

DC - Direct Current

xv

LIST OF SYMBOLS

V - Voltage

θ - Angle

Ω - Ohm

I - Current

kV - Kilo-Volt

m/µs - Meter per Micro-second

R - Resistance

L - Inductance

C - Capacitance

µs - Micro-second

kA - Kilo-Ampere

mH - Millie-Henry

µF - Micro-Farad

t - Time

% - Percent

- Tower surge impedance

- Attenuation coefficient

- Damping coefficient

H - Height

- Probability current

xvi

- Field of influenced of object

Ng - Number of flashes to ground per square kilometer per year

xvii

LIST OF APPENDICES

APPENDIX TITLE PAGE

A 1) 275/132kV Transmission line and 81

Transmission Tower Model - EMTP

2) Matlab Simulation of lightning strokes 81

(represented by dots) terminating on

Structure (vertical rod), and surrounding

ground-plan view with current

3) Matlab Simulation of lightning strokes 84

(represented by dots) terminating on

structure (vertical rod

4) Matlab Simulation of field of influence of 88

vertical cylinder can be used to represent

a building structure

1

CHAPTER 1

INTRODUCTION

1.1 Introduction

High overvoltage transients caused by lightning is considered a major source of

disturbances in high voltage transmission line systems. There is a consensus that

lightning starts from the charge separation process (positive and negative), which is due

to transportation of lightweight particles to higher regions by the rapid updrafts of moist

air, usually in hot humid areas. This charge separation is known as the vertical

thunderstorm dipole. It can be performed within the cloud or between the cloud and the

earth which creates electric fields that eventually bring out the breakdown known as

lightning. The overvoltage introduced by lightning have traditionally been estimated

using conventional and simplified methods. More involved calculations become possible

with digital computer programs such as Electromagnetic Transients Program (EMTP). In

such a program, each power system component can be modelled in great detail.

2

The characteristics of lightning surges on overhead transmission lines, which

result from lightning strokes, depend on how there are caused. They can be broadly

divided into four types:

a) Tower/ground wire surge - The stroke terminates on the tower

structure/ground wires without any flashover to the phase conductors.

b) Shielding failure - The stroke passes through the protective zone of

the ground wires and terminates on the phase conductors.

c) Back flashover - The same as a), but followed by a flashover to the

phase conductors. This type of flashover is called back flashover.

d) Shielding failure flashover – The same as b), but followed by a

forward flashover to the ground/ground wires or tower.

1.2 Problem Statement

Part 1: Lightning Simulation Study on Line Surge Arresters.

A recent incidence from direct lightning strike on the shielding conductor of a

275/132kV quadruple circuit transmission line had caused the breakage of the conductor

at four portions. This incident happened between transmission line Pulu to

Serdang(275kV) and Balakong to Serdang(132kV). Figure 1.1 shows a direct stroke on

the earth wire between two towers has caused the wire to snap into 4 portions. Line

arresters are installed on the 132kV lines. The location of the affected arrester was not

that closest to the point of strike but rather further down at the next tower. The arrester at

the nearest tower was not effected. Figure 1.2 shows the tower locations.

3

Figure 1.1 Transmission line had caused the breakage of the conductor at four

portions[1]

Figure 1.2 The direct stroke on shield wire between T70-T71 affected three TLAs

installed at T69 and T68 [1]

4

Part 2: Protection Design of Simple Structure

There are standard methods to design and install the lightning protection devices

for structures. Among the concepts used is the rolling sphere method which determines

the exposed areas to lightning strikes. Lightning rods, usually the conventional Franklin

rods, are installed on top of buildings and structures is protect the exposed areas from

lightning threats. The rolling sphere method described above is based on a number of

assumptions such as the average lightning peak current, which may limit the protection

reliability to a certain condition only. This simulation work aims to consider all possible

lightning current magnitudes and the corresponding ground flash density. The simulation

is run for long time (teens or hundreds of years) and this is possible using a computer

simulation. The performance of the designed lightning protection can then be studied.

1.3 Objective

The objectives of this project are:

1) To study and investigate a recent incident where a direct lightning strike on the

earth shielding conductor of a 275/132kV quadruple circuit transmission line as

below:

a) Arrester at the nearest to the point of strike is not effected rather further down

at the next tower.

b) Lightning strike at shielding wire caused the breakage of conductors at four

points.

5

2) To develop a program to simulate the probability nature of lightning strike using

Monte Carlo Simulation and to simulate the lightning protection of simple

structures.

1.4 Scope of Project

Design and analysis:

Modeling 275/132kV Quadruple Circuit Transmission Line use ATP-EMTP

Simulation

Monte Carlo Simulation using MATLAB

1.5 Organization of Thesis

The thesis is organized in the following manner. Chapter 2 describes the

literature review of the project which includes the lightning strikes phenomenon

on transmission line and transmission tower, and the protection design of simple

structures. Chapter 3 describes on the methodologies used. Results and

discussion are described in Chapter 4 followed by conclusions in Chapter 5.

6

CHAPTER 2

LITERATURE REVIEW

2.1 Lightning Problem for Transmission Line

Lightning strokes to transmission line and tower of 275/132kV quadruple circuit

are classified into two groups which are direct stroke and induced voltage. Direct stroke

is the phenomenon of thunder cloud directly discharge into transmission line and it is

considered the major source of disturbance in transmission line system [3]. Induced

voltage is introduced when the thunderstorm generates negative charges and the earth

objects develop induced positive charges. When cloud discharges to some earthed

objects other than the transmission line, the line is left with a huge concentration of

charge (positive) which cannot leak instantaneously. The transmission line and the

ground will act as a huge capacitor charged with a positive charge and hence

overvoltage occurs due to these induced charges [3,6]. This phenomenon is not so

critical for system voltages more than 66kV.

7

2.2 Effects on Transmission Line Protection

When a direct lightning stroke occurs, lightning current of large amplitude will

be injected into the transmission line. Lightning can strike on transmission lines in many

ways. However, only the lightning strokes, which can cause transients on phase

conductors of the transmission line, may influence the surge arrester. They are: direct

stroke to a phase conductor and strike to the overhead shield wire or tower, which then

flashes over to the phase conductor [10].

2.2.1 Backflashover

When lightning strikes a tower, a traveling voltage is generated which travels

back and forth along the tower, being reflected at the tower footing and at the tower

top, thus raising the voltage at the cross-arms and stressing the insulators. The insulator

will flashover if this transient voltage exceeds its withstand level (backflash).

Backflashover voltages are generated by multiple reflections along the struck tower and

also along the shield wire for shield lines at the adjacent towers. The backflashover

voltage across insulator for the struck tower is not straight forward. The peak voltage

will be directly proportional to the peak current [7].

8

2.3 Travelling Wave

Traveling wave occurs when lightning strikes a transmission line shielding

conductor, phase conductor or tower. A high current surge is injected as the lightning

strikes. The impulse voltage and current waves divide and propagate in both directions

from the stroke terminal at a velocity of approximately 300 meters per microsecond with

magnitudes determined by the stroke current and line surge impedance [6].

Figure 2.1 Reflection and refraction at tower after lightning strike

2.4 Lightning Current

Wave shape and amplitude of lightning current are influenced by some stochastic

factors, including geographic location, geologic conditions, climate and weather, etc.

Thus, they change every time. But investigations show that although the lightning

currents differ every time in waveform and magnitude, all exhibit the basic

characteristics of a double-exponent wave. It can be given by:

9

(2-1)

where:

I, is the amplitude of the lightning current; α, ß are attenuation coefficients. [8]

2.4.1 Characterization of The Lightning Discharge

The lightning discharge current is defined by its shape and characteristic

parameters. Given the random nature of lightning, the parameters identifying each stroke

follow probabilistic laws which have to be considered. IEEE guidelines consider a

triangular shape, it can be shown in Figure 2.2. The current amplitude follows a

probabilistic law given by the cumulative probability of exceeding the amplitude I, :

[12]

(2-2)

where I is given in kA.

10

Figure 2.2 Lightning current shape, according to IEEE guidelines (negative polarity)

.

Peak current amplitude (lightning) and rise time of lightning stroke can effect to

the overvoltage that occur in transmission line because the higher peak current

magnitude and shorter front time will increase the overvoltage. It can be shown in

Figure 2.3 and Figure 2.4. This will lead to backflashover [11].

Figure 2.3 Peak current magnitude (kA) versus flashover rate

11

Figure 2.4 Rise time lightning current versus flashover rate

2.5 Line Insulation Flashover Model

The leader propagation model is used to represent line insulation flashovers[14]:

(2-3)

where:

- Leader velocity (m/s)

d - Gap distance (m)

- Leader length (m)

u(t) - Applied voltage (kV)

Eo= 520 (kV/m)

12

The critical flashover voltages U50% of 275 kV and 132kV circuits are 1120 kV

and 880kV respectively. Flashover voltage of all line insulators in the simulated section

is randomly varied, according to the normal distribution. Standard deviation for the line

insulation flashover voltage was 3% [2].

Figure 2.5 Critical flashover voltage for 275/132kV transmission line

Line insulators from tower to conductor can be represented as a capacitor. The

tower to conductor has equivalent capacitance of about 80 pF for 132kV lines [12]. The

transient-voltage withstands level of a power apparatus is not a unique number. An

apparatus may withstand a high transient voltage which has a short duration even it has

failed to withstand a lower transient voltage with longer duration. This characteristic of

the insulator is known as the volt-time characteristic of the insulation. However, a

simplified expression for the insulator voltage withstand capability can be calculated as

below [12]:

13

(2-4)

where:

- a flashover voltage (kV),

- 400*L,

- 710*L,

- elapsed time after lightning stroke, µs.

The back flashover mechanism of the insulators can be represented by volt-time

curves. When a back flashover might occur, a parallel switch is applied. If the voltage

across the insulator exceeds the insulator voltage withstand capability, the back

flashover occurs. The back flashover is simulated by closing the parallel switch. Once

the back flashover occurs, the voltage across insulator goes down to zero. Figure 2.6 and

Figure 2.7 show the insulator model and the waveform of voltage across insulator, when

back flashover occurs at 4 μsec [4].

14

Figure 2.6 Model used for string of insulator up 275/132kV.

Figure 2.7 The back flashover mechanism

15

2.6 Ground Flash Density

The Ground Flash Density, Ng, has a linear effect on lightning outage rates.

There have been important developments in measurements of Ng, in the 1980s. Based

on a power-law regression between CIGRE Lightning Flash Counter readings and local

thunder days (TD) values for the same period [8]. Ng is given as:

Ng = 0.04 T (2-5)

The flash/100km/year, , is used to calculate total hit on the transmission line which is

given by:

(2-6)

where:

h = average conductor height, m

b = overhead ground wire separation distance, m

Ng = ground flash density, flashes/ /year

Na = flashes/100km/year

16

2.7 Tower Footing Resistance

The tower footing behavior is characterized by a lumped resistance. This

resistance is constant according to IEEE guidelines, while in CIGRÉ the effect of soil

ionization is taken into account. The decrease of the tower footing resistance when the

lightning current amplitude exceeds a critical value Ig is given by [9]:

(2-7)

where R0 is the low current footing resistance (non-ionized soil) and the critical value of

the lightning current is given by the soil ionization threshold field, Eg, using the equation:

(2-8)

where:

Ro = low current footing resistance (Ω)

Ri = tower footing resistance (Ω)

ρ = soil resistivity (Ωm)

I = impulse current (kA)

Ig = soil ionization limit current (kA)

Eg = soil ionization critical electric field (kV/m)

[ Eg = 400 (kV/m]

17

2.8 Transmission Line Tower

A direct stroke to a transmission line is very rare and most of the lightning strikes

to the top of a transmission tower. As a result, in calculation of lightning, tower models

have been developed using a theoretical approach or an experimental work. The accurate

representation of the transmission tower has been the subject of much discussion. In

lightning surge simulations, the tower model used can range from simple lumped

inductances or resistance to complicated nonuniform transmission line circuits.

Representation of the tower as a lumped element is only valid if surge current rise time

is long compared to surge travel time in the tower. So for a steep-front wave the tower

must be modeled as a distributed parameter element [4].

2.8.1 Development of Tower Model

Several formulas for the tower surge impedance have been used in the past.

Wagner’s and Hileman’s model indicates that the tower impedance varies as the wave

travels from top to bottom, being lowest at the tower top and increasing as the wave

travel down the tower [9]. Kawai later performed measurements on isolated tower

(without ground wires connected) and obtained similar result, although the magnitudes

were appreciably lower [9]. Later on Chisholm et al. performed some experiments and

found that the tower response to a horizontal current, resulting from a midspan stroke, is

different from the response to a vertical surge, where the tower impedance decrease

from top to bottom [9]. All these result are obtained considering the tower alone, without

ground wires connected [9].

18

Next, Ishii et al, measured the surge response of the typical double circuit 500kV

transmission tower, with ground wires, for vertical stroke current. Based on this

measurement, they developed a multistorey transmission tower model to be used in the

multiconductor analysis with ElectroMagnetic Transients Program (EMTP). The

multistorey transmission tower model consists of distributed parameter lines

representing tower surge impedance and parallel R-L circuits representing an attenuation

of a travelling wave along the tower [5].

2.8.2 Tower Model

The surge impedance expression proposed by Sargent [5] has been widely used

as a tower model for traveling wave calculation. According to this expression, the tower

under measurement is approximated by a cone, and a surge impedance of 170Ω is

obtained for this shape. In this case, it is treated that the velocity of surge propagation in

the tower is equal to the velocity of light (300 m/µs) and there is no surge attenuation.

On the other hand, a surge impedance of 100Ω to 115Ω, a surge propagation velocity of

210 to 240 m/µs and a surge attenuation coefficient of 0.8 to 0.9 obtained by Kawai et

al. through experiments on an actual tower used as second model [5].

Figure 2.8 Kawai tower model [5]

19

In the new model an inductance is connected parallel with the resistance

determining the attenuation coefficient, enabling a more accurate approximation of the

characteristic of the wave tail. This inductance is a parameter to determine the shape of

the wave tail, and has nothing to do with the lumped inductance often used to represent

the tower itself. The damping resistance is determined from the resistance per unit length

of a transmission line calculated from the postulated surge attenuation coefficient of a

tower [13].

The transmission line tower model, used in simulation is presented in Figure 2.9.

The value of R can be obtained by calculating and dividing the tower into upper and

lower truncated cones as shown in Figure 2.10. Section of the tower from the bottom

crossarm to the ground is represented as propagation element, which is defined by the

surge impedance ZT and wave propagation speed on the tower was taken to be equal to

the velocity of light. Sections on the tower top [between tower top and top crossarm and

between crossarms] modeled as inductance branches. Branch inductance is determined

according to the section length, tower surge impedance and the propagation velocity. In

the parallel to the inductance branches a damping resistors are introduced [19].

20

Figure 2.9 Mathematical calculation for multistore tower model

Figure 2.10 Tower equivalent model

21

2.9 Surge Arrester

Four general classes of devices that have been used to limit over voltage and

permit low (more economical) insulation levels of equipment [7]:

Spark gaps

Expulsion-type arresters

Gapped valve-type arrester

Gapless-Metal oxide arrester

Overvoltage protective devices use spark gaps connected in series made with a

nonlinear silicon carbide (SiC) material. The spark gaps provided high impedance

during normal conditions. Nowadays, the physical construction of modern high voltage

surge arrester consists of metal oxide discs inside a porcelain or polymer insulator.

The use of line surge arresters to improve transmission line lightning

performance or to avoid double circuit outages has increased over the last decade. Many

line surge arresters are in service today and substantial service experience has been

accumulated. The majority of line surge arresters are installed on lines having nominal

voltages between 44kV and 138kV, but the application of this type of technology has

been extended to the distribution lines and also to the transmission lines up to 500kV.

Line surge arresters are installed on 132kV lines, mainly to reduce double circuit

outage rate. Line surge arresters are normally installed on all phase conductors of one

circuit of the double circuit line. Arresters are installed on all towers of the considered

132kV line as shown in Figure 2.11. With this arrester installation configuration, double

22

circuit outages are eliminated, but there exists possibility to have flashovers on the

circuit without arresters [2].

Figure 2.11 Line arrester installed on 275/132kV

Lightning stroke performance of the line without line surge arresters is presented

in Table 1 (per circuit flashovers). As expected, the majority of the flashovers happen on

132kV circuits. Line lightning performance strongly depends on the tower footing

resistance. For the tower footing resistance less than 10Ω, zero flashover rate is obtained

(line is equipped with two shield wires with a negative shielding angle) [2].

23

Table 2.1 Flashover rate for different circuit without line surge arrester

(flashover/100km/year). Refer to Figure 2.6 for location of C1, C2, C3 and C4.

Table 2 Line double circuit flashover rate different arrester installation

configuration (Flashover/100km/year)

The number of double circuit flashovers depends on the tower footing resistance,

and may reach value of 35 % of the line total flashover rate, for the tower footing

resistance of 40Ω. The number of the triple circuit flashovers (simultaneous flashovers

24

on two 132kV circuit and on one 275kV) is very low. The best improvement in the line

total flashover rate is obtained by the installation of the arrester on the bottom

conductors of both 132kV circuit and on the one top conductor of one 132kV circuit (the

best three arrester installation configuration) [2].

When line surge arresters are installed on all phase conductors of one 132kV

circuit, double circuit flashover are completely eliminated (actual installation on the

considered transmission line). But, it is to note that with this arrester installation

configuration line total flashover rate remains high. Arrester installation configuration

with the arresters on the bottom conductors of both 132 kV circuits and on the one top

conductor of one 132 kV circuit is very attractive, because this configuration

substantially reduce line total flashover rate, reducing in the same time line double

circuit flashover rate [2].

2.10 Transmission Line Model

Figure 2.12 Transmission line model

25

There are five types of the line/cable in ATP (EMTP) which are[16]:

1. Bergeron: Constant parameter KCLee or Clark models

2. PI: Nominal PI-equivalent (short lines)

3. JMarti: Frequency dependent model with constant transformation

matrix

4. Noda: Frequency dependent model

5. Semlyen: Frequency dependent simple fitted model.

J.Marti is a suitable model to represent the multiphase transmission line. This

model considers frequency attenuation, the geometrical and material of the conductor

including skin effect and conductor bundling and the corresponding electrical data are

calculated automatically by ATP-EMTP program. It also generates high order frequency

dependent model for overhead line and cables.

2.11 Monte Carlo Simulation

A Monte Carlo method is a technique that involves using random numbers and

probability to solve problems. The term Monte Carlo Method was coined by S. Ulam

and Nicholas Metropolis in reference to games of chance, a popular attraction in Monte

Carlo, Monaco. It is a method for iteratively evaluating a deterministic model using sets

of random numbers as inputs. This method is often used when the model is complex,

nonlinear, or involves more than just a couple uncertain parameters. Monte Carlo

technique can be used in order to build the computer program for the evaluation of the

performance of overhead lightning shielding system. Analysis of atmospheric

overvoltage in power plants or transmission line there was always a problem how to

http://vertex42.com/ExcelArticles/mc/MonteCarloSimulation.html#ref

26

determine amplitude of the lightning current which is striking the protected object and

cause overvoltage. Development a computer program to represent an algorithm which

will determine the mentioned amplitude in same range for entered protected object is

necessary. The program is based on a statistical Monte Carlo analysis on the 3-

dimensionally simulated system.

2.11.1 The 3-Dimensional Electrogeometric Model

The basic feature of the 2-dimensional electrogeometric model of Whitehead is

the simple criterion of shortest path (from the leader tip) determines the target point in

protection on structure. This target point of the lightning stroke is determined when the

tip of the descending leader reaches a point when the distance from the leader tip to the

protective target point equals the striking distance. The field of influence of any

structure to a descending lightning leader is hence described by arcs with centers at the

various parts of the structures having a radius equal to its striking distance [17].

2.11.2 3-Dimensional Simulation of Fields of Influence

To extend the 2-dimensional EG model to a 3-dimensional system, fields of

influence of a structure described by its space of influence whose extreme radius is

defined by its striking distance are now considered. For example, the field of influence

of a vertical rod can be described by a vertical cylinder with a hemispherical top, both

having a radius equal to its effective striking distance r as illustrated in Figure 2.13.

27

Similarly, the fields of influence of a horizontal wire above ground can be represented

by a horizontal cylinder (Figure 2.14). Figure 2.15 also illustrates the fields of influence

of a rectangular block above ground which can be used to represent a building structure

or a patch of trees, etc. In all cases, the field of influence of the ground plane is

represented by a horizontal plane at its effective striking distance rs above the ground.

The termination point of the lightning stroke is determined on the basis that an object

will be struck if its field of influence is meet first by the leader tip on its way to ground.

As in the case of the example given in Figure 2.13, stroke A will terminate on the rod

and stroke B will terminate on the ground [17].

2.11.3 3-Dimensional modeling of the Lightning Stroke

The lightning stroke is characterized principally by the lightning leader approach

angle and stroke current magnitude. The probability density function of the vertical

angle of approach of the lightning stroke is given by [17]

(2-9)

28

Figure 2.13 Fields of influence of a vertical rod and ground. Rs and rsg are the

effective striking distances of the vertical rod and ground respectively [17]

Figure 2.14 Fields of influence of horizontal wire and ground [17]

29

Figure 2.15 Fields of influence of rectangular block and ground [17]

To fully describe the stroke in 3 dimensions, a horizontal angle having a

uniform probability distribution of between 0 and 360 degrees is incorporated. The

AIEE current distribution used is represented by an array with 250 current values stored

in a data file. The IEEE WG distribution is given by [17]

(2-9)

where I is the stroke current in kA and P(1) is the probability of current exceeding I.

Striking distance is related to stroke current magnitude.

(2-10)

where I is in kA and is in meters.

30

2.11.4 Ground Flash Density

The frequency of strokes to an area under study is determined by the ground

flash density which is the number of ground discharges per square kilometer per year.

The shielding failure rate of a shielding system is a function of the ground flash density.

The distribution of all prospective ground discharges within the area of study is taken to

be uniform as there is no reason to consider otherwise [17].

2.11.5 Shielding Effect of a Vertical Rod

The most common and simplest form of lightning protection is using a vertical

rod which has the function of intercepting a lightning stroke before it can strike a nearby

object it is protecting, and then discharging the current to ground [17].

Figure 2.16 Display of lightning strokes (represented by dots) terminating on

structure (vertical rod) and surrounding ground - plan view [17]

31

CHAPTER 3

METHODOLOGY

3.1 ATP-EMTP Simulation

The Alternative Transients Program (ATP) is considered to be one of the most

widely used universal program system for digital simulation of transient phenomena of

electromagnetic as well as electromechanical nature in electric power systems. With this

digital program, complex networks and control systems of arbitrary structure can be

simulated. ATP has extensive modeling capabilities and additional important features

besides the computation of transients.

ATPDraw for Windows is a graphical, mouse-driven preprocessor to the ATP

version of the Electromagnetic Transients Program (EMTP). In ATP Draw the user can

construct the digital model of the circuit to be simulated using the mouse and selecting

predefined components from anextensive palette, interactively. Then ATP Draw

generates the input file for the ATP simulation in the appropriate format based on built

circuit. Figure 3.1 shows an overview of ATPDraw commands and functions.

32

Main menu Tool bar icons Component tool bar Circuit window

Component selection menu

Figure 3.1 Overview of ATPDraw commands and function

3.2 Typical EMTP Applications

ATP-EMTP is used world-wide for switching and lightning surge analysis,

insulation coordination and shaft torsional oscillation studies, protective relay modeling,

harmonic and power quality studies, HVDC and FACTS modeling. Typical EMTP

studies are:

Lightning overvoltage studies

Switching transients and faults

33

Statistical and systematic overvoltage studies

Very fast transients in GIS and groundings

Machine modeling

Transient stability, motor startup

Shaft torsional oscillations

Transformer and shunt reactor/capacitor switching

Ferroresonance

Power electronic applications

Circuit breaker duty (electric arc), current chopping

FACTS devices: STATCOM, SVC, UPFC, TCSC modeling

Harmonic analysis, network resonances

Protection device testing

3.3 Creating Simulation File

Simulation file is created by keying the parameter of the circuit into the

components which are called out to the circuit window. A data window will pop out

after clicking on that component and the required parameters for the component will

show up. The input data can directly inserted to the special column provided in the data

window.

The EMTP input data structure consists of several important parts that consist of

the simulation setting or called miscellaneous data cards as shown in Figure 3.2. It

control the simulation setting as time interval between processing loop, the maximum

simulation and several frequency parameter that effected the inductance and capacitance

value in the branch section. The second part of the input data is called branch segment.

In this segment, the parameter of the transformer, transmission line, and basic element

34

are placed in the special columns provided in the data window by clicking on that

element.

Figure 3.2 Data window for simulation setting.

The third part is the source segment where all the source parameter are placed.

The procedure to insert the data is same with branch segment as shown in Figure 3.3.

This included the impulse and ramp type source that important in transient study. The

final part is the plot segment and this is where the voltage at different nodes are

requested for plotting purpose. This step is carried out with the probe components

located at the measured nodes.

35

Figure 3.3 Data window for inserting the parameter

3.4 Creating Punch File

When involving with frequency dependent overhead line or underground cable,

the characteristic matrics would have to punch by EMTP. In creating the punch file, two

simple steps have to be, the first process is to locate the parameter for the requested

apparatus in appropriate location in the data window. In order to create the punch file,

the second steps involve the punching process using the EMTP software.

This process is quiet similar to the simulation process but the result from the

computation are the punch file usually with extension of *.pch instead of the*.pl4 file

obtained from normal simulation. This file could further be pasted inside the main input

data file by connecting directly the component to the system circuit in circuit window

36

and thus automatically called out when needed by “INCLUDE” command inside the

input data file of the EMTP simulation. Figure 3.4 shows the data window for

transmission line.

Figure 3.4 Data window for transmission line

3.5 Simulation

Simulation involve the simplest procedure involving the used of the EMTP

command line. By clicking the “Run ATP” command or simply press F2, the simulation

process can now begin. The time needed to finish the simulation depends on the

complexity of the simulation file, number of branch that are requested to be plotted, time

interval between computation loop and the maximum time of the simulation. Some

complex simulation will take about three hours to finish and consume large amount of

computer main memory.

37

3.6 Plot File

As the result of the request node in the simulation, a *.pl4 file will be created

after the simulation has ended. This file can be plotted using the external software

specially design for viewing the result such as PCPlot and TPPlot that usually support

three plot data for each graph. This chart viewing software especially for ATP versions

of EMTP can only be used in MSDOS environment and with DBOS simulation software

running. There is another new plotting program called plotXY to generate scientific line

plots using data collected from *.pl4 file.

3.7 Transmission Line

Simulation on overhead transmission line is conducted through PI subroutine file

in EMTP. This model considers the geometrical and material of the conductor including

skin effect and conductor bundling and the corresponding electrical data are calculated

automatically by the LINE CONSTANTS, CABLE CONSTANTS or CABLE

PARAMETER (LCC) subroutine file. PI setup is a supporting routine to generate

frequency dependent model data for overhead line and cables. It is also generates high

order frequency dependent model for overhead line and cables.

Figure 3.5 Transmission line model

38

In this simulation the PI model was used. The geometrical and material data for

the overhead line conductors are specified as below [16]:

Phase no: Phase number 0 = ground wire (eliminated)

RESIS : Conductor resistance at DC (with skin effect) or at Freq. Init. (no skin

effect)

REACT : The frequency independent reactance for one unit spacing (meter/foot).

Only available with no skin effect.

Rout : Outer radius (cm or inch) of one conductor

Rin : Inner radius of one conductor. Only available with skin effect.

Horiz: Horizontal distance (m or foot) from the center of bundle to a user

selectable reference line.

VTower: Vertical bundle height at tower (m or foot).

VMid : Vertical bundle height at mid-span (m or foot). The height h=2/3* VMid

+1/VTower is used in the calculations.

Separ : Distance between conductors in a bundle (cm or inch)

Alpha : Angular position of one of the conductors in a bundle, measured counter-

clockwise from the horizontal

NB: Number of conductor in a bundle

3.8 Transmission Tower

The transmission model consists of seven sections divided at the upper, middle

and lower phase cross arm positions (not including insulator strings) is shown in Figure

3.6. Each section consists of a loss free transmission line and a lumped constant

consisting of a damping resistance shunted by an inductance

39

Figure 3.6 Multistorey transmission tower

The surge impedance takes into account of the tower configuration, the height

and the radius of the tower. There are shown in Figure 3.7 and Figure 3.8. The

parameters of the 275/132kV quadruple tower model is shown in Table 3.1. These data

are determined by using the following equations.

(3-1)

(3-2)

(3-3)

(3-4)

where:

= Tower surge impedance

= Attenuation coefficient

40

= Damping coefficient

V = Surge propagation velocity

R = Resistance

r = Radius of tower

H = Height

L = Inductance

Figure 3.7 M.Ishii’s tower model for a double line tower

41

Figure 3.8 Tower equivalent radius

42

Table 3.1: Parameters of the 275/132kV quadruple tower model

Name Symbol Value

Tower surge impedance 85Ω

Propagation velocity 300m/µs

Attenuation coefficient 0.7

Damping coefficient 1

Damping resistance (Ω) R1

R2

R3

R4

R5

R6

R7

2.85

5.65

5.65

8.25

3.95

3.95

30.31

Damping Inductance (µH) L1

L2

L3

L4

L5

L6

L7

0.9

1.8

1.8

2.62

1.26

1.26

9.64

Height H1

H2

H3

H4

H5

H6

H7

2.8

5.55

5.55

8.1

3.88

3.88

17.95

43

One of the important aspects which must be considered in tower modeling is to

simulate the transmitted wave from the tower top and the reflected wave from the tower

base. The surge will propagate from the tower top and will reflect from the tower base.

The surge impedance of the tower is represented by a distributed parameter, Z, which

takes into account of surge velocity, tower height, and the surge impedance on the

transmitted and reflected wave. The modification of M.Ishii’s tower model for a

quadruple circuit line tower modeling is shown in Figure 3.9.

Figure 3.9 Modified M.Ishii’s tower model for a quadruple circuit line tower

modeling

44

3.9 Insulator String

The insulators are represented by capacitors in parallel with voltage dependent

flashover switches connected between the respective phases and the tower. This is

shown in Figure 3.10. In this study, a capacitance value of 80 pF was used.

Figure 3.10 Insulation string model

3.10 Lightning Source Selection

The lightning source was simulated by using Heidler model with 20kA

magnitude and 0.5µs front time. The current surge is a single stroke with positive

polarity. The current source can be represented by the following equation and the wave

shape of the fast front current surge by using Heidler model is shown in Figure 3.11.

(3-5)

45

where:

Amp = Multiplicative number in (A) or (V) of the function, does not

represent peak value of surge.

Tf = the front duration in (sec), which is interval between t=0 to time of the

function peak.

Ta = the stroke duration in (sec), which is interval between t=0 and the point

on the tail where the function amplitude has fallen to 37% of its peak value.

N = factor influencing the rate rise of the function.

A 20MV DC type source was used as the lightning input step voltage. It is

injected at the middle point on the earth wire between tower 2 and tower 3. Figure 3.12

shows the input voltage waveform

(MV)

(µs)

Figure 3.11 Waveform of fast front voltage surge using Heidler model, 20MV with

0.5µs fast front time

46

Figure 3.12 Waveform of voltage using DC model, 20MV with 0.5µs fast front time

Figure 3.13 shows voltage at the tower top when using a DC model source as an

input. Waveform of multistorey tower is influenced by the surge attenuation. The surge

will propagate from the tower top to the tower base. From Figure 3.13, voltage at the

tower top rose approximately to 1.7MV. The traveling wave will travel to the tower base

in 0.3µs and the tower base voltage at that point is -1.0MV. After that, the wave will

reflect to the tower top at 0.6µs time scale and voltage rose up to 1.0MV. This

phenomenon will be repeated and can be explained by using the lattice diagram.

47

Figure 3.13 Voltage at tower top by using a DC model source as input

3.11 Monte Carlo Simulation

The lightning performance of an overhead line can be measured by the flashover

rate, usually expressed as the number of flashovers by 100 km and year. Due to the

random nature of lightning, an accurate evaluation of the lightning performance must be

based on a statistical approach. A Monte Carlo simulation is the most usual method for

this purpose. The computation of flashover rate and shielding failure rate at transmission

line will be performed by using a Monte Carlo Simulation. The main aspect of the

Monte Carlo procedure embedded into the ATP can be summarized as follows:

a) The calculation of random values includes the parameters of the lightning stroke

phase conductor voltages, the footing resistance and the insulator strength.

b) Overvoltage calculations are performed once the point of impact has been

determined.

48

c) If a flashover occurs in an insulator string, the run is stopped and the flashover

rate is updated.

d) The convergence of the Monte Carlo method is checked by comparing the

probability density function of all random variables to their theoretical functions;

the procedure is stopped when they match within the specified error.

The overall procedure is illustrated in Figure 3.14. Note that for a specific

design, the lightning parameters as well as the soil resistivity are allowed to vary in

accordance to known distribution functions. For each sample, a two part analysis is

performed. The first part determines the lightning termination point (and thus the

probability of shielding failure). For this purpose, the electrogeometric model for

lightning termination is used. This method determines the probability of shielding failure

for any power line in a general terrain. Figure 3.14 illustrates the basis of the method.

The lightning streamer is assumed to propagate from the top with equal distribution per

unit area. When it approaches the power line, it will terminate at the nearest point within

the striking distance of the lightning. From this construction, the probability of shielding

failure is computed.

49

N = 1

Generate sample of lightning parameter based

on ground flash density

Store result the maximum overvoltage flashover (Nmax)

N = N + 1

Yes

No Is N > Nmax

Generate a sample of soil resistivity Generate reports

Figure 3.14 Flow chart of Monte Carlo simulation on transmission line

50

3.12 Project Flow

The project focuses on the model of 275/132kV quadruple transmission line and

transmission tower to investigate the performance of transmission line due to lightning

strike. Protection of simple structure is done by using MATLAB Simulation. The overall

project flow is shown in Figure 3.15 and Figure 3.16 shows the protection of simple

structure (vertical rod) due to lightning strikes flow chart.

51

Start

Design and Analysis

Modeling and Simulation - ATP-EMTP Simulation model of

transmission line - Monte-Carlo Simulation

Result Analysis and Evaluation - Analysis of transmission line performance

due lightning strike - Protection of simple structure due to

lightning strike

System Optimization

Literature Review Literature work and review on the surge analysis of the transmission line and tower and protection of simple structure from lightning strike

Done

Report Writing

Figure 3.15 Project flow chart

52

Generate sample of lightning parameter based on ground flash

density

Calculate striking distance (rs) based on lightning current amplitude and calculate high of the vertical rod

No

Yes

Lightning terminated on ground

Lightning current amplitude= Lightning current use in calculate striking distance

(rs)

Lightning terminated on vertical rod

Figure 3.16 Protection of simple structure (vertical rod) due to lightning strikes.

53

CHAPTER 4

SIMULATIONS RESULTS

AND DISCUSSIONS

4.1 Introduction

This chapter presents the results of the simulations carried out, namely the ATP-

EMTP simulation for surge arrester study and the MATLAB simulation for the lightning

protection study. For the surge arrester study, a 275/132kV quadruple transmission line

system consisting the transmission line and 5 towers was simulated. Two source model

were used, namely the Heidler model and DC model. The transmission tower was

modeled according to modified M.Ishii’s model.

The lightning protection study incorporating the Monte Carlo probability concept

was simulated using MATLAB simulation. The equation described in section 2.11.3

were utilized.

54

4.2 Line Surge Arrester Study

4.2.1 Transmission Tower

L2 L3 L4 L5 L6 L7

RT

X02 X03 X04 X05 X06 X07 X08 L1 X01

R1 R2 R3 R4 R5 R6 R7

Figure 4.1 Complete multistorey model

Figure 4.1 shows a complete multistorey tower model simulated in the ATP-

EMTP program. A lightning strike with 20kA peak and 0.5µs fast front time was chosen

as the input. The lightning current surge was injected in the top of a standalone tower.

The parameters of the tower model are as shown in Table 3.1. Figure 4.2 shows the

resultant output voltages at the tower top, tower base and at each crossarm of the tower.

The purpose of this simulation is to show the traveling waves propagate from the tower

top to the tower base. As can be seen in Figure 4.2, the voltages along the tower is

reducing starting at the tower top towards the tower base. There is also a slight time

delay due to propagation delay.

55

V:X06 V:X05 V:X04 V:X03 V:X02 V:X01 V:X08 V:X07

Figure 4.2 Voltage at tower top, tower base and each crossarm of the tower

4.2.2 Transmission Line and Tower Circuit Model on EMTP Simulation

Figure 4.3 shows the simulation circuit of 275/132kV quadruple circuit

transmission lines connected to the transmission towers. In the simulation, 5 towers was

used. A lightning surge of DC type with a peak voltage of 20 MV was injected on the

earth wire at midspan.

56

To tower 4,5

To tower 1

R

B

Y

R

B 132kV

275kV

Y

Tower 3Tower 2

Figure 4.3 The simulation circuit of 275/132kV quadruple circuit transmission line,

and transmission towers.

Figures 4.4 to 4.9 show the voltage oscillograms at each of the crossarm position

corresponding to each conductor as well as corresponding voltage across the insulator

strings of 275kV and 132kV circuits at tower 3. Voltages at red phase and blue phase at

circuits 275kV in Figure 4.4 and Figure 4.5 show the same voltage swing pattern. The

voltage of red phase rose about 4MV which is maximum voltage approximately 1.8µs

and maximum insulator string voltage at each phase is 2MV. Then, Figure 4.6 and

Figure 4.7 show the voltage at yellow phase circuit 275kV and red phase circuit 132kV.

As can be seen, the voltage rose sharply to 2.25MV which is maximum voltage

approximately 2.5µs and insulator string at each phase is swing between 0.1MV to -

0.1MV. Figure 4.8 and figure 4.9 show the same phase voltage pattern and insulator

voltage swing. As can be seen in Figure 4.8, the maximum blue phase voltage and

insulator string at circuit 132kV are 1.25MV at 4.4µs and 0.5MV at 9 µs. Figure 4.9

57

shows the maximum yellow phase voltage and insulator string is 1.5MV at 4.4µs and

0.4MV at 9 µs.

Figure 4.4 Voltage at red phase and insulator string tower 3 (275kV)

Figure 4.5 Voltage at blue phase and insulator string tower 3 (275kV)

58

Figure 4.6 Voltage at yellow phase and insulator string tower 3 (275kV)


59

Figure 4.8 Voltage at blue phase and insulator string tower 3(132kV)

Figure 4.9 Voltage at yellow phase and insulator string tower 3(132kV)

Figure 4.10 to Figure 4.15 show the voltage oscillograms at each crossarm for

tower 4. Figure 4.10 shows the maximum red phase voltage and insulator string at

circuit 275kV are 1.1MV at 4.4µs and 0.5MV at 9 µs. Then, Figure 4.11 and Figure 4.12

show the maximum voltage at blue and yellow phase, and insulator string at circuits

275kV have same voltage which is 1.2MV at 6µs for phase voltage and 0.1MV for

insulator string. Voltage at red phase at circuit 132kV is decreased by 0.3MV but still

show the same pattern voltage swing in Figure 4.13. Figure 4.14 shows the voltage at

blue phase and insulator string at circuit 132kV. The maximum phase voltage is 1.1MV

60

at 4.5µs and for insulator string is 0.4MV. This follows by Figure 4.15 which is the

maximum yellow phase voltage is 1.2MV at 6µs and insulator string is 0.1MV



61



62



Table 4.1 shows the tabulated data for the maximum voltage at each phase

voltage and insulator string at tower 3. Table 4.2 shows the tabulated data for maximum

voltage at each insulator string at tower 4. From Table 4.1 and Table 4.2, it can be seen

that the differential voltage between phase voltage and string insulator at tower 3 is

higher than tower 4. The configuration of surge arrester is shown in Figure 4.16 using L

arrangement of arrester. Based on critical flashover voltage, it shows that all surge

arresters at both towers which are tower 3 and tower 4 at circuit 132kV were affected by

the lightning strike.

63

Table 4.1 Voltage between each phase and insulator string at Tower 3

Tower 3 Phase

Voltage(MV)

Insulator

Voltage (MV)

Phase Voltage – String

Insulation Voltage (MV)

R phase (275kV) 4 2 2

B phase (275kV) 4 2 2

Y phase (275kV) 2.25 0.1 2.15

R phase (132kV) 2.25 0.1 2.15

B phase (132kV) 1.25 0.5 0.75

Y phase (132kV) 1.5 0.4 1.1

Table 4.2 Voltage between each phase and insulator string at Tower 4

Tower 4 Phase

Voltage(MV)

Insulator

Voltage (MV)

Phase Voltage – String

Insulation Voltage (MV)

R phase (275kV) 1.1 0.5 0.6

B phase (275kV) 1.2 0.1 1.1

Y phase (275kV) 1.2 0.1 1.1

R phase (132kV) 0.9 0.1 0.8

B phase (132kV) 1.1 0.4 0.7

Y phase (132kV) 1.2 0.05 1.15

64

- With surge arrester installation

- Without surge arrester installation

Figure 4.16 Lightning Surge Arrester Configuration L-Arrangement

4.3 Lightning Protection of Structures Study

4.3.1 Simple Structure Protection Result

The most common and simplest form of lightning protection is by using a

vertical rod which has the function of intercepting a lightning stroke before it can strike

a nearby object it is protecting, and then discharging the current to ground. In this

simulation study, 1500 strokes were a applied in square ground with an area of 1 km²

and number of flashes to ground per square kilometer per year, Ng = 15 strokes/

km²/year. Figure 4.17 shows the distribution of lightning flashes on a 1 km² ground area

with an Ng of 15 strikes/ km²/year over 100 year period.

65

Figure 4.17 Distribution of lightning flashes on a 1 km² ground area with an Ng of 15

strikes/ km²/year over 100 year period.

Figure 4.18 (a) and (b) show the distribution of lightning flashes on a 1 km²

ground area with an Ng of 15 strikes/ km²/year over 100 year period with lightning

strokes terminating on structure which is vertical rod with current 2.5kA, 10kA and

20kA. The striking distance is influenced by the lightning current. For this study, the

range of current is between 2.5-20kA. According to Figure 4.18 (c), the higher lightning

current will bring wider striking distance, it can be seen corresponding to 20kA current.

66

(a)

(b)

Figure 4.18 Display of lightning strokes terminating on vertical rod

67

(c)

Figure 4.18 Display of lightning strokes terminating on vertical rod (cont.)

Figure 4.19 to Figure 4.22 show the lightning strokes (represented by dots)

terminating on structure (vertical rod), and the surrounding ground-plan view with of

current 2.5, 5 and 10kA. It shows that the protection area is influenced by the current

magnitude which is lightning strike. A vertical rod is placed in the middle of a square

plot of ground of area of 1 and 1500 strokes were applied to the area under study.

In this study, the concepts of electromagnetic model which is “striking

distance”( are applied. Rolling sphere method was used for the determination of

protection radius (or target point) of lightning stokes. Here any point or surface on a

structure touch by rolling sphere whose radius equals striking distance is protected from

lightning strike. The analysis of the performance of any lightning shielding system is

complicated by the fact that the occurrence and nature of lightning is statistical and that

structures their surroundings are asymmetrical. Analysis on 3 dimensional system are

required. The radius of effective striking is calculated to determine the height of the rod

68

that can withstand from the lightning strike. is field of influenced of object where is

given by:

(4-1)

The protection area is influenced by the lightning stroke current and height of the

rod. Height (h) of rod above a flat roof or horizontal plane are considered to protect

points on that plane up to a horizontal distance r from a horizontal conductor or to

horizontal radius r from a vertical rod, where r is given by:

(4-2)

where r and h in meters

The lightning discharge current is defined by its shape and characteristic

parameters. Given the random nature of lightning, the parameters identifying each stroke

follow probabilistic laws which have to be considered in IEEE guidelines. The current

amplitude follows a probabilistic law given by the cumulative probability of exceeding

the amplitude I, . The probability current exceeding I(P(I)), where I is the stroke

current in kA is given by:

(4-3)

69

Figure 4.19 Vertical rod and its effective striking with current 2.5kA

Figure 4.20 Vertical rod and its effective striking with current 5kA

70



Table 4.3 shows lightning stroke (kA) with effective striking ( , height of rod

(h) and probability of lightning strikes (P). The protection area is influenced by the

71

lightning stroke current and height of the rod. The radius of effective striking is able to

determine the height of the rod that can with stand from the lightning strike.

Table 4.3 Lightning stroke (kA) with effective striking ( , height of rod (h) and

probability of lightning strike (P).

Lightning stroke (kA) Effective striking

(meter)

Height of rod (h)

(meter)

Probability of

lightning strike

2.5 15 2 0.9986

5 22 5 0.9914

10 36 18 0.9499

15 78 45 0.8685

Figure 4.23 and Figure 4.24 show the basic implementation of 3-dimensional of

the electrogeometric model of the lightning stroke on structures such as building that

required to be protected. In both cases, the field of influence of the ground plane is

represented by a horizontal plane at its effective striking distance (equation 2-9)

above the ground. The termination point of the lightning stroke is determined on the

basis that an object will be struck if its field of influence is met first by the leader tip on

its way to ground. Other strokes will terminate on the ground if they do not meet the

field of influence.

72

Figure 4.23 Field of influence of a rectangular block above ground which can be used

to represent a building structure or a patch of trees with current 2.5kA with 2

dimensional electrogeomatric model.

Figure 4.24 Field of influence of vertical cylinder can be used to represent a building

structure or a patch of trees with current 2.5kA (3 dimensional electrogeomatric model).

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CHAPTER 5

CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusion

The ATP-EMTP simulation study is supposed to show that the arrester at the

nearest point of strike is not effected rather the ones further down at the next tower.

This can also be explained from the travelling wave theory where at the exact location of

the strike, the current splits into 2 (I/2). As it travels to the next tower, the traveling

surge induced coupled voltage, which is a fraction of the traveling voltage. As a result,

the total stress is higher at the adjacent towers compared to the exact location. In the

incident sited, when lightning stroke the earth wire, the wire snapped and fell. Both

portions then broke again due to high current and caused the breakage of the conductor

at four portions. Based on the result obtained, all surge arrester at both tower (tower 3

and tower 4) were affected by the lightning strike. From the simulation results,

differential voltage between the phase conductor and the crossarm at the insulator string

for each phase shows that the adjacent tower which is tower 4, has less differential

voltage than nearest tower (tower 3). Therefore, the simulation results show that the

74

phenomenon cannot be conclusively reproduced within the ATP-EMTP simulation. This

may indicate that the phenomenon may be a one-off special case event.

A study which focus on many factors such as circuit outage, flashover and

backflashover, insulation failure and shielding failure has been done. The ATP-EMTP

simulation program has been used to carry out the study and the results explain the

phenomenon from theoretical and practical points of view. For transmission line

modeling, the configuration of the overhead line must be known such as number,

location and spacing between conductors. Besides that, skin effect and other properties

may also be considered in the model. The configuration of the tower structure such as

height and radius must be known. The phenomenon which may include the travelling

wave effect (reflection etc) has been studied to prove that when a lightning strikes, the

arrester at the nearest to the point of strike is not effected rather the one further down at

the next tower.

Monte Carlo concept has been used to estimate the probability of lightning

strikes and lightning protection of simple structures. The most common and simplest

form of lightning protection is by the use of a vertical rod which has the function of

intercepting a lightning stroke before it can strike a nearby object it is protecting, and

then discharging the current to ground. The analytic method used is based on a 3-

dimensional implementation of the electrogeometric model. The protection area is

influenced by the lightning stroke current and height of the rod. The radius of effective

striking is able determine the height of the rod that can withstand the lightning strike.

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5.2 Recommendation

Based on the simulation study on 275/132kV quadruple transmission line, below are two

computer softwares are suitable to be used in future study :

Sigma slp is PC Windows based software, which has been specially developed to

enable quick and easy determination of transmission line lightning performance.

This software provide an alternative way to bring the precise result on

275/132kV quadruple circuit transmission line in term of to prove that the surge

arrester location of the affected arrester was not at the nearest tower to the point

of strike but affected at the adjacent tower. The arresters at the nearest tower

were not affected.

A computer program MFASP (Multiple Flashover Across Same Phase in

Different Towers) is developed by [18] which is able to simulate the multiple

flashovers across all phases including on the same phase in different towers.

In protection of simple structure a computer program for the evaluation of the

lightning performance to protect structure such as shielding lines, transmission lines,

buildings and tree patches from lightning stroke is recommended to be built. The

analytic method used is based on a 3-dimensional implementation of the

electrogeometric model. Monte-Carlo technique also can be done using C language to

manipulate the statistical distribution of the lightning stroke.

76

REFERENCES

[1] Iryani Mohamed Rawi, “Tripping report- Post mortem study on the root cause of

earth wire failure between T70-T71 and TLA(gapless type) at T68 &T69 for

132kV BLKG-SRDG line”, Engineering Department (Lines and cable)TNB

Transmission Division, 2007

[2] Y.A Wahab, Z.Z Abidin and S.Sadovic, “Line Surge Arrester Application on the

Quadruple Circuit Transmission Line”, IEEE Bologna Power Tect Conference,

June 23, 2003.

[3] C.A.Nucci and F.Rachidi, “ Lightning Induced Voltage”, IEEE Transmission and

Distribution Conference, April 14 , 1999.

[4] M. T. Correia de Barros, J. Festas, H. Milheiras, N. Felizardo (IST - Universidade

Técnica deLisboa / Instituto da Energia - INTERG), M. Fernandes (REN - Rede

Eléctrica Nacional), “Methodologies for evaluating the lightning performance of

transmission lines”

[5] Masaru Ishii, Tatsuo Kawamura, Teruya Kouno, Eiichi Ohsaki, Kazuyuki

Shiokawa Kaneyoshi Murotani and Takemitsu Higuchi, “Multistory transmission

Tower Model For Lightning Surge Analysis”, IEEE Transactions on Power

Delivery ,Vol. 6, No. 3, July 1991

77

[6] M S Naidu, V Kamaraju, “ High Voltage Engineering” , Third Edition, New

Delhi : Tata Mcgraw-Hill, 2004

[7] Siti Rugayah Binti Dugel, “Insulation Coordination of Quadruple Circuit High

Voltage Transmission Line using ATP-EMTP”,Universiti Teknologi Malaysia,

2007.

[8] J. A. Martinez, and F. Castro-Aranda, “Lightning Performance Analysis of

Transmission Lines Using the EMTP”, IEEE Transmission,2003

[9] T. Hara and 0. Yamamoto, “Modelling of a transmission tower for lightning surge

analysis, IEE Proc.-Cener. Transm. Distrib., Vol. 143, No. 3, May 1996

[10] James T. Whitehead (Chairman 1985-1989) and William A. Chisholm (Chairman

1989-1992), John G. Anderson, Roger Clayton, Hamid Elahi, Andrew J. Eriksson,

Stanislaw Grzybowski, Andrew R. Hileman, Wasyl Janischewskyj, Vito J. Longo,

Charles H. Moser, Abdul M. Mousa, Richard E. Orville, Dee E. Parrish, Farouk

A.M. Rizk, Joseph R. Renowden, “IEEE Working Group Report Estimating

Lightning Performance of Tkansmission Lines I1 - Updates to Analytical Models”,

IEEE Transactions on Power Delivery, Vol. 8, No. 3, July 1993

[11] Gustavo Carrasco H and Alessandro Villa R, “Lightning Performance of

Transmission Line Las Claritas – Santa Elena Up 230 kV,” International

Conference on Power Systems Transients – IPST 2003 in New Orleans, USA

[12] Haifeng Li, Gang Wang and Zhiwei Liao, “Distinguish Between Lightning

Stroke and Fault Using Wavelet – Multiresolution Signal Decomposition”, IEE,

Michael Faraday House, Six Hills Way, Stevenage, SGI 2AY, 2004

78

[13] Toshiaki Ueda, Takamitsu Ito, Hideto Watanabe, Toshihisa Funabashi and Akihiro

Ametani, “A Comparison between Two Tower Models for Lightning Surge

Analysis of 77kV System”, IEEE Transaction, 2000.

[14] M. Kizilcay, C. Neumann, “Backflashover Analysis for 110-kV Lines at Multi-

Circuit Overhead Line Towers, “Presented at the International Conference on

Power Systems Transients (IPST’07) in Lyon, France on June 4-7, 2007

[15] P. Yadee and S. Premrudeepreechacharn, “Analysis of Tower Footing Resistance

Effected Back Flashover Across Insulator in a Transmission System”, Presented at

the International Conference on Power Systems Transients (IPST’07) in Lyon,

France on June 4-7, 2007

[16] ATPDRAW version 3.5for Windows 9x/NT/2000/XP. Users' Manual

[17] A.C.Liew, C.M.Gui and Sr. M. I, “Performance Assessment of Lightning

Shielding Systems”,1990

[18] A.C.Liew and J.P.Wang, “Multiple Flashovers Across Same Phase In Different

Towers”,1996

[19] T. Yamada, A. Mochizuki, J. Sawada, E. Zaima T. Kawamura A. Ametani M.

Ishii S. Kato Markus Junker, Thomas Schneider, Max J. Ammanno, Andreas T.

Schwarzbacher, and Kai-Uwe Lauterbach, “Experiment Evaluation Of A UHV

Tower Model For Surge Analysis” IEEE Transactions on Power Delivery, Vol.

10, No. 1, January 1995

80

APPENDIX A

1) 275/132kV Transmission line and Transmission Tower Model - EMTP

2) Matlab Simulation of lightning strokes represented by dots) terminating on

structure (vertical rod), and surrounding ground-plan view with current

3) Matlab Simulation of lightning strokes represented by dots) terminating on

tructure (vertical rod

4) Matlab Simulation of field of influence of vertical cylinder can be used

to represent a building structure

1) 275/132kV Transmission line and Transmission Tower Model – EMTP

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Tower 5 Tower 4 Tower 3 Tower 2 Tower 1

2) Matlab Simulation of lightning strokes (represented by dots) terminating on

structure (vertical rod), and surrounding ground-plan view with current

data=1500; %random lightning stike r4=0.2; r5=0.2; a=0.4; % coordinate x b=0.5;% coordinate y c=0.6; % coordinate x d=0.5;% coordinate y %start simulation x=rand(data,1); y=rand(data,1); [lat,lon] = SCIRCLE1(a,b,r4); [p,t] = SCIRCLE1(c,d,r5); s=size(lat) %data for circle s=size(p)

82

for h=1:s for k=1:data; if x(k)>=c&y(k)>=d if x(k)<=p(h)& y(k)<=t(h) x(k)=c; y(k)=d; end end if x(k)<=c&y(k)>=d if x(k)>=p(h)& y(k)<=t(h) x(k)=c; y(k)=d; end end if x(k)<=c&y(k)<=d if x(k)>=p(h)& y(k)>=t(h) x(k)=c; y(k)=d; end end if x(k)>=c&y(k)<=d if x(k)<=p(h)& y(k)>=t(h) x(k)=c; y(k)=d; end end end end for i=1:s for j=1:data; if x(j)>=a&y(j)>=b if x(j)<lat(i)& y(j)<=lon(i) x(j)=a; y(j)=b; end end

83

if x(j)<=a&y(j)>=b if x(j)>=lat(i)& y(j)<=lon(i) x(j)=a; y(j)=b; end end if x(j)<=a&y(j)<=b if x(j)>=lat(i)& y(j)>=lon(i) x(j)=a; y(j)=b; end end if x(j)>=a&y(j)<=b if x(j)<=lat(i)& y(j)>=lon(i) x(j)=a; y(j)=b; end end end end scatter(x,y,2) plot(p,t,'r') hold scatter(x,y,2) plot(lat,lon,'r')

3) Matlab Simulation of lightning strokes (represented by dots) terminating on

structure (vertical rod) and surrounding ground-plan view with current

84

r=0.1 [X,Y,Z] = cylinder(r); X=X+0.5; Y=Y+0.5; h=1.0;%high of rod h=h-1; z=Z+h; z(1,:)=z(1,:)-h; surf(X,Y,z) hold r2=0.005 [X,Y,Z] = cylinder(r2); X=X+0.6; Y=Y+0.5; Z=Z+1.0; h=0.5;%high of rod h=h-1; z=Z+h; z(1,:)=z(1,:)-h surf(X,Y,z) r3=0.005 [X,Y,Z] = cylinder(r3); X=X+0.4; Y=Y+0.5; Z=Z+1.0; h=0.5;%high of rod h=h-1; z=Z+h; z(1,:)=z(1,:)-h surf(X,Y,z) r4=0.1000005 [X,Y,Z] = cylinder(r4); X=X+0.5; Z=Z+0.5; Y=Y+0.5;

85

h=0.1;%high of rod h=h-1; z=Z+h; z(1,:)=z(1,:)-h surf(X,Y,z) r=0.2; %radius data=1500; %random lightning strike a=0.4; % coordinate x b=0.5;% coordinate y c=0.6; % coordinate x d=0.5;% coordinate y %start simulation x=rand(data,1); y=rand(data,1); [lat,lon] = SCIRCLE1(a,b,r); s=size(lat) %data for circle for i=1:s; for j=1:data; if x(j)>=a&y(j)>=b if x(j)<=lat(i)& y(j)<=lon(i) x(j)=a; y(j)=b; end end if x(j)<=a&y(j)>=b if x(j)>=lat(i)& y(j)<=lon(i) x(j)=a; y(j)=b; end end if x(j)<=a&y(j)<=b if x(j)>=lat(i)& y(j)>=lon(i) x(j)=a; y(j)=b; end end if x(j)>=a&y(j)<=b if x(j)<=lat(i)& y(j)>=lon(i)

86

x(j)=a; y(j)=b; end end end end scatter(x,y,2) plot(lat,lon,'r') Rod r=0.005 [X,Y,Z] = cylinder(r); X=X+0.5; Y=Y+0.5; h=50;%high of rod h=h-1; z=Z+h; z(1,:)=z(1,:)-h surf(X,Y,z) hold r=47/100; %radius data=1500; %random lightning stike a=0.5; % coordinate x b=0.5;% coordinate y %start simulation x=rand(data,1); y=rand(data,1); [lat,lon] = SCIRCLE1(a,b,r); s=size(lat) %data for circle for i=1:s; for j=1:data; if x(j)>=a&y(j)>=b if x(j)<=lat(i)& y(j)<=lon(i) x(j)=a; y(j)=b;

87

end end if x(j)<=a&y(j)>=b if x(j)>=lat(i)& y(j)<=lon(i) x(j)=a; y(j)=b; end end if x(j)<=a&y(j)<=b if x(j)>=lat(i)& y(j)>=lon(i) x(j)=a; y(j)=b; end end if x(j)>=a&y(j)<=b if x(j)<=lat(i)& y(j)>=lon(i) x(j)=a; y(j)=b; end end end end scatter(x,y,2) plot(lat,lon,'r')

5) Matlab Simulation of lightning strokes (represented by dots) terminating on structure (vertical rod)

r=0.1 [X,Y,Z] = cylinder(r); X=X+0.5; Y=Y+0.5;

88

h=1.0;%high of rod h=h-1; z=Z+h; z(1,:)=z(1,:)-h; surf(X,Y,z) hold r2=0.005 [X,Y,Z] = cylinder(r2); X=X+0.6; Y=Y+0.5; Z=Z+1.0; h=0.5;%high of rod h=h-1; z=Z+h; z(1,:)=z(1,:)-h surf(X,Y,z) r3=0.005 [X,Y,Z] = cylinder(r3); X=X+0.4; Y=Y+0.5; Z=Z+1.0; h=0.5;%high of rod h=h-1; z=Z+h; z(1,:)=z(1,:)-h surf(X,Y,z) r4=0.1000005 [X,Y,Z] = cylinder(r4); X=X+0.5; Z=Z+0.5; Y=Y+0.5; h=0.1;%high of rod h=h-1; z=Z+h; z(1,:)=z(1,:)-h surf(X,Y,z)

89

hold data=1500; %random lightning stike r=0.2, r=0.2; a=0.4; % coordinate x b=0.2;% coordinate y c=0.6; % coordinate x d=0.7;% coordinate y %start simulation x=rand(data,1); y=rand(data,1); [lat,lon] = SCIRCLE1(a,b,r1); [p,t] = SCIRCLE1(c,d,r2); s=size(lat) %data for circle s=size(p) for h=1:s for k=1:data; if x(k)>=c&y(k)>=d if x(k)<=p(h)& y(k)<=t(h) x(k)=c; y(k)=d; end end if x(k)<=c&y(k)>=d if x(k)>=p(h)& y(k)<=t(h) x(k)=c; y(k)=d; end end if x(k)<=c&y(k)<=d if x(k)>=p(h)& y(k)>=t(h) x(k)=c; y(k)=d; end end

90

if x(k)>=c&y(k)<=d if x(k)<=p(h)& y(k)>=t(h) x(k)=c; y(k)=d; end end end end for i=1:s for j=1:data; if x(j)>=a&y(j)>=b if x(j)<=lat(i)& y(j)<=lon(i) x(j)=a; y(j)=b; end end if x(j)<=a&y(j)>=b if x(j)>=lat(i)& y(j)<=lon(i) x(j)=a; y(j)=b; end end if x(j)<=a&y(j)<=b if x(j)>=lat(i)& y(j)>=lon(i) x(j)=a; y(j)=b; end end if x(j)>=a&y(j)<=b if x(j)<=lat(i)& y(j)>=lon(i) x(j)=a; y(j)=b; end end end end scatter(x,y,2) plot(p,t,'r')

91

hold scatter(x,y,2) plot(lat,lon,'r')

penjelasanatp

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275132kv transmission

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