1477 noremyliahbintihusin2011

SIMULATION STUDY ON LIGHTNING EFFECTS TO 132 kV

UNDERGROUND CABLE

NOR EMYLIAH BINTI HUSIN

UNIVERSITI TEKNOLOGI MALAYSIA

PSZ l9:16 Pind. l /07

NOIES : * lf fhe thesis is CONFIDENTIAL or RESTRICTED, pleose oftoch with the letler fromthe orgonisotion wifh period ond reosons for confidentiolity or restdction.

UNIVERSITI TEKNOTOGI MATAYSIA

DECLARAIION OF THESIS / UNDERGRADUATE PROJECT PAPER AND COPYHGHT

Author's fullnome : NOR EMYLIAH BINTI HUSIN

Dote of birth : 9 JANUARY 1988

Title : ShiUtAllON SIUDY ON LIGHTNING EFFECIS IO 132 kV

UNDERGROUND CABI.E

AcodemicSession: Zlt0/2011

I declore thot this thesis is clossified os:

E coNFrDENTrAr.

i] RESTRTcTED

I .1 | oPEN AccEss

Contoins confidentiql informotion under the Otficiol SecretAct 19721*

Contoins restricled informotion os specified by theorgonisolion where reseorch wos done)'

I ogree thof my lhesis to be published os online open occess

Dote: z$trftlAY20ll

fulltexf)

I ocknowledged thot UnivenitiTeknologi Moloysio reserves the right os follows:

'1. The thesis is the properly of UniversitiTeknologi Moloysio.2. The Librory of Univenili Teknologi Molopio hos the right fo moke copies for the purpose

of reseorch only.3. The Librory hos lhe righl to moke copies of the thesis forocodemic

SGNATURE OF

ASITOC PROF DR(NEW rC NO. /PASSPORT NO.)

Dote: 20ilt l,tAY 2ol l

'2wr'' -*)Wa '

NAI,IE OF SUPERVISOR

"I hereby declare that I have read this thesis and in my opinion

this thesis is sufficient in terms of quality and scope

for the award ofthe degree of

Bachelor of Engineering @lectical) "

Name of Supervisor : Assoc. Prof. Dr. Zu B. AMul Malek

: 20fr lvtav 2011

SIMULATION STUDY ON LIGHTNING EFFECTS TO 132 kV

UNDERGROUND CABLE

NOR EMYLIAH BINTI HUSIN

A thesis submitted in partial fulfillment of the

requirements for the award of the degree of

Bachelor of Engineering (Electrical)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

MAY 2011

I declare that this report entitled "Simulation Study On Lighning Efects to 132kY

Underground Cable" is the result of my own research except as cited in the

references. The report has not been accepted'for any degree and is not concurrently

submitted in candidature of any other degree.

Name : Nor Emyliatr Binti Husin

Date :20trMaY2011

To my Beloved

Father,

Husin Bin Sa’adon

Mother,

Majenah Binte Omar

Sisters,

All my friends and relatives,

All my teachers and lecturers,

For Their

Love, Encouragement, Support, Motivation, Sacrifice and Best Wishes

ii

ACKNOWLEDGEMENT

First and foremost, I am greatly thankful to Allah SWT for giving me the

opportunity to finish my Final Year Project successfully. I would like to express my

gratitude to my supervisor, Assoc. Prof. Dr. Zulkurnain B. Abdul Malek for giving

his valuable time, advice and continuous encouragement towards the completion of

my project from beginning till the end.

Secondly, I wish to convey my appreciation to my family, who has been so

tolerant and supporting me. Thanks for their encouragement, love, and emotional

support that they had given to me.

I also would like to extend my appreciation to all my friends who were there

for me and giving me advices and motivations, regardless of their busy schedules.

Finally, I would like to thank those involved directly and indirectly in completion of

my project. Their kindness and helpfulness are much appreciated.

Thank You So Much.

iii

ABSTRACT

Underground cable is commonly used in situation where power need to be

transmitted across river or sea or through heavily populated areas. Even though

underground cables are not directly exposed to hazard, lightning can induce a

potential on the insulation of the underground cable. About 80% of the lightning

strikes in Malaysia produce current in excess of 20 kA. This study was done to

determine the possibility of having insulation breakdown of the underground cable

either by direct stroke or by induction. The simulation was performed using

Alternative Transient Program version of the Electromagnetic Transients Program

(ATP-EMTP) software to determine whether the induced voltage due to lightning

can cause any insulation breakdown. A network system consisting of 132 kV

Cu/XLPE/SCW/MDPE underground cable with a span of 150 meters was modeled.

A 40 kA lightning current with 1/50 µs characteristic has been injected into the

system. Several models to represent the whole system in electronic circuit have been

designed and analyzed. The study showed that for the varied parameters, there is no

event severe enough to commence any insulation puncture in the underground cable

system.

iv

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

TABLE OF CONTENTS vi

LIST OF FIGURES viii

LIST OF TABLES x

LIST OF SYMBOLS xi

1 INTRODUCTION

1.1 Background Study 1

1.2 Objectives 2

1.3 Problem Formulation 2

1.4 Scope of Project 3

2 LITERATURE REVIEW

2.1 Introduction 4

2.2 Standard Lightning Wave Shape 5

2.3 Underground Cable Parameters 6

3 METHODOLOGY

3.1 Introduction 9

3.2 Digital Simulation Program 10

3.2.1 Operating Windows 10

3.2.2 ATP Setting 11

3.2.3 Data Setting 12

v

3.2.4 PlotXY 12

3.3 System Configuration 12

3.3.1 Lightning Source 14

3.3.2 Soil Model 16

3.3.3 Underground Cable Model 17

3.4 System Data 17

3.5 Observation Profile 19

4 RESULTS AND DISCUSSIONS

4.1 Introduction 21

4.2 Circuit Model Representation For The System 22

4.2.1 Sheath and Armour Represented 22

By Resistor


By an Inductor


By Resistor and Inductor in Series

4.3 Induced Voltage On Different XLPE Insulation 38

Cross-Sectional Layers

4.4 Induced Voltage Across Cable Insulation At 41

Different Distance From Strike Point

4.5 Induced Voltage On Cable Insulation At 43

Various Depths From Strike Point

4.6 Discussions 45

5 CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions 46

5.2 Recommendations 47

REFERENCES 48

vi

LIST OF FIGURES

FIGURE NO TITLE PAGE

2.1 Lightning impulse wave shape 5

2.1 Underground cable circuit model 8

3.1 Dialog box for ATP settings 11

3.2 132 kV cable dimensions layer 13

3.3 Cable layout configuration network 14

3.4 The Heidler type source 14

3.5 Dialog box for Heidler source 15

3.6 Lightning wave shape injected into the system 16

3.7 Soil model circuit representation 16

3.8 Underground cable model representation 17

3.9 Observation profile for different insulation level 20

4.1 Circuit model for the system when R2 = 100 Ω 22

4.1 (a) Voltage induced at V1 when R2 = 100 Ω 23

4.1 (b) Voltage induced at V2 when R2 = 100 Ω 23

4.1 (c) Voltage induced at V3 when R2 = 100 Ω 23

4.1 (d) Voltage induced at V4 when R2 = 100 Ω 24

4.2 Circuit model for the system when R2 = 10 kΩ 24

4.2 (a) Voltage induced at V1 when R2 = 10 kΩ 25

4.2 (b) Voltage induced at V2 when R2 = 10 kΩ 25

4.2 (c) Voltage induced at V3 when R2 = 10 kΩ 25

4.2 (d) Voltage induced at V4 when R2 = 10 kΩ 26

4.3 Circuit model for the system when L = 1 mH 27

4.3 (a) Voltage induced at V1 when L = 1 mH 27

4.3 (b) Voltage induced at V2 when L = 1 mH 28

4.3 (c) Voltage induced at V3 when L = 1 mH 28

vii

4.3 (d) Voltage induced at V4 when L = 1 mH 28

4.4 Circuit model for the system when L = 100 mH 29

4.4 (a) Voltage induced at V1 when L = 100 mH 29

4.4 (b) Voltage induced at V2 when L = 100 mH 30

4.4 (c) Voltage induced at V3 when L = 100 mH 30

4.4 (d) Voltage induced at V4 when L = 100 mH 30

4.5 Circuit model for the system when R2 = 1 kΩ and L = 1 mH 32

4.5 (a) Voltage induced at V1 when R2 = 1 kΩ and L = 1 mH 32

4.5 (b) Voltage induced at V2 when R2 = 1 kΩ and L = 1 mH 32

4.5 (c) Voltage induced at V3 when R2 = 1 kΩ and L = 1 mH 33

4.5 (d) Voltage induced at V4 when R2 = 1 kΩ and L = 1 mH 33











4.8 Induced voltage across the outer cable insulation 38

4.9 Induced voltage across the inner cable insulation 39

4.10 Induced voltage at the outer cable insulation (CDEGS) 39

4.11 Induced voltage at the inner cable insulation (CDEGS) 40

4.12 Induced voltage near from the strike point 41

4.13 Induced voltage far from strike point 41

4.14 Induced voltage near from the strike point (CDEGS) 42

4.15 Induced voltage far from the strike point (CDEGS) 42

4.16 Induced voltage near the earth surface 43

4.17 Induced voltage when the cable buried deeper 43

4.18 induced voltage near the earth surface (CDEGS) 44

4.19 Induced voltage when the cable buried deeper (CDEGS) 44

viii

LIST OF TABLES

TABLE NO TITLE PAGE

3.1 Air and soil characteristics 18

3.2 Dimensions and properties of intermediate 18

conductor components

3.3 Thickness and properties of intermediate 18

component’s insulation

3.4 Parameters data 19

4.1 Maximum voltage induced for different values of R2 26

4.2 Maximum voltage induced for different values of L 31

4.3 Maximum voltage induced for different values of R2 and L 37

4.4 Maximum voltage induced for different observation 40

profile from different software

ix

LIST OF SYMBOLS

ρs - Soil resistivity

c - Speed of light

εo - Permittivity of vacuum

εr - Relative permittivity

Ω - Ohm

kΩ - Kilo-Ohm

TΩ - Tera-Ohm

A - Ampere

kA - Kilo-Ampere

V - Volts

kV - Kilo-volts

m - Meter

km - Kilometer

H - Henries

mH - Mili-Henries

p.u - Per unit

µ - Micro

F - Farad

pF - Pico-Farad

µF - Micro-Farad

r - Radius

t - Time

s - Second

µs - Micro-second

I - Current

CHAPTER 1

INTRODUCTION

1.1 Background Study

Underground or submarine cables are used to transmit power across crowded

areas or body of water such as river or sea. For some cases, it is impossible to

accommodate for distribution using the overhead line system approach and as an

option the underground cable become necessary to replace the overhead line system

for transmission and distribution.

Lightning is the transient discharge of a static electricity generated in parts,

cells of storm clouds. Even though underground cables are not directly exposed to

natural hazard such as lightning, it is such a way that lightning can induce current

and voltage into the cable. The effects of electric fields due to direct lightning strikes

on ground to underground cable need to be considered.

2

1.2 Objectives

The objectives of this study are as follows:

1. To design and model circuit that represent soil and underground cable to run

the simulation using Alternative Transient Program version of

Electromagnetic Transient Program (ATP-EMTP);

2. To investigate the effects of lightning strike to ground on underground cable

system over various condition due to its current and induced voltage;

3. To verify any possibility of having insulation breakdown or damage due to

lightning induced voltage and current;

4. To compare the analysis (ATP-EMTP) with the previous research (CDEGS).

1.3 Problem Formulation

The analysis was carried out on a 132kV Cu/XLPE/SCW/MDPE

underground cable having a span of 150 meters. The single phase circuit has its

sheath grounded with both-end-bonding method. Along the cable span, two straight

through joints were installed.

There are undoubtedly many possible factors that can cause failure to the

system but this analysis particularly intended to prove that lightning currents and its

induced voltages are the main reasons for the recently observed and reported

insulation failure.

3

1.4 Scope of Project

This project emphasizes on the voltage induced when 40kA lightning current

injected into the aforesaid system designed. The 132kV rated underground cable

system was modeled by taking into consideration all parameters involve. The

analysis will be based on voltage induced due to lightning strike on ground for the

determination of any possibility that can cause insulation failure or breakdown to the

underground cable.

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

Overvoltage is a condition where the voltage raised higher than it’s rated. A

transient overvoltage is a high voltage which has a rapid rise to the peak value and

slowly decays to zero value [1]. Transient overvoltage can cause breakdown of

insulation.

A typical natural source of transient overvoltage events is lightning.

Lightning is natural phenomena that accomplished by thunder which is very intense

and unpredictable that can induce overvoltage. The current diffusion in the ground

may also affect underground networks.

When lightning strikes the ground, the discharge current diffuses uniformly

into the surrounding soil. The electric field strength in soils at a radius of r meters is

given by the following equation, by determining of lightning current distributed in

radius around lightning strike point in hemisphere [2, 3].

5

2

( ) ( )2

s sI

E r J rr

(2.1)

ρs soil resistivity (Ωm)

J(r) current density at radius r (A/m2)

I lightning current amplitude (A)

2.2 Standard Lightning Wave Shape

The Basic Lightning Impulse Insulation Level (BIL) are specified for the

standard lightning impulse wave shape. The general lightning impulse wave shape is

illustrated in Figure 2.1 below.

Figure 2.1: Lightning impulse wave shape

tf

tt

6

BIL implies the limits up to which the insulator could withstand impulse due

to lightning stoke. The front time and the tail time of the impulse is represented by tf

and tt respectively. Front time is the interval between t=0 to the peak voltage or

current. While tail time is the interval between t=0 to where the function amplitude

has fallen 50% of its peak value. The standard lightning impulse wave shape is 1/50

µs which means 1µs for the front time and 50 µs for the tail time.

2.3 Underground Cable Parameters

The line equations are the same for underground or submarine cables and

overhead lines because the parameters R’, L’, G’, C’ per unit length are distributed

along a cable in the same way as on an overhead lines.

'( ) '( )dV

R j L Idx

(2.2)

'( ) 'dI

G j C Vdx

(2.3)

Overhead lines are simple in geometry. There are more variations in

underground and submarine cable geometries. Shunt conductance G’ is negligible

on overhead lines but in underground cable it is much larger and represents dielectric

losses [4].

' tan . 'G C (2.4)

7

The shunt capacitanc C’ is much larger than on overhead lines because the

conductors (core conductor, sheath etc) are very close together. The value for

inductance L’ is small which typically

of L’overhead. While the value for C’ is large

which typically 20 times of C’overhead. The parameter L’ and C’ can be converted to

surge impedance Z and wave speed c by the following equation [4].

'

'

LZ

C

(2.5)

1

' 'c

L C

(2.6)

Give typical values for underground cable

Z 30 to 70 Ω (

of overhead line)

c 160 000 km/s (

of overhead line)

The shunt capacitance for insulation between core conductor and sheath, or

sheath and amour, or sheath and soil can be calculated using equation (2.7).

2'

ln

o r

out

in

Cr

r

(2.7)

εo permittivity of vacuum

εr relative permittivity

rout outside radius of insulation

rin inside radius of insulation

8

Since C’ of an underground cable is very large, it may be good enough to

represent a “short” cable as a lumped capacitance, if the frequencies are not high.

Figure 2.2: Underground cable circuit model

Zseries

½ Yshunt ½ Yshunt

CHAPTER 3

METHODOLOGY

3.1 Introduction

With the support of many computer simulations software package, analysis of

the transient overvoltage becomes more accurate, efficient and easy. Transient

overvoltage studies on underground cable due to lightning strike are very important

to determine any possibility of having insulation failure or breakdown. The selection

of suitable simulation software according to the supporting modal and analysis of the

project will facilitate the work for designing the model, running the simulation and

analysis of the result.

Running and executing this simulation only take small amount of time but

deciding on the parameters of the components and circuit models representation for

source, cable and soil are the actual challenge when performing the analysis. The

correct and accurate model design is essential to ensure reliability of the analysis.

The parameters setting for models used in the simulation are very important since the

simulation result depends on the data and circuit model.

10

3.2 Digital Simulation Program

The Alternative Transient Program (ATP) and Electromagnetic Transient

Program (EMTP) are one of the most widely used software by electric power

industry for digital simulation of electrical system transient phenomena of

electromagnetic as well as electromechanical nature in electric power systems. ATP

program is a powerful tool for modeling power system transients [5].

The Alternative Transient Program version of the Electromagnetic Transients

Program (ATP-EMTP) is an integrated engineering software tools that have been

used world-wide for switching and lightning surge analysis, insulation coordination

studies and etc.

ATPDraw is a graphical preprocessor to the ATP version of the EMTP.

ATPDraw has a standard Windows layout and offers a large Windows help file

system. User can build up the electric circuit in the program by selecting predefined

components from an extensive palette.

3.2.1 Operating Windows

Circuit window is the container of circuit objects and the circuit is built up in

this window. User can load the circuit objects from disk or simply create an empty

window to start building a new circuit from file menu.

11

3.2.2 ATP Setting

Before user run the simulation, several option for the active circuit window

must be specified. Figure 3.1 shows an example of dialog box for the simulation

setting. Under simulation type user can switch between Time domain, Frequency

scan and Harmonic frequency scan (HFS). Tmax is the end time of simulation in

seconds and delta T is the time step of simulation in seconds [5].

Figure 3.1: Dialog box for ATP settings

12

3.2.3 Data Setting

After selecting a component user must specify the value for all parameters

used in the simulation. The component dialog box will pop out after double click on

that component and user must keying in the required data in the columns provided.

3.2.4 PlotXY

PlotXY is a plotting program to generate scientific line plots using data

collected from *.pl4 files created with the program ATP. A *.pl4 file will be

automatically created after user has run the simulation [5].

3.3 System Configuration

The system consists of a 132kV Cu/XLPE/SCW/MDPE rated cable with a

length of 150 meters buried underground at a depth of 1.5 meters. The cable

dimensions are illustrated in the Figure 3.2 below [6].

13

Figure 3.2: 132kV cable dimensions layer

To enable the injection process and to allow the injected current to penetrate

into the soil accordingly, a steel conductor that acts as a conductor with a length of

0.5 meter and diameter of 0.01 meter is added into the system with half of its length

buried in the ground. Figure 3.3 illustrate the cable layout configuration network in

the system into the Cartesian plane [6].

14

Figure 3.3: Cable layout configuration network

3.3.1 Lightning Source

The lightning stokes represent by surge function of Heidler type 15 forms.

The type of source can be set to be either current or voltage. Amp is the

multiplicative number in Ampere or Volt and it does not represent peak value of the

surge. T_f is the front duration time in seconds which is the interval between t=0 to

the function peak. The stroke duration which is the interval between t=0 to the point

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

represented by tau in seconds. Tsta is the starting time in seconds, Tsto is the ending

time also in seconds and n is the factor influencing the rate of rise of the function.

The maximum steepness will be increased if the value of n increase.

Figure 3.4: The Heidler type source

15

Figure 3.5: Dialog box for Heidler source

The lightning surge current used in this study is defined by the following

double exponential type function:

( ) ( )mI t I e e (3.1)

where Im = 40 kA, α = 1.4x104 s

-1 and β = 6x10

6 s

-1. The lightning surge waveform is

characterized by a rise time of 1 μs and a half-value time of 50 μs, which are typical

values for lightning strikes. The lightning surge current wave shape as shown in

Figure 3.6 below is injected at the ground above the cable [6].

16

Figure 3.6: Lightning wave shape injected into the system

3.3.2 Soil Model

Besides soil resistivity, the electric breakdown strength of soil was one of the

important value to consider. Dielectric strength of soils is considered as the value of

the electric field intensity, which causes breakdown under homogeneous field

configuration. Figure 3.7 shows the soil model representation used for this

simulation.

Figure 3.7: Soil model circuit representation

(f ile heidler.pl4; x-v ar t) c:XX0001-XX0004

0.0 0.2 0.4 0.6 0.8 1.0[ms]

0

5

10

15

20

25

30

35

40

[kA]

C1 and R1 - Soil

17

3.3.3 Underground Cable Model

From the previous chapter many parameters need to be considering in

modeling the underground cable circuit. Figure 3.8 shows the underground cable

model distribution in this analysis.

Figure 3.8: Underground cable model circuit representation

3.4 System Data

The characteristics of air and soil used in the analysis are shown in Table 3.1.

For the purpose of simplifying the computation, a uniform soil type was chosen. The

permeability and permittivity are relative to the free space values of 1.2566x10-6

Henries/meter and 8.854x10-12

Farads/meter, respectively.

C2 - Coating

C3 – Insulation (outer)

C4 – Insulation (inner)

L and R2 – Armour and Sheath

18

Table 3.1: Air and soil characteristics

Layer Resistivity (Ωm) Relative

Permeability (p.u)

Relative

Permittivity (p.u)

Air 1x1018

1.0 1.0

Soil 328 10.0 25.0

The dimensions and properties of the intermediate components are specified

as in Table 3.2. The thickness and properties of intermediate component’s insulation

are specified as in Table 3.3.

Table 3.2: Dimensions and properties of intermediate conductor components

Components Inner Radius

(m)

Outer Radius

(m)

Relative

Resistivity

(p.u)

Relative

Permeability

(p.u)

Core 0 0.01025 1 1

Sheath 0.02625 0.02855 1.635636 1.000022

Amour 0.04055 0.04395 30.160664 696.323412

Table 3.3: Thickness and properties of intermediate component’s insulation

Components Thickness

(m)

Resistivity

(Ω)

Relative

Permittivity

(p.u)

Relative

Permeability

(p.u)

Core 0.016 8.98x1013

2.35 1.000023

Sheath 0.012 8.98x1013

2.35 1.000023

Amour 0 8.98x1013

2.35 1.000023

19

The dielectric strength of cross linked polyethylene (XLPE) insulator is

around 20 – 160 MV/m. Based from equation (2.7), the following data shown in

Table 3.4 were obtained.

Table 3.4: Parameters data

Components Inner

radius (m)

Outer

radius (m)

Shunt

capacitance

C’ (pF)

Coating (C2) 0.04395 0.04695 1980.00

Outer insulation (C3) 0.02855 0.04055 139.023

Inner insulation (C4) 0.01025 0.02625 372.596

3.5 Observation Profile

To study the effect of different insulation level and thickness against the

lightning induced voltage, the observation profile are located as shown in Figure 3.9

below. The induced voltage was compare between inner insulation and outer

insulation.

20

Figure 3.9: Observation profile for different insulation level

To study the effect of different distance from strike point on the induced

voltage due to lightning current on the cable insulation (inner insulation), the

voltages were measured at different points. The value of induced voltage will be

compared between two different points to verify the effects for different distance

from strike point.

The cable depth was varied in this analysis to investigate the effect of

different depth of cable buried by changing the value of the soil parameters for

different depth level. The cable depth was varied by changing the value for the soil

resistance, R1. Higher value of the resistor indicates that the cable has been buried

deeper.

CHAPTER 4

RESULTS AND DISCUSSIONS

4.1 Introduction

The simulation has been carried out based on the configuration and

observation profile. The data were collected for desired response using ATP-EMTP

digital simulation software and the induced voltage wave shape were analyzed to

determine the effects of lightning to the underground cable system. The results will

also be compared with the previous research which used a different simulation

program. The previous research performed the analysis and simulation using Current

Distribution, Electromagnetic Fields, Grounding and Soil Structure (CDEGS)

simulation program.

22

4.2 Circuit Model Representation for The System

The simulation has been done using several different models to represent the

whole system in electronic circuit. The suitable circuit will be used and the result

will be compared with the previous research results.

4.2.1 Sheath and Armour Represented By Resistor

Figure 4.1 shows the armour and sheath for the cable were represented by

resistors, R2. The voltage induced at the outer insulation of the cable is labeled V1

and for inner insulation of the cable is labeled V2. V3 and V4 represent the voltage

induced for different distance from strike point for outer and inner insulation for the

cable respectively.

Figure 4.1: Circuit model for the system when R2 = 100 Ω

Figure 4.1 (a), (b), (c) and (d) show the voltage induced at V1, V2, V3 and

V4 respectively when R2 = 100Ω.

R2 = 100 Ω

C1 = 221.35 pF

R1 = 80 TΩ

C2 = 0.00198 µF

C3 = 139.023 pF

C4 = 372.596 pF

23

Figure 4.1 (a): Voltage induced at V1 when R2 = 100 Ω

Figure 4.1 (b): Voltage induced at V2 when R2 = 100 Ω

Figure 4.1 (c): Voltage induced at V3 when R2 = 100 Ω

(f ile 4.pl4; x-v ar t) v :XX0016

0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

10

20

30

40

50

[V]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

20

40

60

80

100

120

[V]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

40

80

120

160

200

[V]

24

Figure 4.1 (d): Voltage induced at V4 when R2 = 100 Ω

Once the value for resistors R2 were increase to 10 kΩ as shown in Figure 4.2

below, the following results shown in Figure 4.2 (a), (b), (c) and (d) were obtained.

Figure 4.2: Circuit model for the system when R2 = 10 kΩ


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

20

40

60

80

100

120

[V]

R2 = 10 kΩ

C1 = 221.35 pF

R1 = 80 TΩ

C2 = 0.00198 µF

C3 = 139.023 pF

C4 = 372.596 pF

25

Figure 4.2 (a): Voltage induced at V1 when R2 = 10 kΩ

Figure 4.2 (b): Voltage induced at V2 when R2 = 10 kΩ

Figure 4.2 (c): Voltage induced at V3 when R2 = 10 kΩ


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

500

1000

1500

2000

2500

3000

[V]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

1000

2000

3000

4000

5000

6000

[V]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

2

4

6

8

10

12

[kV]

26

Figure 4.2 (d): Voltage induced at V4 when R2 = 10 kΩ

The voltage increased if the value of R2 which represent the armour and

sheath of the cable increased. The wave shapes also smoothen with the increase in

R2. As can be seen in Figure 4.1 (a), (b), (c) and (d), there were some damping at the

peak of the response. The maximum voltage induced across the observation profiles

are listed in Table 4.1 below.

Table 4.1: Maximum voltage induced for different values of R2

Profile R2 = 100 Ω R2 = 10 kΩ

V1 (V) 41.7225 2859.71

V2 (V) 106.969 5874.33

V3 (V) 177.552 10768.1

V4 (V) 112.391 7661.15


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

1000

2000

3000

4000

5000

6000

7000

8000

[V]

27

4.2.2 Sheath and Armour Represented By an Inductor

Figure 4.3 shows the armour and sheath for the cable were represented by an

inductor. Different values of inductor were used to determine the effect to the

voltage induced across the insulation.

Figure 4.3: Circuit model for the system when L = 1 mH

Figure 4.2 (a), (b), (c) and (d) show the voltage induced at V1, V2, V3 and

V4 respectively when L = 1 mH.

Figure 4.3 (a): Voltage induced at V1 when L = 1 mH


0.00 0.02 0.04 0.06 0.08 0.10[ms]

-400

-300

-200

-100

0

100

200

300

400

[V]

L = 1 mH

C1 = 221.35 pF

R1 = 80 TΩ

C2 = 0.00198 µF

C3 = 139.023 pF

C4 = 372.596 pF

28

Figure 4.3 (b): Voltage induced at V2 when L = 1 mH

Figure 4.3 (c): Voltage induced at V3 when L = 1 mH

Figure 4.3 (d): Voltage induced at V4 when L = 1 mH


0.00 0.02 0.04 0.06 0.08 0.10[ms]

-800

-500

-200

100

400

700

[V]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

-1500

-1000

-500

0

500

1000

1500

[V]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

-1000

-500

0

500

1000

1500

[V]

29

When the sheath and armour were represented by an inductor, the waveforms

of the voltage induced across the cable insulation looked like a sinusoidal wave

shape.

When the values of L were changed to 100 mH as shown in Figure 4.4 below,

the following waveforms shown in Figure 4.4 (a), (b), (c) and (d) were obtained. The

wave shape is similar but the frequency response increase and the voltage induced

also increased drastically.

Figure 4.4: Circuit model for the system when L = 100 mH

Figure 4.4 (a): Voltage induced at V1 when L = 100 mH


0.00 0.02 0.04 0.06 0.08 0.10[ms]

-7000

-5000

-3000

-1000

1000

3000

5000

7000

9000

[V]

L = 100 mH

C1 = 221.35 pF

R1 = 80 TΩ

C2 = 0.00198 µF

C3 = 139.023 pF

C4 = 372.596 pF

30

Figure 4.4 (b): Voltage induced at V2 when L = 100 mH

Figure 4.4 (c): Voltage induced at V3 when L = 100 mH

Figure 4.4 (d): Voltage induced at V4 when L = 100 mH


0.00 0.02 0.04 0.06 0.08 0.10[ms]

-8

-4

0

4

8

12

[kV]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

-20

-15

-10

-5

0

5

10

15

20

[kV]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

-12

-8

-4

0

4

8

12

[kV]

31

Table 4.2 shows the maximum voltage induced across the observation

profiles for two different values of inductor, L.

Table 4.2: Maximum voltage induced for different values of L

Profile L = 1 mH L = 100 mH

V1 (V) +396.543

-285.917

+8211.11

-6659.28

V2 (V) +658.352

-623.906

+10235.2

-6708.82

V3 (V) +1425.17

-1330.39

+17389.3

-15699.1

V4 (V) +1093.57

-970.861

+11900.4

-11261

4.2.3 Sheath and Armour Represented By Resistor and Inductor in Series

Different results were obtained by manipulating the value of resistor, R2 and

inductor, L. Figure 4.5 shows the circuit used to determine these effects. Figure 4.5

(a), (b), (c) and (d) show the voltage induced at V1, V2, V3 and V4 respectively.

32

Figure 4.5: Circuit model for the system when R2 = 1 kΩ and L = 1 mH

Figure 4.5 (a): Voltage induced at V1 when R2 = 1 kΩ and L = 1 mH

Figure 4.5 (b): Voltage induced at V2 when R2 = 1 kΩ and L = 1 mH


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

150

300

450

600

750

900

[V]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

200

400

600

800

1000

1200

[V]

R2 = 1 kΩ

L = 1 mH

C1 = 221.35 pF

R1 = 80 TΩ

C2 = 0.00198 µF

C3 = 139.023 pF

C4 = 372.596 pF

33

Figure 4.5 (c): Voltage induced at V3 when R2 = 1 kΩ and L = 1 mH

Figure 4.5 (d): Voltage induced at V4 when R2 = 1 kΩ and L = 1 mH

By changing the value for R2 to 10 kΩ and keep remain the value of inductor,

L as shown in Figure 4.6, the waveforms become smoother and no ripples but the

voltages were increased as shown in Figure 4.6 (a), (b), (c) and (d) below.


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

500

1000

1500

2000

2500

[V]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

300

600

900

1200

1500

[V]

34





0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

1000

2000

3000

4000

5000

6000

[V]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

1000

2000

3000

4000

5000

6000

7000

[V]

R2 = 10 kΩ

L = 1 mH

C1 = 221.35 pF

R1 = 80 TΩ

C2 = 0.00198 µF

C3 = 139.023 pF

C4 = 372.596 pF

35



When the inductor values were set to 3 mH and resistor is 1 kΩ as shown in

Figure 4.7, the ripple is higher as shown in Figure 4.7 (a), (b), (c) and (d) below.


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

2

4

6

8

10

12

[kV]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

1000

2000

3000

4000

5000

6000

7000

8000

[V]

36





0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

300

600

900

1200

1500

[V]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

400

800

1200

1600

2000

[V]

R2 = 1 kΩ

L = 3 mH

C1 = 221.35 pF

R1 = 80 TΩ

C2 = 0.00198 µF

C3 = 139.023 pF

C4 = 372.596 pF

37



For these three different values of R2 and L, the maximum voltage induced

across the insulation can be concluded as in Table 4.3 below

Table 4.3: Maximum voltage induced for different values of R2 and L

Profile R2 = 1 kΩ

L = 1 mH

R2 = 10 kΩ

L = 1 mH

R2 = 1 kΩ

L = 3 mH

V1 (V) 846.901 5200.48 1212.08

V2 (V) 1105.76 6241.79 1379.03

V3 (V) 2018.14 11383.6 3109.58

V4 (V) 1370.6 7864.41 2168.12


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

500

1000

1500

2000

2500

3000

3500

[V]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

500

1000

1500

2000

2500

[V]

38

As a conclusion for this section, when the value for R2 is increased, the wave

shape for the voltage across the cable insulation is smoothen but the voltage seem to

be increased as well. While by increasing the value for L, it will result in a high

ripple at the wave shape and the voltage across the cable insulation is increased.

4.3 Induced Voltage on Different XLPE Insulation Cross-Sectional Layers

Based from the discussion above, the suitable circuit model to do further

analysis is chosen to be as shown in Figure 4.6 with the value to represent the sheath

and armour is set to be R2 = 10 kΩ and L = 1 mH. Figure 4.8 shows the induced

voltage at the outer insulation and Figure 4.9 for the inner insulation of the

underground cable when 40 kA lightning current injected into the system.

Figure 4.8: Induced voltage across the outer cable insulation


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

1000

2000

3000

4000

5000

6000

[V]

39

Figure 4.9: Induced voltage across the inner cable insulation

Figure 4.10 and 4.11 shows the induced voltage at the outer and inner

insulation from CDEGS simulation from previous study respectively.

Figure 4.10: Induced voltage at the outer cable insulation (CDEGS)


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

1000

2000

3000

4000

5000

6000

7000

[V]

40

Figure 4.11: Induced voltage at the inner cable insulation (CDEGS)

The maximum voltage induced across the insulation of the cable for this two

different software were listed in the Table 4.4 below. It can be seen that the

lightning current induced a large potential to the cable at the inner insulation

compared to the outer insulation. The induced voltage at the outer insulation should

be larger than the inner insulation since it is closer to ground surface but smaller

value was recorded and this might be due to the thickness factor.

Table 4.4: Maximum voltage induced for different observation

profile from different software

Profile ATP-EMTP CDEGS

Outer cable insulation (kV) 5.20048 726

Inner cable insulation (kV) 6.24179 1032

41

4.4 Induced Voltage Across Cable Insulation At Different Distance From

Strike Point

To determine the effect of different distance from strike point, the following

waveforms were obtained. Figure 4.12 shows the induced voltage near to the strike

point while Figure 4.13 shows the induced voltage far from the strike point. The

result should shows that the further distances from strike point the less voltage will

induced in the insulation.

Figure 4.12: Induced voltage near from the strike point

Figure 4.13: Induced voltage far from the strike point


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

1500

3000

4500

6000

7500

9000

[V]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

2

4

6

8

10

12

[kV]

42

Based from Figure 4.12 and 4.13, the induced voltage far from strike point

was higher than near the strike point. This might be due to the soil or cable model

representations are not accurate and several other parameters need to be considers in

modeling the circuit.

Figure 4.14 and 4.15 were obtained from previous research and the induced

voltage across the insulation layer decreased with the distance.

Figure 4.14: Induced voltage near from the strike point (CDEGS)

Figure 4.15: Induced voltage far from strike point (CDEGS)

43

4.5 Induced Voltage On Cable Insulation At Various Depth From Strike

Point

To determine the effect of different depth of the buried cable, the value of the

soil parameters resistor, R1 were change. Figure 4.16 shows the cable buried near to

the earth surface and Figure 4.17 shows the cable buried deeper. The induced

voltage was decrease as the cable is buried deeper.

Figure 4.16: Induced voltage near the earth surface

Figure 4.17: Induced voltage when the cable buried deeper


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

100

200

300

400

500

600

700

[kV]


0.00 0.02 0.04 0.06 0.08 0.10[ms]

0

10

20

30

40

50

60

70

[V]

44

Figure 4.18 and 4.19 shows the result obtained from CDEGS simulation

program. As the depth of the cable is further increased, the induced voltage was

found to be decreased

Figure 4.18: Induced voltage near the earth surface (CDEGS)

Figure 4.19: Induced voltage when the cable buried deeper (CDEGS)

45

4.6 Discussions

The analysis has been carried out by modeling the soil and several different

circuits for 132kV underground cable based on its parameter into the ATP-EMTP

simulation program. The voltage induced in the cable insulation layer has been

observed. Various conditions have been considered in the simulation.

Based from the results, there will be no possibility of having insulation failure

or breakdown to the cable. Since the dielectric strength of cross linked polyethylene

(XLPE) is around 20 – 160 MV/m.

CHAPTER 5

CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

From the simulation study conducted, a series of conclusion can be made

based from the observation profile and analysis on the 132kV

Cu/XLPE/SCW/MDPE rated underground cable system. The conclusion that can be

made in case of lightning, it may not damage cable insulator. It depends on

amplitude of impact current, electric breakdown strength of insulators, grounding

system configuration and cable length. The effect of electric fields due to direct

lightning strikes on ground to underground cable were showed in the form of the

safety depth of buried cable, the impacting current to cable and the overvoltages

dropped XLPE insulator cable [2]

47

5.2 Recommendations

After completing this analysis, these are several recommendations:

i. The circuit model of the cable and soil need to be improved in terms

of adding other parameters.

ii. The configuration of the circuit need to be modified to get more

accurate result.

iii. Using other simulation program software that more suitable to carry

out the study.

48

REFERENCES

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edition.

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2. N. Klairuang, W. Pobpom and J. Hokierti, Member, EEE (Nov. 2004). Effects

of Electric fields Generated by Direct Lightning Strikes on Ground to

Underground Cables. International Conference on Power System

Technology – POWERCON, Singapore.

3. Zeqing Song, M. R. Raghuveer, Jingliang He (2002). Complete Assessment of

Impact of Lightning Strikes on Buried Cables. IEEE Canadian Conference On

Electrical & Computer Engineering.

4. Hermann W. Dommel (Sept. 2010). Underground and Submarine Cable

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7. Hermann W. Dommel (Jan. 2010). Sources and Machine Models. The

University of British Columbia. Power System Consultants, Vancouver,

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Underground Cables. University of Cape Town.

9. L. Marti (Dec. 1993). Simulation of Electromagnetic Transients in

Underground Cables using the EMTP. IEE 2nd

International Conference on

49

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12. M. Paolone, E. Petrache, M. Nyffeler, and J. Schoene (Aug. 2005). Lightning

Induced Disturbances in Buried Cables - Part II: Experiment and Model

Validation. IEEE Transactions On Electromagnetic Compatibility, Vol. 47,

No. 3.

13. B. Gustavsen, J. A. Martinez, and D. Durbak (July 2005). Parameter

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IEEE Transactions On Power Delivery, Vol. 20, No. 3.

14. P. Wagenaars et al. (Feb. 2010). Approximation of Transmission Line

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University of Technology. IEEE Transactions on Dielectrics and Electrical

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16. Overvoltage

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

17. Lightning

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

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

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