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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
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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
4.2.2 Sheath and Armour Represented 27
By an Inductor
4.2.3 Sheath and Armour Represented 31
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
4.6 Circuit model for the system when R2 = 10 kΩ and L = 1 mH 34
4.6 (a) Voltage induced at V1 when R2 = 10 kΩ and L = 1 mH 34
4.6 (b) Voltage induced at V2 when R2 = 10 kΩ and L = 1 mH 34
4.6 (c) Voltage induced at V3 when R2 = 10 kΩ and L = 1 mH 35
4.6 (d) Voltage induced at V4 when R2 = 10 kΩ and L = 1 mH 35
4.7 Circuit model for the system when R2 = 1 kΩ and L = 3 mH 36
4.7 (a) Voltage induced at V1 when R2 = 1 kΩ and L = 3 mH 36
4.7 (b) Voltage induced at V2 when R2 = 1 kΩ and L = 3 mH 36
4.7 (c) Voltage induced at V3 when R2 = 1 kΩ and L = 3 mH 37
4.7 (d) Voltage induced at V4 when R2 = 1 kΩ and L = 3 mH 37
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]
(f ile 4.pl4; x-v ar t) v :XX0017
0.00 0.02 0.04 0.06 0.08 0.10[ms]
0
20
40
60
80
100
120
[V]
(f ile 4.pl4; x-v ar t) v :XX0046
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
(f ile 4.pl4; x-v ar t) v :XX0047
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
(f ile 4.pl4; x-v ar t) v :XX0016
0.00 0.02 0.04 0.06 0.08 0.10[ms]
0
500
1000
1500
2000
2500
3000
[V]
(f ile 4.pl4; x-v ar t) v :XX0017
0.00 0.02 0.04 0.06 0.08 0.10[ms]
0
1000
2000
3000
4000
5000
6000
[V]
(f ile 4.pl4; x-v ar t) v :XX0046
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
(f ile 4.pl4; x-v ar t) v :XX0047
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
(f ile 5.pl4; x-v ar t) v :XX0016
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
(f ile 5.pl4; x-v ar t) v :XX0017
0.00 0.02 0.04 0.06 0.08 0.10[ms]
-800
-500
-200
100
400
700
[V]
(f ile 5.pl4; x-v ar t) v :XX0046
0.00 0.02 0.04 0.06 0.08 0.10[ms]
-1500
-1000
-500
0
500
1000
1500
[V]
(f ile 5.pl4; x-v ar t) v :XX0047
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
(f ile 5.pl4; x-v ar t) v :XX0016
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
(f ile 5.pl4; x-v ar t) v :XX0017
0.00 0.02 0.04 0.06 0.08 0.10[ms]
-8
-4
0
4
8
12
[kV]
(f ile 5.pl4; x-v ar t) v :XX0046
0.00 0.02 0.04 0.06 0.08 0.10[ms]
-20
-15
-10
-5
0
5
10
15
20
[kV]
(f ile 5.pl4; x-v ar t) v :XX0047
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
(f ile 1.pl4; x-v ar t) v :XX0140
0.00 0.02 0.04 0.06 0.08 0.10[ms]
0
150
300
450
600
750
900
[V]
(f ile 1.pl4; x-v ar t) v :XX0169
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.
(f ile 1.pl4; x-v ar t) v :XX0174
0.00 0.02 0.04 0.06 0.08 0.10[ms]
0
500
1000
1500
2000
2500
[V]
(f ile 1.pl4; x-v ar t) v :XX0175
0.00 0.02 0.04 0.06 0.08 0.10[ms]
0
300
600
900
1200
1500
[V]
34
Figure 4.6: Circuit model for the system when R2 = 10 kΩ and L = 1 mH
Figure 4.6 (a): Voltage induced at V1 when R2 = 10 kΩ and L = 1 mH
Figure 4.6 (b): Voltage induced at V2 when R2 = 10 kΩ and L = 1 mH
(f ile 1.pl4; x-v ar t) v :XX0140
0.00 0.02 0.04 0.06 0.08 0.10[ms]
0
1000
2000
3000
4000
5000
6000
[V]
(f ile 1.pl4; x-v ar t) v :XX0169
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
Figure 4.6 (c): Voltage induced at V3 when R2 = 10 kΩ and L = 1 mH
Figure 4.6 (d): Voltage induced at V4 when R2 = 10 kΩ and L = 1 mH
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.
(f ile 1.pl4; x-v ar t) v :XX0174
0.00 0.02 0.04 0.06 0.08 0.10[ms]
0
2
4
6
8
10
12
[kV]
(f ile 1.pl4; x-v ar t) v :XX0175
0.00 0.02 0.04 0.06 0.08 0.10[ms]
0
1000
2000
3000
4000
5000
6000
7000
8000
[V]
36
Figure 4.7: Circuit model for the system when R2 = 1 kΩ and L = 3 mH
Figure 4.7 (a): Voltage induced at V1 when R2 = 1 kΩ and L = 3 mH
Figure 4.7 (b): Voltage induced at V2 when R2 = 1 kΩ and L = 3 mH
(f ile 1.pl4; x-v ar t) v :XX0140
0.00 0.02 0.04 0.06 0.08 0.10[ms]
0
300
600
900
1200
1500
[V]
(f ile 1.pl4; x-v ar t) v :XX0175
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
Figure 4.7 (c): Voltage induced at V3 when R2 = 1 kΩ and L = 3 mH
Figure 4.7 (d): Voltage induced at V4 when R2 = 1 kΩ and L = 3 mH
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
(f ile 1.pl4; x-v ar t) v :XX0169
0.00 0.02 0.04 0.06 0.08 0.10[ms]
0
500
1000
1500
2000
2500
3000
3500
[V]
(f ile 1.pl4; x-v ar t) v :XX0174
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
(f ile 1.pl4; x-v ar t) v :XX0071
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)
(f ile 1.pl4; x-v ar t) v :XX0075
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
(f ile 1.pl4; x-v ar t) v :XX0040
0.00 0.02 0.04 0.06 0.08 0.10[ms]
0
1500
3000
4500
6000
7500
9000
[V]
(f ile 1.pl4; x-v ar t) v :XX0123
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
(f ile 1.pl4; x-v ar t) v :XX0075
0.00 0.02 0.04 0.06 0.08 0.10[ms]
0
100
200
300
400
500
600
700
[kV]
(f ile 1.pl4; x-v ar t) v :XX0075
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
1. M S Naidu and V Kamaraju (2004). High Voltage Engineering. 3rd
edition.
Tata McGraw-Hill Publishing Company Limited
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
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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
Parameters. The University of British Columbia. Power System Consultants,
Vancouver, Canada.
5. Lázló Prikler, Hans Kr. Høidalen (2002). ATPDraw for Windows 3.5 User’s
Manual.
6. Aida Sulinda (Nov. 2009). An Electro-Magnetic Transient (Emt) Analysis
On A 132 kV Rated Cu/XLPE/SCW/MDPE Cable System And Its Related
Networks. Universiti Teknologi Malaysia.
7. Hermann W. Dommel (Jan. 2010). Sources and Machine Models. The
University of British Columbia. Power System Consultants, Vancouver,
Canada.
8. H. D. Einhorn, B. L. Goodlet (June 1940). Lightning Over-voltage in
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
Advances in Power System Control, Operation and Management, Hong
Kong.
10. U. S. Gudmundsdottir, C. L. Bak and W. T. Wiechowski (Feb. 2010).
Modeling of Long High Voltage AC Underground Cables. Fredericia,
Denmark.
11. M. A. Hanna and A. Y. Chikhani, M. M. A. Salama. Modelling Of
Underground Cable Systems in Non-Homogeneous Soils. Royal Military
college of Canada.
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
Determination for Modeling System Transients - Part II: Insulated Cables.
IEEE Transactions On Power Delivery, Vol. 20, No. 3.
14. P. Wagenaars et al. (Feb. 2010). Approximation of Transmission Line
Parameters of Single-core and Three-core XLPE Cables. Eindhoven
University of Technology. IEEE Transactions on Dielectrics and Electrical
Insulation Vol. 17, No. 1.
15. C. K. Jung J. B. Lee J. W. Kang X. H. Wang Y. H. Song. Sheath Current
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University, Iksan, Korea
16. Overvoltage
http://en.wikipedia.org/wiki/Overvoltage
17. Lightning
http://en.wikipedia.org/wiki/Lightning