raj emtp model
TRANSCRIPT
ii
INSULATION COORDINATION OF QUADRUPLE CIRCUIT HIGH VOLTAGE TRANSMISSION LINES USING ATP-EMTP
SITI RUGAYAH BTE DUGEL
A thesis submitted 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
MEI 2007
iv
To my beloved husband and dear children, who are always giving their support and
understanding. They are always with me when I need support and advice and without
their understanding, I will not be able to complete my master study
v
ACKNOWLEDGEMENT
I would like to express my sincere appreciation and special thanks to my project
supervisor, Prof. Dr. Zulkurnain Abdul Malek, for his support, advices,
encouragement, guidance and friendship. I wish to thank the grateful individuals from
TNB research and TNB Generation. I am grateful for their cooperation and willingness
to assist me in this matter.
I am also would like to thank all my friends especially Adzhar Bin Khalid for
their assistance towards the successful completion of this project. I am also indebted to
Universiti Teknologi Malaysia (UTM) for their assistance in supplying the relevant
literatures.
Last but not least, I wish to thank my beloved husband, Surmazalan B. Ngarif
who give me his undivided attention and support throughout this research.
vi
ABSTRACT
A significant number of faults in overhead transmission lines are due to
lightning strikes which cause back flashovers and hence single or double circuit
outages. The continuity and quality of the power supply is therefore can be severely
affected by the outages, especially in Malaysia where the isokeraunic level is rather
high. The lightning performance of transmission lines is also influenced by the
transmission line configuration itself. In Malaysia, the TNB's transmission lines consist
of 500 kV or 275 kV double circuits, and 275/132 kV quadruple circuits. It is known
that the lower portion of the 132 kV line apparently has the lowest lightning
performance.
The application of transmission line arresters is also known to be the best
method in improving the lightning performance of transmission lines in service.
However, its usage requires proper coordination and placement strategy to ensure
optimum improvement in lightning performance.
In this work, the ATP-EMTP simulation program was used to study the
lightning performance of the quadruple circuit transmission line behaviour towards
lightning activities. The models used include those for the surge arresters, overhead
lines, towers and insulators. All models were based on the data supplied by the utility.
Initial results show that the configuration 6 gives the best protection or lowest
flashover rate.
vii
ABSTRAK
Kebanyakkan gangguan bekalan pada talian atas penghantaraan adalah
disebabkan oleh panahan petir yang mana telah mengakibatkan kerosakkan dan
gangguan bekalan pada litar sediada dan litar berkembar. Gangguan bekalan ini telah
mengakibatkan keterusan dan kualiti bekalan elektrik terganggu teruk. Tahap panahan
petir di talian atas penghantaran adalah juga dipengaruhi oleh configurasi talian atas
itu sendiri. Di Malaysia, talian penghantaran TNB adalah terdiri dari 500kV atau
275kV litar berkembar dan 275/132kV litar berkembar empat(quadruple circuits).
Telah dikenalpasti bahawa pada bahagian bawah talian 132kV adalah merupakan tahap
panahan petir yang terendah.
Penggunaan penangkap kilat untuk talian atas adalah merupakan cara terbaik
dalam memperbaiki tahap panahan petir di talian atas yang sedang beroperasi. Walau
bagaimanapun, penggunaanya memerlukan koordinasi yang tepat dan lokasi yang
strategik bagi mendapatkan kesan yang optimum.
Untuk kajian ini, aturcara simulasi ATP-EMTP telah digunakan bagi mengkaji tahap
dan aktiviti panahan petir terhadap litar berkembar empat. Model yang digunakan
adalah termasuk penangkap kilat, talian atas penghantaraan, menara dan penebat.
Semua data yang digunakan untuk dimodelkan adalah diperolehi dari pembekal
elektrik Keputusan dari simulasi yang dibuat menunjukkan configurasi 6 telah
menghasilkan perlindungan yang terbaik dan kadar gangguan bekalan yang terendah
viii
UTM(PS)-1/02
School of Graduate Studies
Universiti Teknologi Malaysia
VALIDATION OF E-THESIS PREPARATION
Title of the thesis: INSULATION COORDINATION OF QUADRUPLE CIRCUIT HIGH
VOLTAGE TRANSMISSION LINES USING ATP-EMTP
Degree: MASTER OF ENGINEERING (ELECTRICAL POWER)
Faculty: KEJURUTERAAN ELEKTRIK
Year: 2007
I SITI RUGAYAH BINTI DUGEL hereby
declare and verify that the copy of e-thesis submitted is in accordance to the Electronic Thesis and
Dissertation’s Manual, School of Graduate Studies, UTM
_____________________
(Signature of the student)
______________________
(Signature of supervisor as a witness)
Permanent address:
No 17, Lorong Gurney off Jalan Semarak,
54100 Kuala Lumpur, Wilayah Persekutuan.
Name of Supervisor: Prof Madya Dr Zulkurnain
Bin Abdul Malek
Faculty: KEJURUTERAAN ELEKTRIK
TABLE OF CONTENTS
CHAPTER TITLE PAGE TITLE PAGE i
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES xiii
LIST OF FIGURES xv
LIST OF ABBREVIATIONS xviii
LIST OF SYMBOLS xix
1 INTRODUCTION 1
1.1 Background 1
1.2 The Objectives of the Research 2
1.3 Scope of Study 3
2 LITERATURE REVIEW 3
2.1 Case Study by Kerk Lee Yen(TNBT Network SB) 3
2.1.1 Objective 3
2.1.2 Methodology 4
2.1.2.1 Line Section 4
2.1.2.2 Basic input data 4
CHAPTER TITLE PAGE
10
2.1.3 Configuration of TLA installation 5
2.1.4 Result 5
2.1.5 Various installation of TLA 6
2.1.6 Simulation Result 7
2.1.6.1 Application of 3 TLA per tower 7
2.1.6.2 Application of 2 TLA per tower 7
2.2 Case Study by S.J Shelemy and D.R.Swatek 7
2.2.1 Objective 7
2.2.2 Introduction 8
2.2.3 Model Overview 8
2.2.4 Methodology 9
2.2.4.1 Tower Model 9
2.2.4.2 Line Termination 10
2.2.4.3 Insulator String 10
2.2.4.4 Tower Ground Resistance 10
2.2.4.5 Point of Contact 11
2.2.4.6 Lightning stroke 12
2.2.5 Results 12
2.2.6 Conclusion 13
2.3 Case Study by Y.A.Wahab, Z.Z.Abidin and S.Sadovic 13
2.3.1 Objective 13
2.3.2 Introduction 14
2.3.3 Model Overview 14
2.3.4 Methodology 14
2.3.4.1 Electromagnetic model 15
2.3.4.2 Tower footing resistance model 16
2.3.4.3 Line insulation flashover model 16
2.3.4.4 Tower Model 17
2.3.4.5 Transmission Line Surge Arrester 17
CHAPTER TITLE PAGE
11
2.3.4.6 Corona model 18
2.3.5 Result of Lightning Performance 18
2.3.6 Conclusions 20
3 TRANSMISSION SYSTEM 21
3.1 Transmission Line and Ground Wire 21
3.2 Insulator 22
3.3 Insulation Coordination 23
3.1.1 Definitions of Insulation Coordination 23
3.3.2 Insulation Coordination 24
3.3.3 Insulation Coordination Involves 24
3.3.4 Selection of Insulation Levels 24
3.3.5 Basic Principles of Insulation Coordination 25
3.3.6 Insulation Withstand Characteristics 26
3.3.7 Standard Basic Insulation Levels 26
3.4 Arching Horn 27
3.5 Earthing 28
3.6 Tower Types 28
3.6.1 Tower with wooden cross arm 29
3.7 Design Span 30
3.8 System Over voltages 30
3.9 Fast Front Over voltages 31
3.10 Fast Front Over voltages 31
3.11 Metal-Oxide Arresters 33
3.12 Gapped TLA and Gapless TLA 33
3.13 Surge Lightning Arrester placement (TLA) 34
3.14 Comparison of Available Surge Arresters (Gapless Type) 35
12
CHAPTER TITLE PAGE
4 TRANSMISSION SYSTEM 37
4.1 System Modelling 37
4.2 EMTP Simulation 37
4.3 Selected model and Validation 38
4.4 Transmission Line 38
4.5 Line exposure to lightning 39
4.6 Shielding Failure 40
4.7 Overhead Transmission Lines 41
4.8 Line length and Termination 41
4.9 Tower Model 42
4.10 Tower footing resistance model 45
4.11 Insulators 46
4.12 Backflashover 46
4.13 Corona 47
4.14 Line surge arrester 47
4.15 Selection of Lightning Configuration 51
5 AVAILABLE METHOD FOR LIGHTNING 52
PERFORMANCE IMPOVEMENT
5.1 Additional Shielding Wire 53
5.2 Tower Footing Resistance 53
5.3 Increase the Tower Insulation 54
5.4 Unbalance Insulation 54
5.5 Transmission Line Arrester 55
5.6 Installation of TLA based on TFR 55
5.6.1 Additional of TLA at low TFR Section 57
5.6.2 Installation of TLA on one circuit 58
5.6.3 Coordination of Gap Spacing fot Transmission 59
13
CHAPTER TITLE PAGE
5.6 Extended Station Protection 61
6 SIMULATION METHOD 61
6.1 ATP-EMTP Simulation 61
6.2 Selected Model and Validation 62
6.2.1 Tower Model 62
6.3 Model And Parameters Used In The Simulation 66
6.3.1 Tower Model 66
6.3.2 Transmission Line model 67
6.4 Selection of Lightning Parameter 70
6.5 Lightning Amplitude 70
6.6 Time of Rising 71
6.7 Time of Falling 71
6.8 Limitation of Simulation 74
6.9 Statistical Approach 74
7 SIMULATION: 275 kV DOUBLE CIRCUIT 75
AND 275/132kV QUADRUPLE CIRCUIT LINE
7.1 275/132kV Quadruple Circuit and 75
Specification used in this Simulation
7.1.1 Model Used In The Simulation 78
7.2 Lightning Surge Arrester Configuration 79
7.3 Results Of Simulation For Lightning 80
Current of 17kA And Strike at Tower 2
7.3.1 Response without transmission line arrester 80
7.3.2 Response with transmission line arrester 81
7.3.2.1 TLA with configuration 1 82
7.3.2.2 TLA with configuration 2 83
14
7.3.2.3 TLA with configuration 3 83
7.3.2.4 TLA with configuration 4 84
7.3.2.5 TLA with configuration 5 85
7.3.2.6 TLA with configuration 6 85
7.3.2.7 TLA with configuration 7 86
7.3.2.8 TLA with configuration 8 87
7.4 Results Of Simulation For Lightning 88
Current of 120kA And Strike at Tower 2
7.4.1 Response without transmission line arrester 88
7.4.2 Response with transmission line arrester 89
7.4.2.1 TLA with configuration 1 89
7.4.2.2 TLA with configuration 2 90
7.4.2.3 TLA with configuration 3 90
7.4.2.4 TLA with configuration 4 91
7.4.2.5 TLA with configuration 5 92
7.4.2.6 TLA with configuration 6 92
7.4.2.7 TLA with configuration 7 93
7.4.2.8 TLA with configuration 8 94
7.4.2.9 TLA with configuration 9 94
7.5 Summary of the Simulation 95
7.4 Limitation of simulation 98
8 RECOMMENDATION AND CONCLUSION 99
REFERENCES 101
15
LIST OF TABLES
TABLE NO. TITLE PAGE
2.1 Section of BBTG-RSID 132 kV 4
2.2 Flashover rate for individual section of line 5
2.3 Various installation of TLA 6
2.4 Strike distances for the Nelson River HVDC 11
transmission line
2.5 Critical peak lightning current amplitudes for 11
the Nelson River HVDC transmission line towers
2.6 Back flashover rates and shielding failure rates 12
per 10,000 lightning strikes
2.7 Two-line stroke distribution to flat ground 15
2.8 Flashover rate for different circuits without line 18
surge arresters( flashover rate/100km/year)
2.9 Line total and multi circuit flashover rate without 19
line surge arresters( flashover rate/100km/year)
2.10 Line Total Flashover Rate Different Arrester 19
Installation Configurations( flashover rate/100km/year)
2.11 Line Double Total Flashover Rate Different Arrester 20
Installation Configurations( flashover rate/100km/year)
3.1 Conductors Type and Their Specification 22
3.2 Number of insulator set required based on voltage 23
and type of insulator set
16
TABLE NO. TITLE PAGE
3.3 Standard Basic Insulation Levels(BIL) 27
3.4 Arching distance and BIL for various circuit 27
and towers
3.5 Tower types and deviation angle 29
3.6 The major differences between gapped SLA 32
and gapless SLA
3.7 SLA placement and energy consideration 34
3.8 TLA Placement and Energy Consideration 35
3.9 Data on Gapless Transmission line arrester 36
manufactured by several company
4.1 Balakong to Serdang 132kV line information 39
4.2 Value for A0 and A1 based on 8/20 us residual 48
voltage supplied by manufacturer for the
application of Pinceti’s arrester model.
5.1 Arrester installation strategy to eliminate double 56
circuit flashover
7.1 Parameter of the 275kV double circuit tower model 77
7.2 Value for A0 and A1 based on 8/20 us residual voltage 75
supplied for the application of Pinceti’s arrester model
with 120kV rated Siemens 3EQ4-2/LD3
7.3 Line Performance For Different TLA Configuration 95
For Lightning Current of 17kA
7.4 Line Performance For Different TLA Configuration 97
For Lightning Current of 120kA
17
LIST OF FIGURES
FIGURE NO. TITLE PAGE
4.1 Model of Transimission Line 40
4.2 Overhead Transmission Line, Tower and Insulator 42
model
4.3 Tower Representation for Quadruple Circuit 43
Transmission Line
4.4 M. Ishii’s tower model for a double circuit line tower 44
4.5 Pinceti’s arrester model used for representing 49
surge arrester
4.6 Relative error of residual voltage for representing 49
Siemens 120kV rated 3EQ4-2/LD3 SA with Picenti’s
model compared to manufacturer performance data
4.7 Example of Gapless-type Surge Arrester installed 50
at 132kV BLKG-SRDG
4.8 Different arrester Installation Configurations 51
5.1 Available Method for Lightning Improvement 52
5.2 Unbalance tower insulation for double circuit line 55
5.3 Circuit location and TLA placement for a double 56
circuit line
5.4 Additional TLA at Low TFR section along the high 57
TFR section
5.5 TLA added only at one circuit of a double circuit 58
line tower
18
FIGURE NO. TITLE PAGE
5.6 Extended station protection 60
6.1 M.Ishii’s tower model for a double circuit line tower 64
6.2 Tower equivalent radius 64
6.3 Modified M.Ishii’s tower model for a quadruple 66
circuit line tower modeling
6.4 Voltage Amplitude for Time of Falling 20µs 72
6.5 Voltage Amplitude for Time of Falling 50µs 72
6.6 Voltage Amplitude for Time of Falling 100µs 73
6.7 Voltage Amplitude for Time of Falling 200µs 73
6.8 Voltage Amplitude for Time of Falling 500µs 73
7.1 Simulated 275/132kV quadruple circuit line 76
7.2 Conductor identification for 275/132kV double 76
circuit line used in simulation
7.3 Modified M.Ishii’s tower model for a quadruple 78
circuit line tower modeling
7.4 Current injected at top tower 2 80
7.5 Lightning strike has caused voltage rise at top tower 2 80
7.6 Voltage measured at tower 2 which are connected to 81
275kV Line
7.7 Flashover Voltages when TLA are equipped at 82
conductor RBT and RBT1
7.8 Flashover Voltages when TLA are equipped at 83
conductor RBT132, RBT131 and BBT131
7.9 Flashover Voltages when TLA are equipped at 83
conductor RBT131, YBT 131 and BBT131
7.10 Flashover Voltages when TLA are equipped at 84
conductor RBT, RBT1 and RBT131
7.11 Flashover Voltages when TLA are equipped at 85
conductor RBT132, RBT131, YBT132 and YBT131
19
FIGURE NO. TITLE PAGE
7.12 Flashover Voltages when TLA are equipped at 85
conductor RBT, RBT1, RBT132 and RBT131
7.13 Flashover Voltages when TLA are equipped at 86
conductor RBT, RBT1, BBT, RBT132 and RBT131
7.14 Flashover Voltage when TLA are equipped at 87
conductor RBT, RBT1, YBT, RBT132 and RBT131
7.15 Current injected at top tower 2 88
7.16 Lightning strike has caused voltage rise at top tower 2 88
7.17 Flashover Voltage across insulators when TLA are 89
equipped at conductor RBT and RBT1
7.18 Flashover Voltage across insulators when TLA are 90
equipped at conductor RBT132, RBT131 and BBT1
7.19 Flashover Voltage across insulators when TLA are 90
equipped at conductor RBT132, RBT131 and BBT1
7.20 Flashover Voltage across insulators when TLA are 91
equipped at conductor RBT, RBT1 and RBT131
7.21 Flashover Voltage across insulators when TLA are 92
equipped at conductor RBT132, RBT131, YBT132
and YBT131
7.22 Flashover Voltage across insulators when TLA are 92
equipped at conductor RBT, RBT1, RBT132
and RBT131
7.23 Flashover Voltage across insulators when TLA are 93
equipped at conductor RBT, RBT1, BBT, RBT132
and RBT131
7.24 Flashover Voltage across insulators when TLA are 94
equipped at conductor RBT, RBT1, BBT, RBT132 and RBT131
7.25 Flashover Voltage across insulators when TLA are 94
equipped at all conductors of 275kV and 132kV lines
20
LIST OF ABBREVIATIONS
ac - Alternating Current
ACSR - Aluminium Conductor Steel Reinforced
AIS - Air Insulated Substation
ATP - Alternative Transient Program
BFR - Back Flashover Rate
BIL - Basic Lightning Insulation Level
CB - Circuit Breaker
CBPS - Connaught Bridge Power Station
CFO - Critical Flashover
EMTP - Electro Magnetic Transient Program
FDQ - Frequency Dependent Q Matrix
GIS - Gas Insulated Substation
GPS - Global Positioning System
IEE - The Institution of Electrical Engineers
IEEE - Institute of Electrical and Electronic Engineers
IVAT - High Voltage and Current Institute
LOC - Leader Onset Conditions
MO - Metal Oxide
MOV - Metal Oxide Varistor
OPGW - Optical Fibre Composite Ground Wire
SA - Surge Arresters
SiC - Silicon Carbide
S/S - Substation
21
TFR - Tower Footing Resistance
TLA - Transmission Line Arresters
TNB - Tenaga Nasional Berhad
ZnO - Zinc Oxide
22
LIST OF PRINCIPLE SYMBOLS
µF - micro-Farad
µH - micro-Hendry
µs - nicro-second
A - Ampere
C - Capacitive
Ng - Ground Flash Density per Kilometer2 per year
kA - kilo-Ampere
kJ - kilo-Joule
kV - kilo-Volt
L - Inductive
MV - Mega-Volt
R - Resistance
Uc - Maximum Continuous Operating Voltage
Ur - Rated Surge Arrester Voltage
Km - kilometer
V - Volt
Z - Impedance
Zt - Surge Impedance
CHAPTER 1
INTRODUCTION
1.1 Background
Transmission system in services can be divided into two which are overhead
transmission system and cable type transmission system. The main focus here is the
overhead transmission systems, which are directly subjected to lightning over voltage.
A significant number of the faults on overhead transmission lines are due to lightning.
Lightning Faults may be single or multiple, and their elimination causes voltage dips
and outages. Therefore, the outage rate of a line and the quality of the delivered voltage
depend on the lightning performance of the line.
Many procedures have been presented over the years with the aim of predicting
the lightning performance of transmission lines. Modern understanding about lightning
phenomena and lightning attraction mechanisms allowed developing methods for
estimating the lightning performance of overhead lines which avoid such empiricism.
2
For this purpose, the performance of transmission lines is estimated using ATP-EMTP
simulation programs
1.2 The Objectives of the Research
The main objective of the project is to improve the lightning performance of
transmission lines by the application of line surge arresters on the quadruple circuit
transmission line and to analyze different line surge arresters application configurations
in order to optimize application of this technology to the existing and to the future
quadruple transmission lines.
1.3 Scope of Study
The main scope of this project is to study the applications of surge arresters on
transmission line to improve the lightning and transient performance of the
transmission line which is includes:
Arrangement of line arresters for optimum technical and economic
Performance which include where or which tower along the line
arresters to be installed
The rating and withstand energy of the surge arresters
The arresters configurations
3
CHAPTER 2
LITERATURE REVIEW
The purposes of these Studies are to measure the performance to eliminate
circuit trippings on Overhead Transmission Line Protection for double and quadruple
circuit transmission line. The performance of the system are justified by installation of
transmission line arrester (TLA) and analyzing different line surge arresters application
configurations also to determine best location and configuration of TLA installation.
2.1 Case Study by Kerk Lee Yen(TNB Transmission Network SB): Studies on
Optimum Installation of TLA for BBTG-RSID 132kV
2.1.1 Objective
The prime focus of this study is on elimination double circuit tripping by
installation of transmission line arrester (TLA) and also to determine best location and
configuration of TLA installation.
4
2.1.2 Methodology
The study using Sigma SLP software developed by Sodovic Consultant.
Simulations are performed assuming no shielding failure as the software could generate
only vertical stokes.
2.1.2.1 Line Sectioning
Based on tower footing resistance (TFR) and soil resistivity measurement
collected, BBTG-RSID is sectionalized to 3 sections as follow to simply the analysis:
Table 2.1: Section of BBTG-RSID 132 kV
Section
No.
Tower Average TFR
(ohm)
Soil Resistivity
(ohm-meter)
Land Profile Average
Length(km)
1 1 - 5 8.86 200 Bushes/Flat
Land
1.5
2 6 – 29 56 1000 Hilly 7.2
3 30 - 39 5.04 30 Flat land 3.0
2.1.2.2 Basic input data
i ) Tower structure – standard drawings
ii ) Total Thunderstorm day –200 thunderstorm days (Worst case scenario)
iii) Type of lightning arrester – NGK gapless
5
2.1.3 Configuration of TLA installation
1) 1-3 arrangement
2) Double bottom
3) L-arrangement
4) I – arrangement
2.1.4 RESULT
1. Without TLA installation
Result of flashover rate for the transmission line without TLA installation as
table below:
Table 2.2: Flashover rate for individual section of line
Section Total Flashover
(Flash/km-year)
Single
Circuit
Flashover
Double Circuit
Flashover
1 (T1 – T5) 0 0 0
2 (T6 – T29) 55.71 35.05 20.65
3 (T30 – T39) 0 0 0
6
Above result shows that total flashover rate for both sections 1 and 3 are
essentially zero. Hence, no installation of SLA is required for these two sections. The
main factor that minimizes the flashover rate is their good tower footing resistance
(TFR) values. TFR of these two sections are reasonably well maintained with values
below requirement – 10 ohm
However, section 2 records high total flashover rate from simulation performed.
Double circuit flashover constitutes about 37% of total flashover. As section 2 is hilly
area, TFR readings are excessively high with an average of 56 ohms. High TFR hence
contributes to higher back flashover.
2.1.5 Various installation of TLA
Table 2.3: Various installation of TSLA
No Scenario Total Flashover
(flashover/km/year)
Single Circuit
Flashover
Double Circuit
Flashover
1 1-3 arrangement 24.97 24.49 0.48
2 Double bottom 9.6 8.64 0.96
3 L-arrangement 3.36 3.36 0
4 I – arrangement 19.21 19.21 0
7
2.1.6 Simulation Result
2.1.6.1 Application of 3 TLA per tower
Configuration 3 and 4 are capable of eliminating double circuit flashover.
However configuration “L” is the most effective solution as it helps to reduce single
circuit flashover to the lowest compared to configuration “I”
2.1.6.2 Application of 2 TLA per tower
Configuration 2 “Double Bottom” records lowest total flashover rate. However,
configuration 1 “1-3 arrangement” is more effective in reducing double circuit tripping
2.2 Case Study by S.J Shelemy and D. R. Swatek from System Planning
Department, Manitobe Hydro, Manitoba, Canada
2.2.1 Objective
Study on Lightning Performance of Manitoba Hydro’s Nelson River HVDC
Transmission Lines using Monte Carlo Model
8
2.2.2 Introduction
A Monte Carlo model of the lightning performance of Manitoba Hydro’s
Nelson River HVDC Transmission Lines has been constructed in PSCAD/EMTDC
Version 3. The value of key parameters is randomly drawn from user specified
probability density functions (pdf’s). Most significant of these are the pdf’s of the
positive and negative lightning stroke amplitudes which have been derived from actual
data measured within 1km radius buffer of the lines. Estimates of the back flashover
rate and shielding failure rate were calculated using various “zone-of-attraction”
models.
2.2.3 Model Overview
A hierarchical multi-layered graphical representation of the conductor-tower-
insulator-ground system was implemented in PSCAD/EMTDC Version 3. For each
run(1 run = 1 lightning stroke), random number generators select values for the pre-
ionization tower footing resistance and for the amplitude and rise time of the lightning
current pulse based on user defined probability density functions(pdf’s). Transmission
tower geometry, stroke amplitude, and initial location are fed into zone-of-attraction
model in order to determine the most likely point of contact between the stroke and the
conductor-ground system
Each tower is represented by the detail traveling wave model. False reflections
from the artificial truncation are eliminated by a multi conductor surge impedance
termination. The non-linear time dependent characteristics of the insulator strings are
9
represented by the “Leader Progression Model” (LPM). The outcome of each run
stored in a “Monte Carlo Accumulator”. Which compare the number and nature of
insulator flashover to the total number of lightning strokes in order to obtain the rates
of back flashover and shielding failure.
2.2.4 Methodology
Lightning outage statistics are estimated by way of a monte carlo simulation, by
which we mean a multi-run case in which the key model parameters (pre-ionization
footing resistance, lightning stroke rise time, lightning stroke peak current amplitude,
and lateral position of stroke), for each separate run, are randomly drawn from a pre-
defined pool of values. The Monte Carlo simulation was run for a total of 20,000
lightning strokes (10,000 strokes for both positive and negative lightning)
2.2.4.1 Tower Model
The tower was divided into five equivalent transmission line sections including
the upper member, two cross arms, tower base, and a single equivalent of four parallel
guy wires. The propagation time along the tower member is taken to be 3.92 x 10-9
sec/m. A 5 nsec simulation time step is used.
10
2.2.4.2 Line termination
To prevent false reflections from the truncations, the line model is terminated
into its multi-conductor surge impedance.
2.2.4.3 Insulator String
The insulator string was modeled as a stray capacitance (0.476pF) in parallel
with a volt-time controlled circuit breaker. The recursive equations selected by CIGRE
for leader velocity v (t) and unabridged gap length are used.
V(t) = kLe(t)( e(t) - E50 ) m/sec
x
2.2.4.4 Tower Ground Resistance
High Magnitudes of lightning current flowing through ground decrease the
ground resistance significantly below the measured low current values.
Rt = Ro/ √( 1 + Ir )
Ig
Ig = 1 ρEo
2π Ro ²
11
A PSCAD/EMTDC Version 3 component was developed to calculate each individual
tower grounding resistance.
2.2.4.5 Point of Contact
Electromagnetic models that treat the zone-of-attraction as a strike distance
include the strike distance to ground Rg, The strike distance to the shield wire, Rs and
the strike distance to the pole conductor, Rc. Five electromagnetic models were studied
as table below:
Table 2.4: Strike distances for the Nelson River HVDC transmission line
Model rg rs rc
Young 27 Im0.32 1.07I rg 1.046 rg
Love 10 Im0.65 rg rg
IEEE 1992 T&D 9 Im0.65 1.256 rg 1.256 rg
Brown & Whitehead 6.4 Im0.75 1.274 rg 1.180 rg
Eriksson N.A 6.8 Im0.74 5.9 Im
0.74
List of the critical peak current amplitudes predicted for the Nelson River HVDC
transmission line tower as table below
Table 2.5: Critical peak lightning current amplitudes for the Nelson River HVDC
transmission line towers
Model Critical Current(kA) Young 25 Love 30
IEEE 1992 T&D 70 Brown & Whitehead 20
Eriksson 15
12
2.2.4.6 Lightning Stroke
The lightning stroke was modeled as a current impulse, idealized as a triangular
wave. Because insulation occurs shortly after the lightning strike, the fall time was
fixed at 100 micro-sec.
2.2.5 Results
Using fault data for the Nelson River HVDC transmission lines collected
between 1998 to 2000, faults were correlated to lightning strikes occurring at the same
time and location. Over this period of time the FALLS program found 5066 negative
lightning strokes and 530 positive lightning strokes within 1 km radius buffer of the
transmission line. Out of these lightning strikes, only 6 are found to have caused
lightning failure and due to shielding failures and back flashovers. The result of the
simulation of lightning strike to the Nelson River HVDC transmission line as listed in
table below:
Table 2.6: Back flashover rates and shielding failure rates per 10,000 lightning strikes
Model Back Flashover Shielding Failure Young 2 11.2 Love 3.3 58.5
IEEE 1992 T&D 6 75.5 Brown & Whitehead 7.5 3
Eriksson 2.1 6.2 Measured 3.6 7.1
13
From the result above, model of Young’s, Love’s and the IEEE 1992 T&D
greatly over predicted the number of shielding failures. On the other hand the two
remaining models, Brown & Whitehead and Eriksson’s model predicted failure rates
closer to those actually observed, however the Brown & Whitehead model predicted a
disproportionately high ratio of back flashovers to shielding failures. Of the models
tested, Eriksson’s model yielded failure rates most consistent with the recorded data.
2.2.6 Conclusion
Through this analysis, the estimation of the back flashover rate and shielding
failure rate were calculated using various zone-of-attraction models and Eriksson’s
model yielded failure rate most consistent with lightning correlated fault data
measured.
2.3 Line Surge Arrester Application on Quadruple Circuit Transmission Line
by Y. A. Wahab, Z. Z. Abidin and S.Sadovic
2.3.1 Objective
This paper is dealing with the application of line surge arresters on the
quadruple circuit transmission line and to analyze different line surge arresters
application configurations in order to optimize application of this technology to the
existing and to the future quadruple transmission lines.
14
2.3.2 Introduction
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. With this arrester configuration, double circuit outages are eliminated but there
exists possibility to have flashovers on the circuit without arresters.
Based on the positive experience with the surge line arresters on 132kV double
circuit lines, it was decided to extend line surge arrester application to the quadruple
circuit lines: 2 x 275kV and 2 x 132kV. By the application of the line arresters on
132kV circuits only, line overall lightning performance is improved since the majority
of the flashovers will happen to 132kV circuit.
2.3.3 Model Overview
The circuit needs to be modeled is a quadruple circuit transmission line
Balakong-Bandar Tun Razak, being commissioned in 1992, consists of two 275kV
circuit and two 132kV circuit. Route length is 10.6km and number of towers is 37.
Average line span is 300m. Line is operating with an average ground flash density of
10-20 strokes/km squared/year
2.3.4 Methodology
15
All computer simulations are performed using sigma slp simulation software tool.
2.3.4.1 Electromagnetic model
Line span is divided into short sections (10-15m each), in order to accept
lightning stroke to the ground wires or to the phase conduction along the span. A total
number of 20 to 30 thousand strokes are used in the electromagnetic simulations.
Following striking distances are used:
The Striking Distance to the conductor (CIGRE)
rc = 10I 0.65
The striking distance to earth (IEEE)
re = 5.5I 0.65
The striking distance to tower top
rT = 1.05 rc
I(kA) – lightning stroke current
Two line CIGRE stroke distributions are modified to represent stroke distribution to
flat ground as table below:
Table 2.7: Two-line stroke distribution to flat ground
Parameter Shielding Failure
range ( I < 15.9 kA)
Backflashover
Range( I > 15.9 kA)
Im (kA) 48.4 26.4
σ 1.33 0.605
16
2.3.4.2 Tower footing resistance model
The tower footing impulse resistance by the following equation:
Ri = Rt / √ ( 1 + I )
Ig
Ig = 1 ρEg
2π Rlc²
where:
Rt - Tower footing resistance at low current and low frequency, (ohm)
(Rt = 10 – 40 ohm)
Ri - Tower footing resistance, (ohm)
Ig - The limiting current to initiate sufficient soil ionization,(A)
I - The lightning current through the footing impedance, (kA)
ρ - Soil resistivity ( 100 ohm-m)
Eg - soil ionization critical electric field (kV/m), (Eg = 400 kV/m)
Rlc - tower low current resistance
ρ - 50
Rlc
2.3.4.3 Line insulation flashover model
The leader propagation model is used to represent line insulation flashovers:
Vl = 17 0d (u(t) ) - Eo e0.0015u(t)/d
17
D – l L
Where :
V1 = Leader velocity, m/s
d = Gap distance, m
l L = Leader length, m
u(t) = Applied Voltage, kV
E0 = 520, kV/m
2.3.4.4 Tower Model
Section of the tower from the bottom cross arm to the ground is represented as
propagation element, which is defined by the surge impedance Zt and the propagation
length Iprop. Wave propagation speed on the tower was taken to be equal to the velocity
of light. Section on the tower top(between tower top and top cross arm) are modeled as
inductance branches parallel with damping resistors
2.3.4.5 Transmission Line Surge Arrester
Polymer housed line surge arrester with an external gap is used with the
following characteristic:
Rated Voltage: 120kV
Series gap spacing: 650mm
IEC Line discharge class: II
Critical flashover voltage: 620kV
18
2.3.4.6 Corona model
The influence of the corona is modeled by the capacitance branches which are
connected between conductors and ground
2.3.5 Result of Lightning Performance
Line lightning performance is first determined for the line without arresters and
then several arrester installation configurations are studied. Lightning performance of
a line without line surge arresters is presented in table below:
Table 2.8: Flashover rate for different circuits without line surge arresters
( flashover rate/100km/year)
Rt(Ω) C1(275) C2(275) C3(132) C4(132) 10 0 0 0 0 15 0 0 0.78 2.14 20 0 0 5.66 4.88 25 0 0.19 12.69 10.92 30 0.19 0.39 20.69 20.69 35 0.19 0.58 29.67 33.58 40 0.19 0.19 42.55 46.85
From the above table has shown the majority of the flashover happened on
132kV circuits. For the tower footing resistance less than 10Ω, zero flashover rates is
obtained. Table below is line total, single, double and triple line flashover rates
presented.
19
Table 2.9: Line total and multi circuit flashover rate without
line surge arresters ( flashover rate/100km/year)
Rt(Ω) Total Single Double Triple 10 0 0 0 0 15 2.93 2.93 0 0 20 8.39 6.24 2.14 0 25 18.35 13.08 5.07 0.19 30 32.6 23.81 8.19 0.58 35 49.26 32.41 14.64 0.78 40 65.64 41.98 22.84 0.78
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 40 Ω. Results of the simulation for the different line arrester installation
configuration are presented in tables below:
Table 2.10: Line Total Flashover Rate
Different Arrester Installation Configurations ( flashover rate/100km/year)
Rt(Ω)
o : o o : o o : o o : o o : o
o : o o : o o : o o : o o : o
o : o o : o o : o o : o o : o
o : o o : o o : o o : o o : o
10 0 0 0 0 15 2.93 0 0.19 0 20 8.39 0.78 2.14 0 25 18.35 2.53 6.24 0.58 30 32.6 5.66 9.37 0.97 35 49.26 8.78 15.62 3.12 40 65.64 13.08 23.62 3.89
o - Without Lightning Surge Arrester
o - With Lightning Surge Arrester
The substantial improvement in the line total flashover rate is obtained by the
installation of line arresters on the two bottom conductors of 132kV circuits than the
20
three arresters installed on the all phase conductors of one 132kV circuit. The best
improvement in the line total flashover rate is obtained by the installation of the
arrester on the bottom conductor of one 132kV circuit and on the one top conductor of
one 132kV circuit.
Table 2.11: Line Double Total Flashover Rate
Different Arrester Installation Configurations ( flashover rate/100km/year)
Rt(Ω)
o : o o : o o : o o : o o : o
o : o o : o o : o o : o o : o
o : o o : o o : o o : o o : o
o : o o : o o : o o : o o : o
10 0 0 0 0 15 0 0 0 0 20 2.14 0 0 0 25 5.07 0.19 0 0 30 8.19 0 0 0 35 14.64 0.58 0 0.19 40 22.84 1.17 0 0.39
When line surge arresters are installed on all phases conductors of one 132kV
circuit, double circuit flashover are completely eliminated. 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 132kV
circuits and on the one top conductor of one 132kV be able to reduce line total
flashover rate and at the same time reducing double circuit flashover rate.
2.3.6 Conclusions
21
Lightning Performance with different voltage levels can be improved by the
installation of the LSA on the lower voltage level circuits only and the ‘L’ arrester
configuration will give the best improvement in the line total flashover rate
CHAPTER 3
TRANSMISSION SYSTEM
3.1 Transmission Line and Ground Wire
Three type of transmission tower are being used in the transmission system,
whish sre the old single circuit, double circuit and the quadruple circuit. The current
practiced is to build double circuit or quadruple circuit due to the needs to transfer
large quantity of power. The double circuit transmission lines are used for voltage from
132kV, 275kV to 500kV. The quadruple circuits are used either for 132kV/132kV
circuit or for 275kV/132kV circuit.
The conductor used in transmission lines is called ACSR (Aluminium
Conductor Steel Reinforced). The ACSR conductor consists of aluminium and steel
stranding. Two conductors are used per phase and are kept apart at a distance of
22
400mm by the use of spacers. For quadruple circuit line design the 275kV lines used a
configuration of 2x400mm squared bundle namely zebra and 132kV lines uses a
configuration of 2x300mm squared bundle namely batang. The earth wire used is
ACSR 60mm squared namely skunk. Two earth wires are used per tower, one on each
side
Table 3.1: Conductors Type and Their Specification
3.2 Insulator
Insulators are defined as non-conductive materials that cover separate or
support a conductive material to prevent a passage of electricity to ground. From the
point of transmission system, the insulator are being used to separate the conductors
that carries large amount of current and the tower body that are directly connected to
ground. The insulators are very important to the operating performance of the
transmission system itself. The insulator provide mechanical support to the conductors
and all the current carrying parts and subjected to normal operating and transient
voltage
Conductor Code Name
Nominal Cross Sectional Area
(mmⁿ)
Actual Cross Sectional Area
(mmⁿ)
Maximum Resistance At 20C (Ω)
Diameter (mm)
Voltage (kV)
ACSR Curlew
500 n/a n/a n/a 500
ACSR Zebra
400 428.9 0.0674 28.62 275
ACSR Curlew
300 338.5 0.0892 24.16 275 & 132
ACSR Curlew
150 n/a n/a n/a 132
23
Standard materials used on transmission tower insulator are usually glass and
porcelain because it has high dielectric strength and easily spotted if break. The type
used are pin and cap types.
Table 3.2: Number of insulator set required based on voltage and type of insulator set
Type of Insulator set
Installation location 132kV insulator
units
275kV insulator units
Upright Light Duty Tension Set
Upper end of the slack spans between terminal tower
10 20
Inverted Light Duty Tension Set
Lower end of Slack end with line end and earth end arching horns
10 16
Jumper suspension Set
Heavy angle towers to maintain the electrical clearances between the jumper loops to the tower body
13 20
3.3 Insulation Coordination
3.3.1 Definitions of Insulation Coordination
IEC: The selection of the dielectric strength of equipment in relation to the
voltages which can appear on the system for which the equipment is intended
and taking into account the service environment and characteristics of the
available protective devices
IEEE: The selection of insulation strength consistent with expected over
voltages to obtain an acceptable risk of failure
General: The protection of electrical systems and apparatus from harmful over-
voltages by the correlation of the characteristics of protective devices and the
equipment being protected
24
3.3.2. Insulation Coordination
Insulation coordination is an optimization process where the attempt is made to
keep the overall cost of insulation, protection devices and service interruption
to a minimum.
For self-restoring insulation some failures have to be tolerated. However,
insulation failures should be confined to areas where they cause minimum
damage and least interruption of supply; and they should not compromise the
safety of operating personnel.
3.3.3. Insulation Coordination Involves
Estimating of credible over voltages that may appear in the network, their peak
values, wave shapes and frequency of occurrence.
Exploring means of reducing and/or diverting the over voltages.
Selection of insulation levels to achieve the performance criteria.
3.3.4. Selection of Insulation Levels
25
For Voltages up to 300 kV
♦ Insulation is designed to withstand lightning and power frequency
overvoltages.
♦ Sufficient margin is kept between the maximum overvoltage and the
minimum withstand strength.
For Voltages Higher than 300 kV
♦ Choice of insulation and tower dimensions to withstand switching
overvoltages.
♦ Check the number of failures due to atmospheric overvoltages.
♦ Check the ability of the design to withstand power frequency
overvoltages under different operating conditions.
3.3.5. Basic Principles of Insulation Coordination
The process of correlating the insulation strengths of electric equipment with
expected overvoltages and with the characteristics of surge protective devices.
Main Issues:
♦ System overvoltages, their wave shapes, peak values and probabilities
of occurrence.
♦ Withstand characteristics of different types of insulation to different
types of overvoltages.
♦ Measures used to reduce system overvoltages and protective devices to
divert them
26
3.3.6. Insulation Withstand Characteristics
Voltage/Clearance Characteristics
♦ Withstand voltage as a function of gap spacing for lightning and
switching surges.
Voltage/Time Characteristics
♦ Withstand voltage as a function of time to crest of the voltage surge.
Observations
♦ Lightning overvoltage is important for high voltage systems.
♦ Switching overvoltages are more important in extra- and ultra-high
voltage systems.
3.3.7. Standard Basic Insulation Levels
Standard BILS developed for various system voltages based on experience.
Test voltage levels for other types of surges and tests are usually associated
with the equipment BIL.
Standard BILS originally intended irrespective of how system was grounded.
27
It became recognized that lower voltage arresters could be used on solidly
grounded systems thus providing lower protective levels (better protection) for
equipment insulation.
Resulted in reduced insulation levels (one or more steps lower).
At EHV, much greater economic incentive to use lower insulation levels
through better arrester protection.
Table 3.3: Standard Basic Insulation Levels(BIL)
System Voltage
Class (kV)
Standard BIL Reduced BIL
(kV)
115 550 450
138 650 550
161 750 650
198 900
230 1050 900
287 1300
345 1550
*For effectively grounded system using 80% arrester
3.4 Arching Horn
Arching horn put at the live end of the conductor string to create a preferred
path for lightning impulse to prevent flashing over at the conductors and insulators,
which might damage it. Table 3.3 shows at arching distance and BIL at various circuit
and tower design
Table 3.4: Arching distance and BIL for various circuit and towers
Circuit & Towers No.of Insulator
Disc
Arching Distance
(m)
BIL (kV)
275kV High Insulation Suspension
16 2.16 1819
28
275kV Low Insulation Suspension
16 1.78 1411
275kV High Insulation Tension
2x20 2.62 1440
275kV Low Insulation Tension
2x20 1.83 1100
132kV Suspension 10 1.40 1160 132kV Tension 2x14 1.87 1000
3.5 Earthing
The basic lightning protection consists of atroke interceptor (earth wire), a
down lead (tower) and an earth connection, whose primary function is to dissipate the
lightning current safely into the ground. When the lightning struck the earth wire, a
large amount of current flows through the tower and into the ground through the
grounding system. The potential of the tower will be raised above the earth potential by
an amount equal to or at least to the product of current and impedance of the earth path.
If the potential rise minus and conductor voltage are much higher than the withstand
voltage of the arching horn, a back flashover would occur from the tower to the
conductor.
It is found that the BFR of a shielded line are very sensitive to tower footing
resistance of the tower and that the BFR decrease with the decrease of the tower
footing resistance. In addition, the discharge of the lightning currents into the ground
will raised the potential around the earth point and those potential are related to the
earth resistance and soil resistivity. Good earthing will reduce the BFR as well as the
spread of dangerous voltages around the earth point.
3.6 Tower Types
29
The tower family are usually selected based on their distribution of line angle.
Line angle could be grouped such that angle would follow a pattern of light medium
and heavy suspension and medium and heavy tension types. Tower types are divided
into four categories:
1. 23 Series tower : 2x132kV – twin(duplex) 2x300mm sq. “Batang”
2. 24 Series tower : 2x275kV – twin(duplex) 2x400mm sq. “Zebra”
3. 2423 Series tower : 2x275kV + 2x132kV – twin(duplex) 2x400mm sq.
“Zebra” + twin(duplex) 2x400mm sq. “Zebra”
3. 2323 Series tower : 2x132kV – twin(duplex) 2x300mm sq. “Batang” +
2x132kV – twin(duplex) 2x300mm sq. “Batang”
Table 3.5: Tower types and deviation angle
Tower Type Angle of Dviation
Suspension Tower (Line-tower) 0-2
Tension Tower (Section Tower) 2-10
Tension Tower (Medium Tower) 10-30
Tension Tower (Heavy Tower) 30-60
Tension Tower (Right Tower) 60-90
Tension Tower (Terminal Tower) 0-10
3.6.1 Tower with wooden cross arm
The advantages of wooden cross arm is its higher impulse level and its good arch
quenching properties, which result in a better lightning performance of the line. The
30
275kV cross arm is made from 4 pieces of chengal timber , 2 strut and 2 tie members
and the 132kV design is made from 3 pieces of chengal timber, 2 strut and 1 tie. Due to
its structursl strength limitation, wooden cross arm are used only in light suspension
tower while the heavy suspension and tension towers are fitted with steel cross arm and
longer tension strings.
3.7 Design Span
Span is defined as a distance between a tower top to the next adjacent tower with
both tower are in the same tower family. The three terms used for span are:
1. Basic Span defined as horizontal distance between centres of adjacent
supports on level ground from which the height of standard supports is
derived with the specified conductor’s clearances to ground in still air at
maximum temperature
2. Wind Span defined as half the sum of adjacent horizontal span length
supported on any on tower
3. Weight Span defined as equivalent length of the weight of conductor
supported at any one tower at minimum temperature in still air
3.8 System Over voltages
Characteristic:
♦ They appear during abnormal operating conditions or during transitions
between steady states.
31
♦ They can have values much higher than system operating voltage.
♦ They form a threat to the integrity of the system and the safety of
personnel.
Classification:
♦ By origin:
internal overvoltages
external overvoltages
♦ By waveshape:
temporary overvoltages
slow front overvoltages
fast front overvoltages
3.9 Fast Front Over voltages
Due to lightning strokes hitting towers, ground wires, or phase conductors.
Can also be induced by coupling with structures hit by lightning.
Frequency of occurrence depends on the thunderstorm activity in the area
which is measured by the number of thunderstorm days per year.
The amplitude of the overvoltage surge generated by atmospheric discharge
depends on the discharge current, line surge impedance and tower footing
resistance.
3.10 Surge Arresters
32
The application of surge arresters on distribution lines started around 1975 in
Japan. Field trial of surge arresters 66kV, 77kV and 138kV lines were carried out in
and around 1980 in Japan and the United States. An external air gap in series with the
surge arrester was introduced in 1985 to electrically isolate the surge arrester from the
system. No international Standards specific on TLA available. Table below
summarizes the basic requirements of TLA
Table 3.6: Fundamental requirements for surge arresters on line(TLA)
Functional Practical
Suppress over voltages and prevent flashover
at the instant of lightning
Light and compact
Is able to cut off follow current before
operation of the circuit breaker
Easy to install on towers
Not operate under the switching over voltages Minimum maintenance and easy to inspect
Not cause permanent fault and impedance
circuit re closing in the event the arrester fails
Long life and adverse weather proof
Safe and explosion-proof
The idea of using metal oxide-surge arresters to prevent lightning fault on lines has
existed quite a long time. However, there was a practical concern on “stresses” that
these surge arresters may be subjected when installed on towers and the line tripping
that the disconnecting device fail to operate to isolate the faulty arresters.
Four general classes of devices that have been used to limit over voltages and
permit lower (more economical) insulation levels of equipment:
♦ spark gaps
♦ expulsion-type arresters
♦ gapped valve-type arresters
33
♦ (gapless) metal-oxide arresters
Devices do not provide the same degree of protection
Spark gaps have been used up to 245 kV in locations with modern lightning
activity.
3.11 Metal-Oxide Arresters
Advantages using Metal-Oxide arresters as below:
Use metal-oxide (zinc oxide) for non-linear resistor element.
Metal-oxide has a much more non-linear characteristic than silicon carbide.
Characteristic is so flat that current at normal (1 per unit) voltage is in
milliamps range that element can conduct continuously without overheating.
No series gap required
Some early versions used a shunt gap across some of the elements to reduce
discharge voltage at high currents. No longer used in current designs.
Present metal-oxide arresters have better protective characteristics than gapped
silicon-carbide arresters and also other advantages.
Metal-oxide arresters are very suitable for HVDC applications due to
possibility of using parallel columns to share duty.
3.12 Gapped TLA and Gapless TLA
34
Both type of TLA are being used in many utilities worldwide to prevent
lightning faults on transmission lines. However some utilities may prefer one to the
other. Both types have advantages and disadvantages owing primary to the fact that the
gapless TLA is connected directly to the system while gapped TLA is only connected
directly to the system temporarily during the gap (spark over) operation. Table below
shows the major differences between gapped TLA and gapless TLA. This table is used
as basis for selecting of gapless TLA in this modeling
Table 3.7: The major differences between gapped TLA and gapless TLA
Subject Gapped TLA Gapless TLA
Basic Construction
Metal-oxide surge arrester unit in series with external air gap connected between live phase conductor and earth
Metal-oxide surge arrester directly connected live conductor and earth
Operation Principle
When lightning strikes the tower or shield wire, there will be a rise of voltage on the tower. The voltage across the insulator may reach sufficiently high value and cause the gap to spark over. A large lightning surge arrester is discharged through surge arrester and overvoltages are suppressed. As lightning surge current is discharged, resistance of ZnO block increases and current becomes small.
Metal oxide surge arrester to suppress the overvoltages across the insulator. Disconnecting device will operate to isolate the arrester in case the arrester fails during service
TLA Reliability
Faulty arresters may reduce the breakdown strength of the SLA and upset the overall insulation coordination. Gap distance critical. Air gap operation can be affected by conditions during service.
Very critical because faulty arrester would cause the line to trip
Faulty arrester isolation
Provided by external series air gap
Arrester is usually equipped with a disconnecting device to isolate faulty arrester. The disconnecting devices operation must not affect line clearance or impedance line re-closing
Electrical Stresses
Not subjected to temporary over voltages. Lower arrester rating and smaller arrester feasible
subjected to temporary over voltages on the system. Higher electrical stresses on the arresters
35
MOV block and polymeric housing
Installation
More hardware needed (external spark gap rods). Gap distance critical
Less hardware needed. Spaces on the strength of (existing) towers may be the limiting factors for large and heavy SLA
Maintenance
Periodic inspection and maintenance of surge arresters and spark gap rods recommended
Periodic inspection and maintenance of surge arresters recommended
Subject Gapped TLA Gapless TLA Arrester size and weight
Smaller arrester unit possible Connected continuously to the system and subjected to over voltages in the system. Bigger and larger arrester may be required
Energy sharing Energy less assured and can be affected by the “non-ideal” air gap spark-over
Better energy sharing between arresters
Operational Risk
Failure of air gap to operate correctly and consistently. Gap operation may be affected by conditions in service
Failure of the disconnecting device to operate to isolate faulty arresters
3.13 Surge Lightning Arrester placement (TLA)
The placement of arrester for black-flashover, direct stroke and induced surges are summarized below :
Table 3.8: TLA placement and energy consideration
Strokes TLA Placement Energy Consideration
High energy direct strokes to line without shield wire
Fir arresters on the other phases and adjacent structures if high TFR causes back flashover from struck phase and structure to another phase
Arrester must withstand discharge energy and high current amplitude in lightning impulse.
Low energy direct strokes arising from shielding failure also occurring on unshielded lines
Fit arresters to phases for which shielding failure is expected
Shielding angle
Backflashover – low energy injected into the
Fix arresters on exposed structures on those phases most likely to suffer
Low energy rating adequate because most
36
3.14 Comparison of Available Surge Arresters (Gapless Type)
There are number of high voltage surge arrester manufactured by several
company which can be discussed here as mean of reference in designing the
transmission line arrester. Below is the data for SLA which is PROTECTA*LITE by
Ohio Brass, PEXLIM R120-YH145H by ABB and SLA.2.120.030 by Sediver
Table 3.9: Data on Gapless Transmission line arrester manufactured by
several company
PROTECTA*LITE PEXLIM R120-YH145H
SLA.2.120.030
Manufacturer Ohio Brass ABB Sediver Rated Voltage (kV) 120 120 120 Uc (kV) 92 MCOV (kV) 98 98 96 Nominal discharge current (kA)
10 10 10
Line discharge class
2 2 2
Energy capability (kJ/KVur)
5.1 5.2 5
Insulation material ESP Silicon Silicon Creepage distance (mm)
4,694 3,726 3,736
Weight (kg) 18 25 32 Length (mm) 2,140 1,216 1,470
phase conductor from the structure
back flashover energy is discharged into the shield wire earthing
Induced surges greater than line insulation
Install arresterson all phases on all structures exposed to high induced surges
Low energy rating adequate because discharge is shared by many arresters and structures
37
CHAPTER 4
METHODOLOGY
4.1 System Modelling
The main emphasis is to identify the models of power system components to be
used in the lightning studies. For each component, the important model parameters will
be described and typical values will be provided.
38
4.2 EMTP Simulation
EMTP is a computer simulation program specially designed to study a transient pheno
mena in the power system It contains a large variety of detailed power equipment
models or builds in setups that simplify the tedious work of creating a system
representation. Generally, this simulation software can be used in design of an
electrical system or in detecting or predicting an operating problem of a power system.
ATP-EMTP is used in this simulation process of observing the electrical response of
the transmission system. To represent the electrical response of the transmission
system, electrical model of the transmission system apparatus have to be selected and
validated to gain high accuracy result.
4.3 Selected model and Validation
Models are circuit or mathematical or electrical representation of a physical apparatus
so that its characteristic by the means of an output when applied with certain input. In
EMTP simulation, the input and output that are usually observed are current, voltage,
power and energy. A complete set of representation of a transmission system are
combination of every model of the transmission line apparatus itself.
4.4 Transmission Line
39
The line which is Quadruple circuit 2 x 275kV and 2 x 132kV from Balakong to
Bandar Tun Razak was commissioned in January 1995. The 12.07 km long line span
across the urban areas of Balakong, Seri kembangan and Serdang with a number of
spans cut across plantation, jungle and hills. The line comprises of 37nos. of 2423
series towers with steel cross-arms. The detail of the overhead transmission line system
as below:
Table 4.1: Balakong to Serdang 132kV line information
Line length (km) 12.07
37 (No. T49A – No. T85A) Number of Tower
Suspension: 11 Tension: 16
Tower 2423 series
Cross arms Steel
Span Length (m) Min; 173 Max: 530 Avg: 335
TFR (Ohm) Min: 1.1 Max: 11.0 Avg: 3.7
Altitude from sea level(m) Min: 37 Max: 142 Avg: 77
Terrain 16 towers on flat land and 21 towers on hills
4.5 Line exposure to lightning
How often an overhead transmission line is likely to be struck by lightning must
be known to assess its lightning performance. For this purpose, the first step is to
characterize the lightning activity in the region crossed by the line. Number of
lightning activity can be calculated as :
25.104.0 Dg TN =
40
Ng = Number of flashes to ground per square kilometer per year
h = Average height of the line
b = Width of the line
Ns = Total hit to line
The Lightning performance of an overhead line depends on the ground flash density of
the region and on the incidence of lightning strikes to a line.
Fig. 4.1: Model of Transimission Line
4.6 Shielding Failure
PMU Balakong PMU Bdr TunRazak S/S
OHLine 1000 MVATransition Transition
Underground Cable 1000 MVA
Underground Cable 1000 MVA
Switching Switching
( )bhN
N gs += 09.14
10
Lightning
41
The phase conductor exposure to lightning is evaluated using an electrogeometric
model. Line span is divided into short sections (10m to 15m), in order to accept
lightning stroke to the ground wires or to the phase conductors along the span.By using
IEEE 1992, the following striking distances are used :
The striking distance to a conductor :
rc = 1.256 rg
The striking distance to earth :
rg = 9Im 0.65
The striking distance to top tower :
rt = 1.05 rc
Im(kA) = 70kA (Lightning Stroke Current)
4.7 Overhead Transmission Lines
The overhead lines are represented by multi-phase models considering the
distributed nature of the line parameters due to the range of frequencies involved
Phase conductors and shield wires are explicitly modeled between towers and only a
few spans are considered. The line parameters can be determined by a line constants,
using the tower structure geometry and conductor data as input.
4.8 Line length and Termination
42
Since peak voltage at the struck tower is influnced by reflections from the
adjacent tower sufficient number of adjacent towers at both sides of the struck tower
should be modeled to determine the overvoltages accurately. Number of line span need
to modeled in such that the travel time between the struck tower and the fartest tower
is more than one-half of the lightning surge front time. Fig 2, shows the model of
transimmision line and tower used for lightning studies
Fig. 4.2: Overhead Transmission Line, Tower and Insulator model
4.9 Tower Model
Transmission line tower model used in all simulation is represented as in Fig 3.
Section of the top tower (between tower top ad top cross arm and between cross arm)
are modeled as inductance branches which is determined according to section length,
tower surge impedance and the propagation velocity.
Phase Conductors and Shield Wires
Insulators
Towers
43
Section of the tower from the bottom cross arm to a ground is represented by
the surge impedance Zt and the propagation length Iprop as in Fig 4 . Wave
propagation speed on the tower was taken to be equal to the velocity of light. Detail
parameters as shown in Fig.4
This tower model is based on the work of M.Ishii, which is recognized as a
detail tower model widely used in Japan for EMTP simulation purpose. This tower
model does not consider the tower wrm, which is available with new tower model
develop by other author. There is six-tower model parameter, which is important in
selecting its parameter
♦ Zt = Tower Surge Impedance
♦ VL = Surge Propagation Velocity
♦ γ = Attenuation coefficient
♦ α = Damping coefficient
♦ R = Damping resistance
♦ L = Damping Inductance
44
Fig 4.3: Tower Representation for Quadruple Circuit Transmission Line
Fig 4.4: M. Ishii’s tower model for a double circuit line tower
275 kV circuit U50% = 1120 kV Parallel Resistance-Inductance branch 132 kV circuit U50% = 880 kV Propagation element Zt, Iprop
45
This double circuit tower model could be extended into quadruple circuit tower
model with little modification. To produce high accuracy result, current impulse test
should be conducted to the quadruple tower to validate its voltage and current
response so that the selected parameter of Zt, R and L could be modified to increase
the accuracy of the simulation. Formula used for double circuit tower could be
modified to be used as quadruple tower model as follows:
H = h1 + h2 + h3 + h4 + h5 + h6 + h7
Ri = -2Zt1 x ln√γ x h1
h1 + h2 + h3 + h4 + h5 + h6
R7 = -2Zt2 x ln√γ
Li = α x Ri x 2H
Vt
4.10 Tower footing resistance model
Steel towers are represented as a single conductor distributed parameter line
terminated by resistance representing the tower footing impedance. By using a soil
ionization model, the tower footing impulse resistance is described by the following
equations :
Rt = Ro
√(1 + I/Ig)
Ig = ρEg
2π Rlc ²
46
where:
Ro - Tower footing resistance at low current and low frequency, (ohm)
(Ro = 10 – 40 ohm)
Rt - Tower footing resistance, (ohm)
Ig - The limiting current to initiate sufficient soil ionization,(A)
I - The lightning current through the footing impedance, (kA)
- Soil resistivity ( 100 ohm-m)
Eg - soil ionization critical electric field (kV/m), (Eg = 400 kV/m)
Rlc - tower low current resistance
The tower footing low current resistance was varied between 10 – 40 ohm and
the ratio between the soil resitivity and the tower low current resistence was kept
constant at 50 and typical tower grounding resistance is between 10 – 100 ohms.
4.11 Insulators
The insulators are represented by voltage-dependent flashover switches in
parallel with capacitors connected between the respective phases and the tower. Refer
to Fig.4.2
Typical capacitance = 80pF/unit
4.12 Back flashover
47
The back flashover of the insulators can be represented by volt-time curves.
CIGRE suggested that the leader propagation model is used to represent line insulation
flashovers and can be calculated using the equation as below :
V1 = 170d u(t) - Eo e0.0015(u(t)/d)
d – l1
Where :
V1 = Leader velocity, m/s
d = Gap distance, m
l1 = Leader length, m
u(t) = Applied Voltage, kV
Eo = 520 ( kV/m )
Critical flashover voltage ( U50%) of 275 kV circuits was 1120kV and value for
132kV was 880kV.
4.13 Corona
The influence of the corona is modeled by the capacitance branches, which are
connected between conductors and ground. Although corona effects may reduce the
peak of lightning related over voltages by 5 – 20%, in this study corona is neglected in
order to be on the pessimistic side and take the worst condition of the lightning struck.
From the evaluation procedures implemented in PLASH and DESCARGA, the corona
effect does not significantly affect the computation result
48
4.14 Line surge arrester
For representing the non-linear characteristic of ZnO surge arrester, Pinceti’s
model has been planned to be used in simulation. Pinceti’s model was introduced in
year 1999 and are the easiest model to be used. The model is from the IEEE working
group with some minor difference. The model can be realized directly rom
performance data rom residual voltage with various current impulses supplied by the
manufacturer
The inductance value can be obtained directly from residual voltage in kV of ½,
¼ or 1/20 us impulse and 8/20 us impulse of the same current impulse. The formula
used to obtained the inductances is as below. All value obtained are in Uh
L0 = 121
20/8
20/820/1 )(V
VV − (Ur)
L1 = 41
20/8
20/820/1 )(V
VV − (Ur)
For the non-linear element A0 and A1, the value can be obtained from 8/20 us
impulse data as supplied by the manufacturer. The table bellows shows the value of A0
and A1 based on the recommendation from the author
49
Table 4.2: Value for A0 and A1 based on 8/20 us residual voltage supplied by
manufacturer for the application of Pinceti’s arrester model.
I [kA] A0[p.u] A0[V] A1[p.u] A1[V]
2x10-6 0.810 - 0.623 -
0.1 0.974 - 0.788 -
1 1.052 109829 0.866 90410
2.5 1.096 121875 0.910 101192
3 1.108 - 0.922 -
5 1.147 134199 0.961 124437
10 1.195 153797 1.009 129858
20 1.277 - 1.091 -
Fig. 4.5: Pinceti’s arrester model used for representing surge arrester
Polymer housed line surge arrester with gapless type is choosen to be used for
the lightning performance improvement. The example of SLA installation as in Fig 6.
50
-6.00
-4.00
-2.00
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
1
Rel
ativ
e E
rror
[%]
5 kA 1/10 us1 kA 8/20 us2.5 kA 8/20 us5 kA 8/20 us10 kA 8/20 us100 A 30/60 us250 A 30/60 us500 A 30/60 us1 kA 30/60 us
Figure 4.6: Relative error of residual voltage for representing Siemens 120kV rated
3EQ4-2/LD3 SA with Picenti’s model compared to manufacturer performance data
The selection of gapless type compare to gapped type is as per appendix 1.
Both types have advantages and disadvantages owing primarily to the fact that the
gapless type is connected directly to the system (and continuously exposed to the
system voltage and to any over voltages that may appear on the system) while gapped
type is only “connected” directly to the system temporarily during the gap (spark over)
operation. Proposed Surge arrester (manufactured by ABB) has the following
characteristics:
Rated Voltage 120 kV
Uc(kV) 92kV
MCOV(kV) 96kV
Nominal discharge current 10kA
IEC Line discharge class 2
Energy capability(kJ/KVur) 5.2 (kJ/kVmcov)
Insulation Material Silicon
Critical Flashover voltage 620 kV
Creepage distance(mm) 3,736mm
Weight(kg) 25kg
Length(mm) 1,216mm
51
Fig 4.7: Example of Gapless-type Surge Arrester installed at 132kV BLKG-SRDG
The arresters can be modeled as nonlinear resistors with 8 x 20us maximum
voltage-current characteristics. SiC surge arresters will be installed at 132kV circuits
only because the lower voltage (132kV) circuits of the quadruple line have lower line
insulation critical flashover voltages, which means that the majority of the
backflashover will happen on the 132kV circuits
4.15 Selection of Lightning Configuration
Several arrester installation configuration will be studied with maximum
number of the arrester to be used is less or equal to three. The example installation
configuration are as Fig 7.
52
1) 1-3 arrangement 2) Double bottom
3) L-arrangement 4) I - arrangement
Fig 4.8: Different arrester Installation Configurations
- With `Line Surge Arrester Installed
- Without Line Surge Arrester Installed
CHAPTER 5
AVAILABLE METHOD FOR LIGHTNING PERFORMANCE IMPOVEMENT
53
There are several methods available for improving the lightning performance of
a transmission line in services. This method can be applied for improving the lightning
performance of a transmission line already in services.
Fig. 5.1: Available Method for Lightning Improvement
5.1 Additional Shielding Wire
Shield wire could be added or modified to a tower design. The shielding angle
could be decrease or in the case of quadruple circuit, additional of an under running
and over running ground wire to the 132kV circuit could be done. Improvement in the
performance of the 132kV circuit are expected due to coupling of the lower phases and
upper phases with over running ground wire are comparable with the normal double
circuit line. However, this solution would translate into high cost especially if the
provisions are not in the original tower design. It would eliminate a large number of
interruptions but not enough to obtain a new demanded degree reliability.
Increasing
Additional Shiels
Line Surge
Foot resistance
Under built Ground
54
5.2 Tower Footing Resistance
Resistance value for transmission line with high Footing Resistance can be
improved by method of counterpoise that could lead to improve the performance of the
line. However this method is often difficult and expensive especially in hilly terrain. In
the case of quadruple circuit line with good grounding and low lightning performance,
this method ie useless because the low performance of the lower portion of the
quadruple circuit line are caused low coupling with the ground wire, lower insulation
and sacrificial nature of lower circuit due to the tower height.
5.3 Increase the Tower Insulation
This method can be used to increase the lightning performance of the line but also
would require a large modification of the clearance and mechanical strength of the
tower structure, which would lead to high cost. The insulation of the station equipment
would also have to be increased to cope up with the modification, which is not a very
good choice for a line in services.
5.4 Unbalance Insulation
55
This method is only applicable to double and quadruple circuit line. Double circuit
outages could also be reduced by use of unbalanced insulation, which the basic
principle of unbalanced insulation is to install one circuit at a higher insulation level
than the other circuit. The decrease in double circuit outage rate depends on the
insulation differential and on the tower footing resistance. Unbalanced insulation does
not reduce total line outage rate.
Double circuit flashovers and flashovers on the higher insulation circuit are
reduced, but with an inceased number of flashovers on the lower insulation circuit
which is not a very reliable and good solutions for improving the lightning
performance of a line. Rhis method maybe cheap considering the fact that the only
thing that should be done is to decrease the arching distance of one circuit and to
maintain the next circuit arching distance but this method will affect realibility and
quality of power.
5.5 Transmission Line Arrester
Double circuit outages can be eliminated by installation of line surge arresters on
all conductors of all circuit, which is uneconomical considering the total amount of
money compared to the improvement gain. Lower TLA configuration could result in
performance improvement. There are several methods available for optimizing the
application of TLA for improving the lightning performance of a transmission line in
services.
56
Fig 5.2: Unbalance tower insulation for double circuit line
5.6 Installation of TLA based on Tower Footing Resistance(TFR)
This method is used for improving a lightning performance of a double circuit line
with high TFR on certain section of a line. This method is based on a strategy of
arrester installment as in Figure 5.1. This strategy is based on an assumption that the
higher TFR the higher the current have to be diverted by the surge arrester.
Table 5.1: Arrester installation strategy to eliminate double circuit flashover
No TFR(Ω) TLA location
1 TFR < 10 No TLA
2 10 < TFR < 20 3
3 20 < TFR < 40 2 & 3
4 40 < TFR 1,2 and 3
Circuit with lower Insulation level
Circuit with higher Insulation level
57
Fig. 5.3: Circuit location and TLA placement for a double circuit line
Base on the strategy as in Table 5.1, an improvement of a lightning performance can be
conducted based in this procedure:
♦ Divide the line into several sections and apply arrester installation configuration
related to the section’s tower footing resistance.
♦ Apply same arrester installation configuration throughout the particular line
section.
♦ Perform statistical study in determining the arrester energy duties
♦ The most energy sensitive installation is a configuration with arrester installed
on all conductors. Lightning current have to be shared by TFR, ground wire and
surge arresters.
5.6.1 Additional of TLA at low TFR Section
1
3
2
1
2
3
58
These methods are proposed by ABB for increasing the availability of the line.
This procedure specially designs for protecting the line against the abnormal lightning
surges (frequent or high amplitude) and reduce the outages caused by such lightning
surges. Two steps needed to perform this procedur are:
♦ Place TLA at all tower section with high TFR
♦ Add additional TLA at one tower at both of the low TFR section along the
section of high TFR that have been equipped with TLA
Fig. 5.4: Additional TLA at Low TFR section along the high TFR section
5.6.2 Installation of TLA on one circuit
Double circuit flashover can be reduced using arrester installation configuration, which
are three and more arresters on one circuit installation scheme. An important difference
between the application of line surge arresters on one circuit and unbalanced insulation
is in the fact that line surge arresters substantially reduce the number of flashovers on
the other circuit, hence improving total line lightning performance
1 2
3
45
6 7
59
Fig. 5.5: TLA added only at one circuit of a double circuit line tower
5.6.3 Coordination of Gap Spacing fot Transmission Line Arrester with
External Gap
The purpose of adding an external gap to the TLA are to protect the TLA from
acceleration aging due to leakage current and to protect the TLA from being stressed
from switching over voltage that could be in duration of 2 second which could also
caused accelerated ageing of TLA. Gap distance of TLA external gap are coordinated
based on two main references, the maximum switching over voltage predicted to the
TLA added only at one circuit
60
system and the lightning impulse withstand voltage of the system insulation with TLA
added. This is based on the gap distance that wide enough for not permitting operation
of TLA when switching over voltage occurs but low enough to ensure operation of
TLA when lightning over voltage occur.
5.7 Extended Station Protection
By locating TLA on towers near a substation, the risk of back flashover near the
station is eliminated. This result in reduction of steepness and amplitude of coming
travelling wave, thus improving the protection performance of station arresters and
eliminating the need for additional expensive metal-enclosed arresters even for large
GIS.
Usually a gapped TLA with higher rating are applicable to cope with the
probability of being stressed by switching over voltage however higher rated compare
to the substation surge arrester are advisable so that the TLA are less stressed by the
switching over voltage. TLA with external gap are also applicable but the gap distance
must be kept as minimum as possible so that the surge can be reduce effectively
61
Fig. 5.6: Extended station protection
CHAPTER 6
Substation
62
SIMULATION METHOD
6.1 ATP-EMTP Simulation
The study is performed with the aid of ATP-EMTP software. This software
program is a computer simulation program specially design to study a transient
phenomena in the power system. It contains a large variety of detailed power
equipment models or builds in setups that simplify the tedious work of creating a
system representation.
Generally this simulation software can be used in design of an electrical system
or in detecting or predicting an operating problem of a power system. To represent the
electrical response of the transmission system, electrical model of transmission system
apparatus have to be selected and validated to gain high accuracy result
6.2 Selected Model and Validation
In this simulation, the parameters as input and output and need to be observed
are current, voltage, power and energy. The models are circuit or electrical
63
representation of a physical apparatus and the characteristic can be observed through
the output when the input applied. A complete set of representation of a transmission
system are combination of every model of the transmission line apparatus itself
6.2.1 Tower Model
M.Ishii multi-storey tower model is selected as tower model for EMTP
simulation purpose. This tower model does not consider the tower arm, which is
available in other model. The parameters need to be modeled using M.Ishii model are :
Zt = Tower Surge Impedance
VL = Surge Propagation Velocity
R = Damping Resistance
L = Damping Inductance
Hi = Height of Tower
Where:
H = h1 + h2 + h3 + h4 + h5 + h6 + h7
The value of surge impedance for each level of the tower can be based on IEEE
and CIGRE formula for inverted cone
Z = 60 x Loge cos0.5x tan (R/H)
64
If R << H, this equation can be reduced to:
Z = 60Loge (H/R) – 1 (2)
Where:
R = equivalent radius of tower
H = Height of tower
The value of R can be obtained by calculating and dividing the tower into upper
and lower truncated cones as shown in Figure 6.2 and equivalently replacing them as
cone as defined by the following formula.
R = ( r1H2 + r2 H + r3H1 ) ( applicable for eqn.2 only )
2H
where :
r1 = Tower top radius, m
r2 = Tower midsection radius, m
r3 = Tower base radius, m
H1 = Height from base to midsection, m
H2 = Height from midsection to top, m
R1
Zt2
Zt1
L2
L1
R2
65
Fig. 6.1 : M.Ishii’s tower model for a double circuit line tower
r1
r2
H
r3 R
Fig. 6.2: Tower equivalent radius
From double circuit model can be extended to quadruple circuit model
by adding surge impedance, damping resistance and damping inductance.
Formula used for double circuit tower could be modified to be used as
quadruple tower model as follow:
H = h1 + h2 + h3 + h4 + h5 + h6 + h7
Zt3
L3
Zt4
L4 R4
R3
66
Ri = (-2Zt1 x ln√ γ ) x hi
h1 + h2 + h3 + h4 + h5 + h6
R = -2 Zt2 x ln√γ
Li = α Ri x 2H
Vt
6.3 MODEL AND PARAMETERS USED IN THE SIMULATION
6.3.1 Tower Model
67
Fig. 6.3 : Modified M.Ishii’s tower model for a quadruple circuit line
tower modeling
6.3.2 Transmission Line model
J.R. Marti model is selected to represent the transmission line model for this
simulation. The technique used by J.R. Marti to transfer the circuit into time domain
are by FD-line and FDQ-line models. In this model, the characteristic impedance
g 12.60
7.65
2.8
5.55
17.95
T1
T2
T3
T4
T5
T6
T7
Zt1
R1 L1
Zt2
R2 L2
Zt3
R3 L3
Zt7
R7 L7
Zt4
R4 L4
Zt5
R5 L5
Zt6
R6
Vth1
Vth2
Vth3
Vth4
Vth5
Vth6
Vth7
6.10
37.35
29.70
22.40
15.05
L6
68
function Zc(w) in the frequency domain equivalent circuit is synthesized with RC
network with constant R’s and C’s. This network and then be transferred directly into a
time domain circuit as:
Emh(t) = ∫ fk(t – u)ap (u)du
ap (t) = y-1 e-γ(w)t
An alternative approach to the lengthy process of evaluating the convolution
integral at each time step of the simulation is to synthesize e-γ(s)t
by the sum of first order terma;
e-γ(s)t = k1 + k1
+ ………..+ k1
s + p1 s + p1 s + pm
Where
Emh(s) = Fk(s) e-γ(s)t
= Fk(s)∑ k1
s + pl
= ∑ Emh(s)
The wave transfer source in the circuit can be expressed as m sources connected
in series, each component source given by
Emh(s) = k1 Fk(s) e-st ----------------------------------------- ( 28 )
s + pl
69
In the ideal line model, there is only one partial source which corresponds to
equation (28) with k1 = 1(pole at ∞ )
s + pl
By comparison with ideal case, the partial source Emh(s) of equation 28 can be
interpreted as ideal wave propagation Fk(s) e-st (pure delay) shaped by first-order terms
k1 damping and distortion).
s + pl
Equation 27 can be transferred directly into the time domain as;
emh(s) = ∑ emhi(t)
The first order term in equation 29 result, after discretization with intergration
rule, in a difference equation that has the same form as a single RL circuit, except for
additional time delay t ;
emhi(t) = ai emhi(t - t) + bi fk (t - t) + ci fk (t – t – t )
Where, if the trapezoidal rule is used for the discretization,
ai = 2 - pii and bi = c = kii
2 + pii s + pm
The forward function in equation, 27 formally defined as Fk(s) = Vk(s) +
Zk(s)Ik(s), which implies, when transferred into the time domain, a convolution can be
avoided by ZcIk = Vk – Ekb and therefore
Fk(s) = 2Vk(s) – Ekh(s)
And Fk(t) = 2Vk(t) – ekh(t)
70
The partial voltage sources of equations 30 are DC source at time t with values
calculated from past values of the quantities involved. The time domain-line model that
represents all the line parameters R, L, G and C are continuously distributed and
frequency dependent. The process to find an RC synthesis network for the
characteristic impedance function Zc(w) and to expand e-γ(w)t into simple terms as in
equation 26 is explained by J.R Marti
In this simulation which is used J.Marti model, the geometrical and material
data for overhead line conductors are specified as below;
♦ 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.
If Auto bundling checked:
♦ 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 line.
71
♦ NB: Number of conductors in a bundle.
6.4 Selection of Lightning Parameter
Positive polarities are selected as a basis of the simulation and it is assumed that
the lightnings used are a single stroke although the statistic shows other wise. From the
statistic show that 33% of the negative stroke are single stroke and the percentage of
stroke decrease exponentially as the stroke perflash increases. The surge arrester used
in this simulation did not have a curve shift capability as needed in the study of the
effect of multi stroke lightning to surge arrester.
6,5 Lightning Amplitude
The amplitude is based on statistic by TNB, 6kA is the lowest current recorded,
17kA is a average and 110 kA lightning is the highest probability of peak current
recorded but there are probability of higher magnitude lightning to strike. Higher
magnitude current as high as 475kA have been recorded by the LDS system but the
probability of occurrence are very low and it is assume that the mechanical failure of
the electrical system can occur and higher peak current more than 200kA are neglected
The over voltage caused by higher peak current will decrease because of the
outward back flashover, but because of nature breakdown of air insulation, the delay of
72
breakdown will left an impulse that manage to escape the outward back flashover. This
impulse will propogate to the termination and a portion of its energy will be diverted to
the earth by the surge arrester. Energy absorbed by the surge arrester caused by the
variety of peak current can be observed by using the simulation.
6.6 Time of Rising
The range of rise time for typical lightning impulse is in the range of 0.1 to 20
µs. It assume that the rising time for all of the lightning impulse used in the simulation
is 8 µs.
6.7 Time of Falling
For observing the effect of time of falling to the energy observed by the gapless
ZnO surge arrester, several wave shape with time of falling of 20, 50, 100 200 and 500
are applied to simulation. Time of falling of 75µs and with effect of lightning surge
arrester are applied to final simulation.
The effect of time of falling of the lightning impulse to the energy absorbed by the
surge arrester can be predicted by using the simulation. As shown on the graph below,
energy absorbed by surge arrester are increased by inceasing in time of falling
73
(file modelQC6S4F.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 0 10 20 30 40 50 60[us]
-300
-150
0
150
300
450
600
[kV]
Fig. 6.4: Voltage Amplitude for Time of Falling 20µs
Fig. 6.5: Voltage Amplitude for Time of Falling 50µs
(file modelQC6S4F.pl4; x-var t) v:RBT v:YBT v:BBT v:BBT132 v:YBT132 v:RBT132 0 10 20 30 40 50 60[us]
-200
-100
0
100
200
300
400
500
600[kV]
74
(file modelQC6S4F.pl4; x-var t) v:RBT v:YBT v:BBT v:BBT132 v:RBT132 v:YBT132 0 10 20 30 40 50 60[us]
-200
-100
0
100
200
300
400
500
600[kV]
Fig. 6.6: Voltage Amplitude for Time of Falling 100µs
(file modelQC6S4F.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 0 10 20 30 40 50 60[us]
-200
0
200
400
600
800[kV]
Fig. 6.7: Voltage Amplitude for Time of Falling 200µs
(file modelQC6S4F.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 0 10 20 30 40 50 60[us]
-200
0
200
400
600
800[kV]
Fig. 6.8: Voltage Amplitude for Time of Falling 500µs
75
6.8 Limitation of Simulation
EMTP Simulation cannot shows a number of improvement or performance that
can be achieve since its only shows voltage and current response in real time. This
could jeopardize the reliability of the simulation result where error from component
level are carried into overall simulation level. Error on component level must be kept
as low as possible by optimizing it for certain range of response that are predicted to
take place in overall simulation level.
6.9 Statistical Approach
The breakdown’s improvement are shown by applied diffirent LSA
configuration and performance are stated as flashover per single stroke lightning
injected to the system. The output of the simulation are the flashover that would occur
for each phases of the 275kV/132kV transmission line
76
CHAPTER 7
SIMULATION : 275 kV DOUBLE CIRCUIT AND 275/132kV QUADRUPLE
CIRCUIT LINE
The purpose of this simulation is to validate the performance of 275/132kV
quadruple transmission line circuit with specification based on the TNB transmission
line in services. Since the tower responses are not accurate so the the voltage response
from this simulation cannot be refered as final output. Noted that even this simulation
is using a perfect system based on TNB specification, but the result doesn’t show the
actual performance of the system and this simulation only to show the capability of
EMTP simulation
7.1 275/132kV Quadruple Circuit and Specification used in this Simulation
275kV Double Circuit and Specification used in this Simulation taken from TNB
design parameter. The length for the line from tower to tower are 300m and Tower
footing resistance is fixed to 10 ohm and the parameter of 24 series multi-storey tower
77
are taken from TNB tower design. This simulation only based on 3 towers with peak
value of 110kA and wave shape of 1/6us are applied at top of tower. It is assumed that
no extensions are added to the towers and all 3 towers are suspension type. Lightning
path impedance are assume to be 350 ohm. Model of the simulated tower and circuit
are as shown below :
Tower 1 Tower 2 Tower 3
Fig. 7.1: Simulated 275/132kV quadruple circuit line
RBT1 RBT
YBT1 YBT
BBT1 BBT
RBT131 RBT132
YBT131 YBT132
BBT131 YBT132
Fig. 7.2 : Conductor identification for 275/132kV double circuit
line used in simulation
78
Table 7.1: Parameter of the 275kV double circuit tower model
Zt1 85 Tower Surge impedance
Zt2 85
Propagation Velocity Vt 300m/us
L/R 2H/Vt
Zt2/Zt1 1
Damping Coefficient 1
Attenuation Coefficien 0.7
R1 2.85
R2 5.65
R3 5.65
R4 8.25
R5 3.95
R6 3.95
Damping Resistance
R7 30.31
L1 0.9µH
L2 1.8µH
L3 1.8µH
L4 2.62µH
L5 1.26µH
L6 1.26µH
Damping Inductance
L7 9.64µH
H1 2.8m
H2 5.55m
H3 5.55m
H4 8.1m
H5 3.88m
H6 3.88m
Height
H7 17.95m
79
7.1.1 MODEL USED IN THE SIMULATION
Fig. 7.3: Modified M.Ishii’s tower model for a quadruple circuit line
tower modeling
g 12.60
7.65
2.8
5.55
17.95
T1
T2
T3
T4
T5
T6
T7
Zt1
R1 L1
Zt2
R2 L2
Zt3
R3 L3
Zt7
R7 L7
Zt4
R4 L4
Zt5
R5 L5
Zt6
R6 L6
Vth1
Vth2
Vth3
Vth4
Vth5
Vth6
Vth7
6.10
37.35
29.70
22.40
15.05
80
7.2 Lightning Surge Arrester Configuration Used in the Simulation
Configuration 3
275kV
132kV
Configuration 4
275kV
132kV
Configuration 1 Configuration 2
275kV
132kV
275kV
132kV
Configuration 6
275kV
Configuration 5
275kV
132kV 132kV
Configuration 7 Configuration 8
275kV
132kV
275kV
132kV
81
7.3 RESULTS OF SIMULATION FOR LIGHTNING CURRENT OF 17kA
AND STRIKE AT TOWER 2
7.3.1 Response without transmission line arrester
Fig. 7.4: Current injected at top tower 2
Fig.7.5: Lightning strike has caused voltage rise at top tower 2
(file modelQC6S4.pl4; x-var t) v:VS 0 10 20 30 40 50 60[us]
-100
100
300
500
700
900[kV]
(file modelQC6S4.pl4; x-var t) c:IS -VS 0 10 20 30 40 50 60[us]
0
4
8
12
16
20[kA]
82
Fig. 7.6: Voltage measured at tower 2 which are connected to 275kV Line
From Figure 7.6 shown high value of flashover voltage measured which is about
1.2MV at RBT, RBT1, BBT, BBT1,RBT132, RBT131 and high potential voltage rise
at YBT and YBT1
7.3.2 Response with transmission line arrester
Line lightning performance is determined for the line with arresters mounted on
tower for different configuration. Its effectiveness is observe with taking into account
that the number of the arresters to be used is minimum possible and flashover can be
eliminated efficiently. The characteristic of the SLA are base on the 120kV rated
Siemens 3EQ4-2/LD3 station class surge arrester.
(file modelQC6S4.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:BBT132 v:YBT132 0 10 20 30 40 50 60[us]
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2[MV]
83
Table 7.2: Value for A0 and A1 based on 8/20 us residual voltage supplied for the
application of Pinceti’s arrester model with 120kV rated Siemens 3EQ4-2/LD3
Current 120kV A0(pu) A0(v) A1(pu) A1(v)
1 203154 0.900 182839 0.720 146271
100 226086 0.974 220208 0.788 178156
1000 249018 1.052 261967 0.866 215650
5000 278124 1.141 317339 0.957 266165
10000 294000 1.195 351330 1.009 296646
20000 326046 1.277 416361 1.091 355716
7.3.2.1 TLA WITH CONFIGURATION 1
(file model120C1.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT131
0 5 10 15 20 25 30[us]0.0
0.2
0.4
0.6
0.8
1.0
1.2
[MV]
Fig. 7.7: Flashover Voltages when TLA are equipped at conductor RBT and
RBT1
From the Figure 7.7 shown TLA with configuration 1 were eliminated flashover at Red
phase of 132kV but flashover still occurs at insulator RED and BLUE phase of 275kV
line
84
7.3.2.2 TLA WITH CONFIGURATION 2
(file model120C2.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT1 v:RBT131
0 5 10 15 20 25 30[us]-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2[MV]
Fig. 7.8: Flashover Voltages when TLA are equipped at conductor
RBT132, RBT131 and BBT131
From the Figure 7.8 shown TLA with configuration 2 were eliminated flashover at Red
phase of 132kV but flashover still occurs at RED and BLUE phase of 275kV line
7.3.2.3 LSA WITH CONFIGURATION 3
(file model120C3.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT131
0 5 10 15 20 25 30[us]-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2[MV]
Fig. 7.9: Flashover Voltages when TLA are equipped at conductor
RBT131, YBT 131 and BBT131
85
From the Figure 7.9 shown TLA with configuration 3 were eliminated flashover at one
of the RED phase of 132kV but flashover still occurs at RED and BLUE phase of
275kV line
7.3.2.4 TLA WITH CONFIGURATION 4
(file model120C4.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT1 v:RBT131
0 5 10 15 20 25 30[us]-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2[MV]
Fig. 7.10: Flashover Voltages when TLA are equipped at conductor RBT,
RBT1 and RBT131
From the Figure 7.10 shown TLA with configuration 4 were eliminated flashover at
RED phase of 275kV and one of the RED phase of 132kV but flashover still occurs at
RED phase of 132kV and BLUE phase of 275kV has critical potential rise
86
7.3.2.5 LSA WITH CONFIGURATION 5
(file model120C5.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT131
0 5 10 15 20 25 30[us]-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2[MV]
Fig. 7.11: Flashover Voltages when TLA are equipped at conductor
RBT132, RBT131, YBT132 and YBT131
From the Figure 7.11 shown TLA with configuration 5 were eliminated flashover at
RED phase of 132kV but flashover still occurs at RED and BLUE phase of 275kV
7.3.2.6 LSA WITH CONFIGURATION 6
(file model120C6.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT1 v:RBT131
0 5 10 15 20 25 30[us]-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2[MV]
Fig. 7.12: Flashover Voltages when TLA are equipped at conductor RBT,
RBT1, RBT132 and RBT131
87
From the Figure 7.12 shows TLA with configuration 6 are capable to eliminate
flashover at RED and BLUE phase of 275kV and RED phase of 132kV. Flashover at
all phases of 275kV and 132kV were eliminated
7.3.2.7 LSA WITH CONFIGURATION 7
(file model17C7.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT1 v:RBT131
0 5 10 15 20 25 30[us]-0.2
0.0
0.2
0.4
0.6
0.8
1.0
[MV]
Fig. 7.13: Flashover Voltages when TLA are equipped at conductor RBT,
RBT1, BBT, RBT132 and RBT131
From the Figure 7.13 shows that TLA with configuration 7 are capable to eliminate
flashover at RED and BLUE phase of 275kV and RED phase of 132kV. Flashover at
all phases of 275kV and 132kVkV were eliminated
88
7.3.2.8 LSA WITH CONFIGURATION 8
(file model17C8.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT1 v:RBT131
0 5 10 15 20 25 30[us]-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2[MV]
Fig. 7.14: Flashover Voltage when TLA are equipped at conductor RBT,
RBT1, YBT, RBT132 and RBT131
From the Figure 7.14 shows that TLA with configuration 8 are capable to eliminate
flashover at RED and BLUE phase of 275kV and RED phase of 132kV. Flashover at
all phases of 275kV and 132kV were eliminated
89
7.4 RESULTS OF SIMULATION FOR LIGHTNING CURRENT OF 120kA
AND STRIKE AT TOWER 2
7.4.1 Response without transmission line arrester
Fig. 7.15: Current injected at top tower 2
Fig. 7.16: Lightning strike has caused voltage rise at top tower 2
( f ile m o d e l1 2 0 C 1 .p l4 ; x - v a r t ) v :V S 0 1 0 2 0 3 0 4 0 5 0 6 0[u s ]
-1
0
1
2
3
4
5
6[M V ]
( f ile model120C1.p l4; x -v ar t) c :IS -V S 0 1 0 2 0 3 0 4 0 5 0 6 0[u s ]
0
2 0
4 0
6 0
8 0
1 0 0
1 2 0
[kA]
90
7.4.2 Response with transmission line arrester installed
7.4.2.1 TLA WITH CONFIGURATION 1
(file model120C1.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT1 v:RBT131
0 5 10 15 20 25 30[us]0
1
2
3
4
5[MV]
Fig. 7.17: Flashover Voltage across insulators when TLA are equipped
at conductor RBT and RBT1
From the Figure 7.17 shows that TLA with configuration 1 are capable to eliminate
flashover at RED phase of 132kV only and flashover still occurs at other lines of
275kV and 132kV
91
7.4.2.2 TLA WITH CONFIGURATION 2
(file model120C2.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT1 v:RBT131
0 5 10 15 20 25 30[us]-0.5
0.5
1.5
2.5
3.5
4.5[MV]
Fig. 7.18: Flashover Voltage across insulators when TLA are equipped
at conductor RBT132, RBT131 and BBT1
From the Figure 7.18 shows that TLA with configuration 2 are capable to eliminate
flashover at RED phase of 132kV only and flashover still occurs at other lines of
275kV and 132kV
7.4.2.3 TLA WITH CONFIGURATION 3
(file model120C3.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT1 v:RBT131
0 5 10 15 20 25 30[us]-0.5
0.5
1.5
2.5
3.5
4.5[MV]
Fig. 7.19: Flashover Voltage across insulators when TLA are equipped
at conductor RBT132, RBT131 and BBT1
92
From the Figure 7.19 shows that TLA with configuration 3 are capable to eliminate
flashover at one of the RED, YELLOW and BLUE phases of 132kV and flashover still
occurs at other lines of 275kV and 132kV
7.4.2.4 TLA WITH CONFIGURATION 4
(file model120C4.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT1 v:RBT131
0 5 10 15 20 25 30[us]-0.5
0.5
1.5
2.5
3.5
4.5[MV]
Fig. 7.20: Flashover Voltage across insulators when TLA are equipped
at conductor RBT, RBT1 and RBT131
From the Figure 7.20 shows that TLA with configuration 4 are capable to eliminate
flashover at RED phase of 275kV only and flashover still occurs at other lines of
275kV and 132kV
93
7.4.2.5 TLA WITH CONFIGURATION 5
(file model120C5.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT1 v:RBT131
0 5 10 15 20 25 30[us]-1
0
1
2
3
4
5
[MV]
Fig. 7.21: Flashover Voltage across insulators when TLA are equipped at
conductor RBT132, RBT131, YBT132 and YBT131
From the Figure 7.21 shows that TLA with configuration 5 are capable to eliminate
flashover at RED and YELLOW phases of 132kV only and flashover still occurs at
other lines of 275kV and 132kV
7.4.2.6 TLA WITH CONFIGURATION 6
(file model120C6.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT1 v:RBT131
0 5 10 15 20 25 30[us]-1
0
1
2
3
4
5
[MV]
Fig. 7.22: Flashover Voltage across insulators when TLA are equipped at
conductor RBT, RBT1, RBT132 and RBT131
94
From the Figure 7.22 shows that TLA with configuration 6 are capable to eliminate
flashover at RED phase of 275kV and 132kV only and flashover still occurs at other
lines of 275kV and 132kV
7.4.2.7 TLA WITH CONFIGURATION 7
(file model120C7.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT1 v:RBT131
0 5 10 15 20 25 30[us]-1
0
1
2
3
4
5
[MV]
Fig. 7.23: Flashover Voltage across insulators when TLA are equipped at
conductor RBT, RBT1, BBT, RBT132 and RBT131
From the Figure 7.23 shows that TLA with configuration 6 are capable to eliminate
flashover at RED phase of 275kV and 132kV only and flashover still occurs at other
lines of 275kV and 132kV
95
7.4.2.8 TLA WITH CONFIGURATION 8
(file model17C8.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT1 v:RBT131
0 5 10 15 20 25 30[us]-1
0
1
2
3
4
5
[MV]
Fig. 7.24: Flashover Voltage across insulators when TLA are equipped at
conductor RBT, RBT1, BBT, RBT132 and RBT131
From the Figure 7.24 shows that TLA with configuration 8 are capable to eliminate
flashover at RED phase of 275kV and 132kV and one of the YELLOW(YBT) phase of
275kV but flashover still occurs at other lines of 275kV and 132kV
7.4.2.9 TLA WITH CONFIGURATION 9
(file model120C9.pl4; x-var t) v:RBT v:YBT v:BBT v:RBT132 v:YBT132 v:BBT132 v:RBT1 v:RBT131
0 5 10 15 20 25 30[us]-1
0
1
2
3
4
5
[MV]
Fig. 7.25: Flashover Voltage across insulators when TLA are equipped at
all conductors of 275kV and 132kV lines
From the Figure 7.24 shows that TLA with configuration 8 are capable to eliminate
flashover at RED phase of 275kV and 132kV and one of the YELLOW(YBT) phase of
275kV but flashover still occurs at other lines of 275kV and 132kV
96
7.5 Summary of the Simulation
Simulation using minimum lightning current shows that no flashover occurs at any
circuit. Hence, no installation of LSA is required. There are two circuits of 275kV and
one circuit of 132kV line were experiencing flashover by using average lightning
current 17kA and all the circuits are affected by applying maximum lightning current
of 120kA.
Table 7.3: LINE PERFORMANCE FOR DIFFERENT TLA CONFIGURATION
FOR LIGHTNING CURRENT OF 17KA
Phase No
LSA
1 2 3 4 5 6 7 8
RBT √ √ √ √ X √ X X X
RBT1 √ √ √ √ X √ X X X
YBT X X X X X X X X X
YBT1 X X X X X X X X X
BBT √ √ √ √ X √ X X X
BBT1 √ √ √ √ X √ X X X
RBT132 √ X X √ X X X X X
RBT131 √ X X X √ X X X X
YBT132 X X X X X X X X X
YBT131 X X X X X X X X X
BBT132 X X X X X X X X X
BBT131 X X X X X X X X X
X - Flashover occurs at Transmissin lines
√ - No Flashover occurs at Transmission lines
97
Table 7.3 shows various installation configuration of TLA at the circuits and the results
are as below:
1. Application of 3 TLA per tower
Configurations 2 to 4 demonstrate application of 3 arresters at various
phases to reduce flashover. These configurations are not capable to reduce all
circuit flashover at transmission lines
2 Application of 4 TLA per tower
Configurations 5 to 6 demonstrate application of 4 arresters at various
phases to reduce flashover. Configuration 5 is capable to eliminate flashover at
275kV circuits and not at 132kV. However, configuration 6 is the most
effective solution as it helps to eliminate flashover by using minimum SLA
compared to other configuration
3 Application of 5 TLA per tower
Configurations 7 to 8 demonstrate application of 5 arresters at various
phases to reduce flashover. Both configurations are capable to eliminate
flashover at 275kV and 132kV circuits as efficient as 4 TLA per tower. Since
the cost of TLA is expensive, configuration 6 is the best selection in term of
performance and cost involved.
98
Table 7.4: LINE PERFORMANCE FOR DIFFERENT TLA CONFIGURATION
FOR LIGHTNING CURRENT OF 120kA
Phase No
LSA
1 2 3 4 5 6 7 8 LSA at all
Feeders
RBT √ √ √ √ X √ X X X X
RBT1 √ √ √ √ X √ X X X X
YBT √ √ √ √ √ √ √ X √ X
YBT1 √ √ √ √ √ √ √ √ √ X
BBT √ √ √ √ √ √ √ √ X X
BBT1 √ √ √ √ √ √ √ √ √ X
RBT132 √ X X √ X X X X X X
RBT131 √ X X X √ X X X X X
YBT132 √ √ √ √ √ X √ √ √ X
YBT131 √ √ √ X √ X √ √ √ X
BBT132 √ √ √ √ √ √ √ √ √ X
BBT131 √ √ X X √ √ √ √ √ X
X - Flashover occurs at Transmissin lines
√ - No Flashover occurs at Transmission lines
4 Application of 3, 4 and 5 TLA per tower
Configuration 1 to 8 demonstrate application of 2 to 5 arresters at various
phases to reduce flashover. From table 2 shows that configuration 1 to 8 are not
capable of eliminating flashover since the lightning current is excessively high. The
flashover at all phases only can be eliminated by installing LSA at all phases.
99
In the real world scenario, double circuit outages from the peak lightning current can
be eliminated by only using 4 TLA at the 132kV lines. Perfect protection for all
circuits can be achieved by installing LSA at every line and it is uneconomical since
the cost of SLA is expensive. Sigma slp simulation software is one of the simulation
program which is capable to eliminate double circuit outages.
7.6 Limitation of the simulation
Since this simulation cannot simulate multiple lightning strokes, the result is
only shows voltage and current response in real time, which cannot shows a
number of improvement or performance that can be achieved.
The improvement of double circuit tripping and back flashover cannot be seen
thru this simulation where by in real world experiences, installation of LSA at
every phases at highest lightning current are not necessary since double circuit
tripping can be eliminated by configuration 6.
Error on component level are carried into overall simulation level, which could
jeopardize the reliability of the simulation result
100
CHAPTER 8
RECOMMENDATION AND CONCLUSION
A design of TLA configuration can be based on targeted protection level and
performance required. Some configuration takes a large number of TLA but did not
provide any large system improvement. Lightning performance of the quadruple circuit
transmission line, having different voltage levels, can be improved by the installation
of the line surge arresters on the lower voltage level circuits only.
From the result of the simulation done using average lightning current of 20kA and
maximum lightning current of 120kA, configuration 6 and configuration 9 is the most
effective solution as its helps to eliminate flashover by using minimum TLA compared
to other configuration. Since the cost of TLA is expensive, configuration 6 is the best
selection in term of performance and cost involved.
To achieve zero flashover, all tower and circuits have to be equipped with TLA
which is uneconomically. The cheapest way to improve overhead line performance is
improving tower footing resistance. Vigorous effort shall be made to improve tower
101
footing resistance of the line. Analysis shows that the zero flashover rates could be
achieved with good footing resistance
Installing line surge arresters on the lower voltage circuits will prevent flashovers
on these circuits, but also improve coupling between lower and higher voltage circuits.
In addition, line surge arresters divert stroke current along the phase conductors,
reducing in this way the current through the tower footing resistance
To optimized TLA placement on a transmission tower depends on the tower
footing resistance value and the physical shape of the tower itself. EMTP simulation is
needed to observe the efficiency of the configuration. Not all phase conductor are
needed to be protected to eliminate flashover, an optimized configuration can produce
acceptable result.
In the event where TFR could not be improved further, application of transmission
line arrester is necessary. With availability of 4 TLA per tower for lightning current
17kA, configuration 6 is preferred compared to other configurations. Configuration 6 is
not only eliminates flashover but also cost effective since it only used minimum TLA.
For maximum lightning current, to eliminate total flashover will incurred high cost
since TLA need to be installed at all phases.
To completely eliminate circuit tripping and reduce flashover, Four arrester
configuration with the arresters installed on the top conductors of 275kV and on the top
conductor of the 132kV circuits substantially reduces line total flashover as shown in
configuration 6 is highly recommended
102
List of References: [1] Ali F.Imece, (1996). Modelling Guidelines For Fast Front Transient. IEEE
Transactions on Power Delivery, Vol. 11, No. 1.
[2] Y.A.Wahab, Z.Z. Abidin and S.Sadovic. Line Surge Arrester Application on the
quadruple Circuit Transmission Line [3] T. Yamada, A. Mochizuki. Experimental Evaluation of a UHV Tower Model
For Lightning Surge Analysis
[4] Zulkurnain Abdul Malek. The Application of EMTP Simulation for the Application and Improvement of Insulation Coordination in a Distribution System
[5] Minoo Mobedjina and Lennart Stenstorm(ABB Switchgear). Improved Transmission Line Performance Using Polymer-Housed Surge Arresters [6] Zainul Arif bin Mohamed (2001). Overvotage Protection Insulation
Coordination Studies – Application of Surge arresters on Transmission Lines (Line Arrester). UTM, Skudai : Final Report
[7] Jose Alberto Gutierrez. Non Uniform Line Tower Model For Lightning Transient Studies
[8] John G. Anderson. IEEE Working Group Report: Estimating Lightning
Performance of Transmission Lines II Updates to Analytical Models
[9] IEEE Guide for Improving the lightning Performance of Transmission Lines [10] L Stenstrom. Energy Stress on Transmission Line Arresters Considering The
Total Lightning Charge Distribution [11] Anjana Havanur . Insulation Co-ordination: A Case Study [12] M. T. Correia de Barros. Methodologies for Evaluating the lightning
Performance of Transmission Lines
[13] TNB Transmission Network (2002). Transmission Line Lightning Performance: Sigma SLP Software Presentation
[14] Sediver. Double Circuit Outage Reduction using Surge Line arrester [15] IEEE (1999). IEEE Guide for the Application of Insulation Coordination, New
York: (IEEE Std 1313.2-1999)
103
[16] CIGRE 97 9wg 100 12 IWD: Diagnostics indicators of metal-oxide surge
arresters in service
[17] IEC 60099-4 (2004-05). Metal-oxide surge arresters without gaps for a.c systems
[18] Ohio Brass TLA (Protecta*Lite) Product Information [19] ABB TLA (PEXLIM) Product Information [20] Sediver TLA (SLA) Product Information [21] ATP-EMTP User Group (July 1995). EMTP Rulebook version 2.0: ATP-EMTP
User Group [22] D. Carroll (March 1998). Introduction to EMTP Data Structures Basic Circuit
Examples: ATP-EMTP User Group. [23] Hussein Ahmad (1998). Kilat dan Perlindungan: Penerbit Universiti Teknologi
Malaysia Skudai Johor Malaysia [24] J. R. Marti et al (1993). Transmission Line Models for Steady-State and
Transient Analysis: [25] IEEE/NTUA Athens Power Tech Conference. Planning Operation and Control
of Today’s Electric Power Systems Athens: Greece, September 5-8,1993 [26] K. Nakada et al (1997). Energy Absorption of Surge Arrester on Power
Distribution Lines due to Direct Lightning Strokes: IEEE Transactions on Power Delivery Vol. 12 No. 4 October 1997.
[27] L. Dube (1996). User’s Guide to Model’s in ATP: ATP-EMTP User Group [28] Motoyama H. (1996). Experimental Study and Analysis of Breakdown
Characteristic of Long Air Gaps with Short Tail Lightning Impulse: IEEE Transactions on Power Delivery Vol. 11 No. 2 April 1996.