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

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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.