EARHTHING PERFORMANCE OF HV/MV SUBSTATION AND …eprints.utm.my/id/eprint/54608/1/NornikmanRahiminMFKE2015.pdfSistem grid pembumian pencawang sediada telah menggabungkan faktor keselamatan

EARHTHING PERFORMANCE OF HV/MV SUBSTATION AND ITS EFFECT

ON NEARBY STRUCTURES

NORNIKMAN BIN RAHIMIN

A project report submitted in partial fulfilment

of the requirements for the award of the degree of

Master of Engineering (Electrical-Power)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

JUNE 2015

ii

Specially dedicated to my beloved parent,

Rahimin bin Ismail and Norhayati binti Lop Ahmad,

my lovely wife Noriratul Mazuin Binti Mazani,

my doughter Nurin Auni Irdina, in-laws parents, families and siblings,

whom endlessly supporting me throughout my journey of education.

iii

ACKNOWLEDGEMENT

In the name of Allah, Most Gracious, Most Merciful, Praise be to Allah, the

Cherisher and Sustainer of the Worlds. With His permission I have completed my

Master Degree of Electrical Engineering (Power) and hopefully this works will

benefit the development of the Ummah all over the world.

I would like to express my sincere gratitude to my supervisor, Prof. Dr.

Zulkurnain Abdul Malek, who has supported me throughout my work with his

guidance, patience, motivation, enthusiasm and enormous knowledge whilst

allowing me the room to work in my own way. I attribute the level of my Master

Degree to his encouragement and effort which without him this report would

not have been possible to be written and completed. It is an honor for me having

this opportunity doing the project under his supervision.

In preparing this project report, I was in contact with several people,

researchers, academicians, and practitioners. They have contributed towards my

understanding and thoughts In particular, I would like to convey my deep sense of

appreciation to TNB staff from Transmission Division and TNBR for their guidance,

helps, and advices throughout the progress of the project.

Last but not least, my sincere appreciation also extends to all my family,

colleagues, administrative staffs at Faculty of Electrical Engineering, UTM and

others who have provided assistance at various occasions. Their views and tips are

useful indeed. I owe my deepest appreciation to my beloved wife Noriratul Mazuin

Bt Mazani for supporting me spiritually throughout my life. May Allah s.w.t will

bless all of you.

iv

ABSTRACT

Nowadays, with more of suburban area developed into an urban area, power

system for transmission and distribution have become more critical with the growing

of load demand in the area. A substation, previously located away from other other

structures, are now standing next to residential buildings and other public structures,

raising concerns over public safety factor. Increasing energy demands have caused

the utility company to increase the capacity of a substation, and hence consequently

increases the system fault current level. The existing and installed earthing grid

systems had incorporated the safety factor based on the old fault current level, which

is now may not be sufficient for the new fault current level capacity. During the

propagation of fault current, there exist the earth potential rise (EPR) along the

conductor at the surface of the soil, the touch potential (TP), and the step potential

(SP), all of which may become lethal when over a certain level. The values of ERP,

TP and SP must comply to the safety level as described in the IEEE 80-2000

standard. Several factors that contribute to the ERP value are the fault current level,

soil resistivity and grid geometry. The CDEGS (Current Distribution,

Electromagnetic Fields, Grounding and Soil Structure Analysis) software was used

to analyse the effects of changes in the fault current level, soil resistivity and grid

geometry to a substation earthing grid performances as well as to the earthing grids

of nearby structures. Simulation results show that TP and SP values at nearby

structure are significantly increased with the increasing of fault current and soil

resistivityIn the worst case, the TP increases to more than 4000% and the SP to more

than 5000%.Appropriate improvements to the existing substation earthing grid

system, namely, increment in the mesh conductor numbers, increment in the number

of installed vertical rods, and incremment in the depth of the vertical rod, were

proposed. Simulation results shows the proposed improvement methods significantly

improve the TP and SP values.

v

ABSTRAK

Pada masa ini, banyak kawasan pinggir bandar telah membangun menjadi

kawasan bandar, sistem kuasa untuk penghantaran dan pengagihan telah menjadi

lebih kritikal dengan pertambahan permintaan beban di kawasan tersebut. Sebuah

pencawang dahulunya terletak jauh dari struktur-struktur lain lain, kini terletak

bersebelahan dengan bangunan-bangunan kediaman dan struktur-struktur awam lain

dan ianya telah menimbulkan kebimbangan terhadap faktor keselamatan awam.

Keperluan tenaga yang bertambah telah memaksa syarikat utiliti meningkatkan

keupayaan pencawang terlibat, dan ini telah sekaligus meningkatkan tahap arus rosak

sistem sedia ada. Sistem grid pembumian pencawang sediada telah menggabungkan

faktor keselamatan berdasarkan tahap arus rosak lama, yang berkemungkinan tidak

mencukupi untuk kapasiti paras arus rosak yang baru. Semasa pengagihan arus

rosak, wujud kenaikan potensi bumi (EPR) di permukaan tanah di sepanjang

konduktor. Potensi sentuhan dan potensi langkah (SP) (TP) akan terhasil, yang mana

ianya mungkin membawa maut apabila melepasi satu tahap tertentu. Nilai ERP, TP

dan SP mestilah mematuhi tahap selamat sebagai ditetapkan di dalam piawaian IEEE

80-2000. Beberapa faktor yang menyumbang kepada peningkatan nilai ERP ialah

tahap arus rosak, kerintangan tanah dan geometri grid. CDEGS (Current

Distribution, Electromagnetic Fields, Grounding and Soil Structure Analysis) ialah

perisian yang digunakan untuk menganalisis kesan dari perubahan tahap arus rosak ,

kerintangan tanah dan geometri grid kepada kecekapan grid pembumian sebuah

pencawang, serta grid pembumian struktur-struktur berdekatan. Keputusan simulasi

menunjukkan bahawa nilai TP and SP di struktur berdekatan nyata sekali bertambah

dengan penambahan arus rosak dan nilai kerintangan tanah, di dalam kes terburuk,

nilai TP bertambah sebanyak lebih 4000% dan SP bertambah lebih daripada 5000%

daripada nilai normalnya. Penambahbaikan yang bersesuaian boleh dilakukan kepada

sistem grid pembumian pencawang sediada, iaitu dengan menambah bilangan

konduktor pada grid, meningkatkan jumlah dipasang rod menegak dan mendalamkan

kedalaman rod menegak, telah dicadangkan. Keputusan simulasi menunjukkan

kaedah penambahbaikan ini dapat memperbaiki nilai TP and SP.

TABLE OF CONTENT

CHAPTER TITLE PAGE

DECLARATION i

DEDICATION ii

ACKNOWLEDGEMENT iii

ABSTRACT iv

ABSTRAK v

TABLE OF CONTENTS vi

LIST OF TABLES viii

LIST OF FIGURES ix

1 INTRODUCTION 1

1.1 Background 1

1.2 Problem Statement 3

1.3 Objectives 3

1.4 Scope of the Project 4

1.5 Report Outline 4

2 EARTHING GRID SYSTEM 6

2.1 Introduction 6

2.2 Earth Potential Rise (EPR) 7

2.3 Grounding Grid Consideration 8

2.4 Mathematical Equation 9

2.5 IEEE Standard for Substation Grounding System 12

2.6 Critical Review of Previous Work 12

2.6.1 Soil Resistivity and Soil Characteristic 12

2.6.2 Fault Current Level 14

2.6.4 Effects on Near By Structure 14

vii

2.7 Summary 15

3 METHODOLOGY 16

3.1 Introduction 16

3.2 Modelling Earhting Grid And Simulation

using CDEGS 17

3.3 Earthing Grid System Performance

Analysis 17

3.4 Case study 19

3.5 Soil Resistivity Data 19

3.6 Grounding Grid Construction 23

3.7 Earthing Grid Energization Factor 24

3.8 Safety Limit 25

3.9 Summary 26

4 EFFECTS OF FAULT CURRENT LEVEL

AND SOIL CHARACTERISTICS 27

4.1 Introduction 27

4.2 Case Study 1 27

4.2.1 Actual Soil Resistivity

(Soil 1: control sample) 27

4.2.2 Soil Resistivity Increased

by 2 Times (Soil 2) 29





4.2.5 Case Study 1 Result Comparisons 34

4.3 Case Study 2 35

4.3.1 10kA fault current 35

4.3.2 20kA fault current (Soil 1) 36


viii




4.4 Case Study 3 43

4.4.1 Adjacent Grid, 10kA fault current (Soil1) 44







4.5 Summary 55

5 SUBSTATION EARTHING GRID IMPROVEMENT 56

5.1 Introduction 56

5.2 Increasing Mesh Conductors Number 57

5.2.1 Modelling in SESCAD 57

5.2.2 MALT Simulation Results 58

5.3 Increasing the Number of Installed Vertical Rod 58



5.4 Deepen the Depth of Vertical Rod 60



5.5 Comparison for Grid Improvement Result 62

5.6 Summary 63

6 CONCLUSION AND RECOMENDATION

6.1 General Conclusion 64

6.2 Recommendation for Future Study 66

REFERENCES 67

LIST OF TABLES

TABLE NO. TITLE PAGE

3.1 Actual measurement reading from 132kV/33kV

Setia Alam substation 19

3.2 Increased soil resistivity data 21

4.1 Results comparisons for case study 1 34



5.1 Comparison of different improvement method 63

x

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Basic Shock situation in IEEE 80-2000 standard 7

2.2 Wenner method measurement arrangement 19

3.1 Flow chart of project methodology 16

3.2 Flow chart of CDEGS methodology 18

3.3 Soil 1 soil characteristic graph 21




3.7 Main earthing grid construction in SESCAD 24

3.8 Earthing grid energization in MALT module. 24

3.9 Short circuit fault current level in TNB’s ESAH 26

3.10-3.11 MALT module safety limit setting and value 26

4.1-4.4 Soil 1 results 28-29

4.5-4.8 Soil 2 results 29-30

4.9-4.12 Soil 3 results 31-32

4.13-4.16 Soil 4 results 33-34

4.17-4.20 20kA Soil 1 results 36-37

4.21-4.24 20kA Soil 4 results 38-39

4.25-4.27 30kA Soil1 results 49-40

4.28-4.31 30kA Soil 4 results 41-42

4.32-4.35 Adjacent 10kA Soil 1 results 42-43




4.48-4.51 Adjacent 30kA Soil1 results 49-50

xi


5.1-5.2 Additional earthling mash grid conductor 57

5.3-5.4 Additional earthling mash grid conductor results 58

5.5-5.6 Additional vertical rod 59

5.7-5.8 Additional vertical rod results 60

5.9 Deepen vertical rod length 61

5.10-5.11 Deepen vertical rod length results 61-62

CHAPTER 1

INTRODUCTION

1.1 Background

By definition, earthing is the practice of establishing electrical connection

between metallic frame of equipment, structures or electrical circuits, and a metallic

grid which is normally buried in the soil. The purpose of the earthing practice is to

maintain such parts at zero potential or at the same potential with respect to the earth,

thereby preventing the presence of dangerous or undesirable potential differences

between adjacent parts. Earthing systems also used as earth fault currents detection

by protective relaying systems beside provide low impedance paths through the earth

for load currents. In other application, earthing systems are used to shield control

cables and other low voltage wiring from the effects of electromagnetic interference

(EMI) and capacitive coupling by minimizing system the voltages. Electrical surge,

such as lightning discharges, fault currents caused by earth fault conditions, and

switching currents caused by normal system operations can caurse potential

differences in elsectrical substations and other facilities. In the event of fault current

travel through the earth grid and other metallic earth conductors produces earth

potential rise (EPR) which can be dangerous to humans and may cause damage and

malfunction to equipment and systems.

2

Electrical substations, being electrical facilities meant for transformation of

system voltages from one level to the other are common places for generation of

EPR during earth faults and other system abnormalities. Therefore, it is very crucial

to provide an effective earthing system in this facilities. In normal practice, an earth

grid is installed in the form of horizontal conductor meshes and sometimes combined

with vertical earth rods to ensure the safety of personnel and equipment within the

substation and also the safety of humans and livestock in its vicinity area. There are

three main purpose of the substation erthing grid which is to safely carry and

dissipate fault currents into the earth both under normal and short-circuit conditions,

discharge lightning strokes to earth and reduce step and touch potentials to safe

levels and facilitate fault detection by protection relays.

To design an effective grounding system, these basic requirement should be

take into consideration.

(a) The resistance of the earthing grid to remote earth must be sufficiently low to

ensure operation of the earth fault protective relays at the substation and

along lines and cables connected to it.

(b) The earth potential gradient within and near the substation should be such

that under earth fault conditions, ‘step’ and ‘touch’ voltages are confined to

safe levels.

(c) The earthing grid must be isolated from services entering the substation to

prevent transfer of earth potentials to telephone lines, water mains, railway

sidings in event of earth potential rise (EPR) in the substation, which may be

in kilovolts at times.

(d) The earthing grid should have sufficient capacity to carry the maximum earth

fault currents liable to be imposed on it without overheating, suffering

mechanical damage or undue ionization of soil around buried earth electrodes

and conductors.

3

1.2 Problem Statement

Required power of the big cities keeps growing every years. With this

significant numbers of growth, it is necessary to establish new high voltage (HV) or

medium voltage (MV) substation to satisfy power demand in densely populated

urban areas. The area available for installing HV/MV substation is restricted and

becomes more and more expensive in the city.

Considering this condition, earthing resistance of the substations must be low

enough to satisfy safety (step voltage, touch voltage, earth potential rise) and

electromagnetic compatibility requirements (earth potential rise, potential difference

inside the station affecting the secondary wiring). With more of suburban area

developed into urban area, substation which are previously located far from other

building are now standing side-by-side with other residential and public building.

This situation can not be avoided due to limitation of available land for development.

This can get even worse when the current substation have to be upgraded with higher

capacity of transformer to cater for increased of energy demand in the area. In order

to provide a safety condition for adjacent facilities, the current grid system have to be

re-analysed to include these factors. This work aims to provide safety analysis on the

adjacent earthing grid system.

1.3 Objectives

The objectives of this work are:

1. To simulate and analyse the performance of substation earthing grid system

with the changes of fault current level and soil resistivity value. The observed

parameters are ERP, TP and SP.

2. To simulate and analyse ERP, TP and SP values on nearby structures affected

by changes of fault current and soil resistivity.

3. To propose methods to improve the substation grid performance and to carry

out simulation of the proposed methods to evaluate their effectiveness.

4

1.4 Scope of the Project

The main scopes of this research are as follow:

i. Study and analysis is based on 132/33kV Substation grid system which is

typically installed in TNB system.

ii. Analysis on soil resistivity are based on example of actual reading from new

in construction 132/33kV Setia Alam Substation.

iii. Substation grid system for urban area are assumed as 100mx50m area to

simplify the simulation study.

iv. Simulation and analysis performance of substation grounding system by

using CDEGS software as for below case study:

a. Increase of fault current level from 10kA to 30kA.

b. Improvement of the substation earthing grid design to meet IEEE

standard of safety level.

v. The simulation result and discussion will focus on Step Potential and ground

potential rise.

1.5 Report Outline

Report writing is conducted in order to document the project’s objectives,

scopes, methodology and the results. All methodology involved is documented and

explained in detail for understanding purposed.

5

This project report consists of six chapters. In Chapter 1, the project is

elaborated clearly including the objectives and scopes of the project. In Chapter 2,

the literature review of previous study and gap. In this chapter also will explain

principles of Earth potential Rise (EPR) thoroughly for deeper understanding.

Chapter 3 will explain the development model used in CDEGS simulation and

simulation steps. In Chapter 4, all the result obtain from CDEGS simulation for all 4

study cases and in chapter 5 will focus on improvement method to main earthing

grid. Chapter 6, will elaborate the conclusion and recommendation for future work

68

4.2 Recommendation for Future Study

For the future study, it is recommended that study can focus on improvement

of earthing grid system performance under worst case scenario with soil4

characteristic and 30kA fault current level. This project can be improve by

performing the following:

i. Research on soil improvement material, a technique to improve soil

resistivity.

ii. Research on earthing grid improvement method, in example Sphere

type earthing and plate type earthing.

iii. Research on other method to improve earthing grid system

performance.

REFERENCES

[1] Jozsef Ladanyi. “Analyses of the Earthing Resistance of HV/MV

Transformer Stations with Different Earth Electrode Arrangements

and Soil Structures,” IEEE 04371640, 2007

[2] A. Phayomhom, S. Sirisumrannukul,T. Kasirawat ,A. Puttarach.

“Safety Design Planning of Ground Grid for Outdoor Substations in

MEA’s Power Distribution System”, IEEE 05491481, 2010.

69

[3] C. Amornkul, A. Pruksanuba, A. Phayomhom. “Safety design

planning for ground grid of two neighbouring distribution

substation in MEA's power system” IEEE 06839794, 2014

[4] “IEEE Guide for Safety in AC Substation Grounding,” IEEE std 80-

2000, Jan. 2000.

[5] “Current Distribution, Electromagnetic Fields, Grounding and Soil

Structure Analysis (CDEGS); Software package manuals”, Safe

Engineering Services & technologies Ltd., Montreal, Quebec,

Canada.

[6] “TNB's Electricity Supply Application Handbook, Third (3rd)

Edition”, Tenaga Nasional Berhad. Nov-2011.

[7] Swapnil. G. Shah, Nitin. R. Bhasme “Design of Earthing System for

HV/EHV AC Substation” Journal IJAET, Jan 2014.

[8] Lin Li, Rang Cui, Tiebing Lu and Haoliu Yin, “Influence of Soil and

Conductor of Ground Grid on Safety of the Grounding System” IEEE

journal , 00874701, 2004.

[9] A. Puttarach, N. Chakpitak, T.Kasirawat, and C. Pongsriwat,

“Substation Grounding Grid Analysis with the Variation of Soil layer

depth Method”, IEEE journal, 04538604, 2007.

[10] Mohamad Nassereddine, Ali Hellany, Jamal Rizk, “How to Design

an Effective Earthing System to Mitigate the Safety of the People”,

IEEE journal, 05227944, 2009.

EARHTHING PERFORMANCE OF HV/MV SUBSTATION AND …eprints.utm.my/id/eprint/54608/1/NornikmanRahiminMFKE2015.pdfSistem grid pembumian pencawang sediada telah menggabungkan faktor keselamatan

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