Faculty of Electrical Engineering

IMPACT OF DISTRIBUTED GENERATION ON POWER SYSTEM

PROTECTION

Dawood Saleem Ahmed

Master of Electrical Engineering (Industrial Power)

2016

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IMPACT OF DISTRIBUTED GENERATION ON POWER SYSTEM

PROTECTION

DAWOOD SALEEM AHMED

A dissertation submitted in partial fulfilment of the

requirements for the degree of Master of Electrical

Engineering (Industrial Power)

Faculty of Electrical Engineering

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

2016

DECLARATION

I declare that this dissertation entitles “Impact of Distributed Generation on Power System

Protection” is the result of my own research except as cited in the references. The

dissertation has not been accepted for any degree and is not concurrently submitted in the

candidature of any other degree.

Signature :…..……..………………….. ...............................................

Name: : Dawood Saleem Ahmed

Date: :.....………………………… ................................................

APPROVAL

I hereby declare that I have read this report and in my opinion this dissertation is sufficient

in terms of scope and quality for the award of Master in Electrical Engineering.

Signature :…………:……………. .............................................

Supervisor Name : Dr. Hidayat Bin Zainuddin

Date: :……………………………….. ................................

DEDICATION

This dissertation work is dedicated to my wife, and my big family; you are good examples

and you have taught me to work hard for the things that I aspire to achieve.

i

ABSTRACT

This dissertation describes a simulation study of the impact of distributed generation (DG) interconnection to an existing distribution system of an Iraq system. The increase load demand in many countries pushes the electrical company to use DG technology to meet their load. From the literature review, it was found in spite of many positive effects of DG such as reduce the power losses and reduce voltage drop; the parallel operation of DG with an existing distribution system has many technical problems. One of the most significant issues of parallel operation is the change of fault level and suitability of existing protection system that indeed needs to be maintained within acceptable limits as defined in the international standards. Therefore, this dissertation is performed to investigate the impact of DG based synchronous generator driven by diesel engine on both the fault level and protection system. A small part of the distribution system in Baghdad capital-Iraq which the DG is currently interconnected at 11kV bus has been chosen and modeled using DIgSILENT PowerFactory version 15. The impacts of DG installation at three different locations, i.e. two possible locations which are 33kV and 132kV buses as well as the actual location have been investigated. The dissertation basically includes two investigations which are; examine the change in the fault level without the presence of DG and with DG interconnection at three interconnection locations by executing three-phase fault at each bus of the network as well as investigate the suitability of protection devices through performing single-line-to-ground and three-phase faults at 33kV and 11kV feeders within the distribution system. The results show that after an extensive simulation study, the increase in short circuit level is noticeable at the buses where the DG is interconnected and the protection performance of unidirectional overcurrent relay suffer from blinding and sympathetic tripping as well as the under reach of distance relay, therefore, a series remedy is needed for safety purposes and to reliability of the system.

ii

ABSTRAK

Disertasi ini menerangkan tentang kajian simulasi kesan sambungan Penjana Teragih (PT) kepada system pengagihan yang sedia ada dalam sistem Iraq. Peningkatan permintaan beban di banyak negara memaksa syarikat elektrik menggunakan teknologi PT untuk memenuhi beban mereka. Daripada kajian literatur, didapati walaupun banyak kesan positif PT seperti mengurangkan kehilangan kuasa dan mengurangkan kejatuhan voltan operasi selari PT dengan sistem pengagihan yang sedia ada mempunyai banyak masalah teknikal. Salah satu isu yang paling penting ialah perubahan aras kerosakan dan kesesuaian sistem perlindungan sedia ada yang sememangnya perlu dikekalkan dalam had yang boleh diterima seperti yang ditakrifkan dalam piawaian antarabangsa. Oleh itu, kajian ini dijalankan untuk menyiasat kesan penjana segerak PT berasaskan enjin diesel terhadap aras kerosakan dan sistem perlindungan. Sebahagian kecil daripada sistem pengagihan di Bandar Baghdad, Iraq yang mana PT disambungkan di bas 11kV telah dipilih dan dimodelkan menggunakan DIgSILENT PowerFactory Versi 15. Kesan pemasangan DG di tiga lokasi berbeza iaitu dua lokasi kemungkinan, di bas 33kV dan 132 kV serta lokasi sebenar telah disiasat. Disertasi pada dasarnya menyentuh dua kes utama iaitu; memeriksa perubahan dalam aras kerosakan tanpa kehadiran PT dan dengan sambungan DG di tiga lokasi sambungan melalui pelaksanaan kerosakan tiga fasa pada setiap bas rangkaian serta menyiasat kesesuaian peranti perlindungan dengan melakukan kerosakan talian tunggal ke bumi dan kerosakan tiga fasa pada penyuap 33 kV dan 11kV dalam sistem pengagihan. Keputusan kajian simulasi menunjukkan peningkatan yang banyak pada aras litar pintas adalah ketara pada bas disambungkan dengan PT dan prestasi perlindungan bagi geganti arus lebih satu arah mengalami masalah terpelantik kabur dan simpatetik serta di bawah jangkauan geganti jarak. Oleh itu, penyelesaian yang serius diperlukan untuk tujuan keselamatan dan untuk meningkatkan kebolehpercayaan sistem.

iii

ACKNOWLEDGMENT

First my praise is to the Almighty “Allah”, on whom we ultimately depend. Then, I would

like to sincerely thank my supervisor Dr. Hidayat Bin Zainuddin and my Co-supervisor Dr.

Mohd Hendra Bin Hairi for their guidance, advice, and support.

This research would not be possible without financial support from the ministry of

electricity Iraq.

I am greatly indebted to all the teaching staff for their helpful recommendation, supports,

and giving infinite during my study in UTeM.

iv

TABLE OF CONTENTS

PAGE

DECLARATION ................................................................................................................. APPROVAL ......................................................................................................................... DEDICATION ..................................................................................................................... ABSTRACT ........................................................................................................................ i ABSTRAK .......................................................................................................................... ii ACKNOWLEDGMENT .................................................................................................. iii TABLE OF CONTENTS ................................................................................................. iv LIST OF TABLES ............................................................................................................ vi LIST OF FIGURES ........................................................................................................ viii

LIST OF APPENDICES ................................................................................................. xii LIST OF ABBREVIATIONS ........................................................................................ xiii LIST OF SYMBOLS ....................................................................................................... xv

CHAPTER

1. INTRODUCTION ......................................................................................................... 1

1.1 Background ........................................................................................................... 1 1.2 Motivation for Research ....................................................................................... 3 1.3 Problem Statement ................................................................................................ 4 1.4 Objective of Research ........................................................................................... 4

1.5 Scope of Research ................................................................................................. 5 1.6 Contribution of Research ...................................................................................... 5 1.7 Organization of Dissertation ................................................................................. 6

2. LITERATURE REVIEW ............................................................................................ 8 2.1 Introduction ........................................................................................................... 8 2.2 Distributed Generation .......................................................................................... 9 2.3 Types of Distributed Generation ......................................................................... 11

2.3.1 Solar Photovoltaic Generation 11

2.3.2 Wind Turbines 13

2.3.3 Fuel Cells 14

2.3.4 Micro Turbines 15 2.3.5 Induction and Synchronous Generators 16

2.4 Islanding of a Power Network ............................................................................ 19 2.5 Interconnection Protection .................................................................................. 22 2.6 Impact of Distributed Generation on Power System Grid .................................. 25

2.6.1 Impact of DG on Voltage Regulation 26 2.6.2 Impact of DG on System Losses 27

2.6.3 Impact of DG on Short Circuit Level 27 2.6.4 Impact of DG on Distribution System Protection 30

2.6.4.1 Coordination Protection Problem 31

2.6.4.2 Sympathetic Tripping 34 2.6.4.3 Blinding of protection 35

2.7 Summary ............................................................................................................. 38

v

3. RESEARCH METHODOLOGY .............................................................................. 39 3.1 Introduction ......................................................................................................... 39 3.2 Power Flow Study ............................................................................................... 40 3.3 Radial Line Fault Current Calculation ................................................................ 44 3.4 DIgSILENT PowerFactory ................................................................................. 54

3.4.1 Power Flow Study in DIgSILENT 54 3.4.2 Short Circuit Calculation in DIgSILENT 55

3.5 Modeling of the Iraq system in DIgSILENT ...................................................... 58 3.6 Methodology of Analysis .................................................................................... 61

3.6.1 Load Flow Study 62 3.6.2 Fault Level Study 62

3.6.3 Protection System Study 62 3.7 Summary ............................................................................................................. 63

4. RESULTS AND DISSCUSSION .............................................................................. 64

4.1 Introduction ......................................................................................................... 64 4.2 Description of the Network Used ....................................................................... 67 4.3 Validation study .................................................................................................. 71

4.3.1 Load Flow Analysis Using IEEE System 71 4.3.2 Short-Circuit Analysis Using IEEE System 75

4.4 Load Flow Analysis ............................................................................................ 78

4.5 Short Circuit Level Investigation ........................................................................ 82 4.6 Performance of the Protection System ................................................................ 95

4.6.1 Blinding of Protection 95

4.6.1.1 Case 1: 3PH fault at 90% of feeder FA3 96 4.6.1.2 Case 2: 3PH fault at 90% of feeder SB4 97

4.6.2 Sympathetic Tripping 103 4.6.2.1 Case 1: 1LG Fault at OHL of Feeder FA3 103 4.6.2.2 Case 2: 1LG Fault at 90% of Feeder F-1 107

4.6.2.3 Case 3: 3PH Fault at 90% of Underground Feeder FA3 109

4.6.2.4 Case 4: 3PH Fault at SB4 112 4.6.3 Reduction in Reach of Distance Relay 116

4.6.3.1 Case1: Without DG Interconnection 116 4.6.3.2 Case2: With DG Interconnection 120

4.7 Summary ........................................................................................................... 125

5. CONCLUSION AND RECOMMENDATION ...................................................... 127 5.1 Conclusion ........................................................................................................ 127 5.2 Achievement of Research Objective ................................................................. 128 5.3 Significance of Research Outcomes ................................................................. 129 5.4 Suggestions for Future Research ...................................................................... 129

REFERENCES .............................................................................................................. 131 APPENDIX A ................................................................................................................. 140 APPENDIX B ................................................................................................................. 149

vi

LIST OF TABLES

TABLE TITLE PAGE

2.1 Classification of DG depending on range of size 9

4.1 IEEE 4 node voltage-phase A 73

4.2 IEEE 4 node voltage-phase B 73

4.3 IEEE 4 node voltage-phase C 74

4.4 IEEE 4 node branch current 74

4.5 Comparison of 3HP and 1LG fault results 78

4.6 Base Case Load Flow at Al-Farabi Substation 80

4.7 Load Flow at Al-Farabi Substation with DG1 81

4.8 Variation of fault current [kA] at different buses 91

4.9 Rate of change in the fault current level 92

4.10 Change in the Equivalent Impedances at the fault points 93

4.11 Time overcurrent characteristics of relays R6, R7, and R9 98

4.12 Characteristics of overcurrent relay at intertie point 98

4.13 Characteristics of overcurrent relay at AL-Sebaq and up to

AL- Farabi substation 99

4.14 Results of 3PH fault at 90% of feeder FA3 99

4.15 Results of 3PH fault at 90% of feeder SB4 100

4.16 Results of 1LG fault at FA3 OHL 104

4.17 Results of 1LG fault at feeder f-1 107

4.18 Results of 3PH fault at feeder FA3 111

vii

4.19 Distance relay zones setting and reach operation 124

4.20 Reduction in reach as ratio % 124

A.1 Synchronous generator data 140

A.2 Excitation system model IEEE type DC2 (EXDC2) data 141

A.3 Diesel governor model (DEGOV) data 142

A.4 Transformer TR3 data 142

A.5 Transformers TR1 and TR2 data 143

A.6 Distribution transformers 143

A.7 Sub-transmission line data 132kV 143

A.8 Overhead line data 144

A.9 Underground cable 11kV (3×150 mm2) data 144

A.10 Underground cable 33kV (1×400 mm2) data 144

A.11 Underground cable 132 kV (1×800 mm2) data 144

A.12 Load data 145

A.13 Transformer data 146

A.14 Load data 147

viii

LIST OF FIGURES

FIGURE TITLE PAGE

2.1 (a) Equivalent circuit of PV cell; (b) V-I array characteristic 12

2.2 Schematic diagram of PV inverter for grid connected operation 13

2.3 Power conversion from wind power into electrical power available to

the consumer 14

2.4 Fuel cell diagram 15

2.5 Schematic Diagram of a Micro-Turbine 16

2.6 (a) Induction generator; (b) synchronous generator 18

2.7 Diesel engine set 19

2.8 Intentional islanding of part of the distribution network 22

2.9 Simplified representation of the network used for the analytical

analysis 30

2.10 Simple radial distribution power system 33

2.11 Sympathetic tripping 34

2.12 Blinding of Overcurrent Relay 36

3.1 A typical bus of the power system 41

3.2 Distribution substation and radial feeder 45

3.3 Three phase fault connection 47

3.4 1LG fault (a) general representation; (b) interconnection of

sequence networks 50

3.5 Flow chart of the study 53

ix

3.6 Illustration of the developed superposition method 57

3.7 Part of 400kV and 132kV sub-transmission connection 61

4.1 33/11kV Substation equipped with two 31MVA transformers 66

4.2 A Single Line Diagram of Typical 11/0.4kV Substation 66

4.3 Single line diagram of Al-Farabi substations 70

4.4 IEEE 4 node test feeder 72

4.5 Pole Configuration 72

4.6 Impedance diagram of the IEEE 4 node test feeder 77

4.7 Interconnection of resultant equivalent sequence networks of 1LG

fault 77

4.8 Load Flow at AL-Farabi 132 kV Bus-Bar 79

4.9 Load flow at AL-Farabi 132 kV Bus Bar with DG1 81

4.10 Load Flow at AL-Farabi 132 kV Bus Bar with DG1 82

4.11 3PH fault without DG; (a) at AL-Farabi bus, (b) at bus 33A, (c) at

bus11A 85

4.12 3PH fault at AL-Farabi bus (a) with DG1, (b) with DG2, (c) with

DG3 87

4.13 3PH fault at 33A bus; (a) with DG1, (b) with DG2, (c) with DG3 88

4.14 3PH fault at 11A; (a) with DG1, (b) with DG3, (c) with DG3 90

4.15 Variation in current level 94

4.16 Percentage variation in current level 94

4.17 Time overcurrent (50, 51) characteristic plot of relays R6, R7, and R9 101

4.18 Overcurrent relays characteristic (50, 51) of relays RA, R2, R3, R4,

R5 and R7 101

4.19 Increase in pickup time of overcurrent relay due to DGs

x

interconnection with fault at LF3 102

4.20 Pickup time of overcurrent relays with 3PH fault at feeder SB4 102

4.21 Characteristics of relays R6, R9, and RDGCL 104

4.22 1LG fault at downstream of FA3 105

4.23 Operating time of relays with TR1 open-isolator 106

4.24 Operating time of relays with TR1 closed-isolator 106

4.25 Characteristic of relays R4, R5, and RDGL1 108

4.26 Operating time of relays of 1LG fault at F-1 108

4.27 3PH fault at 90% of underground cable FA3 110

4.28 Characteristic plot of R6, R7 and R9 case fault at LF3 111

4.29 Operating time of 50 and 51 characteristics plot curves of 3PH 112

4.30 50 and 51 characteristic plot of relays RA, R2, R3, R4, R5, RDGL1

and R7 113

4.31 Overcurrent relay characteristic plot, (a) without DG2, (b) with DG2 114

4.32 3PH fault at end of SB4 115

4.33 Fault at 80% end TL1 without DG 117

4.34 CB state of fault at 80% of TL1 without DG 118

4.35 Fault at 20% at end of TL5 without DG 118

4.36 CB state of fault at 20% at end of TL5 without DG 119

4.37 Fault at 50% of TL2 without DG 119

4.38 CB state of fault at 50% of TL2 without DG 120

4.39 Fault at 80% at end of TL1 with DG1, DG2, and DG3 121

4.40 Fault at 20% at end of TL5 with DG1, DG2, and DG3 122

4.41 Fault at 50% of TL2 with DG1 122

4.42 Fault at 50% of TL2 with DG2 123

xi

4.43 Fault at 50% of TL2 with DG3 123

4.44 Reduction in reach as ratio % 125

B.1 A typical portion of the radial distribution network 153

B.2 General operating characteristic of various inverse time relays 156

B.3 VT equivalent circuit 157

B.4 CT equivalent circuit 158

B.5 Characteristic of mho distance relay on R-X plane 160

xii

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Systems Data 140

B Analysis and Modeling 149

xiii

LIST OF ABBREVIATIONS

Abbreviation

AC

ACSR

AAAC

CT

CHP

DC

DG

DR

DN

DSG

EPS

FC

FCL

GEN

IEEE

IDMT

𝐼𝑝

LV

LTC

Specification

Alternative Current

Aluminum Conductor Steel Reinforce

All-Aluminum-Alloy Conductor

Current Transformer

Combined Heat and Power

Direct Current

Distributed Generation

Distribution Resource

Distribution Network

Distributed Synchronous Generator

Electric Power System

Fuel Cell

Fault Current Limiter

Generator

Institute of Electrical and Electronics Engineers

Inverse Definite Minimum Time

Pickup Current

Low Voltage

Load Tap Changer

xiv

𝑚𝑚𝑓

OC

OHL

ONAN/ONAF

PCC

p.u.

PV

RCS

SFCL

TR

TDS

T

VT

XLPE

UTeM

Magneto Motive Force

Overcurrent Relay

Overhead Line

Oil Cooling/Forced Air Cooling

Point of Common Coupling

Per Unit

Photovoltaic Cells (Solar Cell)

Remote Control System

Superconductor Fault Current Limiter

Transformer

Time Dial Setting

Operating Time

Voltage Transformer

Cross-Linked Polyethylene

Universiti Teknikal Malaysia Melaka

xv

LIST OF SYMBOLS

Symbol Specification

ρ Air Density

𝑈 Wind Speed

𝐶𝑃 Power Coefficient of Rotor (Aerodynamic)

𝑍 Impedance

R Relay

Δ Delta Transformer Configuration

𝑌 Wye Transformer Configuration

RMS Electromechanical Transient

EMT Electromagnetic Transient

1

1 CHAPTER 1

INTRODUCTION

1.1 Background

The first and simplest form of power generator in Iraq was developed in 1917 in the

form of diesel-driven direct current (DC) generators, operating in the city of Baghdad. The

generator, however, only served a small number of consumers. Following the success,

other Iraqi cities began installing diesel stations and their distribution networks, such as the

city of Kirkuk and Basrah in 1918, the city of Mousal in 1921, and the city of Ramadi in

1927.

In present, Iraq has around eight steam generation plants, 20 gas-powered facilities,

and six main hydroelectric plants with expected capacity of 11,120 MW though some are

being repaired. Among the power supplies, 40 percent is thermal, 22 percent is hydropower

and 38 percent is gas-powered. The major problem faced by the power grid and electricity

industry in Iraq is the shortage in a generation. This is mainly due to aging power plants,

plus the lack of proper routine of overhaul maintenance. In addition, the political and

economic circumstances in Iraq during the past 20 to 30 years make it difficult to install

new generators. Generally, shortage in power generation, rapid rise in demand and

consumption, and degradation of system components (due to aging and other reasons) all

lead to long hours of load shedding and operation beyond standard limits (Hassan and

Moghavvemi, n.d.; Reda et al., 2006).

One potential solution for these problems is the installation of small-size diesel

generating units (defined here as distributed generating (DG) units). In reality, due the fact

2

that load concentration in major cities and chaotic situation which hinder the construction

of remote power stations with adequate transmission facilities, the addition of these DG

units has to be in the already established stations, with condition if they are geographically

possible due to shortage of space.

DG such as diesel engine can be easily directly installed in synchronous generator

compared with conventional power generation. Therefore, many countries are interested in

accommodating and extending DG in their distribution networks. Cost of the transmission

line and distribution network construction is rising; however, the cost of DG technologies

is descending. This makes it more economical to increase loads from DG to distribution

feeders compared to expanding the transmission line and distribution facility (Willis and

Scott, 2000). DG at distribution level has positive impacts on the system voltage profile

and substations capacity. However, the extent of such benefits depends greatly on the DG

size and location. Heavily loaded systems need more than one DG to rectify the voltage

profile and to achieve other DG promised benefits (AlHajri and El-Hawary, 2007).

By integrating DG into the utility power grid, the line upgrades could be postponed,

then there exists the possibility of a greater efficiency of the power delivery. The Power

flow should be reduced, thus, minimizing losses. Particularly, the heavily loaded feeders

or the transmission corridors could be relieved. This is also potential as opportunity for

improving power quality, allowing the consumers and utility equipment to be more durable

(To et al., 2007). However, DGs have significant impacts on electric utility power delivery

systems. With higher levels of DG penetration, greater impacts are expected on both the

transmission and distribution systems. DG basically will induce many protection issues to

the distribution system during an event of a fault, for example, blinding and sympathetic,

overcurrent relay and under-reach of distance relay (Sharkh et al., 2014). These impacts on

protection system are mainly due to DG contribution to the fault current which are not

3

considered in the planning stages. Furthermore, the presence of such DG causes the change

of fault level and consequently on the previously mentioned protection problems.

1.2 Motivation for Research

To achieve the desired support from DG to the grid either by small part or most of

the load, this means a large number of DG generators have to be embedded in the

distributed network. However, large capacity installation of DG will induce severe power

system problems. In the case of DG in Iraq, there have been registered problems of

protection system without apparent reason. The worst case was a major fire in both DG

system and the distribution substation, in addition to fatality to lives of employees who

worked in the field of electrical network maintenance (Mozina, 2001). Therefore, the

existing protection system should be more effective or work well to avoid such problems.

For these reasons, this study will focus on investigating the impact of the DG on short

circuit levels, which certainly will affect the protection system performance. However, to

ensure successful large scale penetration of DG generators in existing distribution network,

it is necessary to examine and understand the nature of these problems. Thus, researches

need to be conducted to develop approaches for successful integration of DG generators in

existing network.

The influence of DG based synchronous generator driven by diesel engine on

protection coordination includes blinding, sympathetic of overcurrent, reduction in reach of

distance relay and fault withstand capacity of devices, which have not been investigated in

detail for medium voltage networks.

4

1.3 Problem Statement

Nowadays, global power electricity demand is growing at a tremendous rate. The

main concern of any electrical utility is to generate adequate electricity to meet consumer

demand. One potential solution is by installing DGs, which are small-scale generators

interconnected to the power distribution system such as diesel generator system.

As traditional distribution systems have been designed to operate radially, the main

issue will be the power flow by the new interconnected generation to existing power

distribution system. In radial systems, the power flows from the upper terminal voltage

down to customer site. Therefore, the protection system is easy to handle as long as the

fault current only flows in one direction (Jenkins et al., 2008). However the presence of

DG based diesel generator system in distribution system will change the fault level and

consequently lead to protection system problems, such as blinding and sympathetic of

overcurrent relay and under reach of distance relay. Thus, more complex protection

investigation is necessary to overcome the appearing problems in a radial system.

To improvise the new configuration, distribution system design regarding DG

technology, sizing and location must be taken into account these affect the short circuit

levels and the protection chains strength.

1.4 Objective of Research

The objectives of this project are:

To analyze the short circuit levels of the distribution system connected with DG

based synchronous generators at different location of different voltage levels.

To evaluate the performance and suitability of existing protection devices

(overcurrent and distance relay in terms of blinding, sympathetic and under reach)

against changing in short circuit levels.