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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.
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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.
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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.
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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.
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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
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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
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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
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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.