EFFECT OF EMBEDDED GENERATORS ON
SRI LANKA POWER SYSTEM FREQUENCY
FLUCTUATIONS
MASTER OF SCIENCE
L.N.W. ARACHCHIGE
uru
1
iimlljf
82429
DEPARTMENT OF ELECTRICAL ENGINEERING
UNIVERSITY OF MORA TUWA
SRI LANKA
JULY 2004
824-2CJ
''.:;''" ,
~ .. "
.'
Executive Summary
The purpose of this research was to review the current utility operating methods and
associated technical issues, basically on frequency stability in Sri Lanka when
considering embedded generation connected to distribution network, and to examine the
prospects for future active operation and control of the network.
A comprehensive software based study was done which allowed identifying some
prospective modifications for a more active approach to the operation of the power
system to accommodate the expected amount of embedded generation that is likely to be
connected in the coming decade in order to meet the government targets.
Different loading conditions based on the load curve was assed and technical issues on
protection, basically Rate of Change of Frequency (ROCOF) protection and load
shedding were covered in detail, and a new load shedding scheme was proposed.
Guidelines were suggested to the future modifications and control of the network. These
will allow the embedded generation developers and the Ceylon Electricity Board (CEB)
to maximize the potential of embedded generation and improve the utilization of their
network.
DECLARATION 
The work submitted in this thesis is the results of my own investigation, except where 
otherwise stated. 
The work included in the thesis in pa11 or whole has not been submined for any other 
academic qualification at any institution. 
j 
Miss L.N.W. Arachchige !}!: I 0 I 0 ~I 2.00 't 
(Author) Signature Date 
Or. D.P.N. 0!"anayakkara 
iJ/ rl~<·t/ 1u Jor/r 
(Supervisor) Signature Date"'' 
~ 
:. .... 
.,; 
~ 
/ 
Executive Summary 
The purpose of this research was to review the current utility operating methods and 
associated technical issues, basically on frequency stability in Sri Lanka when 
considering embedded generation connected to distribution network. and to examine the 
prospects for future active operation and control of the network. 
A comprehensive software based study was done which allo\.ved identifying some 
prospective modifications for a more active approach to th;: operation of the power 
system to accommodate the expected amount of embedded generation that is likely to be 
connected in the coming decade in order to meet the government targets. 
Different loading conditions based on the load curve was assed and technical issues on 
protection. basically Rate of Change of Frequency (ROCOF) protection and load 
shedding were covered in detail, and a new load shedding scheme was proposed. 
Guidelines ·were suggested to the future modifications and control of the network. These 
will allow the embedded generation developers and the Ceylon Electricity Board (CEB) 
to maximize the potential of embedded generation and improve the utilization of their 
network. 
--!,.-
" 
.... -
~ 
:.. .... 
.., 
,.~ 
Acknowledgement 
It is a great pleasure to thank those who were behind me in completing the research 
successfully. 
First of all I must thank ADB, Post Graduate Division and all who decided to award me 
with the scholarship. 
I would like to express my gratitude to Dr. D.P.N. Nanayakkara (Senior Lecturer, Dept. 
of Elect. Engineering. University of Moratuwa): my research sJpervisor for proposing 
such an interesting topic and for guiding me through out the research. 
My special thanks go to Prof. J.R.Lucas, (Prof. of Elect. Engineering, University of 
Moratuwa). Dr.Jahan Peiris (Consultant, Hydro-Thusmania), Dr.Thrishantha 
Nanayak.kara (Senior Lecturer, Dept. of Elect. Engineering, University of Moratuwa), 
Dr.Sarath Perera (Senior Lecturer. School of Electrical, Computer and 
Telecommunications Engineering, University of Wollongong, Australia), and Dr.Ranjith 
Perera (Head/ Dept. of Elect. Engineering, Uni\ersity of Moratuwa). I would like to thank 
Ms Kamala Gamage for guiding me specially in using the simulation tools. 
I would also like to thank Prof. P.D.C. Wijayathunga (Dean, Faculty of IT. University of 
~1oratu\va),and all the Electrical Engineers at the CEBr)Nho helped me in collecting the 
information. Thank you very much for your kind support. 
Last but not least I would also like to thank all my friends Vajira, Kancl1tl~a. Latin, 
Chandana, Rangika, Bandula and all the oth~rs who helped me in various ways and 
specially my mother and sister for encouraging me all the way through. . . .._ 
...... 
,\.fiss Lidula Silakshi Widanagama Arachchige 
Department of Electrical Engineering 
Uni\'ersity of.\1oratuwa. 
yf 
.,.~ 
II 
Fig.1.1.1 (a) 
Fig. I. 1.1(b) 
Fig.2 
Fig.2.2.1 
Fig.2.2.4 
Fig.3.1.1 
Fig.4.2 (a) 
Fig.4.2 (b) 
Fig.4.2 (c) 
Fig.4.2 (d) 
Fig.4.2 (e) 
Fig. 4.3 (a) 
Fig. 4.3 (b) 
Fig. 4.3 (c) 
Fig.4.3(d) 
Fig. 4.3(e) 
Fig.5.1 (a) 
Fig.5.1(b) 
Fig.5.1(c) 
Fig.7.1(d) 
Fig.5.2(a) 
Figures & Tables 
Installed Generation Capacity by Type 
Daily load curve of the country on 17112/2003 
The structure of the hierarchical control of a power system 
Block Diagram of the Frequency Control in a Power System 
Functional Block Diagram of Power Generation and Control 
Load shedding criteria 
Modeled Sri Lankan Power System j 
Modeled Power Station 
Modeled Under frequency relay of a generator 
Modeled time settings of the generator under frequency relay 
Modeled Under Frequency Load Shedding Relay 
System Response at 40MW Loss of Generation 
System Response at 80MW Loss of Generation 
System Response at l67MW Loss of Generation 
Page 
3 
3 
9 
I I 
13 
15 
19 
20 
20 
21 
21 
?.., 
_.) 
?"' 
_.) 
24 
Actual Frequency Response Plot on a Particular Day at 16.9% Loss of 
Generation 24 
Simulated System Response at 15.9% Loss of Generation 25 
Rate of change of frequency vs. time at Balangoda Embedded Power 
Station at a loss of 8% generation at 12.0.)} hours on 27/08/2003(medium 
"' 
loaded condition) 27 
Power System frequency vs. time at a loss of 8% generation at 1200 hours 
on 27/08/2003(mcdium loaded condition) ,.,... ' 28 
Power System frequency vs. time at a loss of 8% generation at 1200 hours 
on 27/08/2003(medium loaded condition) -comparison .._ 29 
..... 
Po"ver System frequency vs. time at a loss of 15% goo.eration ,Stt 1200 
hours on 27/08/2003(medium loaded condition) 30 
Power System frequency vs. time at a loss of 15% generation at 1200 
hours on 27/08/2003(medium loaded condition) 31 
Fig. 5.2.1 Simple Static Load Shedding Criteria 32 
Fig.5.2.2(a) Proposed Load Shedding Scheme 38 
111 
Fig.5.2.2(b) Power Systerr1 frequency vs. time at a loss of 11.5% generation at 1930 
hours on 27/08/2003(peak loaded condition) 39 
Fig.5.2.2(c) Rate of change of frequency vs. time at a loss of 11.5% generation at 1930 
hours on 27/08/2003(peak loaded condition) - at Balangoda Embedded 
power station 
Table 1.1.1 Summary of Existing Power Stations 
Table 1.1.2 (a) Existing Grid Substation Capacities 
Table 1.1.2(b) Existing Transmission Line Lengths j 
Table 1.1.3 Distribution Line Lengths 
Table 1.2.1(a) Existing Embedded Generators 
Table 1.2.1 (b) Connected Mini Hydro Capacities at GSS 
Table 2.2.2 Example H constants 
Table 4.4.2 Summary of overload 
Table 5.1 Embedded Generator responses at Major Generation losses 
Table 5.2.1 (a) Present Load Shedding Scheme 
Table 5.2.1(b) Under Frequency Settings of existing Generators 
Table 5.2.2(a) Frequency violations in year 2003 
Table 5.2.2(b) Basic Load Shedding Scheme 
Table 5.2.2(c) Basic Load Shedding Scheme with selected feeders 
.. ,. 
" 
-;. .... 
yl 
; ' 
~ 
,.~ 
40 
2 
4 
4 
5 
6 
7 
I 1 
25 
28 
33 
34 
36 
36 
37 
IV 
Executive Summary 
Acknowledgement 
Figures & Tables 
Chapter 1 Introduction 
1.1 Sri Lankan Power System 
1.1.1 Present Power Generation Faciliti9 
1.1 .2 Present Transmission System Facilities 
1.1.3 Present Transmission System Facilities 
1.2 Embedded Generation 
1.2.1 Current Status of Embedded Generation 
1.2.2 Embedded Generators in a Distribution network 
1.2.3 Over and under frequency protection 
1.2.-t Rate of Change of frequency protection 
C hapter 2 Power System Stability and control 
2.1 Control of Electric Po'' er System 
2.2 Frequency control 
2.2.1 
f 
Model of Frequency conf~ 
2.2.2 Dynamic System Model 
2.2.3 Frequency dependency of loads 
••. r 
2.2.4 Turbine Control 
2.2.5 Load Shedding -
.. 
...... 
..; 
C hapter 3 Load Shedding 
3.1 :\-fethods of overload detection 
3.1. I Static Load Shedding 
3.1.2 Dynamic Load Shedding 
3.1.3 Adaptive Load Shedding 
Contents 
Page 
11 
111 
2 
') 
... 
3 
4 
5 
5 
8 
8 
8 
9 
9 
10 
10 
I I 
12 
12 
13 
~ 14 
14 
15 
16 
16 
v 
Chapter 4 
Chapter 5 
Conclusions 
3.2 Construction of a load shedding program 
3.2.1 Total load to be shed 
3.2.2 Load shedding stages 
3.2.3 Frequency settings and time settings 
Modeling Approach 
4.1 
4.2 
4.3 
4.4 
Selection of the software 
Modeling the Network 
CEB r egulations on risk to the ~etwork 
Methodology 
4.4.1 Effect ofEmbeddcd Generation j 
4.4.2 Load shedding 
Results & Discussions 
5.1 
5.2 
Effect of Embedded Generation 
Load Shedding 
5.2.1 Present Load Shedding Scheme 
5.2.2 Proposed Load Shedding Scheme 
Recommendations --~ .. 
References 
... : 
~ 
..... 
.,; 
16 
16 
17 
17 
18 
18 
19 
22 
25 
25 
26 
27 
27 
31 
32 
35 
41 
42 
43 
"' 
. ~··-'Y ~
VI