ASSESSMENT OF EFFICIENCY AND
CONDITION BASED OPTIMUM LOADING OF
TRANSMISSION LINES
A dissertation submitted to the
Department of Electrical Engineering, University of Moratuwa
in partial fulfillment of the requirements for the
Degree of Master of Science
by
WITHANAGE DON ANANDA JAYASIRI
CHANDRAKUMARA
Supervised by: Prof. HYR Perera and Eng. LAS Fernando
Department of Electrical Engineering
University of Moratuwa, Sri Lanka
September 2005
University of Moratuwa
11111111111111111111111111111111111
84772
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Designing of transmission lines in Sri Lanka has been done considering average
weather conditions through out the year. Whereas in the real situation, weather
conditions are seasonally varying. Therefore, based on the seasonal variation of
weather condition in Sri Lanka, existing transmission network can be optimally
loaded delaying future construction of transmission lines.
Abstract
Transmission lines in any transmission network is the critical part or the one of the
major limiting factors for power transfer capability of the transmission network.
The thermal power transfer capability of Overhead Transmission lines is primarily a
function of the height of the conductor above the ground. This height affects the
safety of the public and is therefore clearly specified in legislation.
Different methods for determination of Power Transfer capability of transmission
lines are available. These include deterministic and various probabilistic approaches.
The latter include a model simulating condition that affect the safety of the
transmission line relating specially to the conductor position from which a measure of
safety is developed. This measure can be used by designers to optimally design the
transmission line from current loading point of view.
The deterministic approach has been used by most utilities around the world, as it is
quick and simple. That method assumes bad cooling conditions that will result in the
line design temperature being achieved.
Probabilistic methods use actual weather data and conditions prevailing on the line to
determine the likelihood or probability of a certain condition. In this project,
condition was taken as the conductor temperature rising up to the design temperature,
which is 75 degree Celsius.
IV
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DECLARATION 
The work submitted in this dissertation is the result of my own investigation, except 
where otherwise stated. 
It has not already been accepted for any degree, and is also nol being concurrently 
submitted in whole or part to any University or Institution for any other degree. 
J Chandrakumara 
29.11.2005 
We I I endorse the declaration by the candidate 
~ 
Prof. HYR Perera 
~~ 
Eng. LAS 'Fernando 
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CONTENTS 
Declaration 
Abstract 
Acknowledgement 
List of figures 
List ofTables 
List of Symbols 
Chapters 
1. Introduction 
1.1 General Background 
1.2 Goals 
1.3 Methodology used to accomplish goals 
2. Operation of Transmission Network 
2.1 Transmission Network in Sri Lanka 
2.2 Arrangement of the transmission Network in 
Sri Lanka 
2.3 Loading pattern of selected lines 
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3. Methods used to design Transmission Line Current rating 
3.1 Methods for determination of current rating 
3.1.1 Probabilistic methods available 
3.1.2 Deterministic Method 
4. Assessment of efficiency of Transmission Lines 
4.1 Design values of current carrying cap_ii~ty of 
Selected transmission lines " 
4.2 Utilization ofTransmission Lines 
4.3 Calculation of annual efficiency 
5. Case study 
5.1 Collection of Data 
5.2 Analyzing Data 
5.2.1 Sample Calculation 
5.3 Summary of Calculation 
5.4 Assessment of possible current ratings 
5.5 Criteria for selecting optimum current rating 
5.6 Voltage variation at receiving end 
5.7 Assessment of Power Loss 
5.8 Effect on Sag due to optimum loading 
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6. Conclusion and Recommendation 
6.1 Conclusion 
6.2 Discussion 
6.3 Recommendation for future researches 
References 
Appendix A Calculation of annual average charge 
Flow along selected two lines 
Appendix B Data collected and calculation of 
Current ratings at Sites 
Appendix C Calculated optimum current ratings of 
Two selected transmission line 
Appendix D Daily average operating Amperes of 
Selected two Transmission lines 
Appendix E Financial analysis on power loss along 
The transmission line 
Appendix F Different conductor types used in the 
Transmission network in Sri Lanka 
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Acknowledgement 
I wish to express my appreciation and sincere thanks firstly to the University of 
Moratuwa for providing me the opportunity of following the Master's Degree 
Program in Electrical Engineering and Professor HYR Perera, Head of the 
Department of Electrical Engineering, University of Moratuwa and Mr. LAS 
Fernando, Deputy General Manager (Transmission Operation and Maintenance), 
Ceylon Electricity Board, who guided and encouraged me as Project Supervisors to 
achieve the goals of the project despite their load of work and responsibilities. Their 
advice and insight were immeasurable. 
j 
I would extend my sincere gratitude for Transmission Design branch, System Control 
Center and my colleagues and brother Engineers of Transmission Operation & 
Maintenance Branch of the Ceylon Electricity Board. Special thanks go to my 
subordinates in the Hot Line Maintenance unit of the Ceylon Electricity Board. 
While I regret for my inability to specifically mention individuals, I am grateful to 
all the staff of the University of Moratuwa and my colleagues who were helpful in 
numerous ways to make my endeavor a success. 
Last, but not least, I thank my beloved wife Thamara and children Kalana and 
Imalsha for their affection, appreciation, support and understanding towards me in 
achieving the aspiration. 
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List of Figures 
Figure Page 
2.1 Present average Loading patterns of 220 kV 
Kotmale - Biyagama Transmission line 6 
2.2 Present average Loading patterns of 220 kV 
Kotmale- Anuradapura Transmission line 7 
2.3 Specimen Daly Load Curve of Transmission System in Sri Lanka 7 
2.4 Map of selected two transmission lines 8 
2.5 Sketch of the Transmission Network in Sri Lanka 9 
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5.1 Calculated Optimum Loading Patterns of 220 kV 
Kotmale - Biyagama Transmission line form January to March 27 
5.2 Calculated Optimum Loading Patterns of 220 kV 
Kotmale- Biyagama Transmission line form April to September 28 
5.3 Calculated Optimum Loading Patterns of 220 kV 
Kotmale - Biyagama Transmission line form October to December 29 
5.4 Calculated Optimum Loading Patterns of 220 kV 
Kotmale - A'pura Transmission line form January to April 30 
5.5 Calculated Optimum Loading Patterns of 220 kV 
Kotmale- A 'pura Transmission line form May to September 31 
5.6 Calculated Optimum Loading Patterns of 220 kV 
Kotmale - A 'pura Transmission line form October to December 32 
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List of Tables 
Table 
2.1 a Existing 132k V transmission network of Sri Lanka 
2.1 b Existing 220 k V transmission net work of Sri Lanka 
4.1 Design values of current carrying capacity of 
selected transmission lines 
5.1 
5.2 
5.3 
5.4 
5.5 
5.6 
5.7 
5.8 
5.9 
5.10 
5.11 
5.12 
5.13 
Designed parameters of selected two transmission lines 
Sag corresponding to different temperatures 
Calculated Optimum Loading pattern of220 kV Kotmale- . 
Biyagama Transmission line from January to March .t 
Calculated Optimum Loading pattern of220 kV Kotmale-
Biyagama Transmission line from April to September 
Calculated Optimum Loading pattern of 220 k V Kotmale -
Biyagama Transmission line from October to December 
Calculated Optimum Loading pattern of220 kV Kotmale-
A' pura Transmission line from January to April 
Calculated Optimum Loading pattern of220 kV Kotmale-
A' pura Transmission line from May to September 
Calculated Optimum Loading pattern of220 kV Kotmale-
A' pura Transmission line from October to December 
Calculated optimum current ratings and corresponding Voltage drop 
and power loss of 220 kV Kotmale - Biyagama Transmission line from 
January to March 
Calculated optimum current ratings and corresponding Voltage drop 
and power loss of220 kV Kotmale - Biyagarna Transmission line from 
April to September 
Calculated optimum current ratings and corresponding Voltage drop 
f 
and power loss of220 kV Kotmale Biyagama Tr~mission line from 
October to December 
Calculated optimum current ratings and corresponding Voltage drop 
and power loss of220kV Kotmale Anuradapura Transmission line from 
January to April 
Calculated optimum current ratings and corresponding Voltage drop 
and power loss of220kV Kotmale - Anuradapura Transmission line from 
Page 
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6 
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16 
25 
27 
28 
29 
30 
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32 
33 
33 
33 
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May to September ..,. ?4 
Calculated optimum current ratings and corresponding Voltage drop. 5.14 
6.1 
and power loss of220kV Kotmale Anuradapura Transmission line.Jrom 
October to December 
Calculated Optimum Current rating of220 kV Kotmale -Biyagarna 
Transmission line 
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36 
VII 
Table Page 
6.2 Calculated Optimum Current rating of220 kV Kotmale - Anuradapura 
Transmission line 36 
6.3a Recommended optimum current ratings of220kY Kotmale -
Biyagama Transmission line from January to March 37 
6.3b Recommended optimum current ratings of220kV Kotmale-
Biyagama Transmission line from April to September 38 
6.3c Recommended optimum current ratings of 220k V Kotmale-
Biyagama Transmission line from October to December 38 
6.3d Recommended optimum current ratings of220kY Kotmale-
Anuradapura Transmission line from January to December 38 
AI Actual average flow of charge along 220 kY Kotmale -Biya{ama 
A2 
Bl 
B2 
B3 
B4 
CI 
C2 
C3 
C4 
C5 
C6 
C7 
C8 
C9 
CIO 
Cll 
Transmission line 
Actual average flow of charge along 220 kY Kotmale - Anuradapura 
Transmission line 
Data collected and calculated current ratings at Kotmale 
Data collected and calculated current ratings at Biyagama 
Data collected and calculated current ratings at Anuradhapura 
Data collected and calculated current ratings Mahailukpallama 
Probability Distribution of current ratings for 220 kV 
Kotmale- Biyagama Transmission line from January to March 
Probability Distribution of current ratings for 220 kV 
Kotmale- Biyagama Transmission line from January to March 
Probability Distribution of current ratings for 220 kV 
Kotmale- Biyagama Transmission line from April to September 
Probability Distribution of current ratings for 220 kV 
Kotmale- Biyagama Transmission line from Aprit,..to September 
Probability Distribution of current ratings for 220 k'V 
Kotmale - Biyagama Transmission line from October to December 
Probability Distribution of current ratings for 220 kV 
Kotmale - Biyagama Transmission line from October to December 
Probability Distribution of current ratings for 220 kV 
Kotmale- Anuradapura Transmission line from January to April 
Probability Distribution of current ratings for 220 kV 
Kotmale- Anuradapura Transmission line from January to April ,.,_ 
Probability Distribution of current ratings for 220 kV Kotmale - , 
Anuradapura Transmission line from May to September 
Probability Distribution of current ratings for 220 kV Kotmale-
Anuradapura Transmission line from May to September 
Probability Distribution of current ratings for 220 kV Kotmale-
Anuradapura Transmission line from October to December 
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VIII 
Table Page 
Cl2 Probability Distribution of current ratings for 220 kV Kotmale-
Anuradapura Transmission line from October to December 59 
OJ Average Operating data of220 kV Kotmale - Biyagama 
Transmission line 60 
02 Average Operating data of220 kV Kotmale - Anuradhapura 
Transmission line 61. 
E Financial analysis on power loss along the transmission line 62 
F Different ACSR Conductor types used in Transmission network 65 
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List of Symbols 
Symbols 
Qc 
Qr 
Qs 
ta 
tc 
tr 
R 
d 
do 
Pr 
v 
~f 
kr 
K: 
Ka 
e 
a 
Qs 
A' 
e 
He 
Zc 
z1 
He 
We 
Ww 
s 
0 
f 
E 
T 
a 
L 
Description 
Conductor current, A 
Convected heat loss, W/ft 
Radiated heat loss, W/ft 
Heat gain from the sun, W/ft 
Ambient temperature, °C 
Average temperature of conductor, °C 
Air film temperature, °C 
AC resistance, n/ft 
Conductor diameter, in 
Conductor diameter, ft. 
Density of air, lb/ft3 
Velocity of air stream, ftlh 
Absolute viscosity of air, lb/h 
j 
Thermal conductivity of air at temperature trW/ft. 
Temperature of conductor, K 
Ambient temperature, K 
Coefficient of emissivity, 0.23 to 0.91 
Coefficient of solar absorption, 0.23 to 0.91 
Total solar and sky radiated heat, W/ff 
Projected area of conductor- d/12 
Effective angle of incidence of the sun's rays, degrees 
Altitude of sun, degrees 
Azimuth of sun, degrees 
Azimuth of line, degrees 
Elevation of conductor above~ level, ft 
Conductor weight ' 
Wind force on conductor 
Catenary length along conductor 
Sag 
Stress or T I A 
Young's modules 
Tension of the conductor 
; ' 
Coefficient of linear expansion of conductor .... ~ · 
Span 
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