INVESTIGATION OF VOLTAGE PROFILE 
IN LOW VOLTAGE DISTRIBUTION 
NETWORK 
 
 
 
A dissertation submitted to the 
Department of Electrical Engineering, University of Moratuwa 
in partial fulfillment of the requirements for the 
Degree of Master of Engineering 
 
 
 
By 
PRABHATH CHINTHANA DEVASURENDRA 
 
 
Supervised By: Prof. Ranjit Perera 
 
 
 
Department of Electrical Engineering 
University of Moratuwa, Sri Lanka 
 
 
2006 
 
86330 
 
 
  
Abstract 
 
Rural Electrification (RE) development constitutes construction of new substation 
with the capacity of 100 kVA to 160 kVA with MV feeding of 1 to 3 km. RE scheme 
covers one village or sometimes several villages. The Low voltage lines which are 
constructed along the roads in the village feeds the houses of the villagers. In the past 
after constructing a RE scheme, LV lines are added without considering the voltage 
drops even though CEB has to follow voltage regulation limits according to the 
Electricity Act. As a result just after the construction of RE schemes the villagers 
experience the voltage drops which results in not fully achieving the objectives of 
rural electrification. Several years ago CEB with the agreement of GOSL the lengths 
of LV feeder from the transformer substation was limited to 2.5 km. After a study 
CEB found that this length is also bigger and it causes voltage drops and Low 
Voltage side loses and decided to limit it to 1.8 km. This limit affect the development 
of rural electrification in the country because after every 1.8km feeder length, 
transformer substation is needed to be constructed. 
 
There is no proper tool or method to decide the lengths of LV lines considering the 
consumption of the village houses. This study develops a tool to guide the Rural 
Electrification Engineer to decide the LV line length in RE schemes considering the 
consumption pattern and the consumer distribution in the village minimizing voltage 
drops & power loses and providing electricity to maximum number of houses of the 
villagers. 
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 not being 
concurrently submitted for any other degree. 
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P.C. Devasurendra 
Date o 1 /o:L/ztJo~ 
Well endorse the declaration by the candidate. 
Prof. Ranjit Perera 
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Contents 
Declaration 
Abstract 
Acknowledgement 
List of Figures 
List ofTables 
Chapters 
1. Introduction 
1.1 Background 
1.2 Power Utilities in Sri Lanka 
1.3 Expansion of Electricity 
1.4 State Responsibility I 
1.5 Expected Social & Economic Improvements 
by Village Electrification 
1.6 Problems in Rural Electrification 
1.7 Selection of Rural Electrification Schemes 
1.8 Evaluation Criteria Used in RE Schemes 
1.9 Reasons for not obtaining electricity 
1 .I 0 Changes, which have occurred after obtaining electricity 
2. Problem Statement 
2.1 Preliminaries 
2.2 Problem Identification 
2.3 Other Related 
3. Proposed Solution 
3.1 Methods and Techniques 
4. Theoretical Developments 
4.1 Basic Theory of The Analysis 
4.2 Mathematical Derivations 
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4.2.1 Trapezoidal consumer distribution pattern 
4.2.2 Rectangular consumer distribution pattern 
4.2.3 Triangular consumer distribution pattern 
5. Application of the Proposed Method 
5.1 Applications 
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6. Results and Analysis 
7. Conclusions 
References 
Appendices 
Appendix A Programs 
Appendix B Distribution Layout of an RE Scheme 
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Acknowledgement 
Thanks are due first to my supervisor, Professor Ranjit Perera, Head of the 
Department of Electrical Engineering, for his great insights, perspectives, guidance 
and sense of humor. My sincere thanks go to Dr Wijekoon Banda, Planning Branch, 
Ceylon Electricity Board and Mr Bogahawatta, Chief Engineer, Ceylon Electricity 
Board, for helping in various ways to clarify the things related to my academic work 
with excellent cooperation and guidance. Sincere gratitude is also extended to 
Electrical Superintendents in several customer service centers (C~) of CEB, for 
providing me necessary data. Lastly, I should thank many individuals, friends and 
colleagues who have not been mentioned here personally in making this educational 
process a success. 
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List of Figures 
Figure Page 
1.1 Graphical Representation of Increase of Electrified Households 12 
1.2 Electrified Households 12 
2.1 A typical RE scheme 15 
2.2 General Arrangement at a Distribution Substation 16 
3.1 Scheme Layout Sketch 22 
3.2a Simple representation of the feeder 23 
3 .2b The connection pattern of loading of houses to the feeder j 23 
3.2c The approximated connection pattern 24 
3.2d Trapezoidal distribution pattern 25 
3.3 Algorhythm-1 27 
3.4 Algorhythm-2 28 
4.1 A line-to-neutral equivalent circuit 29 
4.2 Phasor Diagram 29 
4.3 Trapezoidal consumer distribution pattern 31 
4.4 Rectangular consumer distribution pattern 34 
4.5 Triangular consumer distribution pattern 36 
5.1 Sketch of a Proposed Scheme 38 
6.1 Plot ofFeeder-1 Loading Between Poles Vs Length of Feeder 42 
6.2 Plot of Feeder- I Loading with an Approximation 42 
6.3 Approximation Plot of Loading of Feeder-1 43 
6.4 Sectionalized Plot of Feeder- I 43 
6.5 Plot ofFeeder-1 Branch-I Loading 45 
6.6 Plot of Feeder- I Branch- I Loading with an Approximation 45 
6.7 Approximation Plot of Loading ofFeeder-1 Branch-I 46 
6.8 Sectionalized Plot ofFeeder-1Branch-l # 46 
6.9 Plot ofFeeder-lBranch-2 Loading "/ 47 
6.10 Plot of Feeder-1 Branch-1 Loading with an Approximation 48 
6.11 Approximation Plot of Loading of Feeder-1 Branch-2 48 
6.12 Sectionalized Plot of Feeder-1 Branch-2 49 
6.13 User Interface of The Programme s.t.' 
6.14 Display of Input Data for Feeder- I 51 
6.15 Display of calculated Voltage drop & Power loss for Feeder-! 52 
6.16 Voltage Drop Variation For Feeder- I ~ 
6.17 Display of Input Data for Feeder-1 Branch-1 :.•- 53 
6.18 Display of calculated Voltage drop & Power loss for Feeder- I Branch-JV 53 ., 
6.19 Voltage Drop Variation For Feeder-IBranch-1 54 " 
6.20 Display of Input Data for Feeder-! Branch-2 54 
6.21 Display of calculated Voltage drop & Power loss for Feeder- I Branch-2 55 
6.22 Voltage Drop Variation For Feeder-lBranch-2 55 
List of Tables 
Table Page 
1.1 Percentage Electrification Level (By Districts) 2 
1.2 Rural Electrification Projects 4 
1.3 Rural Electrification Programme ( 1998 - 2005) j II 
5.1 Sample Data Table 39 
6.1 The data of the feeder- I of Maha Ingiriya Substation 41 
6.2 Results ofFeeder-1 from Sectionalized Plot ofFeeder-1 44 
6.3 Results of Feeder-] Branch-1 from Sectionalized Plot of Feeder-1 Branch- I 4 7 
6.4 Results ofFeeder-1 Branch-2 from Sectionalized Plot ofFeeder-1 Branch-2 50 
6.5 Comparison of Results ofTwo Methods 56 
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