L b / O C H 
DISTRIBUTION SYSTEM RELIABILITY ASSESMENT 
AND TECHNIQUES FOR IMPROVEMENT. 
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 
A.D. JANAKI RUPASINGHA 
LIBRARY 
UNIVERSITY OF MORATUWA, SRI LANKA 
MORATUWA 
Supervised by: Prof. Ranjit Perera 
6 Z \ 3 < 
Department of Electrical Engineering 
University of Moratuwa , Sri Lanka 
April 2008 
University ot Moratuwa 
91261 
91281 
DECLARATION 
The work submitted in this dissertation in 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 
A.Dj^J^fpSsTngha 
Date:08/04/2008 
I endorse the declaration by the candidate. 
Prof. Ranjit Perera 
ABSTRACT 
Although reliability indices were introduced in the past as Key Performance 
Indicators to gauge the activities of electricity utilities, reliability studies on 
electricity network are rarely carried out to determine what improvements can 
be made in the future. The data collected in the past has been only used for 
manual calculation of reliability indices in the various operating divisions with 
no attempts made to study & effect improvements based on them. 
This study focused on the following, 
• A study of the sustained failure indices such as SAIDI & SAIFI making 
use of the SynerGEE software package for medium voltage distribution 
network, as an initial computation of indices. 
• Comparison of the results with values for reliability indices obtained in 
practice using past data from operating divisions & their system control 
centres in the CEB. 
• Identification and selection of mitigation techniques in Kalpitiya that is 
a heavily salt polluted area of the North Western province of Sri Lanka. 
• Analysis of the effectiveness of the selected mitigation techniques to 
improve the reliability level in the Kalpitiya area and a financial analysis 
to justify the viability of the project. 
• Proposing methods for reliability improvement, such as better 
maintenance practices, policies, augmentation of lines and improvement 
of switching arrangements. 
ii 
The tool available in the SynerGEE software package for reliability calculation 
in the distribution network has not been used effectively in the past for 
calculations and mitigation planning purposes due to unavailability of proper 
data base. 
In this study the SynerGEE software package has been used to calculate the 
sustained failure indices such as SAIDI and SAIFI for the medium voltage 
distribution network of the North Western Province initially with mitigation 
techniques applied. Further it is recommended that similar studies are 
conducted in other areas of the CEB as well and techniques applied to critical 
regions with much benefit to be derived in the future. 
ACKNOWLEDGEMENT 
First I thank very much Prof. Ranjit Perera without whose guidance, 
support and encouragement, beyond his role of project supervisor this 
achievement would not be end with this final dissertation successfully. 
I take this opportunity to extend my sincere thanks to Mr. Lalith 
Fernando -DGM (Planning & Development)-Rl, Mr. S.R.K. Gamage- CE 
(Planning) -R1 & Dr. Wijekoon-CE (Planning)-R3 for encouraging me to 
carry out this project.. 
I also thank Mr.A.C.S Wijethilaka- System Planning Engineer (NWP), 
Mr Kapila Weerasuriya-CE(Development),Mr. A.K. Dayaparendran, 
Mr.W.S. Silva, Mr Kamal Perera in the Distribution Planning Branch, 
Region 1, for facilitation me with the necessary data and the information. 
It is a great pleasure to remember the kind cooperation of all colleagues 
in Post Graduate programme and all family members for backing me 
from start to end of this course. 
iv 
LIST OF ABBREVIATIONS 
AAC- All Aluminum Alloy Conductors 
ABS- Air Break Switch 
ACSR-Aluminum Conductor with steel reinforcement 
AR- Auto Reclosure 
CAIDI-Customer Average Interruption Duration Index 
CAIFI-Customer Average Interruption Frequency Index 
CSC- Consumer Service Centre 
DDLO- Drop Down Lift Off 
DGM- Deputy General Manager 
GDP- Gross Domestic Product 
GSS- Grid Sub Station 
HT - High Tension 
LBS- Load Break Switch 
LT - Low Tension GSS- Grid Power Station 
NWP- North Western Province 
PSS- Primary Substation 
SAIDI-System Average Interruption Duration Index 
SAIFI-System Average Interruption Frequency Index 
SIN-Substation Identification Number 
SIR -Silicon Rubber 
CONTENTS 
Declaration i 
Abstract ii 
Acknowledgement iii 
Abbreviation iv 
List of Figures viii 
List of tables ix 
1 Introduction 
1.1 Background 1 
1.2 Motivation 2 
1.3 Objective 3 
1.4 Scope of work 3 
1.5 SynerGEE Software Package 4 
2 Distribution System Reliability in NWP of Sri Lanka. 
2.1 NWP Province 6 
2.2 Electricity Distribution Network of NWP 6 
2.3 Reliability Assessment for NWP Province 8 
2.4 Average Reliability Indices for Year 2005 & 2006 10 
2.5 Causes for system outages 11 
2.6 Feeder tripping details 18 
3 Methodology 
3.1 Updating the map of MV distribution network 22 
3.2 Data collection 23 
3.3 Data analysis and Calculation 25 
3.4 Modelling the network in SynerGEE 28 
3.5 Assigning in put data to the digitized model 29 
3.6 Reliability analysis 30 
vi 
4 Calculation Exposure zone reliability and 
Effectiveness of the mitigation techniques 
4.1 Exposure Zone Reliability estimation 32 
4.2 Quantification of the effectiveness of the mitigation 38 
techniques 
5 Frequently Repeated Breakdowns in MV Distribution 
network and Solutions for them 
5.1 DDLO without having minimum clearance 41 
5.2 MV Breakdowns due to way-leaves 41 
5.3 Improper connection of HT jumpers 42 
5.4 Jumper connection without allowable clearance 43 
5.5 Corrosion of concrete poles in coastal areas 43 
5.6 Sagged MV line touching LT poles 44 
5.7 Improper Electrical Connections 45 
5.8 HT or LT conductors are not tensioned properly 45 
5.9 Insulator pollution 45 
5.10 Usage of incorrect fuse size 45 
5.11 High earth impedance at substations 47 
5.12 Two HT circuits are drawn on the some poles 47 
6 Result and Analysis 
6.1 Analysis of the Result obtained from the SynerGEE reliability 50 
tool 
6.2 Case Study ( Selected Mitigation Technique) 55 
7 Conclusion and Recommendation 
7.1 Conclusion and discussion 64 
7.2 Proposals for Improvement of the network 65 
vii 
References 7 4 
Annexure 
Annexure 2.1 The map of Electricity Distribution Network of NWP 75 
Annexure 2.2 The definitions of the reliability indices 76 
Annexure 3.1 A performance report about daily functions of each 77 
CSC 
Annexure 3.2 Daily report on 33kV feeder trippings 79 
Annexure 3.3 Summery report of failures 80 
Annexure 3.4- HT breakdowns/failures recorded at the DCC 84 
Annexure 3.5 Sin numbers and the number of customers assigned 87 
to sub stations 
Annexure 4.1 Questionnaire prepared to distribute among the 90 
consumers 
Annexure 6.1 Co-relation between rainfall and operation frequency 91 
of HT DDLO 
Annexure 6.2 Puttalam- Kalpitiya Feeder 92 
List of Figures 
Figure 2.1 Analysis of recorded outages 9 
Figure 2.2 Percentage of effected consumers due to different outage categories 9 
Figure 2.3 Percentage of consumer hours lost due to different outage categories 10 
Figure 2.4 Analysis of LT faults 12 
Figure 2.5 Identified reasons for LT failures reported to each CSC 14 
Figure 2.6 Restoring time vs. percentage of LT faults reported 15 
Figure 2.7 HT faults reported in 2005 15 
Figure 2.8 Identified reasons for HT failures reported each CSC 17 
Figure 2.9 Restoring time vs. percentage of HT faults reported 18 
Figure 2.10 Fault rate vs. percentage of total circuits 21 
Figure 4.1 Frequency Distribution of M V power failure of the selected area 35 
Figure 4.2 Frequency Distribution of M V power failure of the selected area 36 
Figure 5.1 Incorrectly fixed DDLOs 41 
Figure 5.2 Tree branches touching M V conductors 42 
Figure 5.3 Improper electrical connections 42 
Figure 5.4 Jumper connections without allowable clearance with cross arms 43 
Figure 5.5 Corroded concrete poles at coastal areas 44 
Figure 5.6 Sagged M V Line touch on LT pole 44 
Figure 5.7 Improper Electrical connections 45 
Figure 5.8 Damaged DDLO fuse bases 46 
Figure 5.9 Untidy connections of transformer tail wires 48 
Figure 5.10 Damaged L T fuse bases 48 
IX 
List of Tables 
Table 2.1 M V distribution facilities at the end of 2006 7 
Table 2.2 Network details of each area at the end of year 2006 8 
Table 2.3 Summary of the annual average event - 2005 & 2006 8 
Table 2.4 Reliability indices of N W P network for year 2005 & 2006 11 
Table 2.5 Contribution from the transmission & distribution network to reliability indices 11 
Table 2.6 Summary of Average L T breakdown details for year 2005 & 2006 12 
Table 2.7 Summary of HT breakdown details 16 
Table 2.8 Summary of feeder tripping details 18 
Table 2.9 Fault rate of each feeder 19 
Table 3.1 Breakdown categories 25 
Table 3.2 Equipment failure rates and repair time assigned for the model 27 
Table 3.3 Letter allocation of sin number for the areas & CSCs 30 
Table 4.1 Summarize result of the survey 34 
Table 4.2 Cut set of average time taken to restore the power supply 36 
Table 4.3 Reliability indices for Exposure Zones 38 
Table 4.4 Mitigation zones and their effectiveness 39 
Table 6.1 Result from SynerGEE Software package 50 
Table 6.2 Table of comparison between the feeders of N W P 53 
Table 6.3 SAIDI & SAIFI comparison Table 54 
Table 6.4 Comparison of general capabilities of Insulators 57 
Table 6.5 SAIDI & SAIFI comparison with both type of insulators 58 
x