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 
Chapter 1 
Introduction 
1.1 Background 
The reliability studies on power systems are very important in order to take 
decisions to develop & rehabilitate the power system to produce a satisfactory 
service to customers. Much consideration has been given in all countries to 
improve the reliability of power systems since it has an immense impact on 
economy of each country. A reliability study committee was appointed several 
years ago to study and recommend measures to be taken to improve power 
system reliability & power quality in the Ceylon Electricity Board (CEB ) which 
is the main electricity utility responsible for most of Generation, Transmission 
& most of distribution of the electricity in the country. 
Based on the recommendation of the committee the monitoring of reliability 
indices, System Average Interruption Duration Index (SAIDI), System Average 
Interruption Frequency Index (SAIFI), Customer Average Interruption 
Duration Index (CAIDI) & Customer Average Interruption Frequency Index 
(CAIFI) were started at the provincial level by the system planning engineers. 
However, due to various reasons this attempt to monitor the reliability indices 
was not successful. 
The required data relevant to the failures were recorded in registers at the 
Distribution control centres that carried details of power outages & scheduled 
interruptions along with their reasons. However these data are not used for 
reliability improvement due to improper data recording, inaccurate data etc. 
Thus this indicates that extensive work has to be carried out in the future to 
improve the scheduled maintenance programme to reduce the supply 
breakdowns and to enhance protection and fault isolation techniques with 
proper identification of the fault rectification and supply restoration. The 
objective was to minimize the losses due to unserved energy at the same time 
improving the service to customers. 
There are two major approaches to reliability assessment and prediction: 
1.2.1) Traditional methods based on probabilistic assessment of field data. 
1.2.2) Methods based on the analysis of failure mechanisms and physics of 
failure. 
This study is particularly based on the 2nd method which is more accurate 
and useful for failure analysis and finding reasons for failures. The 
SyenerGEE software package used in this study is also based on the 2nd 
Method. 
The study has been confined to the North western Province ( NWP) of the CEB 
and it includes calculation of the sustained failure indices SAIDI & SAIFI 
aimed at estimating the reliability to customers in the province 
In this project, failure rates and equipment repair times were calculated based 
on the previous data collected from the provincial control centre of NWP for 2 
years and failure rates and equipment repair rates that were calculated for 
each consumer service centre individually. It was observed that it is fair to 
calculate them individually due to the following reasons. 
Failure rates for the equipment heavily depend on 
• geographical location of installation 
• Effectiveness of the mitigation techniques 
• Influence of the animals such as birds, Monkeys and reptiles 
• Skill & Attitudes of the maintenance staff 
1.2 Motivation 
The outcome of this reliability study will develop a methodology to evaluate 
reliability indices such as SAIDI, SAIFI & MAIFI using the SynerGEE software. 
They can be used as guidelines for proper planning of network expansions, 
2 
maintenance schedules and operating policies. As a distribution planning 
Engineer of CEB, the author was motivated to select this topic for her study 
due to above facts. 
The concept of reliability is considered as one of the priorities of Electricity 
utilities in order to improve customer satisfaction. The reliability improvement 
will help industries and the national economy attracting more investors 
participating in production process leading to employment generation in the 
country. 
1.3 Objective 
The objectives of this study is to, 
• Calculate the reliability indices using SynerGEE software package for 
NWP and compare them with the manually calculated values based on 
the actual failures recorded by the Distribution Control Centre 
• Estimate the effectiveness of mitigation techniques 
• Make the recommendations for the reliability improvements 
1.4 Scope of work 
SynerGEE software package has been used in the CEB for more than 4 years 
and tools are available to calculate the SAIDI & SAIFI reliability indices 
although these tools have not been used effectively for the network planning. 
Tools available in SynerGEE to analyse the system reliability have been 
studied and it is required to carry out the following activities to run the 
reliability option in SynerGEE software package. 
Following activities are carried out to model the network and to perform the 
reliability study using SynerGEE Software. 
(1) Updating MV distributions maps of North western Province. 
(2) Data collection- Equipment failure data , number of consumers for each 
substation, MV Failures and their causes, data required to calculate failure 
3 
rates for exposure Zones & to calculate the effectiveness of mitigation 
techniques. 
(3) Data analysis and calculation-categorized the data to calculate the failure 
rates and repair time for the equipments 
(4) Modelling the MV distribution network in SynerGEE and assigning the 
failure rates and their repair time to the switch gear. 
(5) Assigning in put data to digitized model 
• Input data for equipment 
• Input data for substation transformers 
• Input data for exposure/mitigation zones 
(6) Run the Reliability Analysis in SynerGEE. 
(7) Proposing reliability improvements to network. 
1.5 SynerGEE Software Package. 
Reliability is one of a tool available in SynerGEE Software Package to estimate 
the power system reliability [8], SynerGEE Reliability is a comprehensive 
package to aid in the simulation and analysis of distribution system 
reliability. Delivered on the SynerGEE platform, it is a powerful tool for 
investigating root-cause and configuration effects on system and customer 
level reliability. 
SynerGEE Reliability brings you the following features and characteristics: 
• Zone-based failure rates, repair times, and repair costs with provisions for 
single- or three-phase lines 
• Use of failure rates based on historical outages 
• In depth root-cause analysis 
• Comprehensive and detailed switching models 
• By-phase analysis 
• By-cause analysis 
• Sectionalizing, reclosing, pickup 
• Capacity evaluation 
4 
• Unlimited and customizable causes 
• Failure rates by category and subcategory 
• Mitigation over multiple subcategories 
• Comprehensive contingency-based interruption, switching, and pickup 
plans 
• By-phase analysis and results reporting 
• Handling of automatic switches and auto-transfer switches 
Reliability metrics indicate how well a utility serves its customers. More 
specifically, they indicate the value that customers realize through their 
current service. Since quality of service is basic to the long-term health of any 
utility, reliability metrics are a fundamental concern of engineers, managers, 
and executives alike. These metrics often affect financial decisions related to 
long-range and business planning. In addition, as movements toward 
deregulation and open competition continue, issues of distribution system 
reliability become even more important. 
5 
Chapter 2 
Distribution System Reliability in NWP of Sri Lanka. 
2.1 North Western Province (NWP) 
NWP comprises of Puttalam and Kurunegala Districts. For administration 
purposes the NWP is divided into 19 AGA divisions. The total land area is 
7756 sq. km. The total population in 2004 is 2.18 million. North Western 
province is one of the fastest developing provinces in Sri Lanka. Where Sri 
Lankan transport network is concerned many routes linking Northern and 
Central provinces with the city of Colombo pass through the NWP. As a 
result the province has a fast economic growth and geographical diversity 
that has promoted different type of industries established within the 
province. Agriculture is the main income generator of NWP. Paddy and 
Coconut based industries are very common. Since the western boundary is 
demarcated by the sea, several fishery based industries and salt extraction 
industries have been established over the past. Tourism is a key industry 
in the coastal belt from Wennappuwa, to Kalpitiya. Several historical ruin 
kingdoms such as Paduwasnuwara, Yapahuwa etc. and large lakes such as 
Magalle, Thabbowa etc. and Wilpattu national park are some of the tourist 
attraction in NWP. Few industries based on minerals such as clay, sand 
and graphite are located at certain parts of NWP. Large-scale 
manufacturing industries are established at several Free Trade Zones 
located at Makendura, Badalgama and Polgahawela. Hence, NWP is 
providing high contribution for the economic development of Sri Lanka. 
GDP contribution from NWP is 231,975 million Rupees [13 ] 
2.2 Electricity Distribution Network of NWP 
MV network of NWP is fed by five 132/33kV Grid Substations located at 
Puttalam, Madampe, Mallawapitya, Bolawatta and Thulhiriya. The map of 
Electricity Distribution Network of NWP is given in Annexure 2.1. The MV 
distribution is mainly carried out at 33kV except at Kurunegala city limits 
and coastal belt of Wennappuwa and Chilaw areas. To facilitate medium 
6 
voltage distribution and to improve the supply reliability of distribution net 
work in Kurunegala City is carried out at l lkV. In the costal areas 
designed for 33kV overhead lines are energized at l l k V to minimize the 
frequent failures due to salt contamination on line insulators. Bare 
Aluminum conductors ACSR or AAC is used for MV distribution. 33kV 
distribution is done with Lynx or ELM double circuit express lines from 
grid substation up to gantries and several Racoon distributors are used 
from gantries to the distribution transformers. At gantries Auto reclosure 
are connected to avoid entire feeder tripping due to transient faults. Air 
break switches are used to sectionalize the MV circuit. Over current and 
earth fault protection is provided at Grid substation for 33kV feeders. At 
mid points of MV lines, DDLO switches are used to ensure the isolation of 
the exact section during the faults. The distribution facilities of NWP MV 
network are presented in Table 2.1. 
Table 2.1: MV distribution facilities at the end of 2006 
Item Unit Available Installed Quantity 
LBS / ABS Nos. 165 
Auto Re-Closure Nos. 31 
Primary S/S Man/Unman Nos. 01/15 
Gantry Nos. 17 
Boundary Meter Nos. 12 
Capacitor Bank Nos. 5 
Distribution S/S Km 
i. 33kV LT 1913 
i i . l lkV LT 300 
33kV O/H Km 2711.5 
33kV U/G Km 0.12 
l lkV O/H Km 275.4 
The LV distribution system is 400V, 3 phase, and 4-wire. Bare Aluminum 
conductors are commonly used for LT distribution but insulated bundle 
conductors are also used in highly congested areas. Distribution 
transformer capacity is not allowed to exceed 160kVA other than city in 
_ 
7 
limits. Maximum LT feeder length is limited to 1.8km to ensure the 
stipulated voltage at the feeder end. 
MV and LV network details of each NWP Area is presented in Table 2.2 
Table 2.2: Network Details of each Area at the end of year 2006 [4] 
Area Consumers Substations LT lines/km HT Lines/km 
Kuliyapitiya 101288 440 3365 547 
Kurunegala 95065 458 2207 532 
Chilaw 98034 592 4121 891 
Wariyapola 77638 390 2866 769 
Wennappuwa 61525 333 1284 248 
Total 433,530 2213 13843 2987 
2.3 Reliability Assessment for NWP Province 
Distribution Planning group of region 1 of CEB has started collecting data 
related to LT & HT break downs failures since 2005 and data are currently 
available to evaluate reliability of HT network system in NWP. Distribution 
planning group of region 1 has given a quantitative assessment of outages 
and sufficient attention has been given to reliability related issues. 
To collect the failure data of the distribution network, Provincial Control 
centre has been established in September 2004 at the DGM (NWP)'s office. 
The main objective was to monitor and analyse the daily performance of 
CSCs and thereby improving the supply reliability. Data have been taken 
from the Distribution Control Centre of NWP for the analysis given below. 
Table 2.3 shows the summery of the annual average events occurred 
during year 2005 & 2006 in NWP. 
Table 2.3: Summery of the annual average events -2005 & 2006 
Outage Events Effected Consumer.hours 
Type Recorded Consumers Lost 
1 HT Feeder tripping 77 744807 1561427.9 
2 HT Breakdown 212 199001 492505.4 
3 Interruptions 59 104739 526934.8 
4 LT Breakdowns 2151 70855 341266.9 
Definitions for the above mentioned outage types are given below 
HT Feeder Tripping - Entire HT feeder is tripped from the Grid substation. 
HT break down-HT breakdowns in MV distribution. 
Interruption- Scheduled interruptions in MV distribution system. 
LT breakdowns- Breakdown in low voltage distribution network. 
For the purpose of easy analysis recorded events, affected consumers and 
Consumer hours lost are pictorially presented in Figure 2.1, Figure 2.2 and 
Figure 2.3 respectively. 
Fig 2.1: Analysis of recorded outages 
Contribution of Each Outage Category on Total 
Reported Outage 
HT Feeder 
Breakdown tripping 
9% 4% 
/ Interrupptions 
1% 
LT 
Breakdowns 
86% 
Fig.2.2: Percentage of effected consumers due to different outage 
categories 
Contribution of Each Outage Category on Totally 
Reported Effected Consumers 
HT 
LT 
Breakdowns 
Breakdown 
20% 
43% 
**" 
m„ 
Interrupptions 
4% 
tripping 
33% 
9 
Fig:2.3: Percentage of consumer, hours lost due to different outage 
categories 
Contribution of Each Outage Category on total 
Consumer.hours lost 
LT 
Breakdowns 
11% 
HT 
Breakdown 
2 1 % 
Interrupptions 
18% 
Feeder 
tripping 
50% 
Above analysis clearly indicates that feeder trippings reported for year 2005 
& 2006 are only 4% of the total outages but it affected as many as 33% of 
the consumers resulting in losses as much as 50% of the consumer hours. 
Therefore the main contribution to SAIDI values was from HT breakdown 
failures as the 33kV and l l k V outages affected thousands of customers. 
LV outages have limited impact and only a few hundred customers were 
affected by them. 
2.4 Reliability Indices for Year 2005 & 2006 
a) Assumptions 
Reliability indices are calculated based on the following assumptions: 
• Individual breakdowns related to service connection i.e. service wire, 
meter or cut-outs are not considered. 
• Feeder trippings of less than three minute duration due to transient 
faults are not considered. 
Calculated reliability indices based on the assumptions mentioned above 
are presented in table 2.4. The definitions of the reliability indices are given 
in the Annexure 2.2 
10 
Table 2.4: reliability indices of NWP network for year 2005 & 2006 
Reliability Indices 
SAIDI/hrs SAIFI CAIDI CAIFI CIII ASAI 
HT Network Breakdown 53.2 11.8 4.5 0.0007853 1273 
HT Scheduled 
Interruptions 13.3 1.0 13.1 0.0008739 1144 
Entire HT Network 66.4 12.8 5.2 0.0007923 1262 99.2 
LT Network 8.1 9.8 0.8 0.006466 155 99.9 
Entire NWP Network 74.5 22.6 3.3 0.0032496 308 99.1 
The generation and transmission failures in Sri lanka are relatively seldom 
and more frequent failures occurs in the 33kV MV distribution system and 
downwards. Table 2.5 shows the Transmission & medium voltage failure 
contribution to SAIDI 85 SAIFI indices in NWP for year 2006. 
Table 2.5: Contribution from the transmission and distribution 
network to reliability indices 
SAIDI/hrs SAIFI 
Contribution from the 
transmission failures 
12 1.1 
Contribution from the 
Distribution failures 
62.5 22.6 
2.5 Causes for system outages 
Summary of Average HT & LT breakdown reported to each CSC in the years 
2005 & 2006 and judgements of CSC staff about the reasons for 
breakdown are given below. Apart from that feeder tripping details are also 
presented. 
2.5.1 LT Breakdown details and identified reasons 
Average Percentage distribution of LT system faults reported in year 2005 
is shown in Figure 2.4 
11 
Fig. 2.4: Analysis of LT faults 
LT faults reported in 2005 & 2006 
Fuse Broken 
Conductor 
Broken 
2% 
tf failures 
0% 
38% 
fifcaJ^ Service 
Pole Broken 
0% 
mains 
60% 
As shown in Fig.2.4, 60% of the reported faults are service main problems 
and 38% are due to the blown out fuses. 
Table 2.6 shows the summery of average LT breakdowns reported to each 
CSC during the year 2005. 
Table 2.6: Summery of Average LT breakdown details for year 2005 & 2006. 
Area CSC 
Servi 
ce 
Pole Fuse Conductor Transf . Tota l 
Name Mains Broken Blown Broken 
Failure 
s 
Chilaw Chilaw 5465 1 1410 27 1 6904 
Madampe 1527 6 724 34 2 2293 
Puttalam 5918 3 1367 54 3 7345 
Kuliyapitiya Giriulla 1516 55 1860 196 0 3627 
Kuliyapitiya 1873 16 2212 68 3 4172 
Narammala 1260 4 1562 44 0 2870 
Pannala 1741 11 1847 194 0 3793 
Kurunegala Gokarella 1764 8 2466 79 0 4317 
Mallawapitiya 1986 2 1720 4 1 3713 
Pothuhera 2125 3 1109 18 1 3256 
Town 2567 18 833 121 3 3542 
Wariyapola Maho 1615 10 998 26 1 2650 
Nikaweratiya 1678 2 882 53 3 2618 
Wariyapola 2133 6 1689 20 3 3851 
12 
Wennappuwa Bolawatta 1311 6 913 22 5 2257 
Nattandiya 1421 0 1400 3 2 2826 
Wennappuwa 1738 8 949 4 5 2721 
Total 37638 159 23941 984 33 62755 
According to Table 2.6 massive number of service failures have been 
reported from Chilaw and Puttalam CSCs. When comparing with other 
breakdown categories service breakdowns are the most common type of 
breakdown. 
Identified reasons for LT breakdowns reported to each CSC are shown in 
Fig.2.5. It is observed that the reasons for breakdowns vary from CSC to 
CSC. As shown in Fig.2.5, way leaves is the main problem of LT failures of 
CSCs in Kurunegala and Kuliyapitiya Areas. However, aging of equipment 
installed in the network caused the large number of LT failures in Chilaw 
and Wennappuwa Areas. In average 66 numbers of LT fuses blow and 103 
numbers of service breakdowns are reported in a day. 
13 
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Fault clearing time vs proportion of total LT faults are plotted and shown in 
Fig.2.6. 
Fig. 2.6: Restoring time vs percentage of LT faults reported 
o 40 
x: 
Percentage of LT breakdowns 
As shown in Fig.2.6, 50% of the LT faults are restored within 5 hours 
period. However, more than 24 hours were taken to rectify 20% of the LT 
breakdowns. These 20% mainly includes blown out LT fuses at remote 
locations. 
2.5.2 Details of HT Breakdowns 
Percentage distribution of HT system faults reported in year 2005 is shown 
in Fig.2.7. 
Fig. 2.7: Analysis of HT faults 
HT Faults reported in 2 0 0 5 & 2006 
Pole Jumper 
Broken problems 
Conduc tor 0% & Others 
Broken - Z,--- ' 5% 
1% 
HT Fuse 
Blown 
94% 
As shown in Fig.2.7, 94% of the reported faults are due to the blown out 
fuses and 5% are caused by improper jumper connections etc. 
15 
— " . ' 
Table 2.7 shows the summery of average HT breakdowns reported to each 
CSC and deports during the years 2005 8& 2006. 
Table 2.7: Summery of HT breakdown details 
Area 
CSC 
Name 
HT Fuse 
Blown 
Conductor 
Broken 
Pole 
Broken 
Jumper 
problems 
and 
others 
Total 
Chilaw Chilaw 129 3 1 5 138 
Madampe 95 4 0 3 102 
Puttalam 304 6 2 66 378 
Kuliyapitiya Giriulla 214 4 1 9 228 
Kuliyapitiya 126 9 0 8 143 
Narammala 111 0 0 1 112 
Pannala 152 1 1 2 156 
Kurunegala Gokarella 246 6 4 44 300 
Mallawapitiya 124 0 0 4 128 
Pothuhera 152 3 1 5 161 
Town 31 0 0 2 33 
Wariyapola Maho 137 1 0 1 139 
Nikaweratiya 129 1 0 0 130 
Wariyapola 318 0 0 4 322 
Wennappuwa Bolawatta 92 0 0 2 94 
Nattandiya 53 0 0 0 53 
Wennappuwa 38 0 0 1 39 
Total 2451 38 10 157 2656 
Reasons idenfied for HT failurers are given in illustrated in Fig.2.8. In 
puttalam, wariyapola, Gokarella and Giriulla areas, a large number of 
blown HT fuses events are reported in average about 7 HT fuses are blown 
everyday in 2005 8s 2006. 
16 
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Fault clearing time vs. proportion of total HT faults are plotted and 
shown in Fig. 2.9 
Fig. 2.9: Restoring time vs percentage of HT faults reported 
__J 
40.0% 60.0% 80.0% 100.0% 
Perecentage of HT Faults 
According to Fig.2.9, 80% of the HT faults are restored within 5 hours 
period. However, time taken to attend to 10% of the HT breakdowns is 
comparatively high and according to Fig.2.9, it is more than 10 hours. 
Since HT failures disconnect a large number of consumers, their 
contribution on reliability indices is veiy high. A proper program should 
immediately be launched to reduce the restoring time of HT faults. 
2.6 Feeder tripping details 
Table 2.8 shows the summery of average 33kV feeder trippings reported 
during year 2005 8& 2006. The tripping data are enumerated under 
different fault categories in order to identify the possible reasons for feeder 
trippings. 
Table 2.8: Summery of feeder tripping details 
Grid Feeder Feeder Name 
No of Faults Manual 
Tripping OC 
EF 
(Reclosed) 
EF(Not 
Reclosed) 
Puttlam F1 Chilaw / Kalpitiya 36 108 81 173 
F3 Palavi 0 3 14 32 
F4 Anamaduwa 20 52 222 85 
F5 Cement Fac. 1 3 7 14 
35 
30 \ 
25 
20 
15 
10 
5 
0 I 
0.0% 20.0% 
18 
u a m v 
UNIVERSITY OF MOOmmA, SRI LANKA 
MORATUWA 
F7 Wanathawilluwa 0 0 9 6 
F8 Cement Fac. 2 5 , 9 12 , 
Madampe 
F1 Kuliyapitiya 11 18 260 63 
F2 Bingiriya 15 4 252 109 
F3 Chilaw 8 0 43 99 
F4 Nattandiya I 10 51 26 69 
F5 Voice of America 1 1 2 6 
F7 Keeriyankalliya 6 49 29 127 
F8 Buwalka 1 0 8 8 
Bolawatta 
F1 Madampe 13 0 13 44 
F2 Makandura 6 3 47 35 
F3 Voice of America 10 1 47 107 
F5 Bolawatta Primary 1 1 3 23 
F7 Pannala 14 160 31 43 
Mallawapitiya 
F1 Galagedara 25 226 40 66 
F2 Kurunegala Town 7 38 7 48 
F3 Polgahawela 53 9 80 61 
F4 Hiripitiya 16 196 122 44 
F5 Padeniya 40 284 59 29 
F7 Ibbagamuwa 5 143 59 24 
F8 Dodangaslanda 4 64 48 45 
Thulhiriya 
F1 Polgahawela BOI 1 17 2 10 
F2 Kurunegala 20 97 14 52 
F3 Pannala 17 108 9 33 
F5 Kuliyapitiya 22 96 9 53 
Since the feeder lengths are different it is not reasonable to identify the 
worse feeders just by considering the no of tripping events. Hence, a fault 
rate (faults per year per 1km length) of each feeder has been calculated and 
presented in table 2.9 for the analysis to be done on a fare basis. 
Table 2.9: Fault rate of each feeder 
Grid Feeder Feeder Name 
Feeder 
Length/km 
Fault rate 
(Faults / km .year) 
Rank 
Puttlam F7 Wanathawilluwa 90.9 0.099 1 
Thulhiriya F1 Polgahawela BOI 89.4 0.224 2 
Puttlam F3 Palavi 73.8 0.230 3 
91281 
19 
Puttlam F4 Anamaduwa 636.9 0.462 4 
Thulhiriya F5 Kuliyapitiya 237.0 0.536 5 
Madampe F5 Voice of America 7.3 0.548 6 
Madampe F7 Keeriyankalliya 130.7 0.643 7 
Mallawapitiya F7 Ibbagamuwa 283.4 0.730 8 
Bolawatta F3 Voice of America 60.0 0.967 10 
Mallawapitiya F3 Polgahawela 121.3 1.171 11 
Madampe F1 Kuliyapitiya 246.4 1.173 12 
Madampe F2 Bingiriya 219.1 1.237 13 
Madampe F3 Chilaw 37.2 1.371 14 
Bolawatta F2 Makandura 39.9 1.404 15 
Mallawapitiya F5 Padeniya 249.3 1.536 16 
Madampe F4 Nattandiya I 49.2 1.768 17 
Bolawatta F7 Pannala 107.0 1.916 18 
Mallawapitiya F8 Dodangaslanda 48.0 2.417 19 
Mallawapitiya F4 Hiripitiya 124.5 2.683 20 
Thulhiriya F3 Pannala 46.7 2.869 21 
Mallawapitiya F1 Galagedara 98.1 2.966 22 
Mallawapitiya F2 Kurunegala Town 15.2 3.421 23 
Puttlam F5 Cement Fac. 3.2 3.438 24 
Puttlam F1 Chilaw/Kalpiti 61.7 3.647 25 
Puttlam F8 Cement Fac. 3.1 5.161 26 
Mallawapitiya F2 Kurunegala 24.8 5.282 27 
Madampe F8 Buwalka 1.3 6.923 28 
Bolawatta F5 Bolawatta Primary 0.2 25.000 29 
The circuits which have fault rates more than 0.5 can be categorized as 
most unreliable circuits of the system. Special attention should be focused 
on maintenance and way leave clearance of these circuits to reduce the 
extremely high fault rates. Out of the worst circuits indicated in Table 2.9, 
it can be observed that Mallawapitiya F5-Padeniya 33kV feeder has tripped 
at least once a day. 
2 0 
Fig.2.10: Fault rate vs percentage of total circuits 
0 • • • 
0% 20% 40% 60% 80% 100% 
Proportion of total faulted circuits 
Proportion of total faulted circuits vs fault rate is plotted for all 33kV 
distribution feeders and presented in Fig.2.10. It indicates that proportion 
of total faulted circuits of 75% is having more than 0.5 fault rate. Where 
breaker operations and supply reliability are concerned, the present 
situation is not satisfactory and it has to be improved without delay. A 
Large number of manual trippings requested by operation staff for load 
transfer has been indicated in Table 2.8. Even though the duration of 
manual trippings are very short they adversely affect all industries and a 
means should be found to eliminate them. 
21 
Chapter 3 
Methodology 
The methodology to carry out the main activities mentioned under clause 
1.5 of this report is discussed in this chapter. 
3.1 Updating the map of MV distribution network 
Hard copy maps are needed to be updated with the latest 
changes/additions to the network. This information can be obtained from 
the system planning Engineer of NWP. This is required to model the 
network in SynerGEE exactly like the existing system. It is also required to 
have the latest updated map of the area printed by the Surveyor 
Department to identify the exposure zones, required mitigation techniques 
in the relevant part of the network. 
Following data need to be recorded in the map updating process. 
3.1.1 Recording of the line route on the map as accurate as possible. 
3.1.2 Type of conductor (Lynx, Raccoon), Configuration of the circuit 
(vertical, horizontal, delta formation etc.) Number of circuits (Single, 
double, double line etc.) to be recorded. 
3.1.3 All network switchgear items like Auto Reclosers, Sectionalizers ABS, 
LBS, & DDLO need to be recorded with their reference numbers and 
status (whether open or closed). 
3.1.4 All distribution and bulk supply substations need to be recorded with 
their SIN. 
3.1.5 Number of customers for every substation need to be recorded 
individually. 
3.1.6 Network switching arrangements at Gantries, PSS need to be 
recorded. 
22 
3.2 Data collection 
Data required to calculate the equipment failure rates, repair time and 
exposure Zone failure rates & repair time have been obtained from the DCC 
of NWP. The function of the DCC is described in 3.2.1. 
3.2.1 Control Centre Functions 
A performance report about daily functions of each CSC is collected by the 
control centre. The report format is given in Annexure-3.1. At section (a) 
details of LT failures are mentioned according to the type of breakdown. 
Similarly section (b) is for HT outages. CSCs should report whether all 
reported breakdowns have been rectified or if not the number of 
unattended breakdowns on that particular day. Section (c) is for scheduled 
outage information. Thereby outage period and affected sections are 
thoroughly supervised. Section (d) is to mention the ES's judgment of 
possible reasons for reported HT and LT breakdowns. The special incidents 
that happened during the particular day have to be mentioned at section (e) 
which describes about accidents, electrocution, over voltage incidents and 
so on. Details of the distribution network facilities damaged or repaired on 
the day have to be mentioned at Section (f) Section (g) is for information 
about new equipment energization. 
Feeder tripping details and peak current flow on feeders have been 
collected from each Grid substation daily and recorded on the format given 
in Annexure-3.2. As shown in the format the time of fault initiating, the 
indication on relay panel about the type of fault, restored time and isolated 
area are recorded on it. In addition to that the information about manual 
tripping requested by NWP operation staff for load transfer or scheduled 
interruptions are also recorded. 
At the end of the day control centre in charge has to prepare a summery 
report for DGM (NWP) that provides the system outage information of the 
entire province. The format of summery report is given in Annexure-3.3 
All collected details are saved in an outage database prepared by the NWP 
planning division. The database consists of several data tables for different 
23 
type of outages, e.g. LT breakdown, HT breakdown, feeder trippings, 
planned interruptions, equipment outages etc. For each outage the 
database contains the information about date, outage time, restored time, 
reason for outage as well as no. of consumers affected. The no. of 
consumers attached to each substation is updated once in a six months 
period. 
Analyzing the available information the reliability indices, SAIDI, SAIFI, 
MAIFI, CAII, CAIFI are calculated in each month for the province as well as 
for individual CSCs and feeders. A detailed report is published in each 
month and it contains breakdown information and reliability indices 
calculated for LT and HT network for each CSC. Based on the available 
breakdown information the frequently repeating failures are identified and 
passed to the respective CSCs to carry out necessary maintenance 
activities. 
Provincial Control Centre is the interface between CEB System Control 
Centre and CSCs of NWP. CSC staff always consults the provincial control 
centre for the most appropriate switching sequence for interrupting power 
supply to carry out immediate breakdown work or to face any contingency 
situation. At similar occasions, it is the duty of provincial control centre to 
acknowledge the CEB control centre about power interruptions and get the 
working approval to interrupt the feeder supply. 
Apart from that the control centers is responsible for preparing the correct 
switching sequence and pass the relevant information to the operation staff 
at every time when network change is required. 
Any abnormal happening in the net work such as electrocution, failure of 
equipment, accident, over voltage incidents etc control center should 
immediately inform to the related officers and prepare a channel to pass 
necessary information between the relevant parties. 
24 
3.3 Data Analysis & calculation 
Data analysis & calculation can be devided in to 2 group as follows 
3.3.1 Calculation of reliability for equipment 
3.3.2 Calculation Exposure zone reliability and effectiveness of the 
mitigation techniques. 
3.3.1 Calculation of reliability for equipment 
All the HT breakdowns/failures recorded ( Refer Annexure 3.4) at the 
Provincial Distribution Control Centres need to be analyzed and categorized 
to calculate the equipment failure frequency and repair time for Auto 
Reclosers, Sectionalizers, Air Break Switches, Load Break Switches & 
DDLOs. 
Data such as pole breakdowns, Line conductor break downs due to way 
leaves and other failure data related to failure rates calculation & repair 
time for exposure zones need to be analyzed. These data is required to 
calculate the failure rate and repair time for the relevant exposure zones. 
The accuracy of calculated failure frequency & repair time for the 
equipment & the failure rates for the exposure Zones are purely based on 
the accuracy of the data collected by provincial control centre & consumer 
service centre of NWP. 
Breakdowns are categorized and tabulated in table 3.1 as follows: 
Table 3.1: Break down categories 
category Type of failure 
1 DDLO fuse blown 
2 Air break switches /Load break switch operations and 
breakdowns 
3 Auto Recloser trippings & breakdowns 
4 Sectionalizer trippings & breakdowns 
5 Other breakdowns (Conductors broken, Pole breakdown, 
jumper breakdown and etc.) 
Data can be categorized individually for each CSC wise to calculate the 
annual failures rate & repair time for the equipment. 
25 
1. DDLO fuse blown 
Data required for calculating the frequency of annual fuse blown and 
equipment repair time could be gathered from category 1. The method of 
calculating the failure rates and repair time for the consumer service centre 
is shown using the following example. 
Example: In Wariyapola area at Nikaweratiya CSC there are 29 x 3 DDLO 
Switches in the MV network and an average of 72 fuse blown incidents are 
recorded for years 2005 & 2006. Annual average Total time duration 
taken for repairing the DDLO is 410 hours. 
The equipment failure rates & failure repair time for the DDLOs existing in 
Nikaweratiya CSC are calculated as follows: 
Flolal/ 
Failure Rate= — t l m l 
Nlotal 
Ftotai-= Total number of fuse blown failures in Nikaweratiya CSC 
Ntotai DDLOS = Total nmber of installed DDLOs in Nikaweratiya CSC 
Y total = Total number of years 
DDLO Annual Sustained Failure Rate = 72/^ ^  ^  
DDLO Annual Sustained Failure Rate = 0.82 / Year 
Therefore Annual Failure Rate for DDLO fuses in the area under the control 
of Nikaweratiya consumer service centre of Wariyapola area has been taken 
as 1 f/year. 
Repair Time = Tavg ~ dura"on 
Nlotal - incidents 
DDLO Annual Failure repair time = — 
72 
= 5.69 Hours / Year. 
Tavg-duration- Annual Average time taken for repairing during 2005 & 2006 
N total - Total number of incidents recorded during 2005 8s 2006 
26 
Therefore repair time for DDLO fuses in the area under the control of 
Nikaweratiya consumer service centre of Wariyapola area is taken as 6 
hours. 
Same method has been followed to calculate the Annual equipment failure 
rates for ABS/LBS , Secctionalizers 8s Auto Reclosures using the data 
category 2,3 8s 4 respectively while the data category 5 has been used to 
calculate the exposure zones failure rates and repair time. Calculated 
Result are tabulated in Table 3.2 
Table 3.2 shows the generally assigned values for the model and following 
assumptions have been made in assigning the reliability indices for 
equipment, 
• The repair time for the HT fuses installed with in the 0.5 km radius 
from the CSC is taken as 1 hour. 
• The repair time for the HT fuses installed with in semi jungles 8s far 
from consumer service centres is taken as 8 hours. 
Table 3.2 : Equipment failure rates and repair time assigned for the mode I 
Area CSC 
Annual 
Fuse 
failure 
frequen 
cy 
repai 
r 
time 
hour 
s 
Annual 
LBS/ABS 
operation 
frequency 
LBS/ABS 
repair 
time 
Annual 
Sectionalize 
r /AR 
operation 
frequency 
Sectionalize 
r /AR 
repair time 
Chilaw Puttalam 1 6 0.05 8 0.01 8 
Chilaw 0.5 6 0.05 8 0.01 8 
Madampe 0.5 6 0.05 8 0.01 8 
Kuliyap 
itiya Giriulla 1 6 0.05 8 0.01 8 
Kuliyapitiya 1 6 0.05 8 0.01 8 
Narammala 0.5 6 0.05 8 0.01 8 
Pannala 1 6 0.05 8 0.01 8 
Kurune 
gala Gokarella 1.5 8 0.05 8 0.01 8 
Mallawapitiya 0.5 5 0.05 8 0.01 8 
Pothuhera 1 6 0.05 8 0.01 8 
Kur. Town 0.5 5 0.05 8 0.01 8 
Wariya 
pola Mahawa 1 6 0.05 8 0.01 8 
Nikaweratiya 1 6 0.05 8 0.01 8 
27 
Wariyapola 1.5 6 0.05 8 0.01 8 
Wenna 
ppuwa Bolawaththa 0.5 6 0.05 8 0.01 8 
Nattandiya 0.5 6 0.05 8 0.01 8 
Wennappuwa 0.5 4 0.05 8 0.01 8 
3.4 Modelling the network using SynerGEE 
SynerGEE Electric is the network analysis Software being used for 
Distribution Planning MV network needed to be modelled for analysis 
(feeder by feeder). In this process following points need to be noted [8], 
3.4.1 Digitising MV distribution network of NWP model. 
a) Scan map sheet (1:50,000 or lower scale rectified map sheet) 
need to be kept in the background. (Latest map is required for 
more accuracy of digitizing the network.) 
b) Digitizing need to be initiated from the GSS/PSS and to be done 
outwards till the feeder comes across a provincial boundary or 
termination. (Refer the updated hardcopy map and follow down 
each 8s every feeder.) 
All network switchgear items like, Auto Reclosures, ABS, LBS, 
DDLO, Auto Reclosures 8s Sectionalizers have to be installed in 
the digitized network model, in the way that they are physically 
existing in the network. 
c) Since the number of customers per substation is assigned to 
sections in the model, it is better to have separate sections for 
separate substations. 
d) Each section with number of customers (under Description) with 
the relevant SIN of the substation attached. If more than one 
substation is available, multiple SIN numbers are to be entered 
separating each other with a Comma. Total number of customers 
in all substations has to be considered as the number of 
consumers for the relevant section. This is helpful in assigning 
customers to the sections. Indicate the feeder name under section 
ID of each section to identify the feeder to which the section 
belongs. 
28 
3.5 Assigning in put data to the digitized model. 
Input data can be divided in to 3 categories 
a) Input data for the equipment 
i) Annual Sustained Failure rates for equipment( f/year). 
ii) Sustained Repair time for equipment( hr/year). 
b) Input data for substation transformers 
i) SIN for the substation. 
ii) Number of customer for each substation. 
c) Input data for exposure /mitigation zones 
i) Annual breakdown frequency for the exposure zone. 
ii) Equipment repair time for exposure zone. 
iii) Effectiveness of the mitigation techniques. 
a) Input data for the equipment 
Annual sustained equipment failure rates & repair time are assigned to 
switchgears have been taken from table 3.2. As shown in the table it 
has been calculated for every consumer service centre. 
b) Input data for substation transformers 
i) Sin for the substation 
Sin for the transformers is allocated in such a way that it is easy to 
identify the area and the consumer service centre where the 
substation transformer is installed. 
Example : SIN -MW-001 
First letter gives the name of CSC, Second letter gives the name of 
area. 
Number indicates the allocated number for the substation 
transformer. 
Table 3.3 shows letter allocation of SIN for the Areas & Consumer 
Service Centres. 
29 
Table 3.3: Letter allocation of sin number for the Areas & CSCs. 
Area CSC ID No: 
Chilaw ( C) Puttalam PC 
Chilaw c c 
Madampe MC 
Kuliyapitiyaf K) Giriulla GK 
Kuliyapitiya K K 
Narammala NK 
Pannala PK 
Kurunegala ( R) Gokarella GR 
Mallaw apitiya MR 
Pothuhera PR 
Kurunegal Town RR 
Wariyapola (W) Mahawa MW 
Nikaweratiya NW 
Wariyapola WW 
Wennappuwaf P ) Bolawaththa BP 
Nattandiya NP 
Wennapuwa PP 
iiJNumber of customer for each substation 
There are two types of consumers 
1. Bulk Supply Consumers. 
2. Retail Supply Consumers. 
In the case of the bulk supply, it was considered as one customer and 
Number of customer per substation is divided by 3 and that value is 
assigned per phase. 
SIN and the number of customers assigned to the model is given in 
Annexure 3.5. 
3.6. Reliability Analysis 
After assigning the number of customers for each substation, Switchgear 
failure rates & repair time, failure rates of exposure zones and percentage 
of effectiveness of mitigation zones are assigned to network, the model is 
30 
ready to "run" on the Reliability analysis process. As results reliability 
indices SAIDI & SAIFI are generated. 
Once the reliability analysis for the model is run it shows the error 
messages & warnings to be rectified and on successful completion of the 
run, it shows the SAIDI & SAIFI feeder wise as well as for the whole system. 
It is compulsory to rectify the error massages while analysing the warning 
massages. SAIDI & SAIFI values have been obtained for the whole network 
or the part of the net work. These reports in SynerGEE can be easily 
copied to MS Excel/MS Word for easy report generation. 
By this way the existing network is modelled and simulated to estimate the 
reliability of the network. 
31 
Chapter 4 
Exposure zone reliability and effectiveness of the mitigation 
techniques. 
In this chapter the following two topics are discussed in detail. 
4.1 Exposure zone reliability estimation. 
4.2 Quantification of effectiveness of the mitigation techniques. 
4.1 Exposure Zone reliability estimation 
4.1.1 Exposure zone categories. 
When the reliability of the system depend on the environmental factors 
such as the type of the weather conditions , way leaves and distance to the 
sea and geographical location such as Mountains and plains, then 
weighting factors should be applied to the net work for accurate reliability 
analysis. 
MV network distribution system in Sri Lanka, according to their Exposure 
Zones can be categorized as follows. 
i) Coastal area with sea breeze effect 
ii) Coastal area without sea breeze effect 
iii) General rural area 
iv) Coconut Plantation 
v) Thick Jungles 
vi) Semi-thick jungles 
vii) Paddy fields 
i) Coastal area with sea breeze effect. 
Corrosion effect due to the salty wind, in the equipment and aluminium 
conductors are very significant in this type of exposure zones. Kalpitiya & 
Hambantotha coastal areas fall in to this type of exposure zone. 
ii) Coastal area without sea breeze effect. 
Except Kalpitiya & Hambanthota area, other coastal areas in Sri Lanka 
32 
come under this category. There is no sea breeze effect in these areas 
therefore the corrosion level of equipment and conductors, due to the salty 
environment is less severe compared to the zones with sea breeze effect. 
iii) General rural area. 
Most of the rural areas in NWP are coming under this category of exposure 
Zones. Average failure rates of the equipment and conductors can be 
observed. 
iv) Coconut Plantation. 
Some areas inside the coconut triangle come under this category. 
Conductor breakdowns and DDLO fuses blown are prominent in these 
areas. 
v) Thick Jungles 
Jungles with high grown trees and having many branches are classified as 
the exposure zones with thick jungle areas. Minneriya, Singharaja, 
Udawalawe areas are coming under this type. Auto Reclosure trippings , 
Load break swiches tripping are very significant in these areas and the 
equipment repair time is very much more than the average. 
vi) Semi-thick jungles. 
Jungles with bushes and average growing trees are classified in to this 
category. Some areas of Gokarella, Wariyapola and Nikaweratiya are 
coming under this category. 
vii) Paddy fields. 
Equipment failure rates and conductor breakdown rates are very low in 
these areas. Repairing of Equipment broken conductor breakdowns is 
much easier in these types of areas. 
Once the exposure Zones are defined, annual failure rates and equipment 
repair time for the particular zones can be calculated. 
33 
It is required to have a very large number of accurate details in a data base 
to calculate the annual failure frequency rates and repair time for the 
exposure zone. 
According to the IEEE standards it is required to have at least a 5 year data 
base to get the reasonably calculated reliability indices for exposure zones. 
Presently available data base does not produce sufficient information to 
calculate the zone failure frequency and repair time. 
4.1.2 Method of calculating the reliability indices for exposure zones. 
In this section calculation of reliability indices for the exposure zone 
categorized as coastal area without sea breeze effect is discussed in detail. 
a. Calculation of Failure Rates & Repair Time for Exposure Zones 
From the Results of the Survey Carried out by the System Planning 
Group of NWP. 
Questionnaire Prepared by the System Planning unit was distributed 
among the consumers in Wennappuwa area they were requested to monitor 
the MV failures for two years and fill the questionnaire. At the end of year 
2006 the distributed questionnaire were collected from the consumers by 
the Wennappuwwa CSC . Questionnaire distributed among the consumers 
are given in annexure 4.1. 
Total number of consumers in this zone is around 800 consumers and feed 
back was received only from the 242 consumers. The summarized results 
are given in table 4.1. 
Table 4.1 - Summarize result of the survey 
Average time taken to restore the power 
supply ( Hours) 
Frequency 
0.5 1 
0.75 1 
1 7 
1.25 8 
1.5 8 
34 
1.75 6 
2 28 
2.25 50 
2.5 13 
2.75 4 
3 2 
3.5 1 
Details of the selected zone is given below, 
• According to the reliability zone categorization this zone is identified 
as a reliability zone in coastal area without sea breeze effect. 
• Total MV line length in this particular zone is 7.2 km. 
• MV failure have been monitored for 2 years to calculated the failure 
frequency and repair time for the reliability zone -coastal area 
without sea breeze effect. 
Summarized results given in table 41, are plotted as a frequency 
distribution as shown in figure 4.1 which pictorially represents the 
frequency of occurrence of MV power failures having the power restoration 
time between 0.5 hours to 3.5 hours . 
Figure 4.1 : Frequency Distribution of MV power failure of the 
selected area. 
Frequency Distribution 
60 | . -
50 
0 40 
1 30 f o-
£ 20 
10 f t t f f T 
0 • • L -L - J — — — T • * 
0 1 2 3 4 
Average time (Hrs) 
< « 
• 
T f f • • r • • 
35 
An alternative method of plotting this data is to group sets of data of 
approximately equal values together. This is convenient as the total 
number of data is very large and it reduces the amount to be manipulated 
and produces a pictorial representation that is easier to interpret. Therefore 
these data could be group in to the cut sets given in table 4.2. [1] 
Table 4.2 Cut Sets of average time taken to restore the power supply 
Cut Sets Average Time Taken( Hrs) Frequency 
1 0.5-1.74 25 
2 1.75-2.49 84 
3 2.5-3.5 24 
Frequency distribution of MV power failures against the cut sets are given 
in figure 4.2 in form of a histogram. 
Figure 4.2 : Frequency Distribution of MV power failure of the 
selected area- Bar Chart 
100 
80 
60 
>. o c <D 
f 40 
20 
0 
Frequency Distribution 
2.12 
i 
• 
Cut Sets 
ttijli 
i H 
At this point probability has not been considered but this can be deduced 
from the data and the two frequency distribution using the concept of 
relative frequency of probability. 
Average repair time for this particular reliability zone = 1.75+ (2.49-1.75)/2 
= 2 .12 hours 
36 
Therefore, the failure rate, repair time for coastal Zone without sea breeze 
effect is calculated as follows: 
Failure Rate = 
Ftou 
Ftotai = Total no. of failures 
Ytotai= Total number of years 
Ltotai = Total length of MV distribution net work in the particular Zone 
It is possible to calculate the accurate failure rates and repair time for the 
other exposure zones in the same manner. However due to the time 
limitation failure rates and repair time for the other exposure zone were 
calculated based on the current available data at Distribution control 
centre and following assumptions are made in the calculation of reliability 
indices for exposure zones, 
• Breakdowns belonging to the category 5 described under clauses 
3.3.1 of this report are taken for exposure zone reliability calculation. 
• If the duration of breakdown is extremely long due to unavoidable 
circumstances, the time duration of these type of breakdowns are not 
been taken into account. 
* The practical experience of maintenance staff of the Consumer 
Service Centres is taken in to consideration. 
Failure Rate = 
Failure Rate = 0.21 f/yr per km 
As per the figure 4.2 
Repair Time 2.12 hours / yr per km 
37 
Reliability indices calculated for different exposure zones are gi 
Table 4.3 
Table 4.3: Reliability Indices for Exposure Zones 
Exposure Zone Failure frequency 
f/yr/km 
Repair time 
hours / y 
Coastal area with sea breeze effect 0.35 2.12 
Coastal area without sea breeze effect. 0.21 2.12 
General rural area. 0.10 2.50 
Coconut Plantation. 0.35 2.50 
Thick Jungles 0.25 6.00 
Semi-thick jungles. 0.21 4.00 
Paddy fields. 0.01 2.50 
It is difficult to calculate the repair cost associated with breakdowns. If the 
detailed records are maintained for every breakdown, such as material cost 
and labour cost associated with the repair then it is possible to calculate 
the repair costs of the break down. 
Exposure Zones are the tools using which the section failure can be applied 
to the model. Latest scanned map (1:50,000 or smaller) is put into the 
background of the model and it categorizes the sections according to their 
exposure Zones. Stored in the equipment database, an exposure Zone 
represents a present collection of failure data that can be applied directly to 
multiple sections, rather than applying an individual data set for each 
section. All sections assigned to a particular exposure Zone share common 
values for 
• Sustained failure rate per set length of line. 
• Repair time. 
4.2 Quantification of effectiveness of the mitigation techniques [8]. 
From data perspective, mitigation Zones are similar to exposure Zones. A 
mitigation Zone is simply a collection of all the root causes in the system 
with a percentage of mitigation effectiveness assigned to each. When 
38 
assigning a mitigation zone to the sub system root causes are considered to 
be mitigated according to corresponding percentages. Mitigation zones also 
contain fixed and annual cost data that is used by the analysis for costs 
calculations, including those based on initial cost versus cost saving due to 
effective mitigation. However due to the unavailability of data associated 
with the cost of breakdown repairs, the financial savings are not 
considered. 
For NWP electrical distribution system, Mitigation Zones can be separated 
as follows: 
I. Zones that require for Proper maintenance schedules for Way 
leave clearing. 
II. Zones for Replacement of porcelain insulators with silicon 
rubber insulators in coastal areas where sea breeze effect is 
significant. 
III. Zones where Insulator washing is required due to coastal 
spray 
IV. Zones where Squirrel cage for monkeys are required in thick & 
semi thick jungles 
Percentages for the effectiveness of the mitigation techniques are selected 
based on the previous experience of the area engineers 8s maintenance staff 
of CEB. 
Mitigation zones, root causes and the effectiveness of mitigation techniques 
applied to the digitized model are given in table 4.4. 
Table 4.4 : Mitigation zones and their effectiveness 
Mitigation zone Failures mitigated Effectiveness of 
mitigation 
techniques 
Replace the porcelain 
insulators with silicon 
rubber insulators in 
coastal area. 
AR 8& sectionalizer trippings 
Fuse blown, insulator and 
conductor break downs 
60% 
39 
Proper maintenance 
schedule for Way leave 
clearing. 
AR & LBS operations 
Fuse blown, conductor break 
downs 
50% 
Insulator washing AR & LBS operations 
Conductor breakdowns 
insulator and conductor 
break downs 
20% 
Squirrel cage for 
monkeys 
AR & LBS operations 
Fuse blown 
5% 
40 
Chapter 5 
Frequently Repeated Breakdowns in MV Distribution 
Network and Methods to Reduce them 
When the reported outages are analyzed it is noticed that the same 
breakdown has been repeat again and again due to non rectification of the 
real reason. The identified reasons for commonly reported breakdowns and 
suggestions for eliminating them are discussed below. 
5.1 Fixing of DDLOs without having minimum clearance with the 
earthed bodies 
DDLOs that are fixed without leaving minimum clearance with the earthed 
bodies cause earth fault at bad whether situations. As shown in figure 
5.1,an extension arm is provided with DDLO set, which can be used in 
mounting the DDLO base with suitable clearance to avoid flashovers. 
However, it can be seen that in many DDLO sets this arm has not been 
used. As a consequence, the insufficient clearance causes sparks at rainy 
seasons or when birds are sitting on the cross arm on which the DDLOs 
are mounted. 
Fig. 5.1: Incorrectly Fixed DDLOs 
5.2 MV Breakdowns due to way leaves 
In MV network majority of the faults are due to way leaves specially in the 
rural areas . There should be a proper way of managing way leave 
41 
clearance. Line patrolling has to be done at least twice a year to identify 
problematic places. Even though way leaves are cleared by contractors 
there should be a program, monitoring methodology and a feed back 
system in order to get the maximum benefit out of the huge expenses. 
Way leave clearance tenders should be handled with top priority and 
should not be delayed due to any reason. 
Fig. 5.2: Tree branches touching MV conductors 
5.3 Improper connection of HT jumpers 
Improper electrical connection of HT jumpers is the main reason for 
frequent HT breakdowns. Instead of connecting two conductors with a 
binding wire it is recommended to crimp HT connections. 
Fig.5.3: Improper electrical connections 
42 
5.4 Jumper connections without allowable clearance with cross arms 
Jumper connections without having Minimum required clearance with 
cross arms causes earth fault at bad whether situations. 
Fig.5.4: Jumper connections without allowable clearance with cross 
arms 
5.5 Corrosion of concrete poles in coastal areas 
Concrete poles are not suitable at coastal areas due to corrosion problem. 
Instead of poles constructed with normal cement, special cement having 
corrosion resistant characteristics can be used to make concrete poles to 
be used in coastal areas. Similar cements are widely used today in 
construction activities in areas close to the sea. 
Similarly, timber poles also do not stand for a long period and damages are 
noticed about three to four years of service at the buried sections. When 
timber poles are used in coastal areas, it is suggested to cover the buried 
section of the timber pole with fiberglass cover to avoid direct contact with 
the wet soil. This will extend the lifetime of the poles. Alternatively 
corrosion or a similar application that would prevent micro- biological 
action at ground level can be applied. 
43 
Fig.5.5: Corroded concrete poles at coastal areas 
5.6 Sagged MV line touching LT poles 
If HT and LT feeders are drawn on the same route but with poles of 
different heights there is a possibility of having an earth fault due to an HT 
conductor touching an LT pole. This occurs especially when line currents 
are high and the HT conductor sag is maximum. Hence it is recommended 
to use 10m poles instead of mounting both HT and LT on the same poles. 
When poles with two different heights are used for combined run it is 
essential to make sure that the sufficient clearance is maintained between 
HT and LT conductors at all operating conditions. 
Fig. 5.6: Sagged MV line touch on LT pole 
5.7 Improper Electrical connections 
It is recommended to use bimetallic clamps, in order to have perfect and 
durable electrical connections where Aluminum and Copper conductors are 
joined together. Especially at substations feeders should be connected to 
the Copper tail wires with bimetallic clamps. Otherwise rusting on 
Aluminum wire causes high impedance and excessive heating may 
deteriorate the connection. 
Fig. 5.7: Improper Electrical connections 
5.8 HT or LT conductors are not tensioned properly 
If HT or LT conductors are not tensioned properly and resulting loose spans 
can give rise to faults at windy environment or when birds are sitting on 
the conductors. Hence it is recommended to avoid loose spans as much as 
possible. The work of service contractors should be supervised thoroughly 
to avoid LT loose spans. 
5.9 Insulator pollution due to the contamination of salt, dust or 
fungus 
Insulator pollution due to the contamination of salt, dust or fungus may 
cause earth faults especially when light rains occur following the drought 
season. Insulator pollution due to industrial pollutants can be seen at 
certain industrial areas especially at Puttalam cement factory. Fungus on 
insulators has been observed at Dodangaslanda, Mawathagama and 
Galagedera areas. At Puttalam coastal belt, HT lines frequently develop 
earth faults in the dawn due to the leakage currents passing through the 
insulator surface caused by conductive medium formed on insulator disk 
when salt contaminated on the insulator is combined with water dews. 
Unlike other coastal areas Puttalam experiences severe drought thought 
out the year and it would make the situation worse. The present practice is 
cleaning the insulator surface by hand washing. The cleaning frequency 
may depend on the raining pattern and the level of pollution. 
In order to avoid cleaning insulators by keeping the feeder switched off it is 
suggested to introduce the new construction standard for heavily polluted 
areas. For proposed new standard it is possible to evaluate the suitability of 
using Silicon rubber insulators, double galvanized cross arms or fiber glass 
cross arms or any other similar materials to avoid frequent tripping due to 
flashing over. 
Fig. 5.8 : Damaged DDLO fuse bases 
5.10 Usage of incorrect fuse size was the main reason for frequent tripping 
of HT and LT feeders. The correct fuse size needs to be indicated at the 
transformer nameplate and the breakdown staff should be educated to 
refer the nameplate when fuse is chosen for replacement. At many places 
in the network HT fuses are used not for protection purposes but to isolate 
the feeder sections when necessary. Hence it is recommended to use short 
circuited links at these places to short circuit the fuse base. Otherwise 
46 
improper fuse size may violate the protection coordination principles and 
unexpected isolation may take place. 
5.11 High earth impedance at substations 
Transformers often fail due to lightening. It is essential to ensure the 
perfect connection of lightning arrestors to safeguard the transformer. The 
earth impedance should be checked at least once in a year to make sure 
they are within the recommended limits. In case of the places with high 
resistive soil either use of several earth rods or chemical treatment of soil 
will assist in improving substation earth impedances or use the new 
earthing system introduce by CEB. 
5.12 Two HT circuits are drawn on the same poles 
When two HT circuits are drawn on the same pole and one circuit is used 
as an express line it is recommended to use "T" formation rather than "H" 
formation. The express line should be mounted on the top cross arm as the 
top circuit and the bottom circuit can be used as the distributor. Thereby 
minor breakdowns on the distributor can be rectified without interrupting 
the top circuit supply. However, the best method is to use a separate line 
route for the express line as far as possible. 
5.13 Failures due to lightning has been increasing in some parts of NWP. 
The isokeronic level of NWP seems to be higher in the past. Insulator 
failures due to lightning and subsequent earth faults are common during 
the rainy season at tower lines running along paddy fields. Therefore it is 
recommended to fix lightning arrestors at intermediate towers and regular 
monitoring of tower footing resistance to avoid faults due to lightening. 
More attention should be paid on maintaining the earth wire of MV tower 
lines since it is the grounding path for the lighting strokes. 
47 
Fig. 5.9: Untidy connection of transformer tail wi 
5.14 LT cables coming out of the transformer bushing and running up to 
the LT fuse box should not be allowed to lie on transformer body as it can 
then obstruct the cooling of transformer oil. Extra force due to the cable 
weight may be a burden on the transformer LT bushings. Hence it is 
recommended to use a tray on which cables can be properly maintained 
and can be fixed in an orderly way. 
Fig.5.10: Damaged LT fuse bases 
5.15 If either HT or LT fuse base is damaged priority should be given to 
replace it with a new one. Otherwise loose connections will results in 
blowing out fuses repeatedly. 
5.16 Over voltages are commonly appearing on the network due to 
touching of LT conductors each other when high currents are passing 
48 
through them. It is necessary to carry out the system augmentations in 
time to safe guard transformer damages and conductors heating, sagging 
and touching due to feeder over loading and unbalance. 
5.17 Distribution substation's neutral conductor should be properly 
earthed and special attention should be paid to ensure the continuity of the 
earth. Otherwise, when earth faults occur at somewhere in the feeder the 
disconnected neutral results in over voltage conditions due to the phase 
voltage appearing at the disconnected part of the neutral conductor. 
49 
Chapter 6 
Result and Analysis 
6.1 Analysis of the Results from the SynerGEE reliability tool. 
6.1.1 SAIDI & SAIFI values from SynerGEE reliability tool. 
The model was run for the reliability analysis and the results are tabulated 
in table 6.1 below. 
Table 6.1: Results from SynerGEE software package 
Grid 
substation 
Feeder 
SAIFI SAIDI 
Name 
Total Total 
Total System 
12.75 38.545 
Bolawaththa Feeder BOLAFl-Nathandiya 
11.978 37.278 
Feeder BOLAF7-Pannala 
16.638 33.771 
Feeder BOLAF3-VOA 
12.776 28.934 
Feeder NattandiyaPrimaiyF2-
Marawila 
5.593 24.111 
Feeder BolaPrimaryFl-Yikkala 
4.252 22.427 
Feeder NattandiyaPrimaryFl-
ThalawilaMar 
5.336 19.857 
Feeder BOLAF2-Pannala 
6.247 12.722 
Feeder LunuwilaPrimaryF2-
Hundirapola 
1.958 10.641 
Feeder BolaPrimaryF2-
Wennappuwa 
1.491 5.866 
Feeder Lunuwila Prinmary Fl-
Marawila 
3.464 8.101 
Feeder BOLAF5-BOLA.PRIMARY 
0.03 0.18 
Puttalam Feeder PuttalamaF4-Anamaduwa 
40.132 57.549 
Feeder PuttF3~Kalpitiya 
11.365 34.44 
Feeder PuttF7-Eluwankulama 
14.196 32.586 
50 
Feeder PalakudaPrimaryFl-
Kalpitiya 4.992 15.542 
Feeder Pudukudirippu Primary-
Udappuwa 
3.047 14.854 
Feeder PuttFl-Keeriyankalliya 
5.53 13.183 
Feeder MangalaelliyaPrimaryFl-
Sinnapadu 
2.95 12.811 
Feeder MadurankuliyaPrimaryFl-
Kadayamot 
1.503 7.293 
Feeder ChilawPrimaryF2-Town 
1.231 6.612 
Feeder ChilawPrimaryFl-
EgodawattaPalliy 
0.753 1.883 
Feeder PuttF5-cement 
0.551 1.377 
Feeder PuttF8-Cement 
0.529 1.323 
Madampe Feeder MADAF4-Nattandiya 
13.442 42.906 
Feeder MADAFl-Kuliyapitiya 
20.813 37.259 
Feeder MadaF2-Bingiriya 
19.087 32.127 
Feeder MadaF7-Keeriyankalliya 
13.452 20.407 
Feeder MadaF7-Chilaw 
6.737 18.191 
Feeder RajakadaluwaPrimaiy-
Kusala 
3.246 15.454 
Feeder MahawewaPrimaryFl-
ThoduwawaThala 
3.236 13.616 
Feeder KottapitiyaPrimaryFl-
karukkupane 
1.485 8.258 
Feeder MarawalaPrimaryFl-
Iranawila 
1.916 4.789 
Feeder MadaF5-VOA 
1.646 3.945 
Feeder MadaF8-Bhuwalka 
0.278 0.695 
Thulhiriya Feeder THULF2-Narammala 
5.654 13.173 
Feeder THULF3-Pannala 
11.848 40.503 
Feeder THULF5-Kpitiya 
18.799 30.088 
Feeder ThulhiriyaFl- Industril Pol 
13.33 36.147 
Kurunegala Feeder Udawalpola Primary F3 
1.943 5.153 
Feeder Udawalpola Primary F4 
0.634 1.835 
Feeder Udawalpola Primary F5 
1.751 5.44 
Feeder Udawalpola Primary F6 
0.847 2.159 
51 
Feeder KuruF6-Ibbagamuwa 
7.093 19.228 
Feeder YanthampalawaF2-
Lakeside 1.314 1.663 
Feeder kURU F7-IbbagamuwaBB 
8.787 21.701 
Feeder KuruFl-Galagedera 
7.173 14.601 
Feeder KuruF2-Narammala(Town) 
4.075 9.111 
Feeder KuruF3-Potuhera 
11.234 21.833 
Feeder KuruF4-Maho(Maspotha) 
11.153 31.95 
Feeder KuruF5-PadeniyaBB 
13.806 32.7 
Feeder Yanthamplawa Primary F1 
1.364 1.917 
The above SAIDI & SAIFI values are used to identify the unreliable feeders 
which contribute high SAIDI & SAIFI values in the system. 
The Results show that SAIDI & SAIFI values have strong inter-relationship 
for the sustained type of failures. For the feeders where the SAIFI values 
are higher than the system SAIFI value, it is observed that SAIDI values are 
also higher than the system SAIDI value. 
SAIFI, SAIDI contribution from the Feeder PuttalamaF4-Anamaduwa, 
Feeder THULF5-Kuliyapitiya, Feeder Madampe F2-Bingiriya & Feeder 
Puttalam F7-Eluwankulama are much more significant to the total system 
while reliability indices contribution.from the Feeder BOLAF2-Pannala & 
Feeder BolaPrimaryF2-Wennappuwa to the total system are low. 
Total feeder length, number of customers & relevant exposure zone for the 
4 feeders where the reliability indices are the most significant & the 2 
feeders where the reliability indices are very low have been tabulated in 
table 6.2 for easy comparison. 
52 
Table 6.2: Table of Comparison between the feeders ofNWP 
Feeder name SAIFI SAIDI Total 
Feeder 
length 
Km 
Total number 
of customers in 
the 
feeder/ system 
The most 
relevant 
Exposure 
zone for the 
feeder 
Feeder PuttalamaF4-
Anamaduwa 40.132 57.549 
636.9 66670 Coconut 
plantation 
Feeder THULF5-Kpitiya 
18.799 30.088 
237.0 38827 General rural 
area 
Feeder MadaF2-Bingiriya 
19.087 32.127 
219.1 43285 General rural 
area 
Feeder BOLAF7-Pannala 16.638 33.771 
107.0 7777 General rural 
area 
Feeder KuruF2-
Narammala (Town) 4.075 9.111 24.8 676 
General rural 
area 
Feeder MadaF7-Chilaw 6.737 18.191 37.2 745 General rural 
area 
Total System 15.55 29.864 2986.9 625,000 
The following reasons can be given to explain this situation 
a) Total length of these feeders are large 
b) The number of customers in the feeder is high. 
c) The feeder traveling through exposure zones are having high annual 
failure rates due to coconut plantations 8s heavy way leaves. 
Example: Feeder PuttalamaF4-Anamaduwa is going through the exposure 
zones, (coastal area with sea breeze 8s coconut plantations) where the 
exposure zone failure rates are having higher values than the other 
exposure zones . Therefore the reliability of this feeder is less than the total 
system average reliability. 
6.1.2 Comparison of the results obtained from SynerGEE with 
manually calculated reliability indices in the control centre of 
NWP. 
53 
Table 6.3- SAIDI & SAIFI Comparison Table. 
Method of calculation SAIDI(hours/Year) SAIFI( Frequency/year) 
Manually calculated 
Reliability indices for the NWP 
distribution system 42.0 11.80 
Results obtained from the 
synerGEE tool for the model 38.5 12.75 
Difference of the value 3.5(8.33%) 0.95(8.05%) 
Reasons for the differences, 
It is revealed that the feeders with high frequency of failure also exhibit 
high failure duration before restoration of supply. High frequency is also 
due to inherent nature of plantations terrain and bad maintenance. High 
duration is due to geographic location and low priority given for restoration. 
However when the actual SAIDI and SAIFI values manually calculated 
using the practical data remarkably differ from the values obtained from 
SynerGEE. The following reasons can be given to explain this situation. 
a) Major events which have taken unusual long repair time have not 
been considered during the calculation of equipment failure rates 
and repair time assigned for SynerGEE software package. However 
during the manual calculation these type of incidents have taken in 
to consideration. Therefore manually calculated values should get 
higher SAIDI and SAIFI values. 
b) Breakdown data for MV distribution network in NWP is currently 
available only for 2 years and the data required to model the NWP 
MV distribution system was calculated from this data base. IEEE 
standards [13] recommend to have 5 year data base to calculate the 
required data to model the MV distribution system. Therefore the 
calculated values from the 2 years data base may not represent the 
accurate and reasonable values required to model the system. 
c) Manually calculated average SAIDI & SAIFI values for year 2005 and 
2006 have been compared with the result from SynerGEE. To have 
54 
more accurate manually calculated SAIDI and SAIFI values it is 
required to have physical average of 5 years or more to compare with 
the result obtained from SynerGEE software package. 
6.2 Case Study ( Selected Mitigation Technique) 
In order to estimate the effectiveness of a selected mitigation technique a 
case study is done selecting Kalpitiya Feeder. The selected mitigation 
technique is replacement of Pin Porcelain Insulators with Composite 
Insulators in Kalpitiya coastal Area to reduce the insulator flash over 
breakdowns. 
MV distribution network is in the vicinity of a lagoon with sea breeze effect. 
Salt is the main contaminator in this area. The salt spray is brought by the 
prevailing south- west monsoon winds blowing over the ocean and the 
lagoon. 
These porcelain insulators are exposed to salt contamination. Therefore 
frequent flash over can be observed in the Puttalam Feeder. Past data show 
that the flash over frequency is having a co-relation with rainfall in this 
area and an analyse of this relationship is made in clause 6.2.1. 
6.2.1. Effect of rainfall on Flash over frequency of MV insulators in 
Kalpitiya 
It is observed that the flash-over frequency is comparatively low during the 
rainy season where there is abundant rain to wash away salt pollutants. 
On the other hands flash over frequency increases during the dry season, 
especially when a slight bristle occurs. 
Annex 6.1 shows, operation frequencies of HT DDLOs due to insulator 
flash overs & way leaves in Kalpitiya consumer service centre area for years 
2005 & year 2006 in relation to the rainfall of the month. Rainfall data has 
been collected from the Meteorological Department. The Data shows that 
failure frequency has a direct co-relation to monthly rainfall in Kalpitiya 
area. 
Minimum rainfall is recorded during the month of June, July, August & 
September in year 2005 and the recorded MV breakdowns are a maximum 
during those months. The same situation can be observed during the year 
2006. 
During the month of October 8& November in year 2006 the maximum 
rainfall has been recorded and failure frequency of HT fuses are in their 
peaks. To verify this fact, the officer in charge of the CSC was interacted 
and according to his explanation most of the HT fuses were blown due to 
the way leaves It appears that this high failure frequency during this rainy 
season is mainly due to way leaves and coconut branches causing line 
faults and due to flash over resulting from salt pollution. These 
observations confirm that, dry months cause insulation flash over due to 
salt pollution, specially in the event of a slight bristle or dew. 
SIR composite insulators have been tested in Kalpitiya area in 1997 [11] 
and the results show that the performance of the SIR composite insulators 
are satisfactoiy even in the heavy atmospheric pollution condition with salt 
contamination. Therefore it is recommended to use the SIR composite 
insulators to minimize break down due to insulator flash over. 
6.2.2 Comparison of Porcelain insulator with Silicon Rubber insulator 
Porcelain has been used as the oldest material for outdoor insulation, and 
it is widely used around the world. In the polluted environment the 
development of leakage current causes •flashover by short circuiting the 
insulator. This is an acute problem in the transmission and distribution 
lines exposed to pollution. Some of the methods presently used to overcome 
these problems are insulator replacement at regular intervals, increasing 
the creepage distances, insulator washing and greasing or coating. Another 
method is to replace the traditional insulators by silicon rubber insulator in 
which high creepage distance can be achieved. Further silicon rubber 
insulators are hydrophobic in nature and they are not affected by water 
with salt pollution. 
56 
Silicon rubber insulator and referred to as composite insulator as they 
consist of three parts , namely a metal fitting for the connection to the 
power conductors and the supporting structure , a fibre glass rod for 
mechanical strength of the insulator and a housing material for protection 
of the fibre glass rod and for use as the insulation. 
Silicon rubber insulators have many advantages over porcelain insulators 
and their comparative general capabilities are given in table 6.6. 
However, the main drawback of the composite insulator is the surface 
aging. Under difficult service stress such as corona discharge, UV 
exposure, chemical attacks etc, chemical reactions can occur on or inside 
the composite material. This may result in loss of hydrophobicity and other 
surface degradation for example tracking and erosion. 
Table 6.4: Comparison of General capabilities of Insulators [ 11] 
Characteristics Porcelain Insulators Silicon Rubber Insulators 
Hydroprobic recovery No Yes 
Light weight No Yes 
Contamination 
Resistance 
No Yes 
Leakage current control No Yes 
Weather Resistance Yes Yes 
Installation Difficult Easy 
Resist UV Yes Yes 
Price of insulator 20 USD 28 USD 
Easy transportation No Yes 
Reliability in the polluted 
environment 
Low High 
Going back to history, the first composite insulators were used on outdoor 
lines during the mid 1960 period. Since then, there have been many 
changes in the material composition and design of insulators. Now 
composite insulators are being used in significant quantities all over the 
world and their prices are decreasing due to the development of technology. 
57 
The most common material used today for composite insulators are silicone 
Rubber (SIR) and ethylene propylene diene monomer (EPDM). The SIR is 
used in two forms: room temperature vulcanized (RTV) and high 
temperature vulcanized. Usually, RTV is used for coating of porcelain 
insulators whereas HTV is used for composite housings. 
6.2.3 Features of MV distribution network Feeder 3 of Puttalam GSS 
This feeder is starting from Puttalam GSS and going Kalpitiya as shown in 
Annexure 6.1. Up to Palakuda the feeder is energized with 33kV and after 
Palakuda primary the feeder is energized with 11 kV to minimized the flash 
over breakdowns, and thereby improve the reliability of MV network 
distribution system. This solution is not the best solution from a technical 
point of view. It provides higher losses and excessive voltage drops in the 
distribution system. 
6.2.4 SAIDI 8b SAIFI improvement of Kalpitiya Feeder with SIR 
insulators. 
Considering the fact that the porcelain insulators are replaceable with the 
SIR insulators in Kalpitiya feeder, only that feeder was run for the 
reliability analysis in SynerGEE. And the results are tabulated in table 6.7. 
In the new model exposure zone reliability has improved from o.35 f/year 
to 0.01 f/year considering that the exposure zone reliability is equal to the 
zones with paddy field where the exposure zone reliability is normally high . 
DDLO Fuse blown frequency has been changed from 1 f/year to 0.5 f/year 
after installation of SIR insulators. 
Table 6.5: SAIDI & SAIFI comparison with both type of insulators 
Kalpitiya Feeder SAIDI SAIFI 
With Porcelain Insulators 24.47 8.00 
With Silicon Rubber insulators 10.69 2.37 
SAIDI improvement to Kalpitiya Feeder is nearly 14 hours. 
58 
6.2.5 Cost Benefit analysis for replacement of porcelain insulators 
with SIR composite insulators 
a) The following assumptions have been made during the calculation, 
i) Reactive Energy losses due to l l kV lines have not been considered 
ii) Hardware for the insulators for the both types, Porcelain & Silicon 
Rubber composite have considered to be the same. 
iii) Installation and transportation cost comparison for the both types of 
insulators have not been taken in to consideration. 
IV) Load factor for the Kalpitiya feeder & Palakuda primary is considered 
as 0.3 as the most of the loads in this area are distributed loads, 
v) Effect of the SAIFI improvement of distribution network due to 
installation of SIR composite insulators have not been taken in to 
account during the financial analysis as it is difficult to quantify the 
SAIFI improvement to the economy of the country. 
b) Line construction features Kalpitiya Feeder. 
• Total line length of the Feeder: 61.7 km. 
" Conductor : Racoon conductors ( 7/4.09). 
• Type of insulators : 33 kV Pin porcelain insulators with creepage 
distance 850 mm and power frequency withstand dry voltage 135 kV 
and weight 12 kg have been installed presently[7]. 
As per the Medium voltage line construction standard of CEB the required 
quantity per 1 km of the following items are as follows 
• Number of 13 M RC poles (500 kg): 14 nos. 
• Number of Pin insulators (33kV): 43. 
• Number of Tension insulators (33kV): 24. 
59 
Total number of Pin insulators in the Kalpitiya Feeder: 43 X 61.7=2654 Nos 
Total number of Tension insulators for 
Kalpitiya Feeder J : 24 X 61.7=1481 Nos 
c) Calculation of total cost of insulators for the Kalpitiya Feeder. 
Description Porcelain Insulators Composite 
Insulators 
Current market price for 
1. Pin Insulator 
2. Tension Insulator 
21 USD 
45USD 
28 USD 
46 USD 
Total cost for 
3. Pin Insulators 
4. Tension Insulators 
2654x21=55,734 USD 
1481x42=16,695 USD 
2654x28=74,312USD 
1481x46=17,066 USD 
Total cost 122,379 USD 142,438 USD 
d) Calculation of the benefit from the SAIDI improvement 
Generation cost per 1 kwh = 6.22 SLR [5] 
Assuming 10% operation & maintenance cost = 0.62 SLR [5] 
Selling cost of lkwh to earn 10% profit margin = 7.52 SLR 
Therefore profit from lkWh to CEB = SLR 0.68 
Total KVA of the Kalpitiya Feeder =17-,535 kVA. 
SAIDI improvement to the MV distribution network =14 hours [Tab 6.7] 
Total increase of kWh units sales due to =17535X14X 0.3 
SAIDI improvements =73,647 kWh 
(Load factor 8s power factor are is taken as 0.3 8s 1) 
Total benefit to CEB from the SAIDI improvement = SLR 73,647 X 0.68 
= SLR 50,080.00 
60 
e) Calculation Operational & Maintenance cost of Porcelain Insulators 
in Kalpitiya Feeder 
• Annual Maintenance cost for insulators washing and Repairing cost 
of MV distribution network due to flash over of insulators in Kalpitiya 
feeder SLR 5350 per km. 
• Total cost for Maintenance for the Kalpitiya Feeder= 5350 X 61.7 
= 330,095.00 SLR 
f) Calculation of the losses in l l kV Distribution in Kalpitiya Feeder 
Palakuda primary is energized with 11 kV. if the presently existing 
porcelain insulators are replaced with SIR insulators the MV voltage can 
be increased up to 33 kV. Total length of MV distribution net work is 15 km 
and the losses due to 1 lkV MV is calculated below, 
Feeder Current of the Palakuda Primary = 222 A 
For the Racoon conductor = R +j X= 0.4095 +j0.9339 
Therefore the total loss of Power, AP = I2 * R X L 
=( 222)2 * 0.4095 X 15X3 
= 908.16 kW 
Losses in 33 kV Distribution 
Total loss of energy, AP = I2 * R X L x3 
= (74)2 * 0.4095 X 15 
= 100.89 kW 
If l l kV primary is converted to 33kV the annual energy saving due to the 
line losses= (908.16 -100.89) X 8760 x0.3 kWh=2,121,505.56 kWh 
Annual saving from the line losses 
=SLR 2,121,505.56 X 0.68= 1,442,623.4 SLR 
61 
g) Calculation of total annual saving from the replacement of Porcelain 
insulators with SIR insulators 
A S losses + A S SAIDI improvement+ A S maintenance 
1 , 4 4 2 , 6 2 3 . 4 + 5 0 , 0 8 0 . 0 0 + 3 3 0 , 0 9 5 . 0 0 
1 , 8 2 2 , 7 9 8 . 0 0 S L R 
Total annual saving from the | = 
Replacement 
Total cost of the additional investment for 1 =( 142,438-122,379) XI15 
SIR insulators J= 2,306,785.00 SLR 
Calculation of additional investments for replacement of l l k V 
transformers with 33kV transformers 
No of 100 kVA transformers in Palkuda primary= 20 nos 
No of 160 kVA transformers in Palkuda primaiy= 17 nos 
Additional investment for the replacement"] 
Of transformers with 33kV [14] j = 20X120,000+17X95,000 
= 4 million 
Overheads = 1 million 
Total investment = 5 million 
Therefore total additional investment -for converting the 
l l k v feeder to 33 kV =5,000,000+2,306,885= 7,306,785.00 SLR 
h) Financial Analysis 
7 306 785 • Calculation of Simple pay back period = — - years 
1,822,798 
= 4.00 years 
• Calculation of the viability of the project: 
The following Assumption have been made during the calculation 
economical life time of the SIR insulator is 15 years 
62 
Discount rate is 12%. 
Present Value of the Benefit= PVB=1,822,798 £ l- (4.1) 
•=' (1+r)" 
In the equation (4.1) 
n = economical life time of the SIR insulator is 15 years 
r = Discount rate is 12%. 
Present value of the benefits of the project, [15] 
PVB= 1,822,798 X 6.810= 12,413,254 SLR 
Present value of the cost of the project, 
PVC=7,306,785.00 SLR 
Net present value of the project , 
NPV= 12,413,254-7,306,785.00 = 5,106,469.00 SLR. 
NPV> 0 therefore the project is viable. 
• Internal Rate of Return of the project 
PVC = PVB 
7,306,785.00 = 1,822,798V 1 —:. 
t r a + r f 
4.008 = Y — -
- (1-hr)' 
From the table for Present value Factor(PVF), When n=15 years , 
PVF=4.001 for r =24% [ 15] 
Therefore the internal rate of return for the project is (IRR) = 24%. 
The above financial analysis shows that the installation of SIR insulators in 
area exposed to the salt pollution is financially and economically viable. 
Therefore it is recommended to install SIR insulators in place of Porcelain 
insulators in the coastal MV distribution network to minimise the 
breakdowns cause by insulator flash over and to improve the reliability of 
power supply. 
63 
Chapter 7 
Conclusion and Recommendation 
7.1 Conclusion & Discussion 
If a proper data base system is maintained for equipment failures and 
repairs time for the CSC wise or area wise it is very effective to use 
SynerGEE Software Package to calculate the reliability indices for 
Distribution Network even at the planning stage. The indices are very 
useful for assessing the severity of system failures in future reliability 
prediction analysis. 
An important feature of this Software Package is that system weak 
sections can be easily identified, thereby focusing design attention on those 
sections of the system that contribute most to service unreliability. It is 
also possible to estimate effectiveness of the mitigation techniques applied 
to the system and estimate the cost & benefit to the power utility as well as 
to the consumer. 
The system performance assessment is a valuable activity for three 
important reasons. 
• Establishing the chronological changes in system performance and 
hence, identification of weak areas and the need for reinforcement 
could be early achieved. 
• Establishing existing indices which serve as a guide for acceptable 
values in future reliability assessment. 
• Enabling previous prediction to be compared with actual operating 
experience. 
64 
The past failure records entered to the data base at DCC in a systematic 
manner is very important. The failure records without all relevant details 
such as section failed, course of failure and mode of failure are not much 
useful for the analysis. Therefore it is recommended to recruit an 
Engineer to analyze the records sent by the CSCs. These information could 
be utilized to plan the rehabilitation & maintenance programme for MV 
Distribution System. Entering the failure data to the data base should be 
carefully done by a properly trained Data Entry Operator and distribution 
control centre engineer should closely monitor this data base. This kind of 
procedure will help to maintain an accurate database. 
It is revealed from the study that the time spent for a breakdown, 
equipment failure rates could be minimized by adopting reliability 
improving techniques which is discussed under 7.2. 
7.2 Proposals for Improvement of the network 
In order to improve the system reliability two remedial measures can be 
taken. 
They are reducing the number of outages and reducing the time taken for 
restoring the supply. The different possible ways of employing these two 
techniques are discussed below. 
7.2.1 Importance of Preparing an Annual Maintenance Plan 
A maintenance plan should be prepared annually describing routine 
maintenance to be attended throughout the year. The outage data collected 
at the control centre as well as the field experience of the operation staff 
may be used to find out the maintenance frequency of each MV line. For 
example, the feeder tripping details indicate that the line insulators 
installed in the coastal areas of Puttalam district should be cleaned once in 
six months period. Similarly the vegetation growth rate, rainfall pattern, 
weather condition and the aging of equipment determine the line 
% 
65 
maintenance requirements and according to that the annual maintenance 
plan should be prepared. 
Other important activity is to make advance preparation work before 
planned power interruptions for maintenance or construction activities. 
Thereby outage time can be optimized and number of consumers affected 
may be minimized by proper planning and arranging alternative feeding 
routes. The other advantage of power outage plan is that the public can be 
notified in advance about power interruptions. Many activities can be 
planned to be carried out simultaneously at the same interruption period 
and the supply outage time can be utilized to a maximum. 
Both maintenance and outage plan will assist in preparing material and 
labour allocation as well. Proper planning also assists in optimum 
utilization of outage time as well as other resources such as material, 
labour and transport. 
7.2.2 Improving workmanship through Training 
It is frequently observed that CEB breakdown staff is under trained with 
respect to safety issues, selection of proper material and tools, efficient and 
productive ways of completing their day-to-day activities. In order to reduce 
the number of outages and time taken for restoration all categories of 
breakdown staff should be trained on outage management techniques such 
as quick identification of breakdowns and the solution which can be 
applied permanently repairing the breakdowns in a way so as to prevent 
frequent repetition of such break downs. 
At the same time training will assist them to study new techniques and 
advance practices in breakdown management. Apart from that the staff 
may be educated on the importance of neatly recording details of 
breakdowns and subsequent analysis to identify weak areas. In addition 
that staff should be trained on the ways of developing personal 
relationships with customers. 
66 
Instead of routine training programs it is suggested to prepare training 
programs targeting special groups of employees. Each program preferably 
consisting of several modules, each of which can be independently followed 
according to the time availability and the requirement of the staff groups. It 
is suggested to prepare several video documentaries to serve different 
aspects of training, which would be self explanatory in nature and enabling 
the trainees to develop their existing skills. If video programs are available 
the productive training camps can be arranged at the work place itself or 
even at a CSC. Staff can be motivated for training if the rule is imposed for 
having the minimum training requirement for them to be eligible for the 
next promotion. 
Not only the internal staff but the outside people willing to get a good 
knowledge on electrical related technical activities could be trained by the 
CEB Since CEB is the largest organization in Sri Lanka having the latest 
equipment and experts on electrical technology. If this method of training is 
introduced then CEB can enforce contactors to use only such trained staff 
in contract gangs for CEB work. Perhaps CEB can serve national needs by 
marketing our expertise on electrical technology in the field of training the 
electricians. 
For each year a large number of students on various disciplines such as 
technicians, draughtsman, clerical staff, typists etc passing out from the 
government technical colleges apply and seek an opportunity for training in 
the CEB. These trainees are at present paid only a government approved 
allowance during the training period. If proper training programs are 
arranged then trainees can be employed on a reasonable payment and 
maximally utilized by CEB for it's development activities. It will be 
beneficial for both parties and the CEB can get valuable work with 
reasonable payment to trainees while giving them an opportunity to be 
trained on specialized work. 
67 
7.2.3 Adopting Quality Improvement Techniques 
High quality of workmanship of the breakdown staff is a necessary factor to 
achieve a higher reliability level. Even though the technical staff has been 
trained to carry out their normal duties there is no assessment on how 
they apply the knowledge gathered at the training program. Hence it is 
essential to set up a technical auditing team to evaluate the procedures 
and practices expected to be followed according to technical specifications 
and codes as well as the technical construction maintenance standards. 
Based on the results of the technical auditing, training needs of the staff 
can be identified. Apart from that the experience of technical auditing can 
be used to review the technical specifications and standards. 
Presently many utilities practice well proved quality-improving method like 
the 5S concept and quality circles to improve productivity. Some sections of 
CEB have demonstrated that good improvement can be achieved by 
adopting these techniques. For example the CSC environment can be well 
arranged and prepare a consumer friendly environment just by rearranging 
the different sections and equipments. The stores can be well arranged by 
placing material on shelves in a methodical order. Properly labeling items 
will help the staff to find out any equipment with minimum time. Similarly 
all instructions to consumers and staff can be displayed on the notice 
board and they will guide consumers. It will avoid embarrassment due to 
improper communication and irregular practices. The disposable items 
such as damaged meters, transformers and poles can be arranged neatly 
without obscuring the staff and consumers. All printed format should be 
unique at all CSCs and should be printed in both languages. The 
breakdown vehicle should be equipped with a material box ensuring the 
availability of minimum stock of material, which is essential to attend 
breakdowns at minimum time. A tool box should be issued to each 
linesman and it should be enforced that he carries it at every time when he 
is called up on to rectify a breakdown. All staff should be compelled to use 
safety equipment and thereby the accidents can be minimized. Computers 
should be fully utilized in preparing estimates, stock balance registers, 
68 
SMC registers etc. These are a few ways where some improvement can be 
done using productivity improving methods like 5S and quality circles. 
Also all categories of the staff should be given an opportunity to get 
involved in improving productivity of their day-to-day activities by 
forwarding solutions they could suggest through experience. A quality 
circle is the well-known management technique widely used aiming to 
collect ideas of all categories of staff for improving quality and productivity 
and it is a well proven method of management by opinion Quality circles 
can be set up at every division to collect ideas of all categories for the 
development of normal activities. 
In order to make these concepts popular among the staff a competition 
should be arranged annually among all divisions of the province with 
rewards for the best office and the best idea. 
Preparation of customer service standards will be the initial step in 
achieving the quality certificate. It is time for CEB to document suitable 
service standards policies and establish the achievable quality target based 
on the existing system performance. Where outage management is 
concerned the target may be the best SAIFI, SAIDI values to be achieved 
based on provinces with the best performance. It is high time to introduce 
the system productivity and quality-improving program aimed at more 
reliable system. 
7.2.4 Employing Advance Technology 
Adaptation of advance techniques in maintenance and construction of CEB 
facilities is one way of improving system reliability. The following proposals 
describe how the system reliability can be improved by introducing advance 
technology. 
(a) For coastal areas Copper conductors and all Aluminium Alloyed 
Conductors (AAAC) show very high resistance to corrosion compared 
with ACSR conductors. Hence it is suggested to use such conductors 
for LT distribution in coastal areas. 
69 
(b, Similarly HT lines in coastal areas are subject to frequent earth 
faults due to salt contamination and fallen conductors. The present 
practice is to construct 33kV lines and energize them on l l k V 
However, long distribution with l lkV overhead conductors cause 
large voltage drops and heavy energy losses. Hence it is suggested to 
use polymer insulators and AAAC conductors that are corrosion 
resistive in order to reduce frequent earth faults on HT lines in 
coastal areas due to salt contamination as well as due to corroded 
and fallen conductors. 
(c) Network switching can be done using load break switches in place of 
Air break switches; hence the network switching can be done without 
interrupting the supply. These results in improving the MAIFI value 
significantly. 
(d) It is time to introduce hot line maintenance technique for HT 
maintenance activities. Hence, power interruptions made for 
maintenance activities can be totally eliminated 
New technology such as fault indicators, auto reclosers 
sectionalizers should be introduced in efficient fault identification 
and fault isolation. Thereby the faults can be identified with 
minimum time and the outage can be limited to minimum number of 
consumers. A further step can be brought forward by introducing 
distribution automation techniques with fault indicators and 
autoreclosers. Hence, their operation details are automatically sent 
to the control room and remote operations are made possible 
depending on the requirement. Thereby time taken for fault 
identification and subsequent switching operations can be reduced 
significantly. 
(f) Application of thermal vision techniques to identify defective points 
m distribution line is very popular in utilities operating overhead 
network for power distribution. This technique is widely used as a 
preventive maintenance technique. It is suggested to introduce such 
70 
techniques to identify weak points in the network in advance prior to 
their development in to serious faults leading to break downs. 
(g) An Advance communication network is essential to exchange 
information among system operators. Present communication 
system has disadvantages such as not being powerful enough to 
cover the entire NWP. If this internal communication network can be 
upgraded to cover the entire province then all breakdown vehicles, 
CSCs, grid substations and the control centre can be linked together 
and operational information can be passed between them effectively. 
Hence, the time taken for restoration can be reduced and reliability 
indices can be improved through efficient system operations. Since 
CEB communication facilities such as towers are abandoned at 
certain locations of NWP it is proposed to carry out feasibility study 
for rehabilitation of the existing communication facilities and 
developing them to cover the entire province. 
(h) Establishing a Research and Development division may facilitate to 
introduce and develop new technology applications using local 
expertise with minimum cost. For example the feasibility of 
developing necessary hardware and software for remote monitoring 
and operation of distribution facilities such as air break switches, 
auto reclosers, boundary meters, relays, fault indicators and 
retrofitting them into the existing facilities should be investigated. 
Distribution automation solutions can easily be developed with local 
expertise and at minimum cost to suit our requirements. A 
necessary support can be taken from local universities or local R and 
D institutions such as Auther C. Clerk centre. 
(i) When primary transformer fails it would take more time to replace it. 
If mobile primary unit can be made by mounting a transformer and 
other accessories on a truck, it can be used to feed the network until 
the faulty transformer is repaired or replaced. Thereby outage period 
can be minimized. 
7.2.5 Asset Management 
Asset management is an important concept in maintenance work. The 
asset database has all information about the distribution facilities installed 
in the network. By referring the database it is possible to obtain the 
information about the equipment type, spare part list, age of the 
equipment, maintenance history, dimensions, nameplate data, installed 
location etc. Asset management database is a very useful tool in 
maintenance activities. At present it is not practiced within the distribution 
region. Hence, it is necessary to collect the information and prepare a 
database and initiate the asset management task. It will improve the 
productivity of maintenance and assist in improving system reliability. 
7.2.6 Re-introduction of commissioning reports 
When new construction is completed it is essential to have a system to 
issue a commissioning report. The construction division should energize 
the system and should produce a commissioning report to verify that the 
construction work has met the required standards. The present practice is 
to hand over the constructed and completed work only by counting the 
material installed. Hence, actions have been taken to enforce 
commissioning reports for all construction work in order to reduce possible 
breakdown in the future due to the incompliance with construction 
standards. 
7.2.7 Formulating the operational code of practice for distribution 
network 
At present scheduled power outages are not carried out in a systematic 
way. It is necessary to formulate a methodology to issue work permit for 
carry out maintenance and construction activities in distribution 
equipment. To avoid hazardous situations and ensure safety of public, 
employees and equipment installed in the network it is essential to prepare 
a methodology to isolate the network. It should describe the responsibility 
and duty of each party and all steps should be well documented in order to 
72 
identify the locations, equipment and persons related to each outage at a 
later stage. 
Similarly at serious outage conditions such as one transformer going out of 
service substation at the grid there should be an emergency plan 
describing the way of maintaining supply to essential loads by changing 
feeding arrangements. 
At present several industrial zones are available within NWP and these 
places should be given high reliable supply at all possible situations. The 
way of maintaining high reliable supply at any contingency situation can be 
ensured only if there is a contingency plan for network operations. 
Hence, a code of practice should be prepared to cover all those aspects. 
73 
References 
[1] Roy Billington and Ronald N Allan, "Reliability Evaluation Engineering Systems", 
Pitman Advanced Publishing program, London, England, 1984. 
[2] Roy Billington, "Reliability Evaluation of power systems", Longman Scientific and 
Technical Publications, UK, 1987. 
[3] IEEE, "IEEE Full Use Guide for Electric Distribution Reliability Indices", IEEE Std 
1366-2001, March 2001. 
[4] Ceylon Electricity Board, "Annual Report of the Provincial Control Centre- NWP 
2005", Ceylon Electricity Board, 2006. 
[5] Ceylon Electricity Board, "Genco Tariff Study 2004-2006 by Energy Sales Branch", 
Ceylon Electricity Board, 2007. 
[6] Mohan Munasingha, "The Economics of Power System Reliability and Planning 
theory and case study", Johns Hopkins University Press, Baltimore, 1979. 
[7] Aditya Birla Group, "Jaya shree Insulators", Aditya Birla Group, 2001. 
[8] Advantica Stoner Inc., " User Guide-SynerGEE electric 3.5 version", Advantica 
Stoner Inc., Carlisle, PA, 2003. 
[9] Ceylon Electricity Board, "Medium Voltage Construction Standard for 33 kV 
Distribution Lines", Ceylon Electricity Board, September 1997. 
[10] M.A.R.M. Fernanado, J.B. Ekanayaka, A.C.S. Wijethilaka, D.C.D.G. Wijerathna and 
S.M. Buwanski, " Recommendations for insulator Pollution- Flashovers in Sri Lanka 
with Special emphasis on a study of composite insulators", "ENGINEER" Journal of 
IESL, Vol XXXIII No 32, October 2000, pp 7-18. 
[11] R . Ramakumar, "Reliability Engineering", CRC press LLC, United States, 2000. 
[12] Central Bank of Sri Lanka, "Annual Report 2006" Sarvodaya Vishwa Lekha (Pvt) 
Ltd., March 2007. 
[13] Ceylon Electricity Board, "Standard Construction Cost for year 2008", Ceylon 
Electricity Board, November 2007. 
[14] Paul.G.Keat and Philip K.Y.Young, "Managerial Economics, Economic tools for 
today's decision makers", 4th Edition, Pearson Education, 2nd Indian Reprint, 2005. 
Annexure 2.1 
NETWORK MAP 
75 
Annexure-2 .2 
Definitions of Reliability Indices 
The definitions of electricity distribution system reliability indices as given in IEEE 
standard number P-1366 are summarized below. 
K r x J V , ) 
a. System Average Interruption Duration Index (SAIDI)= 
b. System Average Interruption Frequency Index (SAIFI)= 
NT 
I t o ) 
NT 
I ( r x N ) 
c. Customer Average Interruption Duration Index (CAIDI)=- ' 
d. Customer Average Interruption Frequency Index (CAIFI)= 
e. Customer Interrupted per Interruption Index (CIII)= 
NT 
N. 
E N. 
T 
T 
f. Average System Availability Index (ASAI)= [l - £ ( r , * N,)/(NT *r))]*100 
(V ID,*N.) 
g. Momentary Average Frequency Interruption Index (MAIFI)=-
NT 
Where, 
rt = Restoration time in minutes, 
Nt = Total Number of Customers Interrupted 
NR =Total Number of Customers served 
N0 =Number of Interruptions 
T = Time period under study 
IDI =Number of interrupting device operations 
76 
Annexure-3.1 
DAILY REPORT ON THE PERFORMANCE OF C.S.C 
Date (DD/MM/YY) : From 8 a.m. of ( / / ) to 8 a.m. of ( / / ) 
Area : 
C.S.C. : 
Prepared by : 
Weather Condition (Fair/Windy/Rainy/Stormy/ ) 
01. Details of LT Breakdowns 
Type 
No. of breakdowns to be 
attended today 
No. of breakdowns to be 
unattended today 
Service mains (Loose Connection) 
Service mains (Service wire Problems) 
Service mains (Cutout Problems) 
Service mains (Meter Problems) 
Pole Broken (Natural/Accident) 
Conductor Broken 
Fuse Blown 
Fuse Blown:(Substation Names and Sin. Number) 
Sub. Name Sin No. Sub. Name Sin. Name 
02. Details of HT Breakdown 
77 
03. Failure analysis 
Reason for Failure LT HT Reason fbr Failure LT HT 
Vegetation Consumer Fault 
Branches coming from distance Sabotage 
Burnt jumpers and Conductors Accidents due to vehicles 
Loose span and entanglement Due to broken poles 
Cracked insulators, L/A and Transformer 
bushings 
Transformer failures 
Due to animals and birds Burnt tail wires and cables 
Non availability of LT Protection Aging of fuses 
ACB trippings, fuses blown Bad weather 
UG Cable fault Others 
04. Details of HT scheduled interruptions 
Interrupted 
Feeder No. 
Feeding 
Grid 
Interrupted 
Section 
Interruption 
Scheduled at Interruption Given at Interruption 
Requested by From To From To 
05.Details of Over Voltages/Fire/Electrocution/Accidents or any other special incidents 
Incident Reported Time 
Type (Over 
Voltage/Firel/Accident/Electrocution) 
06.Details of Equipment (Failed/Rectified/Replaced) today 
Equipment Type (TF/LBS/Auto 
Recloser/Arrestor) 
ID No. Location Report Date and Time 
Rectified or Replaced 
by 
07.Details of energized jobs (PCB/DCB/SA/ADB/Bulk Supply/ ) 
Job Name Job Type (PCB/DCB/SA/ADB/Bulk Supply/Cost Paid/Chinese/RE) 
08.Any Assistance (Material/Gang/Vehicle/Tools) immediately required to ES/CSC/from other 
Type of Support 
(Material/Vehicle/Gang/Tool) Details of Work Relevant Branch 
78 
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eq
ue
st
 
B
y 
R
ea
so
n 
Is
ol
at
ed
 
Se
ct
io
n 
79
 
Annexure-3.3 
Provincial Monitoring Center - North Western Province 
Daily Report on 1. Details of breakdowns 
LT failures HT failures 
CSC Reported Unattended Reported 
today 
Unattended 
today Service Sub Service Sub Reason 
Connection Station Connection Station 
Kuliyapitiya C.S.C 
Giriulla C.S.C 
Narammala C.S.C 
Pannala C.S.C 
Wariyapola C.S.C 
Nikaweratiya C.S.C 
Maho C.S.C 
Kurunegala C.S.C 
Gokarella C.S.C 
Mallawapitiya C.S.C 
Pothuhera C.S.C 
Chilaw C.S.C 
Puttalam C.S.C 
Madamape C.S.C 
Wennappuwa C.S.C 
Bolawatta C.S.C 
Nattandiya C.S.C 
Bingiriya 
Anamaduwa 
Kalpitiya 
2. Interruption details 
C.S.C Interrupte d feeder 
Interrupted section Appro. No. of 
t./fs 
Interruption 
scheduled at 
Interruption 
given at Interruption given to 
From To From To From To 
80 
3. Tripping details 
33kV FEEDER TRIPPING IN GRID SUBSTATIONS NORTH WESTERN PROVINCE 
Normal 
current 
Peak 
Currant 
Peak 
Time 
EF 
GSS Feeder Feeder Name O/C A/ 
R 
Others Manual Total 
Puttalam 120A F1 Chi law 
75A F3 Kalpitiya 
180A F4 Anamaduwa 
115A F5 Cement Fac. 
30A F7 Wanathawilluwa 
85A F8 Cement Fac. 
Sub Total 
Madampe 205A F1 Kuliyapitiya 
160A F2 Bingiriya 
80A F3 Chi law 
80A F4 Nattandiya I 
40A F5 Voice of Ameri 
160A F7 Keeriyankalliya 
115A F8 Buwalka 
Sub Total 
Bolawatta 145 A F1 Madampe 
160A F2 Makandura 
145 A F3 VOA 
280A F4 Negombo I 
60A F5 Bolawatta Prima. 
210A F6 Negombo II 
140A F7 Pannala 
70A F8 VeyangodaI 
110A F9 Veyangoda II 
Sub Total 
Mallawapitiya 138A F1 / H5 Galagedara 
112A F 2 / H 6 Kurunegala town 
104A F 3 / H 7 Polgahawela 
F4/H1I Hiripitiya 
148 A F5/H12 Padeniya 
67A F6/H13 Spare 
162 A F 7 / H 4 Ibbagamuwa BB 
45 A F8/H14 Dodangaslanda 
F Maho BB 
Sub Total 
Tulhiriya 79A F1 Industrial Zone 
45 A F2 Kurunegala 
65A F3 Pannala 
223A F5 Kuliyapitiya 
Sub Total 
4. Reasons for Changes in Feeder Current. 
Grid Feeder Reason 
5. Grid outages/ Total failures 
81 
Grid Starting time Energized time Duration 
6. Energized Jobs 
CSC Job Name Type PCB/DCB/ADB/Bulk Job No 
7. Major Incidents 
CSC/Grid Incident Reported Time Action taken 
8. Details of equipment (failed/rectified/replaced) today 
Equipment Voltage Location Reported date And time 
Rectified or 
replaced by 
9. Reliability Information 
82 
Type of 
Outages No. of Events 
Effected 
Consumers SIDI Information SAIFI Information 
LT 
HT 
Feeder Tripping 
Interruptions 
Total 
Prepared by : 
Approved by : 
83 
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se
 B
lo
w
n 
U
riy
aw
a 
D
D
LO
 
4:
00
:0
0 
P
M
 
4:
55
:0
0 
P
M
 
A
na
m
ad
uw
a 
6/
24
/2
00
6 
H
T/
55
28
/0
6 
1 
0 
0 
0 
Fu
se
 B
lo
w
n 
P
ut
ta
la
m
a 
F4
 A
an
am
ad
uw
a 
D
93
0 
3:
50
:0
0 
P
M
 
5:
20
:0
0 
P
M
 
28
1 
A
na
m
ad
uw
a 
3/
9/
20
05
 H
T/
20
77
/0
5 
1 
0 
0 
0 
Fu
se
 B
lo
w
n 
S
an
ga
tti
ku
la
m
a 
o/
»/
zu
uo
 o
.o
u.
uu
 
P
M
 
0/
 I
U
/Z
U
U
O
 o
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u
.u
u 
A
M
 
23
7 
A
na
m
ad
uw
a 
9/
6/
20
04
 H
T/
58
5/
04
 
0 
0 
1 
O
th
er
s 
J/
D
IU
K
B
U
 
a
i 
R
ab
aw
ew
a 
9:
50
:0
0 
A
M
 
3:
50
:0
0 
P
M
 
A
na
m
ad
uw
a 
7/
25
/2
00
4 
H
T/
20
1/
04
 
1 
0 
0 
0 
Fu
se
 B
lo
w
n 
U
riy
aw
a 
T/
D
D
LO
 
8:
40
:0
0 
A
M
 
12
:2
5:
00
 P
M
 
A
na
m
ad
uw
a 
2/
17
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00
5 
H
T/
18
27
/0
5 
1 
0 
0 
0 
Fu
se
 B
lo
w
n 
Th
on
ig
al
a 
10
:1
0:
00
 A
M
 
11
:2
0:
00
 A
M
 
A
na
m
ad
uw
a 
7/
13
/2
00
6 
H
T/
57
00
/0
6 
1 
0 
0 
0 
Fu
se
 B
lo
w
n 
P
ut
ta
la
m
a 
F4
 A
an
am
ad
uw
a 
D
93
1 
11
:1
0:
00
 A
M
 
12
:4
0:
00
 P
M
 
48
3 
A
na
m
ad
uw
a 
9/
3/
20
06
 H
T/
61
83
/0
6 
1 
0 
0 
0 
Fu
se
 B
lo
w
n 
P
ut
ta
la
m
a 
F4
 A
an
am
ad
uw
a 
D
92
9 
6:
15
:0
0 
A
M
 
12
:3
0:
00
 P
M
 
42
8 
A
na
m
ad
uw
a 
7/
15
/2
00
6 
H
T/
57
25
/0
6 
1 
0 
0 
0 
Fu
se
 B
lo
w
n 
P
ut
ta
la
m
a 
F4
 A
an
am
ad
uw
a 
D
93
1 
9:
40
:0
0 
A
M
 
10
:1
5:
00
 A
M
 
48
3 
A
na
m
ad
uw
a 
7/
10
/2
00
6 
H
T/
56
65
/0
6 
0 
1 
0 
oo
nu
uu
ui
 
0 
B
ro
ke
n 
P
ut
ta
la
m
a 
F1
 C
hi
la
w
 
D
D
LO
 
D
93
3 
10
:3
0:
00
 A
M
 
2:
40
:0
0 
P
M
 
48
07
 
A
na
m
ad
uw
a 
7/
10
/2
00
6 
H
T/
56
64
/0
6 
1 
0 
0 
0 
Fu
se
 B
lo
w
n 
P
ut
ta
la
m
a 
F1
 C
hi
la
w
 
D
93
3 
D
D
LO
 
10
:3
0:
00
 A
M
 
2:
40
:0
0 
P
M
 
48
07
 8
6 
Sin numbers and number of consumers assigned to the substation 
Consumer Data for Wennppuwa area. Annexure 3.5 
s in n u m b e r Total number of customers 
PP111 382 
PP113 195 
PP114 345 
PP115 245 
PP116 86 
PP117 1 
PP118 271 
PP119 1 
PP120 1 
PP121 1 
PP122 416 
PP123 1 
PP124 90 
PP125 264 
PP126 272 
PP128 220 
PP129 833 
PP130 104 
PP131 374 
PP132 367 
PP133 859 
PP134 7 
PP135 1 
PP136 198 
PP137 626 
PP138 1 
PP139 513 
PP140 334 
PP141 374 
PP142 13 
PP143 269 
PP144 153 
PP145 567 
PP146 93 
PP147 586 
PP148 684 
PP149 253 
PP150 203 
PP151 563 
PP152 1 
PP153 1 
PP154 1 
PP155 1 
PP156 1 
PP157 1 
PP158 1 
PP159 274 
PP160 190 
PP161 263 
PP162 1 
PP163 735 
PP164 383 
PP165 233 
PP166 327 
PP167 239 
PP168 596 
PP169 126 
PP170 174 
PP171 115 
PP172 1 
PP173 428 
PP174 398 
PP175 95 
PP176 201 
PP177 254 
PP178 214 
PP179 1 
PP180 375 
PP181 237 
PP301 271 
PP302 133 
PP303 175 
PP304 93 
PP305 1 
PP306 200 
PP307 36 
PP308 1 
PP309 1 
PP310 1 
PP311 1 
PP312 167 
PP313 1 
PP314 1 
PP315 310 
PP316 296 
PP317 173 
PP318 1 
PP319 185 
PP320 1 
PP321 283 
PP322 122 
PP323 159 
PP324 398 
PP326 1 
PP327 291 
PP328 75 
PP329 1 
PB001 1 
PB002 320 
PB003 461 
PB004 226 
PB005 226 
PB006 269 
PB007 146 
PB008 1 
PB009 295 
PB010 166 
PB011 57 
PB012 312 
PB013 1 »! 
PB014 311 
PB015 1 
PB016 222 
PB017 156 
PB018 299 
PB019 323 
PB020 320 
PB021 1 
PB022 233 
PB023 101 
PB024 222 
PB025 328 
PB026 242 
PB027 311 
PB028 180 
PB029 155 
PB030 237 
PB031 267 
PB032 290 
PB034 290 
PB035 111 
PB036 365 
PB037 1 
PB038 192 
PB039 405 
PB040 291 
PB041 126 
PB042 322 
PB043 277 
PB044 295 
PB045 23 
PB046 160 
PB047 471 
PB048 526 
PB049 170 
PB050 103 
PB051 118 
PB052 276 
PB053 58 
PB054 236 
PB055 137 
PB056 254 
PB057 481 
PB058 193 
PB059 185 
PB061 10 
PB062 245 
PB063 168 
PB064 137 
PB065 1 
PB066 116 
PB067 1 
PB068 187 
PB069 1 
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