JIMMA UNIVERSITY
JIMMA INSTITUTE OF TECHNOLOGY
FACULTY OF ELECTRICAL AND COMPUTER
ENGINEERING
POWER STREAM
INTERNSHIP HOSTING COMPANY
EEU SOUTH WESTERN REGION JIMMA
INTERNSHIP DURATION
FROM OCTOBER 8, 2016 TO FEBRUARY 8, 2017
ADVISOR: Mr. Alebachew T. and Tesfaye B.
SUBMISSION DATE:
FEB 28, 2017
JIMMA, ETHIOPIA
Group members
Name
Id no
1.
YARED ENGIDA ……………………………………….T06257/05
2.
MIHRETU DESALEGN…………………………………..01562/05
3.
WORKU BELAY …………………………………………02087/05
4.
WENDESEN AFESA ……………………………………..02070/05
5.
FENTAHUN ASEFA……………………………………..01108/05
Declaration
We, understated group of students declare that this intern ship report is our own work. We confirm
that: This work was done mainly for internship students at JIMMA institute of technology. With the
exception of many quotations, this report is entirely our work.
Signature
1) YARED ENGIDA………………………………………
2) MIHERTU DESLIGN…………………………………..
3) WORKU BELAY……………………………………….
4) WENDESEN AFESA…………………………………..
5) FENTAHUN ASEFA…………………………………...
Approved by
Company supervisor
Academic mentor
_______________________
______________________
February 2017
INTERNSHIP REPORT OF JIMMA EEU 2016/2017
Acknowledgement
First of all we would like to thank God that helped us to finish this internship program & report
safely. Secondly, we would like to give a precious thanks for JIMMA INSTITUE OF
TECHNOLOGY and school of electrical and computer engineering department for better support
and we do not want to forget Mr BIKILA WAKJIRA, Mr IYASU BIRHANU, and Mr WENDEMU
ASTATKE, they are Engineers that works in JIMMA EEU Company in the department of operation
and maintenance team and business department. We want to give them a precious thanks and
appreciate the method of treating the students in every aspect. A special thanks for our mentor Mr
ALEBACHEW TENA and TESFAYE, we do not want pass before thanking all of the workers in
the company. Finally, we want thanks our friends who have been advise us on different things as its
necessary.
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INTERNSHIP REPORT OF JIMMA EEU 2016/2017
Executive summary
The great importance of the Internship program is undeniable because it gives the student a chance
to link his/her theoretical background to the real world applications. It also helps the student to
develop different personal skills and take a uses at the real world experience that a waits after
graduation. During the last four months, we were working in EEU, JIMMA south west region.
During our time there, we are worked in two different sectors. These are Transmission in substation
and Distribution systems design and construction case team but we are executing our intern ship
program with the distribution sector of EEPCO in JIMMA south west region. This report discusses
the above points deeply and the design, project proposal also included, so that we tried to include the
benefits we gained from our internship program.
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Table of Contents
Acknowledgement ................................................................................................................................................i
Executive summary ............................................................................................................................................. ii
List of figures ..................................................................................................................................................... vi
List of table........................................................................................................................................................ vii
Acronyms ......................................................................................................................................................... viii
CHAPTER ONE .................................................................................................................................................1
Background of EEPCO ...................................................................................................................................1
1.1 Brief history of EEPCO ...................................................................................................................................1
1.2 EEPCO Establishment...................................................................................................................................1
1.3 Establishment of JIMMA substation .............................................................................................................1
1.3.1 Main customers of the company ............................................................................................................2
1.4 EEPCO'S Vision and mission........................................................................................................................3
1.4.1 EEPCO'S Vision ........................................................................................................................................3
1.4.2 EEPCO’S Mission ..................................................................................................................................3
1.5 Main products or services..............................................................................................................................3
1.5.1 Generation/supply systems .....................................................................................................................3
1.5.2 Transmission and substation systems .....................................................................................................3
1.6 Main customers of the company....................................................................................................................4
1.7 Organizational structure of EEPCO and EEU ...............................................................................................5
CHAPTER 2 ....................................................................................................................................................7
Over all internship experience .............................................................................................................................7
2.1 How we get Into the Company ......................................................................................................................7
2.2 Section we Have Been Worked .....................................................................................................................7
2.3 overall interconnected power system with their equipment’s .......................................................................8
2.3.1 Substations .............................................................................................................................................9
2.3.2 Distribution.......................................................................................................................................... 17
2.3.2.1 Medium voltage networks ........................................................................................................... 17
2.3.2.2 Distribution transformer .............................................................................................................. 18
2.4 Tasks that we have been executing ............................................................................................................ 19
2.5 Challenges faced......................................................................................................................................... 22
2.5.1. Academic challenges .......................................................................................................................... 22
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2.5.2. Work area challenges ......................................................................................................................... 22
2.6 Measures taken to overcome the challenges .............................................................................................. 22
CHAPTER 3 ..................................................................................................................................................... 23
Overall benefit we gained from the internship ................................................................................................. 23
3.1 Improving our Practical Skills .................................................................................................................... 23
3.2 upgrading our theoretical knowledge ......................................................................................................... 24
3.3 Improving our interpersonal communication skills .................................................................................... 24
3.4 Improving our team playing skills.............................................................................................................. 25
3.5 Improving our leadership skills .................................................................................................................. 25
3.6 work ethic related issues............................................................................................................................. 26
3.6.1 Personal ethics ..................................................................................................................................... 26
3.6.2 Professional ethics ............................................................................................................................... 27
3.7 Entrepreneurship skills ............................................................................................................................... 27
CHAPTER FOUR ............................................................................................................................................ 28
Contribution to the company ............................................................................................................................ 28
4.1 The task we performed for the company .................................................................................................... 28
4.2 Design steps in power distribution network ............................................................................................... 28
4.2.1 Design of low voltage network............................................................................................................ 29
4.2.1.1 Selection of transformer .............................................................................................................. 29
4.2.1.2 Selection of Fuse Rating ............................................................................................................... 31
4.2.1.3 Selection of Feeders Cables and Conductors ............................................................................... 31
4.2.1.4 Selection of Service Drops Conductors ........................................................................................ 32
4.2.1.5 Types of cables used for construction of overhead lines ............................................................. 32
4.3 Simulation Line diagram of city feeder by Visio software ........................................................................ 34
4.4 Result and discussion ................................................................................................................................. 36
CHAPTER FIVE ................................................................................................................................................... 37
Project: Reduction of voltage unbalance by using voltage regulator ............................................................... 37
5.1 Abstract ...................................................................................................................................................... 37
5.2 Introduction ............................................................................................................................................ 37
5.3 The problem identified ........................................................................................................................... 38
5.4 Objective ................................................................................................................................................ 38
5.4.1 General objective ............................................................................................................................ 38
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5.4.2 Specific objective ............................................................................................................................. 38
5.5 Literature review .................................................................................................................................... 38
5.6 Methodology .......................................................................................................................................... 39
5.7 The basic linear regulator ....................................................................................................................... 39
5.8 Design..................................................................................................................................................... 40
5.9 Result and discussion ............................................................................................................................. 42
CHAPTER SIX ................................................................................................................................................ 43
Conclusions and recommendations .................................................................................................................. 43
6.1. Conclusion ................................................................................................................................................. 43
6.2. Recommendation ....................................................................................................................................... 44
Reference .......................................................................................................................................................... 45
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List of figures
Figure 1.1. EEPCO`S Transmission line length distribution………………………………………...4
Figure 1.2. Organizational structure of EEPCO……………………………………………………..5
Figure 1.3 Organizational structure of south western region Distribution system (JIMMA)………..5
Figure2.1. transmission line………………………………………………………………………….7
Figure2.2. voltage transformer……………………………………………………………………….9
Figure 2.3. Arrester………………………………………………………………………………….10
Figure2.4. JIMMA substation isolator…………………………………………………………... …11
Fig2.5. Single Bus substation Arrangement………………………………………………………....12
Figure2.6. JIMMA substation bus bar………………………………………………………….........12
Figure2.7.JIMMA substation circuit breaker……………………………………………………......13
Fig2.8. current transformer………………………………………………………………….……….14
Figure2.9a. 33/15kv power transformer………………………………………………….……….....16
Figure 2.9b 15kv power transformer………………………………………………………….…......16
Figure2.10–JIMMA substation control room………………………………………………………..18
Figure2.11. 200kv transformer……………………………………………………………………....21
Figure 2.12. System flow (block diagram)…………………………………………………………..31
Figure 4.1 Line diagram of city feeder…………………………………………………………........36
Fig 5.2 linear regulator functional diagram………………………………………………………….41
Fig 5.3 simple diagram from JS to JC……………………………………………………………….42
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List of table
Table 1 Main customers JIMMA sub-station…………………………………………………….....5
Table 2.1. Collected data…………………………………………………………………………...28
Table4.1 selection transformer by load criteria………………………….………….……………...31
Table4.2. Selection transformer by no. of customer………………………………….………….....31
Table4.3. selection transformer by maximum distance……………………………………….…....31
Table4.4. selection transformer by fuse rate………………………………………….….…………32
Table4.5. selection transformer by feeder cable……………………………………………..….….32
Table4.6.selection transformer by service drop conductor…………….………………….………..33
Table4.7. cable Current carrying capacity…………….………………….…………….….……….34
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Acronyms
A
Ampere
AC
alternative Voltage
CEO
Chief Executive Officer
CT
Current Transformer
DC
Direct Current
EEPCO
Ethiopia Electric Power Corporation
HRC
High Rapture Capacity
HV
High Voltage
ICS
inter connected systems
KV
Kilovolt
KVA
Kilovolt ampere
KW
Kilowatt
LV
Low Voltage
MV
Megavolt
MVA
Mega volt AMPER
SCS
Self-Contained System
V
volt
VT
Voltage transformer
EELPA
Ethiopian Electric Light and Power Autority
EEU
Ethiopian electric utility
ACSR
Aluminum conductor steel rain forced
JS
JIMMA substation.
JC
JIMMACITY
LA
light arrestor
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CHAPTER ONE
Background of EEPCO
1.1 Brief history of EEPCO
Over the past century, the electric power industry continues to shape and contribute to the welfare,
progress, and technological advances of the human race. The growth of electric energy consumption
in the world has been nothing but phenomenal. In Ethiopia, the past half a century especially the
past two or three decades shows an incredible increase in the demand of electric energy.
Ethiopia first got an electric light in 1898, when emperor MENILIKII acquired a generator to light
up for the palace. The Italian company known as CAMPANINAZIONALEIMPREZI, had the right
to generate, distribute and sell electricity in Ethiopia during the Italian invasion.
It is in 1948 that Ethiopian government established SHEWA electric power to take over the
generating, distributing and selling electricity to the then town of Addis Ababa and its vicinity. And
in 1955 it was reorganized as Ethiopian electricity Light and Power Authority (EELPA) for the
purpose of generating, transmitting, distributing and selling electricity throughout the country.
1.2 EEPCO Establishment
The Ethiopian Electric Power Corporation (EEPCO) was named in 1997 after serving in the name
of Ethiopian Electric Light and Power Authority (EELPA) which was established in 1956.
EEPCO is responsible for generating, transmitting, distributing and selling of electric energy
throughout the country.
1.3 Establishment of JIMMA substation
The substation was established in 1979.The substation obtain its input from Gibe one. The
generation feeds 132KV to the substation then divides by step down around JIMMA city and online
to different areas (AGARO, BONGA). The oldest substation has only one transformer (132/15KV)
that has only four lines. Those are: Line 1-kochi, Line 2-hydro, Line 3-city, Line 4-Agri.
Currently the substation has fulfilled with many control equipment, switching and protection and
three winding transformer is installed (132/33/15) to feed nearby small town. It receives power from
GILGEL Gibe hydro power plant and from transmission lines and it transforms high to low voltage.
It distributes electricity to customers and supervises and protects the distribution network to keep it
working safely and efficiently. Now days the substation has 6 bays (incoming and outgoing
terminals).
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Those are; 1. Bay1-The old Abba line now this line used to synchronize old sub-station and new
sub-station (132KV),
2. Bay2-Bonga line (132KV),
3. Bay3-transformer132/15KV,
4. Bay4-Gilgel Gibe line (13 2KV incoming),
5. Bay5-Agaro (132KV),
6. Bay6-trafo132/33KV
Transformer 132/15KV has the following lines: i) Kochi line
ii) JIMMA university line
iii) City line
iv) KITTO campus line
v) AGRI-line and
Transformer 132/33KV has the following lines: I) LIMU genet line1
II) SOMBO Line2
1.3.1 Main customers of the company
The customers of the company are all of those who are connected or have an electrical energy
access. They could be put in to the following categories:
a) Domestic customers
b) Commercial
c) Street light
d) Industrial (HV and LV)
Transformer 132/15KV has the following outgoing lines:  Kochi line
 JIMMA university line
 City line
 KITTOFURDISA campus line
 AGRI line
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1.4 EEPCO'S Vision and mission
1.4.1 EEPCO'S Vision
To be a center of excellence in providing quality electric service to everyone’s doorstep and being
competitive in energy export. [4]
1.4.2 EEPCO’S Mission
The main mission of the company is to provide adequate electricity of generation, transmission,
distribution, and sales services, through continuous improvement of utility management practices,
and responsive to the socio-economic development and environmental protection needs of the
public. [4]
1.5 Main products or services
EEPCO manages and operates power-generating facilities, the national transmission and distribution
grids, and is also responsible for the supply of electricity for plenty of customers with a high
coverage of most towns in Ethiopia.
According to EEPCO’S corporate plan, in addition to re-organizing the corporation, to be power self
-sufficient and to be able to export to other countries, to start different power generation plants,
complete the construction of different power plants, and rising power coverage to greater percent in
the coming three years are the plans that are going to be implemented.
Generally the main services of EEPCO are summarized as follows:
1. Generation
2. Transmission and
3. Distribution of electricity throughout the country.
1.5.1 Generation/supply systems
The corporation has two electric energy supply systems that are the Interconnected System (ICS)
and the Self Contained System (SCS). The main energy source of ICS is hydro power plants and
mini hydro’s for SCS and diesel power generators allocated in various areas of the country.
1.5.2 Transmission and substation systems
The electric energy generated from the main hydro power plants is transported through high voltage
transmission lines rated 45, 66, 132, 230 and 400 kV. Where the substation is constructed at
different level of voltage and number of customer at that area and also depend on the center of the
load to be located.
Distribution systems
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Power distribution in both ICS and SCS is effected at a primary voltage of 33kV and 15kV lines,
consisting entirely of 3-phase, 3-wire feeders, and is stepped down to a utilization voltage of
380/220(3-phase, 4-wire) using 3-phase transformers. These transformers can have capacity of 50
KVA, 100 KVA, 200KVA or 315KVA.
1.6 Main customers of the company
The customers of the company are all of those who are connected or have an electrical energy
access. They could be put in to one of the following categories:
e) Domestic customers
f) Commercial
g) Street light
h) Industrial (HV and LV)
Number of Customers
Numbers of customers are those who are connected to get electric energy. The total number of
connected customers at present has been reached higher as counted by the authorized stake holders.
the number of customer of the country is classified by the usage of the electricity, this means that
there are ICS and SCS customer, so due to that sometimes there is a case of classifying the customer
as an active, suspend, in process and pending on the past years but ICS domestic and own
consumption customers are adjusted as its required. [1]
Table 1 Main customers JIMMA sub-station
Line
KV
Customer
Capacity
CT ratio
Kochi
15
Dippo, Era, Jiren, water treatment,
5.6MW
600/5
Kamo, Bulbul, Serbo
JU Main Campus
15
Jimma University
3.3MW
150/5A
City
15
Beno, Kera, Dedo town, Bus
5MW
200/5A
2MW
100/5A
2MW
100/5 A
Station
Agri
15
Agri College, Gabriel Church,
Frenji areda, Airport, Melko, Seka,
Alma
Kitto campus
15
Kitto campus
Among 33KV outgoing line Limu genet line and Sambo line
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 Limu genet line1 (3.5MW) feeds to Sombo, Bilida, Kentere, Babu, Kosa, Anbuwye, Limu
town
 Sombo Line2(3.5MW) feeds to Atnago(Limuseka,gejib and Atnago town) and Bage(mecha,
chalelaki and Bage town
1.7 Organizational structure of EEPCO and EEU
The Ethiopian Electric Power Corporation will split into three entities at the end of this Ethiopian
fiscal year. The three entities that will be under the Ministry of Energy are power generation and
construction, transmission and distribution, and marketing and sales. According to officials of the
corporation, the new re-organization will help the corporation to be efficient in generating and
supplying power to the public.
Currently the structure of the corporation has ten departments under the CEO generation
construction, generation operation, transmission and substation construction, transmission operation,
distribution system, marketing and sales, universal electrification access process, human resource,
corporate finance and supply chain, and services. [1]
Figure 1.1 Organizational Structure of EEPCO
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CEO
Distribution
Retail Business
Wire Business
Meter to Bill
Cycle
Collection
Marketing& Customer
Service Strategy
Meter
Management
Network
Planning
Enforcement
Construction
Maintenance
Operation
Automation
Call Center
Customer Services
Figure 1.2 Organizational structure of south western region Distribution system (JIMMA)
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CHAPTER 2
Over all internship experience
2.1 How we get Into the Company
The University gave us a chance for finding our internship hosting company by ourselves. In doing
so, we could found a company which is suitable for us economically as well as academically. We
found that EEPCO is suitable for us according to our department, interest and its site of location.
After we have decided this, we went to EEPCO south western Distribution office at JIMMA for
submitting a request letter for internship. We found that they are willing to accept us as intern and
they approved our request letter.
We have started our internship program on October 8/2016. The first day when we enter into the
company, the south west region business head Mr. BIKILA WAKJIRA and his colleagues gave us a
warm welcome and he introduced us to different workers of the office.
Next to this, EEU distribution manager assigned a supervisor, Mr. IYASU and Mr. WENDEMU on
the Technical and overall help of our internship program from starting day till the final day of our
internship program, In EEPCO JIMMA South western power distribution. Even though the chief
officer of the substation systems accepted the request application, the substations chief officer also
promised us that we will work, understand transmission in substation systems. From this time on
we have started to know the work flow of the following sections.
1) Transmission line in substation
2) Power distribution
Even though they encourage us to do more, it was unclear to us exactly what our duties to be. This
was because it was the first time that we saw this type of Company. In addition to this our terms of
remark didn’t indicate exactly up to what limit we worked on.
2.2 Section we Have Been Worked
We work in JIMMA EEPCO some parts of power supply. Such as JIMMA power substation and
distribution in southwestern region (JIMMA) that takes lots of our internship program.
The Ethiopian Electric power corporation is very large corporation that has different regional head
offices through the whole of Ethiopia. Among those regional head offices the South western
regional head office is one of largest of head offices of EEPCO in the country.
For the first month we were working in the distribution site that is an introduction to the company.
And on the second month we worked on different working area of the distribution system found in
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the whole JIMMA town and also we were worked with different technicians and engineers to solve
the main fault that happened on the customer area and specifically when the fault happened is very
large and used to us to learn more about the overall system ,then in the third month we were also
working in distribution low voltage (LV) network project in JIMMA and MV network project and
also we get an opportunity to see the substation for some week. Finally in the fourth month we were
working in designing of a line diagram for the feeders of JIMMA substation specifically city feeder
collaborating with utility workers for a better information of our work.
The electric power system provides a means of generating transmitting and distributing energy in
the form of electric current to the ultimate users, the load Generation, transmission, distribution and
load constitute the four basic element of subsystem of an electrical power system.
1. Generation: - generation is simply the conversion of energy from one form to electrical energy.
The heat energy stored in fuels, for example is converted to electrical energy by means of an
electric generator.
2. Transmission: - the transmission system consists of a network of overhead lines or in density
populated areas underground cable the lines are designed to transmit large amount of power
from the point of generation to the load area.
3. Distribution: - the distribution system also consists of a network of overhead lines and
underground cables by which the power is distributed to the ultimate users of electricity that is
the load. These lines are normally shorter than transmission lines, and carry smaller amount of
power.
4. Load: - the utilization of electric power is collectively called load. This includes the users of
electricity in the home (i.e. heating and lighting) in the factory to drive motors and other
machinery.
2.3 overall interconnected power system with their equipment’s
The work flow of the overall system is long and Starts from the high voltage; the process starts with
132 kV input to substation from GILGEL GIBE 1 and GILGEL GIBE 2 by synchronization
technique of the two generation station. The cables Carrying the 132 KV were upgraded earlier from
132 KV lines to cope up with the ever increasing need of electrical energy. The electric power is
receive from GILGEL GIBE1 and gives to the power distribution. Then the distribution system step
down the power and distribute the energy to the customer.
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2.3.1 Substations
The power substation is an integral part of the system and is a juncture point of lines and other
system elements. It is often an interface between any two subsystems, such as generation and
transmission. From all JIMMA substation is one of the biggest substation found in Ethiopia so that
the company has many parts and updated technologies recently but currently JIMMA substation
divided in to two substation those are:
1, old substation
2, new substation
The difference of these two substations is the control, protection relay, the whole capacity of the
station and transformers. this means the new substation receive 230kv where the old one is 132kv
and additionally In old substation control and protection relay is not more digitalized in other hand
the new substation of the control and protection relay is digital.
The JIMMA substation serves three basic purposes. These are:
1. Switching system; is elements which is the in and out of the system. This is accomplished by
relaying equipment; by circuit breakers, disconnects switches and the associated equipment.
2. Stepping down; is concerning on the voltages in the system. This is accomplished by power
transformer.
3. Regulating system voltages, this is accomplished by shunt reactors, shunt capacitors, static
compensators, etc.
The JIMMA substation has is the following work flow sequence
Transmission linevoltage transformer (VT)  ArresterBus bar disconnect orBus barline
disconnect orcircuit breakercurrent transformer (CT) ArrestorPower transformer Earthling
transformer Control and Protection room.
Transmission Line: - the transmission line is coming from GILGEL GIBE generation station. The
station has three phase network to carrying 132kv which is the input of the JIMMA substation.
Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to
electrical substations located near demand centers. This is distinct from the local wiring between
high-voltage substations and customers, which is typically referred to as electric power distribution.
When Transmission lines interconnected with each other, become transmission networks.
Transmission lines mostly use high-voltage phase alternating.
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Electricity is transmitted at high voltages (110 kV or above) to reduce the energy lost in longdistance transmission. Power is usually transmitted through overhead power lines.
High-voltage overhead conductors are not covered by insulation. The conductor material is nearly
always an aluminum alloy, made into several strands and possibly reinforced with steel strands.
Copper was sometimes used for overhead transmission but aluminum is lower in weight for only
marginally reduced performance and much lower in cost.
Figure2.1. transmission line
Voltage transformer (VT):-the JIMMA substation of voltage transformer is intended to receive
power from transmission lines. It used for reducing or stepping down voltage from higher value to
lower value for measuring, protection and to regulate the system. It also used to wave trap. Wave
trap (carrier equipment) used for protection and communication signaling, Voice communication,
protection signaling telex channel, control and monitoring signals.
Voltage transformers are installed to supply the shunt or voltage circuit of instruments and meters
when the service voltage is 380v and higher.
In high voltage substations are used connect the voltage transformers to the bus bars and permit
them to be switched in or out.
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Figure2.2. voltage transformer
Lighting arrestors (Surge diverters):-This protective scheme of LA is like earthing screen and
it works for protecting the equipment against direct-stroke but it cannot protect the system against
direct-stroke but it can protect the system against traveling surges along the line or into the
equipment. For this purpose, lightning arresters are used.
A lightning arrester is a protective device which provides a conductive path to the high voltage
surges in to the ground”. Under normal conditions, the lightning arrester behaves as a perfect
insulator. i.e. it does not take any current from the power system. Under abnormal conditions, it
behaves as a perfect conductor for the high surges which hit the system.
Location of Arresters: The best location that an arrester should be installed at or on the apparatus
itself (connected to its terminals) and should properly be grounded, through the body of the
apparatus.
Figure 2.3. Arrester
Isolator (Disconnecting Switch):- A switching device which can be opened or closed only under
no current condition it provides isolation of a circuit for the purpose of maintenance. It is used to
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disconnect the line to safety maintenance. One of the cardinal measures for insuring fully safety in
carrying out work on pieces of equipment in electrical installations is to disconnect reliably the unit
or the unit or the section on which the work must be done from all other live parts of the installation.
To guard against mistake, it is necessary that this should be done by an apparatus which makes a
visible break in the circuit.
Isolator do not have a control devices, therefore it cannot be used to interrupt currents which drawn
across the contacts. : - additionally to repair or maintenance work on the circuit breaker, both the bus
bar and the line isolator must be opened
There are two types of disconnecting switches in JIMMA substation. These are
1, Bus bar dis connector
2, Line dis connector
Figure2.4. JIMMA substation dis connector (isolator)
Bus bars: - various incoming and outgoing circuits are connected to bus bars. Bus bars receive
power from incoming circuits and deliver power to outgoing circuits. It is made of copper bar,
Aluminum tube etc...
In JIMMA substation the bus bar is energized from GILGELGIBE power station1. The JIMMA
substations use Single bus.
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BUS BAR
Figure 2.5.Jimma substation bus bar
Circuit Breaker: - CB is advice capable of making (breaking) and electric circuit under normal
and abnormal conditions such as short circuits. It can operate automatically and clear fault currents
safely and quickly. It used to interrupt the flow of current, thereby isolating faulty parts of the
system. The operating mechanism of the circuit-breaker gives the necessary energy for opening and
closing of contacts of the circuit breakers.
Circuit-breaker is used for opening and closing circuits; for normal switching operations the
command is given by operator from control room or from switchyard. During short circuits or
Abnormal conditions, relay operates and gives opening command to circuit breaker and circuit is
opened automatically.
There are many types of circuit breaker but In JIMMA substation uses two types of circuit breaker
the one, sulfur hexafluoride circuit-breaker (SF6). There are two types of SF6 gas, single pressure
puffer SF6 gas and double pressure SF6 gas.
Figure2.6. JIMMA substation SF6 circuit breaker
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Current Transformer (CT):-are used for reducing or stepping down AC current from higher
value to lower value for measuring, protection and control systems.
Protective relays in a/c power system are connected in the secondary circuit of current transformers
and potential transformers. The design and uses of these transformers is quite different, from that of
well-known power transformers. In current transformers, primary current is not controlled by
condition of the secondary circuit. Hence primary current is a dominant factor in the operation of
current transformers current transformers must be further classified into two groups. These are
protective current transformers and measuring current transformers.
Figure 2.7.Current transformer
Power transformer: - power transformers are necessary b/n consecutive voltage levels for
stepping up or stepping down the ac voltage and for transforming power from one ac voltage level to
the other. The KVA ratings of power transformers cover a wide range b/n say 5 KVA to 650 MVA.
Very large transformers (250 MVA to 650 MVA) are installed in generating stations very small
transformer (a few VA) is used in low voltage circuits.
In JIMMA substations there are two types of power transformer. Those are 15kv power transformer
and 33/15kv power transformer.15kv transformer is used to JIMMA town. It covers 50-60km. it has
two winding. And 33kv transformer is used to around JIMMA town (LIMU, SEQA). This
transformer covers 90-110km.these power transformer is three winding transformer. The
transformer of 33kv is acts as 15kv transformer. All transformers in south western region substation
(JIMMA) are stepping down transformer.
Protection power transformer:-many devices to protect the transformer these are
a. Non electrical:-it is not uses electrical power. These are
1. BUCHOLZE relay
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2. Pressure Relief Device:
3. Oil level indicator
4. Oil & winding temperature
5. Fans
6. Silica gel
b. Tap changer: - a tap changer is provided with two transformers for maintaining specified
outgoing voltage where the incoming voltage is subjected to voltage variations. The tap changer
is mounted in/on the transformer tank. There are two types of tap changer.
Off load tap changer: - off load tap changer is operated without any load when the transformer at
idle, manually by substation operator.
On Load tap changer: - the daily Voltage variation due to changing load and short period voltage
variations are controlled by on load tap-changers automatically by voltage regulator. It is operated
with load the transformer in operation. On load tap changer operated in three ways.
i.
Remit from control room
ii. Local by electrical pushbutton
iii.
manual using handle
c. EARTHING transformer: - It is used for protect earth fault of delta connected side of power
transformer through earthing transformer neutral current transformer.
Figure 2.8 a. 33/15kv power transformer
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Figure 2.8 b 15kv power transformer
Control and protection room: - in JIMMA substation two control and protection room. The
15kv transformer control room and 33/15kv transformer control and protection room. A substation
control room has following provisions & functions.
a. Metering and instrumentation
b. Tap-Changer control and control of shunt capacitors for voltage control.
c. Normal switches function from control room.
d. Protection of transmission lines, bus bars, transformers auxiliaries etc. in the event of abnormal
conditions such as faults.
e. Voice communication with neigh boring power stations and substation by PLC (power line
carrier).in this room there also DC battery room.
In a traditional substation the function of voltage control by tap chargers and capacitor its performed
by station operators and manual command or by automatic control systems and corresponding relays
and circuit breakers.
In Modern substation the following function of protection, control, monitoring and operation are
performed by the devices in the control room automatically or semiautomatic ally i.e. with the
assistance of human supervision and intervention.
The purpose of PROTECTION is to minimize the adverse effects of faults on a power system.
It is important to keep in mind the following points:
a. Each System element must have its own protection
b. Each protection must have a back-up
c. Protection zones must overlap
d. No single failure shall leave a system element unprotected
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Figure2.10–JIMMA substation control room
2.3.2 Distribution
The Work Flow Structure of distribution
First data should be collected from the existing LV network from the costumer side; the engineers
use the data as an input to their Digitalize and insert it to the software AUTOCAD.
The Work flow structure in plan & design case team starts from the south western (JIMMA) region
distribution System.
Power distribution is intended to control medium voltage network and low voltage network and
mainly on designing of low voltage, rehabilitation and construction of new line. But from all this
We work on the designing of the medium voltage line diagram of JIMMA city feeder, starting from
the five outgoing feeder of substation from out of seven that is utilized by JIMMA and sub areas.
The distribution system also consists of a network of overhead lines and underground cables by
which the power is distributed to the ultimate users of electricity, the line is shorter than
transmission line, and carry smaller amount of power when we compared with long transmission
line.
The electrical distribution network has been classified in to two basic categories: these are:
 Medium voltage (MV) network
 Low voltage (LV) network
2.3.2.1 Medium voltage networks
Medium voltage network is the voltage level which exists between power substation output and
distribution transformer input. JIMMA distribution level can be divided in to two major groups.
A, 33000V:-this is used to round the JIMMA Town.
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B, 15000V:-this is used for JIMMA town.
Where voltage is the measure unit of voltage that means 33kv and 15kv medium voltage lines are
found between power substation and power transformer.
sAccording to voltage level the material we use to construct the network is different in most cases
however sometimes we use the same material for both voltage level lines.
For example, we can use the conductor size the same high rupture capacity fuse (HRC fuse) but
never use the same transformer, surge arrestor in both type.
If we can see the transformer for 33kv line is 33kv/0.4 type this means the incoming power (input) is
33kv and the output is 0.4kv.
On the other hand for 15kv line we use 15000v/400v type, this means the input is 15000v and the
output is 400v.
2.3.2.2 Distribution transformer
A distribution transformer is a device for transferring energy in an AC system from one circuit to
another.
Transformer sizes vary depending on the application and the number of customer and also the types
of institution used that transformer, so that totally the distribution transformer can classified as
follows:
a) 25kv transformer
b) 50kv transformer
c) 100kv transformer
d) 200kv transformer
e) 315kv transformer
Equipment of distribution network
1.Dropout fuse: the melting of fuse causes dropping of fuse element under gravity about its lower
hinged support. There by additional isolation is obtained such fuses are used for protection of
our-door transformers when the linesman observes operation of the fuse.
2.Arrester: - it is used to protect the lightning.
3.Insulator:-it used to insulation for safety.
4.HRC fuse: - is high rupturing capacity cartridge fuse and used for over current for over current
protection of low voltage and high voltage circuit. And etc.
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INSULATOR
ARRESTER
DROUPOUT FUSE
OIL TANKER
FEEDER CABLE
HRC FUSE
Figure2.11. 200kv transformer
2.4 Tasks that we have been executing
In the first few days of the first month our internship program, it was all about getting lectures and
being introduced to the working system and the materials they utilize. As we have already
mentioned, for the last 2- months we were working in the distribution systems Construction and
design case team. The job of the case team starts at point where the voltage is transformed to 15KV
line. The main objective our team was to design and build a reliable distribution network in the city.
To help us achieve these, we used to utilize an engineer’s guide manual for LV network
rehabilitation design process, but most of the networks that were constructed earlier were not
designed in accordance with the manual. For these reason, most of the networks are not reliable and
need re design. Our first task was the rehabilitation and re-design of the network of a 3- phase,
200KVA, 100KVA Transformer after a voltage drop has been tested. This voltage drop is generally
caused by power shortage. But, the important question what should be asking is, what are the causes
for the power shortage? And to answer this question correctly, you need to pay a visit and collect
data’s that would be very important to answer the question correctly, from the location where the
drop has been tested. Among the data’s that are collected, the most important are
1. The phase (R, S and T) the consumer is using and
2. Average energy consumption.
3. The customer’s specific location in the city`s master plan
4. Energy meter contract number
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5. Distance from load center
After data collection, the data is fed to software known as VISIO which is used to digitalized
distribution networks. Then it design distribution network. This software has its own data base
where all the data’s are stored.
After the collection and feeding of the data, we noticed there were two main causes for the power
shortage, namely phase over load & the fact that the transformer’s network covered beyond its
capacity (Distance from load center). This meant that there were so many customers utilizing a
single transformer. When these works over, we started the design work. The new plan/design is
done on the VISO software.
During the design work we were always working as team, discussing and sharing ideas. At the start
of the 3rd month, we wanted to go the substation. We started working that was working on the power
substation. By the time we started working with substation; in power substation system is to receive
the power from power generation and to give the power to distribution. Mainly we worked to control
and protection area of the fault. The faults are over current, earth fault, differential fault, etc. and at
the fourth month , we try to find the exact problem of the customer by preparing a question paper,
so that from the question paper we collect data’s that’s related to the cause for interruption that used
for us to identify the problem in JIMMA city then after collecting the data’s we tried to classify the
overall as a cause of interruption, and from the question paper that was given for the workers we
found many causes for interruption, but the types of cause and interruption that is collected from the
workers is stated below:
1. Unknown: customer interruption with no apparent cause.
2. Scheduled outage : customer interruption due to the disconnection at selected time for the
purpose maintenance
3. Tree contact: customer interruption caused by faults due to the tree limbs contacting
energized circuit.
4. Lightning : due to lightning striking the distribution system
5. Equipment failure : due to deterioration from age, incorrect maintenance
6. Adverse weather: due to heavy wind rain, ice, storms and etc...
7. Human element: customer interruption due to the interference of the utility staff in the
system.
8. Foreign interference: customer interruption beyond the control of the utility such as bird,
animals, vehicles and foreign object.
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9. Over load : customer interruption due to high loaded condition
10. Car accident: due to the collision of cars to the lines.
11. Loss of supply : customer interruption due to the problem in the bulk electricity supply
system
By giving this information to the workers they give us different types of rank from out of 11 by their
own assumption, which cause is mostly or repeatedly happening in JIMMA city feeder this means
that the workers doesn’t have the same assumption about the fault happened on the customer side so
due to that all of them doesn’t have an equal and rational decision on the fault so that finally by
collecting this paper we organized it on a table like below
Table 2.1. Collected data the rank and number of workers give the rank
Cause
of 1
2
3
4
5
6
7
8
9
10
11
interruption
Overload
8
1
3
1
-
-
-
-
-
-
-
Tree contact
-
4
1
3
1
3
-
-
-
-
2
External
-
-
-
-
-
-
-
-
3
3
-
2
-
3
2
-
-
3
1
-
-
-
Car accident 1
-
-
-
-
-
1
1
3
-
2
Human
-
-
3
1
-
-
-
2
-
-
-
of 2
-
1
-
1
3
-
-
2
-
-
-
5
1
2
2
-
-
-
-
-
-
-
-
-
-
1
1
-
1
1
2
1
-
-
--
-
-
1
2
-
-
3
2
force
Windy rain
interference
Failure
distribution
device
Substation
dis
connection
Human
error
Unknown
From the table we saw that overload is selected by 8 workers as number 1, substation disconnection
is more selected by the workers as number 2, tree contact is selected by the workers as number 3,
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and human interference is selected by the workers as number 4, heavy windy rain is selected by the
workers as number 5. Therefore from this information we finalize that overload is the mostly happen
interruption on the customer side at different location on different time.
2.5 Challenges faced
During the last 4- months of our internship experience, there were many every day challenges. But,
we will try to describe the major ones.
We can divide the challenges we have faced in to two main categories.
a. Academic challenges
b.Work area challenges
2.5.1. Academic challenges
As we already mentioned, we were working in EEU, JIMMA and the availability of reading
materials to Develop our knowledge in the working area was always a problem. The other internship
challenge falls on the awareness of the workers.
2.5.2. Work area challenges
During our internship program, there were so many work area challenges, but the scarcity budget
and materials for projects. But when you think about this issue deeply, you will understand it’s a
country wide issue and hence live with it somehow and we believe “Making the best out of what
you have” is the best solution to this particular issue.
Another challenge of the internship it lacks of equipment’s. As we have described above, one of our
work task is maintenance .We know that this task requires the use of necessary tools and
equipment’s. Hence our first duty becomes getting these necessary tools and equipment’s.
In our time with the distribution systems design and construction case team, while we were working
on data’s and designing distribution network Using DIGSILENT software, but we can make it
because we have some limitation on running the software
2.6 Measures taken to overcome the challenges
The measure we have taken in this internship program to overcome the challenges is creating an
awareness for workers starting from the guards about the internship program. The main challenge
we faced is vehicle service but we solved by contacting with the company and the company gives us
a vehicle for some LV network maintenance.
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CHAPTER 3
Overall benefit we gained from the internship
Internships is a method of making opportunity for students potentially valuable and explores general
career avenues as well as specific companies. Such arrangements can provide us with valuable work
experience (both practical and for resume enhancement) and an opportunity to line up a job before
graduation, In addition to securing good work experience.
Internship programs are also potentially valuable to company. Unfortunately, some companies
continue to regard interns as little more than a free source of labor to catch up on filing and other
tedious office tasks. But many business owners and managers realize that internship programs can
provide them with an early opportunity to gauge the talents of a new generation of workers and, in
many cases, sell themselves as a quality place for students to begin their careers after they graduate.
The major benefits that we get for the internship are classified and stated as below briefly.
3.1 Improving our Practical Skills
We gain practical experience of applying our engineering judgment and working successfully with
others.
However, the skills and qualities have a hope by studying Electrical engineering suit many other
professional settings equally well. We can offer:
a. Creativity and an innovative approach to solving problems;
b. The ability to analyze and interpret diverse, complex data;
c. Critical thinking and the ability to evaluate designs maintain and projects;
d. Effective assessment and management of risk, resources and time;
e. Highly developed numeracy and computer literacy;
f. Interpersonal sensitivity, persuasiveness and the ability to work as part of a team;
g. Clear written and oral communication skills;
We started learning from the first days of our internship to the day we finished our work and also
always something new to add on our previous background. To mention few,
1. We have learned how 3-phase (R, S and T) MV and LV lines construction.
2. We have learned how to design and rehabilitate distribution networks using specialized
software known as DIGSILENT that is used by distribution systems design and construction
case team.
3. we have also learned how to enter data to this software and how digitalizing
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4. We have learned how substation equipment operate and there advantages.
5. we have learned the overall transformation of power system from HV to LV
6. We have come to at appreciate the applications of DC source in power systems for protection
and control rooms. Without a DC source it’s even hard to walk in to a substation because all the
protections systems are all associated with DC sources.
7. we have also learned the application of instrument transformers (current transformer and
voltage transformers)
8. We have also understood the processes and the system flow from the transmission to
distribution.
We have tried to describe above most of the things we have developed regarding theoretical
knowledge and practical skills during our internship program. But the everyday experience and
knowledge you learn from the people that had been in the work area for a long time is hard to put in
words.
3.2 upgrading our theoretical knowledge
Internship program gives us the opportunity to apply our theoretical knowledge in real world
environments, In addition to the practical skill. Almost all the courses we took were focused on
theoretical part, thanks to this internship program; we are now able to upgrade our theoretical
knowledge by practice.
Generally speaking, our theoretical knowledge got strengthen more by those practical techniques
invested on Internship Company. they assists us in moving toward our career goals by combining
what we had learned from school, practical and supervised work experience; it thus explained the
necessity of every student to undergo this process.
3.3 Improving our interpersonal communication skills
In the company, we were working with all the staff members and any individual peacefully, by the
experience we have gained from our internship program. Individuals often learn different things
from colleagues through communication. For any individual, communication is an important way of
learning, which can be defined formally as the act, process, or experience of gaining knowledge or
skills.
Good communication is the life blood of the Electrical engineering profession. And it takes many
forms, such as speaking, writing and listening, it has the following advantages.
1. To handle information
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2. To persuade people
3. To improve relationships with others
We learnt that one full system should work efficiently with union of so many professional by
collaborating with each other in order to make good and fantastic work. We was able to improve
how to communicate colleagues and we greatly understand that interpersonal skill is the most
valuable quality in Electrical engineering department.
Finally, what we have observed was to communicate effectively, it is essential that you choose the
suitable medium.
3.4 Improving our team playing skills
Even if tasks are done individuals by the respective person at different section of the company, there
are times at which different individuals come together to work for common goals of the company
for increasing productivity. The most important point in team playing skill is just reaching an
agreement from different points on the work to be done.
Furthermore, to have a common understanding on the task that is to be accomplished, we always try
to listen carefully those individuals with whom we am working. After listening others idea, we
provide an idea which we think it is very constructive for the task being done.
Generally spiking a person with good team playing skill the following qualities
a. Demonstrates reliability
b. Communicates constructively
c. Listens actively
d. Functions as an active participant
e. Shares openly and willingly
f. Cooperates and helps others
g. Exhibits flexibility
h. Shows commitment to the team
i. Works as a problem-solver
j. Treats others in a respectful and supportive manner
3.5 Improving our leadership skills
Leadership is a process of leading the careers of the company. Problems in the company come in all
size, shape and color in different period time. Thus, a person who is in the position of leadership
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seeks optimal solution to problems and should be smart enough to manage those individuals whom
he/she is leading.
What we gain from the internship regarding improving leadership is that to inspire workers into
higher levels of teamwork, there are certain things must be known to do that, these are;
a. Know our and seek self-improvement
b. be technically proficient
c. Seek responsibility and take responsibility for actions
d. Make sound and timely decisions
e.
Know peoples and look out for their well-being
f.
Keep workers informed
g. Develop a sense of responsibility in workers
h. Ensure that tasks are understood, supervised, and accomplished
i. Finally what we grasp is, Becoming a leader isn’t easy because it takes a conscious
commitment and consistent effort to develop one’s leadership skills. But on the positive side,
anyone who is willing to make the effort can become a good leader.
3.6 work ethic related issues
In today’s complex world, Ethical conduct of workers is very important for developing healthy
working environment and increasing productivity.
Ethical work conduct enables us in order to posses’ appropriate behaviors in the work and so we
develop proper relationships with co-workers and it helps us to create good working environment.
There are two common types of ethics. These are
1.Personal ethics and
2.Professional ethics
3.6.1 Personal ethics
These principles of personal ethics are values which are expected to be possessed by all individuals
in their life, and contribute a lot for a smooth interaction among individuals and peaceful
coexistence of a society.
What we gained in the company principles of personal ethics include:
a. Concern for the well-being of others
b. Honesty
c. Compliant to the law
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3.6.2 Professional ethics
Professional ethics refers to the standards or a set of moral principles for regulating behaviors of a
certain defined profession. In order to consider that an activity to be a profession, it should be
carried out by one who has advanced education, knowledge, and skills. Professionals are capable of
making judgments, applying their skills & reaching informed decisions in situations that the general
public cannot, because they have not received the relevant training.
The following are some of the common professional ethical principles what we gained in the
internship period.
1) Punctuality- means keeping the companies work beginning and ending time and to complete a
given task within the given period. That was challenging to become punctual for the 1st days of
work.
2) Office disciplines- in work place you don’t have to disturb the working atmosphere. For
example abstain from opening loud voice, loud music, songs and things which disturb other
workers’ working mood.
3) Reliability- The worker should be qualified for the part he is supposed to be performing.
He/she must have appropriate skill and knowledge for the task assigned.
4) Honesty- Regarding this value each worker regardless of its status should abstain from bad
behaviors such as cheating, bias, corruption etc.
5) Cooperation- Each worker should interact and cooperate with each other while working. That
is because it is through such system problems could be easily solved.
3.7 Entrepreneurship skills
Participating in an internship allows us to gain a better perspective of post-graduation employment
by applying the principles and theories we have developed in the classroom. This practical
application creates an easier transition for us from the classroom to the working world.
While participating in this internship we realize that creativity and problem solving is one of the
starting points of entrepreneurs.
This internship motivates us not to be employee because it enables us to know more about our
career, the real challenges, and way of business establishment in this profession.
To be a good entrepreneur, you must have the following abilities/skills
1.Risk management
2.Self confidence
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CHAPTER FOUR
Contribution to the company
4.1 The task we performed for the company
From the problems listed and due to the offer of the company we choose one of the problem which
is the main problem and hard to point out where and at what transformer rating the fault is
happened, therefore we are tried to classify the overall problem as an interruption, but from the
problem of the company we try to make something that can be worked out on real world so we
choose a title of problem that is no well-organized line diagram of the city, then from this problem
The solution that we tried to solve is started asking a of the engineers and technicians which had a
long term working period in the company which can help us to find and work the more organized
line diagram, then the reason why we select this project is, because of the company doesn’t have an
organized line diagram due to this lack of information they were face some problems like : no
recorded information about transformers and how much loading that transformer takes and etc…,so
that we solve this problem by proposing and preparing a well-organized line diagram of the city
feeder including the rating and the area of the transformer and the length between two poles,
therefore this work is done by gathering information from JIMMA substation feeders to the end of
the city for two weeks then finally we draw the line diagram of JIMMA city feeder by using a
software called VISO.
4.2 Design steps in power distribution network
1, Data collecting
2, Data digitalizing
3, Designing
DATA COLLECTING
the data collection method is very difficult because the data is collect from transformer to
transformer so you have to cover the whole transformer that is utilizing by the city feeder and on the
data collecting system we try to record all of the information that can be seen easily and we contact
with the company for the data’s that can’t be seen by us like; the rating of the transformer and etc.
then from the data we collected we try to list the data’s like this as follows:
1. Types of transformer (100kva, 200kva, 315kva)
2. Types of poles (wood, concrete, steel)
3. Strength of transformer (good, satisfaction, poor)
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4. Pole strength (good, satisfaction, poor)
5. Phase code (3Ø, 2Ø, 1Ø)
6. Strength of insulator
7. Customer breaker contract number
8. Pole with street (yes or no)
4.2.1 Design of low voltage network
In JIMMA power distribution there is so many problems in distribution network. The major causes
are transformer over load and windy rainfall. In this case the engineers Work on the design of
medium voltage network and LV network. This work shall support the effective process of planning
the medium voltage networks in the project areas. This report include a number of tables giving the
necessary information for engineers to make a quick selection of equipment and material for the low
and medium voltage network design. Then use this report for final decision.
Designing Depends up on
1. Capacity of transformer
2. Distance from load center
3. Number of customer
4. Type and size of conductor
5. HRC fuse
6. Number of feeders of transformer
7. Types of ABC cables and etc..
The design is depend on the following selection of material to use different table. All selection
of material depends on capacity of transformer and selection of cables.
4.2.1.1 Selection of transformer
The table below will help the engineer to make a quick decision of what size the transformer of the
planned network should have. The selection of transformer depends on the following criteria.
1.1 Selection Of Transformer By Load Criteria
The transformer is affected by load the transformer. Mostly the transformer is damaged in the case
of unbalanced load. [1]
The load criteria is the following table use
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Table4.1 selection transformer by load criteria
Transformer capacity
Present peak load
Saturated area
Growing area
(KVA)
(KW)
(KW)
100
0-63
0-41
200
64-126
42-82
315
127-198
83-129
1.2 Selection Of Transformers By Numbers Of Customers Connected To The
Transformer
Table4.2. selection transformer by no. of customer
Transformer capacity Maximum number of customer at present
Saturated areas
Growing areas
(KVA)
(NO.)
(NO.)
100
120
80
200
250
160
315
390
260
1.3 Selection Of transformers By Maximum Distance To Customer From
Transformer
Table4.3. selection transformer by maximum distance
Transformer
Maximum
distance
capacity
from the transformer
(KVA)
(m)
100
200
200
290
315
360
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4.2.1.2 Selection of Fuse Rating
Selection of fuse ratings depending on transformer size and number of feeders. Mostly the fuse
rating is less than transformer rating
Table4.4. selection transformer by fuse rate
Transformer capacity Selection of Fuse ratings
One(1) feeders
Two(2)feeders
Three(3)feeders
(KVA)
(A)
(A)
(A)
100
160
63-100
-
200
-
100-200
100-160
315
-
160-300
100-300
4.2.1.3 Selection of Feeders Cables and Conductors
The feeder cables and conductor sizes shall be selected in accordance with this table. the Selection
of feeder cables and conductor sizes is varying from country to country due to different factors and
the type of trans former and the standard that the country [1] used for installation of distribution
transformers, so that in mean time in our country the standard of selecting of feeder cables and
conductors is selected by the following table below;
Table4.5. selection transformer by feeder cable
Transformer capacity
Selection of feeder cables and conductor cross section
Number
Feeders
Main lines
Branch lines
Short branch lines
Of feeders
cables
(KVA)
(No.)
(mm2)
(mm2)
100
1-2
3x70/35
ABC50(3P) ABC25(3P)
ABC25(1P)
200
2-3
3X120/70 ABC95(3P) ABC50(3P)
ABC25(1P)
with small loads
(mm2)
(mm2)
ABC25(3P)
315
2-3
3X120/70 ABC95(3P) ABC50(3P)
ABC25(1P)
ABC25(3P)
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4.2.1.4 Selection of Service Drops Conductors
The conductor sizes for the service drops shall be selected in accordance with this table. Because of
most of the Ethiopian standard service drop conductors are selected by the maintainace engineers
are the stated below by their types, so it’s better to select this materials.
Selection of the ABC cables for service drops.
Table4.6.selection transformer by service drop conductor
Transformer capacity
Selection of service drop conductors
ABC-cables
for
service Remark
drops
(cross section in mm2)
Single phase load
Three phase load
10
Selection is depending on the
16
load
10
Selection is depending on the
16
load
25
4.2.1.5 Types of cables used for construction of overhead lines
Cable means the conducting material is covered by insulated material and Wire means any
conductor material. There uses different cable with different voltage label. There are two types of
cable
1. ABC :-Arial bundled cable
Types of ABC cables according to cross-section of conductor
a. ABC 25
b. ABC 50
c. ABC 95
CONDUCTORS
a. Two types of twisted overhead cable is available, one with the neutral conductors made of Alalloy used as a messenger, one with four or two self-supporting Al-conductor of equal crosssection area. Both types can be used but we recommend the self-supporting type because it has a
higher tensile strength and is easier to install.
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b.The cross-section of the conductors shall be 95 or 50 mm2 for feeder’s cables and 25mm2 for
service cables.
c. The conductors of the cables shall be made of stranded aluminum wires. The cross-section shall
be circular.
Table4.7. cable Current carrying capacity
Cross-sectional area
Continuous rating
Short times rating
A
KA
Mm2
25
71
1.24
50
111
2.47
95
174
4.69
2. AAC:-All Aluminium conductors are not covered by any insulation types. In this time mostly
used to medium voltage network.
Application
this all aluminum conductor is a kind of aluminum product made through stranding aluminum wires.
It is used for the electricity distribution lines with short span length and small load-carrying
capability of the pole. The AAC provides reliable performance for overhead power transmission and
distribution lines. This standard covers hard drawn circular aluminum wires for electric purposes to
be used as component wires of hard drawn aluminum stranded cables and aluminum conductor steel
reinforced.
Equipment used for overhead electric lines construction is:
a) Poles
b) Insulation cup
c) Hook
d) Stays
Poles of electric power in power distribution
The Pole is electrically conductive and must be earthed either by separate earth electrode or by
longitudinal earth conductor.
The power distribution network poles are three types according to made of materials. These are
1) Wood poles
2) Steel poles
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3) Concrete poles
The power distribution the pole mounted is different to different depends on soil types. The space of
pole mounted is 30 meters.
In power distribution network there is two types of poles according to uses. These are
1, low-tension poles (LV)
2, high-tension poles (MV)
Low-tension poles
The low tension poles are poles which carry the low voltage network cable (220v or 380v). The
length of low-tension poles slightly shorter than the high-tension poles. The lengths of these poles
are
i.
8 meter
ii. 9 meter
The length of the poles in to the earth is different in different length these are
In 8meter pole is undergrounded 1.20meter and
In 9meter pole is undergrounded 1.30meter
High-tension poles
The high tension poles is it carry the medium voltage network cable (15kv or 33kv). The length of
the high tension poles are
i.
10 meter
ii.
11 meter
iii.
12 meters
Undergrounded of the poles length is different in different length these are
In 10meter pole is undergrounded 1.40meter and
In 11meter pole is undergrounded 1.50meter
In12meter pole is undergrounded 1.60meter
4.3 Simulation Line diagram of city feeder by Visio software
The overall design of the work is done by the VISO software which include the number of
transformer, distances between the poles and the rating of the transformers, the drawing is taken us a
problem solving for the utility because the company is facing different things like no well-organized
line diagram and they didn’t know where the transformer is located at the city so, due to that we
described above the drawing is drawn with the period of one week after the collecting of the data’s
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by going foot to foot to every transformer and every MV line poles, therefore it was so hard to
count and know the rating of every transformer cause they don’t have a recent data’s about the new
installed transformers in the city, so that depend on the data’s we collected finally we try to draw by
free hand sketching before feeding to the software and after that you see from the diagram the
distance of the poles different from the first some kilometers , finally the overall design of the
JIMMA city feeder is drawn below:
Fig 4.1. Line diagram of city feeder
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4.4 Result and discussion
The total number of the transformer found from the above line diagram is 59 and the total number of
kilometer that the city feeder taken excluding the DEDO road is 18.55km and the total number of
MV poles us per counted its around 346 poles, so that from this data we saw the transformer
location is not customer centered due to that few individual transformer is much loaded than others,
additionally the overall transformer installation is poor, so that the company should re consider
about replacement of the LA, dropout fuse, boxes, HRC fuse
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CHAPTER FIVE
Project: Reduction of voltage unbalance by using voltage regulator
5.1 Abstract
This paper endeavors to present a comprehensive summary of the causes and effects of voltage
unbalance, definitions and mitigation techniques by using a linear voltage regulator. Several causes
of voltage unbalance on the power system and in industrial facilities are presented as well as the
resulting adverse effects on the system and on equipment such as induction motors and power
electronic converters and drives. Standards addressing voltage unbalance are discussed and clarified,
and several mitigation techniques are suggested to correct voltage unbalance problems. This paper
makes apparent the importance of identifying potential unbalance problems for the benefit of both
the utility and customer.
5.2 Introduction
In three phase power systems the generated voltages are sinusoidal and equal in magnitude, with the
individual phases 1200 apart. However, the resulting power system voltages at the distribution end
and the point of utilization can be unbalanced for several reasons. The nature of the unbalance
includes unequal voltage magnitudes at the fundamental system frequency (under-voltages and overvoltages), fundamental phase angle deviation, and unequal levels of harmonic distortion between the
phases. A major cause of voltage unbalance is the uneven distribution of single-phase loads that can
be continuously changing across a three-phase power system [2]. Example problem areas can be
rural electric power systems with long distribution lines, as well as large urban power systems where
heavy single-phase demands, such as lighting loads, are imposed by large commercial facilities,
.Single-phase traction and electric transit and railroad systems can also cause considerable
unbalance on the utility three-phase system unless proper design steps are taken .Additional causes
of power system voltage unbalance can be asymmetrical transformer winding impedances,
asymmetrical transmission impedances possibly caused by incomplete transposition of transmission
lines, and blown fuses on three-phase capacitor banks. Industrial and commercial facilities may have
well balanced incoming supply voltages, but unbalance can develop within the building from its
own single-phase power requirements if the loads are not uniformly spread among the three phases.
Within a user facility, unbalanced voltages can also be caused by unbalanced and overloaded
equipment, and high impedance connections (e.g., bad or loose contacts). [7] A number of methods
can improve voltage regulation. Some use voltage regulation equipment to raise or lower voltage at
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the substation or on the distribution circuit to reduce the voltage Difference between LL and heavyload conditions. Others reduce the impedance of the circuit to reduce the voltage difference or
spread, and still others reduce the load current (i.e. Improve the power factor) to reduce the voltage
drop and, thus, the voltage spread.
5.3 The problem identified
In our internship program from the starting day up to the day we finished our work we have been
seen different problems that has been a very un solvable by the company for the past years but due
to the reason of our work on collecting of data’s for MV network we were seeing different problem
mentioned below :

Transformer is not centered on the customer side

Voltage Unbalance 1∅ and 3∅ network

Phase Unbalance 1∅ and 3∅ network

poor protection at LV side(on the box)

poor LA connection

poor over all transformer installation
5.4 Objective
5.4.1 General objective

The main objective is to propose a solution for Voltage Unbalance 1∅ and 3∅
network
5.4.2 Specific objective

To design and know the percentage of voltage regulation

To mitigate the voltage drop by using a voltage regulator

To calculate the load current of the JIMMA city feeder

To know the receiving end voltage of JIMMA city feeder
5.5 Literature review
Voltage regulation is an important subject in electrical distribution engineering. It is the utilities’
responsibility to keep the customer voltage within specified tolerances. The performance of a
distribution system and quality of the service provided are not only measured in terms of frequency
of interruption but in the maintenance of satisfactory voltage levels at the customers’ premises.
According to GONEN 1, a high steady-state voltage can reduce light bulb life and reduce the life of
electronic devices. On the other hand, a low steady-state voltage leads to low illumination levels,
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shirking of television pictures, slow heating of heating devices, motor starting problems, and
overheating in motors. However, most equipment and appliances operate satisfactorily over some
‘reasonable’ range of voltages; hence, certain tolerances are allowable at the customer’s end. Thus,
it is common practice among utilities to stay within preferred voltage levels and ranges of variations
for satisfactory operation of apparatus as set by various standards such as ANSI (American National
Standard Institution). For example, power acceptability curves given by IEEE indicate that steadystate voltage regulations should be within+6% to−9% for satisfactory operation of various electrical
devices [5]. Voltage regulation calculations depend on the power flow solutions of a system. Most
of the electrical loads of a power system are connected to low voltage/medium-voltage distribution
systems rather than to a high-voltage transmission system. The loads connected to the distribution
system are certainly voltage dependent; thus, these types of load characteristics should be
considered in load flow studies to get accurate results and to avoid costly errors in the analysis of the
system. For example, in voltage regulation improvement studies, possible under- or overcompensation can be avoided if more accurate results of load flow solutions are available, as
demonstrated in this paper. However, most conventional load flows use a constant power load
model, which assumes that active and reactive powers are independent of voltage changes. In
reality, constant power load models are highly questionable in distribution systems, as most nodes
are not voltage controlled; therefore, it is very important to consider better load models in these
types of load flow problems .[5]
5.6 Methodology
The method that we were trying to solve the identified problem is by collecting a data from
transformers of the city and the line of the MV network, LV network and also by asking the
customer what is the main fault or interruption happen on the customer side, By giving the
information to the workers they give us different information by their own assumption, which cause
is mostly or repeatedly happening in JIMMA city feeder this means that the workers doesn’t have
the same assumption about the fault happened on the customer side so due to that all of them doesn’t
have an equal and rational decision on the fault so that finally by collecting the evidence we decide
that overload is the main cause of interruption which is related to voltage unbalance.
5.7 The basic linear regulator
A linear regulator operates by using a voltage controlled current source to force a fixed voltage to
appear at the regulator output terminal. The control circuitry must monitor or sense the output
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voltage, and adjust the current source (as required by the load) to hold the output voltage at the
desired value. The design limit of the current source defines the maximum load current the regulator
source and still maintain regulation.
The output voltage is controlled using a feedback loop. Which requires some type of compensation
to assure loop stability. Most linear regulation have built-in compensation and are completely stable
without external components. Another characteristics of any linear regulator is that it requires a
finite amount of time to correct the output voltage after a change in load current demand.
Fig 4.1 linear regulator functional diagram
5.8 Design
In a circuit, a current needed to be lower in order to keep the voltage drop within permissible values.
So we try to identify The high voltage circuit which should be carried as far as possible, so that the
secondary circuit have small voltage drop this paper is intended to design a VR stated below;
Calculation design of % of voltage regulation of distribution line; to Calculate voltage drop and %
voltage regulation at tail end of following 15kv distribution system of the city feeder taken rating of
materials are capacity of ACSR System have ACSR Conductor (AI 6/4.72, GI7/1.57) with the
following constant of the conductor current is = 205Amp, Resistance=0.2792ohm and
reactance=0ohm, permissible limit of % voltage regulation at tail end is 6%. [2][5]
As stated from the design of line diagram let’s take one transformer that is from substation to final
load, so that the under stated calculation is based on the single diagram of the city feeder,
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Load 5000kw
JIMMA substation
JIMMA city
15kv line
18.55km
point A
Fig 5.3 simple diagram from JS to JC.
From the above simple diagram we try to calculate the voltage drop, where, voltage drop is used to
control the voltage level for the consumers, we have to consider the voltage drop in the line of the
system. All electrical lines have certain impedance that cause a difference between the sending and
receiving end voltage. [6]

Voltage drop
Load current (I) = P/√3V cos∅
Where,
I = line current in amper
P = real power, in kW
V = voltage, in kV
∅ = phase angle between voltage and current
Load current at point A (I)=5000/1.732x15000x0.8=240.6amp
Required no of conductor/phase = 240.6/205 = 1.174 = 1
Distance from source = 18.55km
Voltage drop at the load = ((√3 x (Rcos∅+Xsin∅) x I)/ (no of conductor/phase)) x 1000) x length
Voltage drop at the load = ((√3 x (0.2792x0.8+0x0.6)/ (1 x 1000)) x 18550 = 7.2
Receiving end voltage = sending end voltage – voltage drop = 15000 – 7.2= 14992.824
%voltage regulation at the load= sending end voltage –receiving end volt/receiving end volt) x 100
%voltage regulation at the load = ((15000-14992.824)/14992.824) x 100 = 0.049 %
The voltage variations in 33 kV and 15kV feeders should not exceed the following limits at the
farthest end under peak load conditions and normal system operation regime.

Up to 33kV (-) 9.0% to (+) 6.0%.[6]
So that our design is regulated at this rate, this shows as the JIMMA city voltage drop is good but
not better when we compare with other countries.
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5.9 Result and discussion
The proposed solution is depends on the problem identified on the above topic, so that the solutions
for the stated problems is listed with precise description as follows.
 The transformer that is installed on the customer side should consider many things such as
the number of customer that the given transformer takes due to that the transformer should
place on the center of the customer side.
 The phase unbalance is mitigated by the method of automatic phase balance system or by the
period of installation of LV line. The technician should consider the phase unbalance to
reduce phase unbalance.
 Voltage unbalance is mostly happened cause that is the main cause for burning of materials
and machines, so that to mitigate this problem it’s better to use a voltage regulator.
 The transformer is mostly damaged due to the lack of installation on the boxes that is: the
HRC fuses are not installed properly, so the solution is the HRC fuse with the number of
boxes should increase for the better protection of the transformer.
 Poor LA connection is happened on the period of installation or some factors, so that the LA
should shorted together and transformer body grounded to the earth.
 The overall transformer installation is take many bodies like the company which made a
transformer and also at the time of installation the technician have to careful and know
ledged about the thing about what they are doing.
from the stated problem we choose The effects of voltage unbalance that can result in
adverse effects on equipment and on the power system, which is intensified by the fact that a
small unbalance in the phase voltages can cause a disproportionately larger unbalance in the
phase currents .Under unbalanced conditions, the power system will incurs more losses and
heating effects, and be less stable because when the phases are balanced, the system is in a
better position to respond to emergency load transfers The effect of voltage unbalance can
also be severe on equipment such as induction motors ,power electronic converters and
adjustable speed drives (ASDs), so that finally to reduce voltage un balance we use a linear
voltage regulator as a better solution.
Generally we decide that, when the voltage unbalance is happened the linear voltage regulator sense
the output voltage and back to the feedback to sense the current source and regulate it, but if the
voltage unbalance not happened directly operate like before normally.
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CHAPTER SIX
Conclusions and recommendations
6.1. Conclusion
Internship training should be given for every student perusing professional degree because the
ultimate goal of every student is to get a training and develop our practical ability. The internship
teaches us a lot of things. The internship helps us to know what kind of work an engineer of specific
branch plays in a company. It helps us to get an opportunity of working in groups of qualified
people and teaches us about company ethics. In EEPCO, a day to day activity is to fulfill customer’s
electric power need, so it is important designing the distribution networks. Including power
substation up grading and increasing in number .The improvement of the substation mainly done in
different way to distribution networks. Planning and design of the network is the way of reducing
power losses and the way of satisfying customers need. In this case we worked the new plan of the
MV distribution network which is the line diagram of city feeder. Generally, the knowledge we have
grabbed and the experiences we have developed are so immense and the improvement in personal
skills like team playing ability, communication skill and ethics that we have learned during our time
as an intern student is so priceless. The interesting thing about our time as an intern is that we had
the ultimate fun and joy achieving our goals.
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6.2. Recommendation
First of all we would like to recommend the company about the awareness of the internship program
to students that is the necessity requirements are not full filled like pocket money, vehicle services
for project transportation and etc. The other thing that we got to recommend is on the resource
management of the company. The company does not have the required maintenance for the devices.
When a given device faces a fault it is completely thrown away and replaced by a new one. What we
would like to recommend is that the company should have its own workshop for proper maintenance
of this devices mainly transformer maintenance. In doing so the company would save the cost that is
incurred for buying new devices. Since internet access has become one the main office needs
nowadays, we would like to recommend for a better internet access for the employees so that they
can always update their knowledge and information at all times.
Finally we would like to recommend for our institute JIMMA institute of technology, the thing that
we would like to recommend is the working area that we choose is changed at the final day so due to
that we were facing different problems, so it have to be more organized before it’s too late like us,
like by preparing suitable place and receiving confirmation paper for the student.
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Reference
[1]. Mr. Bikila Wakjira, Mr. Eyasu Berhanu, and Mr. Wondmu Astatke; they are Engineers that
works in EEU at JIMMA utility, interview (2016-10-10 up to 2017-1-30).
[2] .Electrical Distribution System Protection. 3rd edition. Pewaukee, WI: Cooper Power.
Cooper
[3].Power Systems Bulletin 90020 February 2005.Available at www.cooperpower.com.
http://www.eepco.gov.et.com “Facts of EEPCO in brief 2015/16”
[4]. Ethiopia Electric Power Corporation. (2016, January). http://www.eepco.gov.et.com “Facts
Of EEPCO in brief 2016/17.
[5]. International Journal of Electrical Engineering Education October 2000
DOI: 10.7227/IJEEE.37.4.8 Source:
[6]. Welch, lee E. (2004) taking control of voltage drop and reactive power primedia
Magazines and media inc.
[7]. B. B. Banerjee is with Electric Power Research Institute, Power Electronics,
Energy Delivery, Palo Alto, CA 94304.
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