NEKEMTE SUBSTSTION
WOLLEGA UNIVERSITY
COLLEGE OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
INTERNSHIP TRAINING
In
NEKEMTE SUBSTATION
By
NAME
IDNO
SIGNATURE
FENTA FAYERA…… WU001526
WOLLEGA UNIVERSITY INTERNSHIP REPORT ECE
2021 GC
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NEKEMTE SUBSTSTION
July 2021
Nekemte, Ethiopia
DECLARATION
This is to certify that the project report entitled Nekemte Substation being submitted by us
under the supervision and guidance of Mrs.Darartu Akalu.
In partial fulfillment for the award of the Degree Bachelor of science in Electrical
Engineering to Wollega University is a record of bonafied work carried out under our
guidance and supervision.
The result embodied in this project report has not been submitted to any other University or
Institute for award of any degree.
Interns Name
Fenta Feyera
Id.No.
WU001526.
Signature
___________
Temesgen Tasisa
WU002047.
___________
Chalchisa Ayele
WU001351.
___________
Motuma Tashome
WU001870.
___________
Approved By:
Advisor name:
Signature
Date
Mrs.Derartu Akalu
___________
___________
Head of department
Mr.Yohanis Bekuma
Signature
___________
WOLLEGA UNIVERSITY INTERNSHIP REPORT ECE
Date
___________
2021 GC
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NEKEMTE SUBSTSTION
ACKNOWLEDGEMENT
First of all we would like to say thank to Almighty God who bestowed his blessings upon us.
We would like to offer our deepest gratitude to Wollega University College of Engineering
and Technology, for providing this opportunity in our field of study.
Thirdly we would also like to express my heartfelt gratitude to Advisor Mrs.Derartu Akalu,
Mr.Girma Workineh work site supervisor in Nekemte substation for his kind help and we
have special thanks to Nekemte substation with all its employees.
Finally our whole hearted gratitude to our parents for their constant encouragement, love,
wishes and supports us. They all have shared their own remarkable and important knowledge
to our eye opening experience.
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TABLE OF CONTENTS
DECLARATION ....................................................................................................................... i
ACKNOWLEDGEMENT ........................................................................................................ ii
TABLE OF CONTENTS ......................................................................................................... iii
LIST OF FIGURE.................................................................................................................... vi
ACRONYMS .......................................................................................................................... vii
ABSTRACT ........................................................................................................................... viii
CHAPTER ONE ....................................................................................................................... 1
INTRODUCTION .................................................................................................................... 1
1.1 Overview of Ethiopian Electric Power Corporation (EEPCO) ...................................... 1
1.2 Background of Nekemte Substation ............................................................................... 1
1.3 Vision and Mission of EEPCO ...................................................................................... 2
1.3.1 Vision of EEPCO .................................................................................................... 2
1.3.2 Mission of the EEPCO ............................................................................................ 2
1.4 Objectives of EEPCO ..................................................................................................... 3
1.4.1 General objective..................................................................................................... 3
1.4.2 Specific objective .................................................................................................... 3
1.5 Main Products and Service ............................................................................................. 3
1.6 Main Costumer............................................................................................................... 3
1.7 Organization Work Flow ............................................................................................... 4
1.8 Generalization of Substation Single line Diagram......................................................... 4
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1.9 Block Diagram of Nekemte Substation ......................................................................... 5
CHAPTER TWO ...................................................................................................................... 6
OVER ALL INTERNSHIP EXPERIENCE ............................................................................. 6
2.1 The way to get the company .......................................................................................... 6
2.2 The Section of the Company we have working ............................................................. 6
2.3 Definition of Substation ................................................................................................. 6
2.3.1 Types of substation ................................................................................................. 6
2.4 Main objective of major substation in the transmission and distribution ...................... 7
2.5 Function of Substation ................................................................................................... 8
2.6 Equipment found in Nekemte substation (outdoor) and there function ......................... 8
2.7 Some of their function ................................................................................................... 9
2.7.1 Lightening arrestor .................................................................................................. 9
2.7.2 Capacitor voltage transformer (CVT) ................................................................... 10
2.7.3 Insulator ................................................................................................................ 10
2.7.4 Isolator .................................................................................................................. 11
2.7.5 Types of communication in Nekemte Substation ................................................. 12
2.7.6 Circuit Breaker ...................................................................................................... 12
2.8 Transformer .................................................................................................................. 13
2.8.1 Power Transformer ............................................................................................... 13
2.9 Transformer Components and functions ...................................................................... 14
2.9.1 Conservator ........................................................................................................... 14
2.9.2 Temperature Indicators ......................................................................................... 14
2.9.3 Level Gauges ........................................................................................................ 14
2.9.4 Vacuum valve ....................................................................................................... 15
2.9.5 Radiator ................................................................................................................. 15
2.9.6 Tap changer ........................................................................................................... 15
2.10 Transformer Insulating Oil ......................................................................................... 15
2.11 Earthing Transformer ................................................................................................. 16
2.12 Instrument Transformer ............................................................................................. 16
2.13 Auxiliary Transformer ............................................................................................... 18
2.14 Parts of transformer protection .................................................................................. 19
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2.15 The Control Room and its Electrical Components in the Substation ........................ 20
2.15.1 Control Room...................................................................................................... 20
2.15.2 DC 125V Main distribution board ...................................................................... 22
2.15.3 Metering Panel .................................................................................................... 22
2.16 Control and protection Panel ...................................................................................... 22
2.16.1 Protection Panel................................................................................................... 23
2.17 Electrical Transmission Tower Types and Design ..................................................... 24
2.17.1 Definition of Electrical Tower ............................................................................ 24
2.17.2 Parts of power transmission Tower ..................................................................... 25
CHAPTER THREE ................................................................................................................ 26
THE WORK TASK WE HAVE BEEN EXECUTING AND CHALLENGES FACED
DURING INTERNSHIP ......................................................................................................... 26
3.1 The Work Task We Have Been Executing ....................................................................... 26
3.2 The procedures we have been using while performing our work tasks ....................... 26
3.3 Power Interruption (Outage) ........................................................................................ 27
3.3.1 Types of power outage (interruption) ................................................................... 28
3.3.2 Fault Analysis ....................................................................................................... 28
3.3.3 Types of faults....................................................................................................... 28
CHAPTER FOUR ................................................................................................................... 29
OVERALL BENEFIT WE GAINED FROM THE INTERNSHIP ....................................... 29
4.1 Improving our practical skill ........................................................................................ 29
4.2 In terms of theoretical knowledge................................................................................ 29
4.3 In improving our interpersonal communication skill................................................... 29
4.4 In terms of improving our leadership skill ................................................................... 29
4.5 The knowledge gained during internship program ...................................................... 30
4.6 Improving team work skill ........................................................................................... 30
4.7 In terms of understanding about work ethics and related issues .................................. 30
4.8 In terms of entrepreneurship skill ................................................................................ 30
CHAPTER FIVE .................................................................................................................... 31
CONCLUSION AND RECOMMENDATION ...................................................................... 31
5.1 Conclusion ................................................................................................................... 31
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5.2 Recommendation ......................................................................................................... 32
REFERENCES .................................................................................................................... 33
LIST OF FIGURE
Figure 1.1: Over view of Nekemte substation .......................................................................... 2
Figure 1.2: organizational work chart ....................................................................................... 4
Figure 1.3: block diagram of Nekemt substation ...................................................................... 5
Figure 2.1: Lightening arrestor ............................................................................................... 10
Figure 2.2: Bus bar .................................................................................................................. 12
Figure 2.3 Power Transformer ................................................................................................ 13
Figure 2.4: Gauge (Temperature indicator) ............................................................................ 14
Figure 2.5: Current transformer .............................................................................................. 17
Figure 2.6: DC Main Distribution board................................................................................. 22
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ACRONYMS
AC………………………………………………………………………... Alternating Current
CB…………………………………………………………………………….. Circuit Breaker
CT………………………………………………………………………...Current Transformer
CVT……………………………………………………….. Capacitance Voltage Transformer
DC……………………………………………………………………………… Direct Current
DLG……………………………………………………………………Double Line to Ground
EEPCO………………………………...Ethiopian Electrical Power Corporation Organization
HV………………………………………….…………………………………. Higher Voltage
LL…………………………………………………………………………………Line to Line
NGCC………………………………………………………… National Grid Control Centeri
OPGW……………………………………………………………………Optical Ground Wire
PT……………………………………………………………………… Potential Transformer
SCADA…………………………………………….Supervisor Control And Data Acquisition
SLG…………………………………………………………………….Single Lline to Ground
TL…………………………………………………………….……… ……Transmission Line
TSO………………………………………………………..Transmission Substation operation
VT………………………………………………………………………. Voltage Transformer
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ABSTRACT
We carried out our internship at western region transmission Nekemte substation. During our
internship period we have seen and realize what we have seen in Nekemte substation. There
also different equipment used in substation that we learned in our stream. The main
objectives of this internship are to understand and gain the experience to develop knowledge.
Nekemte substation has two sections that are indoors and outdoor section, in each section
there are different materials. That different equipment is complains to gather to give out put
we require. Those are lightening arrester, current transformer, voltage transformer, capacitor
voltage transformer, insulator, conductor, transformer, protective relay, circuit breaker,
control panel and protection panel and etc. We have seen that equipment and its function
during our internship of 120 days
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CHAPTER ONE
INTRODUCTION
1.1 Overview of Ethiopian Electric Power Corporation (EEPCO)
In Ethiopia there are different sources of electric power. From those sources the major and
highest is hydro power sources. Many of Ethiopian society use different machine for
residential to industrial. Hydro power is the more preferable than the other. This implies
Ethiopia has an enormous potential for hydro power development with the generating
capacity of about 45,000MW from hydro. In addition to, Ethiopia has a capacity of
generating more than 1,000MW from geothermal and more than 10,000MW wind and solar.
The Ethiopian EEPCO as public enterprise was establish with the vision of being a center of
excellence in providing quality electric service at every one’s door and being competitive
export industry, is making unserved effort to utilize the untapped water resource for
hydropower developments. The company is also working to realize its mission of providing
adequate and quality electricity generation, transmission, distribution and sales service
through continuous implement of utility management practices responsive to the socioeconomic development and environmental protection need of the public.
1.2 Background of Nekemte Substation
In western region of Ethiopia there are around 12 substations. Those are:1 .Fincha Substation (230Kv)
2. Amert Nash Substation (230Kv)
3. Gedo Substation (230Kv)
4. Nekemte Substation (132Kv)
5. Dedesa Substation (500Kv)
6. Mandi Substation (132Kv)
7. Asosa Substation (132Kv)
8. Gidda Ayana Substation (132Kv)
9. Bedelle Substation (132Kv)
10. Gimbi substation (132kv)
11. Bako substation (132kv)
12. Gidami substation (132kv)
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And other is under construction such as shambu substation. From those let as see our work
site Company which is Nekemte substation and Transmission.
The Nekemte substation was established in 1989 E.C within. This substation obtained 132kv
from Bako substation and Bako substation takes 132kv from Gedo substation. Gedo
substation is taking around 230kv from Fincha generation. Nekemte substations have 10
outputs. The three outputs are 132Kv from bus-bar for Dedesa, Gida Ayana and Bedele
without step down 132Kv; the four outputs are 15kv for Nekemte city and around Nekemte
city like: Hospital, Bake Jama, Wollega University and Arjo Awuraja, and three outputs are
33kv for Boneya Boshe, Nunu Kumba, Gida (mender 10). [1]
Figure 1.1: Over view of Nekemte substation
1.3 Vision and Mission of EEPCO
1.3.1 Vision of EEPCO
To be a center of excellence in providing quality service at every one’s door and be a competitive
exporter of electrical energy.
1.3.2 Mission of the EEPCO
To provide adequate and quality electricity generation, transmission, distribution and sales
services, through continuous improvement of utility management practices responsive to the
socio-economic development and environmental protection need of the public.
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1.4 Objectives of EEPCO
1.4.1 General objective
The general objective is to enable adequate power supply to the customer without
interruption and to know cause of the fault.
1.4.2 Specific objective
The purpose of this project is
to draw the attention to the occurrence of fault to
switchyard and to show how it can affect mechanical hardware of the equipments.
Alternative solutions to increase the immunity of the switchyard in Nekemte substation.
 To know the phenomenon of fault.
 To know the causes, effects or consequences of fault.
 To know the exact location where this problem occurs.
 To know the methods used to solve the problem.
 Improving reliability and safety of the sub-station.
1.5 Main Products and Service
Substation is an integral parts of transformation plan to sustain economic growth rise energy
supply faster than projection .The main product of Nekemte electric substation was
recognized as direct and indirect way. when we say direct it produce electricity for lighting
purposes while indirectly used for private inter price such as:- Golding, grinding, audio
player, printing, baking bread ,and for all system which need supply ,so Nekemte substation
generation produces electricity to the costumers in effective way and also it gives services to
Wollega university, Nekemte city and woredas.
1.6 Main Costumer
As we stated earlier Nekemte electric substation has two input and ten output lines. Those
lines have many customers in Nekemte town and other towns around Nekemte town.
Trafo132/15kv which capacity 25MVA and current 150/1A are: Hospital, Bake Jama,
Wollega University, Arjo Awuraja.
Trafo132/33KVwhich capacity 20MVA and 100/1A are: Boniya Boshe, Mander 10(Gida)
and Nunnu qumba. For other substation 132KV are: Dedessa, Gidda Ayyana and Bedelle.
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1.7 Organization Work Flow
Management
Internal Audit
Corporate Ethics
and Anti-corruption
Chief executive officer
Corporate
Corporate
Communication
Planning
Generation
Operation
Transmissions
Operation
Generation
Contraction
Marketing
and sales
Transmissions
and substation
construction
Human recourses
Corporate
Distribution
system
Services
Corporate finance and
supply chain
Western Region Distribution Chief Officer
Plan and design
case team
Administration
and finance
Construction
case team
Operation
case team
Figure 1. 2: organizational work chart
1.8 Generalization of Substation Single line Diagram
The arrangement of elements from the transmission line side according the international
agreement: - Lighting Arrester→Capacitor Voltage Transformer→ Line Disconnector→ Bus
bar →Circuit Breaker→ Current Transformer (CT) System.
Notice that the shunt reactors have its Own Line Disconnector and Lighting Arrester
Arrangement System and also the order inside charger is Look like this:Transformer →Bridge Rectifier→ Capacitive or Inductive Filter→ Dc
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1.9
Block Diagram of Nekemte Substation
Fincha
substation
(230kv)
Gedo
substation
(230kv)
Hospital
(15kv)
Bako
substation
(132kv)
Bake jama
(15kv)
Nekemte
substation
(132kv)
Wollega
University
(15kv)
Arjo
Awuraja
(15kv)
Busbar
Holeta
substation
(500kv)
Dedesa
substation
(500kv)
Bedele
substation
(132kv)
Gida
Ayana
sub.
(132kv
)
Boneya
boshe
(33kv)
Nunu
kumba
(33kv)
Gida up to
mender (10)
(33kv)
Figure 1. 3: block diagram of Nekemt substation
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CHAPTER TWO
OVER ALL INTERNSHIP EXPERIENCE
2.1 The way to get the company
Wollega university industry leakage submitted our internship letter to EELPA which is
found in Addis Ababa and the head of EELPA see our letter and He wrote letter for Western
Region Substation Office. The heads of EELPA accept us. Then we have received the letter
and submitted to the Western region transmissions /Substation/ Operation and maintenance
office. Chief of western region transmission/substation/ operation and maintenance is seen
our letter and accept our letter, and he had given us important orientation and He had
confirmed. In addition to him other electrician and operators had guide us other electrical
components. After we joined this substation we practice as an intern for four months.
Beginning from first day we tried to see the whole part of this substation. After we join the
substation it generally observation of equipment and power distribution of the substation for
four consecutive months.
2.2 The Section of the Company we have working
The substation has two sections which are:
1) Indoor switch-is one section of the substation which includes protection, control panel,
measuring circuit breaker, dc source those are enclosed at home and operates electrically.
2) Outdoor switch-is the other section of the substation, constructed outside part of substation
2.3 Definition of Substation
Substations are congregation of electrical equipment through which consumers get supply of
electrical power from generating stations. By varying the voltage levels or frequency or any
other aspects, the required electrical quantity can be altered in substations to provide quality
power to consumers. The power system is a constituent of power generation, transmission
and distribution systems. For all the power system operations, substations are required for
their course of action.
2.3.1 Types of substation
The substation can be classified in different ways including the following:WOLLEGA UNIVERSITY INTERNSHIP REPORT ECE
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1. Based on the voltage level
 A.C substation high voltage (HV)
 Medium voltage (MV)
 Low voltage (LV)
 High voltage DC Substation
2. Classifications as
 Indoors substation
 Outdoors substation
3. Based on configuration
 Conventional air insulated outdoor substation
 SF6 GIS (Sulfur hex fluorides gas insulated substation)
4. Based on application and Transmission Substation
 Sending end substation
 Receiving end substation
 Factory substation
 Compensating substation
 Switchyard in generating substation
 Switching station (without power transfer)
 Distribution substation
Nekemte substation is transmission substation because of it sending end the power and
receiving to end the power. [2]
2.4 Main objective of major substation in the transmission and
distribution
Main tasks associated with major substation in the transmission and distribution system
include following:
 Protection of transmission system
 Controlling the exchange of Energy
 Ensure steady state and transient stability
 Load shedding and prevention of loss of synchronism maintaining the system
frequency within targeted limits.
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 Voltage control; reducing the reactive power flow by compensation of reactive
power tap changing
 Secure supply by proving adequate line capacity
 Data transmission via power line carrier for the purpose of network monitoring,
control and protection
 Fault analysis and pin pointing the cause and subsequent improvement in that area of
field.
 Determining the energy transfer through transmission lines
 Reliable supply by feeding the network at various points.
 Establishment of economical load distribution and several associated function [1]
2.5 Function of Substation
Substations are designed to accomplish the following functions, these are: To change voltage from one level to other.
 To regulate voltage compensate for system voltage changes.
 Switch transmission and distribution into and out off the grid system.
 Measure electric power quantities flowing in the circuits.
 Connect communication signal to the circuits.
 Eliminate lighting and other electrical surges from the system
 Connect the electric generation plants to the system
 Make interconnections between the electric systems more than one utilities
 Control reactive power in kilo-voltage-amperes supplied to and the flow of reactive
power in kilo-voltage-amperes in the circuits
 Supply the electric energy to the costumers at lowest cost
 Supply electric power with specified voltage limit
 Supply the electric power within specified frequency limits (50 Hz or 60 Hz) and
etc.
2.6 Equipment found in Nekemte substation (outdoor) and there function
Nekemte substation has the following equipment
i.
Outdoor switchyard
 Incoming Lines
 Outgoing Lines
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 Bus bars
 Transformer
 Circuit breaker, isolator; earthings switches; lighting arrestor, current transformer,
voltage transformer, neutral grounding equipment
 Power cables
 Control cables for protection and control
ii.
Switchgear and control panel building
 Low voltage a.c switchgear
 Control panel, protection panel
iii.
Battery Room and D.C distribution system
 D.C battery system and charging equipment
 D.C distribution system
2.7 Some of their function
2.7.1 Lightening arrestor
Lightening arrestors are the instrument that are used in the incoming feeders so that to
prevent the high voltage entering the main substation. This high voltage is very dangerous to
the instruments used in the substation. Even the instruments are very costly, so to prevent any
damage lightening arrestors are used. In any substation the main important is of protection
which is firstly done by these lightening arrestors.
The substation equipment such as conductors, transformers, etc, is always erected outdoor.
Whenever light surges occur then, a high-voltage pass through these electrical components
causing damage to them (either temporary or permanent damage based on the amount of
voltage surge). Therefore, to avoid this difficulty, lightening arresters are placed to pass the
entire lightening surges to earth. There are other arresters which are used to ground the
switching surges called as surge arresters.
Around arrestor there is surge counter to count how much over current is grounded. This
protective device located at the starting of the Substation end of substation and also provided
near the transformer terminals.
 To protect against Surge Voltages
 Lightning surges
 During phase to Earth fault, voltage in healthy phases may go up.
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 Switching surges.
Figure 2.1: Lightening arrestor
2.7.2 Capacitor voltage transformer (CVT)
CVT is connected in between high voltage line and ground to provide proportionate low
voltage on the secondary side to meters & protective relays.
A capacitor voltage transformer (CVT) is a transformer used in power systems to step-down
extra high voltage signals and provide low voltage signals either for measurement or to
operate a protective relay. In its most basic form the device consists of three parts: two
capacitors across which the voltage signal is split, an inductive element used to tune the
device to the supply frequency and a transformer used to isolate and further step-down the
voltage for the instrumentation or protective relay. The device has at least four terminals, a
high-voltage terminal for connection to the high voltage signal, a ground terminal and at least
one set of secondary terminals for connection to the instrumentation or protective relay.
CVTs are typically single-phase devices used for measuring voltages in excess of one
hundred kilovolts where the use of voltage transformers would be uneconomical.
2.7.3 Insulator
The material which does not allow free movement of electrons or electric charge is called as
an insulator. Hence, insulators resist electricity with their high resisting property.
Insulators are used for insulation purpose while erecting electric poles with conductors to
avoid short circuit and for other insulation requirements.
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2.7.4 Isolator
The use of this isolator is to protect the transformer and the other instrument in the line. The
isolator isolates the extra voltage to the ground and thus any extra voltage cannot enter the
line. Thus an isolator is used after the bus also for protection.
Isolator is a manually operated mechanical switch that isolates the faulty section or the
section of a conductor or a part of a circuit of substation meant for repair from a healthy
section in order to avoid occurrence of more severe faults. Hence, it is also called as a
disconnector or disconnecting switch. There are different types of isolators used for different
applications such as single-break isolator, double-break isolator, bus isolator, line isolator,
etc
1. Earth Switch:
Earth switch to be closed only when isolator main contact is open and there is no voltage on
E/S Side of isolated.
2. Bus-bar:
The bus is a line in which the incoming feeders come into and get into the instruments for
further step up or step down. The first bus is used for putting the incoming feeders in la
single line. The size of the bus bar is important in determining the maximum amount of
current that can be safely carried. Bus bars are typically either flat strips or hollow tubes as
these shapes allow heat to dissipate more efficiently due to their high surface area to cross
sectional area ratio. Bus bars are protected from accidental contact either by a metal
enclosure or by elevation out of normal reach.
Choose of bus-bar schemes for A.C yard depends upon several factor mentioned above, the
important bus-bar includes the following:
 Single bus-bar
 Double bus-bar with one circuit breaker
 Double bus-bar with two circuit breaker
 Main and transfer bus
 Ring bus…etc. From those Nekemte substation use single type bus bar.
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Figure 2. 2: Busbar
2.7.5 Types of communication in Nekemte Substation
1. SCADA system:
SCADA Means Supervisory control and data acquisition system have played a vital
role by providing utilities with valuable knowledge and capabilities that are key to a
primary business function delivering power in a reliable and safe manner. But in
Nekemte substation there is not fully installed and operational.
2. OPGW(Optical Ground Wire) are primarily used by the electric utility industry ,
placed in the secure topmost position of the transmission line where it shields the all
important conductor from lightning while providing a telecommunication path for
internal as well as third party
2.7.6 Circuit Breaker
The circuit breakers are used to break the circuit if any fault occurs in any of the instrument.
These circuit breaker breaks for a fault which can damage other instrument in the station. For
any unwanted fault over the station we need to break the line current. This is only done
automatically by the circuit breaker. Circuit breaker used in this substation is SF6 so let see
it.
SF6 circuit breakers
The use of SF6 circuit breaker is mainly in the substations which are having high input kv
input, say above 220kv and more. The gas is put inside the circuit breaker by force i.e. under
high pressure. When if the gas gets decreases there is a motor connected to the circuit
breaker. The motor starts operating if the gas went lower than 20.8 bar. There is a meter
connected to the breaker so that it can be manually seen if the gas goes low. The circuit
breaker uses the SF6 gas to reduce the torque produce in it due to any fault in the line. The
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circuit breaker has a direct link with the instruments in the station, when any fault occur
alarm bell rings.
2.8 Transformer
The line coming from Bako substation get 132KVso line double winding transformers are
used. Transformer tanks up to 25 MVA capacities are generally oil filled.
The Oil piping should also be blanked at the ends with gasket and blanking plates to avoid in
gross of moisture, dust, and foreign All other accessories like temperature meters, oil flow
indicators, PRVs, buchholz relay, oil surge relays etc.
Transformer is a static device that is used to change voltage in reverse of current without
changing frequency. Transformer is classified into different category based on its
construction and its operation. In Nekemte substation there are four transformers those are:
1) Power Transformer
2) Earth Transformer
3) Auxiliary Transformer
4) Instrumental Transformer (current transformer and voltage transformer).
2.8.1 Power Transformer
Power transformer necessary between consecutive voltage levels for stepping-up or steppingdown the A.C voltage and for transferring power from one A.C voltage level to the other.
There are two power transformer in this substation based on their voltage level those are:
 Transformer 1(132kv/33kv) is give power to Nunu kumba, Boneya Boshe and Gida
Ayana.
 Transformer 2(132kv/15kv) is give power to Wollega university, Bake Jama,
Hospital and Arjo Awuraja.
Figure 2. 3: Power Transformer
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2.9 Transformer Components and functions
2.9.1 Conservator
The Conservator is located at the top of the transformer. Conservator is designed to act as a
reservoir for the transformer oil. The level of the oil in the transformer can rise and fall due
to temperature. The increase of temperature can be caused either by a rise in ambient
temperature or due to increased load on the transformer. An increase in temperature causes
the oil in the transformer to expand. The conservator provides space for this expansion of the
oil. The oil level indicator in the conservator needs to be monitored to ensure that the level of
oil does not fall below the alarm limit. [6]
2.9.2 Temperature Indicators
Various temperature sensing devices are used to indicate the operating temperature of the
transformer. The number and use of the devices varies as to size and application of the
transformer. On small transformers that require no fans or pumps, the indicating device may
be in the form of liquid-filled thermometer mounted at the top of the tank. Large transformers
with fans of pumps, or with a combination of fans and pumps can have up to three
temperatures.
2.9.3 Level Gauges
To ensure that the correct liquid level exists in the transformer, a gauge is provided. This will
be on the main tank if it is the smaller variety with no conservator or on the conservator if
one is fitted. Modern gauges are constructed to show correct oil level for any oil temperature
to ensure correct initial filling.
Figure 2.4: Gauge (Temperature indicator)
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2.9.4 Vacuum valve
All transformers capable of withstanding vacuum have a vacuum valve located on the top of
the transformer. Transformers are filled with oil under vacuum to improve the insulation
value of both the solid and liquid insulation.
2.9.5 Radiator
If electrical transformer is loaded, the current starts flowing through its windings. Due to this
flowing of electric current, heat is produced in the windings, this heat ultimately rises the
temperature of transformer oil. We know that rating of any electrical equipment depends
upon its allowable temperature rise limit. Hence, if the temperature rise of the transformer oil
is controlled, the capacity or rating of transformer can be extended up to significant range.
The radiator of transformer accelerates the cooling rate of transformer. Thus, it plays a vital
role in increasing loading capacity of an electrical transformer. This is basic function of
radiator of an electrical power transformer.
2.9.6 Tap changer
A tap changer is a device fitted to power transformers for regulation of output voltage to
required levels. This is normally achieved by changing the ratios of the transformer/s. tap
changers offer variable control to keep the supply voltage within these limits. It is a
connection point selection mechanism along a power transformer winding that allows a
variable number of turns to be selected in discrete steps. A transformer with a variable turn’s
ratio is produced, enabling stepped voltage regulation of the output. The tap selection may be
made via an automatic or manual tap changer mechanism. Tap changers can be on load or off
load. On load tap changers generally consist of a diverter switch and a selector switch
operating as a unit to effect transfer current from one voltage tap to the next. Tap changers
can be adjusted to fit the application need.
2.10 Transformer Insulating Oil
Transformer oil is one of the most important elements of transformer. It has two functions
which are insulation system and cooling system.
Insulating oil in an electrical power transformer is commonly known as Transformer Oil. It is
normally obtained by fractional distillation and subsequent treatment of crude petroleum.
That is why this oil is also known as Mineral Insulating Oil. Transformer Oil serves mainly
two purposes
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Firstly, it is liquid insulation in electrical power transformer and two it dissipates heat of the
transformer i.e. acts as coolant.
Secondly, it helps to preserve the core and winding as these are fully immersed inside oil and
another important purpose of this oil is, it prevents direct contact of atmospheric oxygen with
cellulose made paper insulation of windings, which is susceptible to oxidation.[6]
2.11 Earthing Transformer
In power systems the faults are not avoidable even after taking utmost care at every stagefrom planning to maintenance .An earthling transformer is a transformer primarily to provide
a neutral point for grounding purpose. The sole duty of the grounding transformer is to pass
ground current during an earth fault, and it carries no useful load. The desirable quantities of
an earthing transformer are low zero impedance and low losses or no load losses. In addition
to this, it is also used to detect whether there is an earth fault on the system or not .So this
transformer is different from power transformer. [6]
2.12 Instrument Transformer
Instrument transformers are used to step-down the current or voltage to measurable values.
They provide standardized, useable levels of current or voltage in a variety of power
monitoring and measurement applications. Both current and voltage instrument transformers
are designed to have predictable characteristics on overloads. Proper operation of overcurrent protection relays requires that current transformers provide a predictable
transformation ratio even during a short circuit. Instrument transformers are high accuracy
class electrical devices used to isolate or transform voltage or current levels. The most
common usage of instrument transformers is to operate instruments or metering from high
voltage or high current circuits, safely isolating secondary control circuitry from the high
voltages or currents. The primary winding of the transformer is connected to the high voltage
or high current circuit, and the meter or relay is connected to the secondary circuit.
Instrument transformers may also be used as an isolation transformer so that secondary
quantities may be used in phase shifting without affecting other primary connected device.
These are further classified into two types which are discussed below. [2]
 Current Transformers
 Potential Transformers
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1. Current transformer (CT)
Current transformers are basically used to take the readings of the currents entering the
substation. This transformer steps down the current from 800 amps to 1 amp. This is done
because we have no instrument for measuring of such a large current. The main use of this
transformer is
 Distance Protection
 Backup Protection
 Measurement
A current transformer is defined as an instrument transformer in which the secondary current
is substantially proportional to the primary current (under normal conditions of operation)
and differs in phase from it by an angle which is approximately zero for an appropriate
direction of the connections. This highlights the accuracy requirement of the current
transformer but also important is the isolating function, which means no matter what the
system voltage the secondary circuit needs to be insulated only for a low voltage.
In Electrical Engineering, a current transformer (CT) is used for measurement of electric
currents in each phase. It is also used for the protection of relays. Current transformers,
together with voltage transformers (VT) (potential transformers (PT)) are known as
instrument transformers. When current in a circuit is too high to directly apply to measuring
instruments, a current transformer produces a reduced current accurately proportional to the
current in the circuit, which can be conveniently connected to measuring and recording
instruments. A current transformer also isolates the measuring instruments from what may be
very high voltage in the monitored circuit. Current transformers are commonly used in
metering and protective relays in the electrical power industry.
Figure 2.5: Current transformer
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2. Potential Transformer
There are two potential transformers used in the bus connected both side of the bus. The
potential transformer uses a bus isolator to protect itself. The main use of this transformer is
to measure the voltage through the bus. This is done so as to get the detail information of the
voltage passing through the bus to the instrument. There are two main parts in it
 Measurement
 Protection
The standards define a voltage transformer as one in which the secondary voltage is
substantially proportional to the primary voltage and differs in phase from it by an angle
which is approximately equal to zero for an appropriate direction of the connections.
A capacitor voltage transformer (CVT), or capacitance coupled voltage transformer (CCVT)
is a transformer used in power system to step down extra high voltage signals and provide a
low voltage signal, for measurement or to operate a protective relays. In its most basic form
the device consists of three parts: two capacitors across which the transmission line signal is
split, an inductive element to tune the device to the line frequency, and a transformer to
isolate and further step down the voltage for the instrumentation or protective relay.
The device has at least four terminals: a terminal for connection to the high voltage signal, a
ground terminal, and two secondary terminals which connect to the instrumentation or
protective relay. CVTs are typically single-phase devices used for measuring voltages in
excess of one hundred kilovolts where the use of wound primary voltage transformers would
be uneconomical. The CVT is also useful in communication systems. CVTs in combination
with wave traps are used for filtering high frequency communication signals from power
frequency. This forms a carrier communication network throughout the transmission
network. It uses on alternating current (A.C) systems to provide a standardized equivalent or
representative voltage compared to that of a higher voltage (HV) primarily system.
2.13 Auxiliary Transformer
Auxiliary transformers are stepped down transformer (15kv/400v) and used to supply low
voltage for AC power system inside substation such as lighting, air conditioner and other AC
supply and DC power system such as protection relays, batteries and telecommunication
system and other DC supply system.
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2.14 Parts of transformer protection
There are two types of transformer protection. Those are:
1. Electrical protection
2. None electrical protection
1. Electrical protection
The primary side and secondary side of the transformer has restrict earth fault relay(REF)
,Over current relay(OC), differential Relay.
 Restrict Earth Fault Relay (REF) is provided in electrical power transformer for
sensing internal earth fault of the transformer.
 Over current Relay it protects electrical power systems against excessive currents
which are caused by short circuit, ground fault and etc.
 Differential relays are used for protecting transformers and generators. they are very
sensitive to the fault occurred within the zone of protection but they are least
sensitive to the fault that occur outside the protected zone.[3]
2. None electrical protection
I.
Buchholz relay: - It is used to give an alarm in case of incipient (slow developing)
faults the transformer and to disconnect the transformers from the supply in the event
of severe internal faults. Ckt is usually installed in the pipe connecting the
conservator to the main tank.
II.
Pressure Relief Device:- It is mounted on transformer tanks to relieve excess
internal pressure that might build during operating conditions.
III.
Oil level indicator:-it is used to indicate oil level in the conservator.
IV.
Oil and winding temperature:-It is used to indicate oil & winding temperature
through acting contacts it protects power transformer from overheating by
interrupting power.
V.
Fans:-It is used for cooling system. It operated manual or automatic by thermal
settled relays.
VI.
Silica gel:-transformers with conservator are equipped with the dehydrating breather.
The dehydrating breather collects all moisture from air and prevents it for entering
the transformer tank. It contains silica gel (SiO2 Crystals) which absorbs the air
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moisture and changes its color during air convection. The silica gel turns blue when
it becomes saturated with moisture after
2.15 The Control Room and its Electrical Components in the Substation
2.15.1 Control Room
The control room is a part of substation that contains many different types of electrical
equipment such as: Different types of panels
 Communications
 Rectifying system
 Different types of alarm
 Lightning
 Battery and charger
 Accessories(oil, silica jet, panels, circuit breaker etc)
 Auxiliary transformer
 Cables and duct
 Radio communications media
 Different types of (four digits, SCADA, fiber optics) and normal phone.
 Data recording area (different size of paper, computer) etc.
1. Different types of controls panels:-Control panels are is closed rectangular shape such
as a door and window. Control panels contains different types of relays, miniature circuit
breaker, interconnecting cables, switches, Sensors heater, fan, breakers, bus-bar, current
transformer, voltage transformer, supply (AC and DC), indicators, push button, single
line diagram, breather, meter(ammeter, voltmeter, wattmeter, energy meter, voltmeter),
resetting system, shunt capacitor, tap changer indicator, HRC, fuses etc.
2. Communication:-We use (fiber optics or OPGW),Mobile Phone . Communication has
its own control panels. The controls panels contain fiber optic board.
3. Rectifying system
 Is used to correct AC supply to DC supply.
 It includes transformer, PCB boards, (electronics board), capacitor, fuse, miniature
circuit breaker.
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4. Types of alarm
 An alarm is too used to notify when faults occurred.
4. Lighting
 Light which is found in control room
 It includes fluorescent lamp, sodium vapor lamp.
5. Batteries and changer
 We have 48v AC and 125v direct current
 The batter which is made up of combination of water and acid i.e. its ratios is 3:1
respectively.
 We measure the amount of water and acid (%age of water and acids) by using
hydrometer.
 This hydrometer contains mercury level of water and acid indicator.
 Up to 2.8 normal conditions and 2.5 it is very perfect.
6. Accessories
 Is available for future purpose.
7. Auxiliary transformer
 It delivers the power for only that substation.
 Auxiliary transformer gives power such as lighting for substation.
 This type of transformer is found only in substations.
8. Cable and duct
 Different types of cables are used for carrying powers.
 Ducts are used for cover cables that available under ground.
9. Phones
 Different types of phones are exists. Those are: 4 digit and normal phone.
 The 4 digit phone is contains SCADA and fiber optics
11. Feeder
A feeder is a conductor which connects the substation (localized station) to the area where
power is to be distributed. Generally, no tapping are taken from the feeder. So that current in
it is remains the same through.
Feeder circuits are used to distribute electrical power to power distribution panels. Many
feeder circuits extend for very long distances, therefore voltage drop must be considered in
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feeder circuit design. In higher voltage feeder circuit, the voltage drop is reduced. However,
many lower voltage feeder circuits require large diameters conductors to provide a tolerable
level of voltage drop. High current feeder circuits also present a problem in terms of the
massive over load protection that is sometimes required. This protection is usually provided
by the system of switchgear or load center where the feeder circuit is originate.
2.15.2 DC 125V Main distribution board
All Protection equipment in control room use 125v from Auxiliary transformer to rectifier
panel AC to DC
Protection
system
AC
DC
Relay
DC
Battery
Figure 2. 6: DC Main Distribution board
2.15.3 Metering Panel
The panel that contains
 Voltmeter
 Ammeter
 KW meters,
 KVAR meters
 KVA meters
2.16 Control and protection Panel
Control panels contain meters, control switches and recorders located in the control building,
also called a doghouse. These are used to control the substation equipment, to send power
from one circuit to another or to open or shut down circuits when needed
In this substation each feeder have its own control panel based on its voltage level therefore
there are three control panel [1]
1. 33kv control panel
 Gida Ayana control panel
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 Nunu kumba control panel
 Boneya Boshe control panel
2. 15kv control panel
 Wollega university control panel
 Arjo Awuraja control panel
 Hospital line control panel
 Bake Jama control panel
3. 132kv control panel
 Bedele control panel
 Dedesa control panel
 Gida Ayana control panel
2.16.1 Protection Panel
Protection Panel is included in control room that is used to protect and control each feeder. In
this protection panel there are different protective device in control panel.
1. Circuit Breaker
a. Gas circuit breaker
b. Air circuit beaker
c. Vacuum circuit breaker
2. Relay
Protective relays are used to detect defective lines or apparatus and to initiate the operation of
circuit interrupting devices to isolate the defective equipment. Relays are also used to detect
abnormal or undesirable operating conditions other than those caused by defective equipment
and either operates an alarm or initiate operation of circuit interrupting devices. Protective
relays protect the electrical system by causing the defective apparatus or lines to be
disconnected to minimize damage and maintain service continuity to the rest of the system.
There are different types of relays.
i.
Over current relay
ii.
Distance relay
iii.
Differential relay
A relay is an electrically controlled device that opens and closes electrical contacts or
activates and deactivates operation of other devices in the same or another electrical circuit.
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i.
Over Current Relay
The over current relay responds to a magnitude of current above a specified value.
ii.
Distance Relay
The distance relay responds to a combination of both voltage and current. The voltage
restrains operation, and the fault current causes operation that has the overall effect of
measuring impedance. The relay operates instantaneously (within a few cycles) on a 60-cycle
basis for values of impedance below the set value. When time delay is required, the relays
energizes a separate time-delay relay or function with the contacts or output of this timedelay relay or function performing the desired output functions. The relay operates on the
magnitude of impedance measured by the combination of restraint voltage and the operating
current passing through it according to the settings applied to the relay. When the impedance
is such that the impedance point is within the impedance characteristic circle, the relay will
trip.
iii. Differential Relay
The differential relay is a current-operated relay that responds to the difference between two
or more device currents above a set value. The relay works on the basis of the differential
principle that what goes into the device has to come out .If the current does not add to zero,
the error current flows to cause the relay to operate and trip the circuit.
The differential relay is used to provide internal fault protection to equipment such as
transformers, generators, and buses. Relays are designed to permit differences in the input
currents as a result of current transformer mismatch and applications where the input currents
come from different system voltages, such as transformers.. Differential relays are often used
with a lockout relay to trip all power sources to the device and prevent the device from being
automatically or remotely reenergized. These relays are very sensitive. The operation of the
device usually means major problems with the protected equipment and the likely failure in
re-energizing the equipment.
2.17 Electrical Transmission Tower Types and Design
2.17.1 Definition of Electrical Tower
The main supporting unit of overhead transmission line is transmission tower. Transmission
towers have to carry the heavy transmission conductor at a sufficient safe height from
ground. In addition to that all towers have to sustain all kinds of natural calamities. So
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transmission tower designing is an important engineering job where all three basic
engineering concepts, civil, mechanical and electrical engineering concepts are equally
applicable. [2]
2.17.2 Parts of power transmission Tower
1) Peak of transmission tower
2) Cross arm of transmission tower
3) Boom of transmission tower
4) Cage of transmission tower
5) Transmission Tower Body
6) Leg of transmission tower
1. Peak of Transmission Tower
The portion above the top cross arm is called peak of transmission tower. Generally earth
shield wire connected to the tip of this peak.
2. Cross Arm of Transmission Tower
Cross arms of transmission tower hold the transmission conductor. The dimension of cross
arm depends on the level of transmission voltage, configuration and minimum forming angle
for stress distribution.
3. Cage of Transmission Tower
The portion between tower body and peak is known as cage of transmission tower. This
portion of the tower holds the cross arms.
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CHAPTER THREE
THE WORK TASK WE HAVE BEEN EXECUTING AND
CHALLENGES FACED DURING INTERNSHIP
3.1 The Work Task We Have Been Executing
In four months of time stay at internship site there a lot of knowledge, experience and
practical skills were obtained or gained. we have been working on indoor and outdoor
systems. Since it was difficult to fully participate in the work, we haven’t done that much so
as the system was complex and also need great experience to rehabilitant other than
understanding it.
During our participation in the section of the company, we have been executing some works
on the operation side after given manuals for our basic understanding. Even though we was
not able to participate in the maintenance section due to the complexity and high of the work,
we know all the basic maintenance procedures. Some works on the substation were
performed manually like gathering data on the indoor and outdoor equipment concerning the
load, charging circuit breaker and controlling the incoming alarms due to earth fault,
overload and short circuit.
Additionally, we have worked how, when and where the fault happened since in the indoor
system has three equipment; these are control panel, protection panel and switching panel. In
such away we have been executing and performing my tasks.
3.2 The procedures we have been using while performing our work tasks
During my internship period we have seen that there are brief procedures that we follow as
alarm give sound and shows red light at the indoor when fault happens.
The following are steps that we should follow when the fault is happened in the substation.
1. Steps to make switch off are as follows
 Make switch off circuit breaker
 Then opening the disconnector
 Switch off line disconnector
 Make grounding for safety during maintenance.
2. Trace fault from the indoor up to the outdoor by referring the drawing manual of the
substation properly.
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3. Then identify problem and maintain it
4. After the technician maintain it to make switch on has its own steps.
 Ground will be disconnected first.
 Switch on line disconnector.
 Switch on bus disconnector.
 Make switch on the circuit breaker.
5.
Indicates as there is fault again and needs solved properly by following the above
consecutive procedural steps and again also apply performing our work task.
Depending up on the experience we gain day to day from the coworkers in the company, we
have been doing our level best without being exhausted by keeping work ethics being
punctual and also by respecting each other during our internship period.
3.3 Power Interruption (Outage)
A power outage (also called a power cut, a power blackout, power failure or a blackout) is a
short- or long- term loss of the electric power to an area. There are many causes of power
failures in an electricity network.
Main cause electric power interruption includes:
 vegetation under tower
 wire insulation breakdown
 wind blowing to the electric lines
 animal contact with wire
 faults at power stations
 damage to electric transmission lines
 substations or other parts of the distribution system
 a short circuit or the overloading of electricity mains
Power failures are particularly critical at sites where the environment and public safety are at
risk. Institutions such as Hospitals, sewage treatment plants, mines, and the like will usually
have backup power sources such as standby generators, which will automatically start up
when electrical power is lost. Other critical systems, such as telecommunication, are also
required to have emergency power. The battery room of a telephone exchange usually has
arrays of lead–acid batteries for backup and also a socket for connecting a generator during
extended periods of outage. [4]
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3.3.1 Types of power outage (interruption)
Power outages are categorized into three different phenomena, relating to the duration and
effect of the outage. [2]
A permanent fault: is a massive loss of power typically caused by a fault on a power line.
Power is automatically restored once the fault is cleared.
A blackout: is the total loss of power to an area and is the most severe form of power outage
that can occur.
Blackouts which result from or result in power stations tripping are particularly difficult to
recover from quickly. Outages may last from a few minutes to a few weeks depending on the
nature of the blackout and the configuration of the electrical network.
Protective relays and fuses are used to automatically detect overloads and to disconnect
circuits at risk of damage. Under certain conditions, a network component shutting down can
cause current fluctuations in neighboring segments of the network leading to a cascading
failure of a larger section of the network. [4]
3.3.2 Fault Analysis
Fault currents cause equipment damage due to both thermal and mechanical processes. Goal
of fault analysis is to determine the magnitudes of the currents present during the fault. Need
to determine the maximum current to insure devices can survive the fault. Need to determine
the maximum current the circuit breakers (CBs) need to interrupt to correctly size the CBs
3.3.3 Types of faults
There are two main types of faults:
Symmetric faults: system remains balanced; these faults are relatively rare, but are the
easiest to analyze.
Un-symmetric faults: system is no longer balanced; very common, but more difficult to
analyze. The most common type of fault on a three phase system by far is the single line-toground (SLG), followed by the line-to-line faults (LL), double line-to-ground (DLG) faults,
and balanced three phase faults [4].
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CHAPTER FOUR
OVERALL BENEFIT WE GAINED FROM THE INTERNSHIP
4.1 Improving our practical skill
The main objectives of internship is to practice and improve the industry work skill for better
understanding of how what they are learning in class can help them with their future.
In improving our practical skill this internship has very important role because we have seen
and worked on different material, measuring parts, control parts, protection parts and other
equipment’s. We have tried our best to correlate our classroom studies to the actual world
zand we have referred books again to remember the theoretical part. We have observed
problems and we have worked on the solution in practice with co-workers of the company.
4.2 In terms of theoretical knowledge
We have also confirmed our theoretical knowledge is in coincidence with the practical one.
We have referred books while in practice to check our classroom theories are interrelated
with the practical work.
4.3 In improving our interpersonal communication skill
We have improved our communication skill through the discussion and by asking each other.
By discussing on problems and solutions, we have recognized that how is important
improving interpersonal communication skill. While interpersonal communication can be
defined as its own area of study. It also occurs within other contexts like groups and
organizations. We were held many presentations so as to develop our interpersonal
communication skill.
4.4 In terms of improving our leadership skill
By referring company’s hierarchy of leadership, we have seen how is important the concept
of leadership in any work area. From top to bottom the leaders in our company have general
manager, administrator, production manager and heads at each section. The general manager
manages all the system and has to be check how the administrator and the technicians are
working. Therefore, the administrator and the technicians are responsible to the general
manager. Heads and all other workers are responsible to the administrator and to the
technicians.
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4.5 The knowledge gained during internship program
 We got ability to understand different electrical equipment with physical contact and
also with their design of transmission line, transmission tower and etc.
 We improve our personal skills training and helped us recognized and improve our
ability.
 We have recognized the role of responsibility in keeping and performing particular
work in a good manner.
 The program will make us in order to have basic knowledge for our future job.
4.6 Improving team work skill
Team Work skills are critical for improving individual task accomplishment because
practical innovations and solutions are reached sooner through cooperative behavior is action
is performed by a team towards a common goal. A team consist more than one person; each
of them typically has different responsibilities. We develop from the team following common
sense like;
 Common purpose
 Interdependence
 Clarity or roles and contribution
 Empowerment
4.7 In terms of understanding about work ethics and related issues
We have understood work ethics being on time to work and to fulfill my responsibilities and
also we have recognized the role of responsibility in keeping and performing particular work
in a good manner. Work ethics and related issues are important in every working area.
4.8 In terms of entrepreneurship skill
We have observed the sense of self confidence and self-steam in order to develop
entrepreneurship skill by developing our classroom knowledge and practical skills, we have
understood how to be an entrepreneur in the substation. We have gained knowledge of
entrepreneurship so as to be self-confident owner and administrator of company within its
personnel workers. An entrepreneur is an important sector even for the countries
development because it creates job opportunities for the society.
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CHAPTER FIVE
CONCLUSION AND RECOMMENDATION
5.1 Conclusion
This internship program has played an important role for us; in case understanding in our
major field to get experience for our work after we graduate and it’s good when we go in real
world. Also we have seen a lot and have learned more than enough by correlating our
classroom studies throughout this practice time.
Additionally we have learned on different control parts, protection parts, and instruments that
work in combine to give desired output to satisfy the customer.
Throughout this internship period we have gained a number of benefits in terms of improving
practical skills, theoretical knowledge, interpersonal communication skills, entrepreneurship
skills, leadership skills and in terms of understanding about work ethics and related issues.
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5.2 Recommendation
As a recommendation, we have given some recommendations to the company. These are
problems on the controlling system and protection of all company’s equipment.
Our first recommendation were on the way of collecting data from control panel that are
recorded every day manually is boring and time consuming so the substation system should
use computerized data collecting system. Our next recommendation were on the controlling
system, the incoming line (outdoor) there are no current transformer and circuit breaker for
protection and controlling of equipment’s and current transformer is should be connected to
the line in the incoming feeder is very important to know how much current is coming from
Gedo substation for protecting device in control panel. Circuit breaker should be exists in
incoming feeder before bus bar is used for protection when fault is happen.
Our final recommendation will be on the general use of SCADA system. The substation did
not start to use this system just the equipment is there. So I recommended for that substation
to use this supervisory control and data acquisition system.
As we know documented data is necessary in order to know everything about that sub-station
or company efficiently for the operators and others. But there is lack of documented data in
Nekemte substation therefore there should be documented data about Nekemte substation in
both hard copy and in website there is no enough data that clearly show about the Nekemte
substation .
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REFERENCES
[1] Company’s manual
[2] M.E.El-Hawary, “Electric power system design and Analysis”, Reston publishing
company, Virginia, 2002.
[3] M Rustebakke, “Electric utility systems and practice”, Johan Wiley and Sons,
Newyork,1983.
[4] Arthur freund,”Ground fault protection for ungrounded distribution systems”, Electrical
construction and maintenance,1979.
[5] Baldwin Bridger, Jr, “High resistance grounding”, Conference record of the Industry
applications society IEEE-IAS 1981 annual meeting, Philadelphia, PA: Oct. 18-24, 1981.
[6] ESHA. Guide on How to Develop a Small Hydropower Plant. Swedish: Europe, 1998
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