MAKERERE UNIVERSITY

COLLEGE OF ENGINEERING, DESIGN, ART AND

TECHNOLOGY
DEPARTMENT OF ELECTRICAL AND COMPUTER
ENGINEERING
BSc. ELECTRICAL ENGINEERING

A REPORT ON INDUSTRIAL TRAINING CONDUCTED

Field Attachment Period (June – August)

By
KISEKKKA JUDE FRANCIS
16/U/463

Field Attachment Report Submitted to Makerere University Kampala

Partial fulfillment of the requirements for the degree of BSc. Electrical Engineering of Makerere
University Kampala
DECLARATION
I Kisekka Jude Francis acting responsibly without conspiracy or coercion whatsoever, and upon
knowing the consequences of forgery, telling lies and Xeroxing, do here by declare that the
information given in this report was my original practical work and findings as a result of my
industrial training

KISEKKA JUDE FRANCIS 16/U/463

Industrial Trainee
Signature
Date: .........................................................

Mr Opolot Rockfell
UMEME Limited
Signature
Date: ..........................................................

Dr. Akol Roseline

University Supervisor
Makerere University
Signature: ..............................................
Date: ......................................................

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ACKNOWLEDGEMENTS
I would like to thank my God, the creator of the world for giving me life, the good health as well
as for wisdom and guidance.
For the success that I achieved up to the end, a debt of gratitude to the management staff,
supervisors and all other Engineers at Umeme Ltd of UMEME Limited for giving me the
opportunity, guidance and commitment as an Industrial Trainee in such company with such a
great reputation. My university supervisor, Dr. Akol Roseline for the endless support and guidance
all throughout my internship and repot writing. Finally, my parents who tirelessly work hard to
provide me with the necessities.

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DEDICATION
I dedicate this report to my lovely aunt and grandma because of all they have done for me.
You hold a special place at my heart; you are my God given angels in this world.

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PREFACE
This report follows a two-month training program with UMEME. Industrial training is quite an
imperative practice that exposes students to institutional practices and agreed norms. Enclosed in
the report is the power and distribution transformers section, Metering section and switch gear
section. It also includes practical work done during my time in this section.

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ACRONYMS
BB Bus Bar

BDV Breakdown Voltage

CB Circuit Breaker

CT Current Transformer

ERA Electrification Rural Agency

HRM Human Resource Manager

HV High Voltage

IR Insulation Resistance

KV Kilo Volts

LV Low Voltage

MV Medium Voltage

OLTC On-Load Tap Changer

PI Polarization Index

PPE Personal Protective Element

RMU Ring Main Unit

TC Tap Changer
TX Transformer

UEB Uganda Electricity Board

UEDCL Uganda Electricity Distribution Company Limited

UEGC Uganda Electricity Generation Company Limited

UETCL Uganda Electricity Transmission Company Limited

VT Voltage Transformer

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List of figures
Figure 1-2: The company structure of umeme .............................................................................................. 5
Figure 1-3: The engineering structure of umeme .......................................................................................... 5
Figure 2-1: Ideal Transformer diagram ......................................................................................................... 7
Figure 2-2: Namungoona substation Power transformer .............................................................................. 8
Figure 2-3:Pin insulator R90 ....................................................................................................................... 10
Figure 2-4: Polymeric insulators ................................................................................................................. 11
Figure 2-5: Reel insulator ........................................................................................................................... 11
Figure 2-6: Reel insulator [2] ...................................................................................................................... 11
Figure 2-7:Outrigger Stay assembly(L) Flying stay assembly(R) ............................................................. 12
Figure 2-8:Surge arrester ............................................................................................................................ 13
Figure 2-9Studs ........................................................................................................................................... 15
Figure 2-10:Bushings of an 11kV transformer on the left and for 33kV on the center and right ............... 16
Figure 2-11: pressure release valve ............................................................................................................. 16
Figure 2-12:Arcing horns and surge arrestors............................................................................................. 18
Figure 2-13:No load tap changer ................................................................................................................ 19
Figure 2-14:A transformer bushing with flash over .................................................................................... 20
Figure 2-15: Key Sector Players in metering performance and regulation ................................................. 21
Figure 2-16:Electromechanical meter ......................................................................................................... 23
Figure 2-17:Digital electronic Meter .......................................................................................................... 23
Figure 2-18:T.O.U meter installed opposite makerere university traffic lights [3] .................................... 24
Figure 2-19:LV-kVA Meter installed in lungujja for a grain miller [3] ..................................................... 25
Figure 2-20: HV-3Ø Metering unit installed in Lungujja ........................................................................... 26
Figure 2-21:Structure of Yaka connection Scheme .................................................................................... 28
Figure 2-24: standard transfer specification (STS) meter ........................................................................... 28
Figure 2-25: Communication cable............................................................................................................. 29
Figure 2-26:customer interface unit. ........................................................................................................... 29
Figure 2-27:Yaka swipe cadets .................................................................................................................... 29
Figure 2-28:A circuit breaker...................................................................................................................... 31
Figure 2-29: Interior of a CB. ..................................................................................................................... 32
Figure 3-1: A table showing the tests carries out on a transformer............................................................. 34
Figure 3-2:Megger Insulation device .......................................................................................................... 37
Figure 3-3:Buchholz relay .......................................................................................................................... 38
Figure 3-4: Temperature relay .................................................................................................................... 39
Figure 3-5:Oil filtration machine ................................................................................................................ 40
Figure 3-6: BDV tester................................................................................................................................ 41
Figure 3-7:Table showing BDV test values ................................................................................................ 41
Figure 3-8: The outlet of oil from the transformer going into the heat running machine. .......................... 42
Figure 3-9: heat running and flow of oil through the machine from the inlet to the outlet......................... 43
Figure 3-10:getting an oil sample from the main tank of the transformer .................................................. 43
Figure 3-11: getting an oil sample from the main tank of the transformer ................................................. 44
Figure 3-12:head gear after it had been cleaned ......................................................................................... 45

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Figure 3-13:cleaning the tap changer using oil ........................................................................................... 45
Figure 3-14:using oil at high pressure to clean inside the tank ................................................................... 46
Figure 3-15Tap changer being cleaned ....................................................................................................... 46
Figure 3-16:meter testing set....................................................................................................................... 48
Figure 3-17:Securing using metallic tamper proof boxes ........................................................................... 49
Figure 3-18:Meter Audit report .................................................................................................................. 50
Figure 3-19:Lay out of Luzira Portbell substation. ..................................................................................... 54

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Table of Contents
DECLARATION ........................................................................................................................................... i
ACKNOWLEDGEMENTS .......................................................................................................................... ii
DEDICATION ............................................................................................................................................. iii
PREFACE .................................................................................................................................................... iv
ACRONYMS ................................................................................................................................................ v
List of figures ................................................................................................................................................ vi
1 CHAPTER ONE: INTRODUCTION ........................................................................................................... 1
1.1 Objectives of industrial training .................................................................................................... 1
1.2 Company background ................................................................................................................... 2
1.3 Administrative Structure. .............................................................................................................. 4
2 CHAPTER TWO: LITERATURE REVIEW ...................................................................................... 6
2.1 Power transformers ....................................................................................................................... 6
2.1.1 Working principle of transformer ......................................................................................... 6
2.1.2 The key components of the transformers .............................................................................. 8
2.1.3 Tap changer system............................................................................................................... 8
2.1.4 Buchholz Relay ..................................................................................................................... 9
2.1.5 Cooling System ..................................................................................................................... 9
2.1.6 Insulators ............................................................................................................................... 9
2.1.7 Pin Insulators ........................................................................................................................ 9
2.1.8 Polymeric Insulators ........................................................................................................... 10
2.1.9 Reel Insulators..................................................................................................................... 11
2.1.10 Stay Insulators ..................................................................................................................... 11
2.1.11 Standard Stay Assembly ..................................................................................................... 12
2.1.12 Outrigger stay assembly ...................................................................................................... 12
2.1.13 Flying stay ........................................................................................................................... 12
2.1.14 Surge Arresters.................................................................................................................... 13
2.1.15 Cross arms and Support Structures ..................................................................................... 13

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 2.1.16 Earthing System .................................................................................................................. 13
2.1.17 Distribution transformer maintenance................................................................................. 14
2.1.18 Parts of a distribution transformer....................................................................................... 14
2.1.19 Distribution Transformer faults........................................................................................... 19
2.2 Metering section.......................................................................................................................... 21
2.2.1 Energy Metering ................................................................................................................. 22
2.2.2 Types of meters ................................................................................................................... 22
2.2.3 Time of Use (TOU) ............................................................................................................. 24
2.2.4 Low Voltage kVA ............................................................................................................... 24
2.2.5 High Voltage Three Phase Metering ................................................................................... 25
2.2.6 Meter Number: .................................................................................................................... 26
2.2.7 Meter Auditing .................................................................................................................... 26
2.2.8 Yaka Pre-Payment System .................................................................................................. 27
2.2.9 Standard Transfer Specification .......................................................................................... 30
2.3 Switchgear section. ..................................................................................................................... 31
2.3.1 Circuit Breaker .................................................................................................................... 31
2.3.2 Construction of the Circuit Breaker (CB). .......................................................................... 32
2.3.3 Arc quenching medium ....................................................................................................... 33
2.3.4 The Ring Main Circuit ........................................................................................................ 33
2.3.5 Types of maintenance carried out on switchgears .............................................................. 33
3 PRACTICAL WORK DONE: ........................................................................................................... 34
3.1 Practical work done in transformers. .......................................................................................... 34
3.1.1 Transformer tests................................................................................................................. 34
3.1.2 Insulation-resistance test on the transformer bushings ....................................................... 36
3.1.3 Observing the internal physical structure of the Buchholz relay and understanding its
operation. ............................................................................................................................................ 37
3.1.4 Observing the internal physical structure of the temperature relay and understanding its
operation.:........................................................................................................................................... 38
3.1.5 Installation of a 1MVA transformer in SERERE district. ................................................... 39
3.1.6 Determination of the Break Down Voltage (BDV) of a transformer. ................................. 40
3.1.7 Heat running of a Power transformer at kireka substation in Kampala. ............................. 42
3.1.8 Tap changer maintenance of transformer number 1 and 2 at kireka substation. ................. 44

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 3.2 PRACTICAL WORK DONE IN METERING .......................................................................... 47
3.2.1 Meter Testing ...................................................................................................................... 47
3.2.2 Check meter tests ................................................................................................................ 47
3.2.3 Visual tests .......................................................................................................................... 48
3.2.4 Securing of meters .............................................................................................................. 48
3.2.5 Meter Reading ..................................................................................................................... 49
3.2.6 DISCONNECTION PROCEDURE ................................................................................... 51
3.2.7 Disconnection of single phase postpaid customers ............................................................. 51
3.2.8 Three Phase Disconnection. ................................................................................................ 52
3.3 SWITCH GEAR SECTION........................................................................................................ 54
3.3.1 Routine maintenance at Luzira Portbell substation. ............................................................ 54
3.3.2 Testing of a CB. .................................................................................................................. 55
4 CHAPTER FOUR: OBSERVATIONS, RECOMMENDATIONS AND CONCLUSIONS ............ 56
4.1 OBSERVATIONS ...................................................................................................................... 56
4.2 RECOMMENDATION .............................................................................................................. 57
4.3 CONCLUSION ........................................................................................................................... 57
5 References .......................................................................................................................................... 59

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1 CHAPTER ONE: INTRODUCTION
1.1 Objectives of industrial training
Industrial training is a prerequisite for every student pursuing a degree course in Electrical
engineering before graduation. In college of engineering, design, art and technology, a period
of eight to ten weeks are reserved at the end of second and third year for this training. These
objectives are divided into different parts as explained below.

To students
• To appreciate the relevance of team work in development of ideas in relevant fields,
through associating with experienced people.
• To develop research and presentation skills.
• To learn something about the world of work and company life through doing fieldwork.
Internship is an opportunity to learn from the “real” work environment therefore it
is important that the prospective intern expects to meet the real work challenges
ranging from lack of adequate facilities like work stations, slow internet, transport
among others.
• To apply the knowledge acquired during school time into real practice. Socially, a
student is able to learn the acceptable code of conduct in the working environment,
which is very important.
• The training period is also important as it helps the trainees to gain confidence in
preparation to making them good workers in future.
• It helps students to acquire different work ethics.
• To help students acquire knowledge and some engineering principles and concepts those
are never taught in class but are very vital in the engineering field.
• Another great objective of this training is to help students be acquainted with engineering
tools and understand how to use them. These may not be available at the University so
students get a chance to learn and use them.
• To help the students learn the codes of conduct of engineering as a profession.
• To aid students appreciate the engineering profession. Students obtain motivation and
love for this profession with the help of this training.

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 • The knowledge obtained in industrial training courses, enhances the work attitude for
any student.
• To present and learn a reality corresponding to the requirements of the company or an
organization where one is training from.
To the University
• To build on ideas students present and ensure smooth running of related research fields.
• To expose the potential of the University in some areas where it may not be known.
• To evaluate the students basing on the report presented.
• It exposes students to different field options thus making carrier guidance process much
easier for the University.
To the company
• Industrial training helps the firm to spot able and committed individuals that are more
hardworking than others and will benefit the company in a very positive way so that
they can be employed
• It teaches and builds upon the required practical and professional skills to future
employees into the industry.
1.2 Company background
UMEME is the largest energy distribution network company in Uganda, by customer numbers,
area of coverage, and assets. It was formed in 2004 when the Government of Uganda sold the
Uganda Electricity Distribution Company Limited to a consortium belonging to Globeleq (56
percent), a subsidiary of the Commonwealth Development Corporation (CDC) of the United
Kingdom and Eskom (44 percent), the electric generating company of South Africa. The transfer
of assets did not take place until 1 March 2005. During 2006, the consortium formed by Globeleq
and Eskom was restructured, with Globeleq becoming the sole owner of UMEME. Because of
internal restructuring within CDC, Actis Capital acquired ownership of the assets previously
owned by Globeleq, thereby making UMEME a 100 percent subsidiary of Actis Capital.

On 15 October 2012, UMEME became listed on the Ugandan bourse in an initial public
offering (IPO). The shares of the company started trading on the USE on 30 November
2012.Umeme stock shares were first cross-listed on the Nairobi Stock Exchange (NSE) on

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14 December 2012. The company expects to use the proceeds from the IPO, estimated at
about US$68 million (UGX: 170 billion), to upgrade the distribution network, establish pre-
paid metering and reduce energy distribution losses.

UMEME Limited’s shared purpose is "An electricity retailer and distribution business
providing an exceptional customer service in a safe, reliable and cost effective manner,
with a highly skilled and well-motivated workforce, generating sufficient profits to sustain
and build the business while providing value to the shareholders.
Umeme Limited is the largest energy distributor in Uganda, Distributing 97 percent of all
electricity in the country. As of June 2015, the company’s total assets were approximately
UGX: 1.775 trillion, with shareholder’s equity of approximately 503.8 billion. As of January
2016,
Umeme’s customer base was about 790,000 with approximately 16,000 customers being
added every month
UMEME Limited core values:
• Safety governs all our actions
• Integrity founded on honesty and ethical behavior.
• Hard work, dedication and achievement of results
• Customer satisfaction
UMEME Limited mission:
• To improve the relationship between the electricity utility and its customers
• To improve the quality of supply to customers
• To re-establish the financial viability of Uganda's electricity distribution business
UMEME Limited focus areas are:
• Loss reduction to 14% within seven years
• Safety for all
• Visible customer service Improvement
• Cost and efficiency improvement
• Revenue collection to over 100%
UMEME Limited method of operation:
• Accurately measure consumption

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 • Produce error free bills
• Provide an acceptable quality of electricity supply
• Treat customers fairly and their property with respect UMEME Limited brand
values:
• Visible Customer service
• Safety of staff and customers is key
• Transparency and openness in all our dealings
• Employees are fundamental
Umeme 2018 targets
• Umeme aims at adding more 200,000 customers to the grid by the end of 2018
• Reduce energy not served from 130GWh to 100GWh there by earning more 15billion Ushs
• Reduce customer hours lost from 120hrs to 90hrs
• Reduce losses to 14.7%

1.3 Administrative Structure.

According to UMEME and the coverage of the distribution network, Uganda as a country is
subdivided into 6 regions and each region is made up of districts (UMEME districts). There
are currently 26 districts in total. Below is a list of the regions and their respective districts;
Table 1-1District structure of umeme

UMEME KAMPALA KAMPALA KAMPALA NORTHER WESTERN EASTERN

REGION EAST SOUTH CENTRAL N REGION REGION REGION

UMEME Banda Najjanankumbi Metro Bombo Masaka Jinja

DISTRICT
Naalya kabalagala Wandegeya Gulu Mbarara Mbale

Kitintale Entebbe Nateete Hoima Mityana Iganga

Mukono Nakulabye Lira Kasese Tororo

Fort portal Kabala

Bushenyi

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Figure 1-1: The company structure of umeme

Figure 1-2: The engineering structure of umeme

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2 CHAPTER TWO: LITERATURE REVIEW
2.1 Power transformers
A transformer has two or more windings wound on ferromagnetic cores coupled by a mutual
magnetic field. For a two winding transformer, the winding with the higher number of turns
will have a high voltage and is called the high voltage (HV) or High Tension winding while
the winding with the lower number of turns is the low voltage (LV) or low tension winding.
To achieve higher magnetic coupling between the windings, they may be formed of coils
placed one on top of another where the low voltage winding is placed nearer the coil and the
high voltage winding on top [1].

2.1.1 Working principle of transformer

The working principle of a transformer depends upon Faraday’s law of electromagnetic
induction. This principle states, “The rate of change of flux linkage is directly proportional
to the induced electromotive force in a conductor or coil”. The transformer is based on two
principles: first, that an electric current can produce a magnetic field and second that a
changing magnetic field within a coil of wire induces a voltage across the ends of the coil
(electromagnetic induction). Changing the current in the primary coil changes the magnetic
flux that is developed. The changing magnetic flux induces a voltage in the secondary coil.
Current passing through the primary coil creates a magnetic field. The primary and
secondary coils are wrapped around a core of very high magnetic permeability, usually iron,
so that most of the magnetic flux passes through both the primary and secondary coils. Any
secondary winding connected to the load causes current and voltage induction from primary
to secondary circuits in indicated directions. The changing magnetic field induces an Emf
across each winding. The primary Emf, acting as it does in opposition to the primary voltage,
is sometimes termed the counter Emf. This is in accordance with Lenz's law, which states
that induction of Emf always opposes development of any such change in magnetic field.
A transformer is a device that steps down or steps up voltages on the power system. It is
probably the most important plant on the network. Shown below is a figure of a power
transformer [2].

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 [2]
Figure 2-1: Ideal Transformer diagram

7
 Figure 2-2: Namungoona substation Power transformer

2.1.2 The key components of the transformers

The key components of the transformers include the bushings and terminals, tap Changer systems,
buchholz Relay, temperature sensors, windings and core steel, main tank and cooling system, oil
and paper insulation and some of the above components are described below;

2.1.3 Tap changer system

The tap changer system is categorized into On-Load Tap Changer and No load tap changer:
In the On load tap changer, the device is fitted on a transformer to regulate the output voltage to
required levels. Transformers with on-load tap changers consist of a diverter switch and a selector
switch operating to effect the transfer of current from one voltage tap to the next. For No-Load
Tap Changer, the design in such a way that easy and perfect tap changing is done mainly on the
cover of the transformer by manual operation. Even minute attention is given to the quality of the
8
materials used so that good contact can be maintained for a long time and perfect insulation can
be assured [2].

2.1.4 Buchholz Relay

This is also known as a gas relay or sudden pressure relay. It is a safety device mounted on
the transformer and is equipped with an external overhead reservoir called a conservator.
This device is sensitive to the effects of dielectric failure in the equipment thus in case of a
slow oil leak or slight overdose, it initiates an alarm signal.

2.1.5 Cooling System

The cooling system of a transformer helps in maintaining the temperature rise of various
parts within permissible limits. Several cooling methods are available but the choice of
picking the right type for particular application depends on factors as rating, size and
location. The different cooling methods include air cooling for dry type transformers,
cooling for Oil immersed transformers, Oil Natural Air Natural type (O.N.A.N), Oil
Natural Air Forced type (O.N.A.F), Oil Forced Air Natural type (O.F.A.N), Oil Forced
Air Forced type (O.F.A.F), Oil immersed water cooled transformers, Oil Natural Water
Forced type (O.N.W.F) and Oil Forced Water Forced type (O.F.W.F) [1].
2.1.6 Insulators
An electrical insulator is a material whose internal electric charges do not flow freely, and
which therefore does not conduct an electric current, under the influence of an electric
field. A perfect insulator does not exist, but some materials such as glass, paper and rubber-
like polymers, which have high resistivity, are very good electrical insulators. In Overhead
power lines, insulators must support the conductors and withstand both the normal
operating voltage and surges due to switching and lightening. Insulators are classified as
either pin-type, which supports the conductor above the structure, or suspension type,
where the conductor hangs below the structure. Insulators used on High Voltage power
lines include the pin insulators, polymeric insulators, post insulators and Disc insulators.

2.1.7 Pin Insulators

A pin insulator consists of a non-conducting material such as porcelain, glass, plastic,
polymer, or wood that is formed into a shape that isolates a wire from a physical support

9
(or "pin") on a utility pole or other structure, provide a means to hold the insulator to the
pin, and provide a means to secure the conductor to the insulator. The pin insulator is
directly connected to the supporting pole. Pin insulators have a value, R-XX, attached to
them that is representative of their insulation properties. This value varies for insulators
used on different voltages. For 11kV, the insulators are R-50 and R-70 whereas those of
33kV are R-90. Listed below are some of the pin insulators used here in Uganda; Pin
Insulator R90 are used on the 33kV line which include the one shown below.

Figure 2-3:Pin insulator R90

2.1.8 Polymeric Insulators

A polymeric Insulator consists of a fiberglass core covered with weather resistance
polymeric shedded sleeve and aluminium end fittings. These insulators offer significant
advantage like better performance in highly polluted environment, flame / arc resistance,
resistance to chemicals and UV rays and are Vandal proof. They are specifically designed
polymeric material insulators with a self-cleaning property, unbreakable, compact and
lightweight compared to porcelain insulators and there surface hydrophobicity is
maintained over a long period. Polymeric insulators are usually used in case of an angle
section. Shown below is a figure of a polymeric insulator;

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 Figure 2-4: Polymeric insulators

2.1.9 Reel Insulators

These are used to fasten LV conductors onto the pole. On LV structures, the reel insulator
is bolted (with a 5/8x12” bolt) directly onto the pole and the conductor fastened onto the
insulators. These insulators are made out of porcelain. They are small. The figure shown
below is of a reel insulator;

Figure 2-5: Reel insulator

2.1.10 Stay Insulators

Stay insulators prevent any high voltages caused by electrical faults from reaching the
lower portion of the cable that is accessible. They form part of the standard stay assembly.
The figure shown below is of a stay insulator;

Figure 2-6: Reel insulator [2]

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2.1.11 Standard Stay Assembly
The Standard stay assembly is used to support poles that carry the lateral tension of the
long straight sections of conductors. For example, termination poles which are situated at
the end of a straight section of utility line, where the line ends or angles off in another
direction. The stay assembly consists of a stay wire, stay insulator, stay rod, stay stub and
stay bracket. Other parts used in setting up the stay assembly include the grips and top pole
make off. It is worth noting that the pit in which the stay stub and part of the stay rod are
buried should be 7ft deep. The figures below show the stay rod and stay stub.

2.1.12 Outrigger stay assembly

The Outrigger stay assembly performs the same role as the standard stay assembly, only
that it is applied when the termination pole is close to the road. If the available space is too
small implementation, then a flying stay is used. The figure below shows a pole supported
by the
Outrigger stay assembly;

Figure 2-7:Outrigger Stay assembly(L) Flying stay assembly(R)

2.1.13 Flying stay

This is a kind of stay whereby the stay is not applied directly to the pole supporting the line.
A stay wire is applied from the pole supporting the line to another pole a few meters away
12
to which the stay is applied. This is used in instances where it is not possible to apply the
stay near the pole supporting the line. An example is when the pole is near a road. A stay
wire is run from the power line pole to another pole across the road upon which a stay is
applied.

2.1.14 Surge Arresters

A surge arrester is a protective device designed primarily for connection between a
conductor of an electrical power system and ground to limit the magnitude of transient
over voltages on equipment. It possesses a high voltage terminal and a ground terminal.
When a lightening surge or switching surge travels along a power line to the arrester, the
current from the surge is diverted through the arrester, in most cases to the ground. The
figure shown below is of a surge arrester;

Figure 2-8:Surge arrester

2.1.15 Cross arms and Support Structures

The Crossarms serve the purpose of supporting the conductors and insulators on the power
line. They differ in construction and specifications depending on the voltage of the power
line (11kV line crossarms have different specifications from those of a 33kV line) and their
location on the power line. Some types of crossarms classified basing on their location on the
power line include the intermediate crossarms, terminal crossarms and pilot crossarms. The
Support structures serve the purpose of supporting equipment (underneath the object and
holding it up) on the power line. For example a pole mounted transformer is supported by the
U-channel transformer platforms, a cross arm is supported by struts.

2.1.16 Earthing System

Earthing means the connecting of apparatus electrically to a general mass of earth in such a
manner that it will ensure an immediate safe discharge of electrical energy at all times.
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Normally on overhead power lines the equipment that are earthed include the transformer
tank for MV side, MV cables (Amour and cable-ends boxes), air break switches, Line
isolator structures, MV lines (different types of construction), MV lines wishborne
construction grounded at all second poles, MV lines Top bracket make off that are grounded
at all second poles, MV lines H-Pole construction, HV lines Towers earth wire top run off.
Grounded at all structures (Steel pylons) and HV lines H-pole conductor suspended
construction.
The process of Earthing in overhead power lines basically involves digging of trenches that
lead to an earth pit (1-2 feet) through which the earth wires are laid and burying of an earth
mat plus earth rods in that pit. In intricate areas like swamps and rocky places, good soil has
to be imported or the earth wire is flown to good soil. It is worth noting that an Earthing
resistance of less than or equal to 10M Ohms is recommended depending on the sensitivity
of the equipment. 1 Ohm or below, if attainable would be the best.

2.1.17 Distribution transformer maintenance

Transformers are named distribution, power or instrument transformers according to the type
or duty they perform. A distribution transformer is one that provides the final voltage
transformation in the electric power distribution system, stepping down the voltage used in
the distribution lines to the level used by the customer (240Volts single phase and 415Volts
three phase). These transformers have outputs of up to 500 kilo Volt Amperes (kVA).
2.1.18 Parts of a distribution transformer.
Transformer tank: It’s a metallic tank in which oil filled for cooling the windings..

The studs are the termination points of the transformer on to which the wiring is connected. These
are the conducting parts and they are connected to the windings of the transformer. Power rating
of a transformer is given in KVA. The studs on the high voltage side are smaller in diameter thus
a smaller cross sectional area owing to the low current following through the high voltage side
compared to the bigger diameter of the studs on the secondary or low voltage side owing to the
high current flowing through them.

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 Figure 2-9Studs

For distribution transformers, in case of need of replacement of studs, 315kVA and

200kVA use the same spares while 25kVA, 50kVA and 100kVA use the same spares.
The bushings: These are insulators through which the conductor must pass to prevent the
conducting part (the stud) from making contact with the transformer body (transformer tank). The
bushings are made up of grooves. Bushings must be water tight, air tight and oil tight. The types
of bushings are oil filled bushings, capacitor type bushing and solid porcelain bushing which the
most common because of its excellent electrical and mechanical qualities. In the case of
distribution transformers, the primary bushings for a 33kV are different from those of an 11kV in
that those for a 33kV have more grooves and bigger grooves than for an 11kV transformer. The
primary bushings for 33kV transformer with ratings of 50kVA and 100kVA are usually slanting
to increase the clearance but this may vary from one manufacturer to another.

15
 Figure 2-10:Bushings of an 11kV transformer on the left and for 33kV on the center and right

The pressure release valve or breather. A transformer tank filled with a cooling liquid is subjected
to internal pressure and has to be provided with a safety valve suitably calibrated for the maximum
allowed pressure so that the overpressure caused by internal faults can be instantaneously relieved
through the valves thus avoiding greater damages such as deformation or burst of the transformer
tank.

Figure 2-11: pressure release valve

Cooling fins. When a transformer is in operation, a lot of heat is created inside the transformer and
this heat may deter the normal operation of the transformer therefore cooling is needed. The
cooling fins increase the surface area to radiate out the heat. Some transformers do not have cooling
fins but they have large transformer tanks for that transformer rating and this helps increase the
surface area to radiate out the heat.

Silica gel breather. Whenever electrical power transformer is loaded, the temperature of the
transformer insulating oil increases, consequently the volume of the oil is increased. As the volume
of the oil is increased, the air above the oil level in conservator will come out. Again, at low oil
temperature; the volume of the oil is decreased, which causes the volume of the oil to be decreased
that again causes air to enter into conservator tank. The natural air always consists of more or less
moisture in it and this moisture can be mixed up with oil if it is allowed to enter into the
transformer. The air moisture should be resisted during entering of the air into the transformer,
because moisture is very harmful for transformer insulation. A silica gel breather is the most
commonly used way of filtering air from moisture.

16
Silica gel crystal has tremendous capacity of absorbing moisture. When air passes through
these crystals in the breather; the moisture of the air is absorbed by them. Therefore, the air
reaches to the conservator is quite dry, the dust particles in the air get trapped by the oil in
the oil seal cup. The oil in the oil sealing cup acts as barrier between silica gel crystal and
air when there is no flow of air through silica gel breather. The colour of silica gel crystal
is dark blue but when it absorbs moisture; it becomes pink. When there is sufficient
difference between the air inside the conservator and the outside air, the oil level in two
components of the oil seal changes until the lower oil level just reaches the rim of the
inverted cup, the air then moves from high-pressure compartment to the low-pressure
compartment of the oil seal. Both of these happen when the oil acts as core filter and
removes the dust from the outside air.

Oil. Oil in distribution transformers acts an insulator as well as a coolant. It also prevents
direct contact of atmospheric oxygen with cellulose made paper insulation of windings,
which is susceptible to oxidation.

Oil conservation tank. This is a drum containing transformer oil mounted on top of the
transformer. An oil level indicator is usually fixed to it. This tank is used to store excess oil
and refill the one in the tank in case the level goes down. In addition, oil in the transformer
tank expands and contracts according to the heat developed and cause the level of oil in the
conservator to rise and fall respectively, so this tank provides space for the expansion of oil.

Oil level indicator. The presence of an oil indicator varies from one transformer
manufacturer to another. This shows the level of oil in a transformer.
Temperature indicator. This is not common on most of the transformers. The
presence of a temperature indicator on a transformer is to indicate the temperature
of oil on the surface.
Arcing horns and the surge arrestors. These protect the transformer against voltage surges
that can be caused by lightning or improper switching in the circuit. They protect the
bushings from flash over due to lightning. Surge arrestors (one for each phase) are connected
to the high voltage side using jumpers and they are shorted at their ends and grounded. Surge
arrestors are connected in parallel. When the voltage on the ungrounded conductor is normal,
17
the surge arrestor has a high resistance and acts as an open circuit preventing current flow
through the surge arrestor to the earth at normal system voltage. Lightning striking near a
power line is a frequent cause of surges which travel in both directions along a wire from
the point of origin. When a surge reaches a surge arrestor, the device must act like a closed
switch to the voltage allowing the voltage to dissipate by passing current through the surge
arrestor to the earth. The surge arrestor must be fast acting and capable of passing the energy
of the surge so it will survive to be ready to repeat the process. The resistance of a surge
arrestor should be above 1Gigaohm (GΩ) so that they do not operate under normal voltage
conditions.

Figure 2-12:Arcing horns and surge arrestors

Tap-changer. It is often necessary to vary the voltage in the primary winding to allow for a varying
voltage drop in the feeder in order to attain a nearly constant output in spite of a varying input.
This can be done using a tap changer. There are two types of tap changers and these are the no-
load tap changer and the on-load tap changer. Distribution transformers use no-load tap changers.
The operation this kind of tap changer involves; disconnections of the transformer from supply
and reconnection after adjustments have been made. Most transformers have tap changers with
five taps with tap 3 as the nominal.

18
 Figure 2-13:No load tap changer
Primary and secondary windings. A transformer consists of two windings made of copper and
insulated from each other by impregnated paper insulation. These windings are magnetically
linked through the core. The winding which is connected to the supply is the primary winding and
the other winding on which the load is connected is the secondary winding.
2.1.19 Distribution Transformer faults
In order to maximize the lifetime and efficiency of a transformer, it is important to be aware of
possible faults that may occur and to know how to catch them early. Regular monitoring and
maintenance can make it possible to detect new flaws before much damage has been done.

Factors causing blowing of transformers or causes of common faults

Vandalism: Some of the transformers in rural areas are vandalized and so some parts
become faulty for example theft of the transformer windings since they are made of copper
and theft of transformer oil.
Lightning due to poor termination of surge arrestors: Surge arrestors on a transformer are
responsible for protecting the transformer against surges usually caused by lightning or
sudden switching. However, if the surge arrestors are terminated poorly, they do not perform
their function therefore the transformer suffers the surges when they occur causing it to
blow. The transformer is prone to flashovers.

19
 Figure 2-14:A transformer bushing with flash over

Overload: Overload is when all three phases of the transformer are overloaded. Overloading of
transformers without looking into their overload capacity is another reason for early failure. It has
become the practice to connect additional loads on the basis of maximum demand recorded at
some point of time without reference to seasonal variations and assuming unrealistic diversity
factors. Unauthorised loads result in unforeseen overloading. Overloading also happens if periodic
checks are not carried out and corrective measures are not taken.

Wide variation in load levels and ambient temperature: Wide variation in load levels and ambient
temperature makes undesirable breathing and ingress of moisture even more intense in the case
of rural distribution transformers. The interchange of air brings oxygen from the atmosphere into
contact with oil. It is well known that moisture weakens the dielectric strength of oil to form
sludge and finally causes a deposit to form on the windings. The deposit may in time be sufficient
to obstruct the ducts placed in the windings for the purpose of oil circulation resulting in
temperatures higher than those for which the transformers are designed. Ultimately, the insulation
of the winding may become carbonized to such an extent as to cause failure
Load imbalance: This is when the phases are not equally loaded that is when one phase is
overloaded. In distribution networks, many customers can be connected to the same phase while
the other phases are less loaded so that one phase is overloaded.
Poor termination and loose connection: Due to poor workmanship and lack of materials, some
transformers have poor lagging and loose connections that result in burning of the studs.

20
2.2 Metering section
The metering engineer headed the metering section. It involved surveying and Inspection, energy
metering, installation of single phase and three phase meters, meter testing, meter auditing and
verification, meter replacement, meter reading and securing of meters.
An electricity or energy meter is a device that is used to accurately measure and record
consumption of energy by an electrical load. The unit of energy is Kilowatt hour (KWH).
Electricity utilities such as UMEME LTD use electric meters installed at customers’ premises to
measure electric energy delivered to their customers for billing purposes. The main sector players
involved in the management and regulation of the metering assets include Umeme, ERA, UNBS,
UETCL and UEDCL. Umeme has deployed a number of metering technologies on the network
which include; post-paid metering and prepaid metering for domestic consumers to guide the
decisions, processes and systems that are used to maximise the technical and operational
performance of metering assets over their lifecycle and ensure that the management of the
changing asset base and requirements is achieved in the most robust, efficient and sustainable
manner. To also ensure the prudent, efficient and reliable delivery of metering services that meets
customers’ and stakeholders’ needs and ensure the safety of the public and personnel that install,
operate and maintain the assets

Figure 2-15: Key Sector Players in metering performance and regulation

Name Role Reference Document

ERA Determine tariff and metering regulations for Tariff structure released on quarterly basis
licensees

UETCL Install safe and accurate boundary metering Power Sales Agreement
assets ( between UETCL and licensees) and
ensure their maintenance

Umeme -Install safe and accurate metering assets and Quality of service Code, Grid Code,
ensure their maintenance Prepayment Guidelines
UNBS -Type Approval certification Weights and Measures rules (2015)
-Test new and in-service meters for licensees

21
 UEDCL Issue a letter of ‘No-Objection to Umeme prior Lease and Assignments Agreement
to disposal of metering assets

2.2.1 Energy Metering

Energy metering is the process of measuring the amount of electric energy consumed by a
residence, business, or an electrically powered device. Electricity meters are typically calibrated
in billing units, the most common being the kilowatt-hour. Meters look the same but differ in the
programming and C.T ratios mainly for security reasons and in the event, where customer asks for
upgrade due to increase in load [3].
2.2.2 Types of meters
There are two types of meters namely;
Electromechanical meters; this is the oldest and most common type of electricity meter. It operates
by counting the revolutions of a non-magnetic, but electrically conductive, metal disc, which is
made to rotate at a speed proportional to the power passing through the meter. The number of
revolutions is thus proportional to the energy usage. The voltage coil consumes a small and
relatively constant amount of power, typically around 2 watts which is not registered on the meter.
The current coil similarly consumes a small amount of power in proportion to the square of the
current flowing through it, typically up to a couple of watts at full load, which is registered on the
meter. The figure below shows an electromechanical meter.

22
 Figure 2-16:Electromechanical meter

Electronic meters; Electronic meters display the energy used on an LCD or LED display, and some
can also transmit readings to remote places. In addition to measuring energy used, electronic
meters can also record other parameters of the load and supply such as instantaneous and maximum
rate of usage demands, volltages, power factor and reactive power used. They can also support
time-of-day billing, for example, recording the amount of energy used during on-peak and off-
peak hours.

Figure 2-17:Digital electronic Meter

Energy meters can be categorized into classes depending on their accuracy. Common classes are
Class 1 for accuracy between -1% and 1%; and Class 2 for accuracy between -2% and 2%. Two
service options include single and three phases and are issued to consumers depending on the size
of the consumers’ load.

Single Phase Supply. This is a form of supply where the consumer is supplied by single-phase
power. It is suitable for consumers whose continuous load current does not exceed 80A. The
energy supplied is measured at low voltage and the load current directly measured by a single-
phase meter. Single-phase supply is classified into two tariffs and that include Domestic (for
energy being used for domestic/ household use) and Commercial (for energy being used for small
commercial use for example in shops).
23
Three Phase Supply. This is a form of energy supply where the consumer is supplied with three-
phase power. It is suitable for consumers with continuous load currents exceeding 80A. Three-
phase energy can be metered either at low voltage or at high voltage.

Low Voltage Three Phase Metering is a type of energy metering applied to consumers with
continuous loads between 80A and 800A. It is categorized into the following tariff categories:

2.2.3 Time of Use (TOU)

This is applied for consumers with continuous load currents between 80A and 100A (+20A). Time
of use metering involves dividing the day, month and year into tariff slots and with higher rates at
peak load periods and low tariff rates at off-peak load periods. This TOU metering tariff comprises
of three rates in Uganda, which are peak (6pm to 12pm), shoulder (6am to 6pm) and off peak
(12pm to 6am).

[3]

Figure 2-18:T.O.U meter installed opposite makerere university traffic lights [3]

2.2.4 Low Voltage kVA

This is applied for consumers with a maximum load of 500kVA and a current rating between 100A
and 800A. In this case the load currents exceed the current ratings of the energy meter. Current
transformers (CTs) are therefore used to transform the load currents to current levels usable by the
meter. Examples of CTs used for kVA-LV include; 200/5A, 400/5A and 800/5A. The CT ratios
are programmed into the meter which enables it to determine the actual load currents and therefore
compute the energy being consumed by the load. This metering tariff comprises of four rates and
24
these are peak, shoulder, off peak and maximum demand charge per kVA. Load and supply cable
are continuous but C.Ts (output 5A) are clamped on them and their s1 and s2 terminal wires are
connected to the meter. Current low and voltage high meaning uses only CTs and voltage of 415
V.

Figure 2-19:LV-kVA Meter installed in lungujja for a grain miller [3]

2.2.5 High Voltage Three Phase Metering

This type of metering is done for consumers with loads exceeding 500kVA up to 10,000kVA
meaning the consumer may have more than one dedicated transformer. The energy supplied to the
consumer is measured at the MV line that supplies the transformer. In this case, the supply voltages
and load currents are too high to be used by the meter. A device known as a metering unit or
Metering transformer, which consists of both voltage and current transformers is used to transform
the supply voltages and load currents to values usable by the meter. The VT and CT ratios are then
programmed into the meter to enable it determine the actual supply voltages and load currents and
therefore determine the energy consumption. There are five tariff rates in this tariff plan and these
are peak, shoulder, off peak, maximum demand charge up to 2,000kVA and maximum demand
charge between 2,000kVA and 10,000kVA. The metering units used in Uganda have a current
rating of 150-300/1A and a voltage rating of 1:1. Customers having a load current below 150A on
the HV side are connected in half tap while those exceeding 150A are connected in full tap. This
kind of metering is also used to measure the amount of energy supplied to the district and the
25
energy supplied by the district to other districts. MV kVA meters are installed at the substation to
meter the energy supplied to the district and also installed at district boundaries to meter energy
supplied to neighboring districts. Those at district boundaries are known as boundary meters.

Figure 2-20: HV-3Ø Metering unit installed in Lungujja

2.2.6 Meter Number:

The quickest way of differentiating meters is by looking at the meter numbers. The
classification of meter numbers include the U2’s for TOU meters, U3’s for LV-KVA meters,
U4’s for HV-KVA meters and U5’s for substation meters.
On Layers of insulation, TOUs have the highest insulation since connection of cables is direct
hence direct connection of high currents. They have a symbol drawn on meter showing 3 layers of
insulation. KVAs and HTs have lower insulation since both make use of CTs that step down the
current. They have a symbol drawn on meter showing 2 layers of insulation (for some the layers
are complete and others incomplete)

2.2.7 Meter Auditing

This is the verification of the current and voltage readings registered by the energy meter using a
multimeter/clamp on meter. This was done for time of use meters. The following values as
26
registered by the meter were noted: load currents, load voltages, load power (real), load apparent
power, power factor. The load currents and voltages were then measured using a multimeter and
then the two sets of values compared. For meters that were tampered with, the two sets of values
were found to be inconsistent. The load currents registered by the meter were found to be less than
those measured by the multimeter were. These customers were fraud charged and their meters
replaced at their cost.

2.2.8 Yaka Pre-Payment System

Yaka is the new prepayment system from Umeme that allows customers to conveniently manage
and control their electricity. It works much like buying airtime for your mobile phone line, when
the units are used up, the customer can buy more to continue using the service. Yaka has maximum
control and monitoring of his electricity usage and consumption and one has access to many
vending options 24 hours, 7 days a week which makes payment for electricity more convenient.
With yaka, you are able to buy electricity units in affordable quantities before use and paper bills
overcoming the problems of disconnections, hassles of reconnections and long queues.
How Yaka works
Upon conversion from a post-paid meter to the Yaka! Meter, you are given a meter number (On
the meter card)
Purchase Yaka! units by paying the amount you want using your specific meter number. You will
receive a 20-digit token
Load the 20-digit token onto your Yaka! meter just as you load airtime on your phone and watch
to see if the purchased units have been added to your balance
Once your units are added, you can now use your electricity. When the units are running low, the
meter makes a continuous beeping noise to warn you. When this happens, load more Yaka! Units.
Type of boxes
One-way boxes: These usually take one meter and are usually grey or cream (rarely). To open the
grey box, they have grooves or slots on the side and need the casing to be slid open upwards.
Ensure when sliding upwards, use the right slot on the side.

Four way boxes: These usually take a maximum of four meters with four upstream CBs and a
common bus bar split into two for load balancing as shown in the figure below. There is also a

27
neutral block and they are usually white in colour. To open them one needs an Allen key. When
covering ensure there is no air gap at the sides. Ensure the incoming neutral is well connected to
the neutral block and then from the neutral block connect the neutral to the meters to avoid meter
malfunction.

Figure 2-21:Structure of Yaka connection Scheme

A Yaka scheme consists of the following;

Standard Transfer Specification (STS) meter: which is the Yaka meter

Figure 2-22: standard transfer specification (STS) meter

Communication cable: passage for communication signals between CIU and STS meter

28
 Figure 2-23: Communication cable

Consumer Interface Unit. It is installed in a convenient place inside house and allows customer to
monitor his power consumption and load energy units.

Figure 2-24:customer interface unit.

Yaka Swipe Card: where the meter account name is written

Figure 2-25:Yaka swipe cadets

29
2.2.9 Standard Transfer Specification
Standard Transfer Specification (STS) is a standard regarding the manufacture of prepaid meters
as well as the vending system used to vend prepaid vouchers. STS is a secure message system for
carrying information between a point-of-sale and a meter, and is currently finding wide application
in electricity metering and payment systems. STS has become the standard to which all prepaid
meters in the industry have to be manufactured using standard cryptography and cryptographic
keys. It is thus imperative that all prepaid meters need to be able to function on all the different
vending systems available and that all vending systems need to use the same standard to be able
to accept all the prepaid meter variants. All prepaid meters in UMEME are STS (Standard Transfer
Specification) compliant. This means that they all use the same coding system. In UMEME this is
a 20 digit encrypted code, preventing fraudulent vouchers from being generated. A token is a STS
(standardized transfer specification) compliant 20-digit number issued upon purchase that will
release the specified amount of electricity (in KWH) on your STS Prepaid Meter. Tokens can be
issued in any amount
How STS Prepaid Electricity Meters Work.

A prepaid electricity meter is a KWH (Kilowatt Hour) meter, measuring electrical consumption.
The main difference is that this KWh meter counts backwards as the electricity is consumed and
has a relay (an automatic switch) which disconnects the power when the KWh reading on the meter
reaches zero. It further incorporates hardware, which has the ability to decode the token number
entered and convert it to KWh.
Prepaid Meters (the hardware) needs software that have the ability to generate a token, which can
be deciphered by the meter and converted to KWh. The software is programmed to only generate
a token if the meter is in credit. In UMEME, all prepaid software functions by using STS
technology. An STS compliant prepaid meter has the ability to function on any STS compliant
software. Since there are numerous prepaid meter manufacturers as well as numerous software
providers, a specific prepaid meter has to be registered on a specific software package before it
will function. All STS compliant prepaid meters are identified by an 11-digit code (account meter
number), and can only be linked to one software package at a time. In order for a prepaid meter to
switch to a different software package, the current software supplier as well as the new software

30
supplier need to issue a code, which is physically punched into the meter, before the meter will
accept tokens generated by the new software company.

2.3 Switchgear section.

In an electric power system, switchgear is the combinations of electrical disconnect switches, fuses
or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used
both to de-energize equipment to allow work to be done and to clear faults downstream. This type
of equipment is important because it is directly linked to the reliability of the electricity supply.
The common types include circuit breakers, electric fuses and isolators.

2.3.1 Circuit Breaker

An Electrical Circuit Breaker is a switching device that can be operated manually as well as
automatically for control and protection of electrical power system. As the modern power system
deals with huge currents, the special attention should be given during designing of circuit breaker
to safe interruption of arc produced during the operation of circuit breaker. There are different
criteria used to categorize circuit breakers

Figure 2-26:A circuit breaker.

According to their arc quenching media the circuit breaker can be divided as an oil circuit breaker,
air circuit breaker, SF6 circuit breaker or Vacuum circuit breaker

According to the servies of the circuit breaker whether outdoor circuit breakers or indoor circuit
breaker.

31
According to the operating mechanism of circuit breaker that includes spring operated circuit
breaker, pneumatic circuit breaker, and hydraulic circuit breaker.

According to the voltage level of installation that includes high voltage circuit breaker, medium
voltage circuit breaker and low voltage circuit breaker.

According to tracking ability of the breaker ie track type or un track type. [4]

2.3.2 Construction of the Circuit Breaker (CB).

The circuit breaker mainly consists of fixed contacts and moving contacts. In normal “on”
condition of circuit breaker, these two contacts are physically connected to each other due to
applied mechanical pressure on the moving contacts. There is an arrangement-stored potential
energy in the operating mechanism of circuit breaker that is realized if switching signal is given to
the breaker. The potential energy can be stored in the circuit breaker by different ways like by
deforming metal spring, by compressed air, or by hydraulic pressure. However, whatever the
source of potential energy, it must be released during operation. Release of potential energy makes
sliding of the moving contact at extremely fast speeds. All circuit breaker has operating coils
(tripping coils and close coil), whenever these coils are energized by a switching pulse, and the
plunger inside them displaced.

Figure 2-27: Interior of a CB.

32
2.3.3 Arc quenching medium
Current can flow through the circuit breaker even when its contacts are open due to the connection
formed by the interaction of the electromagnetic fields formed from the two contacts near each
other. During the flowing of current from one contact to other, the path becomes so heated that it
glows. This is called arc. Whenever, on load current contacts of circuit breaker open there is an
arc in circuit breaker, established between the separating contacts. As long as this arc is sustained
in between the contacts the current through the circuit breaker will not be interrupted finally as
because arc is itself a conductive path of electricity. For total interruption of current the circuit
breaker, it is essential to quench the arc as quick as possible. The main designing criteria of a
circuit breaker is to provide appropriate technology of arc quenching in circuit breaker to fulfill
quick and safe current interruption. There are mainly four types of arc quenching media but three
are currently used in UMEME include air blasts, oil, vacuum and SF6 gas. SF6 gas is the most
commonly used medium because of its properties such as non-reactivity, being inert and odorless,
having a very high density and dielectric strength [4].

2.3.4 The Ring Main Circuit

The Ring Main Unit (RMU) is used to interconnect underground networks. The incoming and
outgoing cables are connected by the RMU’s are connected in form of a ring and distribution
transformers are connected to the RMU’s to serve the industries and homesteads. The lines are
connected directly without any protection because they are protected from the substation while the
transformer is protected by special fuses know as striker pin fuses which trip the transformer when
there is a fault on any of the phases. The tripping of the transformer is done automatically when
the fuses blow. The RMU’s also have quenching medium like circuit breakers that are oil and SF6
which also double as insulators. They also increase the clearance between the contacts. Springs
help in the reset and earthing of the RMU. The figure below shows the RMU.

2.3.5 Types of maintenance carried out on switchgears

There are mainly two types of maintenance carried out on switchgears that include the preventive
or routine maintenance (This is the type of maintenance done to keep the switchgear in good
working conditions and to prevent any damages. The routine maintenance is done often and usually
it involves cleaning, lubrication, greasing and other activities) and corrective maintenance which
is carried out when faults occur and the procedure is dependent on the fault.
33
3 PRACTICAL WORK DONE:
3.1 Practical work done in transformers.
3.1.1 Transformer tests
Transformer tests are tests that were always performed on transformers before they are taken
into the field to be used in operation. This is important that the transformers sent to the field
to be placed in the system are in proper working condition to ensure reliability in power
delivery to consumers. Some of the tests are carried out while the transformer is in the field
as part of maintenance procedures. Below are the tests we performed on transformers:

Figure 3-1: A table showing the tests carries out on a transformer

TEST PROCEDURE PURPOSE OF TEST

Voltage ratio/open We injected 415V at the HV side To ensure that the transformer
circuit terminals of the transformer and left the is outputting the required
LV side terminals open-circuited with no voltage level.
load connected.
Used a digital multimeter to measure the
voltage between the phases; red and
yellow, yellow and blue, blue and red
phases received at the LV side terminals.
Recorded the values

Compared the recorded values with the

expected values.
The recorded values were in the were in
the desired 6% margin in variation with
expected values.

34
Short circuit We Short circuited the LV side terminals To determine the protection
and injected 415V at the HV side settings used on the HV side of
terminals of the transformer. the transformer.
Used a clamp meter to measure the
current flowing at the LV side terminals.
The measured current was compared with
the current ratings available on the
transformer name plate.

Pressure We applied 1.5times the rated To determine whether

voltage on the HV side the transformer shall
terminals of the transformer via be able to handle
a wire from the pressure tester random large
device and short circuit the LV transient voltages
side terminals of the phases
along with the terminal of the
neutral.
The voltage was applied
gradually and attention was paid
to any humming heard coming
from the transformer. The
humming indicates that the
transformer can’t with stand
such a high voltage

35
3.1.2 Insulation-resistance test on the transformer bushings
Tools used include Megger-insulation device, connecting
leads

We Powered the Megger-insulation device and place two connecting leads into the device. The
other ends of the 2 connecting leads were placed on to the points of interest of the transformer.
These points are; the conductor at the High Voltage (HV) bushing and the conductor at the Low
Voltage (LV) bushing, the conductor at the HV bushing and an unpainted-conductive part on the
body of the transformer. The unpainted-conductive part on the body of the transformer is also
called the earth and lastly the conductor at the LV bushing and the earth.
When the connecting leads were placed at any of the above individual point, a test voltage of
5000V was injected into the transformer for a duration of 15seconds using the Megger insulation
device.

36
At the end of 15seconds, a resistance value was observed and recorded. The test was then repeated
for another point of interest. It was observed that the resistance level for all the tests was above
300MΩ.
After all the tests had been carried out, the transformer was given a UMEME number. It is also
marked with paint demarcating that it has been tested. The painting contains the UMEME number,
transformer power rating and high voltage rating.
The transformer was tagged with a PCB-free tag.

Figure 3-2:Megger Insulation device

3.1.3 Observing the internal physical structure of the Buchholz relay and understanding its
operation.
Tools used included Screw drivers.

The Buchholz relay was got from the transformer stores, and it was opened using a screwdriver to
access and observe its internal structure and working functionality.

The internal structure composed of two movable floaters to which part of a contact-set was
attached, and the other part was attached to an immovable rod.
The upper contact-set was connected to the wiring of the alarm system and the lower contact-set
was connected to the wiring of the tripping circuit system.

When the oil levels are high, the floaters are un able to complete the contact-set circuit hence the
Buchholz doesn’t detect a fault.

37

KISEKKA JUDE FRANCIS 16/U/463

When the oil levels are low, the upper floater is able to complete the contact-set circuit to activate
the alarm system.
When the oil levels are extremely low, the lower floater completes the contact-set circuit to activate
the tripping circuit system in order to open circuit the transformer, and prevent it from further
damage due to a fault. Low oil levels indicate that either, the oil in the conservator tank is very
low and the transformer windings are being exposed to impurities such as air.
The relay also has a push-movable structure that has contacts on it as well such that when the
movement of oil across the relay is from the main tank to the conservator tank (wrong direction of
oil flow) the contact-set circuit is completed. This contact-set circuit is connected to the wiring of
the tripping circuit system, thus when the circuit is completed, the transformer is open circuited to
prevent further damage to it.

Figure 3-3:Buchholz relay

3.1.4 Observing the internal physical structure of the temperature relay and understanding its
operation.:
The tools used include Screw drivers

A temperature relay was obtained from the transformer stores and was opened using a screw driver
so that the internal structure was accessed and working functionality observed.

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The temperature relay had a temperature probe that was connected to a tube. The tube was
connected to a plunger within its internal structure. The tube was already filled with neon gas,
which expands at different temperatures.
When the gas expanded, it would increase gas pressure that was used to push the plunger. The
plunger is connected to a contact-set, such that when the plunger moved, the contact-set circuit
would be completed and the respective action implemented.
The relay has 4 contact-set circuits, with each activated at different temperatures. The 1st, 2nd and
3rd contact-set circuits are connected to the wiring of the fans, alarm and tripping circuit systems
respectively such that when a contact-set circuit is completed, the wiring system to which it is
attached is activated.

Figure 3-4: Temperature relay

3.1.5 Installation of a 1MVA transformer in SERERE district.

Installation of the transformer involved several tests. The tests that were carried are shown below:
Insulation-resistance test – this was explained earlier.

Oil filtration test:

The oil filtration test is usually carried out to improve on the insulation properties of the
transformer oil.

The tools used included oil filtration machine and horse pipes.
The oil filtration machine was connected to the transformer at two points: one at the lower end of
the transformer and the other at the upper diagonal end of the transformer using 2 horse pipes.

The machine was powered and it created a vacuum that sucked out the oil from the transformer.
The preferred vacuum was of acceptable pressure, within the range of 15 – 20 bars.

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The inlet valve of the filter machine was then opened, followed by the outlet valve of the
transformer to allow oil to be flow out of the transformer.
The oil was observed to flow into the degassing chamber of the filtration machine. This was
followed by turning on the heaters of the machine.
The outlet valve of the filter machine and the inlet valve of the transformer were then opened. The
inlet pump and outlet pump from the oil filtration machine are turned on and the filtration process
was started.
The oil was heated to a maximum temperature of 80°C. At this temperature 70% of the water in
the oil had vaporized.
The oil that passed through the filter machine left particles behind. It was passed through the
machine for 5hours.
At the end of the 5 hours all, the oil was finally returned into the transformer and left to cool.

Figure 3-5:Oil filtration machine

Having finished the days work, we removed the applied working earth and called control center at
lugogo to handle over the transformer.

3.1.6 Determination of the Break Down Voltage (BDV) of a transformer.

The tools used included a BDV tester.

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A sample of transformer oil was obtained and placed in a bottle. Some of this oil was poured into
the glass component of the BDV tester to rinse it, and then it was poured off.
The remaining oil to be tested was poured into the same component and it was then made inside
the BDV tester where the electrodes are immersed in the oil. The oil was ready to be tested.
F tests were run and for each test, a voltage value was obtained. The average voltage value was
then obtained.
The BDV tester printed out a small form indicating the voltage values for each test and the
average voltage value.

Figure 3-6: BDV tester

Figure 3-7:Table showing BDV test values

TEST VOLTAGE (V)

1 25,000
2 32,000
3 36,000
4 43,000
5 49,000
Average voltage: 37,000V

The average voltage was above 30,000V. Any average voltage value below 30,000V indicated that
the insulation properties of the oil were very low, due to impurities and therefore it had to be
filtrated. The biggest impurity of transformer is moisture.

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3.1.7 Heat running of a Power transformer at kireka substation in Kampala.
Tools used: cotton waste, liquid soap, buckets, insulation testing megger, earth rods, portable earth,
operating stick, spanners, generator, heat-running machine, silica gel, BDV megger.

The transformer was inspected, identifying the hazards and writing them down on the risk
assessment form.

We then proceeded on a safety briefing from the supervisor that included the following pointers:

All workers must put on full PPE during the working period in the substation.

No one should wander off on their own or touch unknown equipment within the substation, in
order to prevent danger to the person.
We then signed into the workers’ register to commence work on the transformer.
Both the HV and LV sides of the transformer were earthed using portable earth and an operating
stick.
The heat-running machine was connected to the power transformer at two points, one to act as the
inlet into the machine as it sucks the oil from the transformer and the other to act as the outlet after
the oil has been filtered and being pumped back into the transformer.

Figure 3-8: The outlet of oil from the transformer going into the heat running machine.

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 Figure 3-9: heat running and flow of oil through the machine from the inlet to the outlet.

The earth cables were removed and proceeded to do some cleaning work round the transformer
including cleaning the bushings that were very dusty and cleaning the cooling fins.

After the cleaning was completed, we proceeded to noting down crucial information about the
transformer which is found on the transformer name plate and also noted down information about
the tap changer of the transformer.

We then unscrewed an oil outlet and took a sample of oil form the main tank for testing.

Figure 3-10:getting an oil sample from the main tank of the transformer
The transformer oil was then tested for its breakdown voltage using the BDV megger that prints
results on a paper slip.

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 Figure 3-11: getting an oil sample from the main tank of the transformer

The breather was then removed in order to replace the silica gel

3.1.8 Tap changer maintenance of transformer number 1 and 2 at kireka substation.

Tools used include cotton waste, bucket, basin, earth rod, portable earth, operating stick, spanners,
silica gel, and electric pump.

The transformer was inspected, identifying the hazards and writing them down on the risk
assessment form.

We then proceeded on a safety briefing from the supervisor that included the following pointers:

All workers must put on full PPE during the working period in the substation.

No one should wander off on their own or touch unknown equipment within the substation, in
order to prevent danger to the person.

We then signed into the workers’ register to commence work on the transformer.

The technical work proceeded as described below:

The transformer was isolated from the bus bar and earthed and thus been disconnected.
The tap changer was then set to the service tap that was tap 9B.

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Spanners were used to unscrew the top cover off after a hose with one end connected to an electric
pump and the other to the tap changer tap was used to pump out oil from the tank into an empty
drum to clearly expose the contacts holding the headgear.
The headgear was lowered into a basin to be washed using oil. The conducting rod was removed
from the tap changer, the contacts holding the tap changer were unscrewed, and a self-loader used
to lift it from the tank onto a gasket where it was cleaned using oil.

Figure 3-12:head gear after it had been cleaned

Figure 3-13:cleaning the tap changer using oil

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The TC tank was cleaned by using oil from the drums at a high pressure after which the oil was
pumped out from the tank into an empty oil drum.

Figure 3-14:using oil at high pressure to clean inside the tank

The tap changer was then then lifted up by the self-loader and placed back into its tank. The rod
was also placed back in the middle of the tap changer and the contacts tightened using nuts and
winding screws.
The headgear was then placed back in its initial position and then tightened using nuts and winding
screws.
New oil was then pumped into the TC tank until it was filled as observed from above it.

Figure 3-15Tap changer being cleaned

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The top cover was placed back after the oil filled in the buccholz relay and the conservator tank.
The transformer was reconnected by switching on both the 33kv and 11kv bays through control
center at lugogo following hanging over the transformer to the control officer.

3.2 PRACTICAL WORK DONE IN METERING

3.2.1 Meter Testing
This involved the testing of the functionality of meters suspected to be faulty by the customer and
those suspected to have been tampered with. A check meter is a meter that is used to test the
accuracy of the existing meter on site. For a case where the customer complained that their meter
was faulty, a check meter was used test its functionality.

3.2.2 Check meter tests

The testing device (check meter) was powered by connecting its power leads to the live and neutral
in the meter box.

The current transformer was connected on the live cable with the arrow on it pointing in the
direction of flow of current.

The settings of the test device i.e. impulses or revolutions per kWh of the meter, percentage error
range and the number of test cycles were set.

The scanning device was then connected to the test device and the customer asked to power on as
many loads as possible.

The scanning device was then pressed on the meter to detect the impulses generated by the meter
for digital meters. For analog meters, the scanning device has a button that was pressed for every
revolution of the meter disc.
After the number of set cycles, the test device showed the percentage error in the meter readings.
The meter was said to have passed if the error was between -5% and 5% and said to fail if the error
was out of this range.

A report was then prepared and the customer given a copy.

The service order was then resolved on ICS and the faulty meters were replaced.

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 Figure 3-16:meter testing set

3.2.3 Visual tests

Visual tests were used in the verification of meters. This involved looking physically at the state
of the seals (terminal cover seals, top cover seals, paper seals) and the physical state of the meter
to ascertain whether it has been tampered with or not. It also involved looking at the connections
to determine whether the meter has been bypassed or not. For cases where the meter was old or
tampered with, the meter anomaly technician issued a ‘notice to consumer’.

3.2.4 Securing of meters

The activity of securing meters was done as one of the loss reduction strategies. This was done by
securing the three phase meters in green metallic boxes while the single-phase meters were placed
in transparent tamper proof boxes. Unauthorized personnel did this to limit access to the meters.

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 Figure 3-17:Securing using metallic tamper proof boxes

3.2.5 Meter Reading

The activity of reading meters was carried out at the beginning of every month. It involved moving
into the field to capture the necessary meter data needed to bill the customers. This involved
interrogating the digital meter for data which included;

Meter number, Name of customer, Account number, Account name, tariff code, Current data;
Import, Rate 1, Rate 2, Rate 3, MD4, MD5, Export, Import lag, Instrumentation data; Phase
voltages, Phase currents, Phase pf’s, Security data, General data, Billing data

Rate 1 is peak period from 6pm to 12pm and unit charge is highest, Rate 2 is shoulder period from
6am to 6pm and its unit charge is higher than rate 3, and finally Rate 3 is off peak period from
12pm to 6am and unit charge is lowest. These units are cumulative over defined period like a
month.

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Maximum demand period is normally 30minutes and MD4 reading is taken as maximum demand
for most KVAs and TOU whereas for HTs it’s MD5.

Demand in every demand period shows the highest demand in that period and it changes from one
period to next only if the demand in the most recent demand period is higher than the existing
maximum demand. It records the highest 3 and takes average to generate the 4th which is taken as
the maximum demand for TOUs and kVAs.
If a consumer with large machines carries out testing for a few minutes and never use the machines
again for the whole month, the maximum demand will be recorded and he will be billed based on
that demand charge.

Figure 3-18:Meter Audit report

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3.2.6 DISCONNECTION PROCEDURE
Before departure: The metering engineer or contractor supervisor briefs disconnection team on
safety procedures and work to be done. Team is advised to inspect all the equipment they will
use; be very polite with all customers and carryout enough risk assessment. Metering engineer
also collects the Disconnection run-off list from the commercial officer

Work equipment, documentation, PPE and disconnection methods are checked

On arrival of team at site: Greet customer and introduce yourselves
3.2.7 Disconnection of single phase postpaid customers
There ae three methods of disconnection

Method 1: Removal of fuse or switching off CB at meter

Test metallic meter box for any leakage using phase tester.

If safe, then proceed to remove fuse of switch CB off Check if there is no other
supply to the premises.
If so, report to commercial officer

Ensure service point is fitted with a seal and seal records delivered to district officer
Method 2: Disconnection of jumper at pole top.
Make a risk assessment of service point to be disconnected and all interfacing
structures and conductors like knocking the pole to know whether its rotten
If safe, climb pole and remove jumper of service cable

Disconnect service cable from meter but leave in the meter box.

Verify there is no other supply to the premises

Ensure service point is fitted with a seal and seal records delivered to district officer

Method 3: Recovery of service cable.

Make a risk assessment of service point to be disconnected and all interfacing
structures and conductors like knocking the pole to know whether it is rotten
Trace route of service cable before disconnecting

Ensure signs and barriers are displayed before work commences

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 If safe, climb pole and isolate all service cables at the pole

Once tested to ensure that it is dead, the service cable to be recovered is dropped to
the ground
A team member stationed at the bottom of the pole receives it and it is marked with
service point details.
Don’t cut cables but rather disconnect service cable from meter and remove from the
meter box.
Verify there is no other supply to the premises

Ensure service point is fitted with a seal and seal records delivered to district officer
3.2.8 Three Phase Disconnection.
There are three methods of disconnection depending on situation on ground;

Method 1: Secured meter box disconnection

Place requisition for the secured box keys

Sign receipt of the keys and go to customer's premises

Do a risk assessment of meter box; look out for bees, wasps, leakages among others.

Open the meter box while looking out for close connections

If safe, take meter readings

Switch off all the tree circuit breakers

Lock the box, return keys to the registry and report readings to the commercial officer

Method 2: If box is unsecured, open jumpers of all three phases at pole top.
Isolate LV circuit from transformer to ensure it is safe for disconnection. Only an
authorized Technical Officer does this.
A risk assessment is done first.

CB is switched off or fuse cutouts removed.

Make a risk assessment of service point to be disconnected and all interfacing

structures and conductors like knocking the pole to know whether it is rotten

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 Once tested to ensure that it is dead, open the three jumpers of all three phases at pole
top

Position jumpers safely at the pole top

Method 3:

Open the HV fuse links at the transformer using operating stick

This is for three phase HV metering customers and is done by only an authorized person

Go to feeder pillar to off load the transformer.

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3.3 SWITCH GEAR SECTION

3.3.1 Routine maintenance at Luzira Portbell substation.

33 kV BB 33 kV BB

BBC BBR

33 /11kV Tx 33 /11kV Tx

11 kV BB

Figure 3-19:Lay out of Luzira Portbell substation.

The bus bar riser is used to lift the bus bar after the bus bar coupler to bring it back to the level of
the other section bus bar.

The bus bar coupler is used to sectionalize the different transformers to support each other while
working in parallel or to work independently when the need arises.

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The Typical maintenance sequence.

Put the circuit breaker off.

Isolate the circuit breaker.

Test wither the circuit breaker is completely off.

Earth the circuit breaker

Disconnect the auxiliary supply

Discharge the springs manually

Visually inspect the circuit breaker and carry out further maintenance.

Safety Measures that were undertaken.

The personnel doing the maintenance should be trained personnel.

The personal must observe the Personal Protective Equipment (PPE), which includes
a helmet, an overall or over coat, safety boots, and safety hand gloves.
Before any work is done, ensure that the power supply is off; ensure that the circuit
breaker is open and that the closing spring is discharged.
Control terminals must not be touched if the power supply is not disconnected.

3.3.2 Testing of a CB.

The contacts are connected properly.

The tools used included equipment and materials used. The continuity test was carried out to
ensure that the contacts are touching properly. The procedure was as follows: -

The spring was charged manually

The circuit breaker is closed by pressing the close button

The leads of the multi-meter are connected to one of the phases and it is in the ohm’s section.

If it makes a quaking sound or the resistance is very low.

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4 CHAPTER FOUR: OBSERVATIONS, RECOMMENDATIONS
AND CONCLUSIONS
4.1 OBSERVATIONS
I observed that safety is one of the most important aspects valued at UMEME Ltd. Since the
product that UMEME sells is electricity, it is important that it is handled with care; otherwise it
can lead to loss of lives. During my internship period, we were taken through a safety training to
ensure that we were well acquainted with the different personal protective equipment required for
the different tasks that are handled by UMEME. This was majorly to ensure that we knew what
protective measures to carry out, in order to fulfill a required task.
Some of the most commonly used personal protective equipment include helmets, safety shoes,
over rolls, gloves, etc.
It was mandatory to have safety briefings, before any task where everyone was checked to ensure
that they were wearing their respective protective equipment before engaging in the task.
The training teams at UMEME were very welcoming and readily provided information about the
operations that are run by UMEME. This provided a good and open learning environment. In
addition, most of the activities undertaken at UMEME are done in teams. I observed that teamwork
efforts are used in almost all sections at UMEME in order to accomplish proper reliability and
high quality power distribution.
During my training in the transformers section, the major challenge that was met in regards to
carrying out work tasks that were scheduled in upcountry areas was transportation
Closing of the transformer’s section workshop meaning we can only do limited tests hence leaving
out most tests to be carried on the transformers.

The company is very centralized; a lot of activity happens at the central offices in lugogo especially
with the stores section
The public needs to be sensitized about the electricity sector on especially about the charges and
the meter reading and the change to prepayment and other details governing the sector.

There is a big gap management between the UMEME management and the UMEME employees
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As of the university, the training period is not enough and so being the facilitation to students.

4.2 RECOMMENDATION
I recommend that UMEME Ltd should increase on the number of transport vehicles allocated to
certain sections, for example the switch gear section, whose work tasks frequently require moving
to upcountry areas, in order for the tasks to be accomplished. If this is done, there shall be less
missed scheduled work tasks and urgent tasks shall be attended to in the scheduled time, thereby
improving upon the reliability of the distribution network.
Students be provided with adequate allowances to cater for their living costs and if possible
trainees be provided with subsistence for work upcountry.
A training workshop should be setup in the transformer’s section where a trainee can easily learn
all the tests carried out on a transformer.
The management of UMEME should bridge the gap between the employees and its self through
interactive activities and social events.
Conferences and public talks should be organized often to sensitize the public about the sector.
Decentralization of the stores and other sections to district level.

4.3 CONCLUSION
I had a lot of exposure, majorly hands on skills from my training at UMEME Ltd. I was able to
understand how each section that I trained from finally contributed to the distribution of electricity
to different places in Uganda.
I have been able to integrate between practical and the theory behind electricity, and more so, I
have gained an insight into the working field. And to UMEME and its staff especially the members
in power transformers, I am grateful for your guidance in my training and I look forward to
working with you again.

The transformers section deals with stepping down electricity to provide acceptable electricity
levels to the end users during electricity distribution. By ensuring that the transformers are properly
maintained as the life span of a transformer depends on its working conditions, then the distribution
of electricity is maintained at an acceptable and high standard.
The switchgear section ensures that the safety equipment like circuit breakers on the network are
in proper working condition such that in case a fault is detected on the network, the affected area

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is isolated to enable the remaining unaffected part of the network to continue in operation so as to
maintain reliability of power distribution.
My over-all experience with interning at UMEME Ltd was a pleasant one.

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5 References

[1] P. A. J., Electrical Transformers and Power Equipment, Fairmont Press, 1998.

[2] S. M, Power System Analysis and Design PWS-KENT, ISBN, 1987.

[3] A. T. e. D, Metering Guide, vol. 1st Edition, ISBN, july, 2002.

[4] [Online]. Available: www.electrical4U.com/electrical-switchgear-protection. [Accessed 21st August

2018].

[5] H. M. F. a. P. Antony, Electrical Distribution Engineering, Fairmont Press, 2007.

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