CHAPTER ONE
1.0
INTRODUCTION
Electricity is a vital service to the economy of a nation. It is regarded as
one of the major inputs in the production process of nearly all goods and
services. It is also necessary to power domestic appliances; therefore it
usefulness is vital in the economic growth of a nation and living condition.
Electrical power system consists of three major components namely;
generation, transmission and distribution systems. No part of these entire
components is independent of the other. Without generation there will be no
where to get power to use conveniently. Transmission is again very essential
and before the power generated gets to the load end, it needs to be distributed
effectively.
I was opportune to work with Ondo State Development and Property
Corporation, an Ondo state government owned establishment that is meant to
relieve the huge amount of electricity burden on the major supplier of electricity
in Nigeria, Power holding Company of Nigeria (PHCN), formerly called
National Electrical Power Authority (NEPA).
During my industrial training, I was exposed to the distribution (including
ITC) part of the power system component mentioned above, which is the major
concern of the establishment.
In this report, I will discuss the huge technical experience that I
learned as a result of working with Ondo State Development and Property
Corporation. There had been grouped into different chapter for the sake of easy
assignment to readers and they are as follow;
Chapter one:
Introduction
Chapter two:
Background to the establishment
1
1.1
Chapter three:
Transformer
Chapter four:
Substation
Chapter five:
Inter – town connection
Chapter six:
Recommendation and conclusion
Aim and Objective of SIWES
Student industrial work experience scheme (SIWES) is an integral part of
some degree and diploma programmes in institution of higher learning in
Nigeria. It is aimed at exposing students to the industrial sector in order to
acquire essential and relevant practical knowledge in their various fields. The
programmed equally had the objective of acquainting student with the practical
relevance and application of the basic theoretical principle learnt in school.
As an electrical electronic engineering student, the programme is
expected to take place outside the school under the supervision of approved
electrical engineer (or contractor) or even in an electrical or electronic company.
At Ondo State Development and Property Corporation, the establishment
where I undertook the industrial training, I was exposed to many practical
experiences such as:
(i)
The technique used in substation
(ii)
Identification and used of electrical equipment
(iii)
Testing of transformers
(iv)
Inter – town connection
2
CHAPTER TWO
2.0
BACKGROUND OF THE ESTABLISHMENT
2.1
Organizational Chart
ONDO STATE DEVELOPMENT AND PROPERTY CORPORATION
BOARD
CHAIRMAN
GENERAL MANAGER
P.R .O
DIRECTOR
F& A
DIRCTOR
PD&C
DEPUTY
DIRECTOR
F&A
INTERNAL
INTER
AUDIT
DEPUTY DIRECTOR
PD&C
HOD
P&D
CSO
HOD
ADMIN
CHIEF
ACCOUNTAN
T
DIRECTOR O&M
HOD
CONSTRUCTION
HOD PPIMU
&
DEPUTY DIRECTOR O&M
HOD MAINTENANCE
HOD OPERATION & MAINTENANCE
3
Foot note:
2.2
 F&A:
Finance and administration
 O&M:
Operation and Maintenance
 PD&C:
Planning, Design and construction
 CSO:
Chief Store Officer
 PPIMU:
Project Price Inspection and monitoring unit
Location of the establishment
Ondo State Development and Property Corporation (OSDPC) is
situated directly opposite the Akure branch of Federal Collage of Agriculture
(FACA) Ado/Owo Road, Akure. The establishment is a three storey building,
which comprises the office of the chairman, the General Manager, Directors and
staff of the establishment.
2.3
Employment Size
The establishment at present has so many workers ranging from
engineers, technologist and accountant. It also has many non – professional
workers helping in substations and in maintenance section.
2.4
`
Sections in the Establishment
i.
Planning, design and construction
ii.
Project price inspection and monitoring unit
iii.
Account
iv
Operation and maintenance
v.
Finance and administration
4
2.5
Planning and Design
Work done here include site survey, sketching of drawings, development
and printing of drawing obtained from the site by the use of drawing instrument,
printing machine, paper – cutting machine and aqueous ammonia for drying.
Recently, the use of auto CAD, a computer based software has been
incorporated to enhance proper saving of data and to get along with the
information technology of today. The construction section of this department is
mainly meant for the installation and servicing of transformer, stringing of poles
and laying of armoured cables.
2.5.1 Project Prince Inspection and Monitoring Unit
This department deals with the control of prices submitted by contractors
by checking of accuracy. It also deals with the production of the bill of
engineering measurement and evaluation (BEME).
2.5.2 Electrical Services
This department deals with the maintenance of public streetlight system,
government offices and parastatals.
2.5.3 Operation and Maintenance
This is where facilities and equipment are kept for operation and
maintenance.
2.5.4 Account
The account section oversees the running of money, by take a proper
record of the income and expenses of the establishment.
5
2.5.5
Finance and Administration
Administrative jobs are done here. Financial fund received from
government are documented here. Details about this department are located in
the organizational chart.
6
CHAPTER THREE
3.0 TRANSFORMER
3.1 Overview of the transformer
Electricity generating stations is often thousands of voltage, most
especially 16kV. This is a very high voltage when compared to the household
need. In reality however, this electrical energy has to be transported to far
distances where it will be consumed by the household consumers. Electrical
voltages tends to drop in value if it is transported through a far distance and
hence the need for finding a way to increase its value so as to cater for the drop
in voltage and then make it to be able to travel through far distance.
3.2 Brief theory of transformer
3.2.1 Definition of transformer
A transformer is a device that makes arrangement for the transfer of electrical
energy from one point to another in a circuit or from one circuit to the other by
the principle of electromagnetic induction. It transfers electrical energy from
one circuit to another through inductively coupled electrical conductors. A
changing circuit in the first circuit (the primary) creates a changing magnetic
field; in turn, this magnetic field induces a changing voltage in the second
circuit (the secondary). By added a load to the secondary circuit, one can make
current flow in the transformer. Thus transferring energy from one circuit to the
other.
The secondary induced voltage Vs is scaled from the primary Vp by a factor
ideally equal to the ratio of the number of turns of wire in their respective
windings:
7
Vs
Vp
=
Ns
Np
By appropriate selections of the numbers of turns, a transformer thus allows an
alternating voltage to be stepped down, by making it less.
A key application of transformers is to reduce the current before
transmitting electrical energy over long distances through wire. Most wires have
resistance and so dissipate electrical energy at a rate proportional to the square
of the current through the wire. By transforming electrical power to a high –
voltage, and therefore low – current from for transmission and back again
afterwards, transformer enable the economic transmission of power over long
distances. Consequently, transformers have shaped the electricity supply
industry, permitting generation to be located remotely from point of demand.
All but a fraction of the word’s electrical power has passed through a series of
transformers by the time it reaches the consumer.
Transformers are some of the most efficient electrical ‘machine’, with
some large units able to transfer 99.75% of their input power to their output.
Transformers come in a range of size from a thumbnail – size coupling
transformer hidden inside a stage microphone to huge units weighing hundreds
of tones used to interconnect portions of nation power grids. All operate with
the same basic principles, though a variety of designs exist to perform
specialized roles throughout home and industry.
3.2.2 Transformer basic principles
The transformer is based on two principles: first, that an electric current can
produce a magnetic field (electromagnetism) and, second, that a changing
magnetic field within a coil of wire induces a voltage across the ends of the coil
(electromagnetic induction). By changing the current in the primary coil, one
8
changes the strength of its magnetic field; since the secondary coil is wrapped
around the same magnetic field, a voltage is induced across the secondary.
FIG1: TRANSFORMER BASIC PRINCIPLES
An ideal step – down transformer showing magnetic flux in the core
A simplified transformer design is shown to the right. A current passing through
the primary coil creates a magnetic field. The primary and secondary coil are
wrapped around a core of very high magnetic permeability, such as iron; this
ensures that most of the magnetic field lines produced by the primary current
are within the iron and pass through the secondary coil as well as the primary
coil.
3.2.3 Induction Law
The voltage induced across the secondary coil may be calculated from
faraday’s law of induction, which state that
dɸ
bgg
dt
gjɸ
bg
ɸ
ggj
Where Vs is the instantaneous voltage, Ns is the number of turns in the
ɸɸ
secondary coil and ɸ equals the total magnetic flux through one turn of the coil.
Vs = Ns
If the turns of the coil are oriented perpendicular to the magnetic field lines, the
flux is the product of the magnetic field strength B and the area A through
9
which it cuts. The area is constant, being equal to the cross sectional area of the
transformer core, whereas the magnetic field varies with the according to the
excitation of the primary.
Since the same magnetic flux passes through both the primary and secondary
coil in an ideal transformer. The instantaneous voltage across the primary
winding equals
dɸ
bgg
dt
gjɸ
bgg
ɸ
gjɸ
Taking the ratio of the two equations for Vs and Vp gives the basic equation for
ɸ
stepping up or stepping down the voltage
Vp = Np
Vs
bgg
Vp
gjɸ
ɸ
3.3
Vs
bgg
Np
gjɸ
b
ɸ
gTypes of transformers
g
A gvariety of specialized transformer designs has been created to fulfill certain
j
engineering applications, though they share several commonalities. Several of
ɸ
the most important transformer types include: auto transformer, polyphase
=
ɸ
transformer,
resonant transformer, leakage transformer, instrument transformer
and so on.
3.4 Classification of transformers
The many uses of which transformers are put lead them to be classified in a
number of different ways:
 By power level: from a fraction of a volt – ampere (VA) to over a
thousand MVA;
 By frequency range: power-, audio-, or radio frequency;
 My voltage class: from a few volts to hundreds of kilovolts;
10
 By cooling type: air cooled oil filled, fan cooled, or water cooled,
 By application function: such as power supply, impedance matching,
output voltage and current stabilizer, or circuit isolation;
 By end purpose: distribution, rectifier, arc furnace, amplifier output;
 By winding turns ratio: step – up, step – down, isolating (near equal
ratio), variable.
 By the type of bushing: open bushing and closed bushing type.
For the sake of this report, I will discuss the last classification which is the
classification by the type of bushing used. Bushing is just like all other
porcelain type insulators and its main purpose is for the purpose of insulating
the transformer terminals. A picture showing the two types of transformer is
shown below:
FIG 2: TWO TYPES OF TRANSFORMER
3.4.1 Closed bushing
The closed bushing transformer is that transformer in which the bushings are
hidden in the transformer. The closed bushing types are often used on 11kV
lines and are often used within the town or city. The base height of such
transformer at a sub-station is often 2 feet. The picture of a closed bushing
transformer is shown below:
11
FIG 3: CLOSED BUSHING TRANSFORMER
3.4.2 Open bushing
The open bushing transformer is that transformer in which the bushings are
shown on the transformer. The open bushing types are often used on 33kV lines
and it is often used for inter – town connection (ITC). The base high of such
transformer at a sub-station is often 4 feet. The picture showing different cross
section of open bushing transformers are shown below:
Fig 4: Cross-sectional view of open bushing transformer
12
Fig 5: Primary terminals of the open bushing transformer
Fig 6: Secondary terminals of the open bushing transformer
3.5 Part of a transformer
A transformer has a lot of different components that it is made up of
some of the components or parts of a transformer are: conservator tank, tap
changer, silica gel, name plate etc
3.5.1 The conservator tank: This tank consists of oil of specified grade and
level to remove heat from the windings of the transformer. The oil also acts as
13
an insulator between the windings. The picture of a conservator tank is shown
below:
FIG 7: CONSEVATOR TANK
3.5.2
Tap changer: This is incorporated in power transformer to facilitate
easy sections of desired turn ratio thereby regulating the output voltage and also
to change phase of power supply. The tap selection varies from one to five
depending on the transformer used. The picture of a tap changer is shown
below:
FIG 8: TAP CHANGER
14
35.3 Silica gel: It extracts moisture from the system and indicates the status of
the transformer oil. The picture of a container of silica gel is shown below:
FIG 9: TAP CHANGER
3.5.4
Name plate: This is an aluminum sheet that contains all the properties
and features of the transformer on it. It contains the rating of the transformer,
the type, the name of the manufacturer, the year the transformer was made and
so on. The picture showing the name plate is shown below at the left side.
FIG 10: NAME PLATE
FIG 11: A TRANSFORMER WITH A COVER CUT AWAY
The picture at the right shows a three-phase oil-cooled transformer with cover
cut away. The oil reservoir is visible at the top. Radiative fins aid the dissipation
of heat.
15
3.6 Transformer testing
The aid of testing a transformer is to check for its effectiveness in
performing the operations it is manufactured for. There are a lot of tests that can
be performed on a transformer but the major ones we dealt with at Ondo State
Development And Property Corporation, during the period of my industrial
training are: earth test, pressure test, ratio test, dielectric oil test. The equipment
required for transformer testing include: generator, hi-potronic tester,
multimeter etc
3.6.1 Ratio test
The essence of ratio test is to know if the transformer windings are correctly
placed where they are supposed to be. To perform ratio test, we need a
generator and a multimeter. We connect the two terminals of the generator
across the terminals of the transformer one after the other. Picking two terminal
at a time and then we power the generator. With a multimeter, we take the
reading one after the other and record the values. The table below shown one of
the tests that we preformed on a transformer.
Phase
Primary side
Secondary side
RY
RY
229
YB
169
BR
58
Ry
8.6
Yb
2.2
Br
6.1
Rn
4.8
Yn
3.5
Bn
1.0
YB
113
228
110
7.3
7.2
0.0
2.3
4.8
2.3
BR
56
167
224
2.3
8.4
6.0
1.0
3.5
4.7
When the generator terminals are placed on the red and yellow phase of the
transformer and the multimeter reading is taken from the phases, we have a
reading of 229 Volts. Because the transformer works by the principle of
electromagnetic induction, part of this voltage is induced into the blue phase
16
and hence we have 169Volts and 58volts as the readings on the YB and BR
phases respectively. For a good transformer, the sum of this induced voltage
should be approximately equal to the main phase voltage. A tolerance of 5v is
often allowed.
This same thing happens when the generator terminals are placed on the YB
and BR phases. The readings on the secondary side are much lower in values
than those of the primary side because we are considering step down
transformer.
3.6.2 Pressure test
Pressure test can be performed on either the transformer or HT lines. The
essence of the pressure test is to know if the transformer or the lines is capable
of withstanding the voltage at which it is rated. It also helps to know if the
transformer can withstand electrical surges. To perform pressure test, we need a
hi-potronic tester, a generator, and a multimeter. Often, to perform a pressure
test, we inject twice the voltage rating of the transformer into it with the help of
hi-potronic tester.
To perform a test, we power the hi-potronic tester using a generator
and then connect the tester to the transformer and start injecting voltage into the
transformer, starting from 0volts. The knob of the hi-potronic tester is adjusted
little by little increasing the voltage. As the voltage injected into the transformer
increases the knob becomes tight and hard to turn.
For a 33kv transformer, we intend to inject 66kV. If the reading trips off before
getting to 40kV, then we conclude that the transformer is bad and had to be
worked upon. If however, it is able to withstand more than 40kV and up to that
66kV, then we conclude that the transformer is good. This same principle
applies to the pressure test on HT lines. The tables below illustrate the
explanation above.
17
Table of pressure test on 11kV transformer
(i) High voltage/ primary side
Terminals
Induced voltage
Time taken
Remark
Red phase
22,000
60
Okay
Yellow phase
22,000
60
Okay
Blue phase
22,000
60
Okay
(ii) Low voltage/secondary side
Terminals
Induced voltage
Time taken
Remark
Red phase
2,000
60
Okay
Yellow phase
2,000
60
Okay
Blue phase
2,000
60
Okay
Neutral
2,000
60
Okay
(iii) Pressure test on 11kV HT line
Terminals
Induced voltage
Time taken
Remark
Red phase
22,000
60
Okay
Yellow phase
22,000
60
Okay
Blue phase
22,000
60
Okay
3.6.3 Earth resistance test
A good soil for a sub-station should have a resistance in the range of 1 to 5
ohms. The earth test is used to test the effectiveness of the earthed materials at
the sub-station. The earth tester or earth meter is used to measure the resistance
of each of the component of the sub-station to earth. Good test should give a
18
result in the range of 0 to 10 ohms. The table below shows a typical reading
obtained from a certain earth test.
Sub-station earthing system
Result (ohms)
Remark
Lightning arrester
8
Okay
Neutral earthing
7
Okay
Transformer frame
9
Okay
Channel iron
8
Okay
Feeder pillar
8
Okay
3.6.4 Dielectric strength (oil) testing
Transformer oil is used in transformer for two purposes: (i) it insulates the
windings of the transformer and (ii) it serve as coolant to the transformer by
absorbing the heat produced. The instrument used for testing the capability of
the transformer oil is called the dielectric tester. The instrument and its
component parts are shown below:
FIG 12: DIELECTRIC STRENGTH OIL TESTING
19
The transformer oil should have a high dielectric strength so as to provide
adequate insulation between the transformer windings. The transformer oil
tester uses the working principle a capacitor. The equipment has two plates as
indicated in figure 3.the gap that should be between these two plates depends on
the ratings of the transformer for which the oil is to be used. Using the steridard
rule, we use 2mm for 11kV and 2.5mm for 33kV transformers.
After the measurement with the steridard rule, we place the plates into its glass
container and rinse with a sample of the transformer oil. We then drop the two
indicating capsules into the glass container and cover with the plate. We then
put the entire structure into the dielectric tester as shown in figure 2.
We energize the oil placing a contain voltage across the plate by pressing the
stir button. The two indicating capsule start rotating indicating that electric field
is established across the plates of the dielectric tester. When the rotation stops,
we then switch the selector knob to manual. We have manual and automatic
options. By manual is meant that we do the test by ourselves. But in the case of
automatic, the equipment does the testing automatically.
After selecting manual, placing the knob at different voltage levels of 500V,
2kV and 3kV we press the raise button and then start looking at the reading
displayed. When a spark is noticed inside the dielectric plates, we take the
reading and press the trip button. We do this for 500V, 2kV and 3kV noting is
readings.
We then switch the selector button to automatic and press the start test
button. Whenever the spark appears, the equipment trip itself automatically and
we can then take the reading, doing the same thing for 500V, 2kV and 3kV.
For 11kV transformer, reading from 12kV upward are satisfactory while for
33kV transformer, reading from35 to 40kV upward are satisfactory.
20
The table below shows an interpretation of a test performed on 33kV
transformer oil:
SAMPLE OF
BVP AT GAP
QUALITY OF
REMARK
OIL UNDER
2.5mm
OIL
TEST
STERIDARD
New oil
Over 50Kv
Extremely
Acceptable
Over 40kV
Clean
Acceptable
Over 40kV
Clean
To be purified
Contaminated
Oil from TX
Over 40 kV
Clean
Acceptable
which has been in
Over 30kV
Less clean
Useable (to be
(contaminated)
purified or changed)
service
21
CHAPTER FOUR
4.0 Substation
A substation may be defined as an assembly of electrical apparatus, which
transforms electrical energy (AC) from one voltage to level to another.
Therefore, substations are vital links in any power system delivering electric
power from the generator station to the consumers.
4.1 Factors to be considered before sitting a substation
There are many factors to consider before sitting a substation, some of which
are:
i. Topography: nature of the land on which the sub-station is to situated must
put into consideration. Such land may not be rocky and the soil resistance must
not be greater than 1.6
ii. Location: a sub-station should be centrally located in the community. It
should be so in order to give room for even distribution of load.
iii. Load demand: size of the community determines the load demand. This in
effect determines the type and ratings of the transformer to be installed.
iv. Nature of transmission line: the type of transmission line from which the
substation is connected determines the type of transformer that will be used for
example, to supply 300kVA electric power to a community, the type of
transformer windings for a 33kV line will definitely be different from that of
11kV line.
Diagrams showing a typical substation are shown below:
FIG 13: SUBSTATION
22
FIG 14: SUBSTATION EXTENSION
4.2 Division of substations
Depending on the purpose, substation is divided into four major divisions.
i.
Step up substations 16kV to 330kV
ii.
Primary substations 330kV to 132kV
iii.
Secondary substations 132kV to 33kV
iv.
Distribution substations
a. 33kV to 11kV
b. 11kV to 415kV
For the sake of my practical experience and personal experience I will limit this
chapter to distribution substation mainly 11kV to 415V.
4.3 Installation of 11kV/415VA distribution substation
The distribution substation is a place where the 11kV primary distribution
voltage is stepped down to the secondary distribution voltage of 415V, three
phases or 240V single phase for use by the consumers.
23
The p[power to the consumers is fed from the distribution substations through a
network of low tension(LT) overhead lines, cable mains and sub main and
service lines.
4.4 Component of distribution substation
A distribution substation is made up of indoor and outdoor equipment. Outdoor
equipment are devices that installed outside. They withstand heavy downpour
and very high temperature for the sun and water view. The device include the
distribution transformer of any power rating, feeder pillar, J &P fuse, lightning
arresters, cable, insulators, sectional (H) pole, etc.
i. Distribution transformer: It is the equipment that transforms the high
voltage of the primary side of the network to the secondary side. Voltage on the
primary side of the transformer is 11kV. This is stepped down to give 415V on
the secondary side of the transformer, which is the L. V. side of the transformer.
The dropper armoured cable carries the incoming electrical energy into the
transformer.
FIG15: DISTRIBUTION TRANSFORMER
24
ii. Feeder pillar: Feeder pillar is a box – like equipment containing a set of
conductors inside it which connect the substation to the distributors serving a
certain allotted area from which tapings are taken. The feeder pillar has some
armoured cable attached to it. These include the incoming feeder cable which
contains the three phases and neutral coming from the transformer. It also has
some outgoing feeder cables connected to the leg of feeder pillar. The number
of these cables is determined by the number of legs that the feeder pillar has.
The cable that carries the feeders up to the distributing poles is called the up
riser cable. Feeder pillar are shown below:
FIG 16: FEEDER PILLAR
iii. Cable: Armoured cable are the most type of cable used in a substation. The
cable used in the construction of a distribution substation depends greatly on the
capacity of the transformer. The picture below shows a role of armoured cable
25
FIG 17: ARMOVRED CABLE
Transformer sizes and cable used for incoming (dropper cable) outgoing (feeder
pillar incoming feeder) servicing are:
Transformer size
Feeder cable (H.T)
Outgoing cable (L. T.)
50kVA
70mm2
35mm2
100kVA
70mm2
35mm2
200kVA
150mm2
70mm2
300kVA
300mm2
185mm2
315kVA
300mm2
185mm2
500kVA
500mm2
300mm2
Cable sizes their current carrying capacity is shown below:
Cable
Current carrying capacitor
35mm2
140A
70mm
200A
150mm2
335A
185mm2 (single core)
380A
185mm2 (3 core or 4 core)
370A
300mm2
550A
500mm2
750A
26
iv. Lightning arrester: Lightning arrester acts as safety values designed to
discharge electric surges resulting from lightning strokes, switching, or other
disturbances \,which is otherwise flash over insulators or puncture insulation,
resulting in a line outage or a possible failure of equipment. They are designed
to pass enough transient energy to prevent dangerous reflection and to cut off
the flow of current through the arrester at the first current zero after the
discharge of the transient.
FIG 18: LIGHTNING
ARRECTOR
The lightning arrester consists of spark gaps in series with nonlinear resistor, the
whole assembly housed inside hermitically spaced porcelain bushing. A line
lead soldered to the metal cap spun over the phase conductor. The earth terminal
at the button of the arresters is connected to the group. Earth terminal of all the
three lightning arresters are joined together and connected to the earth [provided
specially lightning arresters. The lightning arrester discharges down to the earth
the high voltage lightning surge wave while it acts as an insulator for the system
voltage.
Thus, the lightning arrester protection results in the maximum continuity of
electric supply service to the consumer, low maintenance and greatly, reduced
distribution operating costs. The lightning arresters are erected on the top of the
sectional pole structure for the protection of the transformer against lightning.
Lightning arresters are designed by the following:
27
a. Rated voltage
b. Rated frequency
c. Rated current
28
CHAPTER FIVE
5.0 Installation of lines
5.1 Inter-town connection (ITC) network
Inter- town connect (ITC) in electrification is the networking of two or more
towns or states. It basically involves the high tension (HT) line i.e. at the
voltage level of around 132kV, 33kV and 11kV.
5.2 Pole type
i. High tension pole: This is used for carrying 33kV and 11kV lines. It haqs a
length of 33ft, base diameter of 30cm and top diameter of 15cm. the first hole is
8cm from the top where the cross arm is screwed. The next three holes are 12cm
apart. The holes are 2cm wide. These holes are meant for the spindle of the
insulators such as the tension insulator, pot insulator and so on.
ii. Low tension pole: It is 28ft long; with base diameter of 24cm and upper
diameter of 13cm. the first hole is 18cm from the top while the next holes are
20cm apart with the holes being 2cm wide.
There are cases where we have dual carriage poles, a single pole that carries
both the high tension and low tension lines at the same time. Its name is derived
from the function it performs which is the carriage of two lines at the same time.
5.2.1 Advantage of concrete pole over wood and steel poles
i.
It is stronger than wood
ii.
Termite cannot affect it
iii.
It is more economical than steel
iv
Unlike steel, it does not conduct electricity so cannot be affected by
leakage current
29
5.2.2 Disadvantage of concrete poles over steel and wooden poles
i.
It is not as strong as steel
ii.
It takes time to be produced than wooden pole
iii.
It is more expensive than wooden pole
5.3 Processes involved in installation of high tension lines
High tension (HT) is the name given to high voltage level e.g. 11kV,
33kV, etc. during inter-town connection of high voltage electrification between
towns; all the processes mentioned below are needed to be followed.
1. Survey of site
In the surveying of site for ITC, the terrain of that area or route to be affected
should be taken into consideration. The terrain include: sloppy areas, bends,
swampy areas, hills, bridges, junctions …….
The number of kilometer from the starting point of the project to the hook-up
point is noted. This is used to calculate the number of poles to be used during
the project.
The route is journeyed and a true meter is used to measure the distances from
point to point, junction to junction and place to place. The same thing applies to
hilly and rocky areas. Along the route, all existing lines are also taken into
consideration. The picture of a true meter is shown below:
FIG 19: TURE METER
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2. Clearing of site
This process involves cutting of grasses and felling of trees along the proposed
transmission route and creating paths for erecting the high tension poles. The
grasses can be cut manually or mechanically by the use of mower. Bulldozer is
however used for the felling of trees and thick bush. Clearing of bushes and
grasses is necessary for proper visibility during sitting and pegging.
3. Sitting and pegging
Sitting is done to ensure a straight line in places where the poles will be erected.
Sitting involved the use of site rods made steel or alternatively, we make use of
straight pegs with the top painted red for proper visibility through a certain
distance.
Craftsmen will then have to place themselves at certain distance apart usually
called the span (a span is the distance between two poles) each man with his
own sitting rod/peg. The distance is measured with the use of true meter (also
called meter wheel). The span length for residential areas is 45m and non –
residential area is 90m. After a number poles ranging between six and ten, there
should be a sectional poles (H poles). A section is defined from one H-pole to
another H-pole; the technical name for an H-pole is the sectional pole. Section
is placed in between the network so as to give room for isolation of lines in case
the network needed to be worked upon in future.
After sitting and getting a straight line of sight for the poles, pegging is the next
step. Pegging involves the use of wooden peg driven into the soil with the top
painted red. This is the point where the pole will be erected.
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4. Digging of holes
Digging of holes is done manually by the use of long digger and long packing
spade for packing the earth deposits removed as result of the hole dug. The
depth of the hole for high tension line is 6ft while that of low tension line is 4ft.
The holes are that deep so as to give room for stability of the poles.
5. Erection of holes
A mobile crane called ‘HIAB’ does the erection of poles mechanically. Part of
the vehicle made of hydraulic system is used for lifting the pole into the hole.
The poles are guarded into the holes by human effort. A strong wire string is
tied round the pole and the ‘HIAB’ with the help of the mechanical system lift
the pole into the hole.
The hole is then covered and hammered until the pole is firmly erected so that
there is assurance of stability and resistance to wind and vibration.
6. Dressing of poles
Poles are dressed shortly after erection. Dressing involves the fixing of channel
iron or cross arm, tie-strap, pot insulators and all other accessories on the pole.
7. Stringing of conductor
The size of conductors used for 33kV transmission line is 150mm2 Aluminum
bare conductor. The conductors are laid down at the side of the pole according
to the phases i.e. R- Y- B and the conductors are taken to the top of the pole
with the able men.
There are two sectional poles in every section. When the conductor is hung up
at the first pole, the will be pulled towards the second sectional pole with the
help of pull lift; the phases will then be pulled and tensioned without sagging.
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8. Earthing
Earthing is every essential in any installation. So al the metallic part of the pole,
basically the channel iron used has to be earthed. Copper conductor is connected
to the channel iron at the top of the pole. It is passed down and connected to the
earth rod, which is driven down four feet beneath the earth.
A picture showing bundles of copper conductor is shown below.
FIG 20: EARTHING CONDUCTOR
9. Testing
Testing is very important in any installation. After the completion of ITC, all
the component of the transmission line like pot insulator, lightning arrester etc
must be tested to be assured of the effectiveness of the system.
The test carried out on this system is called pressure test on HT line, the
procedure foe doing the step is already explained under the section on
transformer testing.
10. Hooking up
This is the final stage and it involves the connection of the line to the existing
network.
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5.3 Installation materials and accessories
The following materials are accessories used in the installation of lines. Here,
both the high tension and low tension accessories will be considered.
1. Poles
The concrete electric poles used are majorly of two types namely;
the high tension and low tension types. The use of concrete type is mainly
because of its rigidity and resistance to pest which affects the wooden type. For
a high –tension transmission line, the length of the pole used is 33ft (10m) and
for a low tension, the length is used is 28ft (8.5m). The concrete has longer
span, resistant to fire, termites or chemicals.
2. Channel iron
Channel iron is also referred to as the cross arm. It is a metallic iron on which
the spindle, pot insulator and conductors are placed. It comes in different types;
the angle channel iron, which is used when a line is to be drawn at an angle, the
straight channel iron and U-channel iron type. As for the straight channel iron,
the length differs according to the voltage level under consideration. It is 6ft for
11kV and 9ft for 33kV lines. A picture of the channel iron is shown below
FIG 21: CHANNEL IRON
3. Spindle
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The spindle is made of iron or steel that carries the pot insulator on the channel
iron or the wooden cross arm. They are threaded so that the insulator can be
securely screwed on it. A picture of the spindle hooked into a pot insulator is
shown below:
FIG 22: SPINPLE
4. J- hook
This hook is used to for hanging the disc insulator on the channel iron either the
suspension type or other types.
5. Disc insulator
Disc insulator is used with high tension lines. It can be used on a T-pole but it is
often used on a sectional pole for the sake of allowing isolation in case of future
problem with the circuit. The picture of a disc insulator is shown below:
FIG 23: DIS INSULATOR
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6. Pot insulator
The pot insulators are mainly porcelain or ceramic types that carry the
aluminum conductor on the poles. The sizes vary according to their ratings and
voltage level to be transmitted. The picture of a pot insulator is shown below:
FIG 24: POT INSULATOR
7. Bolt and nut
This is used foe fastening the channel iron or wooden cross arm and tie strap to
the pole.
8. Earth rod and earth wire
The metal is made of metal especially iron. It is used earthing the poles and
substation by burying it into the general mass of the earth so that it can prevent
electric shock buy providing a path for the leakage current. The earth wire is
made of copper and it is connected to the earth rod.
9. Aluminum conductor
This is used the transmission of electric power from one point to the other. The
conductors used are of various sizes ranging from 70mm2, 100mm2, 150mm2
depending on the area of use for high tension line, 100mm2 or 150mm2 is used
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while for low tension line 70mm2 is used. For street lighting, we use 35mm2.
The picture below shows a bundle of aluminum conductor.
FIG 25: ALUMINUM CONDUCTOR
10. Jumper spindle
The jumper spindle is used to jump from one side of the sectional pole to the
other for continuity purpose. A bi-metal line tap can also be used for this
purpose.
11. Complete stay
A complete stay comprises of the stay rod, stay wire, stay insulator, stay block
and stay plate. The stay holds the pole firmly to the ground and the stay
insulator on it prevents current from flowing through the wire by isolating it.
The stay wire is made of galvanized steel.
12. Tie strap
This holds the channel iron or the wooden cross arm firmly on the pole. It is
usually attached to the cross arm by means of carriage bolts and to the pole by a
long screw.
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13. Tension clamp
This accessory is pistol-like in shape; it serves as a link between the conductor
and the disc insulator. It is used for clamping conductor to the insulator and it
helps to tension the aluminum conductor by clamping it down with the use of
U-type bolts and nut.
14. Shackle
This is another porcelain made insulator used on the LT line. It is used along
with a D-iron that holds it so that it could roll inside the D-iron so as to ensure
easy stringing of the cable that is passed through it. The combination is bolted
to the pole. Separate picture of the D-iron and the shackle are shown below:
FIG 27: SHACKLE
FIG 26: D-IRON
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CHAPTER SIX
6.0 Recommendation and conclusion
6.1 Recommendations
It is known fact that theory without practical experience renders a profession
sterile. As fundamental engineering principles and thinking processes are the
best studied and developed in an academic environment, understanding of
practical application is better acquired by direct experience. This balance of
academic and practical training was attained during my stay in Ondo State
Development and Property Corporation. Basically, I will like to make the
following recommendations:
a. The students under industrial training should make sure that they make use of
the period by reading books on the area of specialization of their industries. This
will ensure a forecast of application of theoretical knowledge and hence make
them better prepared for the challenges that may arise during the training.
b. The departmental lecturers should make it a point of duty to visit the student
under training. This will infuse seriousness and dedication into the student.
c. The industrial training unit in collaboration with the department should
always assist students in securing industrial placement so that any student who
cannot gat placement opportunity early can be bailed out of such challenges.
d. The company/industries should give more encouragement to students by
making use of them in all area of operations and by allowing them to handle
some projects in order to enhance their practical knowledge.
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e. The students training allowance should be increased by the federal
government so as to make student meet the demand of the present economic
situation in the country and this should be made available to students as early as
possible after the training.
6.2 Conclusion
The students’ industrial work experience scheme undertaken at Ondo State
Development and Property Corporation has given me opportunity to have board
knowledge in the planning and designing of sites, testing of substation devices
and transformers.
Also, it has helped me to acquire professional ethics of my discipline. Through
this, I was able to gain knowledge on how to be customer friendly. Generally,
the SIWES programme has actually achieved its aim and objectives and its
continuity should be encouraged for soild technological background for the
subsequent undergraduates.
6.3 References
1. http://en.wikipedia.org
2. Electrical technology by Eng. Olorunsola Abiodun Joseph
3. Electrical installation theory and practical by Eng. Olorunsola Abiodun
Joseph
4. Ondo State Development and Property Corporation monthly lecture manuals.
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