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A TECHNICAL REPORT
ON
STUDENT INDUSTRIAL TRAINING WORK EXPERIENCE
SCHEME
(SIWES)
AT
POWER HOLDING COMPANY OF NIGERIA
GENERATING STATION
P.M.B 580, DAM SITE, JEBBA
NIGER STATE
BY
OCHAI AMEH KELLY
REG. NO: EE/2006/133
SUBMITTED TO
THE DEPARTMENT OF ELECTRICAL/ELECTRONICS
ENGINEERING
CARITAS UNIVERSITY, AMORJI-NIKE,
ENUGU
IN PARTIAL FULFILLMENT OF THE REQUIREMENT
FOR THE AWARD OF BACHELOR OF TECHNOLOGY
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BITECH) DEGREE IN ELECTRICAL ELECTRONICS.
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DEDICATION
Firstly, I dedicate the report to god almighty who kept me throughout the
training period and fro his protection and guidance over my life. To my
mother Mrs. Cecelia Ochai, and very Rev. Fr. Emmanuel Mathew Paul Ede
and to the entire family of Ochai Adejo and their well wishers. For their care
and support if not for all of you all these would have being a mirage. Thank
you.
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ACKNOWLEDGEMENT
All glory, honour and adoration to god who made this report a
success. I also acknowledge the effort of my superviror, Engr. Ayemo, Engr
Ilori, Mr. Edris Jimoh, Mr. Lamidi, Mr. Olasegiri, whom have contributed
immensely towards the successful completion of my industrial training with
their co-operation, without their effort my industrial training, may not have
gathered enough fact as it is.
Finally to my colleagues for their loving and caring attitudes, I say a
big thank you to you all and may God less you all.
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ABSTRACT
The development of Hydroelectric power station has contributed immensely
to the availability of Electric Power Supply in the country over the past
thirty-five (35) years. Apart from the development of infrastructures
associated with the availability of electricity. The industry has facilitated
engineering training skill acquisition and experience e for staff. Students and
different professionals over the years, most of who are in various
engineering establishment within the country and even beyond.
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TABLE OF CONTENTS
1. ELECTRICAL DEPARTMENT
2. PRODUCTION DEPARTMENT
3. PROTECTION, CONTROL & METERING (PC&M) DEPARTMENT
4. MECHANICAL DEPARTMENT
TITLE PAGE
Dedication
Acknowledgment
Abstract
Table of content
Introduction
Brief history of the company
CHAPTER ONE: ELECTRICAL DEPARTMENT
1.1 Maintenance on the generator
1.2 Maintenance on the slip ring and carbon brushes
1.3 Maintenance on the radiator
1.4 Excitation
1.5 Power transformer
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1.6 Battery bank
1.7 Battery bank maintenance
1.8 The sump ump
1.9 The working principle of the sump pump
1.10 He insulation text of the sump pump
1.11 Circuit breaker
CHAPTER TWO: PRODUCTION DEPARTMENT
2.1 How electricity is been generated
2.2 Auto start of turbine
2.3 Turbine component
CHAPTER THREE: PROTECTION CONTROL AND METERING
3.1 The use and function of a digital multimeter
3.2 Water leakage probe
CHAPTER FOUR: MECHANICAL DEPARTMENT
Auxillary
Generator and workshop
Turbine
Conclusion
References
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INTRODUCTION
The (SIWES) is a compulsory program established by the federal
government for student in school of science and technology, collage of
education, polytechnic and universities in order to achieve the basic
knowledge in their various areas of specification.
These SIWES program was established in Nigeria in 1987 and has
been sponsored by t he industrial training fund (ITF). The importance of
SIWES in the university’s curriculum can not be over emphasized as it
constitute in building the minds of the students against future work
challenges, because it enable them to see far beyond the four walls of the
lecture room, which also give the student experience to be practically
competent in his area of discipline.
HISTORICAL BACKGROUND OF THE ESTABLISHMENT
Jebba Hydro-power generating station is one of the power generating
stations in Nigeria under the umbrella of Nigeria Power Holding Company
of Nigeria (PHCN) formally known as National Electric power authority
(NEPA).
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This station (Jebba hydro power station) was constructed between
1979 and 1984. It was commissioned on the 13th of April 1985 by Rtd Major
General Mohammed Buhari.
The station is bus-divided into three major branches which are:
• Generation
• Transmission
• Distribution
Jebba Hydro Electric power Generating Station is situated about 100km
downstream of Kanji power station. It comprises of six turbines with a fixed
blade propeller type. Each unit (turbine) has rated capacity of 103500kva,
the continuous maximum rating is 16KV and having a power factor of 0.8
and the frequency in which it operates is 50Hz. The total output of the six
(6) units is 560Mw. Each generator is connected to a step-up transformer of
119MCA rating that is 119MVA / 16 / 330KV. There are also three station
service transformers which are rated 4MVA /11KV / 415BV.
There are also four auxiliaries transformer which are rated 2MVA / 11
KV. 415B, taking thee sources from the station service transformer rated.
These auxiliaries transformer are all indoor transforms and supply all the
auxiliaries and station as a whole.
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CHAPTER ONE
INDUSTRIAL TRAINING AND EXPERIENCE GAIN
1.0 ELECTRICAL DEPARTMENT
This department handles the maintenance of electrical equipments and
electrical machine such as maintenance of generator, transformer, electric
motors, illumination of the station and maintenance also on the auxiliaries of
the station.
I was part of the following jobs.
1.1 MAINTENANCE ON THE GENERATOR (2G1 TO 2H6)
The unit in which the maintenance is to be carried out is shut down
from the control room.
The maintenance was carried out on the slip ring, carbon brushes, stator
winding and radiator.
1.2 MAINTENANCE ON THE SLIP RING AND CARBON BRUSHES
It is the slip ring that holds the carbon brushes. The carbon brushes make
contact with the rotor. It is through the carbon brushes that supply get to the
rotor.
The maintenance done on the slip ring is to check for the bad ones.
The bad ones are replace with new ones. The spring on the slip ring enable it
to push the carbon brushes to the rotor.
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That maintenance done on the carbon brushes is to check or the worn
out ones and replace with a new ones. Any worn out one causes the voltage
supply of the rotor to reduce and also causes sparking. The dusty carbon
brushes are clean with neat rag so as to avoid excess or low conductance to
the rotor.
1.3 MAINTENANCE ON THE RADIATOR
Radiator is an instrument that is used for sending out heat form the
Generator in order to cool the engine of the generator.
The maintenance that is done on it is to check for any leakage on it. If
there is any leakage on the radiator it causes low lever of the fluid that is
inside it. The maintenance is also done on the lever of the fluid that is inside
the radiator and also check weather there is no any moisture on the rotor
windings. If there is any moisture present. It is clean with a dry clean rag and
if any leakage the mechanical people is called on to.
1.4 EXCITATION
There are two type of excitation present in the power generator
1. Self excitation
2. Initial excitation (separate)
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At unit start up the generators are separately excited until when 50% of
the rated voltage is generated that is 8kv before changing over to self-
excitation. This is done automatically.
PRINCIPLE IN WHICH IT OPERATE
It uses battery at the initial stage (i.e. the generator is been excited by a
battery) To start the motion. The supply does not go to the generator
directly. It first goes to the AVR (auxiliaries voltage regulator) to regulate
the voltage before getting to the generator. The sources of the supply is the
battery from the battery room. The battery is to start the motor into motion,
which is the initial excitation. When the generator reaches a certain speed (as
above) it will change over i.e. it will not use the supply from the battery
room again, at that point it become self excitation.
1.5 POWER TRANSFORMER
This type of transformer can only be found in the generating station. It
is a step up transformer which step up the voltage supply by the generator
fro m16kv to 330kv and the voltage is sends to the national grid. This type
of transformer is a high voltage transfer. The voltage generated by the
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generator i.e. 26kv is connected to the primary side of the transformer and
give output of 330kv through the secondary side of the transformer.
1.6 BATTERY BANK
Another name for battery bank is battery room. The instruments used
in t he battery room are: battery hydrometer, electrolyte, container and
distills water. Each battery in the battery room has an output voltage of
2volts.
There are two banks in the battery room at Jebba hydropower business
unit. Each bank has a total sum of 55 batteries. Which have a total voltage of
110 volts dec. the cells connected in series to each other.
1.7 BATTERY ROOM MAINTENANCE
The lever of the electrolyte in each cell is checked by mere looking at
the cell physically. The battery is marked with maximum and minimum
lever. For any low electrolyte in the cell. It will top up by adding distill
water to it.
Also the strength i.e. the concentration of the electrolyte is checked
using a hydrometer. There are three reading on the hydrometer, which is
been indicated by three different colors. Any one found low is recharged
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using the battery charter. Any one found not rechargeable again is remove
and replaced with new ones.
n.b. The battery room must be well ventilated (i.e. using extractor fan).
Consequence for not making the battery room ventilated
• It can damage the cell of the battery.
• It can cause suffocation whenever any person gets in.
• It can leads to fire when any small sparking occur in the room.
• It reduces the life of the battery.
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1.8 THE SUMP PUMP
There are two kinds of sump pump
1. The submersible pump
2. The surface pump
The submersible pump: - it is called submersible pump because this type
of pump can be totally immersed inside the water without damaging the coil
inside the pump. It is manufacture in such a way that water will not be able
to get to the motor.
The surface pump: - This pump cannot be immersed inside the water. If
mistakenly immersed inside water it will spoil the coil inside the motor. A
water inlet hose is made with the pump and it is passed to the pump pit.
The tow pumps are both use to discharge water from the turbine pit or sump
pit to the tail race.
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1.9 THE WORKING PRINCIPLE OF THE PUMP
The sump pump works automatically. Then automatic work of the
pump is been control or been energize by the water leakage probe and the
water lever switches. The water leakage probe is put inside the pit, when the
water reaches some certain lever, the pump automatically start and the water
is drain out. When the water is drain to certain lever the pump stop working
automatically. The working principle of the water leakage probe will be
discussed later.
1.10 THE INSULATION TEST OF THE PUMP
It is used to know the insulation strength or capacity of the coil in the motor.
It is essential so as to know whether the pump is in good condition to use or
not. The instrument use for this test is called insulating resistance meter. The
meter has two leads.
The pump has four terminals that is to say that the pump is a three-
phase pump, i.e. the red phase, the blue phase, the yellow phase and earth
phase.
The text is done by using the lead of the meter to test between the
earth and red, earth and yellow and between earth and bnlue. If there is no
deflection on the meter, it shows that the winding of the coil are okay and it
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can be sue. It also show that the resistance of the coil is still in good
condition, but if deflection is observed it shows that the pump is not in good
condition.
1.11 CIRCUIT BREAKERS
Circuit breakers are electrical device that is used for close and open of
electrical circuit. The breakers are design to open under abnormal condition.
The circuit breaker is an advancement of the control switch in which it
can be able to switch off automatically in case any fault arises in the
electrical circuit. It also has the ability to detect any over loading due to
excess mechanical load.
It has a coil in which is design in it. The coil produces a back e.m.f.
The bank e.m.f. that the coil produces is always greater than the normal
current and thereby making the breaker to trip when the back e.m.f.
overcomes the running current.
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CHAPTER TWO
PRODUCTION DEPARTMENT
In this department they monitor the production of electricity and also
monitor the entire generators that are in service in case of any fault.
GENERATION OF ELECTRIC POWER
The water is store in a lake which is called the dam itself. The water from
the lake passes through the trash rack which filters any debris coming in. the
intake gate open for the water to pass through to the penstock went to the
spiral casing where the width of the water is been reduced and this increased
the pressure of the water. At this pint, when the start button is press in the
control room it send an impulse to the solenoid either to open or close, when
it open the pressure rise oil (electrical to mechanical) moved to the main get
which forces the main gate control valve. The pressure oil now enter the
servo motor which make the wicket gate to open (the wicket gate is
connected to the shift ring and the shaft ring is connected to the serve mote.
The impulse sign come from the Electronic Turbine regulator (ETR). When
the wicked gate is open the water fall on the blade, the blade start rotating
and it rotate the shaft. The exciter obtain its initial starting voltage supply at
110v (DC) from the battery bank. The 110v enters the field poles of the
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exciter for its initial excitation. As the unit is motion, the armature cuts the
flux produces by the field poles. The cutting of the flux leads to the
induction of voltage in the armature. The voltage induced in the armature of
the exciter is about 375v (A>), which is converted by the commutators to
37v (DC) and passes in to the collector ring A.C. generator field poles for its
excitation. The generator field pole produces its on flux at a constant speed
of 1154 revolution per minute (rpm).
FOR AUTO START
The following auxiliaries should be place on auto:-
a. Unit control selector
b. Pilot oil pump
c. Emergency pilot oil supply
d. Coiling oil pump
e. High pressure lift pump
f. Shaft seal booster pump
g. Generator breaks
h. Automatic voltage regulator control selector
i. Generator heaters
j. Transformer cooling oil pumps (any 2 of 3 pumps)
k. Circulating oil pumps
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When these conditions are met, relay K16 will be energized and
auxiliaries on auto indication will light. At this time unit can be started
automatically.
2.2 TURBINE COMPONENTS
The main parts of turbine are:
1. Speed Ring
2. Turbine shaft
3. Turbine Bearing or Meaning Bearing
4. The Runner
5. Shift Ring or Regulating Ring
6. Servomotor
1). Speed Ring performs the following functions:
i. It vertical ribs lead the flow of water into the turbine and carry the weight
from above the speed rings.
ii. It takes the force of internal pressure and forms the inner circumference of
the scroll case.
2) Turbine Gates or Wicket Gates
i. They control the amount of water flowing into the turbine runner
They have self lubricating brushing on both ends
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A layer called gate arm is keyed to the slip ring and the turbine gate by a
lock which breaks if some obstruction prevents the gate movement.
3). Turbine shaft
It transmits the mechanical force from the turbine shaft.
4) Turbine Bearing
The main bearing is used to centre the turbine shaft.
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CHAPTER THREE
2.0 PROTECTION CONTROL AND METERING (PC&M)
As the name implies, this department handles all the protection, control
and metering of all department equipment. Some of the equipment
concerned by this section are the start and stop panels, automatic voltage
regulator (A.V.R.). Generator protection and transformer coders, probes,
strainer meter control and so on.
In this department I practically undergo the following jobs.
3.1 The use function of a meter (digital)
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A multimeter: - A multi-meter has many functions, part of the function is to
text the alternating current (AC) voltage, direct current (DC) voltage,
continuity of a conductor, resistivity of conductor e.t.c. To text any of the
function above, the rating on the meter has to be turn to correct before
testing.
For example testing the resistance of a resistor select ohm with the rotary
function switch and there will be a display on the screen and the test is used
to touch the two edges of the resistor.
3.2 WATER LEAKAGE PROBE
This is type of instrument that is used to control the level fo leakage at the
turbine pit.
Water leakage probe
This is the type of instrument that is used to control the automatic operation
of the overhead pump.
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The wate leakage probe has three operating functions: -
i. to start the pump
ii. to stop the pump
iii. To make an alarm to come on.
PRINCIPLE OF OPERATION
The probe uses the principle of magnetic flux to operate.
The probed has three magnetic switches it. The three magnetic switches are
arranging inside it to sweet the purpose in which you want the pump to
operate (i.e. to allow the pump to cut in and cut out).
The fist switch downward stands for the stopped switch, the second switch
upward stand for start and the last switch stand for the alarm. The water
floater is light in weight, it can float on water as the name implies. The water
floarte move upward and downward (i.e. ion the direction of the rod)
depending on the level of the water.
The water floater has a magnet that surrounds the tip (i.e. edge) of the
water floater. It is the present of the magnet that make the magnet switch to
be enabled and disabled. That is to say, to on and to off.
The water leakage probe is located in the turbine pit at the station. The
leakage that comes out from the draft tube goes to the turbine pit, as the wate
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arises the water floater rises upward. As soon as the magnetic area on the
water floater gets to the magnetic switch, a flux is generated between the
water floater and the magnetic switch thereby enabling the switch to get on.
As soon as the water floater get to the start switch, the switch et on and
make the pump to start working and the water present in the turbine pit it
drain off to the tail race and making the water floater to come back to the
stop switch. On getting to the stop switch, the pump will stop working.
There some instance that the rate of water leaking out is more than the rate
in which the pump drains. In this case the water floater will not come back
to the stop switch but instead the water floater continues to arise to the alarm
switch. On getting to the alarm switch, an alarm is cut in at the control room
to notify danger. The workers have to run for solution, by adding another
pump to drain off the water t o disallow flood and to avoid automatic shut
down of the unit.
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CHAPTER FOUR
MECHANICAL DEPARTMENT
The mechanical department is split into three factors:
1. Auxillary
2. Generator and workshop
3. Turbine.
Aulillary
The auxiliary department is responsible maintaining of equipments such as
1. Turbine air compressor
2. Testing the deludge system of the station service transformer
3. Buster pump
Jockey pump
Draft tube crane
i) Turbine air compressor takes in air and at low pressure and sends it
out in high pressure. The pressurized air is used to pressurize the
tellus oil that is used in the governor system. The governor system is
the system that controls the opening of the mechanical gate. The air is
supplied to the top of the old accumulator tank and then compresses
the oil. The pressurized oil is now used as hydraulic to open or close
the mechanical or wicket gate.
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ii) Deludge system
The deludge system is a kind of pipe network around the top of the 330kv
transformers. There are cuss and bulbs that are attached to it. The deludge
system is serves as a protection for the transformer. If the transformer is
over heating or there is five outage on the transformer, the cuss aid bulbs
will melt and air in the pipe will flow out and immediately water will
begin to sprinkle on the transformer at high pressure until the heat or fire
is put out.
It operation is being controlled by hydraulic system.
iii) Jockey pump
Jockey pump is a three phase electric motor attached to a pump for
increasing the pressure of water in the fire pipe. It works for 2 hours non
stop for 36days.
iv). Buster pump
The buster pump is an electric motor attached to a pump which help to
increase the pressure of water in the fire fighting pipe for pitting out fire
in the station power house. It is usually on stand by. It comes up if the
jockey pump is running and the pressure in the pipe is not enough
probably due to the fact that one of the discharge source is open thereby
reducing the pressure in the pipe, therefore the buster pump will pick
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automatically and stabilize the required pressure to put out any amount of
five.
2. GENERATOR AND WORKSHOP
The generator and workshop department is in charge of equipments such as
i. A.C welding machine
ii. Late machine
iii. Magnetic drilling machine
iv. Oil transferring pump
v. Heat exchanger
vi. Power house crane
vii. Power
i) Arc welding machine: The are welding machine is used for welding
two metals i.e. joining two metals or metals together.
ii) Late machine: This machine is used to produce cylindrical objects. It
is used to reduce the external diameter of an objects. It can be used to
produce machine parts.
iii) Magnetic drilling machine: Magnetic drilling machine contains a big
piece of magnet which will attract the drilling machine firmly to the
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piece of metal it wants to drill. It is used for boring hole in the draft
tube during grafting.
iv) Oil transferring pump: The oil transferring pump is used to transfer or
transport oil into the heat exchanger of the turbine.
v) Heat exchanger: Heat exchanger is used to remove heat from the telus
oil going into the thrust and guide leaving respectively. It is
cylindrical in shape, it has a passage for both water and oil in it. The
water in the heat exchanger removes the heat from the tellus oil by
conduction.
vi) Power house crane: The power house crane is a 225T, 70t, 60T, crane.
It is used to lift equipments under these rating with the power house.
3. Turbine
The turbine department is in charge of the following equipments
i. the governor system
ii. turbine pit
iii. Strainer pump
iv. Sump pump
v. Dewatering or unwatering pump.
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The governor system
This system is controls the opening and closing of the mechanical
gate. The system consist of two motors, tellers oil, serve valve etc.
Turbine pit
The turbine pit is a place under the generator where the shaft turbine shaft is
seen to rotate and set the generator rotor in motion. It consist of some
compartment that help to guide the turbine shaft from collapsing. There are
two electric motors in the turbine pit i.e. A. C. inner head pump and D. C.
inner head pump. These pumps are used to evaquate over flow of water from
the pit.
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