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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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