CHAPTER ONE

1.0 INTRODUCTION

1.1.0 HISTORY OF SIWES

The Students Industrial Experience Scheme (SIWES) was initiated by Industrial Training

Fund (ITF) in the year 1973 as a means of blending theory and practical experience which

was missing in our educational system. The scheme was therefore a school training

orientation program designed to expose and prepare students on work they would meet in

post-graduation endeavors.

As a federal parastatal. ITF was established by decree 47 of 1991 and charged with

responsibility of promoting and encouraging the acquisition of skills in industry with a

view to generate a pool of indigenous trained man power sufficient to meet the needs of

the economy. A clause was invented by the fund in 1978 in its policy statement No_1

dealing with the issue of practical skills among locally trained professionals, section15

of the policy states interlaid great emphasis will be placed on certain products of post-

secondary to adapt or orientate easily on their possible post-graduation for environment.

The fund will seek to work out co-operative machineries with industries whereby

students will be trained in industry on technics in line with their area of studies. The

fund will support such mind careers attachment by contributing to the allowance etc.

payable to the students. The scheme was therefore assigned to provide the much needed

practical experience for the students undergoing all courses that demand exposure in

industrial activities and to promote the much desired technical knowledge.

1.1.1 OBJECTIVES OF SIWES

1. To provide the means for students in the institutions to acquire industrial skills and

experience in their field of study.

2. To prepare student on tertiary expected working situation after graduates.

3. To expose students to work methods and techniques in handling equipment and

machineries unavailable in the institutions.

4. To ease the transition from school to the world of work.

5. To provide the students with opportunities to apply their theoretical knowledge

acquired in school.

1.1.2 GROWTH OF THE SCHEME

Since its inception, the scope of the scheme has widened considerably. The number of

institutions grew up with its corresponding increase in the number of student’s population.

During its early years of existence, its operations were not heavy. The students’ population

could easily be managed because the industrial facilities were adequate and many multi-

nationals were expanding their industrial bases in Nigeria. The period witnessed a steady

increase in students’ population as the years went by and this meant a corresponding

increase in the need for placement.

1.1.3 RELEVANCE OF SIWES TO PHYSICS

The Students Industrial Work Scheme (SIWES) in physics is an exercise designed to give

students an opportunity to acquire work experience at detailed stage(s) of their training as

undergraduates. As an important part of the core and total requirements for the award of

B.Tech. (Hons) degree in consonance with the specifications contained in the minimum

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academic standards for physics SIWES training accounts for eight (8) credit unit which

must be earned by each student after the training.

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 CHAPTER TWO

BRIEF HISTORY OF THE COMPANY

2.1.0 HISTORICAL BACKGROUND OF TRANSMISSION COMPANY OF

NIIGERIA (TCN), JOS WORKS CENTER.

The Jos transmission sub-station was built in the mid 70’s (1975/1976) and was

COMMISSIONED in the year 1978.The station originally received 132kV of electricity

from

330/132/33kV Kaduna sub-station for the consumption by Plateau, Bauchi and Gombe

states.

The Jos transmission sub-station switchyard is sectioned into three (3); the330kV, 132kV,

33Kv sections. This switchyard comprises of various power and switching devices with the

breaker system arrangement of one and half breaker arrangement system.

In the year 1981, the supply was upgraded to 330kV, and the sub-station transmits 330kV of

electricity to Gombe,132Kv to Bauchi, and 33Kv to NNPC Zaria road, Toro, Anglo Jos,

Dogon Dutse, JUTH and Rukuba road feeders in Plateau state. Currently, the station

comprises of one 150 MVA, and three 60 MVA power transformer.

2.1.1 THE VISION OF TRANSMISSION COMPANY OF NIGERIA (TCN)

To attain a transmission company with a solid reputation for delivering reliable, cost

effective electric power to the end users in Nigeria and western Sub-region.

2.1.2 THE MISSION OF TRANSMISSION COMPANY OF NIGERIA

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To cost effectively provide, operate and maintain the required equipment and transmission

grid network for evacuating and dispatching high quality and reliable electricity with

minimal technical losses.

2.1.3 ORGANIZATIONAL CHART OF TCN

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2.1.4 VARIOUS DEPARTMENTS AND THEIR FUNCTIONS

The organizational structure being operated by the center currently has evolved after careful

initially analysis and matching of its mandate, objectives and strategies and also taking into

consideration what obtain in similar organization internationally. It has been reviewed

various times and at various stages either by government for such a purpose before arriving

at the current structure summarized as follows with the function carried out by the

constituent division and unit. Here we have legal service units, protocol and public relations

internal audit and under the principal managers there are seven (7) departments.

 Human Relationship Department

The department human relationship ensures the mutual understanding between the

employee and the management. This department is of great value in any working

environment. Human relations is the process of training employees, addressing their

need and fostering a work place culture by resolving conflicts between different

employees or between employees and management.

 Account Department

Payable and receivable inventory, payroll, fixed asset and all other financial element are

handle in this department. This department review the record of each department to

determine the financial position of the company and any changes requires to run the

organization cost effectively.

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  Protection Control and Metering Department; The department protection and

metering is one responsible for providing protection to the installed equipment such

as power transformer, circuit breaker, reactor, instrument transformers among

others using different types of relay and other metering devices. This department is

also responsible for pre commissioning test and termination of newly installed

switch gears before commissioning them.

 Electrical Maintenance Department; This department deals with the maintenance

of power transformers, circuit breakers, reactors, isolators and their operating

mechanisms. This department also carried out maintenance of station battery banks

and the battery chargers.

 System lines Department

This department deals with the maintenance of the grid patrol of 330/132Kv towers,

replacement of conductors, clamps, broken insulator and routine patrol of the grid.

 System Communication Department

This is a department responsible for the interconnection of stations for monitoring of the

overhead cables and for communication between stations. Communication is vital in the

management of all control and protection systems in the switchyard and in inter relation to

other substations.

 System Operation Department

This is a department responsible for the operations and monitoring of installed switch gears

in the switchyard. This department also issue work and test permit and station guarantee to

the other technical department.

2.1.5 OVERVIEW OF SYSTEM AND COMPONENT

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2.1.6 SUBSTATIONS

A substation is a part of an electrical generation, transmission and distribution system that

transform voltage from high to low or the reverse. Between the generating station and the

consumer, electric power may flow through several station at different voltage level. It may

include transformers and other power equipment installed to change the voltage level from

high transmission voltages to lower transmission voltages or at the interconnection of two

different transmission voltages. Generally, substations are unattended relying on SCADA

for remote supervision and control.

2.1.7 THE SWITCHYARD/SWITCHING SUBSTATION

A switching substation may also be known as a switchyard. This is regarded as a subset of

any station where the power equipment are installed for voltage transformation. A

switchyard is commonly located directly adjacent to or nearby a power station usually

covered with gravels to function as an insulator from the bare ground because of its ability

to drain water and reduce water-logged areas thus reducing the risk of electric shocks. The

switchyard consists of transformers, circuit breakers, bus-bars, line isolator, feeders, wave-

trap, sky wires, arrestors current and voltage transformers.

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 Fig. 1 A section of the switchyard at Jos work center

CHAPTER THREE

3.1.0 INTRODUCTION

3.1.1 DEPARTMENTS/UNITS WHERE SIWES WAS OBSERVED

During the twelve month SIWES attachment, the SIWES was observed in four (4) various

departments as followed; Protection Control and Metering Department, Electrical

Maintenance Department, System Lines Department and System Operation Department

3.1.2 PROTECTION CONTROL AND METERING DEPARTMENT

The protection control and metering department is the first department where the SIWES

was observed. It is the department responsible for the protection of switchgears such as

power transformers among others using various protectives relays and the instrument

transformers. This department also carried out the pre commissioning test and termination

of newly installed switchgears.

3.1.3 RELAY AS A PROTECTIVE DEVICE

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A relay is an electrically operated switch which is use in a situation needed to control a

circuit by low power signal with complete isolation between control and controlled circuits

or where several circuits must be controlled by one signal. In other word, a relay can be

described as an automatic device which contained two or more open and close contact that

sense an abnormal condition of an electrical circuit. Relays with calibrated operating

characteristics and sometimes multiple operating coils are used to protect electrical circuits

from faults. In modern electrical power systems, these function are performed by digital

instruments called protective relays. This relays are classified base on their characteristic,

logic, actuating parameters, and operating mechanism.

3.1.4 CLASSIFICATION OF RELAY

As mentioned above, relays are basically classified base on the below four (4) criteria;

1. Operating mechanism

2. Logic operation

3. Characteristic operation

4. Actuating parameters

1 Operating mechanism;

In this classification, relay can either be electromagnetic relay, mechanical or static relay.

In an electromagnetic relay, the opening and closing of relay contacts are done by

electromagnetic action of a solenoid. As for mechanical relay, the opening and closing of

the contacts are done by mechanical displacement of different gear level system. Static relay

is one in which the opening and closing are done by semiconductor switches like thyristor

2 Logic operation;

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Example of this relay are the differential relay and distance protection relay. A

differential relay is one protecting the power transformer and the bus-bar while a distance

protection relay is use in protecting the transmission line respectively.

3 Characteristic operation

Base on characteristics operation relay are categorized as; definite time relay and inverse

definite minimum time relay among others.

4 Actuating parameters

Base on actuating parameters, relay can be categorized as; current relay, voltage relay

among others.

3.1.5 FUNCTION OF PROTECTIVE RELAY

Transformer fault post great danger to people around, reduce the output supply of the station

and the environs at large. This fault may lead to the loss of transformer. As a preventive

measure, relays are set at different location to protect the power equipment most especially

the power transformer. Some of the functions of relay among others in power system

include;

1 Mechanical Protection; Mechanical fault are detected by buchholz relay. This relay is

designed for conservator tank and it detect gas as it rises from the insulating oil due to

electrical arcing or a hot area in the core steel.

2 Over-Current Protection; As the name indicate, the relay trips when the current flowing

in the transformer is above the rated currents of the transformers, the setting of this relay

takes care of the marginal increases and switching surge and operate on substantial changes

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in the currents only. It is normally located on the HV side since current handled are lower

here compared to the LV side.

3 Restricted Earth Fault Protection; This restricted earth fault relay is provided at the

neutral point of the transformer but before earthling. It differs from the normal earth fault

relay to the extent that (EFR) pick-up even line fault whereas, the (REFR) pick-up only the

transformer faults. A fault inside the transformer occurring on one or two phase result in

flow of high current in the neutral. The relay is said to act instantaneously.

4 Differential Protection; this relay keeps a watch on the incoming and outgoing current of

a transformer as long as the current in the CT’s match (taking into consideration the

transformation ratios) the relay remain inactive as long as there is a long balance.

Whenever the balance changes which is possible if there is a fault in the zone between the

two CT’s the differential relay acts tripping off power supply to the transformer.

3.1.6 PRINCIPLE OF RELAYING

Since protective relaying, comes into action at the time of equipment distress, a certain

safeguard is necessary in the unlikely event of its failure to act at the time of need. Hence,

two groups of protective schemes are generally employed-

 Primary protection

 Back-up protection

Primary protection is the first line of defense, whereas back-up protection follows if the

protection of equipment, should the primary protection fail.

3.1.7 MAINTENANCE OF RELAY

In power system, protective relays are very expedient in protecting and monitoring the

switchgears. As such, maintenance of these relays is an imperative policy in the station

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because it improved their efficiency as a protective devices and also increase the life span of

the power equipment. For that maintenance of relay is carried out twice or thrice monthly

mainly to have a better functioning relays and thus increase their efficiency. The major

maintenances culture of this relays are; secondary injection test and primary injection

test

 Secondary injection test; this is done on the relay panel in the control room

to test the relay in order to see whether it will relate with the current

transformer and the circuit breaker to operate in the case of fault. In this test,

it requires the simulation of fault at different current value to the relay using

and electronic device called CMC 356.

 Primary injection test; this is done in the switch yard on the current

transformer to see whether the relay will react to the injected current on the

current transformer to operate the circuit breaker in the case of fault using

CPC 100.

Below is a sample reading for the secondary and primary injection test.

 ROUTINE MAINTENANCE OF MAKERI FEEDER RELAY

Secondary injection test.

 Relay make; NARI

Relay type; RCS 9611C 2 OC+EF

 As met setting

2OC PS=0.7 , TMS=0.08

EF PS=0.2 TMS=0.06

A Pick up values

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 Red; Ipk=0.83A t0=0.81sec

Blue; Ipk=0.74A t0=0.83sec

EF; Ipk=0.2A t0=0.28sec

B Relay calibration

PHASES INJ.SEC.CURREN PS TMS TOP STOP REMARK

RED 1 6.19 10

2 0.5 1 3.72 5 OKAY

BLUE 1 7.72 10

2 0.5 1 4.39 5 OKAY

E/F 0.4 7.18 10

0.8 0.5 1 5.07 5 OKAY

As left settings; 2O/C PS= 0.75 TMS=0.05

E/F PS= 0.2 TMS=0.025

 ROUTING MAINTENANCE ON 33KV RUKUBA FEEDER AT JOS WORK

CENTER

11 SEPTEMBER,2018

Primary injection test

CT RATIO:400/1

PHASE RELAY INJECTED RELAY BREAKER REMARK

SETTING CURRENT(A) OPERATION RESPONSE

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 R PS=1 94 E/F TRIP OPENED OKAY

TMS=0.15

E/F PS=0.2 90 E/F TRIP OPENED OKAY

TMS=0.2

B PS=1 87 E/F TRIP OPENED OKAY

TMS=0.15

3.1.8 REASON FOR THE FAILURE OF A PROTECTIVE RELAY

The reason for the failure of a protective relay include;

 If the protective relay is defective itself.

 If the DC trip voltage supply to the relay fails.

 Disconnection from the relay panel to the circuit breaker.

 If the trip coil in the circuit breaker is defective.

 Absence of signal from the current transformer and voltage transformer.

3.1.9 INSTRUMENT TRANSFORMERS

Electrical equipment of high voltage can’t be connected directly to the relay or the control

panel for safety purpose. For that, the current and voltage transformer are needed for

connecting the power equipment to the relay and the control panel. These transformers

reduce the voltage and current level from higher value to low value for measurement by the

relays.

 Current transformer; this is a transformer that transform current from high current

value to low current value for measurement by the conventional instrument like the

relay. In this transformer, the primary winding carries the current which is to be

15
measured while the secondary winding is connected to the relay. The range of the

current that can be measured by the transformer is 5A-1A. basically these

transformers are of two type; the wound type and the core type in term of

construction

Fig.2 current transformer at Jos working center

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  Potential or Voltage transformer; this is an instrument transformer that transform

voltage from high value to low value for measurement by the relay. The voltage

range of this transformer is 110V. this transformer is of two type; the

electromagnetic and the capacitor voltage transformer.

3.2.0 ELECTRICAL MAINTENANCE DEPARTMENT

This is the second department where SIWES was observed and is the department

responsible for maintenances, repairs and installations of all electrical and non-electrical

equipment or circuits in or outside the switchyard, including DC battery system. This

department also deals with the maintenance of power transformers, circuit breakers,

reactors, isolators, and their operating mechanisms. It also responsible for the

maintenance of the station battery banks and the battery chargers.

3.2.1 TRANSFORMER

A transformer is a static equipment that enables the transfer of electrical energy from a

system of one voltage level to a system of another. To accomplish this, two or three

windings wound over a magnetic core are needed. The windings are electrically separated

but inter-linked magnetically. The energy transfer is by induction most of the times but

sometimes it is partly by induction and partly conduction (auto-transformer), They are

widely used in power systems to transmit power at an economical transmission voltage and

utilize power at an effective voltage.

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3.2.2 BASIC PRINCIPLE OF A TRANSFORMER

Transformer working is based on mutual electromotive force induction between two coils,

which are magnetically coupled. When an AC voltage is applied to one of the windings

(referred to as the primary), it produces alternating magnetic flux in the core made of a

magnetic material (usually some form of steel). The flux is produced by a small

magnetizing current which flows through the windings. The alternating magnetic flux

induces an electromotive force (EMF) in the secondary winding magnetically linked with

the same core and appears as a voltage across the terminals of these windings. Cold rolled

grain oriented steel (CRGO) is used as the core material to provide a low reluctance, low

loss flux path. The steel is in the form of varnished laminations to reduce eddy current flow

and losses on account of this. A schematic diagram of a single-phase transformer is shown

in the figure below.

Fig.3: coil of a transformer.

A single-phase transformer consists mainly of a magnetic core on which two windings,

primary and secondary are wound. The primary winding is supplied with an AC source of

supply voltage V1. The current flowing in the primary winding produces flux, which varies

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with time. The flux links with both the windings and produces induced electromagnetic

forces. The electromagnetic force produced in the primary winding is equal and opposite of

the applied voltage (neglecting losses). The electromagnetic force is also induced in the

secondary winding due to mutual flux. The magnitude of the induced electromagnetic force

depends on the number of turns in the primary and secondary windings of the transformer.

 POTENTIAL-INDUCED

The ratio of the primary potential to the secondary potential is the ratio of the number of

turns in each and is represented as follows;

N1/N2=V1/V2 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2.1

The concept of step-up and down transformers functions on similar relation. A step up

transformer increases the output voltage by taking N 2>N1 and a step-down transformer

decreases the output voltage by taking N1>N2..(Narayana,2007)

 CURRENT-INDUCED

When the transformer is loaded, the current is inversely proportional to the voltages and is

represented as follows;

V1/V2=I2/I1=N1/N2- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2.2

Transformers as an important factor in power system, are regarded as the hearts of AC

transmission and distribution system for the following reasons;

1 Before their invention and use, power generation and supply was as direct current only,

that is in small quantities. Change of voltages here is not normally possible. Their invention

brought in alternating current production and distribution with voltage change at will, to suit

the requirement of the electrical machinery used.

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2 They instituted large scale production and distribution of electrical energy (Increases by

billions of times).

3 They contributed to transporting bulk power through long distances (by increasing to very

high voltages) very economically and reduced high power loss in transmission.

4 Power supply from its generation point to its utilization site, normally passes through 4-6

transformers in all.

The Transmission Company of Nigeria Jos work center comprise of two type of transformer

namely;

1. Power transformer

2. Earthling transformer

3.2.3 EARTHING TRANSFORMER.

Earthling transformer is one of the most important power equipment among the switchgear

in the switchyard. It is mainly for protecting the power transformer against earth fault and

for station service.

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 Fig 4: An Earthling transformer

Some of the important aspect of earthling transformers to be understood clearly is with

regards to earthling of the neutral bushing and its maintenance are;

1. For keeping the neutral at ground potential.

2. For providing easy path to protective circuits of the transformer.

3. To avoid neutral floatation.

 Neutral at ground potential;

Since earth is everywhere, grounding ensures keeping the neutral at ground potential at all

places in the country thereby ensuring constancy of phase to neutral voltage of all

similar(voltage) rating transformers. Then all electrical gadgets (say 220volts) can be

worked anywhere in the country. If the neutral is not earthed it would assume its own

potential. This would result to potential difference between the neutral and phase which

would be different in different transformers and all electrical gadgets would not work

effectively at all places.

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  Easy path to protective circuit of the transformer;

All earth faults protections and transformers are wired through the earth, and grounding.

The neutral ensures easy path for fault current flow. The moment the currents exceed certain

pre-determined values power supply to the transformer is cut off thereby preventing further

damage to the transformer.

 Neutral floating;

An improperly grounded neutral would cause electrical floating. This would cause the phase

to neutral voltage to be different for the 3phases of the same transformer (when the 3phases

are unequally loaded).

Fig. 5; Delta Star Diagram of Flow of Voltage

In Figure 5 (not to any scale) the thin lines of the sides of the triangle represent the primary

voltages and the bold lines of the represented the secondary voltages (with unearthed

neutral).

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Fig.6: Delta Star Diagram of Flow of Voltage

In the case of the figure above, these secondary phase to neutral voltages are equal, as the

loads on the 3phases are balanced, though neutral is electrically floating.

In the case of the second figure, the secondary phase to neutral voltages is unequal. The

floating neutral has shifted so that the phase that has the highest load is provided with the

highest voltage named CN. Then the consumers of the phase AN and BN experience low

voltage(Narayana,2007).

3.2.4 POWER AND EHV TRANSFORMERS TECHNICAL

The Transmission Company of Nigeria Jos work center switchyard contains transformers of

various capacities which includes 60MVA and 150MVA.

 150 MVA TRANSFORMER: Mitsubishi

MAKE: BKS-75000/330

TYPE: IEC60289

STANDARD: HV330,000V

RATED VOLTS AT LOAD: LV123,000

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1. RATED AMPERS: ONAN: 139.96 839.786

ONAF: 174.95 1049.73

2. FREQUENCY 50Hz

3. VECTORGROUP: Yd11

4. TYPE OF COOLING: ONAN/ONAF

5. PHASES: 3/3HV/LV

Tap position 01 to 17

6. IMPEDENCE VOLTS%: 1 5 17

9.3 9.88 12.16

7. MAX. AMBIENT TEMP. 45°C

8. WINDG. TEMP. RISE: 55°C

9. LOAD LOSSES (KW): 75°C 171.2

10. RATED REACTANCE: 75°C 1446.64Ω

11. SYMMETRICAL SHORT CIRCUIT CURRENT: 2sec

12. INSULATION LEVELS:

H.V L.V H.V.N L.V.N ST.WDG

K.V 395 140 38 38 38

K.V .P950 325 95 95 95

13. OIL TYPE :Nitro Libra Nynas.

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14. ACTIVE PART WEIGHT: 51900Kg

15. OIL WEIGHT: 24900Kg

16. TOTAL WEIGHT: 108000kg

17. UP TANK & COVER WEIGHT: 13063Kg

3.2.5 IMPORTANT ASPECTS ON A TRANSFORMER

Some of the important aspect on a transformer includes

 Vector group
 Cooling method
 Maximum ambient temperature
 Top-oil rise temperature
 Winding temperature rise

 Insulation level

 VECTOR GROUPING;

Vector grouping is an indication of the nature of the primary and the secondary connection

between the three phases of a transformer, along with the phase shift (if any) of the

secondary with respect to the primary. For example, a transformer having Dyn11 group; The

above vector group stands for;

D: represents primary HV winding delta connection.

y: secondary LV star connection.

n: indicates that the neutral is brought out.

11: is the phase shifting, which indicates that LV winding leads the HV by 30˚.

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  TYPE OF COOLING: ONAN/ONAF.

The capacity of fans is to create adequate breeze and cooling so that we can draw

100% full load currents. ONAN is an acronym for Oil Natural and Air Natural

indicates the mode of cooling the transformer. The heat generated in the winding is

proportional to the amperes. The same is picked up by the surrounding liquid

medium. Convection currents are set up due to oil portions getting heated up to

different temperature and thus acquiring different specific gravities. During the

circulation process the heat is conveyed to the tank/radiators and later dissipated to

the atmosphere. Thus the oil circulation and air movement is left to the nature and

we don’t do anything about it. As regards the arrangements of this ONAN cooling,

the 150MVA are provided with radiators or oil coolers permanently welded to the

body. The radiators are designed for maximum surface area for a given internal

volume so that heat dissipation into the atmosphere is maximum. In USA it is called

Self Cooled or OA.

In the case of ONAF, certain high speed fans are fitted to the radiators. Here the cooling is

ONAN basis up to certain level of loads. After words, the fans are switched on either

automatically (by temperature controlled relays) or manually to create a breeze through the

entire radiator banks creating a better cooling effect.

 MAXIMUM AMBIENT TEMPERATURE45°C: This means that the transformer

can be installed and operated in places where the ambient temperature does not

exceed 45°C as it is designed to work in good conditions when the temperature of

the transformer increases up to a maximum of 45°C. It also means that we are

expected to take such measures as necessary to bring-down the temperature of 45°C

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 and below in case the atmospheric temperature rises above45°C. Since all the other

temperatures like that of oil windings etc. are relative to this ambient temperature,

we have a good thermometer as a necessity, to read the ambient temperature on

hourly basis.

 TOP-OIL RISE TEMPERATURE 45°C: This means the transformer can be

loaded to such extent as to allow a temperature rise up to 45°Cover and above the

ambient temperature. For example, if the atmospheric temperature is 30°C, then the

temperature of the top-layer oil inside the transformer can go up to a maximum of

30°C+45°C=75°C.

The words TOP-OIL is in view of the fact that inside a transformer, only the top most

portion of oil attains the maximum temperature when compared to middle/ lower or bottom

levels of the oil.

A thermometer is provided to measure this top oil temperature for the purpose normally a

metallic pocket is welded to the top plate so that it protrudes into the oil tank. The pocket is

filled with oil so that it attains the same temperature as the top oil inside the transformer.

The thermometer is provided with a relay setting for alarm and trip, for marginal rise and

abnormal rise in temperature respectively.

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 Fig. 7: Thermometer

 WINDING TEMPERATURE RISE 55°C: This means that the winding

Temperature can increase to 55°Cover and above the atmospheric temperature. Here

again we can allow a temperature rise in the windings up to100°C, which is a sum of 55°C

(the latter figure is the maximum allowable ambient temperature). 40years ago, they put a

normal thermometer with its probe along with that of the scale so graduated that the reading

is 10°C above that of the top oil. But practices over further periods showed that the winding

temperature is directly proportional to the current. So, the manufacturers put a CT in one of

the HV bushings and put a thermometer temperature scale for the indicator needle, which

actually moves in proportion to the HV current. In the case of the winding temperature rise

thermometer, relay settings are made for radiators fans “ON” actuation, alarm and tripping,

for marginal and abnormal rise in the winding temperature respectively. This procedure a

gain has been improved upon. A thermometer which combines both the actual effects of oil

temperature and winding temperatures called the hot spot temperature indicator has been

developed. This meter is normally set to actuate radiator fans at 70°C, alarm at 90°C and

trips at 100°C (these settings are in the case of a power transformer under discussion which

is designed providing for a winding temperature rise of 55°C and vary for other). The hot

spot temperature indicator is located in control panel/alarm panel box. An accessory of the

transformer normally erected adjacent to the transformer.

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 Fig.7: Temperature Indicator

 INSULATION LEVEL: The manufacturer is informing the buyers that though the

operating voltages of this transformer are 330KV (HV side) and 132KV (LV side),

he has provided insulations of 140KV and 28KV respectively. This is a condition

laid out in I.S from the safety factor point of view and everybody follows this

conditions.

3.2.6 CONTROL PANEL/ALARM PANEL

This is a separate rectangular box mounted at the transformer tank, housing as the name

indicates, all alarms circuit of the transformer. The box also houses pot temperature

indicator, fans-on and fans-off switches for local control of radiator fans.

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3.2.7 TRANSFORMER LOSES;

There are 2 types of electrical losses in a transformer;

 IRON-LOSSES: is proportional to the voltages and is at constant levels 24 hours a

day and throughout the year.

 COPPER-LOSSES: keeps on changing according to load or current.

These losses are converted into heat which raises the temperature of the interior parts. This

arises the necessity of a cooling medium which is the transit oil. It is a liquid, non-organic

and is a petroleum by-product.

In maintenance work, the quality of the transformer oil indicates the status of the

transformer.

3.2.8 TRANSFORMER TESTS /MAINTENANCE

In Transmission Company of Nigeria Jos work center, the following test are performed on a

transformer as pre-commissioning test or as a routine maintenance of the transformer. such

test includes;

1. Continuity tests

2. Insulation resistance test

3. Dielectric strength of transformer oil

4. Short circuit test.

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 5. Open circuit test.

Other tests are;

 B.D.V TEST

Break-down voltage test is a measure of the ability of the transit oil to withstand electric

stress without break-down or failure.

 D.G.A TEST

Dissolved gas analysis is a measure of the various gases present in the transformer oil. The

various gases present in the transit oil are a measure of deterioration of some solid dielectric

material or transformer oil decomposition due to internal arcing etc. By studying the gases

and to what extent these gases are present, one can arrive at some of the happenings inside

the transformer for example, if there is high level of hydrogen it is an indication of partial

discharge, arcing or conductor overheating.

 TAN-TEST

In the tan-test or tan-delta test the power factor(PF) or dissipation factor(DF) of the

insulation system (whether solid or liquid or a combination of both) is measured. It is a

number between zero and one PF and DF indicates the dryness of an insulating material.

Their values are almost same in the case of an insulating material. When the insulation

systems get contaminated with moisture and other impurities or pollutant, the power factor

or dissipation factor becomes more. The PF/DF is measured by imposing a voltage across

the insulating medium measuring the current I, and watts w, dissipated.

3.2.9 TRANSFORMER FAILURE

Transformer failure is caused by

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  Winding failure due to mechanical stress.

 Insulation deterioration caused by moisture, overheating, or voltage surge.

 Voltage regulating tap changers.

 Transformer bushing due to general aging, cracking, and internal moisture. Core

failure due to shorted laminations and insulation failure.

3.3.0 CIRCUIT BREAKER

A circuit breaker is an automatically operated electrical switch designed to protect an

electrical circuit from damage caused by overload or short circuit. Its basic function is to

isolate the unhealthy part of the system from the healthy part. Unlike a fuse, which operates

once and then must be replaced, a circuit breaker can be reset (either manually or

automatically) to resume normal operation. Circuit breakers are made in varying sizes, from

small devices that protect an individual household appliance up to large switchgear

designed to protect high voltage circuits feeding an entire city. Its trips off when it senses

overload or a fault on the line and its subjected to hard conditions in the switchyard. The

circuit breaker can be opened manually or automatically. When the circuit breaker senses

any fault, the motor acts on the spring and it breaks the supply or trips off and it then opens

the isolators but there is a spark in the breaker capable of causing a fire outbreak but due to

the arc quenching media in the breaker, it extinguishes the fire. There are various types of

breaker name base on the quenching media.

3.3.1 TYPES OF CIRCUIT BREAKER

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Basically circuit breakers are named base on the quenching media provided in the breaker to

reduce the great arcing that occur in the process of opening the breaker. The various types

of breaker include;

 Sulfur hexafluoride circuit breaker (SF6)

 Air blast circuit breaker

 Vacuum circuit breaker

 Oil circuit breaker

In Transmission Company of Nigeria, air blast circuit breaker is not use due to the great

noise involved in operating the breaker.

 OIL CIRCUIT BREAKER;

In this type of breaker Mineral oil is used as quenching medium due to its property as a

better insulating material than air. In oil circuit breaker, the fixed contact and moving

contact are immerged inside the insulating oil. Whenever there is a separation of current

carrying contacts in the oil, the arc is initialized at the moment of separation of contacts, and

due to this arc the oil is vaporized and decomposed in mostly hydrogen gas and ultimately

creates a hydrogen bubble around the arc. This highly compressed gas bubble around the arc

prevents re striking of the arc after current reaches zero crossing of the cycle. The Oil

Circuit Breaker is the one of the oldest type of circuit breakers.

 VACUUM CIRCUIT BREAKER;

A vacuum circuit breaker is such kind of circuit breaker where the arc quenching

takes place in vacuum. The technology is suitable for mainly medium voltage

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 application. For higher voltage Vacuum technology has been developed but not

commercially viable. The operation of opening and closing of current carrying

contacts and associated arc interruption take place in a vacuum chamber in the

breaker which is called vacuum interrupter. The vacuum interrupter consists of a

steel arc chamber in the center symmetrically arranged ceramic insulators. The

vacuum pressure inside a vacuum interrupter is normally maintained at 10-6bar.

Fig.8; Oil Circuit Breaker.

 GAS CIRCUIT BREAKER (SF6)

A gas circuit breaker is such kind of a circuit breaker that protect the power station by

interrupting electric currents, when tripped by a protective relay. In this type of breaker

Sulphur hexafluoride gas are use as quenching medium in the course of opening the breaker.

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This breaker has low operating noise with no emission of hot gases and relatively low

maintenance.

Fig.9; SF6 circuit breaker

3.3.2 TEST/MAINTENANCE OF CIRCUIT BREAKER

In transmission company of Nigeria Jos work center, the normal maintenance of the circuit

breaker includes;

1. Continuity test of the breaker.

2. Earth resistance test

3. Oil dielectric test in the case of oil circuit breaker.

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 3.3.3 BATTERY BAND/BATTERY BAND MAINTENACE

 DC Supply/Battery band

The DC batteries system is of importance in every station, since it serves as a source of

power to the station in case of power failure as well as supplies power for protection and

metering panels in the control room. The battery bank has two sides, the 50v DC side

and the 110v DC side. The 50v DC side is used for communication and alarm. While the

110v DC side is used for protection. To guarantee or ensure a better efficiency or proper

functioning of the battery banks, proper maintenance is carried out every month which

also involves isolating the battery bank AC supply. The overall voltage of the batteries

of 250v and the voltage of each battery is measured using a multi meter. A hydrometer

is used for the measurement of the specific gravity. The batteries with low electrolytes

are refilled to the maximum using distilled water.

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Fig.10; showing battery band during maintenance

 Battery charger

The battery charger converts the primary AC supply to a regulated DC voltage which

charges the batteries and powers the protection and metering equipment in the station.

When the battery charger is taken off, the batteries supply power without switching or

intervention by operators. This is known as AC supply float mode.

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 Fig. 11; Battery charger

3.3.4 SHUNT REACTOR

Shunt Reactors are inductive loads that are used to absorb reactive power to reduce the

overvoltage generated by line capacitance or suppress the power reduced by loss. An

inductive load consumes reactive versus a capacitive load generate a reactive power. A

transformer as a shunt reactor, a heavy loaded power line, and an under magnetized

synchronous machine are examples of inductive loads. Shunt reactors are mainly used in

transmission networks to consume excess reactive power generated by the overhead

lines under low load conditions and thereby, stabilize the system voltage. Shunt reactors

are normally connected to substation bus bar, but also quite often directly to the

overhead lines. Alternatively, they may also be connected to tertiary winding of power

transformers. The shunt reactors may have grounded or reactor neutral. This transformer

is mainly provided in the station for protecting the power transformer.

3.3.5 SYSTEM LINES DEPARTMENT; This is third department where SIWES

was observed. It deals with the maintenance of the grid patrol of 330/132Kv

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 towers, replacement of conductors, clamps, broken disk insulator and

routine patrol of the grid system.

3.3.6 TOWERS

The main supporting unit of overhead transmission line is transmission tower.

Transmission towers have to carry the heavy transmission conductor at a sufficient safe

height from ground. Main parts of a transmission tower. A power transmission tower

consists of the following parts,

 Peak of transmission tower

 Cross Arm of transmission tower

 Boom of transmission tower

 Cage of transmission tower

 Transmission Tower Body

 Leg of transmission tower

 Stub/Anchor Bolt and Base plate assembly of transmission tower

The main parts of the tower are as shown below;

 Peak of transmission tower: The portion above the top cross arm is called peak of

transmission tower. Generally, earth shield wire connected to the tip of this peak.

 Cross Arm of transmission tower: Cross arms of transmission tower hold the

transmission conductor. The dimension of cross arm depends on the level of

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 transmission voltage, configuration and minimum forming angle for stress

distribution.

 Cage of transmission tower: The portion between tower body and peak is known as

cage of transmission tower. This portion of the tower holds the cross arms.

 Transmission tower body: The portion from bottom cross arms up to the ground

level is called transmission tower body. This portion of the tower plays a vital role

for maintaining required ground clearance of the bottom conductor of the

transmission line.

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Fig 12: Tower Dimension.

41
3.3.7 TYPES OF TRANSMISSION TOWER

There are different types of transmission towers. The transmission line goes as per available

corridors. Due to unavailability of shortest distance straight corridor transmission line has to

deviate from its straightway when obstruction comes. In total length of along transmission

line there may be several deviation points.

According to the angle of deviation there are four types of transmission tower;

 A–Type tower–angle of deviation 00 to 20.

 B–Type tower–angle of deviation 20 to 150.

 C–Type tower–angle of deviation 150 to 300.
 D–Type tower–angle of deviation 300 to 600.

With regard to the force applied by the conductor on the cross arms, the transmission towers

can be categorized in another way.

 Tangent Suspension tower and it is generally A-type tower. A suspension tower

is where the conductors are simply suspended from the tower, the mechanical

tension being equal or same on both each sides. It is a tower that carries a down

ward force and lateral force. These also have for each conductor an insulator

string hanging down from the tower or two strings making a ‘V’ shape. These

are towers used where a transmission line continuous in a straight line or turns

through a small angle.

 Angle tower or tension tower or sometime it is called section tower. All B, C and

D types of transmission towers come under this category. A tension tower is

located between every three or four suspension towers to pull the conductors

which are re-tied in tension tower insulators. This type of tower that carries a

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 longitudinal force and is mostly used in road crossing and deviation in

transmission line.

 TOWER SPANS; The Tower Spans is the distance between two towers, for 330KV

line the span is 500m while for132KV line is 300m.

From Jos work center to Makeri Sub-station 132KV Double circuit line;

we have 95 towers (T1-T95) which make 94 Spans,

Distance = 94*300m/1000 =28.2km~28km

Distance from jos work center to Makeri Sub-station, Terminal Towers ;28km.

3.3.8 SKY WIRE

The sky wire is connected to earth after certain number of towers and serves as a lightening

conductor or lightening arrestor which is connected at the apex or tip of the towers. It

collects or receives all the discharged current by lightening from the tip of the towers and

drains it down to the ground by earthling. Every lightening that strikes adds a minimum of

100KA to the current in the lines. (Narayana and Swamy, 2007)

3.3.9 SYSTEM OPERATION DEPARTMENT;

This is the last department where SIWES was observed. It is the department responsible for

the operations and monitoring of installed switch gears in the switchyard. This department

also issue work and test permit and station guarantee to the other technical department in the

organization.

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3.4.0 THE CONTROL PANEL/BOARDS

This is a board/panel which provides operators with information about power flow,

conditions, efficiency of equipment and working principles of the circuits i.e. current

reading the three (3) phases. Voltage reading of the three (3) phases, transformer winding

temperature, oil temperature, switching equipment alarms and trips, frequency of the main

supply to the equipment e.g. transformers, 33kv feeders Rukuba, Dogon Dutse, NNPC,

Anglo-Jos, Toro, JUTH, Zaria road feeders. The operators also give permits and the isolate

an equipment to be worked on when there is a fault or just preventive maintenance in the

switchyard or anywhere in the station.

Fig. 13: 33Kv relay Panel Board showing different relay protecting the feeders

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 CHAPTER FOUR

CHALLENGES, RECOMMENDATION AND CONCLUSION

4.1.0 CHALLENGES ENCOUNTERED

 Lack of transportation fare.

 Unavailability of safety wears i.e. helmets, overall suits, boots, gloves etc.

 Lack of internet to make researches and lack of access to the various

department libraries.

4.1.1 SOLUTIONS TO THE CHALLENGES ENCOUNTERED

 The welfare of the students should be looked out for, and ITF should try and

pay students before going for the training so that it can ease the stress of

transport fare.

 Safety wears should be made available for every student when the need arises.

 The libraries and internet connections should be made available for research.

4.1.2 ACHIEVEMENTS OF INDUSTRIAL TRAINING AT TCN

 Installation and Commissioning of 60MVA transformer.

 Installation and commissioning of 33KV feeders.

 Installation and commissioning of new current transformers in the 132KV

section.

 Routine maintenance of different power equipment; (circuit breakers, power

transformers, isolators, etc.)

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4.1.3 RECOMMENDATION

 The welfare of the students should be looked out for and ITF should try and pay

students before going for the training so that it can ease the stress of transport

fare.

 Organizations should be advised to provide reference material like internet

facilities or provision of library books.

 Regular check-up of various tests equipment to ensure efficiency by the

organization.

 Provision of Safety wears should be made available for every student when the

need arises by the organization.

4.1.4 CONCLUSION

The program is highly recommended, because it exposes students in regards to practical

knowledge and skills learnt. It also provides student with industrial work experience which

is essential for career development.

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 4.1.5 REFERENCES

1. Alstom Micom 2013. Transformer Differential Protection Application Guide.

Book boom publishers. ISNB541-0214-75-4

1. Blackburn, J.L., Protective Relaying: Principles and Applications. Second

Edition2010 Grand Rapids, Michigan: Baker Academic, 2010. ISNB878-4562 -24-9

2. Narayana, G.A,(2007) Transformers in practice: Knowledge, operation and

maintenance. A first edition printed and published by the Author: Press by terrain

and Reformed Publishing Company, 1990.ISNB254-3248-14-3

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