33 kv/ 11 kv, 7.

5 MVA, Dyn 11
Transformer

Installation and Commissioning.

An Internship Report Submitted in Partial Fulfillment of the

Requirements for the Degree of Bachelor of Science in Electrical and
Electronics Engineering

Submitted By
Name: Md. Azizul Haque
ID No.: 142-0134-011
Advising Semester: Spring 2017

DEPARTMENT OF ELECTRICAL AND ELECTRONICS

ENGINEERING
ATISH DIPANKAR UNIVERSITY OF SCIENCE AND
TECHNOLOGY
March, 2018
 Dedication
I declare that the internship entitled “33 kv/ 11 kv, 7.5 MVA, Dyn 11 Transformer

Installation and Commissioning.” At City Auto Rice and Dal Mills Ltd. Embodies the

results of my own research work, prepared under the supervision of Mr. Ariful Islam,

Asst. Professor Faculty in EEE of Atish Dipankar University of Science &

Technology (ADUST).

We further affirm that the work reported in this internship original and is no part or

whole of the report has been submitted by any other students for the completion of

EEE degree or other Degree.

i
Letter of Permission

ii
Letter of Approval

iii
Letter of Recommendation

iv
iv
 Certificate of Approval
B.Sc. Intern entitled:
“33 kv/ 11 kv, 7.5 MVA, Dyn 11 Transformer
Installation and Commissioning.”

Done under my supervision, meets acceptable presentation that is standard and can be

submitted for evaluation to the department of Electrical and Electronics Engineering

in partial fulfillment of the requirement for the degree of Bachelor of Science (B.Sc.)

in Electrical and Electronics Engineering.

Date…………………….. …………………………………
(Ariful Islam)
Assistant Professor
Dept. of EEE, FST
Atish Dipankar University of Science and
Technology, Banani, Dhaka-1213

v
 Declaration
I hereby declare that this submission is my own work and to the best of my

knowledge it contains no materials, which are exactly, same, which were previously,

published anywhere in print or soft.

Date: …………….
…………………………….
(Md. Azizul Haque)
B.Sc. Student.
ID: 142-0134-011
Dept. of EEE, FST

vi
 ACKNOWLEDGEMENTS
All praises go to Allah, the almighty, for the successful completion of this

internship and fulfillment of author’s dream into reality. However, thanks and

gratitude are also due to the following persons for their continuous support in

completing this internship and in preparing this report.

I render my heartiest gratitude and sincere respect to Mr. Ariful Islam, Assistant

Professor Faculty in EEE for assigning us such a perfect internship report to work and

practice in real for our inspiration, guidance, valuable suggestion, generous support

and continuous encouragement at all stages of this endeavor.

I also convey grateful thanks to Mr. Moni Gopal Boshu. Sr.Manager (Electrical) of

Engineering Department.

I would like to thank to office sub stuff & book shatter for providing us relevant

books, journals & articles at library.

1
 Executive Summary

This internship report is originally written based on the power transformer installation

works. Field level experience on erection and commissioning has been integrated

here. This report can also be used as a guide book to power transformer installation.

In my project site final assembly, operation, inspection and maintenance works has

been done based on the information presented in this report. Connections not written

in this report or operation which deviates from the descriptions should not be done

without consulting with the manufacturer. However, this report can help him if

someone wants to work on transformer installation. Here in the internship report book

covers the following topics- Factory Preparation for dispatch, Cautions for

Transformer Installation, Inspections, Check & Test before Energizing, Trouble

Shooting, Paintings, Re-drying of Transformer at job Site, Preparation of tools,

Instruments and Materials, Supervision of works and safety measures, Inspection of

packages and unpacking, Catalogue for various accessories and Drawing requirements

for erection works. Above all, my internship report book plays a role in transformer

installation works.

2
 TABLE OF CONTENTS
Page
Dedication i.
Letter of Permission ii.
Letter of Approval iii.
Letter of Recommendation iv.
Certificate of Approval v.
Declaration vi.
ACKNOWLEDGEMENTS 01

Executive Summary 02
TABLE OF CONTENTS 03

CHAPTER ONE (Overview of the Organization)

1.1 History 09
1.2 Business Size 10
1.3 Production 11
1.4 Competitors 15
1.5 Summary of the all departments 15

CHAPTER TWO (Plan of Internship Program)

2.1 Electrical Maintenance Department 17
2.2 Duration of Internship 17
2.3 Helping Departments 18

CHAPTER THREE (Training Program)

3.1 Assist Erection Team 19
3.2 Maintain Resister Book 19
3.3 Supervised Transportation and Lifting Work 20

3.4 Assist Transformer Inspection Works 20

3.5 Assist Transformer Testing Works 20

3
 3.6 Supervised DC System & Grounding works 21

3.7 Setting Protection Relay 21

3.8 Check all Installation Follow by Drawing 21

CHAPTER FOUR (Learning Experiences)

A. Knowledge acquired
4.1 Transformer Erection Order 22
4.2 Work in the tank 23
4.3 Lifting of transformer 23
4.4 Transformer Installation 24
4.5 Fitting of Radiators 25
4.6 Operation of radiator valve 26
4.7 Fitting of Conservator 27
4.8 Fitting of Cooling Fan 27
4.9 Oil Piping 28
4.10 Gas Actuated Relay 29
4.11 Fitting of Bushing 29
4.12 De-Aerated Oil Filling Up to The Level Above The Coil 30
4.13 Fitting of De-hydrating Breather 30
4.14 Fitting of Temperature Indicator 31
4.15 Draining The Insulating Oil While Filling With N2 Gas 31
4.16 Cautions for Vacuuming and oil filling 32
4.17 Vacuum Treatment 32
4.18 Oil Filling with Operation of Valve 32
B. Skills learned
4.19 Inspection 35
4.20 Precautions 36
4.21 Oil level 36
4.22 Leakage of Oil 36
4.23 Gas Operated Relay 37
4.24 Silica Gel Breather 37
4.25 Temperature Indicator 37
4.26 Transformer 37

4
4.27 Oil Level 37
4.28 Leakage of Oil 38
4.29 Oil Valves 38
4.30 Gasket Joints 38
4.31 Gas Operated Relay 39
4.32 Dehydrating Breather 40
4.33 Temperature Indicators 41
4.34 Pressure Relief Vent 42
4.35 Pressure Relief Device 42
4.36 Terminal Connections 43
4.37 Auxiliary Wiring 43
4.38 On Load Tap Changer 44
4.39 Radiators 44
4.40 Earth Terminal 44
4.41 Fans 44
4.42 Cooler Control Cubicle 45
4.43 Oil Inspection 46
4.44 Oil Warning 46
4.45 Oil Sampling 46
4.46 Inspection of Sample (BS 5730-1979) 47
4.47 Electrical Strength (BS 5703-1979) 47
4.48 Crackle Test For Moisture (BS 5730-1979) 48
4.49 Acidity (BS 5730-1979) 48
4.50 Sludge (BS 5730-1979) 49
4.51 Flash-Point (Closed) (BS 5730-1979) 49
4.52 Frequency of Testing 50
4.53 Recording The Results 50
4.54 Recommended Action 50
4.55 General 52
4.56 Gasket Joints 52
4.57 Oil Valves 52
4.58 Terminal Connections 52
4.59 Silica Gel Breather 53

5
 4.60 Gas Actuated Relay 53
4.61 Temperature Indicators 53
4.62 Thermometer Pocket 53
4.63 Oil Levels 53
4.64 Pressure Relief Vent 54
4.65 Pressure Relief Device 54
4.66 Earthing 54
4.67 Insulation Tests 54
4.68 Voltage Ratio and Continuity Test 55
4.69 Magnetizing Current Tests 55
4.70 Winding Resistance Measurements 55
4.71 Dielectric Fluid Sampling 55
4.72 Temperature Indicators 55
4.73 Gas Operated Relay 56
4.74 Fans 56
4.75 Cooler Control 57
4.76 Alarm and Trip Circuits 57
C. Observed attitudes and gained values
4.77 Attitude and gained values 58
D. The most challenging task performed:
4.78 Factory Preparation for Dispatch 58
4.79 Inspection on Site 59
4.80 Inspection for Exteriors 60
4.81 Transportation from Factory to Site. 61
4.82 Handling on Site 62
4.83 Location and Site Preparation 62
4.84 Inspection and Test Prior to Operation (Commissioning) 64
4.85 Caution When Energizing Transformer. 65

CHAPTER FIVE (Problem Identification and Solution)

5.1 Routine Maintenance and Inspection (Freq. Weekly) 66
5.2 Periodical Maintenance and Inspection 67
5.3 Oil Leakage Problem 68

6
 5.4 Paint Flanking or Rust Occurrence 69
5.5 Oil Level Discrepancy 69
5.6 Abnormal Noise Level 70
5.7 Foul Odors 70
5.8 Thermometer Reading Discrepancy 71
5.9 Contamination on the Bushing Porcelain 71
5.10 Draining of Insulation Oil 71
5.11 Measurement of Insulation Resistance 71
5.12 Deterioration of Insulating Oil 74
5.13 Standard for the Estimation of Oil Deterioration 75

CHAPTER SIX (DC System, Protection Relay & Grounding)

6.1 DC System 77
6.2 Battery Location 77
6.3 Ventilation 78
6.4 Floor Anchoring 78
6.5 Module Stacking 78
6.6 Precautions to be taken 79
6.7 Release Device and Relay 80
6.8 Instantaneous Over current Relay 80
6.9 Definite Time Relay 80
6.10 Induction Relay 81
6.11 Magnetic overload relay 81
6.12 Thermal overload relay 81
6.13 Reverse power relays 81
6.14 Over current relays with A.C Tripping 82
6.15 Combined overload and earth leakage protection 82
6.16 Protection of Radial Feeders 82
6.17 Protection of Parallel Feeders 82
6.18 Protection of ring mains 83
6.19 Protection of Transformers 83
6.20 Merz-price Protection of transformers Alternators. 83
6.21 Core Balance Earth Fault Protection 83

7
 6.22 Grounding 84
2.23 Neutral Point 85
6.24 Safety Ground 85
6.25 Equipment Ground 86

CHAPTER SEVEN (Drawing Requirements for Erection Works)

7.1 DC System (Battery Layout) 87
7.2 Single Line Diagram of 33/11KV, 2x7.5MVA Substation 88
7.3 Section on A-A 89
7.4 Section on B-B 90
7.5 Section on C-C & D-D 91
7.6 Layout Plan of Outdoor Equipment 92
7.7 Electrical Layout Plan-A 93
7.8 Electrical Layout Plan-B 94
7.9 33KV Control & Relay Panel For Transformer Feeder 95
7.10 11KV Incoming & Outgoing Panel. 96
7.11 Switchgear Foundation Drawing 97

CHAPTER EIGHT

Conclusion 98

REFERENCES 99

APPENDIX 100

8
 Chapter One
Overview of the Organization
1.1 History
The date 6th February, 1972 marks the journey of a valiant effort in Gandaria, Dhaka

- one which marked the beginning of the company known as "CITY OIL MILLS" -

the founder Chairman; Mr. Fazlur Rahman started the group from scraps virtually.

The initial period was marked with a lot of hardships due to the post war era when the

country faced economic fallout. Initially the mission of the company was to produce

mustard oil for the local market consumption. The overwhelming demand for the

product propagated and the company soon found its way into the business arena.

For the next 18 years, the company operated within the vicinity of the Dhaka city and

met the demands of the local market. The revenue generated from this soon gave

away for the entrepreneur to evolve the company, which was by now one of the

largest mustard oil producing plants in the country. A vision - to transform the

company to a 21st century conglomerate of the country started. "City Vegetable Oil

Mills" was established at Rupshi, on the outskirts of Dhaka city. This effort evidenced

an accelerated growth of City Group and the company was soon found to open two

more sister concerns by the year 1994 - "Hasan Vegetable Oil Mills Limited" and

"City Fibers Limited".

Within this period the founder also devised new production units and soon the brand

“TEER" was born, the name itself captivating the hearts and minds of the people.

Appearing in this banner was the flagship product, "TEER SOYABEAN OIL", which

soon found a good market share.

The overwhelming revenue generated and the unprecedented popularity of the

products of City Group soon found its way into the hearts of the people. City Group

9
was by now one of the emerging industries of the country with an ever-expanding

business, which led to 21 sister concerns by the end of the year 2006.

Presently, the company focuses on meeting and responding to the ever-changing

needs of the consumers both home and abroad. Till now City Group is one of the

largest company in the country, and business reaching foreign countries making it one

of the best conglomerates of the country. A year of meticulous work has paid off and

by now CITY GROUP has started its alteration towards an International Standard

Company along with its 23 sister concerns.

1.2 Business Size

City Group is a prominent name in the industrial arena of Bangladesh. The Group has

over 45 years of experience in the edible oil industry and expanded its wings of

production gradually. At present there are 23 sister concerns, each specializing in

different areas of production. Incorporating Flour, Dal, Feed, Salt, Sugar and Pure

Drinking Water in the product line and integrating vertically; the Group has been in

quest of transforming to a 21st century conglomerate.

City Group is dedicated to optimize the quality of the produced consumer items.

Strength lies in the Group's ability to use state-of-the-art technology from Europe and

other countries and imported high grade raw materials which are the finest in the

world. The production facilities are well equipped with top notch machinery from

Singapore, Japan, Switzerland, Germany, USA, Taiwan, Belgium, Thailand, and best

quality raw materials are collected both from overseas and local suppliers. A

vertically integrated concern having more than 15,000 skilled manpower and with a

true depth of market penetration City Group has the physical advantage of all its

mills, factories and establishments being spread over 330 acres of land in the old part

10
of Dhaka i.e. Gandaria; expanding industrial belt at Konapara, Demra, and Rupshi,

Narayangonj and in Chittagong, the commercial capital of Bangladesh.

The secret of success of City Group lies in fulfillment of all its business

commitments, uncompromising attitude in quality maintenance and intimate

relationship with its customers, employees and all other social groups. All the

members of City Group are actively involved in maintaining the ideals established by

Company founder. Almost four decades of this epic industrial journey can only be

termed as a quest for excellence and we welcome you to be a part of it.

1.3 Production

01 City Oil Mills

Started Operation In: 1972, Production Capacity: 200 M. Tons

02. City Re-rolling Mills.

Started Operation In: 1985, Production Capacity (24 hrs.): 100 M. Tons

Functionality: Supports all the civil construction works of the Group with quality MS

Rods, angles, flat bar etc. throughout the year.

03. City Vegetable Oil Mills Ltd.

Started Operation In: 1990, Production Capacity (24 hrs.): 100 M. Tons

Functionality: Refines quality Soya Bean Oil from imported CDSO and Super refined

Palm Olean from imported CPO to meet increasing demand of the local market.

04. City Fibers Ltd.

Started Operation In: 1992, Production Capacity: 16,000 Pcs

Functionality: Supplies all sorts of PP woven bags and Plastic linings to meet in-

house demands

11
05. Hasan Plastic Industries Ltd.

Started Operation In: 1998, Production Capacity (24 hrs.): 40,000 drums

Functionality: Produces PET container

06. Hasan Flour Mills Ltd.

Started Operation In: 1998, Milling Capacity (24 hrs): 200 M. Tons

Functionality: Produces the finest and popular brand of Flour, Atta and Semolina,

“Teer”.

07. Hasan Printing & Packaging Ltd.

Started Operation In: 1999, Production Capacity (24 hrs.): 20,000 Cartons

Functionality: Meets the Group’s own requirement and also supports printing of

labels, stickers and other promotional materials.

08. Hasan Containers Ltd.

Started Operation In: 1999, Production Capacity (24 hrs): 16,000 Pcs

Functionality: Supports the Group with quality plain & printed tin containers made

from plain tin sheets for marketing its own products i.e. refined oils, vanaspati.

09. City Navigations Ltd.

Started Operation In: 2000

Functionality: A fleet of 20 maritime vessels are engaged in carrying raw materials

from Chittagong port and other places.

10. City PET Industries Ltd.

Started Operation In: 2001, Production Capacity: 1000 M. Tons

Functionality: City PET Industries Ltd., the FDA approved factory lifts water from a

depth of 600 feet and purifies it using German Ozone technology and Reverse

Osmosis system to process around 1,00,000 liters of truly hygienic natural mineral

water per day.

12
11. Shampa Oil Mills Ltd.

Started Operation In: 2001, Production Capacity: 600 M. Tons

Functionality: Shampa Oil Mills Limited, was set up as an expansion of the most

popular “Teer Mustard Oil” in the country.

12. City Dal Mills Ltd.

Started Operation In: 2001, Production Capacity (24 hrs.): 250 M. Tons

Functionality: Ensures a purified and constant supply of beans, a key food grain, in

the local market.

13. Farzana Oil Refineries Ltd.

Started Operation In: 2002, Production Capacity (24 hrs.): 1,000 M. Tons

Functionality: Farzana Oil Refineries Limited, has got Vanaspati and Canola Oil in

their product range. The raw materials are directly imported from world’s finest

sources and refined with latest technology to ensure that the product reaches the

consumers in perfect conditions.

14. VOTT Oil Refineries Ltd.

Acquired In: 2004, Situated At: North Patenga on the bank of the river Karnaphuly in

Chittagong

Functionality: The Terminal has more than 50 tanks, including bonded ones, with a

total storage capacity of about 1.5 Lac Tons of Crude Oil, Bitumen, and Lubricants

etc. Within the compound, there is the VOTT Oil Refineries Ltd. having a refining

capacity of about 1100 M. Tons of Crude Oil per day.

15. City Feed Products Ltd.

Started Operation In: 2004, Production Capacity (24 hrs): 500 M. Tons

Functionality: Ensures a constant quality of full range poultry, fish and cattle feeds.

13
16. Deepa Food Products Ltd.

Started Operation In: 2005, Production Capacity: 1,000 M. Tons

Functionality: Deepa Food Products Ltd., has got Vanaspati and Canola Oil in their

product range. The raw materials are directly imported from world’s finest sources

and refined with latest technology to ensure quality products.

17. City Seed Crushing Industries Ltd.

Started Operation In: 2005, Production Capacity (24 hrs.): 1000 M. Tons

Functionality: Produces Soya meals and Rapeseed cakes every day. The raw materials

of Latin America and Europe are processed with technologically superior DESMET

BALLESTRA machines to ensure a rich protein source for poultry and fish.

18. City Salt Industries Ltd.

Started Operation In: 2005, Production Capacity (24 hrs): 250 M. Tons

Functionality: Every micro crystal of “Teer Iodized Salt”, produced in City Salt

Industries Ltd. is a proof of superior quality salt processed in our country.

19. City Sugar Industries Ltd.

Started Operation In: 2006, Production Capacity (24 hrs): 1650 M. Tons

Functionality: Produces Teer Refined Sugar, the highly consumed refined sugar in the

market. This large factory refines imported crude sugar in fully automated SU-Tech

machines of Thailand.

20. C.S.I Power & Energy Ltd.

Started Operation In: 2006

Functionality: Capable of supplying 11 M.W of electricity per day for running

different industrial units of the group.

21. Rahman Synthetics Ltd.

Started Operation In: 2007, Production Capacity (24 hrs): 1, 10,000 Pcs

14
Functionality: Supplies all sorts of PP woven bags and Plastic linings to meet in-

house demands.

22. Hamida Plastic Industries Ltd.

Started Operation In: 2009

23. Shampa Flour Mills Ltd.

Started Operation In: 2009, Milling Capacity (24 hrs): 550 M. Tons

Functionality: With world renowned Buhler machines of Switzerland, this state-of–

the art technology is a valuable addition in City Group’s arsenal in catering to the ever

increasing quality food products of choice.

Pilot Project

*City Auto Rice and Dal Mills Ltd.

Capacity (24hrs): Rice-- 1440 M. Tons, Dal- 200 M. Tons

Functionality: With world renowned Buhler machines of Switzerland, this state-of–

the art technology is a valuable addition in City Group’s arsenal in catering to the ever

increasing quality Rice and Dal products of choice.

1.4 Competitors
City Group is one of the leading conglomerates industries in Bangladesh. The main

competitors of this company are Meghna Group of Industries, Akij Group,

Bashundhara Group, Jamuna Group, S. Alam Group of Industries, T K Group of

Industries and many others.

1.5 Summary of the all departments

Marketing, Sales, Accounts, Administration, Production, Procurement, Import, Export

and Technical & Store departments are worked in company.

15
Marketing: More than 2,000 employees are work in this department. They are

making strong and challenging market in country and abroad. They are always study

market nature and analysis to find out problems and solution.

Sales: Sales is another strong team in City Group. Countrywide they make a network

of sales. They continuously try to grow up the sales volume and relation buildup with

customer.

Finance Department- This department is divided into two parts: 1) Account and 2)

Finance. Both parts are work for making bills, bill collection, bank reconciliation,

Annual budget, employee salary etc.

Procurement- All perches activities control by procurement department. The source

of local perches is Dhaka and Chittagong.

Import & Export- Raw materials for production line and foreign parts import

procedure, custom clearance, export, shipping and related all jobs done by them.

Production- This department always engaged for more productivity. City group have

23 plus productive industry. They are control and run production line. Operation and

QC is also part of them.

Technical Department (Construction, Operation and Maintenance) - This department

is actually run by Engineers. They give their services at Line and system maintenance.

Civil construction, machine installation and maintenance work do by this department.

They also do all type of maintenances about the distribution and connection.

16
 Chapter Two
Plan of Internship Program

2.1 Electrical Maintenance Department

I’ve completed my internship under the maintenance department. Here the

maintenance department is divided into two parts: 1) Mechanical and 2) Electrical.

Both parts are work for installation, maintenance, repairing and modification works.

This department have more than 55 manpower including engineers, technicians and

helpers. Mechanical have 35 person and electrical have others 20 persons in their

team. Both groups have their own workshop separate for regular works. Electrical

department responsible for two type jobs: 1) Power Line 2) Automation. A technical

GM commending the department and both group have section manager to guide them.

2.2 Duration of Internship

I successfully completed my internship in City Auto Rice and Dal Mills Ltd. From

06th March, 2017 to 05th June, 2017. I have completed 288 hours internship on

33kv/11kv, 7.5 MVA, Dyn 11 Transformer Installation and Commissioning of

CARDML. In the below give a table regarding my internship course-

DAY
DATE DURATION DAY ACTIVITY
NO

06 March 2017 9.00 am to

01 Company overview, mission and vision
Monday 5.00 pm

13 March 2017 9.00 am to

02 Factory Preparation for Dispatch
Monday 5.00 pm

20 March 2017 9.00 am to Cautions and Safety for Transformer

03
Monday 5.00 pm Erection Works.

27 March 2017 9.00 am to

04 General Construction and Descriptions
Monday 5.00 pm

17
 03 April 2017 9.00 am to Transformer Erection & Fittings of
05
Monday 5.00 pm Accessories

10 April 2017 9.00 am to

06 Transformer Inspection Works
Monday 5.00 pm

17 April 2017 9.00 am to

07 Transformer Testing Works
Monday 5.00 pm

24 April 2017 9.00 am to

08 Maintenance & Trouble Shooting
Monday 5.00 pm

08 May 2017 9.00 am to

09 Operation of Transformer
Monday 5.00 pm

15 May 2017 9.00 am to

10 Switch Gear and its Application
Monday 5.00 pm

22 May 2017 9.00 am to

11 Battery and Protection Relay
Monday 5.00 pm

29 May 2017 9.00 am to Drawing Requirements for Erection

12
Monday 5.00 pm Works

05 June 2017 9.00 am to

13 Closing Ceremony
Monday 5.00 pm
[Note: Total course duration is 288 hours]

2.3 Helping Departments

The production department always helped us. When we went to field for maintenance

any machine or troubleshooting, they used to cooperate with us in various ways.

These production departments were always engaged in greater production. City group

have 23 plus productive industry. They control and run production line. Operation and

QC is also part of them. So the profitability of the company is largely dependent on

them. I learned about the nature of the machine, operation of the machine and

production process from them.

18
 Chapter Three
Training Program

My training program was designed by the authority of City Auto Rice and Dal Mills

Ltd. They trained me according to their schedule. They have associated me with

various tasks at different times and have given me responsibilities. Here I am trying to

describe in detail which I did during my internship time.

Duties and responsibility

3.1 Assist the Erection Team

I was the first to work with a transformer erection team. While working with them, I

have been watching all the things and acted according to their direction. From them I

was able to learn about the structure and function of the transformer. Physically I

checked all the parts like as Core, Winding, Tank, Fittings & Accessories, Cooling

System, General, Radiators, Conservator, Cooling Fan, Control & Protective Devices,

Oil Level Gauge, Dehydrating Breather, Marshaling Cubicle, Temperature Indicator,

Winding, WTI, OTI, GAR, Pressure Relief Device, and Magnetic Oil Gauge with

them. I also checked all the parts status. Whenever I got damaged and broken in a

piece of equipment, I have informed my supervisor to take necessary measures.

3.2 Maintain Resister Book

According to the packing list, I was given the responsibility of maintaining the

register book to receive the product properly. The representative of the product

suppliers were handing over the product to me. Then I checked the quality of all the

products. After receiving the products, I told my supervisor to provide the necessary

clearance certificate.

19
3.3 Supervised Transportation and Lifting Work

I used to supervise transformer transportation and lifting works. More than 25 skilled

workers worked with me. All the works like as Transportation from Factory to Site,

Handling on Site, Location and Site Preparation, Safety, Inspection and Test Prior to

Operation (Commissioning) done by me.

3.4 Assist Transformer Inspection Works

After fitting the transformer accessories, I used to cooperate with my team in the

inspection work. There were follow two types of inspection works, one is monthly

inspection and another is annual inspections. Monthly inspection done in energized

condition consist of Oil level, Leakage of Oil, Gas Operated Relay, Silica Gel

Breather, Temperature Indicator checking etc. The Annual Inspection done in de-

energized condition consist of Oil Level, Leakage of Oil, Oil Valves, Gasket Joints,

Gas Operated Relay, Dehydrating Breather, Temperature Indicators, Pressure Relief

Vent, Pressure Relief Device, Terminal Connections, Auxiliary Wiring, On Load Tap

Changer, Radiators, Earth Terminal, Fans, Cooler Control Cubicle, Oil Inspection ,

Oil, Oil Warning, Oil Sampling, Inspection of Sample (BS 5730-1979), Electrical

Strength (BS 5703-1979), Crackle Test For Moisture (BS 5730-1979), Acidity (BS

5730-1979), Sludge (BS 5730-1979), Flash-Point (Closed) (BS 5730-1979.

3.5 Assist Transformer Testing Works

The first thing we noticed before energizing the power of transformer testing was that

Gasket Joints, Oil Valves, Terminal Connections, Silica Gel Breather, Gas Actuated

Relay, Temperature Indicators, Thermometer Pocket, Oil Levels, Pressure Relief

Vent,, Pressure Relief Device, Earthing. We are also doing Commissioning Test,

20
Insulation Tests, Voltage Ratio and Continuity Test, Magnetizing Current Tests,

Winding Resistance Measurements, Dielectric Fluid Sampling, Temperature

Indicators, Gas Operated Relay, Fans, Cooler Control and Alarm and Trip Circuits.

3.6 Supervised DC System, Protection Relay & Grounding works

I performed as a supervisor to install DC System including Battery Installation &

Commissioning, Protection Relay, Grounding, Neutral Point, Safety Ground and

Equipment Ground.

3.7 Setting Protection Relay

I cooperated with the expert team on the protection relay setting and Release Device

and Relay, Instantaneous Over current Relay, Definite Time Relay, Induction Relay,

Magnetic overload relay, Thermal overload relay, Reverse power relays, Over current

relays with A.C Tripping, Combined overload and earth leakage protection,

Protection of Radial Feeders, Protection of Parallel Feeders, Protection of ring mains,

Protection of Transformers, Merz-price Protection of transformers, Alternators and

Core Balance Earth Fault Protection installation.

3.8 Check all Installation Follow by Drawing

I checked all the works according to the approved drawing given to me, as instructed

by my supervisor during the transformer erection. If I had ever seen any kind of

missing and mistake, I would immediately inform my supervisor and he provided

necessary guidance and amendments.

21
 Chapter Four
Learning Experiences

A. Knowledge acquired
At my internship I have been able to acquire various types of knowledge about

transformers erection, accessories fitting and maintenance works. It was a challenge

for me at the same time grate opportunity to learn. Down here I will try to share my

acquired knowledge which I learned from my internship program.

4.1 Transformer Erection Order

Erection order of installation for transformer is as follows:

1. Setting of the transformer on base

2. Filling of the transformer tank with oil up to the level above coil

3. Fitting of mounting brackets for accessories

4. Fitting of radiators and coolers

5. Fitting of mountings for bushings

6. Fitting of conservator

7. Fitting of pressure relief device

8. Assembly of pipes of oil circuit

9. Fitting of bushings

10. Fitting of other accessories

11. Fitting cables and wiring of electric system

12. Additional oil filling up to the conservator

13. Oil leak test

14. Checking for installation and

15. Electric field test.

22
4.2 Work in the tank

When opening the transformer tank, precaution must be taken to prevent moisture

ingress. If wet air enters into the transformer, it may be cooled by the transformer wall

below its dew point and may be condensed. It may be lowered the dielectric strength

of the transformer. Do not enter the transformer tank until the nitrogen gas has been

entirely dissipated. When working the tank, take care especially not to drop tools or

foreign substances. Worker should not carry anything unnecessary in the tank. Care

should be taken to see that all nuts, bolts and lead connections are properly tightened

and all parts in right places. Also check the internal terminal connections. When the

work in the tank is completed, the inside of the tank should be inspected. Check that it

is clean and right and no foreign substances are left behind. For inside cleaning dry,

clean and lint free clothes should be used.

4.3 Lifting of transformer

Lifting lugs are located on the upper part of the transformer tank for lifting the

transformer. Lifting eyes are provided on the top core channel for removing the core
23
and coil assembly. If the transformer is lifted without the tank cover, the cable must

be held apart in vertical position by a spreader to prevent distortion of the tank.

4.4 Transformer Installation

4.4.1 Installation on the base- When the transformer is skidded, moved on rollers or

jacked up, take care that it does not damage the base or turn over the transformer. The

transformer is also equipped with jacking bosses. Jack should be placed under the

jacking bosses. The transformer should never be lifted or moved when jacking up

radiators or other accessories. When rollers are used, skids must be placed between

the base and the rollers to distribute the stress.

4.4.2 Fitting of accessories- Position and direction of the accessories and other parts

should be according to the transformer drawing exactly. Before fitting read the

instructions completely. Mishandling will result in damage to the accessories.

4.4.3 Fastening with bolts and nuts- Each bolts and should be screwed tight but in

order to avoid stripping of the bolts, pay attention that it is not over tightened. Use

suitable torque as follows by measuring torque wrench or torque meter.

Table.1 Suitable torque of the iron bolts

Size of bolt Suitable torque for fastening

M10 24.3 - 29.7 N.m

M12 42.4 – 51.8 N.m

M16 105.0 – 129.0 N.m

M20 206.0 – 251.0 N.m

M22 280.0 – 342.0 N.m

M24 354.0 – 433.0 N.m

24
Table.2 Suitable torque of the Stainless bolts

Size of bolt Suitable torque for fastening

M5 2.61 – 3.19 N.m

M6 4.43 – 5.42 N.m

M8 10.8 – 13.2 N.m

M10 21.3 – 26.0 N.m

M12 37.1 – 45.4 N.m

M16 92.3 – 113.0 N.m

Table.3 Suitable torque of the Stud bolts

Size of bolt Suitable torque for fastening

M12 49.0 – 51.8 N.m

M16 107 – 127.0 N.m

M20 206.0 – 245.0 N.m

4.5 Fitting of Radiators

Radiators are shipped separately. Blank covers are attached to the opening of radiators

and radiator valves to prevent moisture. Radiator valve is located on each radiator

connection so that any individual radiator may be removed in time of necessity

without lowering the oil of the transformer tank. Each radiator has the oil drain plug

and an air relief plug. So, it is easy to drain the oil individually. The radiator

withstands the same vacuum (full vacuum) and pressure condition as the main tank.

Radiators should be handled carefully to prevent bending or puncturing the panels.

Radiators are so designed and manufactured that any radiator can be placed at any

pair of flanges. Fit the radiator according to the following procedures-

25
 Hoist the radiator from the stored position and pay attention not to damage other

radiators with the hosting tools

 Remove the blank cover and gasket on the radiator

 Inspect the inside of the radiator visually

 Clean and fitting flange surface of the radiator

 Remove the blank cover and gasket on the radiator valve of the transformer

 Clean and paint the flange surface of the radiator valve

 Clean the gasket groove of the valve. Apply a small amount of adhesive to the

groove and fit the specified new gasket

 Hoist the radiator by crane car with the side of the flange on which the number is

stamped showing upward

 Pull the radiator by hand, incline it and drain the residual oil inside the radiator.

 Fit the radiator to the radiator valve

 Match the radiator valve and flange surface of the radiator and clamp them by

nuts.

 Clamp the pair of nuts located diagonally one after another in order to clamp

evenly (See fig) and

 Clamp them tightly until the radiator valve and radiator flange closely match with

each other.

4.6 Operation of radiator valve

Turn the handle to clock wise direction and set the handle at a vertical position to

open the valve. Turn the handle to anti-clock wise direction and set the handle in

parallel position to close the valve.

26
4.7 Fitting of Conservator

4.7.1 Conservator- The conservator is shipped separately and filled with nitrogen to

keep out moisture. When mounting the conservator on the transformer, it is necessary

to take care of the proper positioning. Hoist the conservator tank by car crane placing

it on the mounting bracket as per the outline drawing.

4.7.2 fitting the protective relay- Install the bushels relay to the conservator before

mounting on the transformer. The relay is connected to the conservator through a

connecting valve. Remove the blank cover of the flange surface and change gasket for

a new one. Install the relay to the conservator and clamp blots tightly and uniformly.

Be sure to set the relay in the direction indicated on the nameplate fitted to it.

4.7.3 Mounting the conservator on the transformer- When the above operation is

complete, lift the conservator using lifting lugs and mount firmly at the specified

location. Be careful not to tilt the unit when hoisting.

4.8 Fitting of Cooling Fan

4.8.1 Fittings- The cooling fans are to be attached to the radiator panel. Mounting

brackets for fan should be fastened on main body with proper tightening. Fans to be

mounted with net as per the G.A drawing. The fans have to be installed to the

supports by nuts fastened surely. The fan motors should be placed so that their cable

outlets would be at bottom of a fan motor.

4.8.2 Cabling- Each fan motor is directly connected to the marshalling box through

four-core armored cable. Proper cable glands (stainless steel) are to be used at entry or

exit point of any boxes. The route of the cable should be as per the specified

drawings. Cable tray or support for running the cable should be provided on the tank

body.

27
4.8.3 Checking- After the completion of wirings, supply the proper power to the fan

motors and make sure that the fans rotate in normal direction and without abnormal

sound.

4.9 Oil Piping

The oil piping should be in accordance with the diagram of PIPING ROUTE and

PIPING SYSTEM shown in the instruction manual and based on the number tag

attached to the each pipe.

a) Removal of blank covers from the separated oil pipes- Oil piping is provided

for connecting the oil circuit of various accessories and some oil piping is transported

separately. Prior to fitting the oil pipes, remove the blank cover from them. Then

remove old gaskets used for the blank covers. In the consequent step, be sure to wipe

off foreign matter with a dry waste. If the painted face is found to be spoiled, repaint

with rust-proof paint.

b) Checking the ventilation of oil pipes- When cleaning of oil pipes is finished,

pass either dry air or nitrogen gas through the oil pipe and make sure that there are no

foreign materials.

c) Removal of the blank cover from the oil pipes on the transformer side-

Remove the blank covers and clean the piping faces. Ingress of any foreign material is

strictly prohibited.

d) Assembling- Apply a small amount of adhesive to the gasket and fit the

gasket. Tighten the clamp bolts in diagonal order and evenly until the flange faces

match.

e) The connecting valves are also joined to oil pipes by means of above

procedures.

28
4.10 Gas Actuated Relay

The gas actuated relay should be erected as follows:

 Remove relay blanking plates

 Remove blanking plate from transformer top pipe

 Fit the top pipe between the relay.

 Make sure that all flanges are clean

 Fit a gasket between each flanged joint and bolt up loosely

 Remove blanking plate from underside of conservator

 Fit conservator isolating valve

 Fit pipe work to conservator flange and relay flange

 Tighten all flange bolts firmly and evenly and

 Ensure that each flange is square and bolts are straight.

4.11 Fitting of Bushing

Bushing should be installed finally to minimize the possibility of being damaged

while installing other parts. Care should be taken in unpacking the bushing package to

avoid damage of the porcelain. Before fitting the bushing, clean the porcelain and the

terminal thoroughly. Bushing should be mounted as shown in outline drawing.

Make connections to both ends of the bushing in such a manner that strain is avoided.

When heavy bus bars are connected to bushings, flexible connections should be used

to prevent damage that might possibly result from expansion and contraction due to

temperature changes. Be sure that all connections are tight enough to prevent local

heat of terminal.

When bushings are installed on the transformer, replace the gasket with a new one.

The flange should be fixed uniformly by nuts in such manner as shown in figure

29
below. Each pair of stud bolt 1-1́, 2-2́ and 3-3́ should be tightened with nuts at same

time in order to fix the flange uniformly.

While working, worker should not use the gloves and tools unless those are tied to the

worker with hempen strings to prevent them being dropped into the transformer tank.

4.12 De-Aerated Oil Filling Up to the Level above the Coil

To prevent direct contact of coil and insulator with atmosphere during assembling of

transformer, it is desirable to fill with the insulating oil first up to a level about 25cm

below the tank cover (Fig-1). It is necessary to carry out a dielectric strength test of

the insulating oil stored in the drums before oil filling.

Take sample form each drum and check whether the contents have the specified

dielectric strength. If not, filter the entire oil content. Oil filling should be carried out

only after its dielectric strength reaches the specified value. There are two methods for

oil filling. The first method is to fill through the drain valve while discharging

(gradually) the nitrogen gas stored in the tank (Fig-2). The nitrogen gas pressure in

the transformer tank should be kept at a valve between 0.005-0.02Mpa during oil

filling.

The second method is to fill after vacuuming the transformer (Fig-3). This is the

superior method.

4.13 Fitting of De-hydrating Breather

When fitting the silica gel breather, do not expose the silica gel charge to the

atmosphere for an undue length of time, otherwise the gel charge will start to absorb

moisture and thus impair its operating property. The breather should be erected as

follows:

30
 Remove oil cup by turning in anti-clockwise direction.

 Remove breather port blanking paper ring from underside of breather body, thus

exposing ports

 Remove blanking plug from top end of breather

 Screw breather body in clockwise direction, onto the transformer breather pipe.

 Fill the oil cup with transformer oil to BS148, to the level indicated

 Replace oil cup but do not overfill.

4.14 Fitting of Temperature Indicator

The instruments are fitted in the marshalling/control cubicle, located on the side. The

instrument bulbs are fitted in their respective pockets found on the tank. Ensure that

the instrument is mounted in a vertical position, as errors, particularly in the

horizontal plane will upset the zero of the switch setting scales. Care is needed when

running the capillary, sharp bends should be avoided particularly where it joins the

instrument and bulb.

The capillary should be supported by suitable clips at intervals of 300 to 450 mm and

a suitable length provided so that the bulb may be freely installed or removed.

4.15 Draining the Insulating Oil While Filling With Nitrogen Gas

After all accessories except dehydration breather (this should be installed after the

completing of oil filling) have been installed, drain off the quantity of insulating oil

from the transformer in order to eliminate foreign matter, dust etc. form the oil as well

as any other parts which may absorb. Supply nitrogen gas into the transformer to

displace insulating oil. Do not allow the transformer internal pressure to become

negative. Seating pressure of nitrogen gas should be from 0.005 to 0.02MPa. After

31
draining the total quantity of insulating oil from the transformer, arrange the machine

parts as illustrated in the last page of this clause (OPETARING OF VALVES) and

carry out oil filling.

4.16 Cautions for Vacuuming and oil filling

 When opening drums of oil, care should be exercised to prevent ingress. It is

preferred to fill oil at low humidity. Drums should be opened only at the time

when the oil is needed. Before filling the oil, take sample from the drum and test

the dielectric strength.

 The oil filling apparatus should be clean and free from moisture. Care should be

taken to prevent moisture from being introduced into the oil through oil line.

 Do not energize the transformer when vacuuming and filling the oil.

Usually the partition wall of tap selector switch compartment cannot withstand at full

vacuum. Before exhausting air from the transformer, connect the equalizing pipe

located between the switch compartment and the transformer tank in order to maintain

the pressure of the compartment as same as that of the transformer interior.

4.17 Vacuum Treatment

Exhaust air from the transformer for more than 12 hours by means of the vacuum

pump and check that degree of vacuum inside the transformer is than 3 mmHg by

McLeod / Pirani gauge.

4.18 Oil Filling with Operation of Valve

4.18.1 Oil Filling

 Put one compound / vacuum gauge through valve (4)

32
  Connect valve (2) to vacuum pump

 Connect valve (1) to oil lone (Intel)

 Connect valve (5) & OLTC drain valve through vacuum tube.

1) Shut valve (1), (3), (8), (9) and (11)

2) Open (2), (4), (5), (6), (7), (8), (9), (10), (12) & OLTC drain valve.

Exhaust air from both the tank & conservator tank until the degree of vacuum is not

less than 10 mmHg.

N.B: If oil filling is performed without radiator, shut valve (10).

3) After the transformer has been carried out vacuum treatment described above,

maintain vacuum for one hour, then open the oil drain valve (1) and pump

degassed oil into the tank. The insulating oil should be through the oil filter press

and vacuum oil pre-conditioner.

4) During oil filling, continue the operating of vacuum pump. When degree of

vacuum becomes more than 3 mmHg, temporarily suspend oil filling and operate

only the vacuum pump in order to achieve required degree of vacuum.

5) When the oil level comes to about 100mm below the oil filter valve (2), stop

vacuum pump and shut (2). Then, continue oil filling under favor of remaining

degree of vacuum.

6) When the indicator of main tank oil level gauge indicates suitable level read from

“oil level-oil temperature pointer” then stop oil filling (shut (1). Oil will go from

main conservator to the OLTC conservator through vacuum tube. After the

closing valve (1), close valve (8) & (9) and remove vacuum tube.

7) Open (7) gradually so that filled oil in OLTC conservator tank is poured into the

OLTC switch compartment.

8) Close valve (4) and take off the vacuum line, the vacuum gauge etc.

33
 9) Attach the dehydrating breather for main tank and close all opening such as oil

filling holes and hand holes completely.

10) Oil filling in OLTC: See section 6 of OLTC installations and commissioning

guide available in the motor drive mechanism. As the bottom filter valve of main

tank is connected to the drain valve of OLTC, so during vacuum cycle OLTC

will be vacuum and during oil filling cycle oil will go to OLTC due to vacuum.

4.18.2 Residual gas release and oil level adjustment- Allow more than 8 hours for oil

to permeate into the immersed parts after oil filling. Then release residual gas from

various parts by loosening the air relief plugs until oil escape.

After residual gas is released, carry out oil level adjustment according to ‘the oil level

and temperature pointer’ shown on the MOG.

N.B: During vacuum operation the valve if available at breather pipe end it has to be

shut, otherwise temporally valve has to be fixed for closing the opening.

34
 B. Skills learned

As an electrical maintenance engineer I think we should know how the transformer is

inspection and testing. My mentor Mr. Moni Gopal Bosu really helped me to achieve

the skill of the work. I did not know how to do a transformer test before my internship

because it’s not possible without field work. Below I’ll describe how transformer

inspect and test.

4.19 Inspection

There are two recommended categories of inspection:

 Monthly inspection can be carried out without any interruption service and by an

observer at ground level.

 At approximately yearly intervals or at convenience, the transformer should be

taken out of service so that a more comprehensive and through examination can

be made. At the same time, the operation of various protective devices and

operating gear can be checked.

4.20 Precautions

35
4.20 Precaution

Personnel engaged on the erection of transformers should remove any loose tools or

personal possessions from their pockets before gaining access to the transformer

interior. Small metal items dropped into the tank would be difficult to remove and

ingress of any foreign material in the interior part is strictly prohibited. Spanners and

similar tools should be secured with strong cord to some external part of txr lid.

To prevent the ingress of dirt, it is essential to clean the area around all drain plugs,

air-release plugs and filter valves thoroughly before draining or commencement of oil

filling. Before breaking a pope work joint or a cover join, ensure that it is clean.

Whenever such a joint is broken, blank it off immediately to prevent the ingress of

dirt or moisture. Before covers are refitted or jointed. A thorough inspection should be

made to ensure that no foreign matter is left inside and all faces are clean and dry.

Monthly Inspection (without service interruption)

4.21 Oil level

Compare the oil level in the gauge of the conservator with the cold oil level marking,

on both prismatic gauge and magnetic oil gauge, making appropriate allowance for oil

temperature if the transformer is not cold. If oil level is low, new oil should be added

to bring the oil up to the correct level at suitable point in time.

4.22 Leakage of Oil

Look for the sign of oil leakage from welded scams, radiators, flanges, plugs, bosses

and valve outlets. If none are found and oil level is correct, then no further action is

required to be taken. If any oil leakage is found, tighten up flange bolts or screw down

valve in question. Do not top up with new oil until any leakage is cured.

36
4.23 Gas Operated Relay

Check if any gas is trapped in the body of the relay. Any gas present would be visible

through the windows and may be indicative of a faulty condition. It should be

siphoned off through the gas test cock of the relay.

4.24 Silica Gel Breather

Ensure that the silica gel crystals are active (blue). If not, replace with new silica gel

in accordance with the instruments. Ensure that the oil seal cup is full of transformer

oil to the indicated level. For tilling, unscrew the cup by turning it.

4.25 Temperature Indicator

Check that the thermometer bulb is properly in position. Ensure that any capillary

tubes are free from any king of interruption for its proper operation. Record reading of

maximum indicating pointer and re-set.

Annual Inspection (in de-energized condition)

4.26 Transformer

Examine the transformer tank and fittings to ensure that no rust is forming especially

at the welded seams. If so, it should be completely removed with a wire brush or other

means and the metal has to be given a coat of zinc phosphate primer paint, followed

by an appropriate undercoat and finally the finishing coat.

4.27 Oil Level

Check the condition of the prismatic oil gauge, if damaged, lower the oil level and fit

a new gauge. Check the condition of the magnetic oil gauge, if damaged, lower the oil

37
level and replace it with new one. Check alarm/trip operation of gauge by lowering

the oil level in the tank. Ensure that the transformer contains oil to the gauge level. If

the oil level is low, top up in accordance with the given instructions.

4.28 Leakage of Oil

Look for signs of oil leakage form welded seams, radiators, flanges, plugs, bosses and

valve outlets. If none are found and oil level is correct, then no further action is

needed to be taken. If oil level is low, new oil should be added to bring the oil up to

the desired level.

If any oil leakage is found, tighten up flange bolts or screw down the valve in

question. Do not top up with new oil until any leakage is cured.

4.29 Oil Valves

Ensure that the drain valves, filter, sampling valves and all air release plugs are fully

closed.

Ensure that the isolating valves between each radiator and the tank, isolating valves

between conservator, turrets and main tank and isolating valves between OLTC

conservator/compartment and main tank are fully open.

4.30 Gasket Joints

Ensure that all gasket joints are properly tightened. This applies to:

 Transformer tank joint

 Inspection covers

 Conservator cover

 Pipe joints

38
 Valve flanges

 Buchholz pipe connections and

 Bushing flanges

After the equipment has been in service for some time, it may be found that the

compression gaskets have shrunk a little and that small oil leaks have been developed

at some of the joints. It is advisable therefore to carry out a general inspection of the

joints after a period of not more than 12 months after commissioning.

To prevent oil leaks all joints fitted with gaskets must be tightened after the first 6 to

12 months in service. Covers secured by welded studs must not be excessively

tightened since too much force may break off the stud. Special care must be taken

when tightening the oil seals on molded terminals. The tightening of all covers fitted

with gaskets must be carried out carried out carefully and gradually to avoid undue

stress on bolts or studs and distortion to covers. Nuts or bolts must be tightened a little

at a time in sequence diametrically opposite wherever possible.

After carrying out the tightening described, if the oil lead still persists, the oil should

be lowered below the gasket level and an inspection of the gasket should be carried

out. If damage or deterioration is evident, a replacement gasket should be fitted and if

necessary the transformer should be vented as described.

4.31 Gas Operated Relay

Check if any gas is trapped in the body of the relay. Any gas present would be visible

through the windows of the relay and may be siphoned off. Any gas trapped in the

relay may be the indicative of a faulty condition and if gas is seen to be present in the

relay body it should be drawn off through the gas test cock. Check that the pipe into

which the relay is connected is not distorted. The angle of the pipe slope is very

39
important. The slope must be upwards towards the conservator at an angle of between

3º and 7º to the horizontal.

4.31.1 Trip Element: Test trip element operation by opening the valve on a bottle of

dry air so that air rushes in, impinges on the flap, depresses it and operates the switch.

The approximate minimum air pressure required to operate the switch should be

recorded for the purpose of future comparison.

4.31.2 Alarm Element: Test alarm operation, by slowly admitting dry air from a air

bottle, so that the alarm element gradually falls until the switch operates. The quantity

of air required to operate the switch may be observed on the graduated scale engraved

on inspection windows on each side of the relay and should be noted for the purpose

of comparison of future tests.

The trapped gases can be withdrawn from the device by means of the cap fitted in the

cover. Air released to atmosphere through the upped cap which has been collected in

the gas chamber during in order to fulfill the chamber with oil.

4.32 Dehydrating Breather

Examine the color of the silica gel charge and if the pink showing has reached half

way up the container, it is recommended that the charge should be changes for a fully

active one.

Changing container and reactivation should be carried out as follows:

 Remove the expanded metal guard retaining nut and the guard.

 Remove the foam pad and oil seal bowl.

 Slacken the two wing nuts at the top of the breather sufficient to slides out the

silica gel container, retaining the top and bottom sealing gaskets in position.

40
 Replace with a reactivated container, ensuring that the top and bottom sealing

gaskets are in position.

 Tightened the wing nuts and replace the oil seal bowl filled to the correct level

with transformer oil.

 Replace the foam pad, guard and guard-retaining nut.

 Place charge in a ventilated oven at a temperature of 14ºC. This temperature

should be maintained until the whole of the gel has been turned blue. The most

effective method of reactivation is to pass a stream of hot air through the gel

container. Suitable reactivates are available for this purpose from silica gel lit.

 Care must be taken to ensure these temperatures are not exceeded, or the moisture

indicating properties of the silica gel will be lost.

 The container should be allowed to cool in a moisture free environment, where it

should be stored until it is required for use.

4.33 Temperature Indicators

Check that the thermometer bulbs are properly in position. Ensure that all capillary

tubes are free from kinks and all joints for any leakage of operating fluid.

Check that the instruments are mounted in a vertical position, as error, particularly in

the horizontal plane, will upset the zero of the mercury switch setting scales.

Check correct operation of the switches. This can be done by rotating the pointer

slowly and steadily by hand. Do not allow pointer to spring back.

4.33.1 Instrument calibration: The indicating accuracy of the instrument should be

checked. Remove the temperature sensitive bulb from its pocket on the tank and

immerse it in an oil bath together with a thermometer and a controlling heating

element.

41
The oil should now be warmed through definite intervals to a maximum temperature

of 120ºC and instrument readings have to be checked against the thermometer. The

instrument should be allowed to steady off at each interval to allow for its inherent

indicating time lag and readings should be accurate to within +1ºC.

4.33.2 Switch adjustment: The mercury switches should be adjusted to operate at the

required valves. Each switch is set by slackening the locking screws on each arm and

moving the left hand setting pointer to the required operating temperature and the

right hand pointer to the resent temperature and retightening both screws should be

done.

The minimum switch differential is obtained by closing the right hand pointer to the

left hand pointer. A built-in stop automatically sets the minimum differential.

When carrying out any adjustment, the mercury switch table should be supported so

that excessive pressure is not applied to the bourdon movement.

4.34 Pressure Relief Vent

Check that the diaphragm is intact. If damaged, fit a replacement.

The diaphragm may be replaced simply by removing the bolted on lip of the

explosion vent. The diaphragm is clamped between two sealing gaskets at this point.

N.B: It is not applicable for this transformer.

4.35 Pressure Relief Device

Check that the valve is closed. Indication of the valve opening is given locally by the

obtrusion of the indicator pin. To reset indicator pin, push the pin flush with the top

cover.

42
4.36 Terminal Connections

Check the integrity of the cable box end clamps and the box fronts should be bolted

up tightly. Check the integrity of the cable end clamps and the clamping screws

should be tightened. Oil leakage problem should be dealt with special attention.

Ensure that all bushings are clean and intact. Check all the lead supports to the

transformer. Ensure that no weight or mechanical strain is imposed on the transformer

terminals

4.37 Auxiliary Wiring

 Check the auxiliary wiring for security of attachment, signs of any damage and

deterioration.

 Visually examine the auxiliary terminations.

 Examine the interior of the cubicle for security of attachment of all fittings and for

ingress of moisture.

 Check and tighten all auxiliary terminations.

 Using a 1000 volt Mugger, test the auxiliary wiring between line and earth and

record the results for comparison purpose.

43
4.38 On Load Tap Changer

It is provided from MR Germany. Further information has been provided in the OLTC

section.

4.39 Radiators

Remove all foreign objects from the radiator panels. Hose radiator panels to remove

all dust and dirt which could impede cooling efficiency. Check all welded seams on

each panel for any leakage or damage.

4.40 Earth Terminal

Check earth terminal for security of attachment. Ensure a good earth contact.

4.41 Fans

Check the fans for security of attachment and signs of conspicuous damage of

deterioration. The impeller and motor should be inspected to ensure that there is no

buildup of dirt or other matter that could cause overheating of the motor, obstruction

of the air path or cause out of balance of the impeller.

44
The motor bearings should be lubricated with lithium based grease. When carrying

out republication, it is essential that every trace of water and dirt is removed from

around the grease nipple and a clean gun should be used. Only a low pressure should

be required to inject the grease.

Motors with lubricators: If lubricators are fitted the fans should be re-lubricated after

16000 hours of running in ambient (up to 50ºC). For each 15ºC above 50ºC the

lubrication period should be halved.

Note: Republication period must not exceed 5 years.

To re-lubricate the motor should be dismantled and the rotor removed, complete with

bearings. The old grease should be washed out with a good quality solvent. The

bearings should be refilled with grease, leaving the housing empty. If a bearing is

removed from the rotor, if should be replace.

4.42 Cooler Control Cubicle

Check the cubicle for damage and security of attachment of tank. Check for damage

and security of attachment of all equipment housed inside the cubicle.

The following test should be carried out:

 Test the operation of the fans by switching the cooler control switch ‘MANUAL’

position.

 Test the operation of fans by switching the cooler control switch to the ‘AUTO’

position and adjust the indicating pointer on the winding temperature indicator

(WTI).

 Check the operations of the contact at the recommended settings for alarm, trip

and fans by rotating the indicating pointer on the temperature indicators. Also

adjust the switches to other temperature settings and test.

45
Oil Inspection

4.43 Oil

The oil supplied with the transformer is a pure hydrocarbon mineral oil conforming to

the requirements of B.S.148 for Insulating oil.

The code of practice for maintenance of insulating oils B.S.5730, deals

comprehensively with methods of sampling, testing and treatment.

The oil in a transformer operating under normal load conditions, adequately ventilated

and free from moisture, will show little oil deterioration after years of service. If, due

to overload or inadequate ventilating conditions, the oil temperature is high for

prolonged periods, deterioration of the oil will be accelerated. Routine oil sampling

and testing should be carried out periodically so that from the information obtained it

may be possible to determine whether the oil is suitable for further service.

4.44 Oil Warning

Excessive and prolonged skin contact with mineral oil should be avoided.

4.45 Oil Sampling

Samples of oil should be drawn from the transformer when the oil is warm. Sampling

of dielectrics is covered by B.S. 5263 and I.E.C. 475.

Samples taken on site are frequently found to be contaminated owing to inadequate

cleaning of the drain valve. It is essential that the valve be first thoroughly cleaned

externally and then wiped with clean material reasonably free from fiber (such as thin

smooth paper), followed by a similar material soaked in clean oil.

Finally, the valve should be flushed by draining off sufficient quantity of oil to ensure

that the sample obtained is representative of the oil at the bottom of the tank.

46
Stopper glass sampling bottles of one liter size are recommended. They must be

absolutely clean and dry and should be rinsed with the first sample drawn. Tests

should be carried out as soon as possible after drawing a sample.

4.46 Inspection of Sample (BS 5730-1979)

A limited but amount of information can be obtained from the odor, appearance and

color of the oil. It should be noted for record purposes. Cloudiness in the oil may be

due to suspended moisture or suspended solid matter, such as iron oxide or sludge.

The moisture can be deleted by crackle test.

If the oil is dark brown, the presence of dissolved aspartames may be suspected. If the

color is green the presence of copper soaps is indicated and it may be expected that

further deterioration of the oil will be rapid. An acrid acid smell is indicative of

volatile acids which can cause corrosion and which may render the oil unsuitable for

treatment on site. A petrol- like or acetylene odor may indicate a low flash point due

to a fault or some other cause.

4.47 Electrical Strength (BS 5703-1979)

Electrical strength is the max. Voltage which can be applied to an insulating material

without breakdown taking place. If frequent transient sparking occurs, this suggests

the presence of foreign matter e.g. moisture, fibrous material, carbon particles etc. and

the oil should be filtered. The electric strength of a sample of oil in service must never

be allowed to fall below 30kV. If it falls to this value, the oil should be reconditioned.

Ensure that any oil added to the system for the purpose of topping up has an electrical

strength of at least 35kV. The test should be repeated after filtering.

47
4.48 Crackle Test for Moisture (BS 5730-1979)

The crackle test is simple and useful test for detecting the presence of suspend

moisture in oil.

A metal rod 12.5 mm diameter, heated to a dull redness is lowered to the bottom of

the receptacle and used to stir the oil thoroughly. During this stirring process no

crackle should be detected. Oil does not pass this test should be suitably treated.

4.49 Acidity (BS 5730-1979)

The pungent odor of the oil will give an indication of the acidity. Acidity will cause

internal corrosion and if such an odor is present, immediate steps should be taken to

ascertain the acidity value.

The equipment and solutions required to perform this test may be obtained from

supplier of laboratory apparatus and chemicals but in case of doubt the advice of oil

supplier should be sought.

When the acidity is below 0.5mg. KOH/g no action needs to be taken if the oil is

satisfactory in other respects. When the acidity is above 0.5mg KOH/g the oil should

be re conditioned or discarded.

If the acidity is allowed to exceed 1.0mg KOH/g, there is a considerable risk of sludge

precipitation and corrosion of metal surfaces above oil level by condensed acidic

vapors. It may be possible to retain oil in service with acidity above this value

provided that frequent internal examination of the transformer is made, but this is not

recommended since the oil may reach a state at which it is not possible, economically,

for it to be reconditioned.

Regular filtration checks the development of acidity but is not effective in removing

acid once it has formed. To remove acid the oil may be returned to the oil supplier for

48
reconditioning or new oil may have to be provided but in either case the lower the

acidity at the time of changing the oil, the less the new filling will be affected by acid

absorption from the core and windings.

4.50 Sludge (BS 5730-1979)

Although severe sludge is not frequently experienced in transformer oil in service, it

is nevertheless a most serious form of deterioration. There is danger of insulation

breakdown owing to the restriction of cooling also a transformer with sludge deposits

is difficult to clean thoroughly without dismantling.

Although there may be no solid deposits visible in oil samples, it is still possible that

sludge may have formed and that the concentration in the oil has not yet reached a

point where deposition is occurring.

The presence of sludge may then be detected by dilution of the oil with heptanes and

it is recommended that this test be carried out if oil approaches 1.0mg KOH/g.

When comparison of records, as suggested under “Recording of results” indicates the

presence of precipitated sludge it may be necessary, even though the acidity may be

within the prescribed limit to consider applying treatment or changing the oil. When

sludge is allowed to accumulate, the oil circulating ducts become choked which

results in results in higher core and winding temperatures with consequent formation

more sludge.

4.51 Flash-Point (Closed) (BS 5730-1979)

Flash-point tests should be made if the oil has been subjected to a high temperature

due to an internal fault or shows any sign of unusual odor, but they are not otherwise

necessary.

49
A slow fall of the flash point of oil in a transformer may occur with increasing age

and is not harmful. A fall exceeding 15ºC may indicate unsatisfactory conditions such

as electrical discharge, excessively high internal temperature, core faults or foreign

matter providing a conducting path between live parts and the frame of the

transformer, in which case the units should be taken out of service for examination.

4.52 Frequency of Testing

Oil in transformer tanks should be inspected annually and if practicable, test for

electrical strength and for crackle. The acidity of the oil should be determined in

every two years. In special cases, where severe operating conditions are encountered

or it is known that the oil is deteriorating at an abnormal rate; tests may be desirable at

every six months or even at shorter intervals.

4.53 Recording the Results

It is essential to keep records of all tests. The acidity should be plotted on a graph with

time as a base and the records should include relevant operating data such as

maximum loads and maximum oil temperatures.

4.54 Recommended Action

The actions to be taken pertinent to testing have been represented below:

 Where a test result is outside the recommended limits, a fresh sample should be

taken for further tests before any other action is taken.

 As a general rule, several characteristics have to be unfavorable in order to justify

rejection of the oil. If the electrical strength is below the limits given then,

irrespective of the values of the other characteristics, action is essential.

50
 Where oil is confirmed as failing to meet the limits and the cause is unknown, it is

advisable to consult an oil supplier or contact the commercial Department at the

address given.

 Where refilling is required following oil treatment the equipment should be

thoroughly flushed through with unused oil before refilling and then refill.

In the following charts, fault analysis is confined to the cause of an alarm or trip.

Major faults occurring within the transformer e.g. to the core and windings should be

reported to the manufacturer for rectification.

Possible causes of alarm/Trip:

 Oil over temperature

 Winding over temperature

 Gas in Buchholz

 Oil surge in Buchholz

 Low oil level.

51
Check & Test before Energizing

4.55 General

Prior to connecting the transformer to the incoming and auxiliary supply lines, it is

necessary to complete the following tests and checks prior to commissioning the

transformer for normal service. It should be visually checked that all equipment is

mechanically satisfactory and that electrical wiring is in accordance with the relevant

drawings.

4.56 Gasket Joints

Ensure that all gasket joins are tight. It includes transformer tank joint, inspection

covers, cable box covers, conservator cover, pipe joints, valve flanges, Buchholz pipe

connections and bushing flanges.

4.57 Oil Valves

Ensure that the following valves are fully closed:

 Drain valve, Filter valves and Sampling and Air-release bosses

Ensure that the following valves are fully open:

*Isolating valves between each radiator and the tank isolating valves between

conservator and main tank. Isolating valves between OLTC conservator /

compartment and main tank.

4.58 Terminal Connections

Ensure that all bushings and palms are clean. Support all leads to the transformer in

such a way that no weight or mechanical strain is imposed on the transformer

terminals.

52
4.59 Silica Gel Breather

Ensure that the silica gel crystals are active (blue). If not, replace with new silica gel

in accordance with the instructions in section available in this manual. Ensure that the

oil seal cup is full of transformer oil to the indicated level. For filling, unscrew the cup

by turning it. Remove the plastic plug inserted in the base of the breather.

4.60 Gas Actuated Relay

Check that the pipe into which the relay is connected is not distorted. The angle of the

pipe slope is very important. The slope must be upwards towards the conservator, at

an angle of between 3º and 7º to the horizontal. Release to atmosphere, through the

petcock, any air, which may have collected in the gas chamber, so that the chamber is

full of oil.

4.61 Temperature Indicators

Check that the thermometer bulb is properly in position. Also check the switch

settings on the instruments are in accordance with the settings recommended in

manual.

4.62 Thermometer Pocket

Ensure that it is full of transformer oil.

4.63 Oil Levels

Check the condition of the oil gauge glass. If damaged, lower the oil level and fit a

new one. Check that the conservator contains oil to the gauge level. If the oil level is

low, top up in accordance with the instructions available in the manual.

53
Check the operation of the magnetic oil level gauge by lowering the oil level

gradually.

4.64 Pressure Relief Vent

Check that the diaphragm is intact. Replace if damaged. For this transformer pressure

relief is not available.

4.65 Pressure Relief Device

Check that the valve is closed. Indication that the valve has opened is given locally by

obtrusion of the indicator pin.

To reset indicator pin push the pin flush with the top cover.

4.66 Earthing

The transformer tank should be effectively earthed before energizing the transformer.

Two earth pads are fitted to the tank side for this purpose.

Commissioning Test

4.67 Insulation Tests

The following insulation tests should be made using a 5000V Megger and the

readings noted.

 HV Windings to Earth

 LV Windings to Earth

 HV Windings to LV Winding

Readings below 75 mega ohms should be reported to the manufacturer.

54
4.68 Voltage Ratio and Continuity Test

Connect a three-phase, 4-wire low voltage supply to the H.V. Terminals; record the

exact values of applied and induced voltages. The transformer rated voltages can now

be calculated from the measured applied and induced voltages and should correspond

to the diagram plate.

4.69 Magnetizing Current Tests

Connect a three-phase, 4-wire, low voltage supply to the H.V. terminals, record and

magnetizing current in each line. Compare the result with the factory tests. These

measured values should be kept for future reference should fault finding tests be

necessary.

4.70 Winding Resistance Measurements

Check the resistance of all windings using a Kelvin double bridge/ transformer

winding resistance meter. This result should be kept for future references.

4.71 Dielectric Fluid Sampling

Samples of fluid taken from the following positions should be tested in accordance

with IEC, and all values recorded.

 Samples prior to erection should be taken from tanker or each individual drum

containing fluid for topping up.

 Samples after final erection and filling should be taken from the sampling device.

4.72 Temperature Indicators

 Adjust and calibrate the temperature indicators.

55
 Check and adjust the switch settings.

 Check operation of alarm/trip circuits.

4.73 Gas Operated Relay

4.73.1 TRIP ELEMENT: Test trip element operation by opening quickly the valve on

a bottle of dry air so that air rushes in, impinges on the flap, depresses it and operates

the switch. The approximate minimum air pressure required to operate the switch

should be recorded for the purpose of future comparison.

4.73.2 ALARM ELEMENT: Test alarm operation, by slowly admitting dry air from

an air bottle so that the alarm element gradually falls until the switch operates. The

quantity of air required to operate the switch may be observed on the graduated scale

engraved on inspection windows on each side of the relay and should be noted for the

purpose of comparison of future tests.

NOTE: It will be appreciated that unless the transformer has been filled with oil under

vacuum, there will be a quantity of trapped air in the windings and core, which will

gradually be liberated during the first month of service. The rate of evolution is

indicated by the behavior of the trip and alarm contacts, and by the volume of gas

measured by the graduations marked on the gas chamber window. In the event of a

fault, the rate of gas evolution is related to the severity of the fault, and the

composition of the gas collected, related to the nature of the fault. The accumulation

of gasses can be withdrawn from the device by means of the cap.

4.74 Fans

Ensure the wiring is in accordance with the wiring diagram inside the terminal box.

Direction of rotation is marked on the impeller, and must be connected accordingly. 3

56
phase motors require a trial connection to the supply; if the rotation is incorrect it can

be reversed by interchanging any two leads. Starting of the fans may be carried out

manually or automatically. The current taken by the motor should be measured

immediately the motor has reached full speed, to ensure that it does not exceed the

nameplate current.

No work should be carried out on the fan without first switching off and isolating the

motor from the electricity supply.

4.75 Cooler Control

Test operation of the fans by switching the cooler control switch to the ‘MANUAL’

Position. Test operation of the fans by switching the cooler control switch to the

‘AUTO’ Position, and adjust the indicating pointer on the Winding temp. Indicator.

4.76 Alarm and Trip Circuits

The transformer is fitted with the following circuits:

Transformer Buchholz relay Alarm and trip

Oil temperature indicator Alarm and trip

Winding temperature indicator Alarm and trip

Magnetic oil gauge Alarm and trip

Pressure relief device Trip

57
C. Observed attitudes and gained values

4.77 Attitudes and gained values.

During the internship time I can able to adopted corporate attitudes and developed my

personality. That was a great opportunity for make a bridge with field technician to

my mentor. They are always help me and finally I gained a corporate values.

D. The most challenging task performed:

4.78 Factory Preparation for Dispatch

The transformer is not dispatch with complete fittings but usually filled with oil. The

tank contains oil to just over the core and windings. Fittings are removed to facilitate

transport. It also indicates (in the G.A. Drawing) the fittings which are removed from

the tank are dispatched separately.

58
The transformer is transported in some sections like the main tank, bushings,

conservator, radiators and other accessories. The dismantled accessories are packed in

crates or boxes. The packing lists are attached with the boxes or crates in water proof

cover along with the delivery documents.

4.79 Inspection on Site

On the arrival at site, the following examinations should be made-

4.79.1 Check for transportation damage and lost parts

If injury or rough handling is evident, a damage claim should be field. ENERGYPAC

ENGINEERING LIMITED must be informed immediately in case of any damages. If

no report is received THREE DAYS after the delivery on site, we can assume that the

transformer and accessories have been delivered without damages.

NOTE: The acceptance procedure must be carried out after each unloading so that the

source of the damage can be located.

59
4.79.2 Check for gas pressure

In order to prevent moisture impregnation, usually the main tank has to be filled with

dry nitrogen gas (approximately 0.02Mpa at 20ºC)

After removing the protective cover for the pressure gauge mounted on the

transformer tank and opening the connecting valve and the gas pressure has to be

checked. After checking the pressure the valve has to be closed tightly. Positive

indication shows that air/water has not entered in to the tank. If the point reads zero,

air ingress might happen. At that point, the insulation resistance of the windings has to

be measured to know the degree of moisture impregnation.

Refer to the “INSTRUCTIONS for INSPECTIONS and MAINTENANCE” for the

criterion of moisture impregnation. Measurement in low humidity atmosphere is

preferable to prevent the live part from moisture impregnation.

4.80 Inspection for Exteriors

4.80.1 Check for damage- Checking must be done if the transformer is dropped

accidentally or reinforcements and piping is distorted.

4.80.2 Rust- When the painting is damaged or the metal parts are rusted, the rust has

to be removed with sandpaper and it should be coated with paint.

4.80.3 Bolts and Nuts- If the bolts and nuts of covers or valves are found in loose

condition then insulation resistance must be measured.

Transport at site and unpacking-

1) It has been referred to transport instructions

2) It has been referred to packages and unpacking.

60
Caution

Before removing a manhole cover, transport plate or other device, vent the

transformer to the atmosphere pressure. Do not enter the transformer until the gas

space has been flushed with dry air or suitable oxygen (not less than 18% oxygen in

tank) supply is available for safety working.

4.81 Transportation from Factory to Site.

The transformer is transported to the substation etc. by trailer or by other means.

It is undesirable to give severe shock to the transformer during transportation. The

traveling speed of the trailer etc. should be regulated according to the conditions of

the road surface. The normal speed is as follows:

Completely paved road --------max 40km/h

Insufficiently paved road ------ max 30km/h

Unpaved road ------------------- max 5-10 km/h

61
When the transformer is shipped by rail, there is no problem while the train is

running. However attention should be paid to prevent shock during loading and

unloading.

It is undesirable to incline the transformer too sharply. The angle of slope should be

within 10º.

It is better to install a tachometer on the trailer or the train or attach a shock meter to

the transformer itself. To measure the angle of slope of the transformer, use a plumb

bob.

4.82 Handling on Site

In addition to the main lifting lugs, the tank has subsidiary jacking lugs. Whenever the

tank is lifted, whether empty or not, make sure the cover is bolted in position with the

full complement of bolts.

When jacking or hauling the transformer, use only the jacking lugs and haulage holes

specially provided for this purpose. Never use anything else, such as the valves or

tank rim for jacking or handling.

For any reason, if the internal parts of transformer are exposed to atmosphere, it must

be done only in dry conditions and moisture must not be allowed to contaminate the

solid insulation.

4.83 Location and Site Preparation

Mount the transformer on a level plinth to give an evenly distributed weight. Easy

access is provided all around in order to read or reach the diagram plate, valves, oil

gauge etc.

62
Storage: It is recommended that the transformer has to be put into service

immediately in its permanent location. If it is not possible, the following precautions

must be taken to ensure the proper storage of transformer.

1) The transformer tank is totally filled with dry nitrogen gas when stored for more

than four months from the date of delivery. The transformer tank should be filled with

insulating oil up to a level lower than the tank cover by 25cm. The gas space between

the cover and the oil should be filled with dry nitrogen. The gas pressure must be

checked periodically.

2) Indoor storage for transformer tank and accessories is strongly recommended.

The accessories may be stored in their boxes to avoid losing them.

When stored at outdoor totally, cover the tank and accessories with strong water proof

sheets to prevent water ingress. Lay wooden beams under the tank and the boxes.

The tank and accessories should be stored in a dry and clean location free from

corrosive gases and fumes.

63
Safety

Attention is drawn to safety in electrical testing.

4.84 Inspection and Test Prior to Operation (Commissioning)

After assembling the transformer, check the installation in accordance with the

following.

1) Construction: Make sure that all parts are located in their proper position, and all

bolts and nut are tightened.

2) Connection: Make sure that electrical connections are complete and wring

complies with wiring diagram.

3) Cooling equipment: Make sure that all radiator valves are open and cooling

control device; cooling fans have been tested for normal operation.

4) Tap changer: Make sure that tap changer operates smoothly and the tap position is

corresponding to the specified voltage. Control device for OLTC is normal condition.

5) Protection relays: Check the control operation.

6) Indicators: Check the oil level gauge or thermometers to confirm their calibration.

7) Dehydrating Breathers: Check the breathers operation.

8) Air release: Check the completion of air release.

9) Valve position: Check the valves are in the proper position.

10) Grounding system: Make sure that the grounding system of the transformer is

complete. (Shine the surface of earthling pads which were painted to prevent rusting

during transportation, remove the paint for good connection of the earthling cable.)

11) Live parts of bushings and lighting arresters: Make sure that phase to phase to

grounding distance is sufficient.

When above inspections are complete, carry out the field test such as insulation

resistance measuring, ration test angular displacement measuring, BCT ration &

64
polarity, Magnetizing current test, % impedance test, Operation test for fan control

cubicle, operational test for OLTC & RTCC panel, Operation of the cooler etc.

4.85 Caution When Energizing Transformer.

When all inspections and test have finished, now the power transformer can be put

into service. Cautions for first energizing transformer are as follows.

 Set tap position according to the line voltage.

 Apply voltage to the transformer without load.

 Observe for an hour to ensure that is a normal condition.

 It is also necessary to observe the transformer for a few hours after loading.

While in service the transformer should be inspected periodically. Refer to the

“INSTRUCTIONS FOR INSPECTION & MAINTENANCE” attached in this report.

65
 Chapter Five
Problem Identification and Solution

It is very important to know this as an engineer while working in the field. When I

was working with my other guys in the field, we tried to find root cause of the

problems. For this case, my mentor always advised me to follow the ‘Maintenance

Schedule’. It was a very interesting fact that most problems were covered by this

schedule. We used to follow two types of ‘Maintenance Schedule’. One of them was

named (a). Routine Maintenance and Inspection (Frequency Weekly) and the other

was- (b) Periodical Maintenance and Inspection. Both topics are described below with

solutions –

5.1 Routine Maintenance and Inspection (Frequency Weekly)

Inspection Matter Problem Identification Solution

1. Confirm there is no oil leakage According to
If oil leakage is found.
between the gaskets and welding part. clause 5.3
2. Confirm that the oil level in the oil
If oil level is not in the According to
gauge is within the safe region (white
safe region. clause 5.5
region).
If abnormal sound is According to
3. Check for abnormal noise level.
confirmed. clause 5.6
4. Check for abnormal offensive If abnormal offensive According to
sound. is confirmed. clause 5.7
5. Confirm the indication on dial type The following relation
thermometer by proper judging from is roughly established, According to
ambient temperature and temperature though it depends on clause 5.8
rise mentioned on the name plate. the cooling conditions.
6. Check for paint deterioration or rust
on the surfaces of tank and radiators If paint flaking is
According to
and at the gape of those parts fastened found.
clause 5.4
by gaskets by bolt such as inspection If rust is found.
cover, hand hole and so on.
7. Confirm there is neither If there is terminal According to
discoloration nor offensive smell. discoloration to purple clause 8.7

66
As terminal is live part, pay attention (or light black).
not to stand close to the terminal. If giving out offensive
smell.
If abnormal voltage, Investigate the
8. Check voltage, current, load and current and load, condition of
frequency with respective instruments. current and load etc. distribution sys.
are confirmed. etc.

Note: (thermometer indication) - (Ambient temperature) = (Temperature rise value of

the thermometer mentioned on the name plate) at 100% load. Simultaneously check
load with ammeter.

5.2 Periodical Maintenance and Inspection

Inspection Matter Period Judgment Treatment

Criterion
1. Accessory with alarm and /or Once a year
trip contacts
a) Confirm the operation of
contacts.
b) Measure the insulation
resistance of the relevant
circuit.
2. Measurement of insulation It is judged as According to
resistance abnormal if 8.11
abrupt change
of exclusive 30kV /2.5 mm Carry out
change from the and above performance
test data on test per item 4
delivery is below.
confirmed.
3. Insulation oil
a) Measurement of dielectric Once a year 0.2 mg KOH/g
breakdown and below.
b) Measurement of total acid Once a year 10¹² Ώ-cm (at
value. 50ºc) and above.
c) Measurement volume Once a year Characteristic
resistively. values specified
d) Performance test this test is in BS-148, If an
performed when an abnormality ASTM, UTE abnormality is
is confirmed form the results of C27, 101 found,
measurements in item #3 (a to perform a
c) After sampling two liters of filtration of

67
 oil specimen, carry out oil, (see item
performance test concerning 7 for oil
respective items specified in filtration
BS-148, ASTM UTE C27-101. method).
4. Inspect for local heat Once a year For loose Refer to
damage, corrosion, or connections heat clause 8.7
contamination of terminals, and corrosion of
/ or loosening and corrosion of contamination is
terminals connections. Check contamination is
for contamination on terminal found See clause 8.9
and porcelain. When the
contamination of
terminal and
porcelain is
found.

5. Confirm that the nuts for Once a year If loose Re-tighten.

fastening tap-changing pieces
are tight enough.

5.3 Oil Leakage Problem

5.3.1 In case of oil from drain valve or drain plug: In case of looseness of valve of

plug, refasten it. If oil leakage still does not stop, replace calve of plug. Exchange of

gasket is performed according to clause 6.1.2.1), 2)

5.3.2 In case of oil leakage from gasket: In case of looseness of fastening part, re-

tighten. If oil leakage still does not stop, the gasket has to be replaced.

1. Exchanging procedure of gasket-Drain oil and exchanging gasket (after draining

the oil thorough the drainage valve of plug until the oil level is below the gasket.

2. Exchanging of gasket-Before fitting a new gasket, in order to remove rust, rubber,

oil and grease from gasket fitting surface of valve, clean with wire brush etc. Wash

off with thinner or alcohol etc. Never reuse an old gasket.

5.3.3 Disposition of insulating oil: The insulating oil removed during 6.1.2 (1) above

should be always poured into the transformer thorough filter.

68
5.3.4 Oil-leakage from welded part:

 The simplest way to repair a small leaking hole is to calk it carefully with a chisel.

 Calking a small leaking hole with putty of paint is temporarily acceptable, but

permanently it is not accepted.

 A hole in cast iron can’t be repaired by welding the cast iron part has to be

replaced.

 Consult with the manufacture for welding of radiators.

 If a leak does not stop of is found in an important part of the equipment, consult

with the manufacturer for the method of treatment.

5.4 Paint Flanking or Rust Occurrence

Where paint flaking or rust occurrence is found, polish with sand paper etc, and

perform repair panting after applying an anticorrosive paint.

5.5 Oil Level Discrepancy

1) If the oil level is above the specified valve-Drain oil thorough the drainage valve or

plug on the lower part of the tank, until the oil level meets the normal position.

2) If the oil level is under the specified valve-add oil thorough the filter valve on the

cover, until the oil level returns to normal position. In the case, check oil leakage

carefully.

Note: depending upon the ambient temperature and temperature rise mentioned on the

name plate the oil level should be in safe region (white region).

69
5.6 Abnormal Noise Level

Whenever there is any abnormality in the noise levels, this can easily be noticed by an

operator used to normal noise and this often leads to discovery of a problems.

5.6.1 Causes of abnormality:

 Resonance of the case and radiator due to exclusive change in voltage and

frequency of the power source.

 Loosening of attachments.

 Abnormal notice from static discharge due some ungrounded metal parts or

imperfect earthling

 The so called inter-layer short-circuits due to defect in core structure as in core,

core clamping metal parts, bolts etc. these can be detected from outside of by

listening at the case even when the increased inside level is small.

5.6.2 Method of treatment

In case of 1) Adjust voltage and frequency to rated values, 2) refasten components

and 3) Perfect earthling it is suggested to consult with the manufacturing body for the

method of treatment.

5.7 Foul Odors

5.7.1 Causes of abnormality

* Local overheats due to loose attachments.

* Local over heat due to over load and

* Generation of abnormal gases.

5.7.2 Method treatment- After disconnection of transformer form the power supply,

In case of 1) retighten connections and 2) lower load to under rated value it is

suggested to consult with the manufacturer for the method treatment.

70
5.8 Thermometer Reading Discrepancy

When the transformer is over loaded, decrease the load to 100% and below. Check the

calibration of the thermometer, if abnormal, replace with new one.

5.9 Contamination on the Bushing Porcelain

After disconnection of transformer from power supply, wash with water or cloth

soaked with ammonia or carbon tetrachloride, then wash with clear water so as to

remove foreign matter.

5.10 Draining of Insulation Oil

To ensure highly reliable transformer operation, it is important to maintain its

insulations in the best possible condition. If it is necessary to drain oil from the

transformer for inspection or repair in the field, bear in mind that exposure of the oil

the atmosphere should be under a clear sky and that exposure time should minimize

within 10 hours if the repair work takes two days it is necessary to refill the

transformer with insulating oil or nitrogen gas to prevent the insulators from

absorbing moisture during the night.

5.11 Measurement of Insulation Resistance

5.11.1 Method of measurement: For insulation resistance measurement, use 1000V,

2000V, 2000MΏ Mugger or electronic tube Mugger.

The value of insulation resistance depends so much on temperature that the

temperature at the time of measurement should be recorded.

The measurement is to be taken with the connections as shown in Figure 4&5.

71
Beforehand make sure that the hand pints 0 when the terminals for lead wire are

short-circuited and points ∞ on open circuit.

[NB: Use 5KV Mugger above 6.6kV system and use 1KV Mugger below 6.6 KV

systems.]

5.11.2 Judgment criterion: As per following instructions

Table 1: Minimum Insulation Resistance in oil at 20ºC

Voltage class (KV) Mega-ohms For Example,

The mugger at 40ºC is 950 M.
1.1 32
Ohms
3.6 68
7.2 135 Insulation Resistance is,
1
12 230
950X-----= 287.8 M. Ohms
17.5 410 3.3
24 670
36 930
52 1240
72.5 1860

Table 2: Insulation Resistance Temperature Correction

Transformer Correction Transformer Correction Transformer Correction

Temperature factor Temperature factor Temperature factor
(ºC) (ºC) (ºC)
95 89.0 55 8.1 15 0.73
90 66.0 50 6.0 10 0.54
85 49.0 45 4.5 5 0.40
80 36.2 40 3.3 0 0.30
75 26.8 35 2.5 -5 0.22
70 20.0 30 1.8 -10 0.16
65 14.8 25 1.3 -15 0.12
60 11.0 20 1.0

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Maintenance of Insulating Oil

The insulating oil of a transformer, used for insulating between core and winding,

windings and charging parts and also for transferring the heat generated in the core

and windings to the cooling equipment for heat radiation. It is required to have the

following characteristics.

 To have dielectric strength.

 To have good cooling effect or have low viscosity.

 To be well refined and be free from such materials as will corrode metal parts or

cause deterioration.

 To be free from such materials as moisture, fibers etc.

 To below pour point so as not to freeze in winter.

 To have little evaporation.

The manufacturing technique for the transformer and its reliability have been

improved to such extent that inside inspection is almost unnecessary and at present,

maintenance means essentially to prevent deterioration. The following explains the

deterioration of oil.
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5.12 Deterioration of Insulating Oil

The insulating oil deterioration gradually as it is used. The causes are absorption of

moisture in the air and foreign materials that the oil. The major cause as oxidation.

The oil is oxidized by contact with air and accelerated by temperature rise of the

transformer and contact with metals like copper and iron.

Beside the above the oil undergoes such chemical reaction as decomposition and

polymerization to produce matters which do not dissolve in oil and such matter

precipitate on the core and the winding. Those matters are called sludge. The sludge

does not directly affect dielectric strength but the sludge that has been deposited on

the winding prevent cooling by oil and that which is extracted and attaches to the

radiator and tank-wall increases temperature rise of the winding and affects indirectly

dielectric breakdown.

5.12.1 Acid value: The sludge formation is practically nil up to 0.2 degree acid value,

but it increases gradually and a formation can be observed at around 0.4 degree acid

value and this increases sharply above.

5.12.2 Specific resistance: The specific resistance of the insulating oil is connected

with the insulation of the transformer and greatly influences the insulation resistance

value of the transformer.

The specific resistance becomes lower with temperature rise of the transformer as in

the case of the insulation resistance.

5.12.3 Dielectric strength: The insulating oil is a main source of insulation for the

transformer and lowering the oil dielectric strength means lowering the dielectric

strength of the transformer itself. Therefore this must be carefully inspected, the

dielectric strength of oil to be 30 KV. For transformer of higher tension, the dielectric

strength of also has to be maintained higher. If treated a maintained sufficiently the

74
insulating oil can have 40-50 KV dielectric strength. The dielectric strength is also

subject to moisture and foreign materials contained in the oil and so more

measurement of dielectric strength does not help to estimate the degree of

deterioration. In measuring the dielectric strength the fluctuation of the measured

values will be so large that they will become useless sampling of oil be done with care

and a proper method of test selected.

5.13 Standard for the Estimation of Oil Deterioration

The following are the standard for judging the degree of deterioration from the

measured values.

5.13.1 Acid value: Table A shows the recommendable standards for insulating oil

regeneration.

Table A: standards of acid value

Standards for treatment Acid value (mg KOH/g)

New oil 0.02 or less

Refinement is desirable, especially in case of extra-

high tension apparatus. In case of a transformer of Less 0.2

30kV of lower voltage up to 0.3 is permissible

The limit necessitates refinement or replacement when

Less 0.2-0.5
convenient refinement or replacement.

The limit necessitates immediate refinement or

Over 0.5
replacement.

5.13.2 Specific resistance: As shown if Figure 8 the relationship between the acid

value and the specific resistance is such that the measured values are inconvenience.

75
Therefore, the standard are be regarded as mere guides. These are rather useful in

checking the influence of moisture.

Table B: Specific resistance

Good Over 1x10¹² Ώ cm

Caution 1 10¹¹-10¹² Ώ cm

Bad Less 1x10¹¹ Ώ cm

5.13.3 Dielectric strength: The dielectric strength of oil has so far been standardized

above 30 kV, however with the change made in the shape of the transformer and the

expansion of use for higher tension the values of the insulating oil should be

resistance as in table 5.

Table 5: Dielectric strength

Transformer of the voltage above 60 kV and of Over 35 KV

nitrogen-sealed tank type

Other type Over 30 kV

On-load tap-changing switches chamber Over 35 kV

76
 Chapter Six
DC System, Protection Relay & Grounding

6.1 DC System

The DC-system consists of a free standing cubicle including Chargers, batteries, and

distribution. Normally the rectifier supplies the load. The battery bank supplies the

load for a limited time if the main supply is interrupted. The DC system shall provide

110V (125V), 24 V DC ± 10% to the consumers in the power plant. The batteries are

typically sized for 5 or 10 hours or: capacity is C10/5 at 1.8V end voltage and 20°C

ambient. Normally current is gone through B-bus to load

Battery Installation & Commissioning

6.2 Battery Location

 Installation of the Battery should be done in a clean, cool and dry location. Ideal

temperature of the location shall be 270C for optimum performance and life.

 Free space of 1mt should be provided on all sides of the battery for ease in

assembly and carrying out periodic checks.

77
 Keep the batteries away from heat generating sources, to avoid temperature

variations among the cells within the battery? The floor where the battery is to be

located should have the capacity for withstanding the weight of the battery.

6.3 Ventilation

Room size shall be selected so as to maintain the Hydrogen gas concentration within

the safe limits (<1% of room volume).n airtight enclosure However, if the batteries

are subjected to excessive overcharge, Hydrozen and Oxyzen will be vented to the

atmosphere. Therefore, the battery should never be installed in an airtight enclosure.

6.4 Floor Anchoring

Mounting channel can be grouted to the floor with the help of the expansion bolts or

suitable foundation bolts. If floor grouting is required, carefully mark the location and

install the floor anchors to match the holes in the mounting frame. If required, use

shims for leveling. Tighten the bolts firmly to anchor the mounting frame.

6.5 Module Stacking

 Use forklift or mobile crane for handling the modules and stacking the system.

 Lift the module slowly and place it on the mounting frame.

 For multiple tier assembly place one module at a time on top of the module

already in place.

 Properly align the module mounting holes and insert M 10x30 bolts, washers.

Care should be taken to support the module to avoid slipping.

 Stack the subsequent modules in similar fashion.

78
 When all the bolts are in place, check that the assembly is plumb and level then

tighten the bolts.

 In case of multiple stack assembly, a minimum gap of 6 inches (150mm) shall be

provided between two adjacent stacks to allow future access for tighting the

module blots and nuts.

6.6 Precautions to be taken

 Use safety wear such as gloves, shoes and eye protectors.

 Tools like wrenches etc. should necessarily be insulated.

 Do not put tools or other equipment over the battery.

 Always work with the battery undergrounded.

 Ensure that the charger is turned off before making or breaking electrical

connections between the battery and the load.

 Ensure that all connections are as per General Arrangement drawing and are

firmly tightened with a torque of 10N-m before the charger is switched on.

 Connect battery negative terminal to charger negative terminal.

79
Protection Relays

6.7 Release Device and Relay

If a protective device acts directly on the holding latch of a switch or a circuit

breaker, it is known as Release Device. If it opens or close an auxiliary circuit as

shown circuit an in fig, it is called a relay. Release devices are used in manually

operated switches and breakers, while relays are used in solenoid-operated breakers.

6.8 Instantaneous Over current Relay

It consists of a solenoid, a plunger and a set of contacts. The solenoid, generally

operated by a current transformer, attracts the plunger when current through it

exceeds the specified value, which results in operation of the relay. Theoretically,

there is no time-lag in operation but in actual practice, there is a time lag of about 240

milli-seconds which decreases as the fault current increase. Discrimination between

successive relays of this type is possible with current ratios of 3:1. Their principle

application is in transformer feeders as the impedance of transformer feeders as the

impedance of transformers permits good selectivity. The instantaneous relays are

unsuitable for circuits with high transient currents.

6.9 Definite Time Relay

This relay consists of a solenoid and a plunger with adjustable time delay feature in

the form of an oil dash-pot or an air escapement chamber. Such a relay operates after

a specified time irrespective of the magnitude of the fault current selectivity amongst

such relays is obtained, if there is a diff. of 0.5 sec. in the setting of the two successive

relays. The definite-time relays are used in-

 Radial or loop circuits having a few sections.

80
  As back-up protection for other forms of protection, and

 On systems with wide variations of fault current due to source impedance.

6.10 Induction Relay

The induction relays have an inverse time-current characteristic with definite

minimum time and are, therefore, also known as.

Magnetic and thermal overload relays- Magnetic and thermal overload relays are

used to provide protection to motor and other sub circuits against overloads.

6.11 Magnetic overload relay

In its plunger or plunger or armature in attracted by the magnet coil when current

through it exceed the specified value resulting in operation of the relay. To ensure its

non-operation under condition of transient overload, time delay feature is provided

with the help of oil dash pots.

6.12 Thermal overload relay

It’s provide the best means of overload protection to motors as the heating

characteristics of the two are similar they are two type-

1) Bimetal type, and 2) Thermistor type.

6.13 Reverse power relays

Reverse power relays are sensitive to direction of power flow and are used on ring

mains and feeders operation in parallel the relay operates when the direction of power

reverses. A directional overload relay combines in one relay the functions of overload

of overload protection as well as reverse power control.

81
6.14 Over current relays with A.C Tripping

Over current relays with A.C Tripping The circuit breaker trip coils are usually

arranged to be operated by a separate source of D.C supply but where the provision

and maintenance of a battery and the associated charging equipment are considered

rather uneconomical over current relays with A.C tripping are used. In their case, trip

coil is energized by the secondary of a current transformer in the protection circuit.

6.15 Combined overload and earth leakage protection

The arrangement which requires two overload and one earth leakage relay is

commonly used for the protection of motor and distribution feeders in solidly earthed

systems. There is no current through the earth fault relay so long as the circuit is

healthy. In case of an earth fault, there is an imbalance and the residual current result

in operation of the earth leakage relay.

6.16 Protection of Radial Feeders

Definite time current relay are best suited for this application. A minimum difference

of 0.33-0.5 sec is required in the time settings of two adjacent relay. The maximum

time delay which will be on the relay nearest to the supply and must not exceed 2

second .The maximum number of section in series in thus limited to six.

6.17 Protection of Parallel Feeders

Protection in the case of parallel feeders is provided by non-directional overload

relays A and B at the sanding end, by directional relay C and D at the receiving end as

shown in fig 11:25 . In the case of a fault between A and C, the power will be feel into

82
the fault from both the ends, relay C will operate first, being instantaneous type.

Relay a will than trip, thus isolating the fault section.

6.18 Protection of ring mains

Ring mains are protected by providing two directional overload relays at each

junction point. Relays of this kind are represented by an arrow and a figure. The

arrow indicates the direction of current which will make the relay operate, and the

figure indicates the infinite minimum time of the relays in seconds.

6.19 Protection of Transformers

Induction type over current relays (IDMTI) are used for the protection of

transformers up to 5MVA for economic reasons even though complete protection is

not provided by these relays are generally set at 125% of the transformer rating,

which helps in riding though the large magnetizing in rush current differential

protection, as described later, is used for the protection of larger transformers.

6.20 Merz-price Protection of transformers Alternators.

Modern alternators are designed to withstand all external faults howsoever severe,

until the overload device isolated the fault section. The most dangerous fault that may

occur in an alternator is a ground on the alternator winding itself. In that case, the

machine will be feeding power in its own fault and destroy itself.

6.21 Core Balance Earth Fault Protection

This form of protection consists of a ring-core current transformer which is designed

to pass over 3-core cables. The output from this current transformer is utilized to

83
energize a current-operate relay as shown in fig 11:28.This arrangement provided

very sensitive earth fault protection and is re-commended for industrial and

distribution feeders in mines.

6.22 Grounding

Grounding is a particular type of security system that is designed to protect the

devices from any kinds of abnormalities or internal fault in the system which can

damage devices. Grounding is often used as a way of coping with flashbacks or

dissociation. In this way, grounding can be considered a variant of mindfulness. The

main purpose of grounding is to protect the devices from any kinds of internal faults

in the system.

Grounding techniques often use the five senses (sound, touch, smell, taste, and sight)

to immediately connect people with the here and now. For example, listening to loud

music, holding onto a piece of ice, or biting into a lemon are all grounding techniques

that produce sensations that are difficult to ignore, thereby directly and

instantaneously connecting you with the present moment.

84
The grounding can be divided into the following three areas with respect to purpose:

1. Neutral Point, 2. Ground Safety Ground 3. Equipment Ground

6.23 Neutral Point

NGR is employed in AC distribution networks to limit the fault current which would

flow from the transformer or generator neutral star point in the event of an earth fault

in the systems. It is used when the neutral of supply transformer is accessible and its

own impedance is not enough to limit fault current. The rating of the protection relays

within the required time. For Grounding Neutral of Transformer or Generator,

Resistors upto 33 KΩ are offered for fault of short duration like 10 sec., 30 sec., 60

sec., continuous etc. Material of resistor is normally Stainless Steel, FeCrAl, Cast

Iron, Copper Nickel or Nichrome.

6.24 Safety Ground

This is made for protecting personnel from injury. These connections are made to

parts of the system that are usually not energized but may become under abnormal or

fault situations.

85
6.25 Equipment Ground

Grounding is made to ensure a low impedance return path for ground current should

an electrical fault occur. Between conductors and equipment enclosure, in order to

secure that a trip of a faulty circuit is made in a short time. In this power plant we

observed those three types of grounding. The ground grid design was made by

CITEC, using the auto grid program following the IEEE 80-2000 standards.

Most important items of grounding are:

 Design criteria is safe & touch voltage is not a absolute Ohm value

 Soil resistivity measurement need to be made

 Network configuration should be known

 Maximum earth fault current should be known

 Station layout should be known

 Number of incoming lines and earthling wires

86
 Chapter Seven
Drawing Requirements for Erection Works

7.1 DC System (Battery Layout)

87
7.2 Single Line Diagram of 33/11KV, 2x7.5MVA Substation

88
7.3 Section on A-A

89
7.4 Section on B-B

90
7.5 Section on C-C & D-D

91
7.6 Layout Plan of Outdoor Equipment

92
7.7 Electrical Layout Plan-A

93
7.8 Electrical Layout Plan-B

94
17.9 33KV Control & Relay Panel For Transformer Feeder

95
7.10 11KV Incoming & Outgoing Panel.

96
7.11 Switchgear Foundation Drawing

97
 Chapter Eight
Conclusion

The main objective of this project was the installation, commissioning, maintenance

and troubleshooting of the 33kV/11kV Transformers. We followed three types of

maintenance scheduling, such as schedule maintenance of oil change and major

buckles relay as required complete the hours of operations, If unexpected problem or

interruption of the transformer to begin troubleshooting as transformer due the

cooling system and shutdown of transformer. It was very helpful to determine the

problem and how to solve the problems of the 3-phase transformer.

As an electrical engineering student, I feel proud to get the opportunity to work in

transformer installation work. But in a matter of deep understanding, it is important to

know about transformer installation mechanical work. I think at least one mechanical

course should be offered in our university. It will help to make more confidence in

installation works a students to improve their performance in internship.

Besides, I have gained a lot of knowledge about switchgear and protective relay as

well as transformer installation while internship, which is presented in this report. I

am hopeful that all the information presented in my internship report will be assisted

specifically by other students and trainee.

98
 REFERENCES

1. Power Transformer Installation Guide, Energy Pac, 33 kv/ 11 kv, 7.5 MVA,

Dyn 11 Transformer Installation, 2016. City Auto Rice and Dal Mills Ltd.,

Gondhrobpur, Rupshi, Rupgonj, NarayanGonge, Bangladesh.

2. CARDML Installation Guide and Training Materials, 2015. City Group

archive.

3. Handbook of Electrical Engineering, S.L. Bhatia, Khanna Publishers, And

Fifth Edition: 1990, Second Printing: 1995. 2-B, Nath Market, Nai Sarak,

Delhi-110006.

4. Theraja B.L. and therajaA.K,a text book of Electrical Technology, second

edition 1989.

5. http://www.google.com/search?q=taansformer/oil&hl

99
APPENDIX

100
101
102
103
104
105
106
107
108
109
110
111
112
113
114