Power distribution, operation and maintenance of comilla palli bidyut samity 1

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Practicum Report On
Power Distribution, Operation and
Maintenance of Comilla Palli Bidyut
Samity-1
Prepared By:
Kawsar Ahmed
ID: 12105297
Prepared For
Engr. Md. Abul Bashar
Associate Professor and Coordinator
Department of Electrical and Electronics Engineering
IUBAT—International University of Business Agriculture and Technology

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Letter of Transmittal
April 15, 2016
Engr. Md. Abul Bashar
Associate Professor and Coordinator
Department of Electrical and Electronics Engineering
IUBAT- International University of Business Agriculture and Technology
4, Embankment Drive Road, Sector 10, Uttara Model Town, Dhaka -1230, Bangladesh.
Sub: Letter of Transmittal of the Practicum Report
Sir,
I am submitting my practicum report on, “Power Distribution, Operation and Maintenance of Comilla Palli Bidyut
Samity-1” to you. Thank you for giving a chance to work with the Power Distribution, Operation and
Maintenance of Comilla Palli Bidyut Samity-1 as part of educational and other facilities. It was superlative
opportunity for me to work on this topic to actualize my theoretical knowledge in the practical area and to have an
enormous experience on the maintenance. With my little knowledge of the subject I tried to make it as interesting
and as accurate as possible.
I would be very kind of you, if you please take the trouble of going through the report and evaluate my performance
regarding this report.
Yours sincerely
-----------------------
Kawsar Ahmed
ID # 12105297
Program: BSEEE

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Training Concern LetterTraining Concern Letter

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Training confirmation letter
Student Declaration
I am Kawsar Ahmed ID# 12105297 student of the Department of Electrical and Electronics
Engineering under the College of Engineering and Technology (CEAT) would like to declare that the
project paper on “Power Distribution, Operation and Maintenance” is prepared for the fulfillment of
Practicum, as the partial requirements of academic purpose from my own concept and idea, after
completion of three months practicum in of Comilla Palli Bidyut Samity-1.
We also confirm that the report is only prepared to fulfill the academic requirement and not for any other
purposes.
Faithfully Yours,
……………………….
Kawsar Ahmed
ID # 12105297
Program: BSEEE

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Acknowledgement
At first I thank to Almighty Allah who gave me energy to complete this task. Then, I would like to express my
gratitude and respect to some generous persons for their immense help and enormous cooperation.
First of all I would like to pay my gratitude to Honorable Vice Chancellor Prof. Dr. M. Alimullah
Miyan for giving me chance to prepare my research about this splendid topic.
I am very much grateful to Engr Md. Abul Bashar Associate Professor and Coordinator of Electrical and
Electronics Engineering Department, (IUBAT) International University of Business Agriculture and Technology. Also
I would like to thanks my practicum supervisor Abu Bakr Siddique
faculty of EEE.
After that I would like to express my special gratitude Md Yousuf Ali, Deputy General Manager
(Technical) in Comilla Palli Bidyut Samity-1. Who helped me a lot by his brilliant guidelines to make this
report, without which it was not possible to conduct it.
I would also like to thank all the faculty members of IUBAT and for their critical advice and guidance.
I have given my best effort to prepare and represent the report. I hope my endeavor will be beneficial to
the audience and urge for exonerate eye for any mistake or error found in the report. Finally, we also feel
it is an important thing to acknowledge and thanks to our faculties and all the employees of Comilla Palli
Bidyut Samity-1 who helped me a lot to provide a valuable forum for the exchange of ideas and
information.
Kawsar Ahmed
ID # 12105297
Program:BSEEE

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Executive Summary
As technology is advancing the consumptions of power is steadily rising. There are three steps for proper
electrification these are:
1. Electric Power generation.
2. Electric Power Transmission.
3. Electric Power Distribution.
This three are equally important for proper electrification, without any one of this three the electricity
system will be incomplete. Power Grid Company ltd is the BPDB (Bangladesh Power Development
Board) wound company which is the only authorized company for the Electric Power Transmission sector
in Bangladesh. Rural Electrification Board (REB) has many sub- stations all over the country which are
connected through the distribution line, these stations are called sub-station. This project paper provides
the synopsis assessment of all the systems existing 33/11KV Comilla Palli Bidyut Samity-1, Chandina.
Rural Electrification Board (REB) has the vast electricity distribution network all over the country & the
electric power plants are connected with the transmission line to assure the continuity of electric power.
The electric power plants produce power & feed in to the transmission line. All power plants are
connected parallel with the transmission and distribution line. Comilla Palli Bidyut Samity-1, Chandina.
Has AIS (Air Insulated Switchgear) switchyard.
Every sub-station is controlled by some experienced manpower, including one in charge, 2/3 engineers,
4/5 technical staffs. All kinds of maintenance work of the sub-station done by them in addition, sub-
station operation work done by the engineers. Every year annual maintenance work is done in every sub-
station in according to the official schedule. This thesis report is prepared in according to the operation
and maintenance procedure of 33/11KV Sub-Station, including emergency maintenance work.

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TABLE OF CONTENTS
Topic Page No
Preparatory Part
Title Page-------------------------------------------------------------------------------------------------------I
Letter of Transmittal------------------------------------------------------------------------------------------II
Training Concern Letter------------------------------------------------------------------------------------III
Training confirmation letter--------------------------------------------------------------------------------IV
Student’s Declaration ----------------------------------------------------------------------------------------V
Acknowledgement- -----------------------------------------------------------------------------------------VI
Executive Summary ---------------------------------------------------------------------------------------VII
Table of Content -------------------------------------------------------------------------------------------VIII
List of Tables ------------------------------------------------------------------------------------------------7I
List of Figures -----------------------------------------------------------------------------------------------7I
Chapter-1
Introductory part
1.1 Origin of the report --------------------------------------------------------------------------------------1
1.2 Objective Of the study ----------------------------------------------------------------------------------1
1.2.1 Broad Objective------------------------------------------------------------------------------------1
1.2.2 Specific Objective----------------------------------------------------------------------------------1
1.3 Scope-------------------------------------------------------------------------------------------------------2
1.4 Background -----------------------------------------------------------------------------------------------2
1.5 Methodology ----------------------------------------------------------------------------------------------2
1.6 Limitations ------------------------------------------------------------------------------------------------2
Chapter-2
Organization Part
2.1 Introduction------------------------------------------------------------------------------------------------3
2.2 Company profile------------------------------------------------------------------------------------------3
2.3 Comilla Palli Bidyut Samity-1--------------------------------------------------------------------------4
2.4 Organizational chart of Comilla Palli Bidyut Samity-1---------------------------------------------5
2.5 Consumer Information of Comilla PBS-1-------------------------------------------------------------6
2.5.1 Tariff-wise Consumer No--------------------------------------------------------------------6
2.5.2 Disconnected Consumer No-----------------------------------------------------------------6

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Chapter-3
Transformer
3.1 Introduction of Transformer-----------------------------------------------------------------------------7
3.2 Classification of Transformer---------------------------------------------------------------------------7
3.3 Parts of the transformer----------------------------------------------------------------------------------8
3.3.1 Transformer Tank----------------------------------------------------------------------------------9
3.3.2 Conservator tank-----------------------------------------------------------------------------------9
3.3.3 Transformer Core---------------------------------------------------------------------------------10
3.3.4 Transformer Coil or Winding-------------------------------------------------------------------10
3.3.5 Silica Gel------------------------------------------------------------------------------------------10
3.3.6 Buckholz Relay-----------------------------------------------------------------------------------11
3.3.7 Radiator--------------------------------------------------------------------------------------------11
3.3.8 Bushing--------------------------------------------------------------------------------------------11
3.3.9 Transformer Tap----------------------------------------------------------------------------------12
3.3.10 Insulation and Impregnation-------------------------------------------------------------------12
3.3.11 Insulation material------------------------------------------------------------------------------12
3.3.11.1 Transformer Oil-------------------------------------------------------------------------------12
3.3.11.2 Electrical grade paper------------------------------------------------------------------------13
3.3.11.3 Press board-------------------------------------------------------------------------------------13
3.3.11.4 Parma wood------------------------------------------------------------------------------------13
3.3.11.5 Conductor material---------------------------------------------------------------------------14
3.3.11.6 Insulating tapes-------------------------------------------------------------------------------14
3.3.11.7 Bakelite----------------------------------------------------------------------------------------14
3.3.11.8 Gasket------------------------------------------------------------------------------------------14
3.4 Transformation Ratio ----------------------------------------------------------------------------------15
3.5 Voltage regulation of transformer--------------------------------------------------------------------15
3.6 Efficiency of transformer -----------------------------------------------------------------------------15
Chapter-4
Power Distribution
4.1 Introduction----------------------------------------------------------------------------------------------16
4.2 Power Distribution--------------------------------------------------------------------------------------17
4.3 Substations-----------------------------------------------------------------------------------------------17
4.3.1 Classification of sub-station-------------------------------------------------------------------------17
4.3.1.1 Indoor Sub-station ---------------------------------------------------------------------------------18
4.3.1.2 Transformer Sub-stations -------------------------------------------------------------------------18
4.3.2 Requirements of Installing a Substation-----------------------------------------------------------18
4.3.3 Equipment of the Substation------------------------------------------------------------------------19
4.3.3.1 Bus-bar ---------------------------------------------------------------------------------------------19
4.3.3.1.1 Single bus-bar system ---------------------------------------------------------------------------19

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4.3.3.1.2 Duplicate bus-bar system -----------------------------------------------------------------------20
4.3.3.1.3 Materials of bus-bars ----------------------------------------------------------------------------20
4.3.3.2 Insulators--------------------------------------------------------------------------------------------20
4.3.3.3 Isolating Switches----------------------------------------------------------------------------------21
4.3.3.4 Circuit Breaker or Auto Circuit Recloser-------------------------------------------------------21
4.3.3.5 Power Transformers--------------------------------------------------------------------------------21
4.3.3.6 Instrument Transformation-----------------------------------------------------------------------22
4.3.3.6.1 Current Transformer (C.T.) --------------------------------------------------------------------22
4.3.3.6.2 Voltage Transformer (P.T.) --------------------------------------------------------------------22
4.3.3.7 Fuse---------------------------------------------------------------------------------------------------22
4.3.3.7.1 Fuse characteristic -------------------------------------------------------------------------------23
4.3.3.7.2 Properties of reliable fuse -----------------------------------------------------------------------23
4.3.3.8 Optimum component protection -----------------------------------------------------------------23
4.3.3.9 Earthling switch ------------------------------------------------------------------------------------23
4.3.3.10 Neutral grounding (Earthing) -------------------------------------------------------------------23
4.3.3.11 Types of grounding -------------------------------------------------------------------------------24
4.3.3.12 Power factor ---------------------------------------------------------------------------------------24
4.3.3.12.1 Methods of power factor improvement ------------------------------------------------------24
4.3.3.12.1.1 Static capacitor -------------------------------------------------------------------------------24
4.3.3.12.1.2 Synchronous condenser ---------------------------------------------------------------------25
4.3.3.12.1.3 Phase advancers ------------------------------------------------------------------------------25
4.3.3.12.1.4 Calculating power factor --------------------------------------------------------------------26
4.3.3.12.1.5 Power factor correction ---------------------------------------------------------------------26
4.3.3.12.1.5.1 Power factor correction has the following advantages -------------------------------27
4.3.3.12.1.5.2 The advantages of power factors improvement ---------------------------------------27
4.3.3.12.1.6 Cost benefits of power factors improvement ---------------------------------------------27
4.4 Substation of Comilla Palli Bidyut Samity-1--------------------------------------------------------28
4.4.1 Circuit Breaker----------------------------------------------------------------------------------------29
4.4.2 Lightning Arrester------------------------------------------------------------------------------------29
4.4.3 CT and PT---------------------------------------------------------------------------------------------29
4.4.4 Fuse-----------------------------------------------------------------------------------------------------29
4.4.5 Metering------------------------------------------------------------------------------------------------29
4.4.6 Isolator--------------------------------------------------------------------------------------------------29
4.4.7 Power Transformer-----------------------------------------------------------------------------------20
4.4.8 Voltage Regulator-------------------------------------------------------------------------------------32
4.4.9 Feeder---------------------------------------------------------------------------------------------------33
4.4.10 Distribution-------------------------------------------------------------------------------------------33

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Chapter 5
Maintenance
5.1 Substation Maintenance--------------------------------------------------------------------------------34
5.2 Line Maintenance---------------------------------------------------------------------------------------34
5.3 Transformer Maintenance------------------------------------------------------------------------------34
5.3.1 Single phase transformer-----------------------------------------------------------------------------35
5.3.2 Power transformer------------------------------------------------------------------------------------39
Chapter-6
Transformer Test
6.1 Testing ---------------------------------------------------------------------------------------------------40
6.1.1 Megger test (Insulation resistance test) ------------------------------------------------------------40
6.1.2 Winding resistance test ------------------------------------------------------------------------------41
6.1.3 Ratio Test ----------------------------------------------------------------------------------------------42
6.1.4 No-load loss test --------------------------------------------------------------------------------------44
6.1.5 Full load loss test -------------------------------------------------------------------------------------46
6.1.6 Impedance test ----------------------------------------------------------------------------------------47
Chapter-7
Supplementary Part
Recommendation --------------------------------------------------------------------------------------------48
Conclusion ---------------------------------------------------------------------------------------------------48
Appendix -----------------------------------------------------------------------------------------------------49
References ----------------------------------------------------------------------------------------------------51
Topics Pages No
List of Table
Table No: 2.1 main features of rural electrification in Bangladesh-------------------------------------4
Table No: 2.2 Tariff-wise Consumer No-------------------------------------------------------------------6
Table No: 2.3 Disconnected Consumer No----------------------------------------------------------------6
List of Figure
Figure3.1: Transformer -------------------------------------------------------------------------------------8
Figure3.3.1: Transformer Tank------------------------------------------------------------------------------9
Figure3.3.2: Conservator tank-------------------------------------------------------------------------------9
Figure3.3.3: Transformer Core-----------------------------------------------------------------------------10
Figure3.3.4: Transformer winding-------------------------------------------------------------------------10
Figure3.3.5: Silica Gel--------------------------------------------------------------------------------------10
Figure3.3.6: Buchholz relay--------------------------------------------------------------------------------11
Figure3.37: Radiator-----------------------------------------------------------------------------------------11
Figure3.3.8: Transformer Bushing------------------------------------------------------------------------11

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Figure3.3.9: Transformer Tap------------------------------------------------------------------------------12
Figure3.3.10: Transformer oil Tank-----------------------------------------------------------------------13
Figure3.3.11: Insulating tapes------------------------------------------------------------------------------14
Figure3.3.12: Sealing / Gasket-----------------------------------------------------------------------------14
Figure4.1: Insulator------------------------------------------------------------------------------------------20
Figure4.2: Auto Circuit Recloser--------------------------------------------------------------------------21
Figure 4.3: Power factor improvement by static capacitor---------------------------------------------25
Figure4.4: Comilla PBS-1 Single Line Diagram--------------------------------------------------------28
Figure4.5: Meter in Comilla PBS-1 Substation---------------------------------------------------------29
Figure4.6: Power Transformer in Comilla PBS-1------------------------------------------------------30
Figure4.7: Power Transformer name plate---------------------------------------------------------------31
Figure4.8: Voltage regulator-------------------------------------------------------------------------------32
Figure4.9: Feeder control panel and display-------------------------------------------------------------33
Figure5.1: Transformer primary coil wire----------------------------------------------------------------35
Figure5.2: Coil binding-------------------------------------------------------------------------------------36
Figure5.3: complete coil binding--------------------------------------------------------------------------36
Figure5.4: core binding of transformer-------------------------------------------------------------------37
Figure5.5: after coil and core binding in the transformer----------------------------------------------37
Figure5.6: After repair complete single phase transformer--------------------------------------------38
Figure5.7: power transformer without tank--------------------------------------------------------------39
Figure5.8: power transformer coil binding in Savar central workshop-------------------------------39
Figure 6.1.1: Megger meter---------------------------------------------------------------------------------41
Figure6.1.2: Multimeter display show value-------------------------------------------------------------41
Fig 6.1.3: Multi-meter connection & output result for Winding resistance test---------------------41
Fig 6.1.4: Winding resistance test result form for 200KVA transformer----------------------------42
Figure6.1.4: HT terminal connected with 3 phase supply----------------------------------------------42
Figure 6.1.5: 3 phase voltage supply regulator----------------------------------------------------------43
Figure6.1.6: Clamp Meter----------------------------------------------------------------------------------43
Figure6.1.7: No current is taking HT side----------------------------------------------------------------43
Fig 6.1.8: Turn ratio test result form for 200KVA Transformer--------------------------------------44
Figure 6.1.9: Measuring the no load current by clamp meter------------------------------------------45
Figure 6.1.10: No load loss test result form for 200KVA Transformer------------------------------45
Fig 6.1.11: LT Terminal is shorted with wire------------------------------------------------------------46
Fig 6.1.12: HT terminal is connected with 3 phase supply --------------------------------------------46

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Chapter-1
Introduction
1.1 Origin of the report:
This report on topic name is “Power Distribution, Operation and Maintenance of Comilla
Palli Bidyut Samity-1” is prepared by Kawsar Ahmed for the Bachelor of Science in Electrical
& Electronics Engineering program at the department of Electrical & Electronics Engineering,
under IUBAT-International University of Business Agriculture and Technology as an integral
part of the internship. He has done this practicum report based on power distribution, operation
and maintenance at Comilla Palli Bidyut Samity-1 under the instruction of Md Yousuf Ali,
Deputy General Manager (Technical) in Comilla Palli Bidyut Samity-1.
1.2 Objective Of the study:
1.2.1 Broad Objectives:
The main objectives are to extrovert my theoretical knowledge to the practical field with
adequate conceptualization and understanding how to operate a substation and maintenance of
the rural distribution network to meet the increasing demand of electricity, to minimize the load
shedding in the rural areas under Rural Electrification (RE) program and thus achieving
reliability of distribution system for greater satisfaction of consumers.
1.2.2 Specific Objectives:-
Achieve the knowledge of regarding my topics. Such as
Observation of rural distribution network
 About the system of REB
 About the system of Palli Bidyut Samity
 About substation
 About transformer
 Maintenance system of REB

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1.3 Scope:-
For preparing this report, I have studied vastly about the process of Electricity transmission and
distribution system, Transmission line, Substation, Transformer, Conductors and maintenance.
This will increase my electrical engineering knowledge about operation and maintenance as well
as help me learn more about more in Future. This report will, without any doubt, be very helpful
for my future life.
1.4 Background of the Study:-
I have studied about 4 years at IUBAT – International University of Business Agriculture and
Technology Department of Electrical and Electronics Engineering. I have learned theoretical
about my subject. So I have applied my knowledge in the practical life.
1.5 Methodology:-
I did visited Savar grid substation and their own distribution station to observe the distribution
system, also visited Savar central workshop for maintenance. For protection purpose REB uses
mostly vacuum circuit breaker and for higher safety SF6 circuit breaker on their substations they
also use auto circuit recloser. I also learn about bus bar arrangement, staking design and
supervision and other electrical equipment. I also observe the departments of REB, it has five
individual departments. They are Nipor Section, Engineering Section, Member Service, Finance
Section and Consultant Service. I observed the revenue collection of the month September which
was done by the Finance Department. During this time I also learn about load shedding and how
they maintain the schedule of load shedding. This observation helps me to complete my
internship and gives me a practical knowledge on electricity generation and distribution.
1.6 Limitations:-
During practicum in Comilla Palli Bidyut Samity-1, a huge amount of information has been
accumulated from the company. The employees were very much cooperative. They helped me a
lot, thus it was very much easy to understand most of the technical terms. But as it is a
commercial organization, sometimes the employees were busy with their official work.
Therefore at all time it was not convenient to communicate with them because of their hard
work. Yet they tried to help me as much as possible by them.

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Chapter-02
Organizational Overview
2.1 Introduction:
Internship is the part of the Bachelor degree in Electrical and Electronic department of IUBAT-
International University of Business Agriculture and Technology. I get the theoretical and
practical knowledge from Internship which is important for my career. I had completed my
degree major area in Power system, Power Station, Switchgear. For this reason I have done my
internship in Comilla Palli Bidyut Samity-1 under Bangladesh Rural Electrification Board which
is the leading electricity distribution company in rural and industrial area in Bangladesh. Comilla
Palli Bidyut Samity-1 has ensured me, the best support for developing the practical knowledge
with the help of the theoretical knowledge. In my internship I have learned how power plant
generate power, what is the distribution system. The objective of this internship report is it will
be the important source for the people, who want to do thesis in power sector or power
distribution system.
2.2 Company profile:
The Rural Electrification Board of Bangladesh has been providing service to rural member
consumers for over 38 years. Continued support from the Government of Bangladesh, the donor
community, consulting partners, and member consumers will help this program continue to
expand, providing the gift of electricity to millions more Bangladeshi households, businesses,
and industries.
Rural Electrification Board Act, 2013 has been established instead of Rural Electrification Board
Ordinance, 1977 (Ordinance No. LI of 1977) and the name of Board is Bangladesh Rural
Electrification Board which was responsible for electrifying rural Bangladesh. Since its
inception, the purpose of the program has been to use electricity as a means of creating
opportunities for improving agricultural production and enhancing socio-economic development
in rural areas, whereby there would be improvements in the standard of living and quality of life
for the rural people.
Today there are 77 operating rural electric cooperatives called Palli Bidyuit Samity (PBS), which
bring service to approximately 1,38,37,163 new connection being made and more than 2,91,534
km of line has been constructed.

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The followings are the main features of rural electrification in Bangladesh as on January, 2016.
Name Number
Number of PBSs organized 77
Number of PBSs operating commercially 77
Number of district under the program 61
Number of Up-Zillas under the program 453
Number of villages electrified 56,302
Total distribution line constructed 2,94,897 Km
Total distribution line energized 2,80,686 Km
Total 33/11 KV sub-stations constructed and commissioned 721 (548 Constructed
by BREB, 85
Constructed by
Private, 88 taken over
from
PDB/DPDC/OTHERS)
Installed Capacity of Sub-stations 7598 MVA
Total number of consumers 1,41,98,117
Total number of irrigation pumps connected 2,37,442
System Loss 12.52% (cumulative), 09.88% (Jan'2016)
Table No: 2.1
REB sets forth the following major objectives in implementing the rural electrification program:
 Ensure peoples participation in policy formulation in a democratic way.
 Provide reliable and sustainable electricity to the rural people at affordable price.
 Improve economic condition of the rural people by using electricity in agriculture,
cottage and agro based industry.
 Improve living condition of rural peoples.
 Bring about entire rural Bangladesh under RE program or an area coverage basis.
2.3 Comilla Palli Bidyut Samity-1:
Since its inception in 1981, Comilla Palli Bidyut Samity-1 is playing a vital role in Agricultural,
Industrial and Socio-Economic Development of Comilla District. The Rural Electrification
Program conducted by Comilla Palli Bidyut Samity-1 has acted a leap-forward in the
development of socio-economic structure of rural areas in Comilla District as well as entire
Bangladesh. It has significant and sustained impact on agricultural growth, industrialization and
business & commercial activities in the rural areas. It is a consumer owned entity organized on
the basic principles of Co-operative for distribution of electric power to its members and operates
on No Loss - No Profit basis for the mutual benefits of all its Members.

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2.4 Organizational chart of Comilla Palli Bidyut Samityof Comilla Palli Bidyut Samity-1:

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2.5 Consumer Information of Comilla PBS-1:
2.5.1 Tariff-wise Consumer No (As on December 2014):
Tariff Consumer
No.
Percentage
(%)
Cunsumer
Connected in Current
Month
Billed Consumer
Domestic 56500 72.73 206 52362
Commercial 6778 8.72 7 3146
Charitable Institute 1542 1.98 3 1468
Irrigation 6778 8.72 7 3146
General Power 6778 8.72 7 3146
Large Power 2 0 0 2
Street Light 6 0 0 3
Table No: 2.2
2.5.2 Disconnected Consumer No (As on December 2014):
Tariff Consumer
No.
Percentage
(%)
Arrear Amount (Tk) DNP List No.
Domestic 4131 47.12 1381 1200
Commercial 400 42.43 927 400
Charitable Institute 150 1.71 79 51
Irrigation 400 42.43 927 400
General Power 400 42.43 927 400
Large Power 0 0 0 0
Street Light 3 50 17 0
Table No: 2.3

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Chapter-3
Transformer
3.1 Introduction of Transformer
A Transformer is a device that transfers electrical energy from one circuit to another by
electromagnetic induction (transformer action). The electrical energy is always transferred
without a change in frequency, but may involve changes in magnitudes of voltage and current.
Because a transformer works on the principle of electromagnetic induction, it must be used with
an input source voltage that varies in amplitude. There are many types of power that fit this
description; for ease of explanation and understanding, transformer action will be explained
using an ac voltage as the input source.
3.2 Classification of Transformer
Transformers are constructed so that their characteristics match the application for which they
are intended. The differences in construction may involve the size of the windings or the
relationship between the primary and secondary windings. Transformer types are also selected
by the function the transformer serves in a circuit, such as an isolation transformer. Transformers
can be constructed so that they are designed to perform a specific function. A basic
understanding of the various types of transformers is necessary to understand the role
transformers play in today’s nuclear facilities. Trade Engineering are manufacturing different
type of transformer but most of them power and distribution transformer giving as below:
a. 2000KVA ~ 28000KVA 33/11KV Power Transformer
b. 5KVA ~ 3000KVA 11/0.415KV Distribution Transformer
c. 50KVA ~ 750 KVA 33/0.415KV Auxiliary Transformers
The applications of each of the following types of transformers:
1. According to Procedure:
i. Step up transformer
ii. Step down transformer
2. According to construction of Core:
i. Core type transformer
ii. Shell type transformer
3. According to Application of Transformer:

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i. Power transformer
ii. Distribution transformer
iii. Auto Transformer
iv. Instrument transformer
Instrument transformer is two types:
a. Current transformer (C.T)
b. Potential transformer (P.T)
4. According to Frequency:
i. Audio frequency transformer
ii. Radio frequency transformer
5. According to Number of phase:
i. Single phase transformer
ii. Poly phase transformer
3.3 Parts of the transformer
1. Transformer tank
2. Conservator
3. Transformer Core
4. Coil or winding
5. Bushing
6. Radiator
7. Breather
8. Silica Gel
9. Transformer oil
10. Oil level indicator
11. Temperature gauge
12. Thermo-meter
13. Buchholz relay
14. Drain coke
15. Earth point
Figure3.1: Transformer

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3.3.1 Transformer Tank
The transformer tank shall be fabricated from steel and shall be of robust construction. Care
should be taken at the manufacturing stage so as not to have leaks during transportation or when
the transformer is continuously operated at rated power.
Transformer tank envelop the active part, filled with
completely with oil. The body has no contact with the
active part. The paint at the inner side is oil resistive and
the outer paint is anti-corrosion. Even it is just a container
but require much consideration during design. With the
exception of radiator elements, all external joints shall be
seam welded. There shall be only one vertical seam weld
for the fin radiator and the other three vertical corner
edges of the transformer shall be formed by bending.
Corner ribs shall be avoided for the fin radiator. The
bearing surface of the tank to which bushings are
clamped shall be substantially flat. All matching faces of
joints shall be made oil tight and finished with a smooth
surface to ensure that the casketing materials make a satisfactory joint. Flanges and covers of
tanks shall be of sufficient thickness to prevent any depression occurring, which would retain
water around the bolts. The horizontal edges of the cover plate shall be bent over the tank flange
to facilitate water dripping out of the tank. The bent collar width shall be about 10mm to 15mm.
All the nut and bolts used shall be hot dip galvanized and spaced at sufficiently close intervals to
avoid buckling of either flange or covers and shall provide reasonably uniform compression of
the gasket. Each transformer shall be provided with a minimum of two closed lifting lugs. The
minimum diameter of the hole or width of the slot shall be 25 mm. The two lifting lugs shall be
located such that there would be a minimum of 50 mm between the lifting chain and the nearest
part of the bushings. All transformers shall be suitable for outdoor mounting on pole or plinth
platforms and shall have four mounting lugs with 12 mm diameter holes suitable for bolting the
transformer to the platform. Bolt hole spacing shall be as specified by the purchaser to suit
mounting requirements.
3.3.2 Conservator tank
Conservator tank is an expansion vessel party filled with
oil and connected to transformer tank. Its function is to
ensure that the transformer tank is completely filled with
oil every time. The system allows the transformer tank to
remain full despite contraction or expansion of the fluid
due to temperature change.
Figure3.3.1: Transformer Tank
Figure3.3.2: Conservator tank

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3.3.3 Transformer Core
In an electrical power transformer, there are
primary, secondary and may be tertiary
windings. The performance of a transformer
mainly depends upon the flux linkages
between these windings. For efficient flux
linking between these windings, one low
reluctance magnetic path common to all
windings should be provided in the
transformer. This low reluctance magnetic
path in transformer is known as core of
transformer. Transformer normally use
laminated silicon steel core for reduce
hysteresis loss and eddy current loss.
Figure3.3.3: Transformer Core
3.3.4 Transformer Coil or Winding
Transformer coil or winding two types one
is primary winding another is secondary
winding or H.T winding and L.T winding.
H.T winding wire is thin than L.T winding.
Transformer winding wire is laminated by
super enamel insulation
Figure3.3.4: Transformer winding
3.3.5 Silica Gel
Silica gel is used in conservator tank to
absorb moisture and remove dust/foreign
impurities from air sucked in. Whenever
transformer is loaded or unloaded, oil
temperature inside the tank rises or falls,
air volume inside the tank changes
resulting in pushing out or sucking in the
air.
Figure3.3.5: Silica Gel

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3.3.6 Buckholz Relay
Buchholz relay is a type of oil and gas
actuated protection relay universally used on
all oil immersed transformers having rating
more than 500 KVA. Buchholz relay is not
provided in relays having rating below 500
KVA from the point of view of economic
considerations.
Figure3.3.6: Buchholz relay
3.3.7 Radiator
Radiators are used in a transformer to cool
the transformer oil through natural air or
forced air flowing in these radiator fins. As
the transformer oil temperature goes down
due to cooling it goes to the transformer tank
from bottom, cool the winding and gets
heated, and then return to the radiator for next
cooling.
3.3.8 Bushing
The bushing is a hollow insulator, allowing a
conductor to pass along its center and connect
at both ends to other equipment. All bushings
shall be of porcelain clad, of the highest
quality. Cree page distance of the bushing
insulator shall be 290mm for 12kV
transformer and 720 mm for 36kV
transformers. The inside of the bushing may
contain paper insulation and the bushing is
often filled with oil to provide additional
insulation.
Figure3.3.8: Transformer Bushing

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3.3.9 Transformer Tap
A transformer tapes connection points along
a transformer winding that allow a certain
number of turns to be selected. This means, a
transformer with a variable turn ratio is
produced, enabling voltage regulation of the
output. The tap selection is made via a tap
changer mechanism.
Figure3.3.9: Transformer Tap
3.3.10 Insulation and Impregnation
The quality of transformer and especially the dielectric strength response of its insulation depend
on the treatment of its active part. TSTL transformers the treatment consists in an alternation of
hot air heating and prolonged vacuum so as to remove all moisture from the insulating materials.
Pre compressed press board spacers used in the active part provide a rigid insulation structure
with low partial discharge levels. A clean, dust free environment ensures the highest standards in
quality. By using automated oil filling and processing system and by virtue of leak proof joints in
the transformers, there is no oil spillage. The oil used for impregnation complies with BS-171
and every consignment received is tested before being pumped into storage tanks.
3.3.11 Insulation material
Apart from main raw materials like ergo, ms, insulating materials are also employed for building
up a transformer. The following are some of the insulating materials used in transformer.
1. Transformer oil
2. Electrical grade paper
3. Press board
4. Parma wood
5. Conductor material
6. Insulating tapes
7. Bakelite
3.3.11.1 Transformer Oil
Insulating oil forms a very significant part in the transformer insulation system and has the
important functions of acting as “Electrical insulation” as well as a ‘coolant’ dissipates heat

P a g e | 2 4
losses. The basic raw material for the
production of transformer oil is crude
petroleum. Proceed transformer oil
will be received by us to use in the
transformer after filtering.
Breakdown voltage strength is the
basic Parameter of the transformer
oil. It serves to indicate the presence
of containing agents like moisture
carbon particles etc. breakdown
voltage should not be less than 50 KV
after filtration. Figure3.3.10: Transformer oil Tank
3.3.11.2 Electrical grade paper
Paper is made from cotton, straw and wooden pulp. Paper is generally used as inner layer
insulation in windings, covering on conductors, paper tubes for terminal load insulation etc.
3.3.11.3 Press board
Pressboard is widely used insulating material for making a variety of components used in
electrical and mechanical design of a transformer like paper. Pressboard is also made from wood
pulp cotton, jute, ham etc.
Generally pressboards are of three grades
i. Grade 3 pre compressed
ii. Grade 3 normal
iii. Grade K
Pressboard can be converted into any required shaped as Runners, spacers, support blocks,
cleats, phase barriers, cylinders etc.
3.3.11.4 Parma wood
Parma wood is used in the areas which require higher mechanical and lower electrical strength.
Parma wood is used for making a variety of insulation components like coil clamping ring, cleat,
support, core and yoke clamp, bolt and nut etc. Haldu and Teak wood seasoned planks are also
used as a filter material between core limbs and enveloping coils and as yoke step filters.

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3.3.11.5 Conductor material
The following types of conductors are used for making different types of coils.
a) Double paper covered rectangular strip.
b) Double paper covered round wire.
c) Super enameled rectangular strip
d) Super enameled round wire.
3.3.11.6 Insulating tapes
This is used in winding coils to maintain the
phase after the former is removed. This is used
on core limbs to bind all the laminations before
inserting LV winding.
Figure3.3.11: Insulating tapes
3.3.11.7 Bakelite
This is used for Ducts, Tap Link Boards, cleats, common rings etc.
3.3.11.8 Sealing / Gasket
The transformers shall be of the hermetically sealed type and provided with a satisfactory lid
sealing gaskets. The gasket shall of the good
quality to maintain the sealing effect through
its life span and shall prevent seeping of oil
due to ageing and extreme operating
temperature. Gaskets provided with the
transformers shall be suitable for making oil
tight joints, and there would be no
deleterious effects on either gaskets or oil
when the gaskets are continuously in contact
with hot oil. No gaskets shall be used in
which the material of the gasket is mounted
on a textile backing. Exterior gaskets shall be
of rubberized cork material, weatherproof
and shall not be affected by strong sunlight. Figure3.3.12: Sealing / Gasket

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3.4 Transformation Ratio
Voltage ratio
Ep/EP = 4.44Np£Φm ∗ 10/4.44Ns£Φm ∗ 10
Or
Ep/Ep = Np/Ns
Current ratio
Ep Ip = Es Is Or Is/Is = Ep/Es
Turns ratio
= = a
(a=Transformation Ratio)
3.5 Voltage regulation of transformer
The difference between the output voltage at no load and the output voltage at rated load, divided
by the output voltage at rated load, is called the voltage regulation of the transformer.
Mathematically,
=
−
3.6 Efficiency of transformer
The output of a transformer is slightly less than the input because of the losses in the windings
and the iron core. The ratio of the two, expressed as a percentage in the efficiency of the
transformer. The output and input are expressed in watts or kilo-watts.
=

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Chapter-4
Power Distribution
4.1 Introduction
This Chapter will focus on the distribution side. Substation is used for distribution purpose. To
establish a substation, there are some important points which have to be maintained. Different
types of substations are used to meet the different requirements. Normally step-up substation is
used at end of the generator side. Circuit breaker is protective element used in substation to avoid
the abnormal situation. Arrester and earthing is also used to avoid the overcharging situation.
Current transformer, potential transformer and bus bar arrangement are the common feature of
distribution substation. Typically, transformer is used to ensure the electricity supply in both end
of the substation and the household.

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4.2 Power Distribution
Electricity distribution is the final stage in the delivery of electricity to end users. A distribution
system's network carries electricity from the transmission system and delivers it to consumers.
Typically, the network would include medium-voltage (less than 50 kV) power lines, electrical
substations and pole-mounted transformers, low-voltage (less than 1 kV) distribution wiring and
sometimes electricity meters.
The same phenomenon is applicable for REB. At first power come to the Grid Station (400 KV
or 230KV)from National Grid, then power transmitted to the substation (400/230 KV) or
230/132KV then 123/33KV. From substation power is transmitted to the bus bar (33/11 KV) and
then to the consumer through transformer.
4.3 Substations
The assembly of apparatus used to change same characteristics of electric power supply e.g.
voltage, ac to dc; frequency etc is called a substation.
4.3.1 Classification of sub-station
There are several ways of classifying sub-stations. However, the two most important ways of
classy- flying they are according to (1) service requirement and (2) constructional features.
According to service requirement: A sub-station may be called upon to change voltage level or
improve power factor or convert a.c. power into d.c. power etc. According to the service
requirement, sub-stations may be classified into:
1. Transformer sub-station
2. Switching sub-stations
3. Power factor correction sub-stations
4. Frequency changer sub-stations
5. Converting sub-stations
6. Industrial sub-stations
According to constructional features: A sub-station has many components (e.g. circuit
breakers, switches, fuses, instruments etc.) which must be housed properly to ensure continuous
and reliable service. According to constructional features, the sub-stations are classified as:
i. Indoor sub-station
ii. Outdoor sub-station
iii. Underground sub-station
iv. Pole-mounted sub-stations

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4.3.1.1 Indoor Sub-station
For voltage up to 11kv the equipment of the substation is installed indoor because of economic
consideration .However when the atmosphere is contain with impurities these substation can be
erected for voltage up to 440 v
4.3.1.2 Transformer Sub-stations
The majority of the sub-stations in the power system are concerned with the changing of voltage
level of electric supply. These are known as transformer sub-stations because transformer is the
main component employed to change the voltage level. Depending upon the purpose served,
transformer sub-stations may be classified into –
1) Step-up sub-station
2) Grid sub-station
3) Secondary sub-station
4) Distribution sub-station
Step-up Substation: Step-up substation is being situated at end of the generator side.
Grid Substation: From the step-up substation, electric power at 400KV, 220KV or 132KV
etc. is transmitted by 3-phase. 3 wire overhead system to the outskirts of the city. Here electric
power is received by the primary grid substation which reduces the voltage level to 66KVor 33
KV or any another type for secondary transmission. Generally grid substation is of outdoor type.
Secondary Substation: From the grid substation, electric power is transmitted at 66 KV or 33
KV or another type by 3-phase, 3-wire system to various secondary substations located at the
strategic points in the city. At a secondary substation the voltage is further stepped down to 11
KV. The 11 KV lines run along the important road sides of the city. It may be noted that big
consumers are generally supplied power at 11 KV for further handling with their own
substations. The secondary type substations are also called outdoor type substations.
Distribution Substation: The electric power from 11 KV lines is delivered to distribution
substations. These substations are located near the consumer’s localities and to 400V or 230V. 3
phase or 4 wire for supplying to the consumers. The voltage between any two phases is 400V
and the voltage between any phase and neutral is 230V.
4.3.2 Requirements of Installing a Substation:
i. It should be located at a proper site. As far as possible, it should be located at the centre
of gravity of load.
ii. It should provide safe and reliable arrangement. For safety, consideration must be given
to the maintenance of regulation clearances, facilities for carrying out repairs and

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maintenance, abnormal occurrences such as possibility of explosion or fire etc. For
reliability, consideration must be given for good design and construction, the provision of
suitable protective gear etc.
iii. It should be easily operated and maintained
iv. It should involve minimum capital cost.
4.3.3 Equipment of the Substation:
The equipments required for a substation which depends on the type of the substation and service
requirements. However a transformer has the following equipments. These equipments are
described in the given below:
4.3.3.1 Bus-bar
When a number of generator or feeders operating at the same voltage have to be directly
connected electrically, bus-bar are used as the common electrical component. Bus-bars are
copper rods or thin walled tubes and operated at constant voltage. Thus electrical bus bar is the
collector of electrical energy from one location.
The selection of any bus bar system depends upon the following-
1. Amount of flexibility required in operation
2. Immunity from total shut-down
3. Initial cost of the installation
4. Load handled by the bus-bar
Classification of bus-bar
1. Single bus bar system.
2. Sectionalized bus bar.
3. Duplicate bus bar.
4. Ring bus bar.
5. One and half breaker arrangement
4.3.3.1.1 Single bus-bar system
As the name suggests, it consists of a single bus-bar and all the incoming and outgoing lines are
connected to it. The chief advantages of this type of arrangement are low initial cost, less

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Figure4.1: Insulator
maintenance and simple operation. However, the principal disadvantage of single bus-bar system
is that if repair is to be done on the bus-bar or a fault occurs on the bus,
4.3.3.1.2 Duplicate bus-bar system
This system consists of two bus-bars, a “main” bus-bar and a “spare” bus-bar. Each bus-bar has
the capacity to take up the entire sub-station load. The incoming and outgoing lines can be
connected to either bus-bar with the help of a bus-bar coupler which consists of a circuit breaker
and isolators. Ordinarily, the incoming and outgoing lines remain connected to the main bus-bar.
However, in case of repair of main bus-bar or fault occurring on it, the continuity of supply to the
circuit can be maintained by transferring it to the spare bus-bar. For voltages exceed- in 33kV,
duplicate bus-bar system is frequently used.
4.3.3.1.3 Materials of bus-bars
Copper and aluminum are used for bus bars. Copper being scare and costly, aluminum is being
increasingly used for bus bars. The material used for bus bars should have low resistivity, higher
softening temperature, good mechanical properties and low cost. Now aluminum is being
increasingly used for various switchgear applications. While using aluminum for bus-bars, the
difficulties arise due to following aspects:
1. Higher resistivity hence associated problems of temperature rise.
2. Lower tensile strength than copper
3. Lower thermal conductivity than copper.
4. Higher coefficient of linear expansion than copper.
5. Higher joint resistance and associated problems about jointing
6. Special welding techniques are necessary.
4.3.3.2 Insulators
We know that the insulator serves two purposes one
is they support the conductors (or bus-bars) and
confine the current to the conductors. In my
internship I have seen porcelain insulator which is the
most commonly used material for the manufacture of
insulators is porcelain. There are several types of
insulators (e.g. pin type, suspension type, post
insulator etc.). And their use in the substation will
depend upon the service requirement. For example,
post insulator is used for bus-bars. A post insulator
consists of a porcelain body, cast iron cap and flanged
cast iron base. The hole in the cap is threaded so that
bus bar can be directly bolted to the cap.

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4.3.3.3 Isolating Switches
In substation, it is often desired to disconnect a part of the system for general maintenance and
repairs. This is accomplishing by an isolating switch or isolator. An isolator is essentially a knife
switch which is designed to open a circuit under no load. In other words, isolator switches are
operated only when the lines in which they are connected carry no current.
4.3.3.4 Circuit Breaker or Auto Circuit Recloser
A circuit breaker is equipment which can open or close a circuit under normal operation as well
as fault condition. In Comilla PBS-
1 substation, all the circuit breaker
is auto circuit recloser which
contains SF6 gas. In closed
position of the breaker, the contacts
remain surrounded by SF6 gas and
the pressure of the gas is 2.8
kg/cm². When the breaker operates
the pressure of the gas is goes to
14kg/cm². We know that the high
pressure flow of SF6 can absorbs
the free electron easily. During my
internship I know that the pressure
of the SF6 circuit breaker are Figure4.2: Auto Circuit Recloser
2.8 kg/cm² in normal condition of the circuit breaker and the abnormal condition this pressure
rise to the 14kg/cm². If the pressure goes down then the circuit breaker do not able to do proper
work and it may be risky for the whole system and also it is dangerous to system protection. This
kind of circuit breaker is costly because of the high cost of the SF6 gas. But it is environment
friendly because it cannot deposit the high amount of carbon. And it also low maintenances cost
and the light foundation requirement. Over all in this grid substation has ensure that the
protection is valid and it is user friendly.
4.3.3.5 Power Transformers
A power transformer is used in a substation to step- up or step down the voltage. It is important
part for a substation. I have also mentioned that power transformer is required for any type of
substation. Except at the power station, all the subsequent substation use step- down
transformers to gradually reduce the voltage of electric supply and finally deliver it at utilization
voltage. The modern practice is to use 3-phase transformers in substation, although 3 single
phase bank of transformers can also be used. The use of 3-phase transformer permits two
advantages. Firstly, only one 3 phase load tap changing mechanism can be used. Secondly, its
installation is much simpler that the three single phase transformers. I know from my internship

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the power transformer is gradually installed upon lengths of rails fixed on concrete slabs having
foundation 1 to 1.5 m deep. For rating up to 10 MVA, naturally cooled, and also forced air
immersed transformers are used. For higher ratings, the transformers are generally normal and
forced air cooled.
4.3.3.6 Instrument Transformation
In the grid substation, the main lines in sub-station operates at high voltage and carry current of
thousand of amperes which we have seen. The measuring instruments and protective devices are
designed for low voltage (generally 110V) and currents (about 5A). Therefore, they will not
work satisfactorily if mounted directly on the power lines. This difficulty is overcome by
installing instrument transformers on the power lines. The function of these instruments of these
instrument transformers is to transfer voltage or currents in the power lines to values which are
convenient for the operation of measuring instruments and relays. There are two types of
instrument transformation viz.
1. Current Transformer (C.T)
2. Potential Transformer (P.T)
4.3.3.6.1 Current Transformer (C.T.)
A current transformer in essentially a step-up transformer which steps down the current to a
known ratio. The primary of this transformer consists of one or more turns of fine wire and
provides for the measuring instruments and relays a current which is a constant fraction of the
current in the line. Suppose in the Comilla PBS-1 substation, a current transformer rated at 100:5
A is connected in the line to measure current. If the current in the line is 100 A, then current in
the secondary will be 5A. Similarly, if current in the line is 50A, then secondary of C.T. will
have a current of 2.5 A. Thus the C.T. under consideration will step down the line current by a
factor of 20.
4.3.3.6.2 Voltage Transformer (P.T.)
It is essentially a step down the voltage to a known ratio. The primary of this transformer
consists of a large number of turns of fine wire connected across the line. The secondary winding
consists of a few turns and provides for measuring instruments and relays a voltage which is a
known fraction of the line voltage. Suppose in the Comilla PBS-1 substation, a potential
transformer is rated at 132KV/33KV is connected to a power line. If line voltage is 132KV, then
voltage across the secondary will be 33KV.
4.3.3.7 Fuse
A fuse is a short pitch of metal, inserted in the circuit, which melts when excessive current flows
thought it i.e. Fuse is a simplest current interrupting devices for protection from excessive

P a g e | 3 4
current. It is used for overload and or short circuit protection in medium voltage (into 650) and
low voltage (up to 400v) installations
4.3.3.7.1 Fuse characteristic
1. Low melting point.
2. High conductivity.
3. Least deterioration due to oxidation.
4. It carries the normal current without overheating.
4.3.3.7.2 Properties of reliable fuse
It must be remembered that fuse wire is always connected to the line wire. Fuse must be of
correct value. For example, in a 15A circuit, the fuse wire used is thick and of 15A rating.
4.3.3.8 Optimum component protection
Fuses reduce short circuit (fault) currents that flow to a low value by "current limitation". There
is no need for complex short circuit calculations and no concerns about costly future upgrades
due to system expansion with increased fault currents. Their compact size offers low cost over-
current protection for the highest short circuit levels.
Safety: Fuses do not produce gas, flames, arcs or other materials when clearing any value of
over-current up to the highest level of short circuit. In addition, the speed of operation on high
short circuit currents limits significantly the flash hazard at the fault location.
Reliability: No moving parts to wear out or become contaminated by dust, oil or corrosion and
no nuisance tripping. If a fault occurs, the fuse immediately operates in its predetermined manner
or co-ordinates with other circuit components. The cause of the fault is then ascertained,
corrected and a new fuse fitted. Fuse replacement ensures protection is restored to its original
state of integrity. It should be stressed that the time taken for the replacement is very small in
relation to the fault correction.
Simple co-ordination: Standardized fuse characteristics and a high degree of current limitation
ensure that there is simple and effective co-ordination between fuses and with other devices.
4.3.3.9 Earthling switch
Earthing switch is connected between the line conductor and earth. Normally it is open. When
the line is disconnected, the earthing switch is closed so as to discharge the voltage trapped on
the line. Though the line is disconnected, there is some voltage on the line to which the
capacitance between line and earth is charged. This significant in high voltage system. Before
starting the maintenance work these voltages are discharged to earth by closing the earthing
switch.

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4.3.3.10 Neutral grounding (Earthing)
The three phase 50Hz AC power systems with neutral grounding at every voltage level are used
for generation, transmission, distribution and utilization. The neutral points (star points) of star
connected 3 phase winding of power transformers, generators, motors, earthing transformers are
connected to low resistance ground. Such a connection is called Neutral grounding
4.3.3.11 Types of grounding
1. Underground system: It is used no more. The neutral is not connected to earth also called
insulated neutral system. In Standard Group this system is used.
2. Solid Grounding: The neutral is directly connected to ground without any intentional
impedance between neutral and ground. The coefficient of earthing is less than 80% for such
systems.
3. Reactance Grounding: Reactance is connected between neutral and ground.
4. Resonant Grounding: an adjustable reactor of correctly selected value to compensate the
capacitive earth currents is connected between neutral and earth. The coil is called Peterson coil
or Arc suppression coil or earth fault neutralizer.
4.3.3.12 Power factor
The cosine of angle between voltage and current in and a c circuit is known as power factor.
4.3.3.12.1 Methods of power factor improvement
Normally, the power factor of the whole load on a large generating station is in the region of 0.8
to 0.9. However, sometimes it is lower in such cases It is generally desirable to take special steps
to improve the power factor. This can be achieved by the following equipments
a) Static capacitor
b) Synchronous condenser
c) Phase advancers
4.3.3.12.1.1 Static capacitor
The power factor can be improved by connecting capacitor in parallel with the equipment
operating at lagging power factor. The capacitor draws a leading current and partly or completely
neutralizes the lagging reactive component of load current. This raises the power factor of the
load. For three phase loads, the capacitor can be connected in delta or star as shown in fig. Static
capacitors are invariably used for power factor improvement in factories.

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4.3.3.12.1.2 Synchronous condenser
A synchronous motor takes a leading current when over excited and therefore, behaves as a
capacitor. And over excited synchronous motor running on no load is called synchronous
condenser. When such a machine is connected in parallel with the supply, it takes a leading
current which partly neutralizes the lagging reactive component of the load. Thus the power
factor is improved.
4.3.3.12.1.3 Phase advancers
Phase advancers are used to improve the power factor of induction motors. The low power factor
of an induction motor is due to the fact that its stator winding draws exciting current which lags
behind the supply voltage by 90°. If the exciting ampere turns can be provided from some other
a.c. source, then the stator winding will be relieved of exciting current and the power factor of
the motor can be improved. This job is accomplished by the phase advancer which is simply an
a.c. exciter. The phase advancer is mounted on the same shaped as the main motor and is
connected in the rotor circuit of the motor. It provides exciting ampere turn to the rotor circuit at
slip frequency. By providing more ampere turns then required, the induction motor can be make
to operate on leading power factor like an over excited synchronous motor.
The electrical energy is almost exclusively generated, transmitted and distributed in the form of
alternating current. Therefore the question of power factor immediately comes into picture. Most
of the loads are inductive in nature and hence have low lagging power factor. The low power
factor is highly undesirable as it causes an increase in current, resulting in additional losses of
active power in all the elements of power system from power station generator down to the
utilization devices. In order to ensure most favorable conditions for a supply system from
engineering and economical standpoint, it is important to have power factor as close to unity as
possible.
4.3.3.12.1.4 Calculating power factor
As was mentioned before, the angle of this “power triangle” graphically indicates the ratio
between the amount of dissipated (or consumed) power and the amount of absorbed/returned
power. It also happens to be the same angle as that of the circuit's impedance in polar form.
When expressed as a fraction, this ratio between true power and apparent power is called the
power factor for this circuit. Because true power and apparent power form the adjacent and
hypotenuse sides of a right triangle, respectively, the power factor ratio is also equal to the cosine
of that phase angle. Using values from the last example circuit:

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Power Factor =
True Power
Apparent Power
Power Factor =
119.365W
169.26VA
Power Factor = 0.705
45.152 = 0.705
4.3.3.12.1.5 Power factor correction
Power factor correction is the method to reduce the lagging power factor in inductive loads by
fixing a high value capacitor across the phase and neutral close to the load. When the Voltage
and Current are in phase with each other in an AC circuit, the energy from the source is fully
converted into another form to drive the load and in this case power factor is in unity. When the
power factor drops, the system becomes less efficient. As a rule a drop from unity to 0.9 in the
power factor increases the current requirement to 15% or more.
A power factor of 0.7% increases the power requirement to around 40%. This is much severe in
the case of inductive loads such as Motors, Refrigerators, Inverters etc. In these inductive loads,
current “lags” the voltage leading to “lagging power factor”. But opposite condition occurs if
current “leads” the voltage. This is called “leading power factor”. Power factor correction is the
method to reduce the lagging power factor in inductive loads by fixing a high value capacitor
across the phase and neutral close to the load. These capacitors have leading power factor so that
it will neutralize the lagging power factor of the load.
4.3.3.12.1.5.1 Power factor correction has the following advantages
a) Load becomes more efficient.
b) It prevents the wastage of energy due to heat generation.
c) Maintains voltage stability.
4.3.3.12.1.5.2 The advantages of power factors improvement
a) Reactive component of the network is reduced and so also the total current in the system from
the source to end.
b) Power losses are reduced in the system because of reduction in current.
c) Voltage level at the load end is increased.
d) KVA loading on the source generators as also on the transformers and lines up to the
capacitors reduces giving capacity relief. A high power factor can help in utilizing the full
capacity of your electrical system.

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4.4 Substation of Comilla Palli Bidyut Samity-1
Figure4.4: Comilla PBS-1 Single Line Diagram

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In figure 4.4 Comilla PBS-1 single line diagram firstly Comilla PBS gets power from Power
Grid Company of Bangladesh Limited (PGCB) and Summit Power Limited. PGCB and Summit
supply 33KV in the auto circuit recloser then substation modify it and distribute it 11KV.
4.4.1 Circuit Breaker
In Comilla PBS-1 use auto circuit recloser (ACR) instead of SF6 circuit breaker. The rating of
this ACR is 360 ampere and 33KV
In this substation use two ACR one in the beginning and other in the ending point of substation.
Both of them use for protection of the substation equipments though they use it as like switch.
4.4.2 Lightning Arrester
Lightning arrester use for protect from over voltage generally from thunder. Here lightning
arrester rating is 36KV.
4.4.3 CT and PT
Current Transformer (CT) and Potential Transformer (PT) use for measuring current and voltage
in high voltage and current. If we want to calculate higher voltage and current directly we will
need bigger measuring instrument which will be higher cost. For this reason we use CT and PT.
Here Current Transformer (CT) ratio is 600:5
Potential Transformer (PT) ratio is 6350:240
4.4.4 Fuse
Fuse generally use for protect from over current. In this substation use drop down fuse or air
break fuse. The rating of this fuse is 220Ampere in primary side and secondary side rating is
110Ampere.
4.4.5 Metering
By the meter we can measure present current,
voltage, power factor and maximum current,
voltage etc. There was analog meter now they
are using digital meter.
4.4.6 Isolator
Isolator is like a switch. It use after the circuit
breaker for ensure line are totally off mode.
Mainly it use while substation or line need
maintenance. Isolator has a manual system for
operation.
Figure4.5: Meter in Comilla PBS-1
Substation

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4.4.7 Power Transformer
Power Transformer is the main part of a substation. In Comilla PBS-1 use 10MVA power
transformer.
Figure4.6: Power Transformer in Comilla PBS-1
In Comilla PBS-1 they use three power transformer every of them 10MVA power. Transformer
can vary up to 5% voltage.

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Figure4.7: Power Transformer name plate
Transformer nameplates general requirements:
Following are the minimum information and Data which to be shown on a transformer nameplate
Name of manufacturer; Serial number; year of manufacture; Number of phases; KVA or MVA
rating; Frequency; Voltage ratings; Tap voltages; Connection diagram; Cooling class; Rated
temperature in °C; Polarity (for Single Phase Transformers); Phasor or vector diagram (For
Polyphase or Three Phase Transformers); % impedance; Approximate mass or weight of the
transformer; Type of insulating liquid; Conductor material of each winding; Oil volume (of each
transformer Container/Compartment); Instruction for Installation and Operation

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4.4.8 Voltage Regulator
Voltage regulator is a device which can voltage up or down in a limitation range according to
consumer demand. Actually voltage regulator is an auto transformer. In Comilla PBS-1 those
transformer we use they can voltage up or down up to 10%.
Figure4.8: Voltage regulator

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4.4.9 Feeder
Distribution feeder circuits are the connections between the output terminals of a distribution
substation and the input terminals of primary circuits. The distribution feeder circuit conductors
leave the substation from a circuit breaker. In Comilla PBS-1 have 9 feeders. Every feeder have
own controlling system and also there has a display which shows maximum current, voltage,
power factor and present current , voltage, power factor, the times its operation. It shows up to
one month data.
Figure4.9: Feeder control panel and display
4.4.10 Distribution
Distribution line is connected form the feeder. For different area needs different feeder. In
distribution system normally 11KV line up to 80% and other are 400 volt ore 230 volt in REB. In
our country maximum consumer need 400volt and 230 volt for this reason we use a transformer
11/0.4 KV or three single phase transformer bank for three phase. In REB they use only single
phase transformer because of lost cost and easy maintenance.

P a g e | 4 4
Chapter 5
Maintenance
Generally Comilla PBS-1 has three type of maintenance those are:
1) Substation maintenance
2) Line maintenance
3) Transformer maintenance
5.1 Substation Maintenance
Every time substation needs maintenance if any problem arises. Without problem substation
needs check all equipment of its quality and condition at least one time in a year.
Note: For maintenance purpose every time substation has to be shut down and line has to ground.
First of all we have to check circuit breaker whether it has any problem or will be any problem.
In the time of power transformer checking it have to be 1000MΩ of insulation test in megger.
Grounding test must in 0.4MΩ
5.2 Line Maintenance
There are many types of line maintenance:
Some of maintenance has to be done immediately which mean whenever problem creates it had
to be solved within four hours. Like over head line tear. For this type of problem immediately
line has to be shut down.
Some of maintenance can be done within 1-2 days like transformer problem.
Some of maintenance can be done within a week like pole or tower got slanted to ground also
trees came to the line.
5.3 Transformer Maintenance
In REB have two type of transformer maintenance.
One is single phase transformer and another is power transformer.
Thy repair single phase transformer in there PBS workshops. And power transformer repair in
central workshop at Savar in Dhaka. I visited both place and saw maintenance.

P a g e | 4 5
5.3.1 Single phase transformer
If any transformer create problem it bring in the workshop and the worker see it what type of
problem. Workers open the transformer and take transformer oil into a separate tank. Then
separate every part from the transformer and mark every part by serial a number. If any
transformer core damage badly which is not possible to repair those type of transformer rejected
totally by workshop worker.
If any transformer coils damage any other problem thy repair it.
Now I am describing how the worker repairs a single phase transformer.
After marking transformer every part when they get time to repair it they take it.
The main part of a transformer is coil binding. In Comilla PBS-1 they bind coil manually by the
worker.
There have two type of coil one is primary coil and another is secondary coil. Secondary coil
strong and hard but primary coil is thin and weak. That is why secondary coil normally do not
damage. Primary coil damage normally and need to repair it. Here in figure5.1 I am showing a
high voltage or primary coil wire.
Figure5.1: Transformer primary coil wire.

P a g e | 4 6
In this figure5.2 I am showing that the worker binding transformer coil.
Figure5.2: Coil binding
In this figure5.3 transformer coil after binding coil.
Figure5.3: complete coil binding

P a g e | 4 7
Figure5.4: core binding of transformer
In figure5.4 worker binding core in coil. After binding coil they bind core in transformer then
they keep coil in heat chamber for absorbing moisture from the coil.
In figure5.5 transformer coil into the tank
Figure5.5: after coil and core binding in
the transformer.

P a g e | 4 8
After all complete they give oil in the tank and connect with bushing.
Figure5.6: After repair complete single phase transformer

P a g e | 4 9
5.3.2 Power transformer
Single phase transformer and power transformer maintenance procedure are same.
Figure5.7: power transformer without tank
Figure5.8: power transformer coil binding in Savar central workshop.

P a g e | 5 0
Chapter-6
Transformer Test
6.1 Testing
A number of tests are required to physically determine the electrical characteristics of power and
distribution transformers. Many of those tests are indicated below:
1. Megger test (Insulation resistance test)
2. Winding resistance test
3. Ratio Test
4. No-load loss test
5. Full load loss & Impedance test
6. Power frequency high voltage test
7. Dielectric strength of oil
8. Polarity test
In “REB” workshop has done 6 tests for a transformer those are:
1. Megger test (Insulation resistance test)
2. Winding resistance test
3. Ratio Test
4. No-load loss test
5. Full load loss test
6. Impedance test
6.1.1 Megger test (Insulation resistance test)
The megger test is a measure of the insulation resistance. Remove solid connections of windings
to ground. The following tests are made using a 1000V megger meter:
• Measure from the high-voltage winding to the low-voltage winding and ground. (Low-voltage
winding is grounded.) H-LG
• Measure from the low-voltage winding to the high-voltage winding and ground. (High-voltage
winding is grounded.) L-HG Table No: 6.1
• Measure from
the high- and low-
voltage windings
to ground. HL-G
SL NO
HT+ Earth LT + Earth HT+ LT Remarks
01 1000+ 1000+ 1000+ OK

P a g e | 5 1
We use a megger meter to measure the insulation
resistance. It range is 0 to 1000+.Megger meter has
two terminal .At the starting of megger testing , we
connect two terminal to the body ( short) to set
megger pointer at “0” position.
Then we connect body to HV side.
1000. Then we connect one terminal to HT side
other terminal to LT side. Megger shows 1000. If
any fault occurs then in megger meter
not show 1000. 1000 means that insulation resistance
property is Ok of transformer. Then we record
megger readings on table6.1.
6.1.2 Winding resistance test
For measuring winding resistance test only a
Multimeter is need. In winding resistance test
LT side connection should be open. No voltage
source is required. Winding resistance only
measured in HT side.
At first two terminal of multi
connected to the HT A & B terminal. Then turn
on the multimeter & set it pointer in Ohm for
measuring resistance. Wait for few second.
Result will show in multimeter display.
After measuring resistance in HT A
we measure HT B & C terminal winding resistance. T
output result is shown in multimeter in fig
Fig 6.1.3: Multi-meter connection & output result for Winding resistance test
We use a megger meter to measure the insulation
to 1000+.Megger meter has
two terminal .At the starting of megger testing , we
connect two terminal to the body ( short) to set
Then we connect body to HV side. In megger shows
1000. Then we connect one terminal to HT side &
other terminal to LT side. Megger shows 1000. If
ult occurs then in megger meter, pointer will
1000. 1000 means that insulation resistance
property is Ok of transformer. Then we record
Figure 6.1.1:
Winding resistance test
For measuring winding resistance test only a
Multimeter is need. In winding resistance test
LT side connection should be open. No voltage
source is required. Winding resistance only
t two terminal of multi-meter is
& B terminal. Then turn
ultimeter & set it pointer in Ohm for
ew second. Figure6.1.2: Multimeter display show value
display.
After measuring resistance in HT A & B terminal, then we measure HT A & C terminal. And last
C terminal winding resistance. The process is shown in fig
is shown in multimeter in figure6.1.4.Then the result is recorded in result sheet.
meter connection & output result for Winding resistance test
.1.1: Megger meter
Figure6.1.2: Multimeter display show value
C terminal. And last
he process is shown in figure 6.1.3. The
ecorded in result sheet.
meter connection & output result for Winding resistance test

P a g e | 5 2
After measuring the winding resistance HT A & B, B & C , C & A terminal in 200KVA
transformer .
Fig 6.1.4: Winding resistance test result form for 200KVA transformer
6.1.3 Ratio Test
The performance of a transformer largely depends upon perfection of specific turns or voltage
ratio of transformer. So transformer ration test is an essential test of transformer. The voltage
should be applied only in the high voltage winding in order to avoid unsafe voltage.
To test transformer ratio test we need 3 phase supply, multimeter and Clamp meter. 3 phase
supply is supplied in HT terminal .By multimeter we measure output voltage. And Clamp meter
for measuring current.
Figure6.1.4: HT terminal connected with 3 phase supply
First, the tap changer of transformer is kept in the position three (3) and LV terminals are kept
open. Then apply 3-phase supply on HV terminals that shown in figr1. Measure the voltages

P a g e | 5 3
applied on each phase (Phase-Phase) on HV and induced voltages at LV terminals
simultaneously.
Figure 6.1.5: 3 phase voltage supply regulator
In the figure 6.1.5 shows 3 phase voltage supply regulator. From that regulator we supply 3
phase voltage to the HV terminal. We can increase or decrease voltage by regulator switch. Red,
Yellow, blue color indicate 3 phase voltage. By regulator switch we increase voltage .In HT
terminals 3 phase voltage are 402V (red), 404V (yellow), 411V (blue). Clamp meter is a meter
that used for measuring current. In fig 6.1.6 shown a Clamp meter. It works like a current
transformer.
Figure6.1.6: Clamp Meter Figure6.1.7: No current is taking HT side

P a g e | 5 4
By turn on the 3 phase voltage supply regulator switch we applied the voltage in HV terminal.
Then we measure current in each phase by Clamp meter that shown in fig 6.1.7. In each phase
current show zero. So, there is no short circuit in LT side. Then we measure LT terminals
Voltage by a multi meter. For 200KVA transformer, measured LT terminals voltage are:
AB terminals =15.41v
BC terminals =15.23v
CA terminals = 15.05v
AN terminals = 8.99v, BN terminals = 8.73v and CN terminals =8.83v.
HV side voltage mean = (402+404+411)/3 = 405.6V
LV side voltage mean = (15.41+15.23+15.05)/3 = 15.23v
So, if we supply 11KV in HT terminals then
LT terminal voltage would be = {(15.23 x 11000)/405.6} V
= 413.04 V
LT neutral to terminal voltage would be = 413.04 V/ √3
= 238.46 V
In bellow Turn ratio test result is show that recorded in test result form in “REB” workshop for
200KVA transformer.
Fig 6.1.8: Turn ratio test result form for 200KVA Transformer
6.1.4 No-load loss test
No load test is also known as open circuit test. No load loss test is used to determine core loss in
transformer. No load losses consisting of the hysteresis loss and the eddy current loss. The
voltage at 50Hz frequency is applied to that LV side with the help of 3 phase voltage supply
regulator. The HV side of the transformer is kept open. For this test we need a watt meter, three
phase voltage supply and clamp meter.
For testing the no load test at first we connect three phase supply to LT terminals .At this test LT
neutral terminal & HT terminals are kept open. When the applied voltage is normal voltage then

P a g e | 5 5
normal flux will be set up. As the Iron loss is a function of applied voltage, normal iron loss will
occur. Hence the iron loss is maximum at rated voltage. Then we applied 403V(red),
402V(yellow), 395V(blue) rated voltage in LT terminal with the help of three phase voltage
supply regulator.
Figure 6.1.9: Measuring the no load current by clamp meter
For measuring the no load current, we hold the clamp meter in the three phase wire in LT side.
The holding process of clamp meter has shown in figure 6.1.9. For 200KVA we measure the no
load current in LT terminal is 6.69A, 6.51A and 4.88A.
A watt meter is connected with LT side. This maximum iron loss is measured using the
wattmeter. This test only measures the combined iron losses consisting of the hysteresis loss and
the eddy current loss. Although the hysteresis loss is less than the eddy current loss, it is not
negligible. Since the HT terminals of the transformer are open, the LT terminals draws only no-
load current, which will have some copper loss. This no-load current is very small and because
the copper loss in the LT is proportional to the square of this current, it is negligible. There is no
copper loss in the HT because there is no HT current. For 200KVA transformer no load loss
shown in 300W in watt meter. The watt meter factor is 2. So, we have to multiply the watt meter
reading with 2. For 200KVA transformer no load loss is 2 x300 = 600W.
Then no load test result is recorded in test result form. The recorded in test result form for
200KVA transformer shown in bellow.
Figure 6.1.10: No load loss test result form for 200KVA Transformer

P a g e | 5 6
6.1.5 Full load loss test
Full load loss test is used to determine copper loss in transformer at full load. Full load loss test
is also known as short circuit test on transformer. The test is conducted on the high voltage (HV)
side of the transformer where the low voltage (LV) side or the secondary is short circuited. For
this test we need a watt meter, three phase voltage supply, clamp meter and wire for short the LT
terminal.
Fig 6.1.11: LT Terminal is shorted with wire; Fig 6.1.12: HT terminal is connected with 3 phase supply
After shorted the LT terminal, we connect the HT three terminal with 3 phase supply that shown
in fig6.1.11. The tap changer position is in 3.After connecting HT terminal with 3 phase supply,
then we turn on the 3 phase voltage supply regulator to supply 3 phase voltage in HT terminal.
The supply voltage required to circulate rated current through the transformer. We applied 3
phase voltage 399V (red), 400V (yellow), 393V (blue) in HT terminal for 200KVA transformer.
We have to measure full load current in three terminal in LT side. An engineer is measuring full
load current with clamp meter. For 200KVA transformer we measured current are 259A, 260A
and 254A in LT terminal.
The watt meter is connected with HT side. The core losses are very small because applied
voltage is only a few percentage of the nominal voltage and hence can be neglected. Thus the
wattmeter reading measures only the full load copper loss.
For 200KVA transformer, full load loss shown in 800 W in watt meter. The watt meter factor is
2. So, we have to multiply the watt meter reading with 2. For 200KVA transformer full load loss
is 2 x800 =1600W. After measuring full load loss, we recorded in test result form.

P a g e | 5 7
6.1.6 Impedance test
For impedance test we need Max voltage in HV and the Minimum that voltage (HT) which can
supply full load current in LT side. So, After Full load loss test we find that for 400V in HT
terminal we get full load current 260 A in LT terminals. The 200KVA transformer is rated for
11KV. So 11000V is the maximum voltage. By that given bellow equation we can test
Impedance. So, 200KVA transformer impedance is
% impedance = (Full load voltage in HV/Max Voltage in HV) x 100
= (400/11000) x 100
= 3.63 %

P a g e | 5 8
Chapter-7
Supplementary Part
Recommendation
During my intern ship I came to know that REB faces lots of problems and they also have some
limitations.
 Transformer stealing is one of the major problems of REB. For this reason transformer
with chain and lock would be better also transformer can be install in near the people
house.
 REB uses 3 single phase transformers for three phase distribution system which is costly
and not efficient. Here three phase transformer would be more efficient.
 Comilla PBS-1maintains substation manually it can be error in some times. Here
automatic control system or programmable logic controller would be better and accurate.
 Comilla PBS-1 is operated by workers for maintenance system. Likes winding binding,
core binding, core cutting etc. During my internship I saw a worker cut down his hand
badly by core which is terrible thing. At least in some specific tasks machine would be
superior.
To complete my internship and to understand the technical terms properly Switchgear and
Protective Relays and Power Station these two courses helped me. So if someone wants to do
internship at REB, they need to complete these two courses and stay in REB’s quarter and it will
be better if they choose it after completion of there all academic courses.
Conclusion
Rural Electrification Board (REB) has the vast electricity distribution network all over the
country and the electric power plants are connected with the transmission line to assure the
continuity of electric power. The electric power plants produce power and feed in to the
transmission line. All power plants are connected parallel with the transmission and distribution
line. REB is now more developing system day by day. As the part of this now REB is using
digital meters instead of analog meters for the consumers. However we have huge lack of
electricity in Bangladesh but all of generation, grid supply, sub-station, consultancy, local
member service of REB is more efficient and taking important role to cover lack of electricity.

P a g e | 5 9
Appendix
Transformer: A static electrical device, which, by electromagnetic induction, regenerates AC
power from one circuit into another. Transformers are also used to change voltage from one level
to another. This is accomplished by the ratio of turns on the primary to turns on the secondary
(turns ratio).
Primary Winding: The coil winding that is directly connected to the input power
Three Phase Power: Three separate outputs from a single source with a phase differential of
120 electrical degrees between any two adjacent voltages or currents.
Ampere (amp): A unit used to define the rate of flow of electricity (current) in a circuit; units
are one coulomb (6.28 x 1018 electronics) per second.
Ambient Temperature: The normal surrounding temperature of the environment in which a
transformer will operate
Current Transformer (CT): A transformer used in instrumentation to assist in measuring
current. It utilizes the strength of the magnetic field around the conductor to form an induced
current that can then be applied across a resistance to form a proportional voltage.
Core: The ferrous center part of a transformer or inductor used to increase the strength of the
magnetic field.
Delta: A standard three phase connection with the ends of each phase winding connected in
series to form a closed loop with each phase 120 electrical degrees from the other.
Delta-Wye: The connection between a delta source and a Wye load.
Flux: The lines of force of a magnetic field.
Forced Air: A method of temperature regulation that involves air from an external environment
being forcibly exchanged with a transformer's enclosed environment.
Inductor: A coiled conductor that opposes change in current.
Inductance: The ability of a coil to store energy and oppose changes in current flowing through
it. A function of the cross sectional area, number of turns of coil, length of coil and core material.
Nominal Voltage: The normal or designed voltage level. For three phase wye systems, nominal
voltages are 480/277 (600/346 Canada) and 208/120 where the first number expresses phase to
phase (or line to line) voltages and the.
Hertz (Hz): Units in which frequency is expressed. Synonymous with cycles per second.
Resistance: The resistance to the flow of electric current measured in ohms (1/2) for a

P a g e | 6 0
conductor. Resistance is function of diameter, resistivity (an intrinsic property of the material)
and length
Earthling: All unbounded exposed metal work within the substation should be electrically
bonded to the earthling system. This includes metal doors and reinforcing in the floor. If a part
cannot be adequately bonded, it will be constructed from a suitable insulating material instead of
metal. All earthling straps will have a minimum area of 35 sq mm copper. The earth cable size
shall be a minimum of 35 sq mm copper.
EMF: Electromotive force. A rise in (electrical) potential energy.
Impedance: The total opposition to electrical flow (resistive plus reactive)
Insulation Resistance: The resistance measured between two insulated points on a transducer
when a specific dc voltage is applied at room temperature.
Load: The electrical demand of a process expressed as power (watts), current (amps) or
resistance (ohms).
Open Circuit: The lack of electrical contact in any part of the measuring circuit.
Terminal: An input/output device used to enter data into a computer and record the output.
Secondary Winding(s): The coil winding(s) supplying the output voltage to the load(s).
Temperature Rise: The additional maximum heat above ambient temperature that the
transformer itself will generate in the normal course of operation.
Acronyms
AC Alternating Current (vs. DC)
DC Direct Current (vs. AC)
HVPS High Voltage Power Supply
LF Low Frequency
PF Power Factor
REB Rural Electrification Board
LVCB Low Voltage Circuit Breakers
MCCB Molded Case Circuit Breaker
MCB Miniature Circuit Breaker

P a g e | 6 1
MVCB Medium Voltage Circuit Breakers
HVCB High Voltage Circuit Breakers
CT Current transformer
PT Potential transformer
ES Earthling Switch
PFI Power Factor Improvement
SPFC Power Factor Correction
References
1. Mehta, V.K, Mehta, Rohit. Principals of Power System. 4th
ed. New Delhi: S. Chand, 2005
2. William D. Stevenson, Jr. Elements of Power System Analysis. 4th
ed. London: Mcgraw-hill,
1982
3. Sharma, D.K. Electrical Engineering. 5th
ed. New Delhi: CBS Publishers, 2002
4. Theraja, B.L. Theraja, A.K. A text book of Electrical Technology 1st
ed. New Delli: S. Chand,
2005
Websites:
5. Google images Retrieved February 22, 2016, from https://images.google.com
6. Google retrieved February 15, 2016, from www.google.com
7. Comilla Palli Bidyut Samity-1 retrieved March 3, 2016, from www.comillapbs1.org
8. Bangladesh Rural Electrification Board retrieved March 15, 2016, from www.reb.gov.bd
9. Wikipedia Retrieved March 22, 2016, from https://en.wikipedia.org/wiki/Transformer
----------THE END----------

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