EHV Power Transformer

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Internship Report

Submitted To: Human Resource PEL

Submitted By: Ahmar Mumtaz

1 University of Engineering & Technology,Taxila.

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Supervisor: SE Muhammad Tayyab

Internship Department: Product Development

Internship Duration: 9June,2014-7 July,2014

Table of ContentsDedication…………………………………………………………3

Acknowledgement……………………………………………4

Executive Summary…………………………………….……....5

Introduction of PEL…………………………………….….…….6

Transformer……………………..…………………………………22

Transformer Design ……………………………………………..24

Transformer Manufacturing…………………………………25

Winding……………………………………………..25

Phasing……………………………………………….29


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Reclamation-Unit 3……………………………29

Core Section………………………………………30

Assembly…………………………………………….32

Testing………………………………………………..35

Conclusion…………………………………………………………39

Reference…………………………………………….40


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DedicationTo all those who have supported, encouraged,challenged, and inspired me. And specially to myBeloved Parents, honorable teachers and friends for alltheir guidance, love & attention which has made itpossible for me to make it up to this point and as wellas the Internship Supervisors who bestowed me with thecourage, the commitment and the awareness to follow thebest possible route, by their unmatchable style and bybest possible training.


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AcknowledgementAll the praises are for the almighty, Allah whobestowed me with the ability and potential to completethis Internship. I also pay my gratitude to theAlmighty for enabling me to complete this InternshipReport within due course of time.

Words are very few to express enormous humbleobligations to my affectionate Parents for theirprayers and strong determination to enabling me toachieve this job.I also appreciate the cordial co-operation from all my Internship Supervisors in thedifferent departments of PEL and also of HR managementfor providing me requisite information and knowledgefor compilation of my complete Internship.

All the employers of PEL helped me a lot in performingall the activities and in gaining the practicalknowledge of industry. They gave me best environmentand knowledge to enhance my skills.


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Executive SummaryPak Elektron Limited (PEL) is the pioneer manufacturer

of electrical goods in Pakistan. It was established in

1956 in technical collaboration with m/s AEG of

Germany. In October 1978, the company was taken over by

Saigol Group of companies. Since its inception, the

company has always been contributing towards the

advancement and development of the engineering sector

in Pakistan by introducing wide range of quality

electrical equipments and hoe appliance and by


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producing hundreds of engineers, skilled workers and

technicians through its apprenticeship scheme and

training programs. I did my internship in Marketing AD

department of PEL.

I learned a lot during my internship period. How to

work individually as well as in groups under relaxed

and stressful environment. How to work under someone’s

supervision. How to manage affairs while launching new

products. Patience is very important in dealings, as

anger can lose your customer. To increase your sales

and stay in competition with top brands it is necessary

to keep your dealers happy by giving them incentives.

During a span of four weeks of training as intern I

thoroughly observed the functions of different

departments of PEL (Pak Elektron Limited). As

apprentice I analyzed the basic working of PEL and

especially Product(PD) development(Power Transformer)

and summarized this in my internship report.

Introduction of PEL7 University of Engineering & Technology,Taxila.

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Pak Elektron Limited (PEL) was in corporated in Pakistan on march

03,1956 as a public limited company under the companies Act, 1913

(replaced by companies ordinance 1984). Registered office of the

company is situated at 17 Aziz Avenue, canal bank Gulberg_ V

Lahore. The company is currently listed on all three stock

exchange of Pakistan. The principal activity of the company is

manufacturing and sales of electrical capital goods and domestic

appliances.

These activities are organized under following divisions.

Power division: manufacture of switchgear, energy meter, and transformers.

Appliances division: manufacture and assembling of refrigerators, air conditioner, microwave oven, television and

washing machine.

BRIEF HISTORY

PAK ELEKTRON LIMITED was set up in 1956 as a joint venture with

one of the largest and renowned manufacturers of electrical

equipment Messrs. AEG of West Germany for manufacturing

Transformers, Switchgears and Electric Motors etc. The entire job

of machinery requirements and layout of the factory building was

planned and implemented by AEG who produced very well balanced


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facility for the design and manufacture of the above equipment

and the commercial production was commenced on 22 November 1956.

Up to 1962, when AEG finally phased out, the designing and

manufacturing of all equipment was carried out jointly by AEG

experts and PEL personnel. PEL staff, in the meantime, had

received specialized training in USA and West Germany which

enabled PEL to establish itself as the leading manufacturers of

electrical equipment in the country with an excellent reputation

for high quality and thus PEL came to be known as "THE QUALITY

CONSCIOUS COMPANY".

After conclusion of agreement with AEG, total share holding of

AEG was purchased by the then sponsors - Malik Brothers. The

production continued with AEG designs with much greater emphasis

on the quality and reliability of the products which earned

unique distinction of supplying electrical equipment to projects

of paramount national importance like Mangla Dam and Tarbela Dam

Projects. PEL equipment was approved by consultants of

international repute including Preece Cardew & Rider (England),

Binnie & Partners (England), Harza Engineering International

(USA) and Miner & Miner International Inc. (USA).

The majority shares were acquired from Malik Brothers by Saigol

Group on 11 October 1978 and immediately on takeover the new

management chalked out both long term and short term plans to put

the company back on the path of progress. As a part of first 9 University of Engineering & Technology,Taxila.

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phase of its BMR Programmer the new management injected the

additional working capital of Rupees 8.98 million and Bridge Loan

of Rupees 7.50 million (against the public issue of its shares)

was provided by the ICP-led Consortium. As a part of long term

plans, the manufacturing of window type Air conditioners was

taken up in 1981 and was immediately established for quality.

The company launched the second phase of its BMR and expansion of

the existing product line in the year 1987 and imported machinery

for the manufacture of Refrigerators and Deep-freezers for a

total value of Rupees 22.11 million. For the project National

Bank of Pakistan - the leading bank of the company provided the

financing. Like Airconditioners these products have also been

well received by the local market, which speaks highly of the

confidence, the consumer has developed in the quality products

manufactured by the company?

During the year 1990 the company has signed an agreement with

Messrs HITACHI of Japan for the manufacture of Vacuum Circuit

Breakers.

The company has entered into an agreement with Pakistan

Industrial Credit and Investment Corporation (PICIC) for a

foreign currency as well as local currency loan of Rupees 25

million for the expansion, balancing, modernization and

replacement of the


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existing plant. The machinery has come into operation in October

1991 and with the balancing, modernization and replacement of

machinery, the production capacity of Refrigerator Section will

reach a level of 252,450 cubic feet.

The management of the Company decided to further expand its

operation by establishing a plant for the manufacture of

compressors for refrigerators and deep freezers. The technical

know-how agreement has been signed with M/S NECCHI Compressori,

Italy for the assembly and progressive manufacturing of

compressors for refrigerators and deep freezers.

Group Profile

In 1948, the Saigols migrated from Calcutta and initiated their

business in Lyallpur (later named to as Faisalabad), the textile

city of Pakistan, under the banner of Kohinoor Industries

Limited.

Kohinoor Textile MillsThe Saigols set up the first major textile unit - The Kohinoor

Textile Mills under the umbrella of Kohinoor Industries Limited.

The Kohinoor Textile Mill has state-of-the-art quality control

from raw material to finished product manufacturing. Its

laboratory is top rated amongst the best laboratories in Pakistan

for testing of textile raw materials, other inputs and yarn.


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Initial Capacity:25,000 spindles

Current Capacity: 71,648 spindles

Pak Elektron Limited (PEL)

In 1978, the Saigol Group of Companies purchased major shares of

Pak Elektron Limited. At that juncture, the company was only

manufacturing transformers and switchgears. With the Saigols in

management, PEL started expanding its product range by entering

into Air Conditioner manufacturing.

Saritow Spinning Mills & Azam Textile Mills

In 1987, the Saritow Spinning Mills and Azam Textile Mills were

established under the banner of Saigol Group of Companies.

Saritow Spinning Mills is a spinning unit with 25,440 spindles

capacity. Facilitated with the most modern and efficient Japanese

and European machinery, its knitted yarn is renowned in the Far

East and Europe for its fine quality. Azam Textile Mills is

reputed for its carded and combed yarn, which is quite popular

for premier knitting and weaving.

Kohinoor Power Company Limited


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In 1991, the first power unit commissioned in Pakistan, in the

Private sector, was Kohinoor Power Company Limited. Its present

production capacity is 15 MW.

Kohinoor Energy Limited

1995, another power unit, Kohinoor Energy Limited, was

established. Kohinoor Power Limited is a 120 MW power plant

located on the outskirts of the city of Lahore. This project has

an annual turnover of $80 million.

VISION STATEMENT


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To excel in providing engineering goods and services

through continuous improvement.

MISSION STATEMENT To provide quality products & services to the

complete satisfaction of our customers and maximize

returns for all stakeholders through optimal use of

resources.

To focus on personal development of our employees

to meet future challenges.

To promote good governance, corporate values and a

safe working environment with a strong sense of

social responsibility.


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Board of Directors

Mr. M. Naseem Saigol ChairmanMr. M. Azam Saigol

Mr. Murad Saigol

Mr. M. Zeid Yousaf Saigol

Mr. M. Abdullah Haroon Saigol

Mr. Haroon Ahmed Khan Managing Director

Mr. Syed Zubair Ahmed Shah NIT Nominee

Mr. Akbar Hassan Khan NBP Nominee U/S 182 of

the Ordinance

Ms. Tahira Raza NBP Nominee U/S 182 of

the Ordinance

Mr. Khalid Siddiq Tirmzi BOP Nominee U/S 182 of

the Ordinance

Mr. M. Khuram Khuwaja NBP Nominee U/S 182 of

the Ordinance

Audit Committee

Mr. Azam Saigol Chairman

Ms. Tahira Raza Member

Mr. Syed Zubair Ahmad Shah Member

Mr. Haroon Ahmad Khan Member


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Company Secretary

Mr. M. Omar Faro

DEPARTMENTS IN PEL The departments which are currently in operation at PEL are as follows:

Common Departments: HR & D IR & A Finance IT FP & Commercial Accounts

Marketing and Sales: Marketing AD Marketing PD CMD CSD

Production Department:

Production AD

Production PD


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PEL has divided the Production department into two

further departments:

Power Division

Appliance Division

POWER DIVISION

PEL’s Power Division manufactures transformers, switchgear,

energy meters, kiosks, compact stations, shunt capacitor banks

etc. All the power equipment is assembled under strict quality

control and in accordance with international standards.

PEL is a major power equipment supplier to Water and Power

Development Authority (WAPDA) and Karachi Electrical Supply

Corporation (KESC).In-spite stiff competition from emerging local

and multinational brands, PEL’s appliances and power equipments

have consistently gained marked share due to constant innovation

and high quality standards. Strategic partnerships with Copeland,

Danfoss, Samsung and others have enabled the Company to


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incorporate new technologies into existing product ranges, thus

introducing new product features.

During the year 2006, PEL retained its market leadership in the

Power Equipment market, increasing its market share from 33% in

2005 to 36% in 2006 in the switchgear market and also maintained

share of 35% in 2006 as well in the energy meters market. PEL’s

leadership in the Power Equipment market is largely due to its

strong Research and Development knowledge and high product

quality.

PEL has the privilege of getting its equipment approved andcertified by well-reputed international consultants such as:

Preece, Cardew and Rider, England Harza Engineering Company, USA Snam Progeti, Italy Societe Dumezm, France Miner & Miner International Inc. USA Ensa, France

Power Division accounted for 47% of the Net Sales of the Company

as of June 30th 2006. The sales and profit participation by the

Division is high due to high quality standards and future growth

opportunities.

The Power Division comprises of three departments;

1. Manufacturing and Quality Control


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2. Design and Development

3. Marketing

PRODUCTS POWER DIVISION

ENERGY METERS

TRANSFORMERS

SWITCH GEAR

TRANSFORMERSPEL has vast experience in design and manufacturing of standard

and special purpose transformers These transformers are available

for various applications.

Distribution Transformers

Auto Transformers

Furnace Transformers

Welding Transformers

PEL transformers have been successfully type tested for impulse

voltage and short circuit tests by KEMA Laboratories of

HollandTransformers are normally supplied in a period of 3 – 4

months after the receipt of orders from respective distribution

companies of WAPDA and varied supply time for private customers.

The Company provides one year after sales service warranty to

WAPDA, KESC and private sector customers. Main Competitors are


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Siemens, Transfopower, Elmetec and Climax, while PEL having a

market share of 38 %.

ENERGY METERSFollowing types of meters are manufactured:

Electro mechanical

Single phase

Three phase_ Direct connected

Three phase _CT operated

Static/Digital

Single Phase

Three Phase Directed connected

Three Phase_CT operated

Three Phase_TOU

PEL manufactures three types of energy meters; Single Phase and

Poly Phase. The electro-mechanical energy meters are manufactured

under license from ABB of USA. The quality of PEL meters has been

certified by KEMA Laboratories of Holland.Single Phase energy

meters provide maintenance-free operations over a long period.

Energy meter orders from WAPDA are received annually and their

supply period is 9 -10 months. Energy meters to KESC are supplied

in a period of 3 - 4 months. The Company provides one year after

sales service warranty to WAPDA, KESC and other customers. In the


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supply of Energy Meters PEL share accounts for 35 % of the total

supplies while the rest is shared by Syed Bhais, Escort and

Telephone Industries.

SWITCHGEARSSwitchgears are one of the highly technical and specialized power

products of PEL. They are produced for indoor and outdoor

installations complying with international installation

standards. A major customer for this product is WAPDA. The

Company provides one year after sales service warranty to WAPDA,

KESC and other customers. In Switchgear, PEL enjoys market share

of 33 % while competitors are Alstom, Siemens and Fico.

POWER TRANSFORMERS

Owing to massive growth in power sector, demand for power

transformers is also growing proportionately for all ratings from

66KV to500 KV. PEL has stepped into this activity by starting the

manufacturing of 132 KV transformers, being the most demanded

rating, and for this purposes has formed a strategies partnership

by signing the two agreement. Based on the demand forecast of

Power Transformers for WAPDA, KESC and other projects, PEL’s

market share is initially targeted to be 20%, growing in five

years.

The main Customers of PEL


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The customers of PEL can be categorized in two categories i.e.home consumers and industrial consumers. Home consumers are thecommon individuals who mostly purchase the home appliances. Theindustrial consumers are as follows:

LESCO GEPCO FESCO IESCO PESCO MEPCO HESCO QESCO KESC AJK Electricity Department

Appliances DivisionBusiness in appliances division has shown mixed trend but the

Company is finally on the right track. Crystal Refrigerator with

Aero design and Danfoss compressor with performance

certification by Danfoss Germany was launched in the February

1999. This has been received very well in the market and our

refrigerator sales have shown an increase of ver 125% since 1999.

This thrust is expected to continue in the following year as a


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result of company’s innovative approach in product development

coupled with an aggressive marketing strategy. Deep Freezer tested and certified by Danfoss Germany and with

improved aesthetics has also been well received by the market. We

have already been supplying our Deep Freezers to Coca-Cola

international and lever Brothers and intend to continue our focus

on institutional sales of this product.

Products of Appliance DivisionAppliance division has following products;

Refrigerators

PEL’s refrigerators are available in 6 series of different

colors, models, prices, and capacities. The series are as follow

Xpression Series

Premier Series

6-Series

Deluxe Series

Smart Series

Mini Series

Air Conditioners

The air conditioners are available in three types;

Split Air Conditioners

Window Air Conditioners

Floor Standing Air Conditioners


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Microwave Oven

PEL also introduce model series of “PEL Silver line” Microwave

Oven. PEL presents 26 different models of oven with different

prices, models and capacities.

Washing Machine

PEL’s washing machines are available in different models. The

series are as follow;

Magic Clean PWM7700

Magic Clean PWM512

Water Dispensers

PEL also Introduce water dispensers. The main purpose to

introduce it is to increase their product line and give value to

their customers.

Generators

From long time Pakistan facing energy crisis, at that time

introduction of PEL Generator is very positive steps toward

appliance sector to facilitate their customers. And they are

working more to increase their product line, produce quality

products, and give value to their customers and become market

leader in home appliance


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LG PRODUCTSLG has entered in a strategic partnership with PEL. According to

this agreement PEL has become the official distributor of LG

products in PAKISTAN from June 2009.

LG products in Pakistan are:

Refrigerator

Split air conditioner

Washing machine

Microwave oven

ISO 9001 Certification

PEL was 16th Company in Pakistan which got ISO 9002 Certification

in 1997, since then PEL Management is applying this International

Standard Practices for Effectively Managing Quality of Products

and Services that Company Offers. The International Standard

Practices in PEL have been Upgraded as per the Revised ISO 9001

Standards and its Scope of Application is expanding ever since

and Top Management is Committed to make PEL a Total Quality

Management (TQM) Company.


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EPC Contracting

With restructuring of power sector in Pakistan and increase ineconomic, commercial and industrial activity, more and more powerutilities and other customers demanded high value packagedsolutions for their transmission system and enterpriseelectrification requirements. To meet this demand PEL establishedan Engineering Procurement and Construction division. PEL EPCDivision consists of human resource with high academicqualifications and experience of local as well as global market.The EPC division delivers custom designed and built solutions infollowing areas.

132kV and 220kV grid stations for power utility companies. 132kV and 11kV substations for industrial and commercial

customers. Integration of private captive power generation plants into

utility network for sale of their surplus power to utilitycompanies.

Electrification of housing projects and industrial parks.


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Services include:

Engineering Project Management Project Execution Turnkey or customized projects Technical support and solution

Awards won by PEL:

Annual Environment Excellence Award-2009

Annual Environment Excellence Awards are instituted jointly

by National Forum for Environment and Health (NFEH), United

Nations Environment Program (UNEP), Ministry of Environment,

Government of Pakistan and the Federation of Pakistan

Chambers of Commerce & Industry (FPCCI). Annual Environment

Excellence Awards are designed to recognize and promote the

organizations which make an outstanding contribution to

sustainable development. They aim to highlight policies,

practices, processes and products from all sectors of

business in the country, which help to achieve economic and

social development without detriment to the environment and

natural resources.

Pak Elektron Limited (PEL) was awarded 6th Annual

Environment Excellence Award for best Health, Safety and

Environment performance. The Award was presented to Pak

Elektron Limited in a graceful ceremony; held on July 09,27 University of Engineering & Technology,Taxila.

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2009 at Hotel Sheraton, Karachi. Mr. Hameed Ullah Jan

Afridi, Federal Minister for Environment, honored the

ceremony by as chief guest whereas Mr. Askri Taqvi, Minister

for Environment, Sindh presided over. Javed jabber (Global

Vice President IUCN), Dr. Kaiser Waheed (Chairman NFEH) and

Naeem Qureshi (President NFEH) were also present on the

occasion. Mr. Yaqub Tabasum (Project Manager Unit-II)

received the Environment Excellence Award on behalf of PEL.

Health & Environment National Excellence Award-2008

On the basis of sound Health, Safety & Environmental

performance; PEL was selected for 4th Health & Environmental

National Excellence Award-2008. These awards are offered by

Help International Welfare Trust, Pakistan in collaboration

with Corporate Social Responsibility (CSR) Association of

Pakistan. The award presentation ceremony was held at Hotel

Regent Plaza, Karachi on April 15, 2009. Mr. Askari Taqvi,

Minister for Environment, Government of Sindh was Chief

Guest of the ceremony and Ms. Khadija Balkhi, President of

CSR Association of Pakistan was the Guest of Honor at the

occasion.

Best Environmental Reporting Award

Pak Elektron Limited (PEL) was awarded the Best

Environmental Reporting Award for 2008 at the 7th ACCA-WWF


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Pakistan Environmental Reporting Awards (PERA) ceremony held

on Earth Day; April 22, 2009 at the Serena Hotel, Islamabad.

TransformerA transformer is an electrical device that transfers energy between two or more circuits through electromagnetic induction.A varying current in the transformer's primary winding creates a varying magnetic flux in the core and a varying magnetic field impinging on the secondary winding. This varying magnetic field at the secondary induces a varying electromotive force (emf) or voltage in the secondary winding. Making use of Faraday's Law in conjunction with high magnetic permeability core properties, transformers can thus be designed to efficiently change AC voltages from one voltage level to another within powernetworks.By Faraday's law of induction

. . . (1)[a]

. . . (2)Combining ratio of (1) & (2)

Turns ratio . . . (3) wherefor step-down transformers, a > 1for step-up transformers, a < 1


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By law of Conservation of Energy, apparent, realand reactive power are each conservedin the input and output

. . . (4)Combining (3) & (4) with this endnote] yields the ideal transformer identity.

Classification of transformerAccording to the construction:

Core type Shell type

According to supply system: Single phase Three phase

According to use: Power transformer Distribution transformer

According to the mode of operation; Step up step down

According to the way of cooling dry type oil immersed self cooled oil immersed force air cooled oil immerse water cooled oil immersed force oil cooled air blast


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Transformer DesignWhenever any client wants to purchase any transformer, it sendsits required specifications to the Marketing department of PEL;this is called Enquiry. The marketing department then sends thisenquiry to the design department. The design department performsthree main tasks:

Estimation of the Cost Dimensional Sketch Datasheet

These three things are then sent to the marketing department,which is the feedback to the client’s enquiry. If the clientfeels satisfied with these things, then it gives the order to themarketing department. The marketing department then sends theSales Advice to the design section, which mainly defines thenumber of transformers to be produced and the duration of thesupply.

When the order is confirmed, then the design department startsits working in full swing. The work is then divided into twosubsections; electrical team performs the electrical design,whereas the mechanical team is mainly concerned with mechanicaldesign.

The electrical design team is mainly involved in the designing ofthe Core, LT and HT windings. The mechanical design team works onthe layout, body of the transformer. The design is made on Pro-Eand AutoCAD software.

The electrical design generally works with a faster pace, becauseit has to inform the Material Planning Control section that thismuch material is required for the production. Same is the case


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with the mechanical team, but since core and winding are toproduce first, so there production starts a bit earlier. Thedesign and its calculations are mainly done via software. Once adesign is finalized and is according to the requirements of theclient, a TR document is prepared that defines each andeverything regarding the design.Data sheet includes allspecification of a transformer.BOQ (Bills of Quantity) containsthe amount of material used for the construction of atransformer.

Transformer ManufacturingIt is divided into four sections:

Winding Section Core Section Assembly Section Testing Section

1.Winding SectionWinding material is usually copper but aluminum can alsobe used. 99.9% pure copper is used with enameled coating.Sheets of copper are drawn into various sizes and theninsulated with specified insulation paper according to therequirement. Insulation paper is normally 0.06mm to 3mm inthickness and the material most commonly used at PEL isprespone because it does not dissolves in oil and alsodoes not absorbs moisture.

Helical Winding

Helical winding is typically used for low voltage and high current winding of large generator transformers. It can have 54 connectors at a time. Each turn is transposed and


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are wound in helix. The main purpose of transposition is to reduce eddy current losses.Unlike the conventional winding, the helical winding has no distinct division into activeand end regions, because each conductor follows a helical path ofconstant pitch and diameter from one end of the machine to the other. In the conventional winding, each conductor follows an axial path in the active region and only has a circumferential component to its path in the end regions.

To understand how a helical winding works, consider the winding length of a diamond lap winding shown in the adjacent figure

(a) to be progressively reduced as by eliminating the so-called central "active" region and allowing the two diamond end windings to coalesce and form a semi-helical winding

(b) The true helical winding evolves from the wave wound diamond winding.

One phase of a two pole helical winding is shown above. Each phase consists of two parallel-connected helical loops, each of which is termed a phase group. Each phase group comprises one right-hand (inner) helical phase band connected in series with a returning left-hand (outer) helical phase band; a right hand phase band being defined as that which traces a right hand screw.

Layer Winding


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This is the most commonly used winding used in PEL forLow voltage and high voltage. It is normally used forvoltages ratings between 90V to 33 KV. It consists of anumber of spiral coils, which are arranged in layers.These layers are separated by cooling ducts in which oilis poured. A good advantage of using layer winding is thatit gives uniform voltage. Secondary winding is always lessthan the primary winding because most of thetransformers made in winding shop are distributiontransformers which are used at consumer station in orderto step down the voltage.

Very large “thermal mass” of conductor and insulation betweencoolingducts: difficult to calculate and control the hot spottemperatures.No radial ducts, some axial ducts, most of them just on ends, notallAround.

Inter-Leaved Disc Winding

A disc-type interleaved winding for transformers. Current is conducted through the winding by three conductors connected in


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parallel and interconnected between the coil discs to provide three different conduction paths. The first and third conduction paths are transposed between adjacent coil discs and progress in radially opposite directions through adjacent coil discs. . Disc winding helps the coil to withstand high impulse voltage. The second conduction path forms a looping pattern throughout thewinding with the conductor forming the second conduction path physically positioned between the other two conductors in each

coil disc. All turns are in contact with MOVING oil to lower hotspot temperatures.

A disadvantage with continuous disc winding is that their strength against impulse voltages is not adequate.the withstand behaviour of disc winding can be increased if two adjacent conductors belong to two different turns.

Apart from interleaving between every double disc.it is also suitable to have more number of discs say four in each interleaved group.

Foil Winding36 University of Engineering & Technology,Taxila.

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This design for winding has been recently introduced at PEL due to its various advantages over other types of windings. Foil winding hasa single copper foil which serves as a single conductor. The advantage of using a single foil of copper is mainly to strengthen flux and to reduce losses. The transformers with this type of winding are more efficient.Moreover it reduces the labor and in turn decreases thecost of transformer. Copper foil is always used in LT because distribution transformers are mainly step down transformers so secondary is always at low voltage as compared to primary. On LT the HT is wound which is usually layer winded. The sheet of copper is passed through a machine which cuts the sheet into different sizes according to the desire rating of the transformer. There are thermo ducts with oil in them in order to keep the transformer cool.

Packet winding

Packet winding is normally used for high voltage. They have large number of turns. It cannot be used for low


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voltages. At PEL 4 packets are normally used in each winding. Packet winding can be easily repaired because eachcoil is in the form of packets so if any single packetis damaged it can be removed and a new packet can be replaced by it which is more economical because in other types of windings the whole winding is to be replaced if it is burned due to short circuit or any other reason.

Foil and layer windings are usually used in LV. Layer, packet anddisc winding is usually used in HV.

Area is increased in foil winding and hence stray losses arereduced.

Disc and packet winding are easy to repair and also thatvoltage is distributed among each packet/disc here. Hencemainly used in high rating transformers.

Insulation Material

Diamond dotted paper (For inter-layer insulation) Press pan sheet (For end collars) Creep paper pipe (For insulation of terminal of tap

changer) Craft paper (Used for insulation in disc winding) Thermo ducts

PhasingIn phasing,first LV winding is placed.Over LV,HV winding is placed and then RV winding is placed.Phasing is done separately for each phase.Taps from LV,HV and RV are taken out.LV has 2 tapsformaking star connection.HV has 4 tapsi.e. 2 for making delta and two taps are given to RV for tap changing,RV has 11 taps for voltage regulation.


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Reclamation-Unit 3 PELI went to reclamation unit for analyzing core,assemblyand testing section of Power transformer.

2.Core SectionIn the core section center, side and yoke limbs of the core aremade. In an electrical power transformer, there are primary,secondary and may be tertiary windings. The performance of atransformer mainly depends upon the flux linkages between thesewindings. For efficient flux linking between these windings, onelow reluctance magnetic path common to all windings should beprovided in the transformer. This low reluctance magnetic path intransformer is known ascore of transformer.

Material for Transformer CoreThe main problem with transformer core is, its hysteresis lossand eddy current loss in transformer. Hysteresis loss intransformer mainly depends upon its core materials. It is foundthat, a small quantity of silicon alloyed with low carbon contentsteel produces material for transformer core, which has lowhysteresis loss and high permeability. Because of increasingdemand of power, it is required to further reduce the core lossesand for that, another technique is employed on steel, which isknown as cold rolling. This technique arranges the orientation ofgrain in ferromagnetic steel in the direction of rolling.

The core steel which has under gone through both the siliconalloying and cold rolling treatments is commonly known as CRGOS


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or Cold Rolled Grain Oriented Silicon Steel. This material is nowuniversally used for manufacturing transformer core.

Although this material has low specific iron loss but still; ithas some disadvantages, like, it is susceptible to increase lossdue to flux flow in direction other than grain orientation and italso susceptible to impaired performance due to impact of bendingand blanking the cutting CRGOS sheet. Both the surfaces of thesheet are provided with an insulating of oxide coating.

Manufacturing of Transformer Core

During core manufacturing in factory some factors are taken intoconsideration,

1. Higher reliability.2. Reduction in iron loss in transformer and magnetizing

current.3. Lowering material cost and labor cost.4. abatement of noise levels.

Quality checking is necessary at every step of manufacturing toensure quality and reliability. The steel sheet must be testedfor ensuring the specific core loss or iron loss values. Thelamination should be properly checked and inspected visually,rusty and bend lamination should be rejected. For reducing thetransformer noises, the lamination should be tightly clampedtogether and punch holes should be avoided as far as possible tominimize cross flux iron losses. The air gap at the joint oflimbs and yokes should be reduced as much as possible forallowing maximum smooth conducting paths for magnetizing current.

Hysteresis Loss:


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The alternating voltage applied to a winding produces alternating magnetic flux and the crystals of silicon steel are subjected to such fluxes and result in spending of energy. This loss is called hysteresis.

Eddy Current Loss:

When alternating magnetic flux flows through the core, asmall emf is induced in the core which causes circulating current. This is called eddy current and the energy dissipated as a result of this is known as eddy current loss.

Machines

Slitting machine is used to cut the big roll of siliconsteel sheet in required sizes (widths) according to therating of transformer.

Power press machines are used to make limbs. They areoperated manually.

After cutting of limbs V punching is done on the yokelimb which is called yoke notching.

PLC cutting machines are also used to make limbs. Thereare two PLC machines. SDRI machine has a capacity of40,000 limbs per day. L.A.E machine has a capacity of60,000 limbs per day. In CNC machines length, width andangle are given as input.

CNC CUTTING MACHINE:

CNC cutting machine perform the same function as the cutting presses but in CNC, we program that machine according to our requirement. Then CNC machine cut the coil automatically. In CNC we do not require workers and work is done quickly.


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3. Assembly Section Core Assembly:

In the core coil assembly coil is fitted in the core and upperyoke limb is inserted to complete the core, then core istightened using upper and lower pressing beams. For coil to coilinsulation and core to coil insulation press pan sheet is used.

Before Connection Test (BCT) In the BCT area turns ratio of the coil is checkedusing TTR meter. Before the transformer is being sent tofurnace it is being tested. This test basically testscore losses also called as iron losses. Turn ratio oftransformer is also checked by using turn ratio meter. Weapply 240V per phase on the LV of transformer and checkthe output current. A tolerance of 5% is acceptable, ifit is above that then the transformer is sent back tothe winding section.

HT, LT ConnectionsIn this section Y-Delta connections are made. Tap changer isconnected with the coil. Connections are made according towork order specifications given by the design department.


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Taping is done on these connections to avoid any shortcircuit.

After Connection Test (ACT)In the ACT area turns ratio of the transformer is checkedusing TTR meter.

Furnace

After ACT transformer is kept in the furnace for 48 to 72 hours according to its rating. It is done to evaporate all themoisture from core or coil. Electric furnaces are also there for this purpose. . Each transformer needs 24 to 36 hours of proper heating inside the furnace. Initial temperature is 120 degrees. After 3 hours the temperature is decreased to 100 degrees. Diamond dotted paper needs proper heating so each transformer should be baked properly. After baking the connections of the transformers are checked. All nuts and bolts are tightened and the transformer is sent for assembling of further parts.

Conservator Tank It is an expansion vessel. The main purpose of conservator is to maintain oil in the transformer above a minimum level. It has a magnetic oil level gauge. It can give an alarm if the oil level falls below the certain limit. It has an oil filling provision along with an oil drain valve. Oil filled transformers witha conservator are equipped with Buchholz Relay. These are safety devices that detect the buildup of gases inside the transformer and switch off the transformer


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in emergency. The conservator has an oil level indicator. It is necessary that the oil level in theconservator must be maintained above a predetermined minimum level.

Cover Plate AssemblyIn this section HT, LT bushings, through bolts, eye boltsconnectors and other parts are inserted in cover plate.

Pre Tanking SectionWhen transformer is unloaded from the furnace it is insertedin the tank as quickly as possible to avoid the getting ofmoisture in the live part. Live part of the transformershould be inserted in the tank in 45mins to 1 ½ hours.

Transformer Oil: The oil serves as dual purpose of insulating medium and coolant. The heat generated inside a transformer is dissipated to the atmosphere or water through the insulating oil. The dissipation of heat is necessary to control the temperature within limits of the class of insulation used. Low volatility is therefore a desirable feature. It will be recognized that fire and explosion are to some extent potential risks whenever petroleum oils are used in electrical equipment. It is therefore necessary that the temperature of the oil in service should be very much lower than the flash point.


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Specification of insulating oil: Low viscosity. Low pour point. High flash point. Excellent chemical stability. High electrical strength. High specific heat. High thermal conductivity. Low solvent power. Low density Cheap and easily available.

Cooling Assembly: Cooling assembly is very important for safety of transformer. By forced cooling, the transformer capacity can be increased by more than 50%.

ONAN-Oil Natural, Air Natural: Asthe name implies this is a self cooled cooling system. Natural circulation utilizes the thermal head produced by heating of oil which rises through the windings as it is heated and through these coolers by natural phenomenonit is Oil natural. Heat is dissipated to atmosphere through radiator banks.

ONAF-Oil Natural, Air Forced: The capacity of the transformer can be increased to its fulldesigned capacity by installing cooler fans below or on surface of radiators to take away the heat at a faster rate. Oil is circulated by the same phenomenon as described above.

Temperature Indicators: Two temperature indicators are installed on the transformer:

1. Oil temperature2. Winding temperature


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These temperature indicators indicate maximum temperature and current temperature. Each indicator has two sets of mercury switches operated by temperature to give alarm and trip.

Paint ShopIn this section,painting o transformers is done either by liquid paint or by powder paint.

4.Testing SectionThe whole assembly is placed in the tank for testing.

Tests done at factory

1. Type tests2. Routine tests3. Special tests

Type Test of TransformerTo prove that the transformer meets customer’s specifications anddesign expectations, the transformer has to go through differenttesting procedures in manufacturer premises. Sometransformertests are carried out for confirming the basic design expectationof that transformer. These tests are done mainly in a prototypeunit not in all manufactured units in a lot. Type test oftransformer confirms main and basic design criteria of aproduction lot.

Routine Tests of TransformerRoutine tests of transformer is mainly for confirming operationalperformance of individual unit in a production lot. Routine testsare carried out on every unit manufactured.


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Special Tests of TransformerSpecial tests of transformer is done as per customer requirementto obtain information useful to the user during operation ormaintenance of the transformer.

Routine Tests:

1. Transformer winding resistance measurement.2. Transformer ratio test.3. Measurement of insulation resistance.4. High Voltage test.5. Measurement of impedance voltage/short circuit impedance

(principal tap) and load loss (Short circuit test).6. Measurement of no load loss and current (Open circuit test)7. Dielectric tests of transformer.8. Induced over Voltage Test9. Oil pressure test on transformer to check against leakages

past joints and gaskets.

1.Transformer Winding Resistance MeasurementTransformer winding resistance measurement is carried out tocalculate the I2R losses and to calculate winding temperature atthe end of a temperature rise test. It is carried out as a typetest as well as routine test. It is also done at site to ensurehealthiness of a transformer that is to check loose connections,broken strands of conductor, high contact resistance in tapchangers, high voltage leads and bushings etc.

There are different methods for measuring of transformer winding,likewise


http://www.electrical4u.com/transformer-winding-resistance-measurement/

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1.Current voltage method of measurement of windingresistance.2. Bridge method of measurement of winding resistance.

3.Kelvin bridge method of Measuring WindingResistance. 4. Measuring winding resistance by AutomaticWinding Resistance Measurement Kit.

2.Transformer Ratio TestThe performance of a transformer largely depends upon perfectionof specific turns or voltage ratio of transformer. So transformerratio test is an essential type test of transformer. This testalso performed as routine test of transformer. So for ensuringproper performance of electrical power transformer, voltage andturn ratio test of transformer one of the vital tests.

The procedure of transformer ratio test is simple. We just applythree phase 415 V supply to HV winding, with keeping LV windingopen. The we measure the induced voltages at HV and LV terminalsof transformer to find out actual voltage ratio of transformer.We repeat the test for all tap position separately.

3.Insulation Resistance Test or Megger Test ofTransformer

Insulation resistance test of transformer is essential typetest. This test is carried out to ensure the healthiness ofover all insulation system of an electrical powertransformer.

1. First disconnect all the line and neutral terminals ofthe transformer.

2. Megger leads to be connected to LV and HV bushing studsto measure insulation resistance IR value in betweenthe LV and HV windings.




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3. Megger leads to be connected to HV bushing studs andtransformer tank earth point to measure insulationresistance IR value in between the HV windings andearth.

4. Megger leads to be connected to LV bushing studs andtransformer tank earth point to measure insulationresistance IR value in between the LV windings andearth.

4. High Voltage Test: (Separate source voltage)

This test is used to check whether winding is insulated fromother parts of transformer or not. First, all the L.Vterminals and body of transformer are earthed. Than 33kvvoltage is applied on the H.V side. IT is checked whetherthe transformer will stand this voltage for 1 minute or not.

5.Load Losses (Short circuit test)

In this test L.V side is short and current is passed through theL.V side. Than V, I, PF and other quantities are measured

6.No Load Losses:(Open circuit test)

In this test H.V side is kept open and voltage is applied on theL.V side. Than V, I, PF and other quantities are measured.


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7.Dielectric Tests of TransformerDielectric tests of transformer is one kind of insulation test.This test is performed to ensure the expected over all insulationstrength of transformer. There are several test performed toensure the required quality of transformer insulation, dielectrictest is one of them. Dielectric tests of transformer is performedin two different steps, first one called Separate source voltagewithstand test of transformer, where a single phase powerfrequency voltage of prescribed level, is applied on transformerwinding under test for 60 seconds while the other windings andtank are connected to the earth. it is observed that whether any failure of insulation occurs ornot during the test. Second one is induced voltage test ofTransformer where, three phase voltage, twice of rated secondaryvoltage is applied to the secondary winding for 60 second bykeeping the primary of the transformer open circuited. Thefrequency of the applied voltage should be double of powerfrequency too. Here also if no failure of insulation, the test issuccessful.In addition to dielectric tests of transformer there are othertype test for checking insulation of transformer, such aslightning impulse test, switching impulse test and partialdischarge test.8. Induced Over Voltage Test

This test is used to check the winding insulation. In this testvoltage is applied on the L.V side because it is easy to provide.On the L.V side twice the rated voltage at four times the normalfrequency is applied. Test time should be greater than 15seconds.


http://www.electrical4u.com/insulation-dielectric-test-of-transformer/



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Conclusion

In spite of huge competition from emerging localand multinational brands, PEL transformers have remained in the spotlight due to constant innovation and priority of quality over cost. PELhelped me a lot in understanding the principlesof transformer design,manufacturing, construction, testing operation and maintenance. PEL helped me to update my knowledge on Power transformers. I learnt a lot during my internship at PEL. It was one heck of a time at PEL.


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Referencewww.wikipedia.com

www.pel.com

www.electrical4u.com

www.antony-anderson.com/unusual/helical.htm

Book: Chapman 4th edition


http://www.antony-anderson.com/unusual/helical.htm

http://www.electrical4u.com/

http://www.pel.com/

http://www.wikipedia.com/

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EHV Power Transformer

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