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WWW.TRANSFORMERS-MAGAZINE.COM ISSUE 1, VOLUME 1 | 1

Jean SANCHEZ, Mladen BANOVIC

TRANSFORMERS MAGAZINE1 | ISSUE 1, VOLUME 1

TransformersMAGAZINEVOL 1 ISSUE 1

Classication of

Transformers Family

Basics of PowerTransformers

A General Overviewof Power TransformerDiagnosis

Issues to Consider whenSubstituting Large PowerTransformers in GeneratingStations

Economical and ReliableTransformer Maintenance

by Holistic Interpretation ofInsulating Oil Condition

Voltage Stresses on

Solid-Liquid Insulation ofLarge Power Transformers

ISSN 1849-3319TRENDS IN POWER

TRANSFORMER FAILURE

ANALYSIS WALLACE BINDER

POWER

TRANSFORMER LIFE

CARLOS GAMEZ


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+

It's not the sizeof the circuit

that mattersbut the energyit transmits

Coiltech 201424-25 September Pordenone

With a creative, uniquecost and time effectiveexhibition and conferenceformat, Coiltech hassuccessfully challenged oldhabits and grown in just fouryears into an establishedmeeting pointof the Coil

Winding industry.

Producers of electricalmotors, generators,transformers and otherinductivities meet to discussnew projects and business

development with marketleaders from all major partsof the supply chain.

marcogarofalo.net

What visitors like about Coiltech

Leading international suppliersInnovative suppliers of all significant components and technologies

Excellent networking opportunity Highly specialized technical presentationsat the World Magnetic Forum Compact format, best use of time, excellent traffic connections

Signupforyourfreee-ticket:www.visitcoiltech.com

Choose your spotyourself:www.exhibitatcoiltech.com

What exhibitors like about Coiltech+

+

Highly competentvisitors with an increasingly internationalbackgroundThe best visitor per exhibitor ratioof any Coil Winding ExhibitionTurn-key stands for better use of time and resources Internet connection includedMinimum effort for organisational issues thanks to theall-inclusive exhibition formula

Transparent, all-inclusive cost with no surprises, three booth formatsto choose from.

For complete visitors profile, see www.quickfairs.net/coiltech*Coiltech is the only show in the industry with certified visitors data (ISFCERT).

Coiltech has a rebooking rate in excess of 90%.At other Coil Winding exhibitions it is about 75%

Exhibitors

2010

47

24

23

2011

61

85

24

2012

85

125

40

2013

129

181

52

Exhibitors sign-up dynamics*

Months10 2 612 4 811 3 71 5 9

Number of unique Visitors*

2010

397

2011

676

2012

941

2013

1286

2014

2013

2012

2011

2010

*As of 28 February, 2014; exhibitors list updated real time on www.quickfairs.net


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NEWS

BASICS OF POWER TRANSFORMERS


What are the basic transformation principles and essen-

tial transformer parts?

Power transformers are key elements of a high voltage elec-

trical transmission grid, which adapt voltage levels to the dif-

ferent needs of electric power users at constant power (dis-regarding the losses).

POWER TRANSFORMER LIFE

Carlos GAMEZ

Part 1: What does transformer life mean?

The concept of life for an electrical asset, such as a power

transformer, is sometimes not properly understood. In this ar-

ticle we review what we mean when we refer to the life of

a transformer and what constrains determine the design and

operational parameters of these assets.

TRENDS IN POWER TRANSFORMER FAILURE ANALYSIS

Wallace BINDER

This article will introduce the reader to the importance of fai-

lure investigations, discuss the need for guidelines and the

standards organisations work that is underway to provide the

guidelines. The concept of using the Scientific Method is int-

roduced and the existing processes are described.

CLASSIFICATION OF TRANSFORMERS FAMILYMladen BANOVIC, Jean SANCHEZ

Transformers are used in the electrical networks everywhe-

re: in power plants, substations, industrial plants, buildings,

data centres, railway vehicles, ships, wind turbines, in the

electronic devices, the underground, and even undersea. It

is very difficult to organise a structured overview of the trans-

former types. Here the attempt is to provide a relatively com-

mon point of view on most of those transformers types.

www.transformers-magazine .com 3

CONTENT


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750 GOOD REASONS

TO VISIT


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VOLTAGE STRESSES ON SOLIDLIQUID INSULATION

OF LARGE POWER TRANSFORMERS

Juliano MONTANHA

Influence of dielectric tests on main insulation design

Dielectric tests are mandatory to define the main insulation

transformer design such as clearances between windings,

windings to core and leads as well. Therefore, it is very im-

portant to understand how and where the voltages are distri-

buted within the transformer during the dielectric tests.

A GENERAL OVERVIEW OF POWER TRANSFORMER DI

AGNOSIS


This paper discusses the main diagnostic methods that could

be performed during service life of a transformer. It will also

attempt to provide the purposes of the main diagnostic me-

thods carried out by different power transformer stakeholders.

ISSUES TO CONSIDER WHEN SUBSTITUTING LARGE

POWER TRANSFORMERS IN GENERATING STATIONS

Relu ILIE, Isidor KERSZENBAUM

The purpose of this paper is to indicate the most important

aspects to be considered when checking the interchangeabi-

lity of transformers, based on authors experience and vari-

ous standards requirements.

ECONOMICAL AND RELIABLE TRANSFORMER MAIN

TENANCE BY HOLISTIC INTERPRETATION OF INSULA

TING OIL CONDITION

Marius GRISARU

A transformer owner or a person responsible for its proper ope-

ration is faced with many diagnostic approaches and most of

them are either inaccurate or unnecessary and irrelevant to in-

dividual case. It is important to carry out the tests that will not

interfere with transformer operation and interpret the results

holistically in the transformer exploitation context, manufac-

ture, internal organisation politics and many other parameters.

EVENTS


CONTENT


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TRANSFORMERS MAGAZINE

EDITORIAL BOARD

Editor in Chief: Mladen Banovic, PhD;

PUCARO Elektro-Isolierstoffe GmbH; Germany

[email protected]

EXECUTIVE EDITORS

Michel Duval, PhD; Hydro Quebec; CanadaPierre Lorin; ABB; Switzerland

Jean Sanchez, PhD; EDF; France

Jin Sim; Jin Sim & Associates, Inc.; USA

Juliano Montanha; SIEMENS; Brazil

Craig Adams; TRAFOIX; Australia

Arne Petersen; AP Consulting ;Australia

Art director: Momir Blazek

Photo: Shutterctock.com

Language Editor: Mirna Harwood

ADVERTISING AND SUBSCRIPTION

Marin Ante Dugandzic+44 20 373 474 69

[email protected]


Transformers Magazine is published quarterly

by Merit Media Int. d.o.o., Setaliste 150. briga-

de 10, 10 090 Zagreb, Croatia. Published ar-

ticles dont represent official position of Merit

Media Int. d.o.o. Merit Media Int. d.o.o. is not

responsible for the content. The responsibili-

ty for articles rests upon the authors, and the

responsibility for ads rests upon advertisers.

Manuscripts, photos and other submitted do-

cuments are not returned.

Subscription rate: $76 (1 year, 4 issues)

Digital subscription: free for registered readers

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private use of patrons. Abstracting is permited

with credit to the source. A per-copy fee must

be paid to the Publisher, contact Subscription.

For other copying or republication permissi-

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Publisher: Merit Media Int. d.o.o.

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Contact: +385 91 222 8820 Croatia

Contact: +44 20 373 474 69 UK

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Subscribe to Transformers Magazine and keeptrack of the latest news and trends in the powertransformer industry.Print Edition 4 issues (1 year) for $ 76

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ISSUE1, VOLUME1 | 1

JeanSANCHEZ,MladenBANOVIC


1 | ISSUE1,VOLUME1

TransformersMAGAZINE

VOL1 ISSUE1

ClassicationofTransformersFamily

BasicsofPowerTransformers

AGeneralOverviewofPowerTransformerDiagnosis

IssuestoConsiderwhenSubstitutingLargePowerTransformersinGeneratingStations

EconomicalandReliableTransformerMaintenancebyHolisticInterpretationofInsulatingOilCondition

VoltageStressesonSolid-LiquidInsulationofLargePowerTransformers

ISSN1849-3319

TRENDSINPOWERTRANSFORMERFAILUREANALYSISWALLACEBINDER

POWER

TRANSFORMERLIFECARLOSGAMEZ

Australasia:

Vince Hantos

[email protected]

Tel: +61 40 768 03 31

India:

Ashutosh Kumar Govil

[email protected]

Tel: +91 99 750 975 34

ADVERTISING

Northern Europe:

Matti Stoor

[email protected]

Tel: +46 70 644 31 94

Spain & Portugal:

Alfonso de Pablo Hermida

[email protected]

Tel: +34 91 715 77 92

Russian Federation:

Alexander Drobyshevski

[email protected]

Tel: +79 03 618 33 42

ROW:

Marin Ante Dugandzic

[email protected]

Tel: +44 20 373 474 69


7/68

The idea about a transormersmagazine was born rom dis-cussions on Linkedin ransor-

mers orum, where people worldwide,rom over 130 countries, take part in24/7 discussions, share their experien-ces and learn about the latest issues re-lated to transormers. Tere is a trulywide range o broad, comprehensive

topics which include all aspects o transormers lietimeand its components such as: parameter specifications romthe grid viewpoint, including smart grid, reliability andefficiency, design, manuacturing, testing, operation andmaintenance, protection, monitoring, diagnosis, ailure,research o the ailure causes, standards, education etc.

Some o the most accomplished experts have told me thatthrough the orum they can still expand as well as rereshtheir knowledge, despite spending decades in the transor-mers field in the best possible environment. Te content isspecifically valuable to the somewhat less experienced, thosewith limited knowledge in this field. In order to prevent thecontent rom being lost somewhere in virtual world in theelectronic orm, the idea o a magazine was born. A group omore active transormer community members made greateffort in preparation o the magazine and, despite their nu-merous private and work commitments, the magazine has

become a reality.Te website has been active or some time now, and it re-gularly brings current global news related to transormers.Te comments received so ar have been very positive andencouraging, especially or the website maintenance teamwho endeavour not only to keep up the good work but toalso strive or improvement in time.

Print magazine brings technical articles regarding the mostrecent topics, with a particular ocus on efficiency increa-sing solutions and solutions or smart grid.

Influence o transormers on the environment is ofen si-gnificantly underestimated, probably because it is a highly

efficient device with efficiency at rated load even greaterthan 99%. However, the efficiency on a system scale is notso high, due to a series o transormers on the electricitys

way rom power plants to consumers, due to loading lowerthan rated, and due to lower efficiency o smaller transor-mers.

It is estimated that about 10% o globally generated elec-tricity is dissipated in grid losses, 40% o that being thelosses in transormers. Tat means 4% o globally gene-rated electricity is wasted in transormers. Significantpower generation (and transmission) capacity and cor-responding energy resources are needed just to supplytransormer losses globally, which is a huge amount anda solid potential or reduction o the environmental im-

pact.

Te additional problem is that transormer fleet ages glo-bally. Tis significantly increases not only financial risksor utilities and industry, but also the risk o even largerenvironmental impact.

Tereore, we encourage thinking and writing about so-lutions and strategies to lower environmental impactthrough urther increase o efficiency, i.e. lower CO emis-sion, ailure prevention, extension o transormer lietime,and decrease o other risks, particularly risks o endan-

gering peoples lives and health. We would like to use thisopportunity to invite you to participate in creation o theransormers Magazine upcoming issues.

Te first issue covers some o the undamental topics suchas reviews o transormer types, insulation design, diagno-sis, lietime, ailure research and transormer replacement.

I wish you a pleasant reading.

Mladen Banovic , Editor in Chie

Dear Readers,

EDITORIAL MESSAGE



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EDITORIAL BOARD

Michel Duval

Dr Michel Duval obtained a B.Sc. and PhD.

in chemical engineering in 1966 and 1970,and has worked or IREQ (Hydro-Quebec,Canada) since 1970. He has made signi-ficant contributions in 3 mains fields oR&D: dissolved gas-in-oil analysis (DGA),

electrical insulating materials and lithium-polymer batteries.In the field o DGA, Dr Duval is well-known or his riangle methodo DGA interpretation, used worldwide. He has developed the use ogas-in-oil standards and participated in the development o the Hy-dran on-line monitor or hydrogen in oil. Dr Duval has establishedthe levels o gas ormation observed in various types o electrical equip-ment. He has been the Convenor o numerous IEC and CIGRE working

groups and the principal author o several IEC international standardsand CIGRE echnical Brochures on DGA. He is also very active in seve-ral IEEE working groups.Dr Duval holds 16 patents and is the author o more than 100 scientificpapers and standards. He is a Fellow at the Chemical Institute o Canada,a Lie Fellow o IEEE, and the recipient o IEC and CIGRE Awards ando the IEEE Herman Halperin Electric ransmission and DistributionAward or 2012.

Pierre Lorin

Pierre Lorin holds M.Sc. Electrical &Mechanical. He graduated in Paris in1992. From 1992 to 1996 he worked atthe Swiss Federal Institute o echnologyin Lausanne (EPFL) where he conduc-ted researches or large utilities in Euro-

pe and North America on reliability and maintenance strategy oroverhead lines.From 1996 till today he has been with ABB Power Products - rans-

ormers Service. He has been active in Research & Development aswell as Product Management, mainly involved in transormers reli-ability, diagnosis methods, on-line monitoring, maintenance, repair,and active noise control. He is now Head o echnology or rans-ormers Service activities globally and the author or co-author oseveral publications in this field. Pierre has represented Switzerlandwithin the CIGRE ransormer Study Committee (A2) or 6 years.He is now leading the Advisory Group ransormer Utilizationwithin CIGRE A2.

Jean Sanchez

Jean Sanchez completed a Ph.D. degreeon organising a general scheme or powertransormers ault diagnosis in 2011 andworked in a rench power transormerreparation actory. Tis work was basedon ormalising and systematising human

expertise and experience on power transormer ault diagnosis oany kind, which was developed over the years in close collaborationbetween transormer users and the reparation actory on ailures andactive part reconstructions. He worked on many transormer designs(core as well as shell type, GSU, substation and industrial transor-

mers), tests (electrical, oil analysis), ault expertise (onsite, and in re-paration workshop), power ratings, and OLC reparations (MR andold rench designs). oday he is working on generator diagnosis (me-chanical, electrical, ancillaries) and maintenance in a major Frenchutility and is the executive editor o the ransormers Magazine. Healso holds a Masters degree in Applied Physics.

Editorial boardof Transformers Magazine consists of expertswith diverse experiences and backgrounds, from different parts of theworld, and of different age. This should ensure as broad view on the mat-ter of the magazines scope as possible. Here we present the editors shortthorough biographies.

TRANSFORMERS MAGAZINE | Volume1, Issue18


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Jin Sim

Jin Sim holds a BSEE rom DankookUniversity in Korea. He attended twograduate schools or Engineering andone graduate school or Business Admi-nistration. He has been in the transor-mer industry or over 37 years in design,

development, manuacturing, testing and management. In 2013,Jin retired as a VP and Chie echnology Officer at SPX ransor-mer Solutions (ormerly known as Waukesha Electric Systems) andounded his own consulting company; Jin Sim & Associates, Inc. Hehas been active in the Electric Power Industry as a leader o sever-al working groups and subcommittees. Recently, Jin was the chair-man o the IEEE ransormers Committee or 20022003. He wasa member o the U.S. echnical Advisory Group or IEC echnicalCommittee 14, Power ransormers and an individual member othe CIGRE. He has also been the NEMA and IEEE delegate to the

ASC C57 Committee.

Juliano Montanha

Juliano Montanha holds a degree in Elec-trical Engineering rom University o SoPaulo Brazil rom 1998 when he startedworking at Siemens Power ransormeractory in Jundiai - Brazil. Juliano hasbeen working with insulation technolo-

gy regarding main insulation design up to 800 kV, including leads

design and winding assembly. He was responsible or winding as-sembly standardisation or local market in 2000.Juliano is a high voltage expert at Siemens ransormer Group andhas participated on a worldwide R&D research with the Siemenstransormers actories.Between 2011 and 2013, he was responsible or insulation designgroup at Jundiai Siemens actory. He was also responsible or imple-mentation o 500 kV electrode in Jundiai actory as well as transientstudies or Power ransormers design like VF studies and ailu-re investigations. Juliano technically supported the manuacturingprocess o HVDC units at Siemens actory in Jundiai and Siemensactory in Mxico in 2010. He has been a member o IEEE since

2014.

Craig Adams

Craig Adams started his career in 1992 asan apprentice electrical engineering tra-desperson with Capricornia ElectricityBoard beore commencing urther engi-neering studies. He joined GEC Alstomin 1997 as a Cadet est Engineer at the

Rocklea Works, and rom 2001 to 2013 held positions o est Ma-

nager and Product Quality Manager. In 2013 he ounded RAFOIXPty Ltd and is currently its Director and Principal Consultant.He has extensive experience in all aspects o transormer testing,routine, type & special tests, and investigative diagnostic techniquesincluding ailure investigations and orensic strip downs. He hasconsiderable experience with routine & type testing o HV & MV

apparatus including switchgear, capacitor banks, high voltage mo-tors and generators, and in the design and upgrading o test acilitiesand equipment.

Arne PetersenArne Petersen received degrees in Elec-trical Engineering rom Odense ekni-kum, Denmark, a Bsc.Eng degree romRMI, Australia and an MBA degreerom University o Queensland, Austra-lia. He is also a chartered engineer and a

ellow member o Institution o Engineers Australia.Arne has five years experience as a transormer designs engineerwith a transormer manuacturer and three years experience in po-wer station design. He also worked as a transormer specialist andmanager o HV Plant or Powerlink, Qld, a major Australian trans-

mission utility, or twenty-seven years.He is currently working as a sel-employed consulting engineerspecialising in transormer technology. Arne has conducted manyinvestigations into transormer ailures and fires in Australia andSoutheast Asia.He is an active member o Cigre, both in Australia and internatio-nally, he was active in several Cigre working groups and is currentlycontributing to Cigre Study committee or transormers (SC A2).

Mladen Banovic

Mladen Banovic obtained his PhD de-gree rom the University o Zagreb in2012. He leads PUCAROs research anddevelopment in transormer insulation,the editorial board o ransormers Ma-gazine, and the ransormers orum. He

managed the development o insulation systems up to 1200 kV andhas been involved in defining ABBs smart grid strategy coveringtransormer insulation and components. Prior to joining PUCA-RO, he led basic research o transormer insulation and transormermonitoring business. He worked on developing and deploying sys-tems or automated testing o transormers in actories and onsite,

sofware packages or automation o transormer design, 2D and 3Dfield calculation and analysis, etc.Mladen is active member o a ew IEC, IEEE, and Cigre workinggroups. He also holds a degree in Electrical Engineering and post-graduate Master o Science degree rom the University o Zagreb.



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PRODUCTS NEWS

The newly-announced purification systems areHVOPS and DOPS: High Vacuum ransor-mer Oil Purification Systems (HVOPS) are single

pass systems intended or quick turnarounds. Diel-

ectric Oil Purifier Systems (DOPS) are designed to

remove all impurities in multi-pass. Unlike HVOPS

equipment, they do not pull a deep vacuum on empty

transormers or dry out. Otherwise, they unction the

same as HVOPS.o find out more, visit: www.oilfiltrationsystems.com

The new generation o monitors uses carbon nano-tube technology and combines total combustiblegas (GS), temperature and load monitoring readings

to provide real-time notification or single and three

phase distribution transormers.

Te monitors are the newest additions to the Born

Smart line o smart grid sensing devices by IUS ech-

nologies. Tey have an accuracy rating o 0.2% to re-

mote transormer monitoring and provide a complete

view o equipment health apart rom regular manual

inspection periods.

M1000 and M2000 immediately detect normal,

abnormal, caution or dangerous conditions and send

alerts either when predetermined conditions are met or

supply a constant stream o inormation.

Source: Business Wire

The new Perception (M) is the latest version othe General Electrics Digital Energy risk ma-nagement sofware, a package used to diagnose the

condition o every transormer in the fleet.

ransormer diagnosis is perormed by the asset owners

in order to maintain a transormer fleet and reduce ope-

rating expenses.

Source: Tomasnet News

In addition to regulation tasks, the APCON(R)also supports special applications such as three-winding transormers, transormer banks, phase shi-

ters or shunt reactors. Te modular system makes itpossible to match the regulators power spectrum to

the respective requirements, claims MR.

APCON is suitable or integration into redundant

network systems with the RSP and PRP protocols.

Source: Maschinenfabrik Reinhausen GmbH

Endesa decided to extend the strategic measures tomake the acilities saer and fitted the camera inthe Maragall substation a ew months ago. Te camera

is very small; in act, i not inormed, one would not

even be aware o its existence. It is suspended rom theceiling corner in Room 4.

Tis device allows thermal monitoring, i.e. analysing

the heat o the most sensitive elements o power trans-

ormers and they are used to signal a warning in the

event o above normal heat detection.

Te tiny thermographic camera has been a major leap

orward in saety and possible fire prevention. Endesa

is pleased with the results and now wants to export the

surveillance camera. Source: El Periodico

Oil Filtration Systemsannounces two new se-ries of transformer oilpurication equipment

IUS Technologies pre-sents new smart trans-former monitors

GEs Digital Energy an-nounces the latest ver-sion of Perception

Endesa installs thermographic camera to monitor

transformers in Maragall substationMR announces new TAP-CON voltage regulator

USA, Texas: Oil Filtration Systems (Clark-

Reliance Company) has announced twonew series of oil purification equipmentto remove impurities from dielectric in-sulating oils.

USA, Texas: IUS Technologies unveiledgroundbreaking distribution transfor-mer monitors - the TM1000 and TM2000at DistribuTECH in San Antonio.

USA, Georgia, Atlanta: GEs Digital Ener-gy has launched the latest version of

Perception (TM) software used by theutilities for management of their powertransformer fleet.

Germany, Regensburg: The market lea-der, Maschinenfabrik Reinhausen GmbH(MR) has released TAPCON, the newvoltage regulator.

Spain, Barcelona: The Maragall substa-tion has been fitted with a tiny thermo-graphic surveillance camera which re-cords everything that happens in powertransformers within a 24 hour period.


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BUSINESS NEWS

Products of M&I Materials Ltd.

l

Apparently, the first power transormer in theworld, insulated and cooled using vegetable oil,will link the 380 kV ultra-high voltage level with the

110 kV grid, writes EBR.

Te insulating oil or the new transormer is made

rom renewable plant resource, is completely bio-de-

gradable, and much less flammable than mineral oil.

Te bio-degradability o the insulating oil means that

additional collecting vessels and separation systems areno longer required at the installation location, resul-

ting in cost savings or these items. said Siemens Ener-

gy ransormers business unit CEO, Beatrix Natter.

Te transormer can be installed and operated in water

conservation areas or areas where environmental pro-

tection applies as it is the worlds first transormer at the

420 kV extra-high voltage level or which no water ha-

zard classification must be issued. Source: EBR

The company intends to reorganise the existingsite and employ extra 100 people to work in thenew buildings. With this investment, the entire eco-

nomy o the Regensburg site will be urther strengthe-

ned. said the Mayor Hans Schaidinger.

Te main objectives o the investment were to reduce

logistics costs and lead times by at least 25 %. Te our

camps operating in the urban area as well as the need

to renew the warehouse equipment and reorganise all

the processes were the reasons or the construction o

the site.

Te construction o the new buildings and reorganisa-tion o the actory premises is scheduled or comple-

tion by the end o 2015. Te new, highly automated

materials management centre is scheduled to start

operation in early 2016.

Source: Maschinenfabrik Reinhausen Gmbh

F

alurrias Capital Partners ormed NADG in

2013 to acquire and grow well-perorming US-

based companies with strong balance sheets that sup-

port mission-critical elements o the electric utility

grid. Te first acquisition made by NADG was IEC,

a Charlotte-based manuacturer o instrument trans-

ormer products.

ACS product portolio includes SCADA, distributi-

on management, outage management and substation

automation. ACS was one o the first companies in the

industry to deliver a truly integrated ADMS platorm,

combining distribution and outage management unc-

tions using a common network model and user interace.

ACS has a tradition o innovation that has kept us at the

oreront o the transormation to an intelligent grid. said

Jos Barbosa, CEO o ACS. ogether with the NADG

leadership and the backing o Falurrias Capital Partners,

we will continue developing new solutions that empower

our customers to meet the challenges they ace today and

in the years to come. Source: Efacec

TransnetBW commis-sions rst vegetableoil 420 kV transformerfrom Siemens

MR invests 24 million($ 33 million) in newmaterials managementcentre

Falfurrias Capital Partners acquire Efacec ACS

Germany: TransnetBW has commissionedSiemens first vegetable oil transformer

with 420 kV voltage level at the Bruchsal-

Kndelweg substation near Karlsruhe.

Germany, Regensburg: Maschinenfabrik

Reinhausen GmbH (MR), the world leader

for the regulation of power transformers

has invested 24 million ($ 33 million) in

strengthening the highly automated ma-

terials management centre in Regensburg.

USA, Georgia: Falfurrias Capital Partners, North Carolina-based private equity firm, has

acquired Norcross, Georgia-based Efacec ACS, Inc. from the Efacec Group for undisc-

losed terms. The company name will change to Advanced Control Systems, Inc. (ACS).


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12 | JULY 2013

Introduction

Nowadays, electric energy is availa-ble almost everywhere, and we donot even think how it was produ-

ced. Production o the electric energyis possible by application o the powertransormers.

Power transormer is a complex assem-bly o elements based on decades-long,worldwide proven technologies. Toseelectrical machines are essential or po-wer grids to transmit electrical power by

minimising Joules effect losses using highvoltage over long distances.

ransormers have been used worldwideor many years and their availability andreliability is a major concern or all electri-city users and the assets owners.

Basics of power transformershe basic acts and the main parts andcomponents o power transormers arepresented in this article to understandwhich diagnoses can be applied accor-dingly.

Basics of PowerTransformersWhat are the basic transformation prin-ciples and essential transformer parts?

ABSTRACT

Power transformers are key elementsof a high voltage electrical transmissi-on grid, which adapt voltage levels tothe different needs of electric powerusers at constant power (disregardingthe losses). This electrical machine is

classically constructed out of copper,steel, paper and insulating oil. All tho-se materials are made into differentcomponents. The main ones are thewindings, tap changing system, core,tank and bushings. The componentsare assembled together to produce apower transformer. Power transfor-mers are developed worldwide using afew basic designs established almost acentury ago, that can be largely adap-ted for many special applications [1].

Keywords

basics, components, power transfor-mers

TECHNOLOGY BASICS



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Electromagnetic basis

A single-phase transormer is basicallymade out o two separate windings thatare inserted into each other into a closedloop o magnetic core. Te voltage ratio(V1/V2, where V1>V2) o the transor-mer is equal to the ratio o the number oturns o the two windings (N1/N2, whereN1>N2) in a first approximation. It shouldbe noted that a classic power transormerrequires alternative voltage.

In a rough approximation, i the trans-ormer losses are disregarded, the power(Voltage x Current) transmitted throughthe windings has a lower current on thehigh voltage (HV) side than on the low

voltage (LV) side. Moreover the Joules

heat effect is proportional to the square othe current transmitted into any ordinaryconductor like transormer windings ortransmission lines.

Both these effects combined at constantpower o elevating voltage reduce heat dis-sipation accordingly by the square o thecurrent, and enable the transmission opower o alternating current and voltageover very long distances rom the energyproducer to the energy consumer while

limiting the power losses in the grid. Tisis possible due to a key grid component -the power transormer. Most o them arethe three-phase transormers or the threesingle-phase transormers.

Tree points could be noted rom theseelectromagnetic principles. First, with the

voltage increase o an electrical network,the Joule losses are reduced. Te trend inlarge countries like Canada, Brazil, Russia,China, South Arica, South Korea, USA,

and Venezuela is the development o the800 kV electrical networks, or the 1000kV to 1200 kV ones in China and India,respectively. Secondly, the two main con-

straints o power transormers are highvoltage and high current, depending onwhether the HV or LV is observed. Toseconstraints are taken into account whenstudying the transormer limits, like over-

voltage (lightning) and overcurrent (shortcircuits). Te reader interested in findingout more about the theory and the practi-ce regarding power transormers couldread [2], a book continuously updated oralmost one century ago!

Active part

Te active part o a transormer is made othe elements that are in contact with the

voltage and the current, and are mainlycomposed o win-dings, core, tap chan-ger bushings. Teother components areancillary componentsnot mentioned here.

Windingshe windings o apower transormerare its main element,like the heart in a hu-man. he windings are handmade outo copper, or sometimes out o alumini-

um coils insulated mainly with severallayers o paper between the turns. hetwo main winding designs and techno-logies have been developed over timewith many variations: the core type andthe shell type windings. he electroma-gnetic basis remains the same in bothcases but the mechanical constructionis dierent. In the core type design, thewinding is enclosing the magneticcore legs, while in the shell type the coreis enclosing (and running through)

the windings. Everytransormer manu-acturer has its ownexperience with thesetechnologies, neithero which is automa-ted.

he manuacturingo windings involvesa lot o human labourand requires signii-

cant experience as well as applicationo the highest quality standards. his is

Nowadays, electric energy is

available almost everywhe-

re, and we do not even think

how it was produced. Pro-

duction of the electric ener-gy is possible by application

of power transformers.

The theoretical and practi-

cal principles of power tra-

nsformers have remained

the same since more than a

century ago.

Figure 1: Three phase power transformer





14/68

because winding conductors are coveredby a type o insulation such as varnish orinsulating paper with a limited mecha-nical and thermal stability. Nevertheless,this insulation type provides protectionrom high overvoltages, high overcur-rents, short-term overheating, and highmechanical stresses in order to preventreduction o the insulation paper dura-bility. It must be taken into account thatthe winding insulation cannot be easilyrepaired or replaced during the servicelie o a transormer and rewinding hasto be perormed only in a specialisedworkshop. A review o winding typesused in power transormers is providedin the article [3].

Core

Te core is an important part o a trans-ormer and generally the heaviest one.Produced rom steel, it has high magne-tic permeability and provides low mag-netic resistance to the magnetic flux. Itis made rom thin steel sheets with thethickness o a ew tenths o a millimetrein order to reduce losses and magneti-sing current. Te main way to producea core is to stack the sheets, cut to desi-red size, onto the automatic machines,and then manually stack them to build a

core. Wound cores provide much betterproductivity or single-phase small dis-tribution transormers.

Te main core parts are the legs (verticalparts), and yokes (horizontal parts). Telegs are mainly situated in a same plainbut the three-phase transormers can haveso called triangular-spaced core legs. Tis

type o transormer is called hexaormer.Small-size transormers, like distributiontransormers, are sometimes producedas hexaormers but their market penetra-tion is very low. Even transormers o up

to 10 MVA have been produced in thisorm but the concept was cancelled dueto complexity. Tey produce lower lossesbut their productivity is lower comparedto transormers with a traditional core.

The manufacturing of core

and windings - the heart of atransformer, involves a con-

siderable amount of manual

labour even to date.

Figure 2: Insulation in power transformer

Figure 3: High voltage bushings of power transformer


TECHNOLOGY BASICSTECHNOLOGY BASICS


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Tap Changer

Most transormers have additional turnsadded to the HV windings and some othose turns are linked to a device calledthe ap Changer. It enables a specificrange o the voltage variation during thetransormer service lie. Te electric cir-cuit o the windings and the tap changer

have some movable contacts. Te twomain types o tap changers are the DE-energized ap Changer (DEC) - me-chanically quite simple type that changesthe voltage while the transormer is notloaded; and the On Load ap Changer(OLC) - a more complex type [4] whichoperates when the transormer suppliesthe load.

It should be noted that the tap changers,the OLCs in particular, are contributingto an increasing transormer ailure rate,mainly due to the movable contacts wea-ring over the years (hot spots, aging me-chanisms) [5].

Bushings

he bushings are the components thatlink the windings to a network throughthe grounded tank. High voltage bus-

hings can be technically complex and,in some cases, their ailure can lead toa transormer explosion quite rapidly.his is because one o the highest volta-ge gradients is between the HV bushingcentral part at ull potential, and thegrounded tank at the distance o just aew centimetres. he insulating oil justbelow is very lammable and i the bus-hing is sparking, it could generate a lot oenergy, open the tank slightly and thenignite the oil, which could lead to an ex-

plosion. For this reason, the HV bushingis manuactured to withstand very highvoltages within a small space illed withpaper and oil between the bushing andtransormer tank.

Insulating materials

Te three most typical insulating mate-rials or the power transormers are: mi-neral oil, paper and pressboard in diffe-rent orms. Te mineral insulating oil isweighted in tons within the tank and canbe used to assess many essential pointsabout the condition o a transormer andsome critical incipient aults. Te paperinsulates the winding turns, while thepressboard strengthens the electrical in-sulation and provides dielectric distanceat specific locations, or example in themain duct between the windings.

Insulating materials, such as paper,pressboard and mineral oil are organicmaterials subject to aging. As the solidinsulation cannot be repaired or repla-

ced easily like other transormer partsand components, it limits the transor-mer service lietime. Tereore, the solidinsulation lietime is the main driver othe lietime o a transormer.

Conclusion

he basic acts about transormersand the main transormer parts andcomponents are briely described abo-

ve. Power transormers can be see n asmain components o any high voltagegrid, which reduce the losses duringthe delivery o electrical energy to wideareas. More details on the topics abovecan be ound i n the literature cited, in-cluding [6] and [7].

References

[1] Mladen Banovic, Jean Sanchez, Classifi-cation o Transormers Family, ransormersMagazine, Vol 1, No.1., 2014

[2] Martin J. Heathcote, J&P Transormerbook, Newnes, 13th edition, 2007

[3] Jean Sanchez, Classic Power TransormersWindings, ransormers Magazine, Vol 1,No.2., 2014 in print

[4] Dieter Dohnal, On-Load Tap-Changersor Power Transormers A Technical Digest,MR Publications, 2009, source :www.reinhausen.com/XparoDownload.ashx?raid=15497

[5] An international survey on ailures inlarge power transormers in service, CIGREElectra No. 88, pp 21-42, 1983

[6] IEC chapters 1 to 21 o the 60076 powertransormers standards, www.iec.ch

[7] Handbook or Transormers, 3rd edition,ABB, 2010

AuthorsJean SANCHEZ completed a Ph.D. degree on pow-er transormers ault diagnosis in 2011 and worked in aFrench power transormer reparation actory. His workinvolved many transormer designs, tests, ault expertise,

power ratings, and OLC repairs. oday he is working ongenerator diagnosis in a major French utility and is the exe-cutive editor o the ransormers Magazine. He also com-pleted a Masters degree in Applied Physics.

Mladen BANOVIC obtained his PhD degree rom theUniversity o Zagreb in 2012. He leads PUCAROs re-search and development in transormer insulation and theeditorial board o ransormers Magazine. He has beeninvolved in the development o insulation systems up to1200 kV and defining ABBs smart grid strategy covering

transormer insulation and components. Prior to joiningPUCARO, he led basic research o transormer insulationand transormer monitoring business. He also holds a de-

gree in Electrical Engineering and postgraduate Master o Science degree rom theUniversity o Zagreb.

Mostly used solid insulating

materials, paper and press-

board, are organic and sub-

ject to aging. They cannot

be repaired or replaced ea-

sily, therefore they limit the

lifetime of a transformer.



16/68

COLUMN

In our industry there are ofen terms orbuzzwords that many o us use with li-berty but might not ully understand

their meaning.

Justifiably, we use a particular word o-ten because the concept it conveys is ocritical importance to the sae and re-liable operation o any electrical asset.We use this word to convey the idea o atime period in which an asset perormsits intended unction so it is important

or any person involved in speciying,purchasing, testing, commissioning,maintaining, operating or disposing o

these assets to have a clear understandingo what lie means in the context o pow-er transormers.

In this series o articles, I am going to talkprecisely about this concept. Troughoutthe articles in the series, we will try to es-tablish what lie is and what it means or apower transormer. We will also explorethe actors that affect it and consider theoptions that an asset owner can utilise toextend and optimise the transormer lie.

In the first article, I will try to establish thecommon definition and understanding o

Part 1: What does transformer life mean?

Power TransformerABSTRACT

The concept of life for an electricalasset, such as a power transformer, issometimes not properly understood.In this article, the first from the seriesof three articles, we review what wemean when we refer to the life of atransformer and what constrains de-termine the design and operationalparameters of these assets.

Keywords

power transformer, life, asset ma-nagement, condition assessment, lifeextension



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Life

Carlos GAMEZ

what transormer lie is. Tis will hopeul-ly serve as the oundation or the articlesto ollow in this series.

his topic is vast and there are asmany opinions as there are experts inour industry. I have tried to remainobjective and base my comments onevidence and acts but I anticipate thatmy personal experience has ound itsway into these articles in one way oranother.

I have also assumed that the reader isamiliar with the basic power transor-

mer concepts and has seen or workedaround these assets at least once in theircareer.

WHAT DOES TRANSFORMERLIFE MEAN?

When we talk about concept o thetransormer lie or any other electricalasset or that matter, we also hear relatedterms and phrases that almost invaria-

bly show up in the same conversation.We oten hear terms like: lie manage-ment, lie expectancy, lie extension,lie cycle, etc.

We will somehow touch on all thoseconcepts but with some luck, we willmention them ollowing a logical se-quence o ideas. I will attempt to explainthese concepts in a clear and understan-dable way; how they relate to day to dayoperation o a transormer leet and

most importantly, what the user/ownero these assets can do in order to mini-mise the operation and maintenancecosts as well as mitigate the risks o un-expected ailures.

Te common denominator in the termsmentioned above is the word lie so itseems only air that we start by settingsome undamental understanding o whatlie means rom the perspective o a po-wer transormer.

Tere are many types, designs and wayso manuacturing power transormers butor the purpose o this discussion, pleaseconsider insulating liquid - filled powertransormers while you are reading artic-les in the series. However, the conceptsexplained and reviewed here can also beapplied to dry transormers, instrumenttransormers, gas insulated transormersand other classes o specialty transormersto some extent.

Common sense tells us that the lie o anasset can be regarded as the period o time

in which the asset will reliably perorm itsintended unction. Tis is not a bad start,but we can do better.

Lie can also be defined in statistical termswhich are particularly useul or insurancecompanies as the Mean ime Between

Failures or MBF. Tis basically meansthat out o a population o transormersthe time between initiation o service andailure is measured and averaged, provi-ding a good idea o the lie expectancy ora transormer belonging to that populati-on or o one with very similar characteris-tics.

Another good reerence is to look at whatthe different standard committees world-wide have to say on the matter.

Te Australian Standard, AS 2374.7 Po-wer ransormers Part 7: Loading Guideor Oil-Immersed Power ransormersestablishes in:

1.4 General limitations and effectsof loading beyond nameplate rating

1.4.1.1 Factors influencing life dura-tion

Te actual life duration of a trans-former depends to a high degree onextraordinary events, such as over-voltages, short-circuits in the system,and emergency overloading.

Te normal life expectancy is a con-ventional reference basis for conti-nuous duty under normal ambienttemperature and rated operating

conditions. Te application of a loadin excess of nameplate rating and/oran ambient temperature higher than

Wait, what? Are transformers not supposed tolast 35 to 40 years?The simple answer is: not necessarily, it depends.



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rated involves a degree of risk and ac-celerated ageing.

Another good reerence would be IEEEC57.91 Guide or Loading Mineral OilImmersed ransormer which establishesthe ollowing.

3. Definitions

3.5 ransformer Insulation Life: For agiven temperature of the transformerinsulation, the total time between theinitial state for which the insulationis considered new and the final state

for which dielectric stress, short cir-cuit stress, or mechanical movement,which could occur in normal service,

and would cause an electrical failure

Further to this definition, IEEE C57.91-1995 provides calculation ormulas orloss o lie as a percentage o per unitlie expectancy, providing a normalisedlie loss equation under various overloa-ding and stress circumstances. Tis rela-tionship is commonly represented in theorm o a Lie vs.emperature curve, as

shown below.

And finally rom IEC 60076-7 Loadingguide or oil-immersed power transor-mers we read the ollowing:

3 erms and Definitions

3.10 transformer insulation life

total time between the initial statefor which the insulation is conside-red new and the final state when dueto thermal ageing, dielectric stress,short-circuit stress, or mechanicalmovement, which could occur in nor-mal service and result in a high riskof electrical failure

3.11 per cent loss of life

equivalent ageing in hours over atime period (usually 24 h) times 100divided by the expected transformerinsulation life.

Te equivalent ageing in hours isobtained by multiplying the relativeageing rate with the number of hours

Te discerning readers would have noti-ced that there is a common thread acrossthese standards. Tey relate to transormer

loading guidelines, mention temperatureas an important actor and talk about theinsulation and the insulation lie. Tis al-ready provides a hint into where we haveto look to understand transormer lie.

It is also not a coincidence that none o thestandards mentioned above define whatthe lie expectancy o a particular transor-mer should be. Wait, what? ... Are transor-mers not supposed to last 35 to 40 years?Te simple answer is: not necessarily, it de-

pends. As we will discuss in these articles,the various mechanisms affecting the lieduration o a particular unit are difficult to

Figure 1: Transformer insulation life

Figure 2: Internal construction of a typical power transformer

It is also not a coincidence that none of the stan-dards mentioned above define what the life ex-pectancy of a particular transformer should be.

0,001

0,01

0,1

1

10

100

1000

50 70 90 110 130 150 170 190

PerUnitofNormalLife

Hoest Spot Temperature (H) [C]


COLUMN


19/68

predict. rying to anticipate events duringthe operation o any given transormer andhow they will ultimately affect its lie is anextremely complex problem.

TRANSFORMERCONSTRUCTION

As we might suspect, the heart o atransormer are the core and the coils(see Figure 2.). hey provide the criticalunction o transorming the incomingpower into dierent levels o voltageand current by means o electromagne-tic induction.

When one thinks about the materials thissubassembly comprises, one thinks o

copper or aluminium or the conductors;structural steel or the tank, clamps andradiators; magnetic steel or the core; mi-neral oil or cooling and dielectric insula-tion; wood or the lead holding structure;ceramics or the bushings; paper boardsand sheets, and tapes or electrical insu-lation. Out o all these components, theones that are most sensitive to tempera-ture and age are the ones with a celluloseconstitution.

Cellulosic materials are those which arederived rom natural vegetable fibres suchas wood, pressboard, Kraf paper, etc.

You might ask, why paper? Te act is thatpaper in combination with an insulatingliquid provides an excellent and versatiledielectric medium that can be applied tocomplex geometries. Paper also providesa good economic balance between thecost o the material and the unction thatit perorms.

However, paper is also the first materialamongst the constituents o the core andthe coils to degrade under thermal stress.While it would take several hundreddegrees Celsius o temperature to meltor cause significant damage to the com-ponents made o steel, copper or metal,it takes merely around 120C to startcausing significant degradation o cel-lulosic materials. In act, the main limi-tation o what temperatures are allowed

to develop in a particular design is set bythe paper. Te transormer designer willmake sure that not a single part o the in-

sulation system is exposed to these kindso temperature.

And i the paper degrades? Why would thataffect the unctionality o the transormer?We know that the primary energy conver-sion unction is perormed by the conduc-tors and the core, right? Well, it turns out

that the insulation system is responsibleor ensuring that conductive elementssubject to a voltage difference stay electri-cally insulated. Should the insulation breakdown between two high voltage elements,it would cease to perorm this unction, thecurrents would flow through paths they arenot supposed to ollow and the eventualconsequence is a catastrophic ailure.

In short, the lie o transormer as a wholeis directly linked to the lie o its insulation

system. I any part o the insulation sys-tem breaks down, the whole transormer

stops working. Albeit ailures can occur inother components, such as core, bushings,current transormers, etc. it is commonlya ailure in the insulation system that leadsto catastrophic outcomes.

Unsurprisingly, most o the efforts in thetransormer manuacturing, operation

and maintenance industries are aimed atimproving, monitoring and maintainingperormance o the insulation system.

I hope you now have a better understan-ding o what lie means in the context opower transormers.

In the next article, we will delve a bit moreinto the molecular structure o the paper,what it means or its electrical and mecha-nical properties and what various mecha-

nisms by which it degrades or loses thoseproperties are.

In short, the life of the transformer as a who-le is directly linked to the life of its insulationsystem.

AuthorCarlos Gamezcurrently works as a Principal Consultantand Product Manager at xMonitor and is a member othe MM Group Holdings where he ocuses in developinginnovative solutions or the electrical asset managementindustry using both his technical and business acumen.Afer graduating in Electrical and Mechanical Engineering

in 1996, Carlos started working as a ransormer DesignEngineer at PROLEC-GE, the biggest transormer actoryor General Electric on the American continent.

Over the course o the ollowing years, he gained expertise working in various rolesin product development, manuacturing improvements, technology and sofwaredevelopment, field engineering and customer service.In 2007 Carlos was seconded by General Electric to move to Perth, WA to start upthe ransormer Division in order to provide field and workshop maintenance andrepair services to customers across Australia.Having ulfilled this mission, in the early 2011 Carlos accepted the position o Prin-cipal Consultant with Assetivity, a leading consultancy firm in Asset Management.Over this period, Carlos developed a holistic point o view by working on projects

within the Asset Management rameworks which eventually shaped the ISO 55000set o standards published in 2014.


Carlos GAMEZ


20/68

Trends in PowerTransformer Failure AnalysisABSTRACT

This article will introduce the reader

to the importance of failure investiga-

tions, discuss the need for guidelines

and the standards organisations work

that is underway to provide the guide-

lines.

The concept of using the Scientific

Method is introduced and existingprocesses are described.

Limitations of postmortem investiga-

tions are identified along with best

practices for investigations.

INTRODUCTION

Failure investigations are becomingincreasingly important in thesedays when assets like power trans-

ormers cost in the millions o euros ordollars and consolidation in the utilityindustry has resulted in the operatorswanting the maximum capability romtheir assets.

ransormer ailures have been investiga-ted since the beginning o the electric uti-lity industry. Each manuacturer can pro-bably identiy their own problem areasrom actory ailures, quality programmeresults and experience. However, the ope-

rators (utilities) may not possess sufficientquantities o a manuacturer or particulardesign to recognise the problem areas. Sta-tistics such as those which, in the US andelsewhere, might result in a recall o anautomobile model which may not exist inquantities sufficient to establish patternso deects. Further, there is no regulatorybody to require such a recall. Te owner/operator o the transormer is expected tobe an inormed consumer. Te good news

is that the power transormer is a highlyengineered and tested product which hasa significant lie span. Te inormed con-sumer can make judgments about opera-tion and maintenance knowing the rootcause o ailures on the system.

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TRANSFORMERS MAGAZINE20


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NEED FOR GUIDELINES

Failure reporting has taken place in theorm o surveys published by organisa-tions such as the International Councilon Large Electric Systems (CIGRE WGA2.37 ransormer Reliability Survey),Edison Electric Institute (EEI ransmissi-on and Distribution Committee), and theInstitute o Electrical and Electronics En-gineers Industry Applications Society(IEEE/IAS). Te EEI stopped publishingthe results o their survey about the timethat the utility deregulation movementgot underway in the US. Some o the sta-tistics reported by IEEE/IAS in the Co-lor Book Series rely on data collected bythe US Army Corp o Engineers in the1970s. It is now lef largely to the user to

develop their own reliability statistics ortransormers.

It was recognised long ago that the deve-lopment o ailure reporting guidelineswas necessary. What was a deect to oneuser might be a major ailure to another.Tis situation was observed in the datacollected by EEI. Tis discrepancy ledto the development o the IEEE Guide

for Reporting Failure Data for Powerransformers and Shunt Reactors on

Electric Utility Power Systems. Unor-tunately, EEI no longer reported ailurestatistics a short time afer publication othe Failure Reporting Guide. As the effortunolded to develop ailure statistics, itbecame clear that ailure analysis guide-lines were also necessary. Te analysisguidelines, i effective, will result in ourimportant things:

- Establish a common set o steps to in-vestigate ailures,

- Ideally, reach the same conclusion on rootcause when presented with the same data,- Result in sharing o perormance bet-ween manuacturers and operators, and- Produce meaningul statistics or trans-ormer perormance (ailure rates, mean-time-to-ailure, and so orth).

STANDARDS ORGANISATIONSWORK UNDERWAY

In CIGRE, there is a Working Group A2.4.5

on ransormer Failure Investigation andPostmortem Analysis which is underway.Te Working Group scope states, TisWG will develop a structured procedure

from the decision to takethe transformerand shunt reactor out of service to careful

dismounting. Te main following activi-ties will be covered by this WG:

- State of the art of postmortem analysis(IEEE C57.125-1991 and any other rele-vant existing documents)- How to make an external and internalinspection of different components- Important information to collect: diag-nostics, protection, operation and main-tenance records, etc.- Availability and significance of designdata, material used, etc.- Documentation during the dismoun-ting, check lists- Additional checks, e. g. clamping pres-sure- Paper sampling: precautions, whichwinding, axial/radial position, correlati-

on with temperature, number of samples,conservation and storage of the samples,

parameters to be investigated (ask Forceto be leaded by SC D1)

- Collection of pictures of postmortemanalysis with examples of common failu-res and the associated failure investigation- Best practices for failure report andscrapping report- Economic aspect of postmortem analy-sis (cost, value, constraints, etc.)

In the IEEE/PES ransormers Commit-tee there is a Working Group on revisiono C57.125 Guide for Failure Investi-

gation, Documentation, Analysis andReporting for Power ransformers andShunt Reactors which has the task orevising and merging two existing do-cuments. hese IEEE Guides have beenused since they were originally publis-hed in the 1980s and 1990s and rea-irmed as recently as 2005. he currentrevision will provide updates to tech-

nologies used in testing and evaluatingtransormer condition and include thework on reliability assessment contai-ned in the previous guide. he Working

WWW.TRANSFORMERS-MAGAZINE.COM ISSUE 1, VOLUME 1 | 21

CourtesyofA-LineE.D.S.,

apremierproviderofforensictransformerdecommissioning

Wallace Binder


22/68

Group is preparing a document whose

scope ...recommends a procedure to beused to perorm a ailure analysis andthe reporting and statistical analysis oreliability o power transormers andshunt reactors used on electric powersystems. he Guide includes:

- Definitions- Steps to Determination and Investigationo a Failure Occurrence- Preparation Items- Data Collection Checklists

- Analysis o common ailure modes- Failure Reporting guidelines (and guid-ance to develop a statistical database orreliability evaluation).

Te Working Group has produced severaldrafs and expects to ballot in the next year.

SCIENTIFIC METHODApplication o the Scientific Method isnecessary when investigating a trans-

ormer ailure or suspected ailure. Tisrequires analysis o the acts and datapresent, establishment o an hypothesiso ailure, testing the hypothesis againstthe available data, collecting more datato confirm or reute the hypothesis, and

reporting the results. esting the hypo-

thesis might include modeling or deve-loping experiments to confirm the results(these experiments may take the orm ocomparison with other non-ailed unitso similar design, testing against establis-hed norms or comparison o test resultson adjacent phases). Afer testing the hy-pothesis, it might be necessary to modiythe hypothesis. Tis iterative process willcome as close as possible to determiningthe root cause o the ailure.

LIMITATIONS OF POSTMOR-TEM INVESTIGATIONSPower transormer ailure investigationsmust start with an understanding o theailure mechanisms possible and an un-derstanding o the system in which thetransormer is applied. Relevant (andsome irrelevant) inormation leading

up to and ollowing the supposed ailure

must be available or analysis. Tis requi-res collection o ault recorder, sequence-o-events recorder, protective relay ope-ration, protective device operation (usesor circuit breakers), and alarm conditionsprior to and subsequent to the outage, ione occurred. Tis data can include pastalarm conditions that have been correc-ted, previous trip operations that haveoccurred, and system events which aresimilar to the current event.

I this type o data is not collected im-mediately afer the suspected ailure ori such data collection is not part o thepractices o the utility, the ailure eventcannot be accurately reproduced. Likewi-se, i routine diagnostic testing is not parto the maintenance routine, comparisono test results with previous trends willbe difficult or impossible. A well execut-

Application of the Scientific Method is ne-

cessary when investigating a transformerfailure or suspected failure.


CourtesyofA-L

ineE.D.S.,

apremierproviderofforensictransformerdecommissioning

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23/68

AuthorWallace Binder has experience in scope development,planning, design, construction, start-up, operation, andmaintenance o distribution, transmission and customerutilisation substations, back-up power generation, trans-mission and distribution lines, and systems.Wallace Binder has been an active member o the IEEE/PES ransormers Committee or more than 30 years. Hehas served twice as Chair o the Working Group on FailureAnalysis, a position he currently holds. He served as Chair

o the ransormers Committee or two years in the late 90s and has contributed tonumerous guides and standards developed by the ransormers Committee.Wallace Binder is currently an independent consultant with his office located in Wes-tern Pennsylvania. He has served a variety o clients - both manuacturers and userso substation apparatus.

ed maintenance programme is critical toinvestigations.

It must also be recognised that, in somecases, the damage done afer a ailure bythe energy available on the power systemcan mask or destroy evidence o the rootcause o the ailure. Tis is one reason thatroutine monitoring o the transormer isimportant:

- to observe detrimental trends in peror-mance o the insulating system which, ilef uncorrected, could lead to ailure re-sulting in an outage, and- identiy events which may have done da-mage to the transormer (such as damageresulting rom through-aults, damagewhich is the result o improper or inade-

quate maintenance and repairs or dama-ge rom abnormal system conditions likeover-voltages, abnormal requency excur-sions, etc).

O course, not all ailures maniest them-selves in an outage or protective deviceoperation. Routine testing or on-line mo-nitoring can detect abnormal conditions.Tese situations are sometimes conoun-ding to the transormer operator Arethese results conclusive enough to remove

the asset rom service to attempt repairsand can repairs be successul? Tere areew transormer operators who run-to-ailure with the additional risks that thispractice entails. But when is the approp-riate time to remove a transormer romservice? oo soon and the system is ope-rating in a higher risk mode or the cost o areplacement is necessary. oo late, and theresult may be a catastrophic ailure. rans-ormers which have a history o test resultscan be better evaluated than those that do

not. Some transormers have operated oryears with low levels o combustible gasbeing generated. Some have long historyo higher than normal tan-delta (poweractor). It is important to know when atest result is out o tolerance and unaccep-table. rending o results may be the bestapproach or the examples given but orother tests, the results can lead to go orno-go results. Experience is generally ne-cessary to properly make this determina-tion. Te C57.125 guide points the reader

to possible conclusions given various setso test data or observed conditions. Finaldetermination o root cause ultimatelyrequires disassembly or dismounting othe transormer to investigate the internalconditions ound ollowing the ailure.

Factors to take into account when ma-king the decision to remove a transormerrom service should include:

- risk o outage- consequence o outage- value o the transormer and surround-ing equipment- the ability o the system to operate wit-hout the transormer in-service.

BEST PRACTICES FORINVESTIGATIONSTe rapid collection o data and observa-tions rom both the transormer and thesystem conditions at the time the decisionis made to remove the transormer romservice, either by human intervention or

by automatic trip, is important to the suc-cessul analysis o transormer ailures.

It is also important to operate and investi-gate in a sae manner. Tis means that allcorporate, regulatory, and rule-governedwork practices must be ollowed to assu-re the saety o personnel and the public.Check with your local authorities to de-termine what practices must be observed.Discussion with experts and the manu-acturer may lead to conclusions as to the

root cause, even i the damage makes thatdifficult. Knowing the values o voltagestress on the insulation, or example, is animportant actor to consider i there is evi-dence o insulation breakdown. Equallyimportant, however, is modeling the vol-tage stress on the transormer provided by

the system. Papers have been written byinvestigators who have discovered volta-ge phenomena caused by external systemconditions, which result in voltage stressesbeyond the capability o the transormerinsulation. Tis example, known as part-winding resonance, has been shown to bethe cause o dielectric ailure. Tere is asolution to prevent the occurrence and itbecomes the decision o the transormeroperator (utility, in most cases) as to whe-ther the solution is economically justifiedor the risk and consequences.

Te design o the transormer and thedesign o the power system to which it isconnected are important aspects o theinvestigation. Te transormer has beendesigned according to the standards spe-

cified in the original purchase agreement.We will discuss the evolution o standardsseparately.

System studies such as the load flow andshort circuit capability o the system maybe important to know in the analysis othe ailure. Less routine studies to deter-mine transient voltages during system dis-turbances may be required in some cases.Expertise in these areas should be made apart o the investigation team.

In uture articles, we will delve moredeeply into the procedures and practicesnecessary to successully determine theroot cause o a ailure. In addition, we willtalk about the symptoms o known ailuremechanisms.


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Classication of

Transformers Family


1. Introduction

Transormers basically perorm a

very simple unction: they increaseor decrease voltage and current or

electric energy transmission. It is precise-ly stated what a transormer is in the In-ternational Electrotechnical Vocabulary,Chapter 421: Power transormers and

reactors [1]:A static piece of apparatus with two ormore windings which, by electromag-netic induction, transforms a systemof alternating voltage and current intoanother system of voltage and currentusually of different values and at thesame frequency for the purpose of trans-mitting electrical power.

Te ocus o this article is on the transor-

mers which enable transmission o energyin the electrical grid, while all other types,such as the instrument transormers (i.e. vol-tage and current transormers) and the au-dio transormers, etc., are excluded. Te aimis to provide an overview o different types

o transormers in as systematic way as pos-sible, rather than elaborating on each type.

Te most important international orga-nisations with ocus on such transor-mers are IEC1 through E14, its technicalcommittee or the world standards; IEEE2

through the ransormers Committeemainly or the American standards andCIGRE3 through the Study CommitteeA2 ransormers which mainly produ-ces technical brochures and guidelineson many subjects. Main standards orthe transormers in question are the IEC60076 [2] and the IEEE C57 [3] series.

2. Classication oftransformers family

As mentioned above, transormers per-orm a very simple unction and they canhave many applications. ransormers are1IEC - International Electrotechnical Commission2IEEE - Institute of Electrical and Electronics Engineers3CIGRE - Council on Large Electric Systems

ABSTRACTTransformers are used in the electrical

networks everywhere: in power plants,

substations, industrial plants, buil-dings, data centres, railway vehicles,

ships, wind turbines, in the electronic

devices, the underground, and evenundersea. The focus of this article is

on transformers applied in the trans-

mission of energy, usually called pow-

er transformers. Due to very versatile

requirements and restrictions in the

numerous applications, ranging from

a subsea transformer to a wind turbine

transformer, a small distribution trans-

former to a large phase shifter trans-former, it is very difficult to provide astructured overview of the transformer

types. Also, different companies sup-

ply different markets and each have

their own classification of the trans-

formers, which makes the transformer

family even more difficult to assort.

This paper will attempt to provide a re-

latively common point of view on most

of those transformers types.

Keywords

classification, distribution transformers,

power transformers, reactors, transfor-

mers

TECHNOLOGY BASICS

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www.transformers-magazine .com

used in every power plant, all grid subs-tations, buildings, in the industry, the un-derground installations, wind turbines,on platorms, marine vessels, under the

sea, etc. Due to peculiarities o all the-se applications, many different types otransormers have been developed in thecourse o history. o simpliy the over-

view o many transormer types, it is use-ul to have some kind o systematic clas-sification. However, this is not easy to dobecause there are many ways o doing it.Te transormer types could be classifiedaccording to their power rating, voltage,current, weight, type o cooling etc., butsuch approach would have a limited ap-

plicability.Probably the simplest and the clearesttransormer classification is according tothe number o phases in:- single-phase transormers- three-phase transormers

In a three-phase system, the single-phaseunits are used in a bank o three trans-ormers linked together. A single three-phase transormer costs approximately

15% less and occupies less space thanone unit o three single-phase transor-mers within the same tank. However,due to limitations during the manuac-turing and mainly transportation, par-ticularly o large units, the transormers

sometimes must be produced as single-phase transormers. Another reason orusing a single-phase unit rather thana three-phase unit, is the possibility ohaving a ourth identical unit as a spa-re. Despite its simplicity and clarity, thistype o classiication does not overly

help in classiication o the whole trans-ormers amily.

Classification according to basic techno-logy o a transormer design and manu-acturing is also ofen used. Tere are twomain technologies or designing and ma-nuacturing the transormers:- core type- shell type

In a shell-ormed transormer, the pri-

mary and secondary windings are quiteflat and are positioned on one leg sur-rounded by the core. In a core-ormedtransormer, cylindrical windings arelike coils and cover the core legs. How-ever, this classification is also limited inthe large portolio o either o those twotransormer types.

ransormers can be classified accordingto the insulating/cooling fluid in:- liquid-filled transormers

- gas-filled transormers (mainly with SF6)- dry-type transormers

As the dry-type, and particularly gas-filled/insulated transormers have limitedapplications in a large power system, thisclassification is also not perect.

Despite not being a perect one, perhapsthe most practical classification used bythe industry is the one according to thetransormer application. According to thisapproach, transormers can be roughlyclassified as:- power transormers

- distribution transormers- reactors

Tis classification could, however, rai-se some questions. Tere are no obvioustechnical reasons or classiying a trans-ormer as a distribution transormerrather than a power transormer but it iswidely used in practice, and it is helpul.Te term distribution transormer is so-mewhat used in the IEC 60076, while it iscommonly used in IEEE C57. Some com-

panies define distribution transormers asthe power transormers below 10 MVA.Te 2.5 or 5 MVA limits are also used el-sewhere instead o 10 MVA.

Te classification above is even more dubi-ous with regards to reactors, because theyare not transormers at all but are usuallygrouped with transormers because theyshare most o the technology with powertransormers and they are designed andproduced in the transormer actories. It

took me some time at the beginning omy carrier to distinguish a reactor rom atransormer and I believe that others hada similar experience.

Te classification by application will beused in this article.

Transformers exist for more than a century

and they can be manufactured and used very

differently according to customers needs.

Since transformers have been in use, many dif-ferent types have been produced and conse-quently their classification is quite challenging!

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3. Power Transformers

Power transormers cover the populationo the largest transormer units by meanso power and voltage ratings. Manuactu-red units range up to 1500 MVA, and upto 1785 kV. Several large phase shifingtransormers consisting o two linkedunits have been manuactured with acombined capacity o 2750 MVA.

Tere are several different classificationso power transormers according to theirpower and voltage ratings or size, and/oraccording to the application.

Classication according to size

Classification according to size is a bit am-biguous because different companies use

different power and voltage range or par-ticular types. Tis discrepancy may be dueto the act that manuacturers divide theirportolio according to the market they sup-ply so, in their specific case, other classifica-tions are considered pointless. Utilities canalso have different fleets; thereore a certainclassification can be better or each utility.Te ranges mentioned here do not renderpresumption o general validity.

Large Power Transformers (LPT)

Tis group covers the largest units in thepower transormers population with pow-er o normally above 200 MVA (limits usedrange between 100 and 250 MVA) andHigh Voltage (HV) o usually at least 220kV. Within this group there is less compe-tition in the market but technical problemssuch as insulation problems (high diel-ectrical stress), magnetic problems (highleakage flux), thermal problems (high hea-ting due to operational losses), mechanicalproblems (high orces due to short-circuit

currents), transportation (large dimensi-ons and very heavy weight), etc. are extre-mely high.

Medium Power Transformers(MPT)Tis group includes transormers with apower range rom 60 to 200 MVA (or 40to 250 MVA), and a high voltage o up toaround 275 kV.

Small Power Transformers (SPT)

ransormers rom roughly 10 to 60 MVAand a maximum service voltage o 170 kVbelong to this group. Other limits used arerom 5 to 40 MVA and up to 145 kV.

Classication according

to application

According to the application, powertransormers can be divided in severalsubgroups:- generator step-up transormers (GSU)- system intertie (interconnecting) trans-ormers

- step-down transormers- phase-shifing transormers (PS)- HVDC converter transormers- transormers or industrial applications- traction transormers- mobile transormers- test transormers

3.1 Generator step-up transormers(GSU) are essential components o thepower plants linking the plant generatorto the transmission network. Built as threesingle-phase or three-phase units in thecore or shell technology, they transorm

voltage rom the generator voltage levelup to the suitable transmission voltage le-

vel, which may go up to 800 kV nowadays.

GSU transormers usually have delta-

connected Low Voltage (LV) windings(energised by the generator), and starconnected HV windings (connected tothe transmission lines). Te connection osuch transormers is mainly YNd.

Tey ofen operate continuously at ullload acing variations in voltage due tochanges o the load or the network re-quirement or reactive power. High ratedcurrents, particularly in the larger units,require a good control o the magnetic

field to avoid localised overheating.

GSU transormers can be very heavy orhigh power rated units which need to de-liver the entire power o the power plantto the grid.

Power transformers cover the highest power and

voltage ratings within the transformers family,and can be classified into several categories.

Figure 1: LPT 265 MVA, 525 kV [4]

Figure 2: MPT [4]

Figure 4: GSU transformer 890 MVA [4]

Figure 3: SPT 12,5 MVA with On-Load Tap Changer [4]


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3.2 System intertie (interconnecting)transormers connect AC systems odifferent voltage levels so that active aswell as reactive power can be exchangedbetween them. Tey can have ully sepa-rate windings or electrically connectedwindings, in which case they are calledautotransormers.

ransormers with separate windings pro-vide a galvanic insulation between the twovoltage systems.

Autotransormer, compared to a trans-ormer with separate windings o theequivalent rating, is a more compact andeconomical solution. ypical voltage ratiobetween HV and LV is between 1 and 2or autotransormers. However, as theyhave connected windings, there is no gal-

vanic insulation between the two inter-connected systems.

Figure 5: Autotransformer 250 MVA [4]

3.3 Step-down transormers can beclassified as a variety o the system intertietransormers. Teir purpose is a voltagetransormation rom the transmission

voltage level down to an appropriate dis-tribution level. However, with penetrationo distributed generation energy directioncan change, and when it happens a step-down transormer becomes a step-up

transormer.3.4 Phase-shifing transormers (PST)are among the most complex transormers.Teir purpose is to control power flowbetween the parallel power lines or cables;

or between the two independent powersystems. o achieve this, they are designednot to significantly change the voltage ma-gnitude but mainly its phase angle (hencetheir name). Voltage magnitude and angleare controlled by superimposing inducedsecondary voltage and some other voltagewith necessary phase displacement to the

main line voltage. When transormer hasone active part, the additional de-phased

voltage can be taken rom the windingonto another core limb but two active partsare necessary or higher ratings so the other

voltage is taken rom the second active part.In such arrangement, the first unit is calledthe booster or series transormer, and thesecond magnetising, regulating, or shunttransormer. All those interconnectionsneeded or the production o the desired

voltage and phase displacement make the

transormer more complex in all stages omanuacturing, rom design to productionand testing. In addition to these complica-tions, the terminology is also not simple.Besides PS, other names such as phaseangle regulating (PAR) transormer orquadrature booster are also used. Te re-erence standard with dual IEC-IEEE logois IEC 62032 Guide or the application,specification, and testing o phase-shifingtransormers [5].

PSs are sometimes considered a varietyo the system intertie transormers as theyare ofen installed in the substations butrom the application point o view, theycan be classified as a particular kind o po-wer transormer.

Figure 6: PST 600 MVA, 230 kV [4]

3.5 HVDC converter transormersare in act AC transormers. Te nameHVDC comes rom the application inthe HVDC converter station, which con-

verts AC current and voltage to DC, andvice versa. Hence, a HVDC transormeris the essential component in the HVDCtransmission system. Reasons or usingthe HVDC systems are loss reduction insome transmission lines, connecting ACsystems with different requencies, con-necting non-synchronous systems or usingunderground or undersea long transmis-sion lines.

Figure 7: HVDC converter transformer [4]

Due to operation in a converter stationclose to power electronic converters, the

transormer is subject to DC electric stressand high current harmonics. Tereore, ithas to be designed and manuactured withspecial consideration or DC insulationand harmonics and as a result, it containsmuch more solid insulation compared toa classic power transormer.

Te reerence IEC standard is IEC 61378-2.Convertor transormers - Part 2 ransor-mers or HVDC applications [6].

3.6 Transormers or industrial ap-plications are used in the industrialplants or supplying high energy deman-ding objects like urnaces or converters.Tose transormer power ratings are ap-proximately 10 MVA but can be techni-cally very complex due to specific needsand/or very high operational constraints.

Furnace power transormers have toprovide very high currents, close to short-circuit currents, at relatively low voltages

in the steel melting and the metallurgicalindustry. Capacity can range up to sever-al hundred MVA with high LV currents,even more than 150 kA; and wide se-condary voltage range. Due to extremeLV currents, the On-load tap-changer


Phase shifting transformers are among the mostcomplex transformers. They are mainly used tobalance the exchange between two networksover two parallel lines as precisely as possible.

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(OLC) is systematically placed on theHV side. Te secondary load can be ACor DC.

Figure 8: Furnace power transformer 95 MVA [4]

Convertertransormers ace higher loadcurrent harmonics due to the distortedwaveorm caused by the semiconductorconverters connected to the transormer.ypical applications are: rectifiers or largedrives, electrolysis, scrap melting urnacesand inverters or variable speed drives.Other applications can be chemical elec-trolysis, DC arc urnaces, graphitisingurnaces, traction substations, copper re-

fining etc.

Te reerence IEC standard is IEC 61378-1 Converter transormers Part 1: rans-ormers or industrial applications [7].

3.7 Traction transormers are used tosupply traction (railway) system and ve-hicles (locomotives). Nowadays, there aredifferent types o traction systems world-wide such as:- DC system (0.6 - 3 kV)

- AC systems:- 12 kV 50 Hz- 15 kV 16 2/3 Hz (this system tendsto decrease worldwide over the years)- 25 kV 50 or 60 Hz

raction transormers are supplied bystationary transormers (line eeder trans-ormers, mainly single-phase substationtransormer).

Locomotives with DC drives require a

three-phase rectifier transormer, alsocalled an on-board transormer. Tesetransormers can travel around as ast as570 km/h, and it is not surprising thatcritical parameters or such transormersare weight, size and appropriate cooling

capacity. Such compact design uses lessmaterial, which increases the losses andtemperatures above the limits or the ma-terials normally used like cellulose andmineral oil. Tereore, aramid, a polyami-de in combination with high temperatureresistant insulating fluids is used.

Figure 9: Traction transformer for a high speed

train [4]

3.8 Mobile transormers are usedwhen power needs to be supplied tem-porarily to a particular place, like in caseso a system ailure, system maintenance,natural disasters, terrorist attacks, civilconstruction, etc. Afer system restora-tion, or completion o the constructionwork, the requirement or power supplywill be significantly changed. Tereore, insuch cases, a permanent substation is notan economical solution.

Figure 10: Mobile transformer [4]

Te main drivers or a design o a mobile

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