Transformers Magazine

Transformers VOL 3 ISSUE 3 JULY 2016

MAGAZINE

Vapor phase COLUMNS: transformer TAP-CHANGER KNOW-HOW drying MARKET REVIEW

INTERVIEWS:

H.E. MOHAMMED M. SALEH WOLFGANG SORGATZ

Transformer condition assessment

ISSN 1849-7268 (Digital)

NEW: ECOTAP VPD

Dynamic testing of OLTC

THE COMPACT CLASS FOR DISTRIBUTION TRANSFORMERS

Superconducting transformers

Integration of distributed grid infeed Transformers and power quality CENTRE OF EXCELLENCE FOR TRANSFORMERS ▪ TRANSFORMER SECURITY – INSULOGIX® VAULT NATURAL ESTER-FILLED TRANSFORMER – FIELD EXPERIENCES ▪ ECOTAP VPD – THE COMPACT OLTC

CONTENT

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INTERVIEW WITH H.E. MOHAMMED MOHAMMED SALEH, DIRECTOR GENERAL AT FEWA H.E. Mohammed Mohammed Saleh, Director General at FEWA, talks about the company’s vision for sustainable growth while preserving the environment along with achieving a balance between economic and social development. He also talks about FEWA’s transformer fleet, procurement policy and specifications development.

INTERVIEW WITH WOLFGANG SORGATZ TLM CONFERENCE Wolfgang Sorgatz talks about the TLM Conference which is a successful and neutral platform for all stake­holders in the transformers industry, from manufacturers of transformers, instruments and materials, to their industrial partners and end customers, such as utilities, power plants and entire municipalities.

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COLUMN: TAP-CHANGER KNOW-HOW INSULATING LIQUIDS – PART II Rainer FROTSCHER In this issue, alternative insulating liquids and their potential for being used with tap-changers is discussed, based on extensive research performed on various alternative liquids over the past 20 years, with the objective of qualifying selected tap-changer models to be used with these liquids.

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COLUMN: ESTIMATING CURRENT AND FUTURE TRANSFORMERS MARKETS Steve AUBERTIN The globalisation of the power and distribution transformers markets and the increase of available market data has presented manufacturers with a new twist on an old problem. How to obtain accurate information about the current and future markets? This article explores some of the issues and reviews some of the sources.

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CONTENT

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NEWS

CENTRE OF EXCELLENCE FOR TRANSFORMERS IN ZAGREB The Centre of Excellence for Transformers in Zagreb is involved in three major areas: continuous research and development, a specialist postgraduate study in transformers, and an international colloquium on transformers. The Centre has been founded by the KONČAR Group in cooperation with its member companies and partners - the affiliated company KONČAR - Power Transformers Ltd. and Zagreb University.

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FIELD EXPERIENCES WITH THE WORLD’S L­ARGEST NATURAL E­STER-FILLED TRANSFORMER Today, electric utilities have to secure electricity supply while maximizing health and environmental safety, particularly in areas of high population density. Monitoring results for the world’s largest natural ester-filled transformer reveal that in almost three years in service the transformer has been operating perfectly, demonstrating the long term suitability as an alternative for mineral oil transformers even at high voltage ratings.

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THE INSULOGIX® VAULT A SECURE SOLUTION FOR YOUR TRANSFORMERS AGAINST THE THREAT OF CYBER ATTACK Chris AMEND, Robert BEGIN The InsuLogix® VAULT is the first solution of its kind to bring together transformer condition monitoring, controls, and substation security in a cyber-secure platform that exceeds North American Electric Reliability Corporation security requirements, all in an integrated, interoperable, and extensible hardware and software architecture.

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VAPOR PHASE TRANSFORMER DRYING – PART II Gregory R. STEEVES The dielectric strength and the life of the insulation are very dependent on its moisture content. During the manufacturing process, the materials absorb moisture with incidental contact with the air and must be efficiently and effectively dried before the transformer shipping and commissioning. Vapor phase drying as part of transformer manufacturing is discussed in this paper.

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ECOTAP VPD COMPACT ON-LOAD TAP CHANGER FOR DISTRIBUTION TRANSFORMERS Maschinenfabrik Reinhausen has recently presented the world‘s most compact on-load tap-changer for distribution transformers - ECOTAP VPD, which achieves maximum costeffectiveness for the entire transformer/on-load tap-changer system. The unit is perfectly tailored to the processes of transformer manufacturers and is highly versatile in application.

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TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Abdulla Hakeem Regional Application Specialist

Benefit from our experience in comprehensive power transformer diagnostics All of the experiences that I have as an application specialist flow into our transformer test systems. Designed by engineers for engineers, our solutions are reliable, portable and robust for daily field use, with individual wiring diagrams and an integrated assessment according to various standards. Our wide range of transformer test sets covers everything from conventional tests such as power factor up to modern methods like dielectric frequency response and SFRA. www.omicronenergy.com/transformer

CONTENT

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Decentralised energy production is on the rise. However, its integration in the existing grid infrastructure is a challenge for distribution grid operators. Regulated distribution transformers and voltage regulators assist the operators in overcoming this challenge.

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TRANSFORMERS AND POWER QUALITY – PART I Petar Milkov UZUNOV

This article investigates the generation of higher harmonics in small transformers supplying power to household, office and industrial equipment. The study is based on the results of the analysis of the magnetic field of the transformers with the Finite Element Method and measurements. Due to the large number of small transformers, they pollute the electrical network and are a factor in lowering the quality of electrical power.

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COST-EFFECTIVE AND FAIL-SAFE INTEGRATION OF DISTRIBUTED GRID INFEED Saskia BAUMANN

SUPERCONDUCTING TRANSFORMERS – PART II Mike STAINES, Mohinder PANNU, Neil GLASSON, Nathan ALLPRESS

Transformers using High Temperature Superconductor (HTS) wire instead of copper conductor, and liquid nitrogen instead of dielectric oil, have been in development for almost two decades now. This paper describes the testing procedure conducted as part of a recently completed HTS transformer demonstration, and some implications for the outlook for this technology.

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ADVANCED TRANSFORMER CONDITION ASSESSMENT – PART I Jon L. GIESECKE

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Aging transformers are an issue that must be understood and addressed. This article offers guidance in setting up a complete Predictive Maintenance programme for the condition assessment of critical oil-filled power transformers and ancillary substation components.

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DYNAMIC ANALYSIS AND TESTING OF ON-LOAD TAP CHANGER Cornelius PLATH, Markus PÜTTER

This article presents an overview of the main testing methods for on-load-tap-changers of power transformers. It discusses in detail the application and analysis of dynamic resistance measurement, which has become increasingly common in recent years.

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EVENTS TRANSFORMERS MAGAZINE | Volume 3, Issue 3

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Er it Vis

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CONTACT US Australasia: Vince Hantos [email protected] Tel: +61 40 768 03 31 France Serge Motta [email protected] Tel: +33 6 95 11 61 20

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EDITORIAL MESSAGE

TRANSFORMERS MAGAZINE ISSN 1849-3319 (Print) ISSN 1849-7268 (Digital) EDITORIAL BOARD Editor-in-Chief: Mladen Banovic, PhD, Merit Media Int., Croatia [email protected] EXECUTIVE EDITORS Michel Duval, PhD, Hydro Quebec, Canada Jean Sanchez, PhD, Utility, France Jin Sim, Jin Sim & Associates, Inc., USA Juliano Montanha, SIEMENS, Brazil Craig Adams, TRAFOIX, Australia Arne Petersen, AP Consulting, Australia Michael Krüger, OMICRON electronics GmbH, Austria Zhao Yongzhi, Shandong Electrical Engineering & Equipment Group Co., Ltd, China Art Director: Momir Blazek Photo: Shutterstock.com Front page: Cover image by Maschinenfabrik Reinhausen GmbH Language Editor: Marina C. Williams ADVERTISING AND SUBSCRIPTION Marin A. Dugandzic +44 20 373 474 69 [email protected] TRANSFORMERS MAGAZINE Transformers Magazine is published quarterly by Merit Media Int. d.o.o., Setaliste 150. brigade 10, 10 090 Zagreb, Croatia. Published art­ icles don‘t represent official position of Merit Media Int. d.o.o. Merit Media Int. d.o.o. is not responsible for the content. The responsibil­ ity for articles rests upon the authors, and the re­sponsibility for ads rests upon advertisers. Man­uscripts, photos and other submitted docu­ments are not returned. Subscription rates: Print edition: $96 (1 year, 4 issues) Digital edition: $54 (1 year, 4 issues) Online edition - full access: $19 (1 year, 4 issues) Online edition - free access: free of charge for r­egistered users www.transformers-magazine.com REPRINT Libraries are permitted to photocopy for the 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 permis­sions, contact Subscription. All rights reserved. Publisher: Merit Media Int. d.o.o. Setaliste 150. brigade 10, 10 090 Zagreb, Croatia Contact: +385 1 7899 507 Contact: +44 20 373 474 69 UK VAT number: HR09122628912 www.transformers-magazine.com Bank name: Zagrebacka banka Bank identifier code: ZABAHR2X Bank IBAN: HR8023600001102375121 Director: Ana Jelcic This issue is printed with the support of Ministry of Science, Education and Sports of the Republic of Croatia

Dear Readers,

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n the Editorial message for the April issue, I wrote about a common interest in forecasting the market and industry trends, and pointed to grid investments of nearly USD750B in the first quarter of this year, which were all announced and covered in our breaking news, as one potential indicator of the future business. Since then we have published announcements on additional investments valued at more than USD1 trillion. While thes­e announcements do not offer a foundation for a­ccurate predictions, they inform our readers on the geographical areas of large investments and enable them to timely prepare for tenders. This is exactly what I hear, especially from the sales p­eople, readers like about Transformers Magazine. Our e-Bulletin is a very practical tool to keep updated with all developments on the global scene. This weekly publication will save you a lot of time, making all publicly accessible information available at a glance. Therefore, I would like to invite all our readers who haven’t subscribed to the e-Bulletin to do so as soon as possible, and en­ cour­age their colleagues, too. The registration is free and very quick to do – all that is necessary is to provide your name and email address at: www.transformers-magazine.com/e-bulletin For readers looking to gain a deeper insight into the market, I recommend reading the market review article. Over the past three months, in the business sector we have seen a few acquisitions – the largest being the acquisition of Crompton Greaves’ T&D business, and several new plants opened – such as the new GE’s instrument transformer facility in Florida. More new plants have been announced, as well as some potentially big sales such as SGB, Tata Steel’s UK business, etc. Some new technology concepts have also been announced, such as new transformer core technology and high efficiency shielded toroidal transformers. The new transformer core technology uses a low-temperature FAST technique (field-assisted sintering technique), which enables direct creation of perfectly sized cores from raw starting materials (iron nitride powders) which don’t require any machining, promising significant savings. But let’s get back to technical issues. Transformers

Magazine has been receiving more and more manu­scripts for technical articles. While this doesn’t affect or slow down our review process, it may mean that an article will not be due for publica­tion immediately after the review process has finished, but in the next available issue. This is important for authors who would like to have their articles published in a specific issue, and who are thus encouraged to check submission deadlines for their manuscripts with our editorial staff. A lot of our recent communication with readers and authors has regarded natural and synthetic esters, voltage regulated distribution transformers and grid resiliency, suggesting that there is a lot of activity surrounding these topics. The communication with organizers of confer­ ences, seminars and other transformer related events is also increasing, indicating that there is a growing awareness of importance of network­ ing and global visibility, both for business and professional development. In this respect, using the opportunities available through Transformers Magazine and its channels (website, e-Bulletin, breaking news, etc.), and combining them with those provided by Transformers Forum, an evergrowing community of 19,000 members worldwide, will create a synergistic effect and enhance your chances for networking and global visibility. It is thus no wonder that more and more people from the industry take advantage of these opportunities. The combined audience of Transformers Magazin­e and Transformers Forum spreads across nearly 190 countries, making them two truly global platforms with all the associated benefits for readers and users. This issue of Transformers Magazine brings an overview of most important news, and features two interesting interviews, a profile of the Centre of Excellence for Transformers, several technical articles and a few advertorials. All pieces provide a lot of technical and business-related content, which I hope you will enjoy. Have a pleasant reading! Mladen Banovic, Editor-in-Chief

www.transformers-magazine.com 9

GRID INVESTMENTS

Utility to procure $6B worth of distribution equipment

BGE to invest $4B over next five years in power system upgrades Baltimore Gas and Electric Company (BGE) in Maryland, USA will invest $4 billion during the next five years in the power system upgrades and expansions in order to ensure fewer power outages and faster restoration of power when outages occur.

India’s state-run utility company Power Grid Corporation will spend $6 billion to procure distribution equipment from domestic vendors on behalf of states, required for implementation of the rural electrification and network strengthen­ ing programmes.

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hrough the online reverse auction conducted in April and May, Power Grid sought supply of critical equipment, including power transformers, distribution transformers, conductors and cables for all states.

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About 110 domestic equipment manufacturers empanelled with Power Grid were participating in the auction. Source: The Economic Times

Vancouver Island to power up with $2B a year over next decade

reparing for summer heat and potentially severe storms, the company has recently invested more than $8 million in critical distribution projects and new technologies as well as in the installation of a new substation and feeder, the company said in a statement. This work is part of the approximately $500 million invested each year in the company’s systems. Source: BGE

BC Hydro is implementing a major capital plan, and will be investing around $2 billion a year over the next decade in the improvement of the electricity infrastructure on the Vancouver Island in British Columbia, Canada.

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s part of this programme, BC Hydro has recently completed a major $36 million expansion of the George Tripp substation in Victoria, BC, which involved adding a new step-up transformer and switchgear breaker equipment, and installing a new 230 kilovolt underground transmission cable that connects to nearby Horsey substation.

Along with the upgrades nearing completion at the Horsey substation, this represents a $73 million investment to upgrade Victoria‘s two major substations. Other capital projects currently under way include multi-million substation projects in South Wellington, Buckley Bay and Campbell River. Source: BC Hydro

Telengana power infrastructure to receive $500M loan approved $6B funding for $1.45B electrification Telengana state in India will receive funding of $6 billion from the Union Government program in Sumatra to develop the state power sector and improve the efficiency of the electricity distribution companies, Transco and Power Generation Corporation.

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he $6 billion funding will be used for the development of electrical infrastructure and the facilities to ensure around-the-clock power supply in state villages. According to the Union Minister Bandaru Dattatreya, the central government has already provided $1.7 bil­ lion for the state efforts to provide electricity to each and every village in the country. Source: Deccan Chronicle

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Indonesia’s state-run utility PLN will receive a $500 million loan from the World Bank aimed to support implementation of the electrification program which will bring electricity to parts of Sumatra which are yet to be connected to the national grid.

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hehe program, which will complement existing power generation investments in Sumatra, involves addition of 28,300 transformers and 40,000 kilometres of power lines. According to the World Bank, the total cost of improving access to electricity in Sumatra stands at

$1.45 billion but funding will not only come from the bank. In Indonesia, 39 million people still do not have proper access to electricity, 9 million of whom live in Sumatra. Source: Jakarta Globe

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Transformers are required to operate in many harsh environments – offshore, arctic, desert, tropical, etc.

PROTECT YOUR TRANSFORMER’S SENSITIVE INTERIOR IN ALL CONDITIONS. MAKE IT LIFELONG.

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The leading European transformer tank manufacturer www.koncar-mk.hr

PROJECTS

PEOPLE

ABB plans for leadership succession; new MDs appointed As part of leadership succession planning, ABB has appointed Tauno Heinola as Managing Director of ABB in Australia, effective 1 October 2016.

US DOE approves $2.5B transmission project The U.S. Department of Energy (DOE) has approved the development of the Clean Line Energy’s $2.5 billion Plains & Eastern Line transmission project in an effort to modernize the grid and accelerate the renewable energy deployment.

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he Clean Line project, designed to deliver up to 4,000 MW of wind power through a 1,135 km direct current transmission line, also includes development of a 500 MW converter station in Arkansas, including a power transformer and associated electrical equipment. The project, which will meet the electricity needs of more than 1.5 million homes in the mid-South and Southeast US, is planned to commence in 2017. Source: EBR

$1.5B sub-Atlantic transmission project with $100M substation proposed USA: With Pilgrim Nuclear Power Station in Plymouth, Massachusetts shutting down permanently in mid-2019, the site is being considered by another energy producer for the construction of a new power substation to be built as part of the $1.5 billion sub-Atlantic transmission project.

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reen Line Devco LLC, a collaborative of Anbaric Transmission and National Grid, are looking to build a $100 million transmission substation in Plymouth to convert the electricity source for that part of the region’s grid to onshore wind and hydropower generated in Maine and Canada. Source: Cape Cod Times

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EIB to support $1.5B transmission project with $720M funding

$1.5 billion electricity transmission project in Scotland, United Kingdom will be supported by funding from the European Investment Bank (EIB).

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he European Investment Bank (EIB) will provide $719.70 million in financing to support the development of a high-voltage direct current (HVDC) power transmission link to connect the electricity grid on either side of the Moray Firth in northern Scotland. Source: EBR

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einola will succeed Axel Kuhr, who will become Managing Director in Japan. The appointments are part of a leadership succession at ABB: Kuhr replaces Tony Zeitoun, who is currently Managing Director in Japan and will retire from ABB at the end of the year, while Pekka Tiitinen, currently President of the Discrete Automation and Motion (DM) div­ ision, will succeed Heinola as Managing Director in Finland. Source: ABB

Alstom T&D India appoints CFO

Alstom T&D India Ltd announced the company appointed Mr. Gaurav Manoher Negi as Chief Financial Officer.

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r. Negi will assumed the position from 1 June 2016 taking over from Mr. S. M. Momaya, who ceased to be a whole-time Director and Chief Financial Officer of the Company as of 31 May 31 2016. Source: Equity Bulls

$1.17B Central Asian transmission project launched

The $1.17 billion CASA-1000 power transmission project has been inaugurated by the officials from Afghanistan, Pakistan, Tajikistan and Kyrgyzstan, after the competent ministries from the four countries finalized the document and decision on the implementation of the project.

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he CASA-1000 project will pave the way for the transmission of electricity from Tajikistan and Kyrgyzstan to Afghanistan and Pakistan through 1,250 km of high voltage transmission line. Two converter stations with power transformers and associated electrical equipment will be built for the project, including a 1,300 MW AC-DC converter station at Sangtuda, Tajikistan. Another high-voltage transformer will be built in the city of Pul-e-Khumri, Baghlan province to ensure supply of 300 MW of electricity to Afghanistan. Source: The Nation; Photo: RFERL

Malaysian transformer maker appoints new chairman Malaysian transformer manufacturer Success Transformer Corp Bhd has announced the company appointed Datuk Chua Tia Guan as its chairman.

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he appointment follows the resignation of Chiam Tau Meng due to personal commitment after heading the company for two years, reports the Edge Market. Source: The Edge Markets

Winder Power appoints new Group Manufacturing Director Winder Power, UK’s manufacturer of power and distribution transformers, announced the appointment of Keith Robertshaw as the Company’s Group Manufacturing Director, effective from 1 April 2016.

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n industry professional with extensive expert­ ise, Keith transitioned from the role of General Manager of the Newton Derby division within W­inder Power. Source: Winder Power

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

WORKS HERE.

S4 SHELL DIALA – PROTECT YOUR TRANSFORMER, OPTIMISE ITS PERFORMANCE, EXTEND ITS LIFETIME Shell Diala S4 is a range of innovative transformer oils developed to meet the challenging conditions faced by your transformers. Produced using Shell’s gas-toliquids technology, they deliver exceptional performance for extending the lifetime of your transformer under conditions of increasing oil stress. The range includes transformer oils that meet IEC 60296 and ASTM D3487 Type II specifications. www.shell.com/lubricants

BUSINESS

Tata Steel sells most of its European assets Following its earlier announcement of the decision to sell its poorly performing business in the U.K., India’s Tata Steel has sold its long products business assets in Europe to investment firm Greybull Capital.

German transformer maker approaches potential buyers in Asia Buyout group BC Partners is approach­ ing potential buyers for its German power transformer maker SGB-SMIT, four years after a sale to China‘s State Grid was halted by political interven­ tion, according to three sources familiar with the matter.

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nformation packages have been sent out to prospective buyers mainly in Asia, the sources said, but a formal auction, which may not be concluded until 2017, has not been launched yet. Back in 2012, China‘s State Grid was in exclusive talks to buy SGB, but it failed to receive political support for a deal as China‘s National Development and Reform Commission had considered the sector to be suf­ fering from overcapacity. SGB Starkstrom was originally part of Germany‘s second-biggest utility, RWE. It was sold to private equity group HCP Capital Group in 2004 and then to BC Partners in 2008. Source: Yahoo Finance; Photo: SGB-SMIT

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reybull Capital will bring in a package of $575 million provided by a combination of banks and its shareholders, to fund working capital and future investments in the business, reports Metal Miner. The deal includes the sale of Scunthorpe steel plant, mills in Teesside and northern France, an engineering workshop in Workington, a design consultancy in York, a bulk terminal, and associated distribution facilities.

Transformers Forum marks a new milestone! In May this year, Transformers Forum, a dynamic community operated through LinkedIn and supported by Transformers Magazine, proudly announced its new milestone – 19,000 forum members!

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ransformers Forum is a busy transformer industry hub offering a unique platform where members can share and discuss their ideas, knowledge, experience and opinions within the industry. This constantly growing community offers experts and novices alike an opportunity to build competence and broaden their technical horizons and experience by taking part in the pool of technical knowledge and

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share purchase agreement has been signed for CG power businesses in Europe, North America and Indonesia for an enterprise value of $126 million. The acquired division, which is expected to be rebranded as Pauwels, makes transformers and switchgears, and provides systems across the transmission and distribution sectors. Source: First Reserve; Reuters

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relevant experience, collected from the members from all over the world. We would like to invite you and your colleagues to join the Forum and check out the advanced features that this platform offers. Connect and engage with your peers through this ac­ tive community and stay in the loop! Welcome!

Tata Steel bidders get cold feet over Brexit

Crompton Greaves‘ power business acquired First Reserve International, a US private equity fund, announced the signing of an investment to acquire a subset of the international power transmission and distribution division of Crompton Greaves Ltd., which will be rebranded as Pauwels.

With this sale, the balance of Tata Steel U.K. business comprises primarily all of its operations at Port Talbot, which manufacture slabs, hot-rolled coil, cold-rolled coil and galvanized coil. After the sale of all U.K.-based assets, Tata Steel will operate only the Ijmuiden (Netherlands) unit. Source: Metal Miner

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Tata Steel has shortlisted seven bidders looking to buy its UK assets – JSW Steel, China‘s Hebei Iron & Steel, US‘ Nucor, Liberty House, Excalibur, PE Players Greybull Cap & Leeds-based PE company Endless.

owever, with the United Kingdom voting to leave the European Union in the recent referendum, several bidders are close to abandoning talks with their Indian owner as the outcome of the EU referendum threatens to deepen the crisis enveloping the UK‘s biggest steel producer. Sky News has learnt that one of the shortlisted seven bidders has signalled that exiting the EU would dimi-

nish the prospects of him pursuing a takeover, with similar concerns expressed by a number of other prospective buyers. Sources said that Tata Steel had raised the possibility of putting its British business into some form of liquidation, but no decisions had been taken. Source: Money Control; Sky News

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

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PRODUCTS

NEW TECHNOLOGIES

TRAX transformer A new transformer resilience concept for and substation testing maximized grid stability solution Siemens has launched a new transform­ er resilience concept developed to achieve maximum grid resilience.

Megger has developed a complete solution for transformer and substation testing – TRAX.

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he concept Pretact for resilient grids comprises a three-pillar-plan to enable customers to prevent failures, protect their equipment and react in cases of emergency. This new concept addresses emergencies, retrofits and new installations along the entire energy value chain to increase network stability by modular feature/ solution architecture for power and distribu­ tion transformers. Source: Siemens

he new solution features a software and an appbased interface. The finest power testing equipment with an added functionality is packed into one box for easy transport and application in the field. Source: Megger

ECOTAP VPD - The new compact class for distribution transformers First dry-pluggable bushing for voltages up to 362 kV

HV-CONNEX Size 7-S is the first drypluggable bushing specially designed for mobile emergency transformers and for high-voltage levels up to 362 kV.

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ONNEX bushing can be simply unplugged and replaced with a new one – without any laborious oil preparation. Power transformers equipped in this way are flexible in their use and easy to transport, enabling them to be used as emergency transformers. This means that damaged transformers can be re­ placed within a very short time. This product innovation encapsulates the extensive know-how of PFISTERER, the world‘s only manufacturer of pluggable bushings for the HV sector. Source: Pfisterer

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PowerBridgeNY helps making greener transformers

PowerBridgeNY, a proof-of-concept center (POCC) program which is advised by the New York Academy of Sciences and provides early-stage investments and services to help inventors and scientists turn their high-tech, clean-energy ideas into a successful business, has helped establishment of a new company which has designed a new green transformer.

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ith the green technology developed within the POCC program, a new high efficiency shielded toroidal transformer has been designed by two engineers-turned-entrepreneurs as a cost-effective and clean-energy alternative to traditional transformers. Source: The New York Academy of Sciences

Maschinenfabrik Reinhausen (MR) launch­ ed a new generation of on-load tap-changers for voltage regulation distribution transformers with the world premiere held at the CWIEME Fair in Berlin yesterday.

Iron nitride transform­ ers could boost energy storage options

he premiere of the new ECOTAP VPD was o­pened by Dr. Nicolas Maier-Scheubeck, Managing Director of MR, while the group of experts includ­ ing Manuel Sojer from MR, Armin Vielhauer from E.ON, Bernhard Schowe-von der Brelie from FGH and Thomas Dederichs from BDEW presented the technical chartacteristics of the product and its application aspects in the power distribution network. The new ECOTAP VPD is the world‘s most compact on-load tap-changer for distribution transformers offering the largest range of services. It achieves maximum cost-effectiveness for the entire transformer/ on-load tap-changer system, is maintenance-free, already satisfies the requirements of the EU Ecodesign Directive for 2021, and can be operated with syn­ thetic and natural esters as insulating fluids. Source: MR

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A team led by Sandia National Labora­ tories, U.S. Department of Energy research and development national laboratory, has developed a way to make a magnetic material that could lead to lighter and smaller, cheaper and better-performing high-frequency transformers. he new method uses a low-temperature FAST technique (field-assisted sintering technique), which enables the creation of transformer cores from raw starting materials in minutes, without decomposing the required iron nitrides, as could happen at the higher temperatures used in conventional sintering, reports ECN Magazine. Source: Sandia National Laboratories; Photo: Randy Montoya

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

DiTAS – TEST SYSTEM FOR DISTRIBUTION TRANSFORMERS New modular system for distribution transformers is optimized for high testing throughput without limitation in quality.

FAST. COMPACT. RELIABLE. AUTOMATED. APPLICATIONS n  Inducedvoltagetests n  Appliedvoltagetests n  No-loadlosstests n  Loadloss/short-circuittests n  Temperaturerisetests

TEChNICAL PARAMETERS DiTAS 170-500/4.8 n  Converterpower:170kVA–170kW n  Compensationpower:500kvarcapacitive n  Frequencyrange:40…200Hz n  Outputvoltage:4.8kV n  Testobjectsize:upto5MVA DiTAS 80-250/4.9 n  Converterpower:80kVA–80kW n  Compensationpower:250kvarcapacitive n  Frequencyrange:40…200Hz n  Outputvoltage:4.9kV n  Testobjectsize:upto2.5MVA

BENEFITS n  Fullyautomatictestproceduresandreporting n  Highestsafetyconditionsforoperatingstaffacc.toIEC62061(SIL3) n  Designwithstaticfrequencyconvertersasuniversalpowersource n  Modulardesignwithintegratedmeasuringunits n  Cost-effectivesystembasedonprovenHIGHVOLTdesign

Visit us at the CIGRE Session in Paris from 22 to 26 August 2016 at booth no. 230.

www.highvolt.de

MARKET OVERVIEW

MARKET REGULATION

Steel world met in Brussels to address overcapacity

Market overview Recently published market research reports provide an insight into the global and regional industry trends and perspectives. We bring you a summary of the made forecasts and highlighted tendencies:

T

the global power and distribution transformers market is estimated to be worth $35 billion in 2016. On a global level, there is pressure on utility companies to refurbish and replace the aging transformer population, and on transformer manufacturers to provide efficient and alternative transformer and material solutions. In this respect, progressing into the next decade more competition is expected to come from China, India and South Korea. The global power transformer market is projected to reach $29.9 billion by 2020 and exceed $34.6 billion by 2022. This means the market will grow at 5.9 % over the coming few years. However, unstable raw material prices are likely to challenge the market demand over the next six years. Large power transformer segment is projected to grow at the highest CAGR of 7.8 % between 2014 and 2020. This market, which had an estimated valuation of $18.35 billion in 2013, is projected to rise to $31.05 billion by 2020. The focus in the coming years will be on large power transformers that run on alternative energy sources. 100 MVA to 500 MVA output power leads the global power transformer market, which accounted for about 68 % of the total industry share in 2015, with gains estimated at 6.2 % over the next few years. Medium transformers market accounted for over 40 % of the overall revenue share in 2014, and is expected to witness significant growth over the next few years. Small transformers segment is estimated to grow owing to high demand for stepping voltages down within a distribution circuit of a building or to supply power to equipment. Smart grids holds a 98.56 % market share in the overall global solid state transformer market, and is ex-

18

pected to grow at a CAGR of 32.71 %. The solid state transformer market in the Asia-Pacific region is in its nascent stage, with a huge market potential in the distribution network of power grids. Growing demand for power and investments in power transmission & distribution network for upgradation and expansion is expected to drive padmounted transformer market at a rate of 5.21 % from 2015 to 2020. Three phase pad-mounted transformer and dry-type pad mounted transformer are the segments with highest growth in pad-mounted transformer market. The North American traction transformer market is estimated to grow at a CAGR of 9.4 % from 2014 to 2019. The global transformer monitoring solutions market is expected to grow at a CAGR of 36 % during the period 2016-2020. One trend that is expected to boost market growth is the introduction of automated high-voltage transformer monitoring solutions. While demand for electricity in emerging markets is the key growth driver, one of the challenges that could hamper market growth is the high price of transformer monitoring systems. The power sector offers a promising future to the global packaged substation market with growing demands for electricity, following increasing urbanization and industrialization in the developed as well as developing nations. Finally, let us note that this year the first shell-type 765 kV transformer has been manufactured at a factory in Memphis, Tennessee, making it the first transformer of this rating to be manufactured locally in the United States in 25 years.

Representatives from around 30 countries including China, Japan, Germany, India, the U.K. and the U.S. met with World Trade Organization, World Steel Association, and Organization for Economic Cooperation and Development (OECD) representatives in Brussels to seek possible solutions to the huge overcapacity that fuels the steel crisis.

T

he main objective of the meeting, which was organized by OECD, was to exchange views on the policy actions that would help reduce steel excess capacity, and to strengthen efforts to increase transparency through information sharing about measures taken to address excess capacity and promote structural adjustment in the steel industry. Source: OECD; Photo: OECD (Flickr)

Union urges immediate government action on U.S. steel crisis

As the United States Trade Representative called a hearing on the global steel industry and its impact on the U.S. steel industry and steel market, United Steelworkers (USW) International President Leo W. Gerard urged the U.S. Government to create an immediate action plan on US steel crisis, reports SysCon Media. As the United States Trade Representative called a hearing on the global steel industry and its impact on the U.S. steel industry and steel market, United Steelworkers (USW) International President Leo W. Gerard urged the U.S. Government to create an immediate action plan on US steel crisis, reports SysCon Media. Source: Sys-Con Media

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Authorized converter Flexible insulation products

COLUMN

Tap-changer know-how Insulating liquids – Part II: Non-mineral insulating liquids 1. General In the previous edition of Transformers Magazine, the typical properties of min­ eral insulating oils were illustrated. In this issue, the column will discuss alternative insulating liquids and their potential for being used with tap-changers. A short update on the Recycled mineral oils chapter (see Insulating liquids – Part I, section 2.4., Transformers Magazine, Vol 3, Issue 2, April 2016) seems to be adequate here. The IEC Standard Management Board has given instruction that recycled mineral oils shall be integrated into IEC 60296 (which, up to now, was dedicated exclusively to unused mineral oils). To execute this, IEC Working Group TC10/ MT38 has been established, which shall immediately revise IEC 60296 and give proper advice on how to recognize and classify recycled mineral oils based on their performance only and not on their provenance. 28 participants have been nominated for the working group by the IEC National Committees, producers of recycled oils among them. 20

O ver the past 20 years, extensive research on various alternative liquids has been performed with the objective of qualifying selected tap-changer models to be used with these liquids. The liquids and eligible tap-changer models have been chosen according to their market share. Really laborious is the evaluation of the arc-quenching behavior, which includes the determination of arcing times at high and low oil temperatures, and the amount and composition of deterioration products, such as carbon (soot), acids and gases. Gases can be toxic, and acids can attack solid insulating materials [1]. For this reason, research work has been focused on vacuum type on-load tap-changer (OLTC) models, so that the alternative liquid can be used both inside the transformer tank and tap-changer oil compartment. Nonvacuum type models (oil switching OLTCs) should only be used with alternative liquids in the transformer tank / tap selector compartment, while the diverter switch compartment is filled with mineral oil. De-energized tapchangers (DETCs) may also be used with alternative liquids.

2. Non-mineral insulating liquids Certain non-mineral liquids have been identified as suitable substitutes for min­ eral insulating oil, providing benefits for special applications. High-temperature or downtown substation transformers need liquids with low flammability (high flash point); transformers in environmentally sensitive areas should be filled with fully biodegradable liquids, and for applications like traction transformers the liquid should be chemically inert. Eligible liquids show significant differ­ ences to mineral insulating oils concern­ ing their composition, properties and performance; therefore, they don’t comply with the mineral oil standards discussed in Insulating liquids - Part I. If such liquids shall be used in tap-changers, each liquid has to be tested and evaluated properly. One apparent difference, for example, is the higher viscosity of some alternative liquids (see Fig. 1). Viscosity affects the timing of the tap-changer switching oper­ ation at (very) low oil temperatures, and

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Rainer FROTSCHER

Over the past 15 years, extensive research on various alternative liquids has been performed with the objective of qualifying selected tapchanger models to be used with these liquids lector which reverses the regulating wind­ ing or switches the coarse tap winding in and out. Capacitive currents of up to 500 mA have to be broken, and recovery volt­ ages up to 40 kV on the opening contacts must be controlled. For liquids showing a higher viscosity than mineral oil, the switch­ ing capacity of the change-over selector is reduced, because arcing-times are longer than in mineral oil. This is prob­ably due to the effect that cold liquid is not delivered fast enough into the hot arcing path to cool and quench the switching arc within the admissible time frame. influences the oil flow which determines the cooling of transformer windings, terminals, contacts and transition resistors. Furthermore, liquid viscosity also influences the arc-quenching behavior. Even for vacuum type OLTCs, low-energy arcs or sparks are produced at the change-over se-

2.1. Ester liquids Ester liquids can be divided in two fam­ ilies: synthetic and natural esters. Syn­ thetic esters (e.g. MIDEL 7131, M&I, U.K.) have been invented in the late ‘70s as an environmental friendly alternative

to the non-flammable, but highly questionable polychlorinated biphenyls (PCBs). Synthetically composed from alcohols and sat­ urated fatty acids, all molecules are near­ly same size, which gives them well-defined properties. They show good o­xidation stability, but are rather expensive. Natural esters, however, are prod­ uced from seed oils, such as soya (e.g. E­NVIROTEMP FR3 by Cargill, U.S.), rapeseed (e.g. SunOhm Eco by Kanden Eng., Japan, or MIDEL eN by M&I, U.K.), sunflower (BIOTEMP by ABB, withdrawn from market) and others. They are a blend of unsaturated and saturated fatty acids in order to achieve a sensible balance between oxidation stability and low-temperature behavior. One exotic variant of natural esters is palm oil (e.g. Pastell Neo, Japan): despite exclusive use of saturated

Figure 1. Viscosity of different insulating liquids on a ln(ln(ν)) scale, and temperature limits w w w . t ra n sfo r m e r s - m a g a z i n e . co m

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High-temperature or downtown substation transformers need liquids with low flammability; transformers in environmentally sensitive areas should be filled with fully biodegradable liquids, etc. fatty acids, it has a low pour point of less than -30 °C, good oxidation stability, but a flash point only slightly higher than min­ eral oil. This palm oil cannot be regarded as a less-flammable liquid. MIDEL eN also shows a pour point lower than -30 °C but is less-flammable at the same time. Here, pour-point depressant additives help to improve the liquid flow at low oil temperatures. The higher the percentage of unsaturated fatty acids, the more the liquid tends to polymerize under permanent air expos­ ure, leading to an increase in viscosity and finally to a jelly-like appearance. As this is not acceptable, it is highly recommended to use natural esters only in sealed applications. Free-breathing application with natural esters may work for distributio­n transformers with limited breathing (ther­e is some long-term experience in the U.S.), but not for highly optimized power transformers and OLTCs. Both synthetic and natural ester liquids are biodegradable, show very low oral and aquatic toxicity, and are classified as “not water endangering”. This allows usage in installations in sensitive environments such as water catchment areas, off-shore wind parks or downtown substations. For the latter, a low fire hazard is essential. E­ster liquids show a much lower fire haz­ ard than mineral oils, not only through the significantly higher flash point, but also through the lower calorific value (Table 1). This means that the energy prod­

uced in a fire is significantly lower than for mineral oils. By using a K-class lessflammable liquid, clearances and fire protection measures can be reduced for both indoor and outdoor transformers [2]. Ester liquids can hold huge amounts of moisture, compared to mineral oil. While a typical mineral oil gets saturated with 50-60 ppm water at 20 °C, natural ester can hold up to 1000 ppm and synthetic ester approximately 2200 ppm of water at 20 °C [3], [4]. This hygroscopic behavior provokes two effects: • the water content in the cellulose insulation of the transformer is lower than with mineral oil; and • the dielectric strength of the liquid stays high even with hundreds of ppm of water (high moisture tolerance). The reason why ester liquids can hold so much water is simply due to their polar structure: water (which is also polar) can easily attach to the acid groups of the ester molecules via hydro­gen bonds; see Fig. 2. The permittivity of ester liquids is roughly 1.5 times higher than that of mineral oils. This leads to more uniform field distributions in combination with soli­d insulation materials. On first glance, this seems to be an advantage, but it also m­e ans that the absolute field strength inside the solids is higher than with min­ eral oils. Therefore, inadequate impregnation or little cavities inside the solids have a more distinct detrimental impact

H O δ+

H O δ-

R

C O

R‘

Figure Polarmolecules molecules and and hydrogen Figure 2.2:Polar hydrogenbonds bondsareareresponsible for responsible for high water absorption capability of ester liquids

on the dielectric strength of the solid i­nsulating material. Another difference in electrical properties of ester liquids is their different streamer propagation behavior, which is visible on inhomogeneous electrode configurations and long insulating dis­ tances. Numerous investigations (e.g. [5], [6]) have revealed that fast streamers in ester liquids develop at lower voltages and have a longer stopping length than in mineral oil. This means that, for tap selectors showing moderately inhomogeneous fields and insulating distances of typically 5-10 cm, lower withstand volt­ ages are achieved. This is true for lightning impulse (LI) as well as for operating frequency (AC) voltage waveforms, and has been verified by numerous full-size tests on different tap selector arrangements. As a consequence, a bigger tap selector size may be appropriate or, as a work­ around, varistors can be added along the regulating winding to limit the AC and LI voltages which are applied during

Table 1. Classification of insulating liquids acc. to IEC61039 (Extract)

Fire point (ISO 2592)

Calorific value (ASTM D240)

Class O

≤ 300 °C

Category 1

≥ 42 MJ/kg

Class K

> 300 °C

Category 2

< 42 MJ/kg and ≥ 32 MJ/kg

Class L

Not quantifiable

Category 3

< 32 MJ/kg

Synthetic ester

Category 3

Natural ester

Category 2

Synthetic ester Natural ester

Class K

Table 1: Classification of insulating liquids acc. to IEC61039 (Extract)

22

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

transformer testing or which can occur as overvoltages in service. On the other hand, homogeneous field configurations do not show this phenom­ e non, probably because the starting point of a streamer discharge which leads to a flashover is not properly defined – it is statistically distributed. So, for typical phase-to-phase or phaseto-ground insulation arrangements with optimized homogeneous field geometry, the full withstand voltages as for mineral oil can be applied. It is highly likely that the streamer breakdown behavior also depends on the absolute level of the applied voltage. It has been found that OLTCs for distribution transformers do not require the said reduction of withstand voltages in ester liquids. With the grade of field inhomogeneity being comparable to bigger-sized tap selectors, the comparatively low LI and AC test voltage levels applied for Um 36 kV or lower are probably not high enough to reveal the differences between ester liquids and mineral oil. Further investigation on this seems to be necessary. For short distances (like in the IEC 60156 or ASTM D877 / D1816 standards – Determination of the breakdown voltage at power frequency), the differences in stopping length are not influential because the insulating distance is just too short. This is why ester liquids achieve the same (or higher) breakdown voltages (BDV) than mineral oil. So, by consider­ ing the BDV only, one cannot judge

Both synthetic and natural ester liquids are biodegradable, show very low oral and aquatic toxicity, and are classified as “not water endangering” the dielectric quality of an ester liquid. Because every brand behaves differently, it would be good if one had an easy m­ethod to quantify the streamer breakdown behavior of an unknown ester liquid in comparison to mineral oil under realistic dielectric field conditions, with­ out the need of running full-size tests on tap-changers. The lubricating behavior has been evaluated as well, as it is an extremely import­ ant parameter for tap-changers. Ester liquids show a comparable (or slightly better) lubricating behavior than mineral oil, and so ensure low mechanical wear and the same mechanical endurance as for mineral oils for all mechanically oper­ating parts. All ester liquids contain acids, which may attack solid non-metal materials, such as nitrile rubber gaskets, plastics or paints. Natural esters are more gentle to these materials than synthetic esters. It has been observed that nitrile rubber gaskets get brittle in synthetic ester but swell in natural ester, with the grade of degeneration depending on the individ­ ual rubber composition. Sophisticated thermoplasts or thermoset materials, as commonly used in modern tap-chan-

gers, may lose some percentage of their mechanical strength when stored in ester liquids. This must be considered in the design process. On the other hand, at least natural esters show an excellent compatibility with cellulose (Kraft paper): cellulose ageing is 2.5 times slower than in mineral oil; it seems as if the ester “protects” the cellulose from ageing [7].

2.2. Silicones Silicone liquids consist of chains of silicone oxide, which have been saturated by methyl groups (siloxane). A huge rang­e of products with different viscosities is available; for electrical purposes, viscos­ ities of 20 mm²/s and 50 mm²/s (at 25 °C) are used. Silicone liquids are usually used in small high-temperature transformers (e.g. traction transformers) or voltage transformers, but very seldom in powe­r transformers. They have an extreme longevity, behave inert, but are not easily biodegradable. Already at moderate field stress, as it can occur on tap-changer electrode configur­ ations, silicone liquids produce clusters (tufts) of semi-solid silicone oxide (Fig. 3).

Figure 3. Semi-solid tufts of silicone oxide; left: after 3 weeks at 20 °C, 2 kV/mm; right: after 6 hrs at 50 °C, 5 kV/mm w w w . t ra n sfo r m e r s - m a g a z i n e . co m

23

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Drawbacks of silicone liquids in combin­ ation with tap-changers is the affinity to build up jelly bridges between electrodes and their insufficient lubrication behavior

Overall, silicone liquids offer only a very limited applicability for on-load tap-changers. They may be used with DETCs if field strength is kept low so that a formation of semi-solid tufts can be avoided and if the DETC is not oper­ ated excessively. Up to 50,000 operations over the whole lifetime of the transform­ er is acceptable. This is also true for the change-over selector of the VACUTAP® VV, which can be operated in silicone liquid without restrictions. This has been verified by tests. Wherever possible, bare electrodes (e.g. terminals, shielding rings) should be coated or paper-wrapped to minimize the detrimental effect of said tufts. In any case, the OLTC oil compartment has to be filled with another approved liquid (mineral oil, ester liquid or HMWH).

of mechanically operated parts. It may be acceptable for DETCs which are seldom operated, but not for OLTCs. To overcome this deficit, a trial has been set up in which 10 % MIDEL 7131 was added to KF-96AE, a 20 mm²/s silicone liquid from ShinEtsu Chemicals (Japan). This in fact improved the lubricating capabil­ ity significantly, but resulted in unwant­ ed side effects: the switching arcs of the change-over selector (low energy arcs) caused some deterioration of both ester and silicone liquid, which ended in an awkward mixture of black soot deposits (produced by MIDEL 7131) and said jelly threads of silicone oxides. This mixture was highly conductive and caused unpredictable dielectric breakdowns. So, the message is clear: The mixing of a silicone liquid with an ester liquid is definitely not recommendable if there is arcing!

In moving oil, these tufts may be washed off the electrode, dissolve completely in the liquid or attach again to other uncoated electrodes as a thread, with un­ known long-term effect on the dielectric strength of the insulating gap. This affin­ ity to build up jelly bridges between electrodes is also the reason why the BDV of silicone liquids is noticeably lower than that of mineral oils or ester liquids. It also hampers their use with higher system voltages (e.g. Um >72.5 kV). Another drawback of silicone liquids in combination with tap-changers is their insufficient lubrication behavior. Tests have revealed that the mechanical wear on sliding friction arrangements, which are common for tap-changers, is mul­tiple times higher than in mineral oil. This leads to a significantly reduced lifetime

2.3. High molecular weight hydrocarbons High Molecular Weight Hydrocarbons (HMWHs, also called LFH, less-flammable hydrocarbons) were invented in the 1970s as the first substitute to PCBs. The major brand was R-TEMP Fluid (by Cooper Industries, USA), which was manu­factured until 2005. Former Cooper scientist David Sundin (DSI) issued an improved LFH called BETA-Fluid, which is still available and is mainly used for distribution transformers in the U.S. In Korea, a local comparable product called MICTRANS-G has been used for less-flammable regulated power transformers in underground downtown substations.

Table 2. Possible combinations of MR tap-changers with alternative liquids OLTC type

HMWH

Synthetic ester

Natural ester

✓

✓

✓

–

✓

✓

–

VACUTAP® VRC/VRE VACUTAP® VRD/VRF 1)

✓

✓

✓

–

VACUTAP RMV-II

✓ –

✓ ✓

✓ ✓

–

VACUTAP® iTAP, ECOTAP® OILTAP® M/RM

✓

✓

✓

–

✓

✓

✓

✓

✓ 2)

✓ 2)

VACUTAP® VV VACUTAP® VM (except VM 300)

Mineral oil inside OLTC oil compartment

OILTAP® V Mineral oil inside OLTC oil compartment

✓ 2)

DEETAP® DU

✓: Approved

✓ 2)

– : Not approved

1) On request

Silicone oil

✓ 2)

Approved non-silicone liquid in OLTC oil compartment.

–

HMWHs are refined from paraffinic pet­ roleum resources. Their long saturated hydrocarbon chains care for low flammability, but are also responsible for a much higher viscosity, which limits their use in cold environments. Principally, these

2)

2) Special case; please consult MR for individual approval

Table 2: Possible combinations of MR tap-changers with alternative liquids

H H

H H H CF3

O

CF

CF2

n

O

CF2

m

CF3

Halogenated polyether (perfluorinated polyether) Halogenated polyether (perfluorinated polyether)

24

H

C

H

C

O CF3 H H

H

HH

H

C

C

C

H C

C H

C H

C H

H

C HH H

C

C H

H

H

H

HMWH (high molecular weight hydrocarbon)

HMWH (high molecular weight hydrocarbon) TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Extensive tests on different tap-changer types and model setups have been perform­ed with various HMWHs, natural and synthetic esters and silicone oils, resulting in possible combinations of MR tap-changers with alternative liquids

liquids work well in all types of tap-changers, because their properties (except viscosity) are similar to “classic” mineral insulating oils. The high viscosity causes longer arcing times which lead to signifi­ cantly reduced switching cap­a cities of the change-over selector. Because ester liquids can fully replace HMWHs, an oncoming fading out of such liquids can be predicted.

2.4. Halogenated polyether Halogenated polyethers (e.g. GALDEN, by Solvay, France) are a liquid family mainly used as a cooling agent for heatexchangers. They are non-flammable, but can be deteriorated by pyrolytic processes, such as arcing. This causes PerFluorolso-Butylene (PFIB) and COF2, which is further deteriorated to, a very aggressive, hydrofluoric acid (HF). One variant of GALDEN, HT200, has been investigated for potential use in transformers and OLTCs. In a project for Italy, initial tests with an OILTAP® M have been performed during 1995-1998. The goal was to develop regulated power transformers, sized 25-40 MVA, for Um 170 kV, with GALDEN filling. The excellent cooling properties and the high liquid density of HT200 should allow for a very compact transformer design. A service duty test was performed which, after 18,000 operations, revealed inadmissibly prolonged arcing times of the switching contacts. The liquid was analyzed and showed the toxic deterior­ation products mentioned above. A vis­ible indication for HF was the dull surface of the diverter switch oil compartment (made of glassreinforced plast­ ic, GRP). Additional 160,000 mechanical oper­ations on a tap selector caused unremark­able mechanical wear and so proved a sufficient lubricating capability.

Even if this project has never been real­ ized, one can state that halogenated polyether can principally be used with vacuum-type OLTCs.

3. Approvals for tap-changers with alternative liquids Extensive tests on different tap-changer types as well as on model setups have been performed with various HMWHs, natural and synthetic esters and sili­cone liquids to determine the limits for use. Complete tap-changers have been worn out in mechanical endurance tests performing up to 1.5 million operations and they were destroyed in high-voltage tests to determine the true withstand voltages of all insulating distances in HMWHs,

natural and synthetic esters. Diverter switches have been stressed in the coldclimate chamber to find the lowest oper­ ating temperature with permissible tim­ ing, and all non-metal materials used in the respective tap-changer types were “cooked” for 180 days in 70-115 °C hot alternative liquids to ensure material compatibility. Several publications have been issued which give details on the test methods used and illustrate the behavior of tap-changers in these liquids [8], [9], [10]. As a summary, Table 2 gives an overview on possible combinations of MR tapchangers with alternative liquids. From the test results, admissible operating conditions have been derived; see Table 3.

Table 3. Parameters and limit values for tap-changers in alternative liquids

R1

CH2 CH CH2

O O O

C C C

R2

R1 O R2 O R3 O

ester Natural ester Natural (triglyceride fatty acid ester) (triglyceride fatty acid ester)

w w w . t ra n sfo r m e r s - m a g a z i n e . co m

C

R3

C

O

O

R1

R3

O

C

C

O

CH2 C

CH2 O

CH2

R2

CH3

R2

CH2 C

C

O

R3

R1

R3

C C

Si CH3

O O

CH3

R2

R1

Synthetic ester Synthetic ester (pentaerythritol (pentaerythritol organic acid ester)

organic acid ester)

CH3 O

Si CH3

CH3 Si

O n

CH3

CH3

Silicone oil (polydimethylsiloxane)

Silicone oil (polydimethylsiloxane)

25

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It is possible to “upgrade” a mineral oil filled regulated power transformer with oil-switch­ ing type OLTC to a modern, less-flammable and environmentally friendly transformer with vacuum type OLTC Please note that the voltage values for withstand voltage and recovery voltage of the change-over selector are expressed as percentage levels of the standard value­s for mineral oil, the values varying with the OLTC type.

4. Retrofitting It is possible to “upgrade” a mineral oil filled regulated power transformer with oil-switch­ing type OLTC to a modern, less-flammable and environmentally friendly transformer with vacuum type OLTC. Some considerations are necessary to ensure a safe and reliable operation with the new liquid (and tapchanger). First, it must be deter­mined if the combination of the tap-changer and desired liquid according to Table 2 is approved. In case of an OILTAP® M, the diverter switch can easily be replaced by a VACUTAP® VM model. Then, the following parameters have to be checked: • Required withstand voltages for all relevant insulation distances • Required recovery voltage on changeover selector

• Required operating temperature range • Material compatibility • Breathing conditions The tap-changer manufacturer will also check the application for possible geomet­ ric incompatibilities (e.g. insulating dis­ tances to tank walls etc.). If one or more limit values defined in Table 3 are violated, adequate measures must be taken: • If the required withstand voltages do exceed the permissible values which have been defined for the chosen ester liquid, the risk of a flashover must be estimated and, if not tolerable, adequate meas­ures must be taken (like surge arresters or var­ istors). In rare cases, a substitution of the tap-changer with a bigger size can be appropriate. • Tie-in measures may need adjustment. • A temperature lockout must be installed to prevent the tap-changer from switch­ ing at liquid temperatures beyond the permissible temperature range. • Unsuitable gaskets should be exchanged to avoid leakage in the long-term. • If natural ester liquids are used, sealing

Author

Dipl.-Ing. (TU) Rainer Frotscher was born in Bremen, Germany on March 4, 1960. He received his Master’s Degree in Electrical Engineering from the Technical University of Munich where he wrote his thesis in high-voltage engineering. Dipl.-Ing. Frotscher works for Maschinenfabrik Reinhausen (MR) in Regensburg, Germany as an expert for special tapchang­er applications. He has been working on various projects concerning the technol­ogy of on-load tap-changers. His area of expertise is the applicability of alternative l­iquids and DGA on tap-changers. As a member of CIGRE and DKE, he has au­thored multiple publications and he contributes to several working groups in CIGRE, IEEE and DKE. Phone : Fax : Email : Address : 26

+49 (0) 941/4090-4136 +49 (0) 941/4090-4005 [email protected] Maschinenfabrik Reinhausen GmbH Falkensteinstraße 8, 93059 Regensburg, Germany

measures like rubber bags or nitrogenfilled expansion tanks have to be applied to prevent the natural ester from persistent contact with oxygen from the ambient air. • If sealing measures are applied, an adequate protection concept for the tapchanger has to be adopted, because the standard oil flow relay may not work properly in combination with sealed expansion tanks. When retrofilling a mineral oil-filled transformer with an ester liquid, it has to be considered that the residual mineral oil remain­ing in the cellulose will reduce the flash point and fire point of the liquid mixture. To maintain a fire point of more than 300 °C, it is recommended to keep the min­ eral oil contamination below 3-5 % [11].

5. Outlook Producing oil from natural gas is one way to face the fading resources for high-qual­ ity crudes which are necessary to produce a good transformer oil. But this process needs a lot of energy. Much less energy is needed to generate synthetic esters, and they are fully biodegradable. Natural esters are presently the only insulating liquids which are really CO2 neutral. Their devel­ opment continues, improving oxidation stability and pour point. Dupont has recently issued a new sustainable ester-based fluid which perfectly fits to the NOMEXTM solid insulation product line, paving the way for high-temperature applications. It looks as if natural ester liquids show the best compromise between usability, price and environmental friendliness of all alternative liquids which are commercially available. But they stay in competition with arable crop which is needed for food prod­ uction. As in many other areas, finding a balance between different interests is a question of social, environmental and economical responsibility. Breeding of oil seeds with higher output continues and can slow down the increment of arable crop needed for industrial vegetable oil products. In this context, however, attempting the use of palm oil as insulating liquid appears questionable from the technical perspective and from the perspective of the accel­ erated tropical rain forest conversion into palm oil plantations. A promising alternative can be oil from a­lgae. Current projects investigate the cultivation of super-efficient microalgae to prod­ uce feedstock from which fuels and maybe

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

A promising alternative can be also oil from algae, because super-efficient microalgae might be cultivated to produce feedstock from which fuels and maybe also an electric­ al insulating liquid can be refined also an electrical insulating liquid can be refined. Algae consume carbon dioxide from the atmosphere and so help solving another apparent problem of mankind. But the biggest benefit is that algae can be grown anywhere, in direct vicinity of the markets where the oil is needed. Not endangering sensitive environments, short routes of transportation - wouldn’t that be great?

Bibliography [1] W. Breuer, G. Hegemann, Behavior of On-Load Tap-Changers in MIDEL 7131 – A PCB-Alternative for Transformers, CIGRESymposium 05-1987, Vienna, Austria [2] M. Lashbook, M. Kuhn, The use of ester transformer fluids for increased fire safety and reduced costs, paper A2-210, CIGRE

w w w . t ra n sfo r m e r s - m a g a z i n e . co m

2012, Paris, France [3] M&I Materials, Technical Data Sheets on MIDEL 7131, http://static.mimaterials.com/midel/documents/technical/ MIDEL_7131_Technical_Information_ Pack_A4.pdf [4] Cargill, Reference Data R2020 on E­ NVIROTEMP FR3, http://www.cargill. com/wcm/groups/public/@ccom/documents/document/na3076889.pdf [5] C. T. Duy, O. Lesaint, A. Denat, and N. Bonifaci, Streamer propagation and breakdown in natural ester at high voltage, IEEE Transactions on Dielectrics and Electrical Insulation, vol. 16, pp. 1582-1594, 2009. [6] P. Jarman, G. Wilson, P. Dyer, F. Perrot, Q. Liu, Z.D. Wang et.al., Electrical Perform­ ance of Ester Insulating Liquids for Power

Transformers, CIGRE SC A2 & D1 Joint Colloquium 2011, Paper PS2-O-5, Kyoto, Japan [7] P.McShane, K. Rapp, J. Corkran et.al., Aging of paper Insulation in Natural Ester Dielectric Fluid, IEEE Transmission and Distribution Conference, Atlanta, USA, Nov 2001 [8] R. Frotscher, On-Load Tap-Changers with Vacuum Switching technology for increased fire safety, reliability and environmental performance, Advanced Research Workshop on Transformers, Santiago de Compostela, Spain, 2010 [9] R. Frotscher, D. Vukovic, J. Harthun, M. Schäfer et.al., Behaviour of Ester Liquids under Dielectric and Thermal Stress – From Laboratory Testing to Practical Use, paper D1-105, CIGRE 2012, Paris, France [10] R. Frotscher, Alternative Liquids for Tap-changers, Technical Publication F0310300, Maschinenfabrik Reinhausen GmbH, Regensburg, Germany, 2014, http://www.reinhausen.com/en/XparoDownload.ashx?raid=86521 [11] Cargill: Recommended Procedures for Retrofilling Oil-Filled Transformers, Section S900-20-2 Reference Document, 2006

27

EVENTS PROFILE

The Centre of Excellence for Transformers in Z­agreb involves com­panies which cover the transformer business from R&D to decommissioning

Centre of Excellence for Transformers in Zagreb Introduction The Centre of Excellence (CoE) for Transformers in Zagreb was founded following the decision by the Management Board of KONČAR - Electrical Industry Inc. (pronounced Konchar) in 2005. Playing a vital role in this enterprise, KONČAR - Electrica­ l Industry Inc. involved all transformer manufacturing companies from the KONČAR Group in the project, including KONČAR Electrical Engineering Institute Inc., as well as KONČAR - Power Transformers Ltd. (KPT), which is a joint venture of SIEMENS and KONČAR. Considering that about 1.5 % of the world transformers production is concentrated in Zagreb, founding the CoE was a logical step towards optimization of transformer R&D, and also a scientific step forward. 28

Even more, it was a course of action to address the education and training problem that we face today in that undergraduate studies simply do not provide sufficient education in this area. The CoE was devised to cover three major areas: continuous research and development, a specialist postgraduate study in transformers, and an international colloquium on transformers. The specialist postgraduate study in transformers is an international programme of study organ­ ized in cooperation with the Faculty of Electrical Engineering and Computing, and the Faculty of Mechanical Engineer­ing and Naval Architecture at Zagreb University. The international collo­quium on “Transformer Research and Asset Management” is a con­ ference held every 2.5 years in one of the picturesque towns of Croatia. This event attracting great i­nterest of researchers and

scientists from all over the world has been sponsored by KONČAR as the Gold Sponsor. The core team of the CoE consists of M­iroslav Poljak, Ph.D., Member of the Man­ a gement Board at KONČAR Electrical Industry Inc.; Boris Potočki, President of the Management Board at KONČAR - Power Transformers Ltd.; Ivan Klapan, President of the Management Board at KONČAR - Distribution and Special Transformers Inc.; Ante Rogoznica, President of the Management Board at KONČAR Instrument Trans­ formers Inc.; Rajko Gardijan, Member of the Management Board at KONČAR - Electrical Engineering Institute Inc.; and Željko Štih, Ph.D., Full Professor at the Faculty of Electrical Engineering and Computing, Zagreb University. The former members include Ivan Milčić and Vladimir Plečko.

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Considering that about 1.5 % of the world transformers production is concentrated in Zagreb, founding the Centre of Excellence was a logical step towards optimization of transformer R&D, and also a scientific step forward

Foundation for the modern transformer business KONČAR - Electrical Industry Inc. boasts more than 90 years of experience in manu­facturing electric power products, including all types of transformers. It all began in 1921, when the production and repair of rotating machines and transformers was started at the site of today’s KONČAR headquarters.

here in 1930 following the idea by the enthusiastic engineer Anton Dolenc (later a famous professor at Zagreb University). The wire had to be varnished in the fac­ tory because it had not been available on the market. The machine was tested oper­ ating under water for hours, and this rep­ resented a world milestone.

The company has had many milestones over its long history. One of them was the development of the first induction ma­ chine with the winding made with an enamel insulated wire, which was manufactured

Today, energy and transportation make the core business of the KONČAR Group, which comprises 18 daughter companies with 3,700 employees, and one affiliated company employing nearly

w w w . t ra n sfo r m e r s - m a g a z i n e . co m

580 people. Approximately 50 % of the Group’s production volume is exported to foreign markets. The Group companies manufacture all types of transformers in Zagreb – from instrument transformers, through distribution and special transformers, to all types of power transformers, as well as transform­ er components and measurement and monitoring systems. Large power transformers are manufac­ tured by the affiliated company 29

PROFILE

In the last ten years, KPT has exported nearly 98 % of its production volume to 86 countries worldwide

1,000 MVA autotransformer under test at KPT

Large power transformers KONČAR - Power Transformers Ltd. (KPT), a joint venture founded with SIEMENS. Over the past 10 years, the factory’s aver­ age annual production has reached over 16,000 MVA. KPT’s portfolio includes generator stepup transformers, large transmission transformers and autotransformers up to 1,000 MVA and 550 kV, as well as transformers for industry purpose such as furnace and rectifier transformers, transformers for railways, and HVDC transformers. The company also delivers transformers for off-shore platforms, able to operate in very harsh conditions.

Since 1949 KPT has manufactured close to 3,000 units with a total capacity of more than 300,000 MVA. Thus far, 18 transform­ ers of different ratings, voltages and designs (including special transformers) have successfully passed short circuit withstand tests at international laboratories such as KEMA and CESI, which is yet another testimony to KPT’s design and technology. Placing its focus on quality and customer satisfaction, the company invests a lot in the continuous product improvement, combining its own in-house R&D capacity with that of KONČAR - Electrical Engineering Institute and SIEMENS.

318 MVA transformer transported by Antonov cargo plane to the Philippines in 2013 30

Moreover, it is KPT’s philosophy to stay committed to the continuous improvement of all processes, aiming to be technically and financially competitive on the global market. Staying true to this attitude, the com­ p­any was able to put the production and non-conformity costs under control. Also, they have established partner relationship with material suppliers as well as their customers worldwide and the results of all t­hese efforts and investments are clearly v­isible in their market competi­tiveness. Over the last ten years, the company has e­xported nearly 98 % of the production vol­ ume to 86 countries worldwide.

Transformer under short-circuit test at KEMA TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Distribution and special transformers KONČAR - Distribution and Special der, the company rather focuses on the solid serve customers who look for advanced soTransformers Inc. (D&ST) is the com­ preparation of the tender documents and lutions for their grid. pany manufacturing distribution and the risk review, knowing that there is no tenspecial transformers, as well as small and der that one can be sure of winning today. There are other special transformers that medium power transformers. Currently D&ST manufactures, and among them is a employing more than 500 people, D&ST The competitive and deregulated market recently developed traction transformer for supplies the domestic market, which is drives the business and requires continu­ KONČAR’s 160 km/h commuter train. its main market, accounting for approxi­ ous investment in R&D. However, recent mately 15 % of the production volume. changes in the raw materials price ratio Always looking ahead, the company is very Company’s largest international markets have also caused changes in product con- open to innovations and invests a lot in are the neighbouring countries, followed cept. For example, the increase in the price R&D. While this has resulted in significant by Europe as a whole, the Middle East of copper in relation to the price of alumin­ changes made in distribu­tion transformers and Africa. Their main export countries ium saw the round core technol­ogy for technology, with power transform­ ers include Sweden, Finland, Germany, distribution transformers, a very well estab­ the focus remains on smaller and gradual France, Switzerland, Austria, Italy, the lished technology which provided excel- steps, such as introducing new materials, Czech Republic, Hungary, Saudi design optimization, etc. D&ST is one Arabia, UAE, Qatar, Nigeria, Ghana, of the first OEMs to have tested new Morocco, etc. KONČAR D&ST is one of the solid and fluid materials as soon as appeared, which has created an first OEMs able to deliver trans­­ they This is a market segment which is very opportun­ity to produce transformers, competitive. While positioning on the formers produced with virtu- particularly special units, with virtually market takes a lot of time, losing this ally any materials available any materials available on the market to pos­ition is very easy, and may happen meet almost any type of requirements. to the company which is not able to ful- on the market to meet almost Closely monitoring all novelties and fil some of the customer requirements. any type of requirements developments on the market, the comWithout a continuous development of products, s­ales and other operations pany is present at all major events and within the company, without changing the lent results, being suddenly outperformed its experts participate in international models and adequate prioritising, it is not by the square and oval core technology working groups for standards developpossible to achieve a long-term success. In with aluminium windings. This was a big ment. With the constant involvement in its strive for excellence, D&ST has managed change that happened over a very short the latest trends and developments, the to set the right targets and build the team p­eriod of time and those OEMs which company was ready in time for the new that works together on all aspects of the failed to adopt this tech­nology very soon EU EcoDesign Regulation for Transform­ business, growing into the company which became uncompetitive. ers and now offers low-loss transformers is a widely accepted and reputed supplier of which meet the Tier 1 requirements of the transformers. D&ST is actively implementing new solu- regulation. Development of new solutions tions for on-load voltage regulation in dis- for even stricter Tier 2 requirements to be Although the price is a decisive criterion tribution transformers to be used in smart enforced in 2021 is already under way. in this segment, it is not the main focus of grid. Although this technology make­s disD&ST operations. When applying to ten- tribution transformers much more com- The company’s efforts also go into improv­ plicated and therefore more expensive, ing quality control and information and by developing its own solution D&ST has communication systems enabling man­ demonstrated the ability and readiness to agement of a large amount of data.

Transformer test bay at KONČAR D&ST with a distribution and a power transformer

PROFILE

Instrument transformers KONČAR - Instrument Transformers Inc. has been manufacturing instrument transformers since 1947, boasting a 70-year experience in this business. Employ­ ing more than 240 people, the company has an an­nual production capacity of 4,000 high voltage transformers and 10,000 medium voltage transformers. KONČAR’s instrument transformers are sold globally in more than 100 countries.

for some product types, KONČAR has sold licences to other manufacturers in China, India and Iran. Open core VT is a unique solution on today’s market, which was first developed in 1966 by Academician Professor Vojislav Bego. He is the author of the voltage balance through which he discovered, in the 1980s, that the definition of the voltage unit, Volt, had an error of 8 ppm. Being verified later by other research, in 1990 the definition of Volt was adjusted by 8 ppm.

800 kV current transformer AGU-765

The key milestones in the company’s 70machine-wound, which is very important. year history include: On request transformers can be • 1973: Production of first 420 kV with a robust and simpl­e transformers Fulfilling the strictest accuracy re- equipped monitoring solution in order to • 1992: Production of combined quirements, KONČAR’s combined prevent equipment damage. trans­f­­ormers • 2003: Production of first 500 kV transformers are the most compact Open core VTs are also practically and 750 kV transformers and cost-effective solution in terms im­mune to ferroresonance, which • 2006: Production begins at the joint venture in China of their purchase price, transpor- can take place only in very few and rare cases of enormously large • 2010: Production of first 800 kV tation, real estate, installation and very capacity. Actually, ferroresonance transformers maintenance costs has never occurred in the grid with • 2012: Production of power KONČAR’s open-core transformers. voltage transformers (PVTs) The primary winding of the open core KONČAR’s instrument transformers are VT consists of several separate sections, KONČAR’s combined transform­ers util­ designed according to customer specifi- enabling compensation of the angle error ise an open core voltage transformer and cations ensuring minimum material con- caused by magnetizing current. In case of a current transformer, which are fully sumption and minimum weight in a PD- an intern­al fault between turns or layers of integrated. This solution, with the comfree design for the power frequency voltage. the primary winding, the fault remains lo- mon main insulation, is unique on the There has been a lot of experience with PD calised in one section, while the grid volt­age market considering that other solutions phenomena in the company as well as sci- is distributed among all other sections, thus are, in essence, two transformers in the entific research, and now this knowledge limiting the fault current within a rang­e same housing. Being the most compact, of mA instead of kA. In this fail­ure mode KONČAR’s solution is also the most costhas been applied in practice. an internal arc cannot happen because the effective one in terms of the purchase KONČAR boasts unique products, such resulting process is slow and non-eruptive. pric­e, as well as transport­ation, real estate, as the voltage transformer (VT) with open Transformer will automatic­ally be discon- installation and maintenance costs, mak­ core, a combined instrument transformer nected without fracturing the insulator or ing it customers’ regular choice. More­ and a power voltage transformer, which causing oil spill. With the increase of the over, with this solution KONČAR is able drive the company’s success in the instru- transformer rated voltage, the influence of to fulfil the strictest accuracy requirement transformers market. What is more, a short circuit is reduced. This provides a ments. The only oil-filled combined transhuge advantage in terms of safety and ex- former at 420 kV level is KONČAR’s! plosion prevention. The en­tire insulation is PVTs or service station voltage transform­ ers provide power supply from a high volt­ Power voltage transformer VPT-362, Estonia age grid, e.g. 550 kV, of capacity up to 333 kVA, at the time being. PVTs are used for supplying substations when a low voltage network is not available, or when transmission is entirely separated from distribution. It is also very convenient for rural electrification. All advantages en­abled by open core are utilised here, simplifying the protection significantly while ensuring maximum s­afety. When on-load regulation is re­quir­e­d, a distribution transformer is simply connected to the secondary of the PVT. 32

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Transformer monitoring system hardware and software

R&D, testing, diagnosis and monitoring KONČAR - Electrical Engineering Institute Inc. has been conducting research on dielectric, electromagnetic and thermal problems, as well as losses, noise and other phenomena, and product development for more than 60 years. Over the last 25 years, the Institute has been actively involved in the research of dielectric problems and losses. The research of harmonics in the medium voltage grid and their influence on the measurement accuracy of instrument transformers, which the Institute has recently pioneered, is now the required research to be conducted in the transmission grid. Following the introduction of ester fluids, the Institute has conducted a very extensive experimental and simulation research on dielectric systems for power transform­ers, which covered both the HVAC and HVDC transformer insulation systems. The Institute also supports KONČAR transformer plants in transformer design.

a vast 60-year experience in the field of phys­ ical and chemical testing of mater­ials used in power engineering, as well as diagnostics of the transformer insulation system condition (oil-paper) for new and operating transformers. The Institute has pioneered the automa­tion of transformer factory testing, develop­ing a test system which pro­vides test reports immediately upon completion of the test. Further, since 2003 the Institute has been

supplying a comprehensive transformer monitoring systems (TMS), for which they have developed their own hardware and software platforms with an in-house solution for communication with IEDs and control centres. The solution is accredited according to latest edition of IEC 61850, making transformer ready for the smart grid. By May 2016, these monitoring systems have been delivered to more than 30 countries, with the main customers being SIEMENS, KONČAR, Hyundai, Hyosung, EPC companies, etc.

KONČAR offers solutions for monitoring large, medium and small power transformers, including overvoltage transient recording and tan delta and capacitance monitoring for bushings Rendering of the HV lab to be built at KONČAR - Electrical Engineering Institute

Another business area of the Institute is on-site diagnostic testing. The Institute boasts a database containing measurement results of instrument and power transformers dating back to 1963. The old­est transformer recorded in the database, which is still in operation, was manu­factured in 1965. The research, product development and on-site diagnostics conducted by the I­nstitute are supported by the Laboratory for Physical and Chemical Testing, which provides experimental laboratory data on material characteristics. The Laboratory is accredited according to IEC 17025, and has w w w . t ra n sfo r m e r s - m a g a z i n e . co m

33

PROFILE

In addition to TMS, the main monitoring product for large power transformers, TMS+ is a solution with an overvoltage transient recorder which customers use as a disturbance recorder. The portfolio also includes TMS mini, a compact and costeffective solution for small and medium power transformers in the range of 40 - 100 MVA. Another product is a solution for tan delta and capacitance monitoring for bushings, utilising three different methods: the sum of currents, referent voltage from VTs, and a comparison between a pair of bushings. The Institute operates a high voltage lab, which is certified according to IEC 17025, providing all types of thermal and dielectric tests of bushings. With the growing testing business, they are now expanding their facilities, building a new lab. Institute’s employees are academically active, and eight of them are involved in the specialist postgraduate study in transform­ ers at the University of Zagreb.

Transformer components KONČAR - Steel Structures Inc. manu­ factures all types of tanks for transformers above 100 MVA. The current annual output of 5,000 tonnes, and the plan to increase it to over 6,000 tonnes per year, positions the company among the leading European manufacturers in this market segment. The customers may benefit from its geographical location, which is almost in the centre of gravity of transformer OEMs, and the ability to support customers, particularly in demanding cases. The biggest transformer tank manufactured by KONČAR - Steel Structures Inc. was delivered in 2012. The tank measured 12.25 m in length, 3.79 m in width, 4.63 m in height, and weighed 56.2 tonnes. Along with the tank cover, which was 11.69 m long, 3.385 m wide, 0.4 m high, and weighed 10.4 tonnes, the whole unit weighed 109 tonnes. In addition to transformer tanks, the company annually manufactures 1,500-2,000 tonnes of welded constructions for other applications, such as ovens for drying transformer windings. Other products include flexibl­e winding mandrels for leading transformer OEMs, as well as vari­ ous tools and constructions for transformer manufacturing plants. The company is currently investing in expanding their product portfolio with new products for transform­ ers, but this will be announced in due time.

Tanks, coolers and other power transformer components 34

In addition, KONČAR - Steel Structures supplies tanks for off-shore plants with strict requirements, such as those accord­ ing to NORSOK M-501 standard for surface preparation and protective coating. Some of the company employees are certified with FROSIO and ACQPA certifi­cates, which enables them to reliably supervise and perform all processes, as required for such applications. The company is not only able to produce welding of the required quality and support transformer OEMs in

Transformer tanks, drying ovens, flexible wind­ ing mandrels and fans for cooling power transformers are among most recognized KONČAR products by power transformer OEMs designing transformer tanks that meet the set requirements, but also to manufacture constructions for such requirements with mixed materials, e.g. steel and stainless steel, which is very demanding. Their success in such complicated systems includes hot deep metallisation for hollow objects, where zinc must not enter the object. This is an extremely complicated process, and KONČAR - Steel Structures is among very few companies able to metalize such large objects. Transformer OEMs can rely on the company’s support when faced with such requirements from their customers. In fact, with all the support the company experts can provide, the more complicated the project, the more transformer OEMs can profit from their cooperation with KONČAR. It is eventually the end customers who profit from such support, which is the ultimate goal of all participants in the supply chain. Even in cases when the object will not be operating in off-shore conditions, customers today tend to require that these standards are met, as this will ensure that they will get better quality.

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Fans for power transformers

KONČAR - MES Inc., another company within the Group, manufactures fans for cooling power transformers. Their big advantage is that they manufacture all components themselves, including

the motors, which enables them to offer short lead times, even when faced with special require­ments, such as particular power supply voltage, corrosion and IP protection, etc. Their fans are delivered

mainly to European transformer OEMs, but also to OEMs in the Middle East, Russia, India and Mexico, while transformers using KONČAR’s fans are delivered all over the world.

KONČAR companies have grown to become reputed market players, covering the entire transformer business and all of its processes, from R&D to decommissioning. Together with the Centre of Excellence for Transformers, they make Zagreb a recognized hub for transformers.

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35

EVENTSINSULATION LIQUID

ABSTRACT Electric utilities have a duty to supply electricity securely whilst being mindful of environmental needs and fire safety, especially in urban areas. Mineral oil in power transformers is the most critical conventional material used. Substituting mineral oil with bio-degradable and renewable liquid such as natural ester, provides a much higher level of safety and sustainability. This article presents monitoring results for the world’s largest natural ester-filled transformer of advanced design. The results show that thus far, over nearly three years in service, the transformer has been operating perfectly, and that there are abso­ lutely no concerns with the operation of such transformers.

KEYWORDS natural ester, Envirotemp® FR3®, large power transformer, field results 36 36

Field experiences with the world’s l­argest natural e­ster-filled transformer TRANSFORMERS MAGAZINE | Volume 3, Issue 3

ADVERTORIAL

Photo courtesy of TransnetBW GmbH

Regulations require from electric utilities to secure electricity supply while maximizing health and environmental safety, particularly in areas of high population density

Envirotemp® FR3® fluid monitoring results

2. Power transformers for new requirements

1. Introduction

For power transformers, which are conventional pieces of electric equipment built according to the physics concepts and with materials developed decades ago, it is critical to implement new materials based on renewable resources to achieve sustainability, reliability, and s­afety.

Today many regulations are in place demanding from electric utility companies to consider a lot more than just secur­ ity of supply when expanding the grid. While operators need to ensure technical performance capability, concerns about issues of personal safety and environmental protection are of no less import­ ance. To be able to respond to these requirements, utilities need innovative technologies to equip themselves for the energy supply market of the future [1].

able – these concepts are the driving force behind the power industry today, with an impact not only on the method of energy generation, but also on the components used. Sparing use of resources and employment of renewable raw materials in place of fossil fuels wherever possible has become a must.

Sustainable, bio-degradable and renew­

Substituting mineral oil with bio-degradable and renewable liquid such as natural ester, provides a much higher level of safety and sustainability

w w w . t ra n sfo r m e r s - m a g a z i n e . co m

37

LIQUID INSULATION

Photo courtesy of SIEMENS

Photo courtesy of TransnetBW GmbH

Figure 1. SIEMENS Envirotemp® FR3®-fluid-filled large power transformer at dispatch from the factory (left); being commissioned at the

Another concept gaining importance is the development and installation of electrical equipment able to provide a high l­evel of health and environmental safety and reliability, particularly in regions of great infrastructure density where reducing the risk level has become a major goal. Insulating oil is the most critical conventional material used in power transformers. As a consequence, the need for achieving a higher level of sustainability and environmental safety has placed f­ocus on natural esters as a substitute for transformer oil. In relation to the in­ creased biodegradability and sustain­ ability requirements, natural ester based fluids are among the most important and widely used alternative liquids.

The world’s largest power transformer filled with natural ester Envirotemp® FR3® fluid, manufactured by SIEMENS, has been operating at the highest voltage level in the Germany’s grid for almost three years 3. Natural ester boosts transformer performance

been limited up to 230 kV until recently.

Natural esters have been used in transformers for decades, predomin­ antly in distribution transformers, and small and medium power transformers. However, their usage in large power high-voltage transformers has

In April 2013, Siemens successfully test­ ed the world’s largest power transformer filled with natural ester E­nvirotemp® FR3® fluid, developed and built at their p­ower transformer factory in Nuremberg, G­ ermany. This transformer is owned and operated by TransnetBW, one of the four transmission network operators in G­ermany.

Table I. Specific data of 420 kV natural ester transformer Rated voltage

420 kV

Rated power

300 MVA

Voltage ratio

405 ± 11%/115/22 kV

Cooling type

KDAF/KNAN

Liquid

Natural ester (Envirotemp® FR3® fluid)

Insulation level

630 kV AC/1425 kV LI/1050 kV SI

Liquid weight

~95 tons

38

Several articles have been published thus far on the various aspects of the transform­ er using FR3 fluid, comparing the properties of natural ester and mineral oil [1], describing design aspects and first service results [3], discussing advantages of using natural esters as insulating liquid in power transformers [4], and presenting aspects of electrical, thermal and mechanical design, as well as manufactur­ing, testing,

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Photo courtesy of TransnetBW GmbH

substation (centre); and in operation (right)

Over the past two and a half years in service, the transformer has undergone many tests and measurements, including gas analysis, water content, breakdown voltage and tan delta analyses of natural ester samples, and more transportation and operation of the FR3filled transformer [5].

unit will have a longer expected life span than a similar mineral oil unit.

Designed to operate at the highest volt­ age level in Germany’s power grid, the transformer’s rated voltage was specified to 380 kV, and its insulation levels meet the standard IEC 60076-3. The transformer also boasts a somewhat special mechanical design, using sealing equipment materials based on fluororubber, and components which were all qualified for operating in natural ester liquid. Specially designed bushings for medium voltage and wye connection

3.1. New design

The world’s largest transformer filled with Envirotemp FR3 fluid is rated at 420 kV, uses new design criteria, and is the largest unit using a renewable resource liquid. The rated power of this transform­er is 300 MVA, with an overload condition of up to 400 MVA [2]. Its cooling performance satisfies the l­ imits prescribed by the standard IEC 60076-2. In regard to the cooling type, the transform­er was designed to use forced cooling for the inner and outer cooling circuit, but also to operate up to 180 MVA load with non-forced cooling. In this design, the esters are not supposed to experience limiting top oil temperatures, so this w w w . t ra n sfo r m e r s - m a g a z i n e . co m

Figure 2. Concentrations of gases dissolved in natural ester 39

LIQUID INSULATION

The water content, dielectric strength and tan delta indicate this is a well prepared and perfectly normally operating transformer the DGA results back that up

The analysis of the moisture in the transformer oil (Figure 3) was based on the oil samples which were taken from the transformer at quarterly intervals in o­rder to evaluate the transformer condition.

Figure 3. Water content in natural ester samples

were type tested in the Research and Test­ing L­aboratory of the transformer factory in Nuremberg. Cable joints with specially designed coupling capacitors were used for the low voltage connection. These capacitors were also type tested in the transformer factory in Nuremberg.

Over the past two and a half years in service, the transformer has undergone many tests and measurements. These included gas analysis, as well as water content, breakdown voltage and tan delt­a analyses of natural ester samples, and more.

4. Experiences from the field

Dissolved gas analysis (Figure 2) was used to reveal the types of gas produced inside the transformer during its time

At the time of the transformer manufacture it was agreed that monitoring of the ester-filled EHV transformer will be jointly performed by the customer and the manufacturer in the coming months and years. Now, we realize that this moni­ toring has yielded valuable results which contribute to the knowledge of e­ster liquid behaviour.

in operation. Notably, the presence of ethan­ e increased over the two and a half years in service. In comparison to the transform­ers using mineral oil, ethane is generated by different natural decomposition processes taking place inside the transform­er with an insulation system which is a combination of natural ester and cellulose. These differences between the two insulation systems are based on the chemical structure of the various liquids, and they are explained in detail in the IEEE DGA guide [6]. Another distinction lies in a different solubility of gases in mineral oil and natural esters. Consequently, many, but not all, normally operating transformers filled with FR3 fluid have a higher ethane content than their mineral oil counterparts. Other hydro­carbon gases remained low [7].

Breakdown voltage and tan delta of nat­ ural ester samples were also regularly measured and showed no significant changes with respect to the required v­alues (Figure 4). Other parameters, such as the density of natural ester sample (Figure 5) and oil viscosity, were also measured to further check the condition of the transformer. While some of these measurements are done on every third sample, all of thes­e

4.1. Monitoring results

Although there have been other similar power transformers developed and put into operation since the time of the transformer manufacture, this is still the world’s largest power transformer of its kind. Using the monitoring data collect­ ed over time, this article brings an overview of the behaviour of the transformer during operation. 40

Figure 4. Breakdown voltage and tan delta of natural ester samples TRANSFORMERS MAGAZINE | Volume 3, Issue 3

All results collected from SIEMENS world’s largest transformer filled with Envirotemp® FR3® fluid show that so far there have been absolutely no concerns with the operation of such transformer parameters help us establish that the transformer is in good condition and that the condition of the natural ester itself has no influence on its performance. The performed measurements and their results show that there have been no abnormalities in the operation of the transformer and that its performance has been perfect and according to all stand­ ard expectations. 4.2. Other measurements

PD measurements and offline insula­ tion resistance measurements were per­ formed before the transformer was put in operation, while further tests and electrical measurements will be conducted in the upcoming months. As there has been no outage of the transformer for a longer period, and with all other meas­ urements indicating a perfect condition of the transformer, there was no need for these tests before. It is important to closely monitor the behaviour of these transformers now to help us understand their long-term behaviour and provide valuable references

and experience for the future, and our findings contribute to this. At the moment, IEC is drafting a standard for inservice natural esters, and this will pro­ vide an additional relevant reference.

Conclusion In the early days, there were certain concerns about building a large power transformer with the use of natural ester fluid­s. However, all of the findings col­lected from monitoring data of the world’s largest transformer of this type demonstrate that this is a transformer with a perfectly normal behaviour, causing absolutely no concern and operating according to all expectations and standards prescribed by the IEEE reference guide. Any differ­ ences in the values are acceptable accord­ ing to the IEEE guide. The water content, dielectric strength and tan delta results indicate that this is a well prepared and a perfectly normally operating transformer – and the DGA results support this. All these findings suggest that this solution is the future for power transformers,

serving not only as an alternative to min­ eral oil now, but also as its replacement in the future. With this in view, applying these solutions now is becoming increas­ingly important in order to gain ex­perience with the alternative liquids that seem to be a perfectly suitable replace­ment for mineral oil.

Bibliography: [1] Ronny Fritsche, Transformers: Nat­ural Esters Replace Mineral Oil - Green­er than ever, Electrical Monitor, April 2015 [2] Ronny Fritsche, Uwe Rimmele, Frank Trautmann, Michael Schäfer, Prototype 420 kV Power Transformer Using Nat­ ural Ester Dielectric Fluid [3] Ronny Fritsche, Ivanka AtanasovaHöhlein, Karsten Loppach, Frank Trautmann, Uwe Rimmele, Michael Schäfer, Gernot Adamietz, Large Power Transformers using Natural Insulation Liquids – aspects of design and first service results [4] Ronny Fritsche, Nachhaltige Elektrische Isolierung Dank Pflanzenölen, A­ utomatisierungs- & Elektrotechnik, 2015 [5] Ronny Fritsche, Großtransformatoren mit natürlichen Isoliermitteln, VDE Diagnostik Tagung; November 2014 [6] C57.155-2014 - IEEE Guide for Interpretation of Gases Generated in Natural Ester and Synthetic Ester-Immersed Transformers, IEEE; 2014 [7] R2070_FR3_Dissolved_Gas_Guide v5 August 2006

Contact Sabine Bowers Business Development Manager Envirotemp® Dielectric Ester Fluids Cargill - Germany Email: [email protected] Web: www.envirotempfluids.com

Figure 5. Density of natural ester sample w w w . t ra n sfo r m e r s - m a g a z i n e . co m

41

COLUMN

Estimating current and future

transformers markets

W

ith the increasing global­ isation of markets and manufacturers keen to explore the attractiveness of less familiar markets, there has never been a greater need for reliable and accurate data and market intelligence to assist in making important marketing decisions. The development of the internet has meant that there has never been more information readily and easily accessible, which has inevitably resulted in a variety of sources of varying

42

degrees of reliability that should assist in the deci­sion making process.

Published research vs tailored research

As the volume has increased, so has the need for a filtering or pre-digesting process to interpret that huge volume of information and turn it into action­ able data. One way in which this filtering process is delivered is in the form of pub­ lished market research reports, and this is particularly the case for transformer markets which are the subject of a pleth­ ora of published reports.

Published market research is inevitably a compromise between providing infor­ mation that is of interest to a wide base of customers and yet targeted enough to answer specific questions of any purchaser. The benefit is that its cost is much lower than that of the tailored research – by a factor of 10 to 20 times – while the drawback is that it has to be used intelligently, or interpreted to ensure the best use of the infor-

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Steve AUBERTIN

mation provided in the report. A market research project which is targeted on one specific country can cost the purchaser

as much as a published report covering an entire region or even one with globa­l coverage. So, how does that trade-off

The globalisation of the transformers market and the increase of available market data has presented manufacturers with a new twist on an old problem – how to obtain accurate information on current and future markets w w w . t ra n sfo r m e r s - m a g a z i n e . co m

b­etween cost and depth of information work in practice? A tailored research project should be designed to provide a large enough budget for a researcher to develop a detailed specification and project plan that will encompass international travel to conduct face-to-face interviews with the senior decision makers who specify, purchase and/or supply transformers. The results of those interviews will be analysed and collated into very detailed market size 43

COLUMN

The usefulness, reliability and value-formoney that can be obtained from a published report is dependent entirely on the knowledge, skill and professionalism with which it is produced and market share tables showing suppliers market position and competitive intelligence for the market segment being surveyed. A published report cannot provide the same level of detail, but it can provide sufficient data and competitive information which is detailed enough to provide reliable working data suitable for most marketing needs. Some of the indir­ect data sources that are available to the authors of published reports are listed below. Sources of information on transformer market size include: • Utility companies published capital and operational expenditure plans • National development plans • Transmission company reliability assessments • Industrial production statistics • Published trade statistics • National generating capacity statistics

44

Sources of information on market shares include: • Suppliers published annual financial reports • Investor presentations • Detailed import data • Industry trade organisations • Anti-trust enquiry reports The usefulness, reliability and value-formoney that can be obtained from a published report is dependent entirely on the knowledge, skill and professionalism with which it is produced. A professionally produced market report will have taken months of diligent research, analysis and experience to produce and it will provide reliable data which can save the purchaser much wasted time and effort, measured not only in terms of the effort required to search through the huge volume of information which is of variable quality, often unsourced, may be contradictory and of questionable reliability; but which may

additionally equate to thousands of manhours and dollars or euros in misguided market initiatives. An example of the data which can be obtained from a published report which can be interpreted to provide detailed information is shown below, and it relates to trade data. Power and distribution transformers are only produced in meaningful quantities in some 50 countries, which means that the market in the other 150 countries is satisfied by imports. By analysis of the annual import statistics of these countries, the market size and market shares of the suppliers can be assessed. Table 1 illustrates the market share of imports by country of origin into Qatar over the period 2011 to 2013. These figures not only show that the market is worth $97 million, but also clearly indicate the largest supplier countries. By applying the knowledge of the manufacturing comp­anies in each of these countries, the market share­s by supplier company can be deduced. Additionally, these aggregated figures can easily be deconstructed by size of transformer, to illustrate which companies are supplying which types of transform­er to Qatar.

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

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COLUMN

The market size calculation for the 50 or so countries that produce power and distribution transformers is a little more complicated. The formula is: production + imports - export = market size. As illustrated in Table 1, trade statistics can be analysed and a similar process will reveal the production data. Most countries collate and publish manufacturing data, but it is usually aggregated at too high a level to be of use. Such data will usually show the value of electrical engineering prod­ ucts produced in a country, but will not show the value of power or distribution transformers produced. This has to be “extracted“ from within the broader heading. This process requires a large input of market knowledge and experience, which is too detailed for inclusion here, but a knowledgeable and professional researcher can deconstruct the data and provide mean­ingful data.

Much of the data freely available claims to be current or up-to-date, but even hard facts must be viewed with caution and interpreted to ensure that the appearance is not misleading

Lies, damned lies and statistics One aspect of interpreting data can be summarised by – don’t just take pub­ lished facts as being set in stone, 100 % accurate. GDP growth rates for a countr­y may be based on three-year-old esti­mates; population figures for some countrie­ s – even UN figures – can be based on a census that was conducted 10 years ago. 46

Table 1. Qatar transformer imports, 2011-2013 Qatar imports 2011 to 2013 averaged

Source country

$ millions



Korea South

26.9



Croatia

22.9



Turkey

12.2



Italy

9.8



France

4.8



Germany

4.7



USA

3.1



Indonesia

3.0



Spain

2.9



Denmark

1.8



Brazil

1.5



Austria

1.2

Other

2.4



97.1

Total

Source: Data from UN Comtrade database TRANSFORMERS MAGAZINE | Volume 3, Issue 3

At first sight, a large geographical market may appear to offer the best opportunities for a new entrant, but appearances may be deceiving, because the most open market and hence the best potential may not be the largest A web source shows that the global instal­ led generating capacity increased from 5,624 GW in 2013 to 5,699 GW in 2014, which indicates that the global demand for GSU transformers was 75 GVA in 2014 (not including replacement for retired plant). In reality, these transformers would have been ordered in 2011 for delivery between 2012 - 2013, for commission­ ing in 2014, so depending on whether you count the market as at the time of order, time of delivery, time of payment, or time of commissioning, these 2014 fig­ ures may actually have been a part of the transformer market as far back as 2011. Just to further confuse the issue, the 2014 data quoted was accessed from the EIA database in 2014, in which the latest year for which hard data is listed is 2012, so the basis of the analysis slips back six years in the past towards 2009 or 2010. Many of the smaller countries do not produce reliable import statistics and a more reliable source is the sum total of

exporting countries statistics to the target country. Certainly there are often large variations between what exporting countries and the recipient importing countries record. Table 1 illustrated the averaged imports into Qatar as recorded by the countries exporting products to Qatar. For comparison, Table 2 shows imports as recorded by Qatar. There are some large discrepancies be­ tween the two sets of figures. It is not unusual, and perfectly understandable, for there to be variations from one year to another. For example, a large order may be supplied and recorded in the exporting country data in one year, but it may not appear in the recipient country until the year after. It is for that reason that threeyears figures have been averaged to iron out the effects of any single year; however, $30 million versus $97 million probably i­llustrates systematic differences in record­ ing protocols between the two sets and a judgement has to be made as to which

Table 2. Recorded transformer imports into Qatar, 2011-2013 Qatar imports 2011 to 2013 averaged

Source country

$ millions



Korea South

9.0



UAE

5.1



Germany

3.5



Italy

2.7



UK

1.2



USA

1.2



Turkey

1.1



Croatia

1.0



China

0.7



Saudi Arabia

0.6

Other

4.1



30.4

Total

Source: Data from UN Comtrade database w w w . t ra n sfo r m e r s - m a g a z i n e . co m

figures to rely on. This judgement requires knowledge and industry experience.

Identifying opportunities It can be misleading to assume that a larg­e market means plenty of opportunity for a new entrant. It can be, and often is argued when assessing a new market entry, that even a small share of a large market is worthwhile pursuing. This may well be the case, but the more important and less often asked question is how accessible that market is. The Asian (including China) market for transformers is worth a little under US$17 billion annually, however over 91 % of the market is satisfied by goods used in the country of manufacture. The total import market share of all Asian countries is 8.65 % or US$1.5 bil­ lion, of which 5.1 % are from other Asian countries. Therefore, manufacturers from every other country are fighting for a share of the US$0.5 billion extra-regional business. The same analysis for Western Europe shows that a similar value (US$0.5 billion) is available to non-European suppliers out of a total market of US$3.6 billion. The region with the largest available free market is North America, where from a total market of US$5.5 billion, 36 % or US$2.0 billion is supplied by non-North American countries.

Future forecasts For many product areas researchers rely on GDP growth forecast as the basis of their view of the future; however, for infrastructure products such as transform­ ers, a heavy reliance on such indicators can be misleading. Transmission and distribution network development may be the result of increased economic activity in any country, but there are many other factors that impact market development. Electrical engineers do not wait until the economists say that GDP has increased by 2 percentage points and then write out an order for a new power station or sev­eral new substations. They are making much more complicated calculations involving load growth, changing load patterns, population development, industry investment, housing starts, maintenance requirements and even climate change. On top of this, they are balancing the demands of capital expenditure versus oper­ ational expenditure. Yes, a new transformer will be more efficient and will pay for it­ self inside 10 years, but without the capital 47

COLUMN Table 3. A global transformer market overview Regional market

Market size $ million

Domestic share

Import share

Intra region share

Extra region share

Extra region available $ million



Western Europe

3,596.0

36.72 %

63.28 %

83.64 %

16.36 %

588.2



Eastern Europe

913.8

69.29 %

30.71 %

78.55 %

21.45 %

196.0



FSU

2,192.9

58.42 %

41.58 %

80.62 %

19.38 %

424.9



Africa

2,158.5

45.64 %

54.36 %

48.28 %

51.72 %

1,116.4



Middle East

2,025.5

11.42 %

88.58 %

31.48 %

68.52 %

1,387.9

Indian Subcontinent

1,354.2

61.98 %

38.02 %

63.84 %

36.16 %

489.7



Asia

16,836.7

91.35 %

8.65 %

96.53 %

3.47 %

584.1

South & Central America

2,006.9

61.42 %

38.58 %

74.41 %

25.59 %

513.5



North America

5,501.1

55.29 %

44.71 %

63.85 %

36.15 %

1,988.6



Australasia

402.0

39.70 %

60.30 %

48.45 %

51.55 %

207.2

Source: UN Comtrade data & Goulden Reports Analysis

Greater insight is required when forecasting future markets for power and distribution transformers than simply searching for the economic forecast with the highest GDP growth. It‘s not that easy. expenditure budget to make the replacement, a 30-year-old unit may have to be left in place even if it is costing m­oney in losses to do so. We have developed models to calculate these factors and to make judgements of future growth rates, but these only assist; they do not provide a definitive answer. When utility com­ panies in some countries were preparing for privatization in the 1990s, theoretically they should have been replacing and enhancing their 40-year-old networks providing plenty of transformer orders. In practice, to conform with the needs of a beauty competition for investors, they cut back all unnecessary expense and dis-

tribution transformer markets declined instead of increasing. Political decisions can also have a detrimental effect on transformer markets, but it is worth noting that the global market for transformers was $40 billion in 2015. 18 % of that was generator transformers, 29 % were transmission transformers and 53 % were distribution transformers. Polit­icians only generally interfere with large newsworthy projects – usually a part of the generator and transmission transformer segments, a relatively small percentage of the total market. Meanwhile, the rest of the infrastructure engineering

Author Steve Aubertin is the Managing Director of Goulden Reports and following a first career in electrical engineering has spent the last 30 years researching and reporting on the global market for electrical products in both published and in the form of tailored research for specific clients. 48

community continues to make sure that the lights don‘t go out. Political inputs into infrastructure development decision mak­ ing and all of the attendant delays that this causes to flagship projects must be a major annoyance to the constructors and the suppliers of the transformers which hang on those decisions. Nevertheless, overall this represents only a small percentage of the global market at any one time. In conclusion, there is a great deal of information available to transformer manufacturers and their strategic planners, some of which is freely available, some of which is charged for. There are three categories: • That which is free – which is probably too voluminous, may be contradictory, is of doubtful reliability and will require pre-digesting or at least prioritising by experienced staff; otherwise, it will take too long to assimilate. • Published market research – which is charged for, but is not generally prohibitively expensive; however, it will need to be interpreted to meet individual needs and used selectively. • Tailored specific research – which is highly targeted, but will need to be care­ fully designed to avoid wasted expend­ iture. Some of the issues raised above will be explored in greater detail in future col­ umns, and the intuitive and counter intuitive problems of sizing, forecasting and predicting market conditions will be discussed in greater detail.

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

FLAT RATE GRAPHIC DESIGN Passion for transformers and design Flat rate design offers a flat-rate pricing structure for all of your graphic design needs. Under a frame agreement concluded at the outset of the project, we deliver all graphic design solutions tailored to your needs at a flat monthly rate.

INTERVIEW EVENTS

FEWA’s vision is to provide electricity and water services aiming to improve the standard of living and achieve sustainable growth

50

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

The company employs more than 2,500 people, and comprises four main directorates, four core and five supporting departments, six main offices and as many as 16 branch offices

Interview with H.E. Mohammed Mohammed Saleh, Director General at FEWA FEWA‘s profile Federal Electricity & Water Authority (FEWA) was established as an independ­ ent entity with an aim to run its own projects, be efficient and self-dependent, and improve people’s lives by dealing with the demands of the public. Established in 1999, FEWA‘s main objective is to cater to the needs of the population in the Northern areas. In pursuing this main goal, FEWA has had to create a balance between the cost of production and the distribution price, while at the same time considering to unify the existing variable pricing strategies, studying the consumption behaviour and creating awareness among the consumers on the efficient use of electricity and water. The company employs more than 2,500 people, and comprises four main directorates, four

core and five supporting departments, six main offices and as many as 16 branch offices. We supply more than 570,000 customers across four cities. FEWA’s vision is to provide electricity and water services to improve the standard of living and achieve sustainable growth by 2021. Seeking simultaneously to achieve UAE‘s vision 2021, the company aims to ensure sustainable development while preserving the environment along with achieving a balance between economic and social development. Looking to improve and provide the best for customers, our goal is to reach a high level of cus­ tomer satisfaction. At the same time, our efforts towards achieving sustainability and higher level of efficiency also include continuous education and raising awareness of the public on different techniques of conserving both water and electricity resources. Finally, we aim to ensure that

The main fleet operation challenges that the utility faces in order to keep the system running uninterruptedly include high temperatures, high humidity level, and dust storms w w w . t ra n sfo r m e r s - m a g a z i n e . co m

51

INTERVIEW

Among other advancements, we are planning to introduce a vacuum-type OLTC in power transformers, and use a new type of transformer oil to ensure better perform­ ance and long life of the equipment

FEWA‘s transformer fleet

kVA in capacity and have the voltage level of 11/0.433 kV, is approximately 15,000. It is important to note that only five percent of FEWA‘s power transformers, both me­dium and low voltage, are more than 20 years old, while the majority of the units are less than 20 years old. A type of failure in the power transformers that we have noticed is cable termination failure, which completely dam­ ages the cable box. In distribution transformers we notice damage to bushings due to high temperature and humidity.

In FEWA‘s transformer fleet there are approximately 75 of ONAN/ONAF power transformers with the capacity level ranging from 50 to 90 MVA, and the voltage level of 132/33 to 132/11 kV. In addition, there are around 280 ONAN/ ONAF powe­r transformers rated between 15 to 25 MVA, and the voltage level of 33/11 kV.

The main fleet operation challenges that the utility faces in order to keep the system running without any interruption include high temperatures, high humidity level, and dust storms. These conditions require high standards of the system maintenance, fast fault diagnosis and rectification to maintain international standards.

The number of distribution transformers in our fleet, which range from 250 to 2,000

In the transformer procurement proced­ ure, FEWA gives preference to local sup-

administrative services are provided in accordance with standards of quality, efficiency and transparency. It is our mission to develop electricity and water facilities infrastructure in order to meet the growing electricity and water demand in the Emirates under FEWA jur­ isdiction in a common goal to enhance sustainable development.

52

pliers, but we are also open to global suppliers through public tenders.

Looking into the future FEWA’s 132 kV transmission grid is constantly expanding to accommodate the current and future load growth requirements and hence satisfy the N-1 criteria for reliability. Additionally, we are cont­inuously enhancing the distribution network to cater for the load growth in each of the regions. In regard to the equipment, FEWA has recently hired a consultant to review and update the specifications for transformers and substations. We are also planning to introduce a vacuum-type OLTC in power transformers, and use a new type of transformer oil to ensure better performance and long life of the equipment. FEWA is also working on p­ilot projects in the field of Automatic Metering System (AMI), and Distribution Management Systems (DMS).

Biography: H.E. Mohammed Mohammed Saleh is the Director General of the Federal Electricity & Water Authority (FEWA) and has over 33 years of experience in the utilities sector.

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Think about the environment while developing, manufacturing and operating transformers.

EVENTS MONITORING

The InsuLogix® VAULT ABSTRACT As the modern world becomes increasingly “wired”, more critical systems and infrastructure are linked via the internet. While that has given rise to incredible new technology efficiency and capability, it has also meant that more countries are vulnerable to hacking and cyber attack. The InsuLogix® VAULT is a state-of-the-art transformer con­ t­rol­ler and monitoring integrator de­ signed to meet the pending U.S. NERC CIP cyber security requirements for grid devices, providing a platform to monitor a utility’s entire fleet. 54

The most advanced and secure solution for your transformers against the threat of cyber attack

A

R­ogers told the House that a number of foreign governments had already man­ aged to penetrate U.S. energy, water and fuel distribution systems, which has potential to damage essential services.

In a recent briefing to the U.S. House Permanent Select Committee on Intelligence, NSA Director Navy Admiral Michael

As recently as December 23, 2015 U­k rainian Power Companies experi­ enc­ e d unscheduled power outages leav­ing 700,000 people without power. Public reports indicate that the Black Energ­ y (BE) malware was discovered

s the modern world becomes increasingly “wired”, more critical systems and infrastructure are linked via the internet. While that has given rise to incredible new technology efficiency and capability, it has also meant that more countries are vulnerable to hacking and cyber attacks.

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Advertorial

InsuLogix® VAULT – Transformer Security Make your transformer the most secure asset in your substation by complying with NERC Critical Infrastructure Program Standards. The InsuLogix® VAULT is designed to meet CIP-002 thru CIP-011 (cyber) and CIP014 (physical) standards as well as IEEE 1686.

As Admiral Rogers stated: “This is not theoretical, this is something that is impacting our nation and those of our allies every day.” In today’s world, reliability in our electric­ al grid requires cyber security. A cyber attack on devices that protect and control equipment in the electrical grid could result in significant outages and dam­ age to equipment. This is especially true for Substation Class Medium and Larg­e P­ ower Transformer (LPT). LPTs are custom-designed equipment that entail significant capital expenditures and long lead times due to intricate procurement process. Pricing varies by size and manufacturer but such units can cost millions of dollars and weigh between 100-400 tons. Pro­curement and manufacturing is a complex process that could extend leadtimes to 20 months. Although the cost of replacing transformers can be considered substantial, it pales in comparison to an actual outage in a large city when multiple units are taken down. Protecting transformers from cyber attack should be a top priority for the owner of these critical assets. on the company’s networks. A report by Bloomber­g News noted a cyber attack which caused a British Petroleum own­e­­d gas pipeline in Turkey to explode. At the time, this pipeline running from B­aku-Tbilisi-Ceyhan was thought to be one of the most secure in the world. In D­ecember 2014, amid the much publicized massive hack of Sony Pictures by North Korea, the German government released a report describing a successful cyber attack that infiltrated the industrial controls of a German steel mill. The report said the attack caused “massive” damage by making it impossible to shut off the blast furnaces and at the same time over working and sacrificing the life of the furnace transformer that supports the mill. w w w . t ra n sfo r m e r s - m a g a z i n e . co m

WEIDMANN ELECTRICAL TECHNOLOG­Y INC. has teamed up with SYNEXXUS Inc., a leading provider of integrated systems for the U.S. military, to develop and produce the most comprehensive transformer health monitoring and security system solution in the market. The W­EIDMANN InsuLogix® VAULT is the first solution of its kind to bring together transformer condition monitoring, con­ trols, and substation security in a cybersecure platform that exceeds North Ameri­can Electric Reliability Corporation (NERC) security requirements, all in an integrated, interoperable, and extensible hardware and software architecture. The InsuLogix® VAULT meets or exceeds U.S. Department of Defense requirements for

development, sourcing and production of technology driven products. The InsuLogix® VAULT promotes inter­ operability through its ability to run both WEIDMANN and third party developed applications in a cyber-secure software platform. It is designed to accept input sources from the widest possible array of third party devices, monitoring equipment, and physical security tools, such as cameras and access control systems. Advanced cyber-secure software running on the InsuLogix® VAULT inte­grates inputs from WEIDMANN and other intelligent electronic devices used in moni­ toring and controlling electrical assets and yard security in electrical substations. Key features include monitoring of a transformer‘s operating condition, control of cooling, alarms, recording of events such as through-faults, AC metering and power quality, local weather, and physical security – including live video and event triggered video recording. The InsuLogix® VAULT controller is a compact, solidstat­e device impervious to physical dam­ age and electronic intrusion with proper installation. Bestselling investigative reporter, Ted Koppel, speculates in his newly published book, Lights Out, that a major c­yber a­ttack

“It is the policy of the United States to enhance the security and resilience of the Nation’s critical infrastructure and to maintain a cyber environment that encourages efficiency, innovation, and economic prosperity while promoting safety, security, business confidentiality, privacy, and civil liberties.” President Barack Obama Executive Order 13636, February 2013 55

MONITORING on America’s power grid is not only pos­­“s­ible but likely, and paints a picture of a U.S. utility infrastructure that is shockingly unprepared. However, given the electric utility industry’s exceptional track record, proactive efforts by NERC to advance security measures, and the a­vailability of technology solutions like the InsuLogix® VAULT, the doomsday scenario imagined by Koppel underestimates the resilience of, and ongoing advancements for, our nation’s electric grid.

The InsuLogix® VAULT provides transformer security now and into the future The InsuLogix® VAULT is designed to support not only the security standards levied on Bulk Electric System (BES) transformers, but on transformers of all sizes and applications, as standards and grid reliability expectations are likely to be placed on smaller systems over time. In addition, to ensure compliance with future regulations, the InsuLogix® VAULT has implemented security controls that meet or exceed policies and standards for a BES Medium Impact Cyber System per CIP-002-5 Cyber Security, and BES Cyber System Categorization. The InsuLogix® VAULT provides cyber-secure data stor­ age, web-based front-end applications, and associated analytic tools hosted on cyber-secure systems that are compliant with Criminal Justice Information System Policy, CJISD-ITS-DOC-08140-5.4. The InsuLogix® VAULT also provides phys­ical security of your transformer and substation through use of video and access control. The InsuLogix® VAULT provides three video and access control packages –

Remote Command Telemetry Unit (RCTU)

Basic, Enhanced, and Pro – offering customers security capabilities at lower prices than previously possible by leveraging the InsuLogix® VAULT’s in-place processing and communications architecture.

windings. These sensors can measure Temperature (T), Moisture (M) directly in the insulation, and winding clamping Force (F), to generate critical transformer health information.

The InsuLogix® VAULT features the abil­ ity to optimize the transformer’s utiliza­ tion rate by helping to find the acceptable bal­ance of insulation loss of life and risk. The system uses WEIDMANN Optimu­m P­ erformance Monitor™ (OPM) and eNamePlate™ software that can simulate and help plan various dynamic loading scenarios before a critical loading decision is made. The results of that decision in terms of the actual loss of life are then calculated and communicated to the user. The InsuLogix® VAULT can be optionally configured with WEIDMANN’s S­ martInsulation™ system of fiber optic sensors embedded directly in the transformer

Maximize your transformer’s performance level with the InsuLogix® VAULT through real-time and future load planning

InsuLogix® VAULT – Flexibility The InsuLogix® VAULT can acquire, aggregate, record and make available key data to SCADA, EMS, and DCS data from WEIDMANN or third party monitors and sensors. Examples of sensors/monitors that can be connected to the InsuLogix® VAULT include: ▪▪ Gas monitors ▪▪ Moisture monitors ▪▪ Fiber optic temperature monitors ▪▪ Online bushing and lightening arrestor monitoring systems ▪▪ Voltage and current sensors ▪▪ Connections to cooling devices such as fans

56

The OPM software embedded in the I­nsuLogix® VAULT is designed specifically for Load Planning and for Asset Managers to simulate and verify transformer per­ formance over a broad range of operating parameters. Typical output would include real-time thermal margins, present and accumulated insulation loss-of-life, predicted maximum normal and emergency loading levels and insulation loss-of-life at future loads all allowing the operator to respond to emergency situations. Util­ ization of the InsuLogix® VAULT will a­llow asset owners to increase peak MVA load capacity, extend individual life of transform­ers, and balance load across the entire fleet. The InsuLogix® VAULT can simulate a variety of operating conditions based on data obtained from the unit specific factory (heat run) test data, and when combined with ambient temperature forecast, perform a location based loading assessment. The InsuLogix® VAULT pro­ vides the asset owner with transformer digi­tal or dynamic nameplate (as compared to analog or static transformer nameplate) for normal and emergency loading scen­

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

arios. In addition, the InsuLogix® VAULT will fuse all of the health monitoring information under one platform by elim­ inating the necessity of having multiple “loaner” devices and multiple algorithms to interpret data from each connected transformer. Ultimately, this could lead to a reduction in resource demands required to monitor multiple devices installed on transformers.

InsuLogix® VAULT – Enhanced Reliability The InsuLogix® VAULT utilizes Optimum Performance Monitoring (OPM) software to establish a WEIDMANN Health Index for your transformer. The OPM software provides “true” real-time health monitoring of your transformer by utilizing key information directly from your transformer. This information is consolidated to provide a WEIDMANN Health Index that will assist Asset Managers to make ever more strategic decisions on transformer loading.

The InsuLogix® VAULT will reduce overall costs by consolidating several individual devices into one box The InsuLogix® VAULT enables simplification of a transformer control design through the following functionalities: loss of voltage or time delay relay, thermal moni­tor, advanced power meter, annunciator, transformer monitor, voltage regu­ lation, touch screen control functions, Ethernet Switch, cellular modem, access control, video monitoring and security alerts. The InsuLogix® VAULT is a third party-friendly platform that enables customers to continue using industry-leading sensors from other manufacturers. The InsuLogix® VAULT will simplify hardware configuration during ordering and installation. The InsuLogix® VAULT remote command telemetry unit (RCTU) comes standard with redundant AC and DC power supply inputs, 32 digital inputs, 16 relay outputs, 8 analog inputs, dedi­ cated metrology inputs (3 phase voltage and 4 current inputs), 8 resistance tem-

InsuLogix® VAULT Optional Smart Display w w w . t ra n sfo r m e r s - m a g a z i n e . co m

InsuLogix® VAULT Monitor

perature detector (RTD) inputs, 4 serial ports, an 8 port Ethernet switch, a cellular modem. This flexibility allows you to reduce and simplify the total footprint of the control box. The InsuLogix® VAULT pro­ vides a scalable platform that allows for most functions found in a typical transformer

control system. Taking full advantage of system capabilities reduces the number of single purpose devices required while also reducing the overall size and consequently the cost of the control cabinet. By enabling the user to conduct convenient, remote site inspections with cameras in the substation, the InsuLogix® VAULT reduces asset physical inspection and maintenance costs. Rather than dispatch­ ing a team to collect data, remote operators can access complete/synchronized transformer system information. Data can be analyzed in fleet views and custom reports through the remote interface to compare performance of similar units. In addition, transformer drawings, test reports and instruction manuals can be downloaded from the remote interface transformer archive “drop box”. The InsuLogix® VAULT utilizes a transformer’s wellness history, sensory data and trending, and capitalizes on the advanced analytics of the system’s OPM diagnostic engine in order to justify a transition from calendar-based mainten­ ance to condition-based maintenance. 57

MONITORING “The VAULT effectively becomes the transformer’s brain, storing and recalling every data point, every event in the life of the transformer. It can then analyze that data, act and learn, protect itself, and communicate by text or email.” K. Shane Smith Manager of Delta Star’s Customer Solutions Group

The InsuLogix® VAULT system inputs can be utilized to trigger alerts to an individual or group. The alerts can be in the form of text messages or email messages such as open door alerts, access control denial of service, annunciation event, and motion detection, to name a few. A good example is false pressure relief and sudden pressure alarms. The InsuLogix® VAULT makes it possible to configure the system to send an email or text message so that main­tenance teams can be dispatched to the substation when an alarm is raised. A camera can be configured to pan-tilt-zoom (PTZ) to see if the Pressure Relief Device (PRD) flag is raised. With the addition of an analog pressure sensor to the control scheme, it is now possible to review current system pressure and review recent history for sudden changes. As an early adopter of the InsuLogix® VAULT, Delta Star, Inc. has started deploying the InsuLogix® VAULT at scal­e on specified transformers, including mobile transformers and mobile sub­station equipment. According to K. Shane Smith, Manager of Delta Star’s Customer Solutions Group, “the InsuLogix® VAULT is a key component of Delta Star’s intelligent, secure transformer. Today’s transformer owners and operators are under increasing pressure to deliver safe and reliable energy more efficiently while maintaining the security of the infrastructure. Our industry is the best in the world when it comes to dependable service, so the bar is already set very high. Delta Star has been custom designing and manufacturing transformers and transformer control systems for decades; never has there been a comparable platform that combines industry-leading interoperability, defense-proven cyber protection, video capability, and redundancy in communications with advanced analytics. The InsuLogix® VAULT 58

RCTU and Display

e­ ffectively b­ ecomes the transformer’s brain – it can store and recall every data point, every event in the life of the transformer – then analyze that data, act and learn, protect itself, and communicate by text or email. All of this while sim­

plifying the overall transformer control scheme. If the response to the product unveiling at the 2016 IEEE Transmission and D­istribution Conference in Dallas is any indication, the industry is eager to embrace and realize the benefits.”

Authors Chris Amend attended the University of Cincinnati and received his B.S. in Aerospace Engineering. He assumed his current role of Director of Project Management at SYNEXXUS in 2014. Prior to coming to SYNEXXUS, he spent 10 years working for the U.S. D­epartment of Defense. His work included the design, integration, test and management of several satellite programs at the Naval Research Laboratory Spacecraft Engineering Division. He also has worked as a Senior Engineer as a member of the F-18 Fleet Support Team providing in service sustainment support of aircraft sub-systems. He holds a Professional Engineering license in the state of Virginia as well as a Program Management Professional certification. Robert Begin attended Clarkson University and received his B.S.E.E. in Electrical and Computer Engineering in 1991. After graduating from Clarkson, he joined EHV-WEIDMANN Industries as a Technical Service Engineer with focus on transformer insulation system design. In 1996 he joined WEIDMANN Systems International as a Sales Account Manager for the Power and Distribution Transformer markets in North America. In 2004 he accepted a position with WEIDMANN-ACTI Inc. as the Business Development Manager for products and services related to transformers in the utility and industrial marketplace. In 2007 he became the Sales Manager for the Power market in the U.S. and Canada and continues to work in this capacity for WEIDMANN Electrical Technology. TRANSFORMERS MAGAZINE | Volume 3, Issue 3

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ABSTRACT Vapor phase drying is the most effect­ ive method for drying transformer insulation in a manufacturing setting. The process does not lend itself well to transformer drying in the field for a variety of reasons, including the difficulty of removing residual kerosene which can cause a potential change in transformer oil flash point. Several techniques are available for transform­ er insulation drying in both the field and in manufacturing. Vapor phase drying as part of transformer manufacturing is discussed in this paper.

KEYWORDS Vapor phase, transformer drying, vac­ uum chamber, VPD

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Vapor phase transformer drying – Part II Vapor phase drying as part of transformer manufacturing process TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Photo courtesy of Končar D&ST, Zagreb, Croatia

EVENTS TECHNOLOGY DRYING

Gregory R. STEEVES

Typical vapor phase steps Loading of coil(s): One or more coils are loaded into the vapor phase vacuum chamber (autoclave). Typically, a number of thermocouples are installed at various locations (depths & heights) in the coils to monitor and record the load temperature throughout the process. If isostatic pressing is part of the system, press plates are set and hydraulics are connected. Leak test and preheat: After the coil is inside the chamber with thermocouples connected, the chamber door is closed. Pressure is reduced by vacuum to a preset level and leak-up rate is checked to verify a tight door seal and vacuum integrity of the chamber. Preheating of the system in preparation for the next step begins. Wet cycle: Vacuum pump(s) lower the pressure in the chamber to the appropri­ ate starting level. Solvent is then intro­ duced into the chamber, heated and circulated through a spray system. Hot solvent being sprayed onto the load at reduced pressure transfers heat. The temperature and pressure of the system provide an environment for rapid wate­r evap­o ration. Sufficient heat is added by the spray system to both replace lost l­atent heat from water evaporation, and also to raise the load temperature for the ‘dry cycle’ step. As the hot solvent contacts the load and transfers heat, its temp­erature drops so that it runs down into the solvent pool for recirculation. In some products, a higher end temp­ erature is required to set epoxy impregnated components. Precise temperature control is required so as to heat rapidly while minimizing overshoot of the upper temperature limit of the insulation. Water evaporating from the load leaves the chamber through the vacuum system and is condensed for collection ahead

Typically 90-95 % of the total water content is removed during the wet cycle w w w . t ra n sfo r m e r s - m a g a z i n e . co m

Sometimes it is advantageous to allow the coil to sit under oil until the production floor is ready to use the coil in the next step of assembly of the vacuum pumps. Relatively small amounts of solvent that carry over with the water are also condensed and collect­ ed. The length of the wet cycle is determined by the load (coil: insulation & winding) size. Typically 90-95 % of the total water content is removed during the wet cy­ cle. It is not possible to remove all of the water content in this part of the cycle because dryness level is dependent on the vacuum level. In this step the vacuum level is controlled to optimize solvent use efficiency in the chamber. The end of the solvent cycle is deter­ mined primarily by the temperature of the load and/or the amount of water collected from the load. The process is instrument driven, but often minimum times are set in the controls based on the load size/mass and coil type. Dry cycle: The solvent is pumped out of the chamber while low vacuum is maintained. After the solvent drain is complet­e, vacuum is no longer limited and the vacuum system is allowed to lower the pressure further causing the remaining moisture to evaporate. Because the load was raised to a specific temperature during the wet cycle, there is adequate residual heat in the coil materials for the remaining water to evaporate without significant temperature drop. Platecoils or other chamber wall heating methods may also be employed to provide radiant heat for this part of the process. Platecoils also serve to minimize heat loss through the insulated chamber walls during high vacuum. This consideration is especially important on vapor phases for shell form transformers, which have a relatively smaller heat sink than core form (higher insulation to met­ al parts ratio). High vacuum continues until the bal­ance of the water is extracted. It is also during

this time that residual vapor phase solvent will evaporate under high vacuum and be removed with the final water for collection. This results in all solvent being removed from the system prior to addition of transformer oil during impreg­nation. Impregnation: Dry, degasified transform­ er oil is pumped into the chamber to submerge the load under oil. Vacuum is maintained until the load is under oil, at which time dry air or nitrogen is used to break vacuum back to atmospheric pressure. In the absence of air and water in the coil, oil fills all voids in the assembly in a process known as impregnation. Oil drain and unload: Transformer oil is pumped rapidly from the chamber so that the coil can be unloaded. Sometimes it is advantageous to allow the coil to sit under oil until the production floor is ready to use the coil in the next step of assembly. Figure 7 is taken from a typical vapor phase cycle. The bright red line is the vac­uum level. Most of the other lines are temperatures read from thermocouples placed in various locations in the insulation being dried. The wet cycle can be seen between hours zero and 105 where it remains relatively flat during the spraying of Isopar to add heat. The temperature lines show how this raises the temperature of the insulation rapidly so that under low pressure, water is removed continuously through this step. After all thermocouples achieve a minimum value (in this case 110 °C), and extracted water measures the expected quantity, Isopar is removed from the vac­ uum chamber and vacuum is no longer limited. As the pressure drops, the relatively small amount of remaining water continues to evaporate. This process continues until endpoint milestones 61

DRYING TECHNOLOGY

Several vacuum chamber configurations are available depending on the factory layout and the coil types to be processed (final pressure, air dewpoint, etc.) are achieved.

Vapor phase vacuum chambers Several vacuum chamber configurations are available depending on the factory layout and the coil types to be processed. With sufficient overhead lift capability, a top loading configuration such as the one in Figure 8 (shown with a hydraulically opened clamshell cover) could be used. End loading configurations such as the one shown in Figure 9 are available with either vertical or horizontal opening doors. A trolley system is used to shuttle the load in and out of the chamber.

Trolleys might accommodate single coils or multiples. Isostatic presses, as shown in Figure 10, may be integrated into the trolley to maintain pressure on the coils which will undergo shrinkage as water is removed from the cellulose.

Dryness / endpoint Several methods can be employed to predict completion of the drying process:

Vacuum level & coil temperature: Piper charts like the one in Figure 11 provide a good indication of the water content remaining in the coil based on its temperature and the final vacuum level achieved. Often there is a hold time that must expire after achieving the vacuum level target with coil temperature maintained above a minimum value to reach the desired dry point as indicated by the chart. Vacuum dew point: Dew point instruments that provide continuous moisture content in the vacuum stream leaving the vapor phase chamber are a good indicator of the dryness of the system. Most dew point instruments come on scale early in the high vacuum dry cycle. The dew point

There is a hold time that must expire after achieving the vacuum level target with coil temperature maintained above a minimum value to reach the desired dry point

Figure 7. Sample vapor phase data curves with insulation temperature and vacuum levels vs time 62

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

drops continuously as the coil dries with dropping pressure achieving dew point values of -30 °C or below. Capture extracted water and measure: The water and solvent condensed from the vacuum stream during the wet (low vacuum) cycle are easily condensed, collected and separated. Filter-separators will strip much of the water and further separation can be achieved by settling as the mixture cools. The water (if desired) can be measured. During the high vac­ uum drying phase, the pressure is too low to collect the water by condensing and it must be frozen from the vacuum stream using a cascade freeze trap. Collected ice is thawed and added to the measured water collected. If complete measurement of the extracted water during the entire cycle is desired, cascade cold traps can be utilized for this part of the cycle.

Figure 8: Top loading clamshell chamber

Solvent handling / recovery VDU (Vacuum Distillation Unit) Though the solvent can easily be filtere­d and water removed, it will gradually accumulate transformer oil. Even after complete draining of the oil after impregnation there is a residual film of oil inside the chamber that will be dissolved into the solvent during the subsequent vapor phase cycle. Since the oil will dissolve into solution, it cannot be filtered out. On systems without an oil impregnation cycle, residual oils within the active parts will eventually cause the same issue. However, as was presented in the vapor pressure chart in Figure 5 in Part I of this paper, the solvent and transformer oil (or other residual oils) can be separated by vac­ uum distillation in a small VDU (vacuum distillation unit – Figure 12) with the likenew solvent returned to the source tank. This continuous maintenance of the solvent ensures that the boiling range re-

The water and solvent condensed from the vacuum stream during the wet cycle are easily condensed, collected and separated w w w . t ra n sfo r m e r s - m a g a z i n e . co m

Figure 9: End loading chamber with trolley 63

DRYING TECHNOLOGY

The continuous maintenance of the solvent ensures that the boil­ ing range remains constant so that results are repeatable from one vapor phase cycle to the next mains constant so that results are repeatable from one vapor phase cycle to the next.

Figure 10: Isostatic press for shell form coil integrated into the trolley

Transformer oil purification equipment Transformer oil purifiers of adequat­e c­apacity to rapidly fill the vapor phase chamber with highly purified oil are an important part of the overall system. Different approaches can be taken to suit each situation. Small purifier with vacuum storage: If adequate vacuum storage is available, oil can be dehydrated to low moisture and degasified to low gas content (typically <10 ppm water and 0.25 % dissolved gas) and then stored under vacuum to maintain these levels. A high speed pump can then be used to transfer oil to the vapor phase when required so that the purifier does not have to be as large to meet the high flow rate demand of the vapor phase. High flow rate purifier: Alternately, a larger flow rate purifier can be used to s­ingle pass the oil from storage and to process it as it transfers into the vapor phase. Multi-stage purifier: For classes of transformers requiring lower water content (1-3 ppm) and lower gas content levels (<0.1 % total gas), multi-stage purifiers are available (Figure 13) to process oil at levels <100 microns (0.10 Torr).

Transformer oil purifiers of adequate ca­ pacity to rapidly fill the vapor phase chamber with highly purified oil are an important part of the overall system 64

Figure 11. Piper chart (moisture equilibrium diagram) By finding the intersection of the final pressure (vacuum) achieved during drying, and the insulation temperature at the final pressure, the colored line at the intersection provides a good estimate of the final percent of moisture (water) remaining in the insulation. 1,000 microns = 1 Torr (millimeter of mercury) = 1.33 mbar TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Conclusion Vapor phase drying is the most efficient and effective method for the drying of transformer insulation in a manufactur­ ing setting. It is advantageous over other methods in terms of time, repeatability and quality of end product.

Author

Greg Steeves is the General Man­ ager and principle engineer of Baron USA, LLC, provider of transform­er dryout and di­ electric fluid processing systems for OEM’s, utilities and field service organizations worldwide. Greg joined Baron USA as Engineering Manager in 1987. He is currently responsible for managing the daily operations and overseeing the application, engineering design and manufacturing of oil purification equipment, vac­uum chambers, vapor phase processing and transform­er dry-out equipment. He earned his degree in Mechanical Engineering from Tennessee Technological University and is licensed in the state of Tennessee.

w w w . t ra n sfo r m e r s - m a g a z i n e . co m

Figure 12. Vacuum Distillation Unit for solvent (VDU)

Figure 13. Multi-stage oil purifier

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EVENTS INTERVIEW

Interview with Wolfgang Sorgatz TLM Conference Introduction

T

ransformer Life Management (TLM) Conference was first held ten years ago, following the idea to create a comprehensive platform where all industry stakeholders – transformer manufacturers, customers and service companies – could partici­pate and have the opportunity to introduce their products and services. The idea was to have all people dealing with transform­ ers and doing business in the transform­ ers industry gathered together in one place.

conference in Germany, we organized the first international TLM Conference in Dubai, followed by Guangzhou in China. They were both very successful. At one of the conferences in China, there were more than 300 participants.

Conference values

TLM Conference is a neutral platform for all stakeholders in the transformers industry, from manufacturers of transformers, transformer instruments and transformer materials, to their industrial partners and end customers, such as utilities, power plants and entire municipalities, which is We started as a German conference, which why it is so successful. They can all meet was organized by ENERGY Suppor­ t, in one place and discuss what can be done ABB and the Schering-Institute for to extend the lifetime of the transform­ High V­oltage Engineering of the Leibniz ers, from all these various, but equally U­niversity of Hannover. It all started with important perspectives. The participants these three partners wishing to contribute can thus access all technical information to the same goal and encourage advance- and get a rounded picture of the complete ment of the industry by having all people management cycle, as well as the mainten­ from the transformer world converge at ance issues involved. So, the conference is streamlined to focus on the transform­ one conference. ers world, but within it, it offers a great In time, as TLM Conference bore great mixture of topics and participants, which success in the German market, we recog- many see as one of the greatest benefits of nized there was the same demand in the participating. international market to have a conference which would focus on the transformers TLM partners industry only. This is where we decided to use the transformers conference manage- TLM Conference is supported by ABB, the ment experience gained in Germany and Schering-Institute of the Hannover Unigo global. Three years after our maiden versity and ENERGY Support. This is an

open conference and this year, which also marks our tenth anniversary, for the first time we have an exclusive media partner – Transformers Magazine.

Conference topics As the conference is growing and chang­ ing, so are the topics. Every year we detect key trends and developments, as well as issues and concerns in the industry that resound all over the transformers world, and among them we try to decide on the best topics we want to address at the conference. In the past we dealt with questions on the regulation of the electricity market and even had guest speakers who talked about this issue. Today, there is an issue of how to extend the lifetime of the equipment. We are faced with different challenges that we wish to combine in the topics we discuss. However, each time the focus of the

The idea behind TLM was to create a com­ pre­ hensive platform where all industry stakeholders could participate and have the opportunity to introduce their products and services 66

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

conferences is the reliability of the transformer operation and its maintenance. These topics cover a lot of other topics and issues, such as test methods, continuous monitoring, interpretation of measurement and monitoring results and asset management. The next TLM conference is taking place in Königswinter, Germany from 26th to 27th September. We expect to have more than 200 participants and over 25 exhibitors as well as around 20 presentations from sev­ eral countries. This year’s topics will be centred around key changes in the energy supply in the areas of monitoring and asset management, as well as insulation liquids and condition assessment. More specifically, the conference will discuss voltage regulators for distribution networks, models for data recognition and asset man­ agement, DGA

TLM Conference is a neutral platform for all stakeholders in the transformers industry

w w w . t ra n sfo r m e r s - m a g a z i n e . co m

67

INTERVIEW

TLM Conference is supported by ABB, the Schering-Institute of the Leibniz University of Hannover and ENERGY Support, with Transformers Magazine as an exclusive media partner techniques, UHF PD detection, FRA, integration of offline and online monitoring, heat transfer in insulation fluids, recycled naphthenic base oils, ester fluids, GtL transformer oil, X-wax inside transformers, special hollow insulators for bushings, as well as topics looking at the far future, such as generation of energy using nuclear fusion technology. It will provide an overview of all the experience and research that we have, including speeches and presentations by our university researchers, a lot of university speakers, as well as some key speakers from the industry, who will all discuss the current situ­

ation, but also talk about new effects and technical methods in the market. Naturally, research and development will form a big and important part of the conference.

Continuous growth TLM is an annually-based conference which is continually growing, and it is expanding to the international market. Since there are many international participants, we provide translation into English, which is the second language of the conference. While the main language is German, a lot

TLM provides an overview of all the experience and research that we have, including speeches and presentations by our university researchers, as well as key speakers from the industry

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of the presentations are actually given in English. A true international conference is the TLM in Dubai, where the official language is English. Regrettably, it will not be held this year due to a political situation in the re­ gion and the complications for some participants from the region to travel to Dubai. However, we are exploring other regions in the world, such as the U.S., Vietnam, Thailand or Malaysia, and looking for opportunities to convey this successful platform there, creating more opportunities for participants from other regions in the world to share the knowledge in the same way we find it to be so fruitful and beneficial. To be able to do so, we need a strong partner in the region, preferably a strong-positioned company who is a leader in the area and knows the key manufacturers and customers.

Exhibition Although we have regular exhibitors and sponsors each year, we are open to new sponsors and offer various sponsorship packages. Gold Sponsorship package includes a complimentary exhibition booth at the conference exhibition area, 3 complimentary conference registrations for

TRANSFORMERS MAGAZINE | Volume 3, 2, Issue 3 4

We are exploring other regions in the world, such as the U.S., Vietnam, Thailand or Malaysia, and looking for opportunities to convey this successful platform there, creating more opportunities for participants from other regions company employees, and 5 complimentary registrations for their customers. It is of great value for the company to be able to select which customers they want to meet at such event and strengthen the relationship with them without any add­ itional costs! Silver Sponsorship benefits also include a complimentary exhib­ ition booth at the conference exhibition area, and a free conference registration for two of their employees. They can in­

vite two of their customers to attend the conference free of charge. Both Gold and Silver Sponsors have an opportunity to publish a full-page print advert in the TLM documentation, such as the conference programme and proceedings, as well as in downloadable documents free of charge. Bronze Sponsors are provided with a complimentary exhibition booth, a complimentary conference registration for one employee, and a 50 % discount on

Wolfgang Sorgatz holds a degree in marketing and engineering. He has a 1­4-year experience in the products of ENERGY Support, where he is responsible for sales, service, training and product development. Wolfgang also has a vast experience in marketing of capital goods in Europe. Before joining ENERGY Support he introduced a new brand in the test and measurement business to the European market. Starting from scratch, this brand has developed into one of the most wellknown brands in the German market today. w w w . t ra n sfo r m e r s - m a g a z i n e . co m

the second conference registration. The options available to exhibitors, which provide balanced opportunities for presenting to the relevant audience, and meeting key industry people and select­ ed customers without additional costs, make TLM a favourable and effective exhibition hub.

Universities and industries collaborate The involvement and participation of different universities, and the specialized knowledge associated with it, gives TLM Conferences an additional, educational value, providing a platform where people from the industry can have an immediate access to most current research and developments. This collaboration between universities, industries and customers is what makes this conference unique.

Wolfgang Sorgatz Technical Director and Sales ENERGY Support GmbH Sperberweg 47 41468 Neuss / Germany 69

TRANSFORMER IN GRID

ECOTAP VPD - the world‘s most compact on-load tap-changer for distribution transformers achieves maximum cost-effectiveness for the entire transformer/on-load tap-changer system

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TRANSFORMERS MAGAZINE | Volume 3, Issue 3

ADVERTORIAL

ECOTAP VPD Compact on-load tap changer for distribution transformers

I

n t h e t r a n s f o r m e r s i n d u s t r y, Maschinenfabrik Reinhausen (MR) is a synonym for voltage regulation. Majority of transformers today operating around the globe are equipped with some kind of a tap-changer from MR. In the past, voltage regulation used to be required only at higher voltage levels in the transmission grid. However, now­adays, due to several reasons, voltage regu­lation is increasingly required in the distribution grid at lower voltage levels.

Having launched the world‘s first tapchanger solution for voltage regulation distribution transformers (VRDTs) ready for mass production in 2012, MR set new standards in this area. In May 2016, at an official launch event at the CWIEME fair in B­erlin, Germany, MR presented a new, more advanced generation of tap changers for distribution transformers - ECOTAP VPD. The new ECOTAP VPD combines the know-how MR has accumulated over the decades in vacuum on-load tap-changers

The operating principle of the proven MR vacuum technology with 500,000 main­ tenance-free tap-change operations ensures reliable operation for decades, without the need to service the primary equipment

with the experience in VRDTs gained through working with transformer manu­ facturers and operators. The ECOTAP VPD provides a superior vacuum technol­ ogy at a price that makes use of VRDTs even more attractive and further expands the range of application.

Technologically superior – economically convincing The compact dimensions of the ECOTAP VPD on-load tap-changer permit installation in virtually any power-rating class of distribution transformers without any major changes to the footprint. What is more, the electro-mechanical operating principle of the proven MR vacuum technology with 500,000 maintenance-free tap-change operations ensures stable and reliable operation for decades, with­ out the need to service the primary equipment. The direct drive with up

Figure 1. The ECOTAP VPD on-load tap-changer (right) and the associated controller (left) w w w . t ra n sfo r m e r s - m a g a z i n e . co m

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TRANSFORMER IN GRID topology and to decouple voltage at me­ dium- and low-voltage levels. Ensuring a stable voltage within a narrow band regulated by standards is a huge challenge for distribution grid operators because they need to integrate a growing amount of renewable energy (increase in voltage) and more new types of demand (decrease in voltage). As a result, the oper­ ators are having to take expensive grid reinforcement measures, even though the thermal capacities of their equipment in the grid are far from being fully exploited. A VRDT with the new ECOTAP VPD solves the crux of the problem – compliance with the voltage band through dynamic adaptation. The low voltage is decoupled from the medium and the voltage band can be re-distributed and therefore used more effectively. The grid‘s ability to absorb power can be increased by up to a factor of 4.

Figure 2. Targeted use of voltage regulation distribution transformers

Voltage regulation distribution transformers are used to maintain a constant voltage in public, industrial, and private distribution grids, but also to avoid expensive grid re­ inforcement and to decouple networks to 20 t­­ap-chang­e operations per minute enables quick re-sponses to changing grid conditions. Nine tap-changer positions, with a mid-position which the operator is free to choose, ensure a large regu­lating range with fine steps between the tap changes. Thanks to its IP54 degree of protection, the ECOTAP VPD can be used outdoors and in selected synthetic and natural esters. Operation in applications with stringent environmental compatibil­ ity and thermal demand requirements is therefore also possible.

and, if necessary, high-voltage levels and responding dynamically to changes in the feed-in and demand. Selective use, focusing on one specific task in the lowvoltage grid, is now a very common application. Nowadays, VRDTs are also used to optimize the cost-effectiveness of the grid

In most cases, by using VRDTs expen­ sive grid reinforcement can be completely avoided and grid equipment put to more economical use. In this regard, reference is generally made to selective use, wher­e individual secondary substations are equippe­d with a VRDT, Figure 2. When VRDTs are used on a feeder basis or in all parts of the grid, the focus is on the medium-voltage grid. Feeder-based use, Figure 3, is always recommended if there is a risk of the volta-

The compact controller, another new feature, certainly lives up to its name as it is just 10 cm wide and 35 cm tall. Using an adapter, it can be installed on the busbar to the width of one single fuse panel to save space. All parameters can be set with ease on the controller, so no laptop is needed.

Wide range of possible applications in public grids VRDTs are real all-rounders – they maintain a constant voltage in public, indus­ trial, and private distribution grids by compensating for fluctuations in the medium 72

Figure 3. Feeder-based use of voltage regulation distribution transformers TRANSFORMERS MAGAZINE | Volume 3, Issue 3

By using voltage regu­la­ tion distribution trans­ formers the grid‘s abil­ ity to absorb power can be increased by up to a factor of 4 Optimization of the grid topology

Figure 4. Voltage regulation distribution transformers used in all parts of the grid

ge band limits being infringed in a larger inter­connected area at the medium-voltage level starting at a certain distance from the primary substation. This may be the case at the end of feeders or due to large fluctuating or constant feed-in and/or consumers. Decoupling the underlying low-voltage grids from the voltage of the affected medium-voltage feeder or ring permits much greater changes in voltage band than would otherwise be possible. This results in greater potential for feedin and demand to be integrated into the medium-voltage grid and the underlying low-voltage grids.

If VRDTs are used in all parts of the grid, all secondary substations not located in the direct vicinity of the primary substation are fitted with new technology. This is a good idea if there is a risk of the voltage band being infringed in the entire medium-voltage grid. The de­sired voltage value on the HV/MV transformer can also be reduced in order to allow an even higher voltage rise in the me-dium-voltage grid. In this way, the VRDTs can prevent or postpone major grid reinforcement measures in the medium-voltage grid.

An efficient distribution grid has as little equipment as possible. VRDTs with ECOTAP VPD increase the efficiency of grid sections and reduce the total number of secondary substations, thereby cutting investment and maintenance costs, Figure 5. The number of secondary substations needed for a grid area is determined firstly by the maximum possible distance between the secondary substation and grid connection points from a voltage standpoint and, secondly, by the maximum demand to be covered and/or the maximum feed-in to be transported. VRDTs dynamically adapt the voltage and thereby permit a larger electrical supply radius around each secondary substation. In this way, even consumers or feed-ins a long distance from the sec­ ondary substation can be connected. The grid operator can combine two second­ ary substations or can be spared from hav­ ing to build a new secondary substation.

Voltage regulation distribution transformers can spare operators from building new substations, resulting in savings for rent, maintenance and servicing of the stations, as well as for investments in replacement or new equipment Figure 5. Voltage regulation distribution transformers help optimize the grid topology w w w . t ra n sfo r m e r s - m a g a z i n e . co m

73

TRANSFORMER IN GRID

ECOTAP VPD in the industrial distribution grid allows equipment to be supplied with a voltage actively optimized for it, reducing energy consumption and costs without limit­ ing the equipment‘s function Figure 6. Voltage regulation distribution transformers help stabilize industrial processes

This results in savings for rent, maintenance and servicing of the stations, as well as for investments in replacement or new equipment. The only requirement is that one transformer is configured so that its performance is sufficient for the enlarged grid area.

Stabilizing industrial processes in volatile grids Industrial processes are extremely dependent on a stable voltage, which isn‘t always provided. In grids with limited gen­erator power, long distances or volatile consumers and producers, the supplying medium voltage may be subjected to large fluctuations in voltage. As a result, production processes may be inter­ rupted, motors may not start or control systems may crash. This can cause serious damage, especially in sensitive industrial processes. In addition to direct impacts on processes, frequent changes in voltage may also have a negative impact on the life of equipment. A VRDT with ECOTAP VPD in the industrial distribution grid ensures that consumers have a stable supply of voltage regardless of the volatility of the medium voltage, Figure 6. Due to the large regu­ lating range, even large fluctuations in the medium voltage can be reliably regulated for many years and without any main­ tenance. The compact dimensions help to keep costs down because the VRDT can be installed in place of the conventional one. 74

Energy costs can also be significantly reduced by optimized voltage. Energy consumption for conventional loads is affected by factors such as the voltage with which the equipment is supplied. If equipment is supplied with a higher volt­age than needed, the equipment con­ sumes more energy than needed. Using a VRDT with ECOTAP VPD in the industrial distribution grid allows equipment to be supplied with a volt­age actively optimized for it. This reduces energy consumption without limiting the equipment‘s function. The VRDT’s con-troller balances the voltage between what is available and what is ideal for consumption. Before the voltage falls to a level where equipment operation is at risk, the VRDT intervenes and restores

the voltage to a level which is ideal for consumption. This enables energy costs to be reduced by up to fifteen percent.

Dispersed generation plants – economically complying with grid connection conditions For integration into the grid, dispersed generation plants based on renewable energies (photovoltaics, wind, biogas) must meet the relevant requirements of the grid operator in the form of grid codes. The provision of reactive power, which depends on grid voltage, is partic­ ularly critical. In cases where the re­ quirements placed on providing reactive p­ower are particularly demanding, mak­ ing the required reactive power available can often only be accomplished either by oversizing the inverters or by requiring the generation plant to operate such that it reduces the amount of active power fed

Figure 7. Voltage regulation transformers in a photovoltaic park TRANSFORMERS MAGAZINE | Volume 3, Issue 3

ECOTAP VPD is perfectly tailored to the processes of trans­ form­er manufacturers and withstands all usual treatment processes in the plant such as evacuation, drying, testing, etc. testing. When developing ECOTAP VPD, MR has used all the knowledge gained though decades of cooperation with transformer OEMs, so that the f­inal product withstands all usual treatment processes in the plant (evacuation, drying, testing, etc.). Practically all re­ nowned transformer OEMs have developed and tested their VRDTs. This means that distribution utilities in most cases can source VRDTs from the same vend­ors they use for traditional distribution transformers.

Figure 8. Voltage regulation transformers in a wind park

into the grid to suit the situation. Neither approach is particularly attractive; the former because it increases the system costs of the generation plant and the latter because it restricts the system‘s output. The operator‘s profits suffer in both cases. The voltage decoupling made possible by the voltage regulation transformer means there is no need to oversize the inverters or reduce the amount of active power fed to the grid, which ultimately makes the generation plant more costeffective. Alternatively, the additional space obtained by using the voltage regulation transform­er can be used to operate an existing generation plant with a higher power rating. Voltage regulation transformers can be integrated in all dispersed generation plants. Typical examples include photovoltaic parks, Figure 7, and wind parks, Figure 8. In the case of wind turbines, voltage regu­ lation transformers can be combined with all drive-train concepts, such as asynchronous generators or full-scale inverters. The voltage regulation transformer can either run on its own or be integrated in the generation unit‘s regu­ w w w . t ra n sfo r m e r s - m a g a z i n e . co m

lation system. Given the very limited amount of space available, particularly in wind turbines, the compact dimensions of the ECOTAP VPD are as important as the large regulating range and the maintenance-free operation in alternative insulating fluids.

Manufacturing voltage regulation distribution transformers Distribution transformers are as simple as they can be. Adding a new function­ ality requires also certain changes in transformer manufacturing plant, from the design through manufacturing to

ECOTAP VPD – more power, more value The new ECOTAP VPD is the world‘s most compact on-load tap-changer for distribution transformers offering the largest range of services. It achieves max­imum cost-effectiveness for the entire transformer/on-load tap-changer system, is maintenance-free, already satisfies the requirements of the EU Ecodesign Directive for 2021, and can be operated with synthetic and natural esters as insulating fluids. The ECOTAP VPD is perfectly tailored to the processes of transformer manufacturers and is highly versatile – be it in public distribution grids, industrial applications or dispersed generation units.

Contact Dr. Sojer, Manuel

Phone +49 941 40 90-2430

Head of Strategy and Marketing Power Quality

Fax +49 941 40 90-902430 [email protected] www.reinhausen.com 75

TRANSFORMER IN GRID EVENTS

Cost-effective and fail-safe integration of distributed grid infeed Highly efficient, controllable distribution transformers and voltage regulators ABSTRACT Grid expansion represents a technically obvious but also very expensive solution for the infeed of renew able energy sources. A more intelligent solution is the implementation o f c o n t ro l l a b le d i s t r i b u t i o n transformers whose ratio can be controlled under load, as well as voltage regulators used in the medium voltage grid.

KEYWORDS voltage regulation, renewables, distribution grid, regulated distribution transformers 76

1. Introduction Photovoltaics, biogas and wind turbines save resources and reduce CO2 emissions. However, they also result in fluctuating energy flow directions, as well as load and voltage fluctuations. Traditional distribution grids with their conventional distribution stations and classic trans­ formers are not designed for these con­ ditions. Capacity could certainly be expanded, but this does not resolve the core issue. The concept was developed for a

world with a small number of large power generation facilities and a large number of loads. While expansion of the grid would cover this inherent system deficiency, it would not correct it. Grid operators are currently faced with completely different tasks, being obligated to provide for the infeed of renewable power sources. With no affordable intermediate storage devices currently available, they must also harmonize supply and demand of power, and smoothen peaks using power generation and load management.

Decentralised energy production is on the rise, but its integration in the existing grid infrastruc­ t­ure is a challenge for distribution grid operators TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Saskia BAUMANN

With their variable voltage under load, regu­ lated distribution transformers and voltage regu­lators can be used as a supplement in grids with voltage range issues transformer appears to be the simplest solution for many operators. These units are essentially small versions of controllable power transformers – a concept known from large transformers and therefore easy to understand. The advantage of this solution is precise control enabled by the tap changer on the high-voltage side. However, this requires that the operator accepts somewhat higher losses, caused by the tap changer design. It includes additional reactors, as well as the risk of feedback loops with the medium-voltage transformer occurring when the regulation of the distribution transformer takes place in small steps once a small voltage change from the MV grid happens.

With their variable voltage under load, FITformer REG – a regulated distribution transformer – and voltage regulators are two of the available solutions providing a supplement for grids with voltage range issues. Both solutions offer a cost-effective alternative to traditional grid expansion and are easily integrated in existing structures.

2. Better voltage control with distribution trans­form­ers for the MV/LV grid (e.g. 20 kV/0.4 kV) There are currently different concepts for regulated distribution transformers, where the integration of a tap changer on the high-voltage side of the distribution w w w . t ra n sfo r m e r s - m a g a z i n e . co m

Designed with a different approach, F­ITformer REG is a regulated distribution transformer whose underlying philosophy is not to regulate voltage “exactly to the volt”, but rather to very flexibly keep it within the allowed voltage range in accordance with EN50160 [1], with ex­ tremely low losses. In order to achieve this, the regulated distribution transformers has been supplemented with a load controller on the low-voltage side in addition to the load-free control range on the high-voltage side. This regulated distribution transformer enables voltage adjustment under load in three stages to ensure distributed infeed from micro power plants. The operating characteristics and dimensions of the distribution transformer remain virtually unchanged. Figure 1 shows the results from the implemented regulation algorithm in an application case. As illustrated, frequent switching caused by the medium power transformer stepping is avoided (point 1) because the limits are not reached. How­ ever, when the voltage of the three phases in the grid increases (as shown by the green lines at point 2), the feed-in is negative (see the blue line at point 3), and the volt­ ages reach the upper limit of the config­ured voltage level (point 4). The transform­er lowers the voltage at point 4 by stepping from position 2 to position 1 shown on the

right-hand axis, where the three steps of the regulated distribution transformer are i­ndicated. After a while, the voltage reaches the lowest limit (point 5) and the transform­ er steps back from position 1 to position 2 on the right axis to increase the voltage. Losses always play a major role when rat­ ing electrical machines and have a big impact on the lifecycle costs, defining the ecological footprint of the transformer. Therefore, in the development of this r­egulated distribution transformer both the control technology and economic factors were considered. In the avail­able ratings from 250 kVA to 630 kVA, the transformer meets the loss requirements according to the European standard, e.g. a distribution transformer up to (not incl.) 1.25 MVA: Pk = Ck+5 % and P0 = A0+20 %,

[2]

where Pk defines the load losses and P0 defines the no load losses. Transformers are divided into classes where A is the class with the lowest and C with the highest losses. For regulated distribution transformers there are additional losses allowed, which enables replacement of transformers in existing substations with regulated distribution transformers, considering that losses have a direct impact on the design as well as the size of a transformer. Depending on the product, utilities must accept that regulated distribution transformers not only cost more, but also imply higher operating costs . This transformer is designed with optimized losses, and therefore reduces these costs. Its control system causes only low additional losses, which could be compensated by an adapte­d design of the active section, so that it exhibits the same low losses as the standard distribution transformer. With an additional focus on keeping acquisi­ tion costs as low as possible, the development of this transformer resulted in a controllable distribution transformer with a shorter amortization time. 77

EVENTS TRANSFORMER IN GRID

240.0

Stufe Position

600.0 480.0

235.0

360.0 3 240.0 120.0

230.0

2

0.0 -120.0 -240.0

225.0

1

-360.0 -480.0

00:00:00 16.03.2012

06:00:00 16.03.2012

12:00:00 16.03.2012

18:00:00 16.03.2012

00:00:00 17.03.2012

Figure 1. Measuring recording during operation of a regulated distribution transformer for 24 hours, starting point 00:00:00

Algorithm implemented in the regulated dis­ tribution transformer ensures that frequent switching caused by the medium power transformer stepping is avoided 2.1. Technological details

The regulated distribution transformer presented in this paper is a special kind of transformer where the windings are produced with three low-voltage taps which are routed from the transformer through the hermetically sealed corrugated wall tank to the control unit. With its compact design, it can also be used to replace former traditional distribution transformers in commonly compact stations without difficulty.

control has been developed. This permits grid operators to gradually expand their conventional distribution stations and adapt them to the changing grid conditions and requirements. In the complete configuration (including all three stages), the intelligent distribution stations (iSub) are equipped with Remote Terminal Units (telecontrol and regulating devices), smart

short-circuit indicators, current/voltage sensors, motor-driven medium-voltage switching devices and a controllable distribution transformer. The modular structure of the iSub also allows the operator to install only individual components in existing stations. The actual distribution station is capable of directly controlling the locally installed controllable distribution transformer, but also to send commands to various other grid components with the existing meas­ ured values, such as to inverters in power generation systems. This enables a very r­apid response to extreme high and low load periods in combination with highly fluctuating infeeds from wind and solar

Highly robust and reliable vacuum contactors are used, which are characterized by especially high reliability, operating safety and compact design. Voltage regulation is implemented in two stages. Voltage limits for slow and fast switching, as well as the desired rated voltage can be entered in the form of parameters. The control system can be individually adjusted to various grid conditions by entering delay times. 2.2. Controllable transformers in the distribution grid of the future

Future distribution grids need more than just controllable transformers. There­ fore, a modular 3-stage concept based on monitoring, telecontrol and load flow 78

Figure 2. Comparison of the two-winding transformer and the voltage regulator autotransformer TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Figure 3. Medium voltage in phase control station

power. For the grid operator, this represents an option to optimize future investments.

In areas where high power generation from al­ t­ernative sources is paired with high industrial loads, it is expedient to combine intelligent power stations with voltage regulators

3. Integration of renewable power sources using volt­ age regulators in the MV grid (e.g. voltage level 10 kV or ficant changes in the operating voltage principle, an autotransformer (Figure 2). A 20 kV) at individual distribution stations. This special feature of autotransformers is that In some applications, it may be expedient to combine intelligent power stations or controllable distribution transformers with voltage regulators. This is particularly the case in areas where high levels of p­ower generation from wind and photovoltaic systems are paired with high power consumption in industrial grids. The current distribution grids in rural areas are often characterized by long transmission lines and low cross-sections – a reliable design for the drop in voltage resulting from the relatively low loads. However, multiples of the load peaks can result in medium voltage systems to which many distributed feeders are connected. In this combination, fluctuating load and infeed conditions can give rise to signiw w w . t ra n sfo r m e r s - m a g a z i n e . co m

make­s compliance with the voltage limits of +/-10  % in the distribution grid levels an ever-increasing challenge. Voltage adjustments in the medium-voltage grid are currently frequently made only with tap changers in the substation transformers. As a result, voltage changes cannot be corrected; instead, the voltage change affects the entire medium-voltage grid, thus necessitating expansion of the grid. The more intelligent option is using regu­ lators to equilibrate the various load conditions with fine-tuned control, main­ taining a constant output voltage. These voltage regulators are independently installed transformers which can sub­ stitute an additional substation in the MV grid. This particular voltage regulator is, in

the primary and secondary windings are connected both magnetically and electric­ ally. The step-up autotransformer can increase the input voltage from 100 V to 110 V with a series connection of the secondary winding to the upper end of the primary winding. This procedure is reversed in the step-down transformer to lower the voltage to 90 V. The integrated mechanical switch enables both functions to be combined, achieving a control range of 20 % (+/-10 %). These parts are mounted in one tank and filled with oil for cooling and insulation purposes. One voltage regulator is connected to one phase of the grid. In the medium voltage substation, there are three voltage regulators installed. The voltage regulator serving as medium voltage substation will be installed in an existing grid. 79

EVENTS TRANSFORMER IN GRID

An economically opti­ m a l g r i d s o lu t i o n should also account for the existing voltage control equipment

Figure 4 presents a comparison between the voltage levels over a period of 24 hours in a summer time with and without using a medium voltage regulator. The graphs clearly indicate that the range of the volt­ age deviation will be minimized due to the direct voltage adjustment in the medium voltage grid.

only be switched when the transformer is de-energized, and of course the primary substation with its medium power transformer with the on-load tap changer, which can contribute significantly to improving the voltage based on its large

control range. This makes it clear that not only should independent voltage control equipment be planned in the grid, but also that the existing and future control equipment requirements must be coord­ inated.

4. Which solution for which grid situation? As both controllable distribution trans­ formers and voltage regulators essential­­ly address the same grid planning issue, the optimum solution for the grid oper­ator must be determined using a planning process. The necessary workflow is described in the next section. The first step in the planning horizon is to determine the critical points in the grid where voltage issues can be antici­ pated. This can be achieved with longterm measurements for the current situation. However, future scenarios require the performance of corresponding grid calculations based on the load and utility forecast. An economically optimal solution should also account for the existing volt­age control equipment. This includes the currently existing distribution transform­ers with their off-load tap changers that can 80

Figure 4. Comparison of voltages for a 24-hour load cycle in summer, with and without the in-phase regulator TRANSFORMERS MAGAZINE | Volume 3, Issue 3

visualization of voltage bands and variant analysis components (Figure 5). The central area presents the voltage profile of the network across all network nodes and dem­ onstrates that the voltages are within the permitted range in both extreme cases a­fter optimization (green colour). The black lines indicate the resulting voltages at the neutral positions of the regulating equipment as the starting point of optimization.

Conclusion

Figure 5. Overview of the optimization environment

Not only should independent voltage control equipment be planned in the grid, but also the existing and future control equipment requirements must be coordinated The planning workflow consists of the following individual steps [3]: - Load/generation forecast with determination of the resulting extreme operat­ ing cases - Determination of the requisite voltage regulating elements - Determination of installation locations - Coordination of control settings with existing grid elements - Equipment configuration The grid nodes to be monitored need not generally be at the end of the supply line. It is therefore especially important to determine the required measuring points of course these can be determined in the context of field testing for an existing grid. Despite this, analytical support would be helpful in simplifying field testing or even rendering it superfluous. Therefore, a corresponding procedure has been developed to determine the minimum required set of measured data based on optimization calculations. The grid calculation program PSS SINCAL [3] is first used to generate a grid model using all necessary information on the grid topology as well as the load and gen­ w w w . t ra n sfo r m e r s - m a g a z i n e . co m

erating units. The starting point for the optimization is then the case in which all grid nodes are explicitly monitored with voltage measurement. Next, the mixedinteger optimization is used to determine the subset of grid nodes to be explicitly monitored, which is absolutely necessary for complete observability regarding permissible voltage limits. The voltage conditions are then implicitly observable for all other grid nodes where the voltage meas­ urement can be eliminated. A grid node is implicitly observable if there is no load or generation condition in which a voltage range is violated at any node under consideration of the explicit measuring points. The results are calculated in a graphical optimization environment with the network editor, parameter configuration unit,

Although the shift in energy policy (“en­ ergy turnaround”) poses a significant challenge for grid operators, solutions are available. The use of intelligent technol­ ogy enables the elimination of expensive and comprehensive grid expansion. This can be applied both to the low voltage grid where regulated distribution transformers can be used for the infeed of energy from distributed producers, and in the medium voltage grid where voltage regulators can compensate for the fluctuating infeed and load. However, the grid situation must first be analyzed. The use of voltage regulators and controllable distribution transformers must be carefully configured if the most cost-effective possible implementation of new resources is to be achieved. The presented controllers and the corresponding innovative planning solutions provide an important contribution and support to the grid operators when confronting the technical and economic challenges posed by the energy turnaround.

Bibliography [1] DIN EN 50160, Merkmale der Spannung in öffentlichen Energieversorgungsnetzen [2] Eco directive 2009/125/EG [3] Ohl, Betz, Wagner, Blug, Mladenovi­c, Optimierte Koordination von Spannungsregeleinrichtungen. EW 12/2015 [4] Website PSS®SINCAL: http://www.siemens.de/pss-sincal

Author Saskia Baumann holds a B.A. in mechanical engineering and an MBA. She joined Siemens in 2011 and has been working in various positions within the distribution transformers segment of Siemens Transformers. Currently she is the responsible product manager for regulated distribution transformer products. 81

TRANSFORMER IN GRID EVENTS

ABSTRACT This article examines issues related to power quality and generation of higher harmonics in single-phase transformers of low power supply, supplying electricity to household, office and industrial equipment. Generation of higher harmonics of these transformers was simulated on basis of the results of the Finite Element Method (FEM) analysis of the magnetic field. Harmonic composition of the current in the primary side was determined using a Fourier transform applied to the curve of the current obtained through the FEM analysis. The results were fully confirmed by the experimental study of the harmonic composition of the current in the primary side of the investigated one-phase transformer. The used approach is unique, and it enables manufacturers to explore the harmonic composition during the design stage, and take appropriate measures to reduce their magnitude.

KEYWORDS FEM, small transformers, harmonics, power quality, electrical power systems

82

Transformers and power quality – Part I Modelling and researching generation of higher harmonics in small single-phase transformers used by domestic and industrial consumers TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Petar Milkov UZUNOV

Due to the large number of small transformers, they pollute the electrical network and are a factor in lowering the quality of electrical power issue of which consumers exactly affect these quality indicators and how this works (i.e. the very mechanism of the process) has been less studied and requires more theoretical and experimental research. Transformers are static electromagnetic devices which occupy an important place in the process of transmission and con­ sumption of electricity. When an AC power source is connected to a trans­form­ er, current flows in its primary circuit, even when secondary circuit is open-circuited. This current is the current required to produce flux in the real ferromagnetic core, and it consists of two components: - the magnetization current, which is the current required to produce the flux in the transformer core, and - the core-loss current, which is the current required to make up for hysteresis and eddy current losses in the core.

1. Introduction Electricity is one of the most widely used forms of energy in our time, which can be attributed to the easy reception, transmission and conversion of this type of energy to consumers. In terms of electricity consumption, this is a type of product which is characterized by a number of indicators that determine its quality. Users requiring high quality of supplied electricity will pay the right price for it. In the transmission of electricity from the source to the consumer, there are various undesirable factors that can be observed: lightning strikes, frequency interference, high harmonics and shock loads. These fluctuations in power consumption and switching to different loads affect others in the network, thus reducing its basic parameters and quality, and adversely affecting the end users, i.e. consumers.

From the graphical representation of the magnetization current in the classical theory of electrical machines [4], one can see that the magnetization current in the transformer is not sinusoidal. The higherfrequency components in the magnetization current are due to magnetic satur­ ation in the transformer core, and they can be quite large compared to the fundamental component. It should be noted here that contempor­ ary designers design transformers so that they operate with a magnetic flux density close to saturation point for the maximum use of the ferromagnetic core material. In general, the more the transformer core is saturated, the larger the harmonic components will become.

Consequently, even when supplied with sinusoidal voltage, their no-load current will have a pure non-sinusoidal shape, i.e. transformers will generate high harmonics which penetrate into the grid and reduce the quality of electricity. The objective of this article is to study the mechanisms of generating higher harmonics and the influence of small single-phase transformers used in house­ hold, office and industrial equipment, which are the external loads, on the quality of the power system. Specific studies were conducted on a single-phase transformer, shown in Figure 1a. Its technical data is outlined in Table 1 and its electrical scheme presented in Figure 1b. Usually, electrical machine textbooks graphically present and explain a distortion of the shape of the current in the primary side [4], while other references [5, 6] describe various analytical models of the generation of higher harmonics in transformers. The finite element method (FEM) offers the most accurate way to determine mechanisms of generating higher har­ monics in transformers based on modelling and analysis of their magnetic field. FEM enables the analysis of the magnetic fields recording the nonlinearity in the used magnetic materials, which is difficult to obtain by the relevant analytical models that are based on the theory of electric and magnetic circuits. The study of the generation of harmonics makes it possible to take appropriate actions to measure, control and improve the perform­ ance of transformers in order to prevent

There is a lot of scientific research and literature discussing the effects of poor power supply quality on consumers [1-3]. Consumers themselves can also aggravate the quality of electricity [3]. However, the

Even a transformer supplied with sinusoidal voltage has non-sinusoidal no-load current, i.e. it generates high harmonics which penetrate into the grid and reduce the quality of electricity

w w w . t ra n sfo r m e r s - m a g a z i n e . co m

83

TRANSFORMER IN GRID them from polluting electricity supply and impairing its quality. Also, it enables proposition and implementation of relevant technical solutions to neutralize this harmful effect and improve power quality.

a)

b)

2. Modelling of the electromagnetic field of the transformer based on Maxwell‘s equations in differential form 2.1. Equations of the magnetic field

The quasi-stationary magnetic field of the transformer was modelled based on the system of differential equations of the electromagnetic field, recorded on  the magnetic vector potential A and the p­otential of the electric field V. The first Maxwell equation reads as follows:    (1) ∇×H = J .

Figure 1. Investigated transformer: a) main view; b) electrical scheme of the transformer

     ∂A (9) From the equations (4) and (5) one can E = −∇V − +ν × ∇ × A, ∂t derive the following:      B rot A where ν × ∇ × A represents moving of . (6) the field. Here, on the right hand side the compo- H = µ = µ ∂D

nent ∂t is ignored due to the electric flux density, and  only  the conductivity current density J is=taken γ E into consideration:

  J = γ E.

(2)

The equation for the continuity magnetic field principle is:   (3) ∇ × B = 0,



where B is the magnetic flux density. Equations (1) to (3), together with the relationship between the magnetic field intensity and the magnetic flux density, which corresponds to

  B = µ H,

(4)

allow usto define the magnetic vector potential A as

  B = rot A .

(5)

The study of the generation of harmonics m­akes it possible to improve the performance of trans­form­ers and prevent pollution of electricity supply 84

From the second Maxwell’s equation,

Applying (9), (2) and (8) to (1), the following result is obtained:

  ∂B , rot E = − ∂t

(7)

    ∂B  ∇×E = − + ∇ × (ν × B) . ∂t

(8)

and the equation (6), the following is derived:

From (8) follows

   ⎛ ∂ A   ⎞  ∇× A  ∇×( ) + γ ⎜ − ν × ∇ × A ⎟ = −γ ∇V . µ ∂t ⎝ ⎠

(10)

 The magnetic vector potential A is cal­ culated by the  use of (10). Then, using (5), (6) and (9), B and H are obtained.

Table 1. Technical data of the investigated transformer

Quantity

Value



Rated power [VA]

130



Primary voltage [V]

220



Rated frequency [Hz]

50



Secondary no-load voltage ±5 % [V] U21 / U22 / U23 / U24

50 / 18 / 18 / 10



Rated secondary current [A] I21 / I22 / I23 / I24

0.5 / 0.5 / 0.5 / 4.5



Number of turns of the primary winding 760

Number of turns of the secondary windings w21 / w22 / w23 / w24

172 / 62 / 62 / 35



Diameter of the wire [mm] • primary winding • secondary winding

0.6 0.6 / 0.6 / 0.6 / 1.4



Material of the transformer core

M530



Class of insulation

F

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

a)

The non-linear model­­l­ing of the material core was performed using the basic curve of magnetization

b) 1 6 5 4 3 2

Figure 2. FEM model: a) region in which equations of the magnetic field are solved: 1 - magnetic core of the transformer; 2 - primary coil; 3,4,5,6 - secondary coils; b) discretized area

Part ∇V in (9) is taken from the definition of the source of electromotive force (e.m.f.). 2.2 Numerical modelling of the single-phase transformer

The analysis of the transformer’s magnetic field was conducted in two dimensions in the region shown in Fig. 2a, divided into a network of 4,014 nodes and 7,960 triangular finite elements of the first order (Fig. 2b). The non-linear modelling of the material core was performed using the basic curve of magnetization shown in Fig. 3a. The transformer was modelled by a combination of the circuit theory and the FEM, which is the best way to simulate the op­ eration of an electromagnetic device and to test the electromagnetic processes therein. The primary winding of the transformer was powered by a voltage source V1 (Fig.

a)

3b). Therefore, the source supplying the primary winding with a sinusoidal voltage had a set voltage amplitude, frequency and initial phase to model the network, supplying transformer with a sinusoidal voltage. Series resistor R1 was connected to the circuit of the primary winding. Its value can be calculated from no-load losses, as shown in the following equation:

U12 , R1 = PPhyst + P eddy hyst eddy

(11)

where Physt is hysteresis losses in the transformer core, Peddy is eddy current losses in the trans­ form­er core, U1 is the effective value (RMS) of the primary voltage.

b)

Figure 3. Modelling of the transformer: a) basic curve of magnetization of the magnetic steel M530; b) circuit and parameters of the power supply, source of e.m.f. w w w . t ra n sfo r m e r s - m a g a z i n e . co m

The distribution of the magnetic field (Fig­ure 4a) was obtained after solving the equation (10) for the time t = 0 to 120 ms with the increment of 1 ms – these were the six periods of the supply voltage. This number of periods was assigned in order to attenuate the transient process from the inclusion of the transformer and obtain the actual shape of the established magnetizing current of the transformer. Har­ monic analysis of this current waveform was performed. Otherwise, if there is a non-steady state process, this will cause incorrect results of the Fast Fourier Transform (FFT) analysis. To prove that the distortion of the current shape is due to the non-linearity of the magnetic characteristics of the ferromagnetic core material and its saturation, an­ other analysis of the transformer magnetic field was performed, substituting the ferromagnetic core material with a material with a linear relation between the magnetic flux density and the magnetic field intensity, that is, a material with constant relative magnetic permeability µ≈1000. As a result, sinusoidal shape of the current through the primary winding in no-load mode was obtained – i.e. the magnetizing current had sinusoidal shape in this particular case (Fig. 5).

3. Experimental study of the harmonic composition of the transformer magnetizing current In order to verify the results of the harmonic analysis of the current obtained by FEM data post processing, an experiment was performed in which the waveform of the magnetizing current of the modelled transformer in no-load mode was meas­ ured using a digital oscilloscope. The picture of the experimental set-up is shown in Fig. 6.

85

TRANSFORMER IN GRID a)

b)

Figure 4. Results from the analysis of the transformer magnetic field: a) distribution of magnetic flux density for the time t = 2 ms; b) the current through the primary winding of the transformer

The tested single-phase transformer was powered by a laboratory autotransformer supplied with single-phase voltage of 220 V RMS with a pure sinusoidal shape. Its secondary windings were not connected to any load. The current waveform of the transformer was taken from the voltage drop on the series resistor R. The current waveform displayed on the digital oscilloscope is shown in Fig. 7. From Fig. 7 it is clearly visible that the current contains high harmonics generated only by non-linearity in the magnetic char­ acteristics of the steel core and its satu­ ration. The RMS value of the current was measured with the multimeter, which is a “true RMS“ device which measured the real RMS value of the current, although it is non-sinusoidal. The measurement results are displayed in Table 2.

current contains pronounced third and fifth harmonics, with RMS values I3 and I5 respectively.

4. Fourier’s analysis of the transformer current Fig. 7 shows the distortion of the shape of the no-load current of transformer, which is caused by higher harmonics generated due to non-linearity of the

The digital oscilloscope has a built-in feature to help realize FFT. RMS values of harmonics are also provided in Table 2. In Fig. 8 the harmonic spectrum of the transformer current is shown. It was found that, in practice, apart from the fundamental harmonic with RMS value I1, the

To prove that the distortion of the current shape was due to nonlinearity of the core, another analysis was performed substituting the ferromagnetic with linear core material

Figure 5. Waveform of the transformer magnetizing current when the core is made from magnetic material with linear properties

Table 2. Results of the experimental study of the current harmonic composition

Magnitude I 0

Harmonic amplitudes I 1 I 3

I 5

Unit

mA

mA

mA

Experience

18

64

18

86

mA 6

RMS value I mA 70

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

To verify the results of the current harmonics obtained by FEM data post processing, the magnetizing current of the transformer was measured using a digital oscilloscope with a built-in FFT

2 5 4

1 3

Figure 6. Experimental set-up: 1 – investigated transformer; 2 – laboratory autotrans­ former; 3 – resistance; 4 – digital oscilloscope; 5 – multimeter

I = I 02 +

2 I1m I2 +…+ km , 2 2

(12)

where Ikm is the amplitude of the higher harmonics with number k = 2, n .

Figure 7. Waveform of the transformer current

magnetic characteristics of the steel core, and saturation effects. In order to obtain a harmonic com­ position of the current through the primary winding, FFT was used. A mathematical programme provided harmonic analysis of the current waveform, as illustrated in Fig. 9. As a result, the harmonic spectrum of the current was obtained, shown in Fig. 9. Fig. 9 shows a screen of a specially developed application displaying the s­hape of the curve of the current, and the results of the harmonic analysis of

the transformer current. It is obvious from the figure that the current of the transformer presents two more pronounced higher harmonics – the third and fifth, which are caused by non-linearity in the magnetic characteristics of the transformer core steel and which distort the shape of the current waveform. From the theory of electrical engineer­ ing it is known that the RMS value of a non-sinusoidal magnitude, as transform­er current, can be calculated by the following equation:

Using this equation and the results from the harmonic analysis, the RMS value of the current can be calculated. Table 3 presents a comparison of this RMS value, together with amplitudes of the harmonics, with the amplitudes of the experimentally measured higher harmonics. It was found that they differ little within the margin of the FEM calculation error, which indicates the correctness of the constructed FEM model of the transformer, especially the approach to modelling and the calculation of the harmonics generated by the transformer due to strong non-linearity in the magnetic properties of the core steel.

The 3rd and 5th current harmonics, which are caused by non-linearity in the magnetic charac­ teristics of the trans­ former core steel, are more pronounced

Table 3. Comparison of the results of the harmonic analysis of the transformer current with FEM and experience

Magnitude I 0

Harmonic amplitudes I 1 I 3

I 5

Unit

mA

mA

mA

Experience

18

64

18

6

70

FEM

8

19

11

68

w w w . t ra n sfo r m e r s - m a g a z i n e . co m

6.43

mA

RMS value I mA

87

TRANSFORMER IN GRID Conclusion This article investigates the generation of higher harmonics in small singlephase transformers supplying power to household, office and industrial equipment. The results of the finite element analysis of the magnetic field have been used to obtain the waveform of the current in the primary side of the transformer operating at no load. Its shape is different from sinusoidal wave, i.e. the current contains higher harmonics, which occur due to non-linear­ ity in the magnetic characteristics of the magnetic materials used in transformers, and due to saturation effect. To obtain magnitudes of these harmonics, harmonic analysis was performed by the FFT. The results of the simulations with FEM were fully confirmed by measurements of the harmonic composition of the magnetizing current of the transformer with a digital oscilloscope. Despite their low p­ower, the fact that there is a large number of such transformers in the electrical grid means that this is a serious pollutant and is therefore a factor in the reduction of the quality of electricity.

To remove this harmful effect and improve power quality it is recommended to connect to the network passive and active filters designed to filter out the 3rd, 5th and 7th harmonics

Figure 8. Harmonic analysis of the transformer current obtained by a digital oscilloscope

To remove this harmful effect and im­ prove power quality, it is recommended to connect passive and active filters to the network, which are designed to filter out the 3rd, 5th and 7th harmonics.

Bibliography [1] C. Tsanev, C. Tsvetkova, Power quality, Avangard Prima, Sofia, 2011(in Bulgarian). [2] J. Arrillaga, D. A. Bradley, P. S. Bodger, Power system harmonics, John Willey & Sons, 2010. [3] J. Schlabbach, D. Blume, T. Stephanblome, Voltage Quality in Electrical Power Systems, IET Power and energy series 36, United Kingdom, 2000. [4] Stephen J., Chapman, Electric machinery fundamentals, Mc Graw Hill, 5th edition, 2010. [5] Krishna Vasudevan, Sridhara Rao, Sasidhara Rao, Electrical Machines I, Indian Institute of Technology, Madras, http://www. nptel.ac.in/courses/IIT-MADRAS/Electrical_ Machines_I. [6] Ismail Daut, Syafruddin Hasan, Soib Taib, Magnetizing Current, Harmonic Content and Power Factor as the Indicators of Transform­ er Core Saturation, Journal of Clean Energy Technologies, Vol. 1, No. 4, October 2013 88

Figure 9. Waveform of the transformer magnetizing current and the results of its harmonic analysis (basic harmonic frequency 50 Hz)

Author Petar Uzunov, Electricity System Operator, received his BSc and MSc degrees in electrical engineering from the University of Gabrovo, Bulgaria in 1988, and his PhD from the same university in 1998. From 1988 to 2007 he was an Assistant Professor, Chief Assistant Professor and Associate Professor at the Basic Principles of Electrical Engineering and Power Energetics Department at the Technical University of Gabrovo. From 2008 to 2012 he headed the department. From 2012 to 2015 he worked at Mechatronica SC, Gabrovo, Bulgaria as the Head of the R&D Department. He is the author of 10 textbooks, more than 60 articles, and two inventions. His research interests include optimal design of electrical machinery, simulations and research of electromagnetic processes in electrical machines and apparatus based on the analysis of electromagnetic field through Finite Element Method and hysteresis modelling. TRANSFORMERS MAGAZINE | Volume 3, Issue 3

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TECHNOLOGY EVENTS

ABSTRACT Superconducting transformers using high current density High Temperature Superconductor (HTS) wire cooled with liquid nitrogen can be lighter and more efficient than conventional powe­ r transformers. This paper describes the 1 MVA 11/0.415 kV HTS transformer developed by a New Z­ealand - Australian team, featuring HTS Roebel cable in the 1.4 kA-rated low voltage winding. Comparison of HTS and conventional transformer designs at 40 MVA rating shows low­ er lifetime cost of losses makes HTS base-load transformers cost-competitive in higher energy cost markets. P­ower density - more MVA in a restrict­ed footprint - could be a deci­ sive advantage in mobile applications.

KEYWORDS superconductor, Roebel cable, cryogenic 90

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Mike STAINES, Mohinder PANNU, Neil GLASSON, Nathan ALLPRESS

Superconducting transformers – Part II Liquid nitrogen, super-high current density – the future of the grid? 3.2 Testing

The load loss of the transformer windings was measured for convenience in an air core configuration with shorted output, as shown in Fig. 4. The extremely low electrical loss necessitates a custom measurement setup with high phase accuracy, subtracting the loss in the short and current leads from the input power. The results are striking (log-log plot, Fig. 5): the load loss increases with current close to a power of 3.5 rather than the familiar quadratic dependence of resistive loss. The load loss is hysteretic, proportional to frequency rather than independent of frequency like normal resistive loss. At 50 Hz the electric­ al loss per phase at rated current is 120 W, only 0.036 %. Because of the steep power law dependence, the loss drops by about a factor of 10 when the current is halved. Assuming a cryocooler with cooling pen­ alty of 13.5 W/W (watts input power per watt cooling power), the electrical loss translates to a load loss of 0.4 %, about half the 10 kW load loss typical of a 1 MVA transformer. Note that this comparison indicates the potential energy savings on load losses using the most efficient cryocoolers currently available. In practice our system used stored liquid nitrogen and a less efficient crycooler. Prediction of load loss is a non-trivial computation compared to the loss in c­opper conductors, but calculations [6] by our collaborator Enric Pardo accurately reproduce our measurements. The blue line in Fig. 5 shows the predicted loss in w w w . t ra n sfo r m e r s - m a g a z i n e . co m

Compared to conventional oil-immersed transformers, HTS transformers can be smaller, lighter, more efficient, and have overload capability without reduction in lifetime the superconductor, while the black line includes the contribution of eddy current loss in the copper terminals of the low voltage winding. The great significance of this agreement of modelling and mea-

surement is that we can now confidently predict the load loss in larger transform­ ers, where the benefits of HTS relative to copper begin to outweigh the higher purchase price.

Figure 4. Setup for load loss measurement, windings in cryostat without core fitted 91

EVENTS TECHNOLOGY

The extremely low electrical loss necessi­ tates a custom measurement setup with high phase accuracy, subtracting the loss in the short and current leads from the input power

Figure 5. Load loss measurements and modelling for one phase of the 1 MVA HTS transformer as a function of current in the low voltage winding

The results of factory electrical testing are shown in Table 2. In testing, the transform­ er performed as designed over a period of months cooled to liquid nitrogen temper­ ature, several weeks of this time drawing current continuously. During insulation testing, a flashover occurred at over 20 kV on HV bushings on two of the cryo­ stats. The problem was traced to the filled epoxy used in adapting the bushings for cryo­genic use. Commercial resin bushings have been tested in cryostats up to 650 kV Basic Impulse Insulation Level (BIL), so this is not a fundamental problem.

will then narrow and may reverse because of the lower core losses of the lighter core possible with HTS. Short circuit fault current performance of the transformer was not tested, but modelling [7] tells us it would be a highly effective fault current limiter, with the impedance jumping rapidly from the normal reactive impedance of 5 % to about 13 % at the onset of a fault. It will then increase sharply as the resistivity of the copper shunt layer in­creases roughly seven-fold from 77 K to room temperature, with fault impedance ultimately approaching 100 %. However the fault current hold time is limited with the standard 0.1 mm thick REBCO conductor by the time taken to heat to room temperature only about 0.15 sec. The recovery time, isolated from the load, would be some tens of seconds. If the fault is not isolated within 0.15 s the HTS wire would suffer irrevers­ ible thermal damage. We estimate the mean tensile stress in the HV winding at peak fault current to be 100 MPa, well below the maximum recom-

The contribution of cryostat losses to the no-load loss was not measured directly but, using a 13.5 W/W cooling penalty as above, we estimate it to be about 0.65 % of rated load, 3/4 of it due to the current leads. As expected, this means the no-load losses of this HTS transformer are significantly high­ er than the conventional equivalent at 1 MVA rating. In transformers with higher ratings, with LV volts of 11 kV or higher, the contribution of the cryostat and current lead losses will become progressively less sig­nificant. The disparity in the no-load losses of HTS and conventional transformers

Prediction of load loss in HTS is much more complex than in copper conductors, but our modelling is in a very good agreement with measurement, enabling us to confidently predict the load loss in l­arger transformers

Table 2. Results of factory electrical testing

Item

Design value

Tested value



Transformer ratio

45.9

45.91

Connection

Dyn11



No-load current

0.25 %

Not tested



No-load loss (core losses only)

1.2 kW

Not tested



Short circuit impedance

5 % min

5.95 %

0.034 % 

0.036 %

Electrical load loss at rated current

Dyn11



Withstand voltage test

28 kV/60 sec/50 Hz

Partial success



Lightning impulse test

75 kV/1.5/50 µsec

Partial success

Partial success = in testing of individual phases phase A complied with all tests. B & C failed at epoxy insulated extensions. 92

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

mended stress for the wire of 700 MPa. The LV winding is not designed to be self-supporting under fault current stresses, and is supported by a 10 mm thick GRE former, with the cable restrained within a 2 mm deep helical recess machined in the former.

It is unlikely that HTS transformers with rat­ ings of a few MVA or less will ever be commercially competitive with conventional transformers

4. Economics It is unlikely that HTS transformers with ratings of a few MVA or less will ever be commercially competitive with conven­ tional transformers. But how do the relative costs stack up at higher ratings? In a recent study, making use of the validated loss modelling method [5], we estimated the Total Cost of Ownership (TCO) of a 40 MVA 110/11 kV HTS transformer design compared to a conventional transformer [8]. The purchase price of the HTS transformer is estimated to be around 65 % high­er than the conventional design. M­ajor components of the cost are the superconducting wire and the cryosystem, each roughly a third of the total. A number of considerations influenced the choice of a 40 MVA rating: it represents a significant step up from previous HTS transformers into the range where commercial compet­ itiveness might be expected, not too l­arge for modelling validity or a design and build project, and a sizeable market sector. We make the assumption that 110 kV rated high voltage windings are achievable with HTS wire. Potential problems with partial discharge at the edges of the thin HTS tape can be circumvented by laminating with metal stabiliser with radi­used edges. Wind­ ings of 138 kV insulation class have been successfully tested [9]. 40 MVA is not an upper limit for HTS transformers. The present limit for conductor critical current is around 90 A/mm at 77 K, 180 A/mm at 65 K. Using wide HTS conductor generally results in higher losses. Fully transposed high current wind­ ings can be realised with Roebel cable, with the limit perhaps around 300 MVA for a 220/22 kV transformer, depending on the strand count in the cable, before resorting to connecting strands in parallel without transposition. The majority of demonstration HTS transformers have in fact used parallel conductors with varying degrees of transposition to achieve high current.

Figure 6. Comparison of the total cost of ownership of HTS and optimised copper 40 MVA transformers as a function of no-load loss evaluation factor A

would be 0.09 %, compared with typical values of around 0.3 % for conventional transformers of this rating. How much is such low loss worth? This depends on the value ascribed to losses - the loss evalu­ ation factor [10], dollars per kW of lifetime losses. These numbers can vary substan­tially in different markets [11] with no-load loss evaluation factors in some European markets twice those in the United States, for example. The loss evaluation factor for load loss, labelled B, is typically 30 % of the no-load loss factor A. Fig. 6 compares TCO as function of no-load loss evalu­ation factor for a 40 MVA 110/11 kV transform­ er design. The copper designs have been optimised for minimum TCO as the loss evaluation factors vary. Fire protection costs estimated at 15 % of purchase price have been included in the copper transformer purchase and installation costs. Apart from cryocooler maintenance costs, maintenance costs have been assumed the same for HTS and conventional transform­

ers and omitted. We will need to accu­ mulate more experience with closed-cycle transformer cooling systems before we can quantify any cost advantage to HTS from eliminating oil maintenance costs. For transformers operating at 100 % load factor (solid lines), e.g. base-load gener­ ator step-up transformers, the savings in lifetime cost of losses compared to a conventional transformer are enough to make HTS competitive in markets with loss evaluation factors greater than about 7,000  US$/kW despite the higher initial purchase price. In the case of transformers operating at lower load factor, with the load loss evaluation factor assumed to be 30 % of the noload loss evaluation factor (dashed lines), the HTS transformer will have higher cost of ownership even at very high loss evaluation factors.

The loss modelling shows that at 40 MVA the load losses (including cooling penalty)

The loss modelling shows that at 40 MVA the load losses (including cooling penalty) would be 0.09 % compared with typical values of around 0.3 % for conventional transformers of this rating

w w w . t ra n sfo r m e r s - m a g a z i n e . co m

93

4.1 Reduced cost of losses

EVENTS TECHNOLOGY

The HTS design is almost 1/3 the weight of a conventional transformer, which can be decisive in some applications, such as transformers in confined space, or mobile transformers 4.2 Eliminating negatives, accentuating positives

To be competitive in a wider market the purchase price of HTS transformers will have to come down, and the HTS transformer will need to derive added value from its other characteristics: smaller size and weight, low fire and environmental risk, and, perhaps, fault current limiting. In the longer term, the purchase price of an HTS transformer will certainly fall. For this study we assumed an HTS conductor price of 50 US$/kAm, the price for a length of wire for which the product of critical current (measured at 77 K) and length is equal to 1 kAm. This is a near term price projection, but the long-term price may be as low as 10 US$/kAm. At that point HTS wire will be cheaper than copper. Cryocoolers can also be expected to fall in price as production volumes rise. The comparison in Fig. 6 already in­cludes fire protection costs for the convention­ al transformer, assumed to be 15  % of purchase price. In some situations merely mitigating the fire risk of oil-immersed transformers with fire protection systems

is unacceptable. HTS transformers with their liquid nitrogen dielectric could be a cost-competitive alternative to SF6 gasinsulated transformers in this niche. The reduction in weight made possible with HTS wire is illustrated by the comparison in Table 3. Two conventional transformer designs are represented, optimised for different loss evaluation factors. The HTS design is not optimised against loss evaluation factor but is driven by the need to keep total losses within the capacity of a single highcapacity cryocooler to contain capital cost. The HTS design is almost 1/3 the weight of a conventional transformer, less than 1/4 that of a “high efficiency” transformer design optimised for higher loss evaluation factor. In some situations this weight reduction will be decisive. Examples are transformers in confined space, or mobile transformers, where the ability to fit a transformer with a larger rating in a given footprint may be a crucial constraint. Transport costs from factory to site can be a significant fraction of the purchase and installation costs, as much as 30 %. The cost scales rapidly with weight, adding significantly to the

OLTCs are one significant aspect of conven­ tional transformer technology requiring further development for HTS service

ownership cost of large conventional transformers. The value of reduced size and weight has not been included in the comparison of Fig. 6. HTS transformers with inherent Fault Current Limiter (FCL) capability could deliver much of the value of standalon­e superconducting FCL in particular network situations [12], for example allowing new generation to be added without the need for circuit breaker upgrades. Resistive fault current limiting capability is comparatively easy to incorporate in an HTS winding. The superconductor will enter a high resistance state as its critical current is exceeded and the fault current will then flow in the met­al stabiliser layer of the wire. If the metal layer has sufficient resistive impedance, it can augment the winding’s reactive impedance and provide additional fault current limiting. On the other hand, the winding resistance must be low enough so that the winding will cool down and become superconducting again when the fault is isolated. The resistance and thermal mass of the HTS windings can be adjusted by modifying the stabiliser layer. However, it is challenging to combine fault current limiting with a fault withstand time much beyond 10 cycles and to have the winding recover from a fault current under load. The transform­ er protection system plays a very important role here. If faults can be isolated in a fraction of a second rather than one or two seconds, the design of conductor and windings for low impedance current limiting HTS transformers becomes more achievable. On-Load Tap Changers (OLTC) are one significant aspect of conventional transform­ er technology requiring further development for HTS service. If OLTC can operate

Table 3. Weight comparison of HTS and conventional 40 MVA transformer designs. The conventional designs are optimised for the given loss evaluation factors A and B

Comparison of optimised conventional and HTS transformer designs

 



A

B

Current density

Peak flux density

Total mass*

 



US$/kW

US$/kW



Tesla

tonnes



Standard

4000

1200

3 A/mm2 1.68



High efficiency

8500

8500

1 A/mm2 1.53 110



HTS

NA

NA

60 A/mm

1.7

72

25

* Includes oil and radiators for conventional, liquid nitrogen and cryostat for HTS 94

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

immersed in liquid nitrogen, the heat load of multiple leads connecting windings to an external oil-immersed OLTC could be avoided. In principle, tap changers with vacuum interrupters should be adaptable to operation in liquid nitrogen but this remains to be demon­strated.

5. Conclusions HTS transformers can be more efficient and lighter than the oil-immersed copper equivalent. Without mineral oil, fire and environmental hazards are eliminated. Resistive fault current limiting can be incorporated if the transformer protection scheme allows the fault isolation time to be short enough. Our 1 MVA transformer project demon­ strates that HTS Roebel cable can be used in high current LV windings and that load losses in HTS transformers can be confidently predicted. HTS transformers can be cost-competitive with conventional transformers: at larger ratings and high load factors on the basis of reduced load losses; in mo­bile transformer applications because more power can be packed in a given weight and space footprint. In the longer run, as the cost of wire and cooling falls with a maturing HTS technology and market, we can expect HTS transformers to become serious competition to the incumbent oil-immersed copper transformer technology in a progressively wider range of applications. For a long time HTS technology had a champ­ ion within the transformer industry in the shape of Waukesha Electric Systems, who had ambitious and clear-sighted goals [13]. With their withdrawal from HTS R&D just a few years ago, there is a pressing need for an industry-led effort to progress this technology to commercial reality.

Bibliography [6] Enric Pardo, Mike Staines, Zhenan Jiang and Neil Glasson, AC loss modelling and measure­ ment of superconducting transformers with coated-conductor Roebel-cable in low-voltage winding, Supercond. Sci. Technol., Volume 28, 114008, 2015 [7] Michael Staines et al, The development of a w w w . t ra n sfo r m e r s - m a g a z i n e . co m

Roebel cable based 1 MVA HTS transformer, Supercond. Sci. Technol., Volume 25, 014002, 2012 [8] Mike Staines, Enric Pardo, Liam Jolliffe, Mohinder Pannu, and Neil Glasson, Prospects for HTS transformers in the grid: AC loss and economics, European Conference for Applied Superconductivity, Poster paper 1A-LS-P-02.06, 2015, www.victoria.ac.nz/robinson/research/ publications/Staines_EUCAS2015.pdf [9] Bill Schwenterly and Ed Pleva, HTS transform­ er development, Presenta­tion for DOE peer review, 2010, www.htspeerreview.com/pdfs/ presentations/day%202/applications/6_AP_ HTS_Transformer_Technology.pdf [10] Dudley L. Galloway and Dan Mulkey, Chapter 2.2 Distribution Transformers, in Electric power transformer engineering, edited by James H. Harlow, ISBN 0-8493-1704-5, CRC Press, 2004, Section 2.2.14.3

[11] T. Fogelberg et al, Energy efficient transformers and reactors - Some incentive models and case studies to show the long term profitability of such designs, CIGRE Session paper 2012, A2-204 [12] Leonard Kovalsky et al, Applications of Superconducting Fault Current Limiters in Electric Power Transmission Systems, IEEE Trans. Appl. Supercond. Vol 15, pp 2130-2133, 2005 [13] E F Pleva, V Mehrotra and SW Schwenterly, Conductor requirements for high-temperature superconducting utility power transformers, Supercond. Sci. Technol. Vol 23, 014025, 2010

Acknowledgement Funding for the 1 MVA Transformer project was provided by the New Zealand Ministry of Science and Innovation under HTS Accelerated Development contract C08X0818.

Authors Mike Staines is a Senior Scientist at Robinson Research Institute, Victoria University of Wellington, with a PhD in Physics obtained in 1979. Mike has been engaged in HTS research since 1987, working in superconducting materials synthesis, wire development, and mea­ s­urement of electrical properties, particularly AC loss, of HTS wire and windings. He was Science Leader for the 1 MVA HTS transform­ er development. His current work focuses on extending the fault current performance of HTS windings, reducing the cost and complexity of transformer cooling systems, and quantifying the value proposition for HTS transformers. Mohinder Pannu is Strategic Engineering & Projects Manager at Wilson Transformer Co Pty Ltd, developing new product applications for the Power industry. He holds a B.Tech (Hons) in Electrical Engineering from The Indian Institute of Technology and an MBA from Monash Mt Eliza Business School. He has background experience in Power Transformer Design, Quality and Test. He is a member of Cigre Australian Panels A2 and D1. Neil Glasson is a Senior Research Engineer at Callaghan I­nnovation, with a PhD in Mechanical Engineering obtained in 1993. Neil has been involved in this transformer project as the lead Engineer since its beginning in 2009. Engineering challenges faced in the project were dominated by the need to efficiently make things really cold - without breaking them – and keep them that way for a long time. Neil came to this role from 10 years as Engineering Man­ ager for a stainless steel fabricator, but had to quickly learn about advanced composite fabrication for this project as many of the components had to not only be compatible with cryogenic temperatures but also be non-conductive. Callaghan Innovation is the government agency charged with accelerating the commercialisation of innovation with New Zealand businesses. Nathan Allpress is a Mechanical Engineer at Callaghan I­nnovation, with a BE (Hons) obtained in 2009. Nathan joined the HTS transformer project after working on aspects of HTS Roebel cable manufacture and testing, making use of that experience in the design of the low voltage winding. Other related research projects he has worked on include the development of a small-scale nitrogen liquefaction plant. 95

RISK ASSESSMENT EVENTS

Load growth coupled with aging transform­ers is a disaster wait­ing to happen

96

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Jon L. GIESECKE

Advanced transformer condition assessment Part I Transformer lifecycle and risk assessment 1. Introduction I write this article from pure experience, having performed transformer maintenance for many years at a major utility, and then being part of an Electric Power Research Institute (EPRI) team tasked with developing a Predictive Maintenance (PdM) process for transformers and substation components. History and experience have proven that there is no magic bullet for maintaining transformer health. Doing annual or periodic inspections is well worth the effort, but common sense thinking leads me to believe that installing full-time monitoring on critical tier 1 assets is probably the best way to avoid an unexpected failure. But not all transformers merit the same level of attention. Utilities and refineries have many transformers with varying complexity and purpose. I recommend rating each one and assigning them in one of the three following tiers. Tier 1 transformers will get the highest lev­el treatment; some will be outfitted with full-time Partial Discharge (PD) monitor­

ing and Dissolved Gas Analysis (DGA). Tier 2 and 3 transformers will rarely be chosen for full-time monitoring. The inspection process for all three tiers must be thoughtfully applied. As transformer experts (substation teams), our job is to maintain the highest level of operational capability for our transformers and sub­ stations. A coordinated program of online and portable monitoring must be used to make sure that we are doing our part. The criticality of each transformer in your care should be ranked and that ranking used to provide guidance to your PdM team on just what is the correct level of monitoring. The lack of a spare transformer and the lead time to have a new one built (typically 18 to 24 months), delivered on site, and installed is a consideration in the overall process. The technology advances: Infrared Thermo­ graphy, Ultrasonic Noise Analysis, Partial Discharge Detection, Dissolved Gas Analysis, and Vibration Analysis are all very high tech and necessary to determine the health of our transformer fleet.

Determining the health of a transformer is a process that can make the difference between a transformer’s long life and an early death w w w . t ra n sfo r m e r s - m a g a z i n e . co m

ABSTRACT Infrared Thermography, Ultrasonic Noise Analysis, Partial Discharge Detection, Dissolved Gas Analysis, Vi­ bration Analysis – all these techniques are great stand-alone diagnostic tools; however, when used properly, combining the data obtained through each technique, an incipient fault can be identified long before it degrades the insulation and creates a failure. This paper will provide guidance in setting up a complete Predictive Maintenance program to be able to provide owners of oil-filled power transform­ ers (4 kV and up), i.e. utilities, refineries, military, mining, etc., with a complete health report and condition assessment of critical oil-filled power transformers and ancillary substation components. The testing described in this paper is done on energized, fully loaded transformers. Author’s vast experience with doing Partial Discharge testing reveals that nearly 80 % of all oil-filled power transformers exhibit some PD. This low level PD activity is not detrimental to the health of the transformer. It is usually a burr or sharp corner that is producing the activity. I consider this just nuisance PD and most times it continues for the entire life of a transformer without a failure related to PD.

KEYWORDS Partial Discharge, Transformer Condition Assessment, Risk Analysis Tool 97

EVENTS RISK ASSESSMENT

In the past 20 years since switching from reactive to predictive transformer main­ tenance, the advancement of technology has exploded Each of the listed technologies is proven very effective; however, combining the information from each technology will provide solid answers to those who ask: How much life is left in my transformer? For many years I have dedicated my career path to the development and use of technology to determine the on-line condition assessment of power transformers and ancillary support equipment. Along with determining the remaining life is the issue of an action plan: repair, replace or continue to trend. In the past twenty-two years since switch­ ing from reactive to predictive trans-

former maintenance, the advancement of technology has exploded. However, the average utility is still doing transformer inspections as it did twenty-two years ago. Consider what information a transformer is willing to give up: it will tell you what is wrong with it if you are willing to listen.

This article will provide knowledge about the latest methods and guidance in setting up a quality program. The goal is to be able to give a complete health report and condition assessment of critical oil-filled power transformers while they remain in service. Remember, the processes de­ scribed in this paper are done on energized, fully loaded transformers. No clear­ ance or blocking is needed to accomplish these tasks. All tests are completely nonintrusive.

2. Analyzing data from history, coupled with field • A transformer makes noise in both the survey information sonic and the ultrasonic range; • A transformer gives off heat which must be removed during operation; • A transformer sends signals of impend­ing insulation failure while in operation.

Each transformer owner has inform­ation and data from each transformer under their care. This data is stored in file cabinets and computer programs and is read­y to go to work for you. Mining the data

Table 1. Risk analysis grading tool Nemx Nemx Xfmr2 Xfmr 2 Xfmr3 Xfmr3 Xfmr4 Xfmr4 Xfmr5 Xfmr5 Xfmr6 Xfmr6 Xfmr7 Test year 2016 1164 1164 Criteria Value Factor Value Factor Value Factor Value Factor Value Factor Value Factor Value Serial number 6536968 R270131A G859918P G859918G M153429 S1689-01

S1689

Leaks N 0 N 0 N 0 N 0 N 0 N 0 N Control wiring condition good Y 0 Y 0 Y 0 Y 0 Y 0 Y 0 Y Winding power factor 0.48 0 0.49 0 0.55 -5 0.45 0 0.71 -5 0.44 0 0.45 Oil power factor @ 25°C 0.04 0 0.032 0 0.079 0 0.073 0 0.043 0 0.054 0 0.021 DGA condition code 3 -8 1 0 1 0 1 0 1 0 1 0 2 Full time DGA monitoring Y 0 N -5 N -5 N -5 N -5 N -5 N Current gas generation - arcing Y -10 N 0 N 0 N 0 N 0 N 0 N Current gas generation - thermal N 0 N 0 N 0 N 0 N 0 N 0 N Oil acidity 0.02 0 0.02 0 0.02 0 0.02 0 0.02 0 0.01 0 0.01 Oil IFT 38.9 0 40.3 0 33.5 0 38 0 36.5 0 40.5 0 40.7 Oil dielectric (D877) 36 0 39 0 44 0 34 0 38 0 38 0 44 Water in oil (% Saturation) 3 0 65 -10 11.3 0 64.1 -10 5.4 0 8.4 0 5.9 PD burst interval in waveform 9 0 8 0 9 0 9 0 9 0 9 0 8 Arcing/sparking in waveform N 0 N 0 N 0 N 0 N 0 N 0 N Lightning arrester test at full voltage N -5 Y 0 Y 0 Y 0 Y 0 Y 0 Y Full time PD monitoring N -5 N -5 N -5 Y 0 Y 0 Y 0 Y Manufacture date

1961

2008

1970

2012

1985

2005

Age in years 55 -28.125 8 1.25 46 -22.5 4 3.75 31 -13.125 11 -0.625

2005 11

Winding temperature (diff. from 55) 26 9 29 9 15 9 17 9 24 9 25 9 26 Highest top oil temp past year 45 0 42 0 38 0 40 0 35 0 45 0 40 Past thermal problems in DGA N 0 N 0 N 0 N 0 N 0 N 0 N

98

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

that already exists, then combining it with current conditions allows us to provide a grade for each transformer. This aids in determining the risk analysis and apply the correct surveillance for each transformer. Once the data is entered into the Excel spreadsheet (Table 1) from your available data source, maintaining the spreadsheet is simple. Data gathered while doing inspections is entered and any changes to the DGA is also entered. The age is changed on all transformers by one click of the mouse. There is no limit to the number of transformers that can be watched simultaneously. Grades are presented numerically as well as a letter, and a secondary grade is also given to indicate the highest possible score achiev­ able when all deficiencies are corrected. The Excel spreadsheet contains formulas built into each cell that do the calculations on the risk of each condition and how it affects the health and life expect­ ancy of each transformer entered on the spreadsheet.

The crucial nature, age, long lead time, and the interconnection of the grid’s electrical system demand that the best maintenance approaches possible are applied to help ensure reliability I have just inspected a critical 500 kV transform­er that is sitting next to a failed transformer that is still smoldering. The operating transformer has partial dis­ charge and arcing confirmed by DGA and by a specialized tool for doing online partial discharge measurements. It also captures arcing from the component under test. Using hind-sight, these transformers should have been outfitted with on-line monitoring which would have seen the catastrophic fault prior to the failure. This is a very serious condition which could result in the loss of electric power to a major portion of a small city.

Examine what you are doing now!

The crucial nature, fragility, age, long lead

• Partial discharge monitoring and ana-

approaches possible are applied to help ensure reliability.

• Sound level measurements (precursor to looseness) • Grading method (transformer assessment and ranking tool) • Template building (tier assignment done here)

A typical inspection program includes the following: • • • •

Visual inspection Dissolved gas analysis Infrared outside control Offline electrical testing

Note: Most utilities are doing this inspection process, which has not changed in the past twenty years, or more.

An enhanced program could include these additional components:

3. Do you think that waiting time for major components, and the inlysis (portable and on-line) until a disaster strikes is the terconnection of the grid’s electrical sys- • Vibration analysis (determine core and coil assembly tightness) tem demand that the best maintenance time to react? The aging of the electrical infrastructure worldwide is a critical problem that each of you face. There is no way to get around that fact. As aging transformers continue to fail, a new level of awareness of the magnitude of the situation becomes very clear. Load growth coupled with aging transform­ ers is a disaster waiting to happen. Many transformers fail unnecessarily. Accurate condition assessment and proper care of these valuable assets is needed now more than ever. With the transform­ er fleet’s average age over 40 years and the new transformer fleet having a high­ er-than-expected failure rate, a proactive approach to PdM is needed. Large power transformers are not off-the-shelf items and must be ordered one to two years in advance. The repair and replace­ ment schedule is critical in most cases.

4. Transformer life cycle management / risk management Determining the condition, health and risk assessment of a transformer is a process that can be the difference between a transformer’s long life and an early death. Certain random failures can occur any time and with little or no warning, but as a transformer ages, there will be meas­urable warning signs that somehow foretell the cause(s) of degradation or impending failure. The insurance industry states that insulation failure is the number one cause of transformer failure. So how do we determine the insulation quality while these transformers remain in service?

Certain random failures can occur any time, but as a transformer ages, there will be measurable warning signs that somehow fore­tell the cause(s) of degradation or impending failure w w w . t ra n sfo r m e r s - m a g a z i n e . co m

Note: Adding these to your existing program could greatly reduce the unexpected failure rate.

Template building is a process where each transformer gets its own criterion sheet. A team of substation engineers gathers information on each transformer and decides what type of diagnostic data should be collected based on the critical­ ity of each transformer. Tier assignment is done at this time. Tier one transformers are considered critical and should get the most attention. Tier two transformers are important but have redundancy and s­pares. Tier three transformers are least important and could run to failure with­ out major upset of the grid. Combining data from several techniques will provide information

Very rarely will a failure occur without first revealing some small change that is detectable utilizing one or more tech99

EVENTS RISK ASSESSMENT

If the source of the fault is located in an area where its sound reaches the tank wall, acous­ tic sensors could triangulate the exact spot of the fault niques. Having stated this, information provided in this paper will direct and assist the reader starting an inspection process or expanding your existing PdM program. This paper is designed to show the bene­ fits of doing a complete Transformer Condition Assessment (TCA). Combining the data from various techniques will provide insight and understanding of often subtle, pre-failure signs. In addition, a complete TCA will provide an as-accurate-as-possible gauge of the health of the transformer’s subsystems, including: pumps/cooling system, Load Tap Changer (LTC), De-energized Tap Changer (DETC) and lightning/surge arresters. Partial Discharge (PD) is unwanted electrical activity. PD is similar to cor­ ona and occurs at high voltage sine wave peaks. Most low-level PD activity is load-dependent. As the load increases, the voltage decreases. When the voltage de­creases, the PD will decrease or disappear completely, and then return when the voltage returns to full value. My experience with doing PD testing reveals that nearly 80 % of all oil-filled power transformers exhibit some PD. This low level PD activity is not detrimental to the health of the transformer. It is usually a burr or sharp corner that is producing the activity. I consider this just nuisance PD and most times it continues for the entire life of a transformer without a failure related to PD. How­ ever, when true insulation breakdown occurs, both indicated and worsened by the PD, and reaches a point that it threat­ens the life of a transformer, a decision must be made to remove the transformer from service. Because PD is present in so many transformers, knowing the present condition of each transformer under your care is critical. Without systematic TCA, there is insufficient information available to confidently decide when to take appropriate 100

action. In a quest to determine unwanted activity, data can be gathered at a moment in time, like taking a snapshot, or continuously over 24 hours or more, like making a movie. Movies generally tell a more complete story. By adding the enhancing technologies to your TCA process, major failures will be averted. Major money will be saved, and a major safety feature will be built into every visit to the high-voltage transform­ er yard. Detecting acoustic and electrical problems on energized equipment

The following PD test described is used to determine the severity of an electrical fault using the burst interval of the PD pattern captured by the High Fre­quency Current Transducer (HFCT). Then, if the source of the fault is located in an

area where its sound reaches the tank wall, acoustic sensors could triangulate the exact spot of the fault. Fault sound reaches the tank wall about 90 percent of time. The remaining 10 percent of faults are too deep within the core and coil assembly, and the sound cannot be detected externally. In these cases, at least the severity of the fault and the fact that the transformer will require some work deep within the windings is determined. Acoustic tests have been used for many years to detect and locate partial dis­ charges in power transformers, but the addition of the HFCT installed on the case ground of the subject transformer makes the process complete. It is more difficult to determine if a problem in an oil-filled transformer is related to mechanical or electrical malfunction utilizing acoustic sensors alone. Partial discharge testing using both acoustic sensors and an HFCT makes the determination easy and increases the protection factor for these utility industry assets. Figure 1 shows acoustic and electrical PD activity obtained simultaneously. The

Asset managers need to know what to do and when to do it to be able to extend transform­ er life or avoid impending failure

Figure 1. Data showing classic partial discharge: the top screen shows Acoustic Emis­ sion (AE); the bottom screen shows Electromagnetic Interference (EMI) TRANSFORMERS MAGAZINE | Volume 3, Issue 3

top portion of the screen shows re­corded acoustic sensor data, and the bottom shows data from the HFCT. In the example presented by this figure, the spac­ ing of both the Acoustic Emission (AE) and HFCT sensors is 16 milliseconds, which is one full sinewave. The test equipment used for this data collection is the TP500A from PowerPD. The TP500 software has built-in bandpass filters which enable the user to filter out noise and pinpoint the PD, arcing or sparking. Source location of the fault is done using the acoustic sensors. Severity criteria

Figure 2. The wave data indicating PD with a burst interval of 2.3 ms

Asset managers need to know what to do and when to do it to be able to extend transformer life or avoid impending fail­ ure. The ability to trend the deterioration process aids the asset manager in de­ ciding when to take action. Figure 2 shows acoustic and PD data measured for amplitude and duration. This is easily trended by comparing subsequent test results under similar conditions. The top window in this fig­ ure shows the AE bursts with sensor #2 (red) being closest to the source. The bottom window shows the PD burst captured from the case ground lead using the HFCT.

Figure 3. Pulse Phase Graph showing no PD activity

The signature captured by the HFCT, in the bottom portion, indicates a severe case of PD. The spacing between the end of one burst and the beginning of the next burst, called burst interval, is getting dangerously close to 2 milliseconds, clearly indicating a failure is imminent. Burst interval is critical information in determining the severity of PD. Going deeper into the burst interval (60 Hz/milliseconds)

A review of test results for acceptance is performed using the following criteria based on burst interval:

Figure 4. Pulse Phase Graph showing small PD activity w w w . t ra n sfo r m e r s - m a g a z i n e . co m

• 8-7 milliseconds: satisfactory (many times 7 to 8 millisecond burst is found and is a non-damaging PD) • 6-5 milliseconds: engineering review and evaluation needed • 5-4 milliseconds: consider removal from service in near future • 3-2 milliseconds: unsatisfactory, make plans to remove and repair now; 101

EVENTS RISK ASSESSMENT

There are times when the DGA is indicating PD, but it is not pos­sible to get any PD to be active until 110 % voltage is reached. Once the PD begins, it will drop off when we back down to the rated voltage e­xperience shows that 2 milliseconds is the critical point for catastrophic failure • <2 milliseconds: removal from service, danger of catastrophic failure Testing at repair facilities allows you to select the voltage you wish to use, anywhere from 50 % to 150 %. There are times when the DGA is indicating PD but it is not possible to get any PD to be active until 110 % voltage is reached. Then the PD will begin, but it will drop off when we back down to 100 %. When the PD begins to deteriorate the insulation, the activity will increase at a lower voltage. If there is a small insignificant nuisance PD, it will have a burst interval of about 8 milliseconds. As the insula­ tion deteriorates the PD begins at a l­ower voltage and stops at a lower voltage. PD is a voltage related event. The Puls­e Phase Graphs, shown in Figures 3 to 6, indicate varying severity of PD based on burst interval and not amplitude. As the PD occurs closer to the zero voltage crossing, the risk of failure increases. My experience has been that 2 milliseconds is the critical cut-off point prior to a cata­ strophic failure. The charts in Figures 3 to 6 are hand-drawn to show examples of burst interval. The wave data in Figure 2 indicates a PD with a burst interval of 2.3 milliseconds (ms). It was recommended to remove this unit from service.

Part II of this paper will discuss lightning/surge arrester testing and vibration and sound level analysis, presenting the case studies and final conclusions. 102

Figure 5. Pulse Phase Graph showing increasing PD activity requiring caution

Figure 6. Pulse Phase Graph showing dangerous PD activity

Author Jon L. Giesecke is an expert in combining technologies used in in-service inspection of high voltage oil-filled power transformers and substation diagnostics, with over 20 years of experience in transformer/substation predictive maintenance and over 25 years in substation electrical maintenance. Prior to forming JLG Associates LLC in 2006, he was employed by EPRI Solutions as a senior project manager in the Substation Predictive Maintenance business area. Mr. Giesecke is also an ITC level III thermographer and has instructed at the FLIR ITC training center. He served on the board of directors of the International Society of Professional Thermographers, Inc. (ISPoT), and chaired the ethics committee. He was also responsible for PdM template development for fossil and nuclear applications. His career in electrical maintenance spans over 30 years with Exelon, formerly Philadelphia Electric Company. During his career with PECO, he held many positions, from helper to foreman, including 4 years of Doble testing, 2 years in outage planning, 2 years as training coordinator for the nuclear group, and 2 years as turbine/generator foreman. TRANSFORMERS MAGAZINE | Volume 3, Issue 3

MOBIL GC

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With this in mind, we organise our TLM Conference. To achieve a stable integrated electricity network, generation, transmission and distribution companies must employ best practice performance methodologies to achieve optimal resilience and a future-proof grid. Interested in learning more and share your knowledge at Transformer Life Management Conference?

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EVENTS DIAGNOSIS

ABSTRACT The dynamic resistance measurement was developed as a supplementary measurement in order to analyse the switching process of the on-load tap changer. The article considers the importance of on-load tap changers and their main testing methods with the focus on dynamic resistance meas­ urement.

KEYWORDS power transformer, on-load tap changer, OLTC, dynamic resistance measurement, DRM 104

Dynamic analysis and testing of on-load tap changer Dynamic resistance measurement TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Cornelius PLATH, Markus PÜTTER… Introduction Power transformers represent the most expensive link between generation and utilization of electric power. One very important component of a power transform­ er is the on-load tap changer (OLTC). As its name suggests, an OLTC permits tap changing, and hence regulating voltage without interrupting the load current. This can be accomplished in various ways, resulting in considerably diversified tap changer designs. The two most common ones are the so-called inductive and resist­ ive type tap changers. Studies, as shown in Figure 1, show that about 30 % of reported failures of sub­ station power transformers are related to the aging effects on OLTCs. Due to this high failure rate, it is very important to monitor the condition of the power transformer’s OLTC closely. Unlike other more static components in a transformer, the OLTC consists of numerous moving parts. Manu­ facturers typically recommend a main­ tenance cycle that mostly depends on the total number of switching operations.

1. Types of OLTCs To analyse and assess the dynamic resist­ ance measurement (DRM) in a proper manner, it is important to know the type and the construction of the OLTC. Ther­e are two common OLTC technologies in the market. The inductive ones, which are typically used in the North America on the low-voltage side, and the resistive OLTCs, which are often used in the rest of the world on the high-voltage side. This article focuses on resistive type tap changers. In general, there are two different types of resistive tap changers: diverter switch and selector switch type, as shown in Figures 2 and 3.

The dynamic resistance measurement was developed in order to analyse the dynamic switching process of on-load tap changers diverter switch at the bottom to switch the load current with its own oil volume. With this OLTC type, the tap selector is switched before the diverter switch, and the type is mostly used in higher power ratings. The selector switch type combines the function of the diverter switch and the tap selector, within its own oil volume, separated from the oil of the main transformer tank.

2. Common methods for OLTC testing Power transformer OLTCs need close monitoring of their condition due to their high failure rate. As a basis for the ana­ lysis, the following diagnostic methods can be used: • Static winding resistance measurement of the individual taps (offline)

The static winding resistance measurement is a very important diagnostic meas­ urement tool and the most commonly used testing method. A conventional s­ tatic resistance measurement can be used to check the winding as well as all of the internal connections, such as the connection from the bushings and the tap changer mobile contacts to the wind­ing, the contacts of the tap selector and the main contacts of the diverter switch. An assessment can be made by comparing the results with the factory report or by

calculating the deviation from the aver­ age of the three phases. • Vibro-acoustic measurements by using acceleration sensors (offline/online)

The vibro-acoustic method is used to detect acoustical signals caused by mech­ anical movement. The recorded profiles, which range up to 10 seconds and between 10 Hz – 100 kHz in time and frequency domain are compared with exist­ ing reference profiles to identify certain failure modes [3]. • Position and torque measurement on the drive axis (offline/online)

The OLTC’s drive mechanism, compris­ ing of a motor, drive shaft and gear, oper­ ates the selector switch while charging a spring to actuate the diverter or selector switch, respectively. The position and torque measurement uses motor supply parameters (current and voltage) to detect mechanical problems and aging of the drive mechanism. The results can be compared with a reference profile or between the taps. • Dissolved Gas Analysis (DGA) of the oil in the tap changer compartment (offline/online)

The DGA in the OLTC compartment has become more common. During the switching process of an OLTC, discharge and heating occurs which generally leads to a higher concentration of gasses in the

The diverter switch types have two parts: a tap selector at the top to select the next tap within the main transformer tank, and a

To analyse and assess the DRM measurement in a proper manner, it is important to know the type and the con­ struction of the OLTC w w w . t ra n sfo r m e r s - m a g a z i n e . co m

Figure 1. Failure location of substation transformers based on 536 failures [1] 105

DIAGNOSIS

Figure 2. Diverter switch with two resistance contacts [2]

tap changer compartment compared to the main tank during normal operation. Thus the interpretation of gas levels sig­ nificantly varies from the interpretation of gas levels obtained from the main tank of the power transformer [4]. Each measurement method is important to analyse the condition of OLTCs.

3. Dynamic Resistance Measurement (DRM) Typical switching times of the diverter or selector switch between 40 and 60 ms make it difficult to detect any effects dur­ ing the switching process using a conventional static winding resistance meas­ urement, which might take a few minutes. Therefore, the principal of the DRM was developed as a supplementary diagnostic method for this specific use. Using the same setup (Figure 4a), the dynamic resistance measurement measures the fast switching process of the diverter

Figure 3. Selector switch with two resistance contacts [2]

The DGA in the OLTC compartment has become more common switch. DRM can detect arcing contacts, switching times of the diverter switch, switching interruptions, due to broken commutating resistors or broken leads for example, and the complete wear of contacts. Therefore, it provides a deeper insight into the OLTC’s dynamic condition. By analysing the recordings, it is possible to draw a number of conclusions related to the condition of the OLTC. There are three different ways to display the dynam­ ic behaviour of the diverter switch: (1) Current curve (2) Voltage curve (3) Resistance curve

Current curve

The current curve, as seen in Figure 4b, is the most common way to interpret DRM measurements, as it is widely used for static resistance measurement and gives the possibility to detect current interruptions. By applying a short circuit to the opposite side of the transformer, the current signal becomes more sensitive, as the current drop (ripple) increases as shown in Fig­ ures 7 and 8. This is a result of a lower time constant due to the shorted main induct­ ance. A direct comparison of the current signal is difficult when measuring with different test equipment, as the ripple is dependent on the dynamic properties of the current source. But the principle and the different stages of the switching process are always visible, regardless of the source parameters. Voltage curve

In further contemplation we will refer only to the current curve.

Alternative to the current signal, the dy­ namic behaviour can also be assessed

Application/ purpose

Problems

Check the windings as well as the internal connections

Contacts alignment, contact wear

Table 1. Common methods for OLTC testing [5]

Measurement method

Static winding resistance

Vibro-acoustic Detect acoustical signals caused by mechanical movement

Linkage/gears, Timing/Sequence, contacts alignment, arcing, overheating/coking, contact wear, transition

Position and torque

Detect mechanical problems and aging of the drive mechanism

Linkage/gears, control/relays, motor, brake, lubrication, contacts alignment

Dissolved gas analysis

Detect higher concentration of gasses in the tap changer compartment

Arcing, overheating/coking

Dynamic resistance

Measure the fast switching process of the diverter switch

Timing/sequence, contact wear, transition

106

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Figure 4a. Typical measurement setup of DRM – current curve

using the voltage or resistance curve. By injecting a DC current, as shown in Fig­ ure 5, the recorded voltage signal seen in Figure 6A can be obtained. When using the voltage curve, however, it is crucial to make sure that the voltage signal does not get cut off due to a voltage limiter of the source, which would make it difficult to analyse the signal. In addition to the cut-off voltage, transients as shown in the e­xample of Figure 6A between stage 1 and 2 would not be seen as clearly if the voltage limit was reached. Analog to the current curve, a direct comparison of the meas­ ured curves is not possible when meas­ uring with different test instruments. Resistance curve

The resistance curve, as seen in Figure 6B cannot be measured directly, but is a calculation derived from the measured voltage and current based on the setup shown in Figure 5. A short circuit on the opposite transformer terminals can be applied to

Figure 4b. Typical dynamic behaviour of the diverter switch in operation – current curve

decrease the time constant of the system. In addition, a high stray inductance may cause a significant inductive voltage, which cannot be separated from the resistive volt­ age part using the setup shown in Figure 5.

To compensate for this effect, a method to determine the inductive part of the voltage by simultaneously measuring the voltage on the opposite winding was introduced several years ago [6].

The current curve is the most common way to i­nterpret DRM measurements, as it is wide­ly used for static resistance measurement and gives the possibility to detect current interruptions

Figure 5. Typical measurement setup of DRM – voltage and resistance curve

Figure 6. Typical dynamic behaviour of the diverter switch in operation – voltage and resistance curve

w w w . t ra n sfo r m e r s - m a g a z i n e . co m

107

DIAGNOSIS

Figure 7. Difference in the DRM when switching up and down1 1

Figure 8. Difference in the DRM when switching the diverter switch in alternating directions1

Measured on MR Type DIII-200-14 27 3 GF, 1966

Test currents in the range of 3-5 A were, in most cases, sufficient to achieve a stable measurement of the switching process The resistive curve has a big advantage of being independent from the current source used. Another advantage is that the v­alues of the commutating resistors can be determined directly. As the in­ duced voltage on the secondary side could be very high, it requires special protection mechanisms for the testing device.

vary during the switching process. In addition, contact resistance, contact movement, interruptions, winding inductance, arcing and bouncing of the contacts may influence the amplitude. • Timing:

As the current curve is currently the most commonly used way to perform DRM measurements, the following sections will focus on this method in more detail.

Differences in timing may indicate mech­ anical problems, excessive wear of contacts and/or contact bouncing. A certain difference may be acceptable and will greatly depend on the design and model of the OLTC.

4. Analysis of measurement results

5. Variation in the dynamic resistance results

Based on this non-invasive testing m­ethod, failures can be detected without opening the OLTC compartment. The type and the construction of the OLTC must be known to be able to analyse and assess the DRM measurement in a proper manner. A reference “fingerprint” measurement, which is taken after commissioning or when the diverter switch is known to be in a good condition, allows efficient analysis.

5.1 Choosing the correct test current

In general, two types of information can be interpreted when looking at the current profile: • Amplitude:

Transition resistors cause the current to 108

When measuring the static resistance, lower test currents in the range of sev­ eral amperes are preferred, especially for HV windings [7]. Although testing of low impedance LV windings may require test currents in the range of 10-20 A, it is recommended that currents should not exceed 15 % of the rated current of the winding. Larger currents may heat up the

windings. As the resistance measurement is temperature-dependent, this could lead to inaccuracies in the measured resistance [8]. In general, these considerations also apply to DRM measurements including the following: Test currents below 3 A or 1 A have shown to be more sensitive to contact bouncing, which can lead to false interpretation of the results. A common effect which can be observed is that a residual oil coating on the contacts causes the current to interrupt several times during the test. These oil residues are usually not considered problematic when the OLTC operates under normal load conditions. In turn, test currents in this range may be able to indicate long-term aging effects such as coking at an earlier stage, but t­hese advantages still have to be investigated further by conducting additional case studies. Higher test currents in the range of 3-5 A were, in most cases, sufficient to achieve a stable measurement of the switching process. In these cases, minor discontinuities, for example due to oil coating on the contacts, did not affect the results. Field tests did not reveal any differences when further increasing the current to 10 A or 15 A.

DRM is a non-invasive testing method whereby failures can be detected without opening the OLTC compartment TRANSFORMERS MAGAZINE | Volume 3, Issue 3

DRM has proved to be beneficial for analysing the switching process and mobile contacts of OLTCs on power transformers 5.2 Secondary short circuit

Shorting the secondary side of the transformer can have two positive effects. First, if the current is interrupted during switch­ ing, the energy stored in the magnetic core may not be released, and the fast change in the current will not generate such a high voltage on the opposite winding. The other positive effect is that the current drop (ripple) while switching was in most cases observed to be twice as high, because the main inductance was short­ ed. This makes the DRM a more sensi­tive m­ethod, but also has an impact on the curves, making them more significant. 5.3 Switching process from tap to tap

When analysing and comparing different taps, it needs to be considered whether the curves differ in case of the OLTC switch­ing up or down. This is important because in the former case some windings are added to the circuit, while in the latter, case wind­ ings are subtracted based on the transformer tap winding and OLTC winding, so the wiring diagram could be different for different transformers. If windings are added, the additional induct­ance needs to be loaded with energy, and if they are subtracted, the loaded energy in the induct­ ance is released. This effect is much more likely if the secondary side is not shorted, as seen in Figure 7. The measured curves also differ when switching from an odd to an even tap pos­ ition, as the diverter switch is rotating in alternating directions (Figure 8). This can usually be seen as different switching times of the individual stages. In addition, bouncing of contacts can sometimes only be seen in one direction. An example of software which allows analysis and comparison of static and dy­ namic resistance measurements is Primary Test Manager (PTM). PTM shows the switching process of the individual taps in a single diagram, so that they can be compared amongst each other easily. As the current signatures of many OLTC designs may vary by their phase and switching direction, the PTM software offers unique filtering options to compare up and down w w w . t ra n sfo r m e r s - m a g a z i n e . co m

operations for even and odd positions and all three phases. This enables the user to analyse measurement results for a comprehensive failure diagnosis.

Conclusion A conventional static resistance measure­ ment can be used to test the winding as well as all of the fixed internal connections. In some cases, however, it is not possible to detect defects using the stand­ ard winding resistance measurement [9]. Therefore, the DRM as a supplementary measurement has proved to be beneficial for analysing the switching process and mobile contacts of OLTCs on power transformers. By using the same test setup as for static resistance, the DRM function enables insight into the fast switching process of the diverter switch to detect mechanical wear-and-tear of the contacts, leads and commutating resistors without additional wiring effort. As a result, the reliability of the OLTC assessment can be improved; maintenance costs can be reduced; and most importantly, unexpected and expensive outages can be avoided.

Bibliography [1] Cigré Working Group A2.3, 2015, TB 642 Transformer Reliability Survey [2] Rudolf Klaus, 50 Jahre VDE Bezirksverein Nordbayern, Die Entwicklung von Stufenschaltern für Hochspannungstransformatoren [3] K. Viereck, A. Saveliev, Acoustic Tap-Changer Monitoring using Wavelet Analyses, ISH 2015, Pilsen, 2015 [4] IEEE Guide for Dissolved Gas Analysis in Transformer Load Tap Changers, IEEE C57.139-2010 [5] Jur Erbrink, Edward Gulski, Johan Smit, Rory Leich, 20th International Conference on Electricity Distribution, Experimental Model for diagnosing on-load tap changer contact aging with dynamic resistance measurements, 2009 [6] E. Woschnagg und H. Koglek, Zum Problem der Widerstandsmessung von niederohmigen Transformatorwicklungen, 1977 [7] OMICRON, Standard electrical tests for power transformers, www.omicron.at [8] IEEE Standard Test Code for Liquid-Immersed Distribution, Power and Regulating Transformers and IEEE Guide for Short-Circuit Testing of Distribution and Power Transformers, IEEE C57.12.90 – 2006 [9] Raka Levi, Budo Milovic, TechCon 2011, OLTC Dynamic testing

Authors Cornelius Plath graduated with a Master’s degree in Electrical Power Engineering and Business Administration from the RWTH Aachen University in Germany. During his studies he was involved with several industry funded research projects on the condition assessment of electrical power apparatuses at the Institute of High Voltage Technology. He joined OMICRON in 2010 as an Application Engineer, and currently holds a Product Manager position. He has extensive international application experience, specializing in the electrical diagnostics of circuit breakers and power transformers. Markus Pütter studied electrical Engineering at the University of Paderborn and graduated in 1997. From 1999 he worked for OMICRON electronics, first as an electrical engineer in the field of transformer diagnostics, and from 2008 onwards as product man­ ager for testing and diagnostic solutions for primary assets. In his role as product manager, he focused on developing innovative solutions for power transformer testing. Markus Pütter was a member of the IEC TC14 transformer committee and the Cigre Working Group A1.39. He was also actively involved in an AM Forum working group focusing on Dynamic Resistance Measurement on on-load tap changers (DRM on OLTCs). Markus passed away in June 2015 following a tragic accident. 109

EVENTS

Photo courtesy of J. Michael Worthington, Jr.

Understanding the complexities of transformers with the Life of a TransformerTM Seminar Doble transformer seminar comes to Dublin this October

O

wners and operators of transform­ ers make tough choices each day when considering what is best for short term individual transformer reliabil­ ity and long term transformer population management. Doble Engineering Company helps engineers and managers in the electric power industry find solutions to these complex transformer ownership issues through its unique Life of a TransformerTM Seminar, which will be held in Dublin, Ireland on 25-28 October 2016. This seminar guides participants through transformer design all the way to failure analysis, equipping attendees with valu­ able knowledge needed to make more informed decisions about these critical

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a­ssets, whether it’s regarding on-site test­ ing and analysis or long-term replacement strategies. Attendees are presented with practical information, which can result in making an immediate, measurable impact on transformer performance and reliability. “You need to have a thorough understand­ ing of the complexities of transformers so you can make informed decisions about transformer maintenance and management,” said Don Angell, vice president of global strategy and solutions at Doble. “Part of our commitment to the power industry includes the sharing of critical, practical knowledge. We bring together experts from across the industry to make

sure our seminar attendees are getting the information they need to excel at their jobs and support the needs of their organizations.” In 14 years of hosting this educational event across Europe, the Middle East and the United States, Doble’s Life of a Transformer Seminars have trained more than 7,500 electric power professionals from over 50 countries. Throughout each sem­ inar, industry leaders responsible for power transformer engineering, manufacturing, maintenance, production and management offer big picture perspec­ tives regarding efficient transformer management with emphasis on the dynamics of that particular region.

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

Agenda topics include everything from specification writing to supplier selection, discussions on various types and components of transformers, overviews of diagnostic testing and monitoring approaches, and transformer population management. Advanced training sessions enable participants to delve more deeply into areas such as calculation methods, short-circuit withstand, thermal design and noise mitigation. An optional half-day laboratory diagnostics seminar is also available for attend­ ees. This course is ideal for those who review oil analysis data to assess transform­er condition. Doble’s laboratory experts detail how to identify and assess rapidly emerging transformer conditions with oil quality analysis, dissolved gas analysis and

w w w . t ra n sfo r m e r s - m a g a z i n e . co m

other diagnostic tools, combining theor­ etical instruction with hands-on examples, practical experience and case studies to illustrate common issues found in the field. The industry expo will include com­ panies such as Celtic Recycling, EKOFluid, Electrical Oil Services, GE Grid Solutions, Mistras Group, Shell UK, Transerv Europ­e and Unifin International. The Life of a Transformer Seminar will directly follow EuroDoble 2016, a peerto-peer knowledge sharing forum for exchanging best practices in maintenance, protection and asset management of p­ower utility assets. More details can be found at: www.doble.com/loateurope.

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EVENTS

CWIEME Chicago now a three-day event After three years of steady growth, North America’s leading electrical manufacturing tradeshow is moving from two days to three – allowing more time for attendees and exhibitors to connect, as well as to offer a professionally-accredited training course and workshop

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his October CWIEME Chicago will return to the Donald E. Stevens Convention Center in Rosemont, Illinois for not just two but three days of buying, selling, networking and knowledge sharing within the electric motor, generator and transformer manufacturing communities. The move is in response to both attendee and exhibitor demand, backed by a steady increase in participation figures over the last few years. In 2015, the show saw a 10 per cent rise in total attendance with a 24 per cent increase in OEM representation. This growth shows no sign of slowing in 2016. “The level of interaction was astounding last year between both the exhibitors and customers,” said Hank Pennington, president of Essex Brownell, supplier of wire, cable, insulation and other components to the motor repair, OEM and electronics markets. “We’ve seen CWIEME Chicago grow over the years and are very excited about the momentum this year. We plan to

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get a bigger booth to keep this momentum going!”

Exclusive CEU-accredited workshops As well as allowing more time for cus­ tomers and suppliers to make new contacts and cement existing relationships, the move to three days also enables the inclusion of a new CEU-accredited 1 day workshop, alongside the regular CWIEME Chicago technical programme. The training programme, will tackle specific design and technical challenges and course participants will benefit from teaching and interaction with expert instructors from the industry and academia. The training programme will be run by Dan M. Ionel, Professor of Electrical Engineering, and L. Stanley Pigman, chair in Power at the University of Kentucky, and Dr Dave Staton, Founder and President, Motor Design Ltd, on the afternoon of day two and the morning of day three, Octo-

ber 5 and 6 respectively. Tickets will be available to purchase on a first-come, firstserved basis. Further details, along with workshop schedules and content overviews, will be published on the CWIEME Chicago website in due course. “We are thrilled to announce the addition of Professor Ionel’s workshops to CWIEM­E Chicago 2016,” said Haf Cennydd, portfolio director at i2i Events Group. “The tailored expert advice he and his colleagues can provide will help to fill important knowledge gaps for electrical engineers at all levels and support their ongoing professional development. The initiative is a clear example of our commitment at i2i Events Group to adding value for our show participants.”

Learning opportunities for all The regular CWIEME Chicago technical programme, meanwhile, will be available free of charge to all attendees and exhibit­ ors at the show. The full schedule for

TRANSFORMERS MAGAZINE | Volume 3, Issue 3

2016 is also yet to be published but last year’s speakers give a strong idea of the caliber of programming. They included K­ onstantinos Laskaris, principal motor designer at Tesla Motors; Timothy Gill, deputy chief economist at the National Electrical Manufacturers Association (NEMA); Ashley Armstrong from the Appliance Standards Program at the US Department of Energy; James Bell, principal consultant at MagnetoDynamics; and Mark Raymond, senior staff engineering a­ssociate at Underwriters Laboratories (UL).

New Exhibitor Zone Another addition in 2016 is the New Exhibitor Zone. By grouping all new exhibitors together, making it quicker and easier for attendees to discover new products and initiate new partnerships. This year’s new exhibitors supply every­ thing from electrical steels, permanent

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magnets, laminations, and insulating oils, to wires, cables, winding machines, and welding equipment. We also see the return of the dedicated Machinery Demo Zone, where attendees can witness all the latest technology and equipment in action.

CWIEME Chicago – North America’s most comprehen­ si­ve showcase for the coil winding and electro-mag­net­ ic industry

“We might not be in a golden age of American manufacturing anymore, but we’re seeing a definite tendency towards re-shoring in the United States which bodes well for the future of the CWIEME community,” Cennydd said. “Many of our attendees and exhibitors at CWIEME Chicago are finding that for mid-to-low volume, higher complexity products, it makes sense to manufacture in the United States. With its long-standing heritage in the industrial heart of America and strong brand values, CWIEME Chicago is committed to spreading the knowledge and facilitating the connections that will help bring American manufacturing back home.”

Dates and opening times: Tuesday October 4, 2016 – 10am to 5pm Wednesday October 5, 2016 – 10am to 5pm Thursday October 6, 2016 – 10am to 3pm Venue: Donald E. Stephens Convention Center, Rosemont, Illinois Admission: Free until Friday September 30, after which an onsite registration fee of $40 will apply for those who have not already registered online. For more information and to register for the event, please visit: www.coilwindingexpo.com/chicago

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EVENTS CALENDAR Transformer Technology Symposium

Power Nigeria Exhibition and Conference

9 – 10 August 2016, Bangalore, India

27 – 29 September 2016, Lagos, Nigeria

This Symposium is organized by an interdisciplinar­y team with expertise in multi-physics simulations in conceptual design and design calculations, finite element (FEM), multi-body dynamics (MBD), computational fluid dynamics (CFD), electro-magnetic simulations (EMAG), fatigue damage durability, manufacturing process simulation (including casting, metal forming, powder forming), and multi-disciplinary optimisation (including shape & topology optimisation and parametric optimisation).

Over the next decade, Nigeria is set to become one of the fastest developing nations for power generation, transmission and distribution with all sectors of the power industry in need of drastic development. This event spread over 3 days will provide insight into the efforts and operations of the Nigerian national electricity distributors and the government, present financial issues and challenges, and feature a workshop on gas to power value chain.

International Council on Large Electric Systems 21 – 26 August 2016, Paris, France

The CIGRE Session 2016 provides an opportunity to listen to contributions from international senior executives as well as experts and specialists through official presentations, panel discussions, technical meetings and poster sessions. In parallel of the Session, a Technical Exhibition is held in the same location. The exhibition offers the opportunity to all visitors, including CIGRE delegates, to discover new services, tools, equipment and materials as well as the most advanced technologies in the field of power systems.

East African Power Industry Convention 2016

Transformers Magazine media partner

Coiltech International Coil Winding Expo and Conference 28 – 29 September 2016, Pordenone, Italy

The seventh edition of one of the fastest growing international exhibitions for the coil & winding industry will bring together leaders in the electro­ mechanical industry who will share information on the market development, new technologies, materials and procedures. The event includes both a conference with speakers from academic institutions and the industry, and an exhibition which traditionally covers all materials and machinery used in the production of electric motors, generators, transformers and winding systems.

21 – 22 September 2016, Nairobi, Kenya

The 2016 EAPIC conference and exhibition will bring together leaders from the regional and international power and energy community to discuss the status of critical projects, spot lucrative opportunities and share best practice. The event includes a strategic conference and a large trade exhibition which provides a platform for public and private stakeholders to engage in discussions around the future of East African energy utilities, giving stakeholders the opportunity to benchmark their operations, achievements and challenges against their peers and seek suppliers who are looking to gain access to projects across the region.

The International Conference on Condition Monitoring and Diagnosis 2016 25 – 28 September 2016, Xi`an, China

The technical program will include papers presented in regular, poster and plenary sessions covering a broad range of topics, such as evaluation of failure and degradation of power equipment based on CMD, advanced sensors and diagnosis techniques for Smart Grid, strategy planning and asset management for power equipment, fusion of large data and smart grid control with CMD techniques for power equipment, insulation structure design and lifetime assessment for HVDC system, and degradation and lifetime assessment of new energy devices for power generation and storage.

Transformers Magazine media partner

CWIEME Chicago 4 – 6 October 2016, Chicago, USA

This year, CWIEME Chicago boasts two changes – it is now a three-day event and it features a new exhibitor zone. Showcasing expert minds and the latest technologies, CWIEME Chicago 2016 is the meeting place for the coil winding, electric motor and transformer manufacturing industries across the Americas. A visit will help you to find the solutions your business needs, meet leading suppliers, network, forge new partnerships and strengthen existing ones.

WEIDMANN Transformer & Technology Seminar 2016 11 – 13 October 2016, Istanbul, Turkey

This newly offered 3-day transformer seminar includes an array of industry experts and companies presenting and discussing topics such as materials and components used in transformers, design of distribution and power transformers, factory testing, operation of transformers and on-site testing. The seminar was developed to give the participants both an introduction and a comprehensive overview about transformer technology.

Transformers Magazine official media partner

Transformers Magazine media partner

Transformer Life Management Conference

2016 EuroDoble Colloquium and Workshop

26 – 27 September 2016, Königswinter, Germany

24 – 26 October 2016, Dublin, Ireland

The main goal of the TLM conference is to find ways for prolonging the residual lifetime of transformers and to reduce unplanned outages. This year the TLM symposium will focus on the question of how to ensure transformer safety and operation in the network in the face of increasing loading and age. The symposium and associated technical exhibition is directed at engineers, physicists, chemists, technicians and consultants involved in the manufacturing, design, operation, assessment and maintenance of transformers, as well as universities and research institutes with an interest in the reliable operation of electrical networks. 114

EuroDoble Colloquium and Workshop is a forum for sharing best practices on managing primary and secondary assets in our ageing power networks, power stations and industrial sites. As the power industry today faces a long list of challenges and concerns, this event brings together peers in the power industry to discuss the pressing topics that impact your job – all to ensure the reliable flow of power. Now in its 22nd year, the 2016 EuroDoble Colloquium and Workshop will focus on three important focus topics: the impact of new technologies, managing safety, and secondary systems. TRANSFORMERS MAGAZINE | Volume 3, Issue 3

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The most recognized global publication for the transformers industry. We give you the most effective tools to

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