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S_p_e a k e r s_________________

 

 

Following are ARWtr2010 key Speakers, who will deliver the below Lectures, on transformers key tipics.

 

 

  1* Janusz TUROWSKI

 

 

Institue of Mechatronics (IMI)

Tecnical University of Lodz-Poland

     
  2* Xose M. LOPEZ-FERNANDEZ
   

Department of Electrical Engineering

Universidade de Vigo-Spain

     
  3* Harold MOORE
   

Power Transformer Consultant

Harold Moore and Associates-USA

     
  4* S.V. KULKARNI
   

Power Author of Transformer Engineering:Design and Practice book

 (1990-2001) Transformer Cropton Greaves Limited-India

Indian Institute of Technology, Bombay-India

     
  5* Ryzard MALEWSKI
   

Power Transformer Consultant

Malewski Electric Inc. Montreal-Canada

     
  6* Miguel OLIVA
   

Chairman of CIGRE A2 Spanish National Transformers Working Group

ABB, Asea Brown Boveri, S.A. - Spain

     
  7* Angelica da ROCHA
   

Convenor of CIGRE JWG-A2/C4-03

CEMIG EHV Planning Department-Brasil

     
  8* Ernesto PEREZ
   

HV Manager for GAS NATURAL FENOSA

GAS NATURAL FENOSA- Group of Energetic Sapanish Company

     
  9* Jeewan PURI
   

Chairman of Audible Sound and Vibration IEEE Subcommitee

Consultant at Transformers Solutions Inc. Mathews-USA

     
  10* Bernhard HEINRICH
   

WEIDMANN Electrical Technology AG-Switzerland

     
  11* Adolfo IBERO
   

Director of HV Division

ARTECHE Instrument Transformers-Spain

     
  12* Hugo GAGO
   

Responsible for IBERDROLA Equipment Specification and Homologation-Spain

(IBERDROLA- Group of Energetic Spanish Companies)

     
  13* Robert DEGENEFF
   

Chairman of IEEE PC57.142 Guide - Swithching Transient Induced by Transformers

Consultant at Utility Systems Technologies, Inc.

     
  14* John LAPWORTH
   

Doble PowerTest Ltd -UK

     
  15* Ricardo LOPES
    Department of R+D+i - EFACEC Energía- Portugal
     
  16* Jorge MARTINS
   

Substation Maintenance Department - Operation Division

REN- Rede Electrica Nacional, SA - Portugal

     
  17* Selim YUREKTEN
   

ENPAY Transformer Components - Turkey

     
  18* Angel de PABLO
   

 GE Energy - Spain

     
  19* Javier IBAÑEZ
   

Technical Management Department

IBERDROLA RENOBABLES- Spain

     
  20* Jorge PLEITE
    Carlos III University - Spain
     
  21* Peter WERELIUS
   

Application Expert and Product Manager

Megger -Sweden

     
  22* Rainer FROTSCHER
   

Maschinenfabrik Reinhausen GmbH - Germany

     
  23* Bruce PAHLAVANPOUR
   

Nynas Technical Co-ordinator & Professor at Cranfield University

NYNAS AB - UK

     
  24* Richard MAREK
   

Chairman of IEEE PC57.110 Guide - Power and Distribution Transformer When Harmonic Loading

Chairman of IEEE PC57.157 - High-Temperature Liquid-Filled Transformers

Chairman of IEEE PC57.96 Guide- Dry-Type Distribution and Power Transformers

IEC TC 14 Delegate for the US Technical Advisory Group

Convenor of IEC/TS 60076-14 for High-Temperature Liquid-Filled Transformers

Applications Research, Energy Solutions Group of Nomex®

DuPont Protection Technologies - USA

     
     
 
Further i n f o r m a t i o n   is going to  u p d a t e.
 
 
Preliminary _L_e_ctures & Abstracts________
 
** Evaluation of Generator Step Up Transformers (GSUs) in USA versus Europa
 
** Importance of The Design Review and Short Circuit Tests in Power Transformers. The Gas Natural Fenosa Experience
 

Based on a strong and well written technical specification it is convenient to assess the suitability of a power transformer for the duties it has been designed for.

 

The experience shows that transformers may differ their behavior during tests than expected from the drawings and calculations. ¿ How to be confident about transformers performance ?

 

The Design Review job allows the purchaser to check and assess the safety margins used by the manufacturer of the transformer. In Gas Natural Fenosa this task is considered as strategic taking into account the consequences of suffering a failure due to a design problem. This task takes years of training in order to perform a fully Design Review job.

 

Design Review shall cover the three main duties of a power transformer:

- Thermal (Power).

- Dielectric (Insulation).

- Electrodynamic (Short Circuit).

 

Software specialized tools tailor-made are required as well as a strong knowledge about transformer design and manufacturing.

 

During the presentation statistics of experience will be shown.

 

Despite of the above mentioned tasks, additional special test (severe short circuit test) accordingly to IEC 60076-5 will determine that your units are the best for the job that has been designed for.

 

Also statistics will be shown regarding the large amount of tests carried out in Gas Natural Fenosa.

 
** Power Transformer end of Life Assessment - PRACANA Case Study (REN-LABELEC-EFACEC)
 

The present lecturer intends to summarize a study with contributions and perspectives about the same transformer, collected from manufacturer, chemical laboratory and utility, providing conclusions concerning the transformer life assessment.

 

REN (Rede Electrica Portuguesa) current network expansion and reinforcement program has led the company to consider the transfer of power transformers between substations. The transfer of transformers which have been in service during several years requires a detailed analysis concerning the condition assessment, lifetime expectancy and cost benefit of the overall operations.

 

A condition evaluation was made on a 35 year old transformer located at REN Pracana substation, in order to decide about its transfer to a new substation located in the same region. This operation would require the partial dismantling, transport, refurbishment in the new substation and commissioning.

Due to the external degradation of the transformer, besides oil and paper degradation, it was decided to perform a full refurbishment, including painting, replacement of conservator and auxiliary equipments, oil replacement and drying of the active part, under REN specification. However, considering REN criteria for refurbishment and transfer, it was decided as relevant, for the decision concerning the transfer, to perform a DPv test (degree of polymerisation test) on some insulating paper samples taken from the bushing and OLTC lead connections.

 

 The results of the test showed that the useful lifetime expectancy of some paper samples taken from the transformer was under 20% of its full lifetime. This means that insulating materials of the transformer were rather aged and this could introduce additional risk to the transport operations and future mechanical performance in service. The cost-benefit analysis was also updated considering this lifetime expectancy under 20% and the business case has lost interest. So, REN decided not to perform the transfer of this transformer. Although it could remain in service in the original substation, since Pracana substation HV line disconnection was in progress, it was declared the end of life of this transformer. 

 
** Causes and Mitigation of Switching Induced Destructive Transformer&Breaker Interaction
 

Circuit Breaker reignitions produce a series of complex voltage transients.  Given the right circuit parameters, these transients can induce resonance in transformer windings resulting in destructive voltage excursions. Many repetitive transformer failures due to switching operations have been observed at some locations while other identical transformers in similar applications have operated satisfactorily. Therefore a better understanding of this phenomenon is needed for assuring the reliable operation of transformers.

 

This lecture describes as to how the breaker reignition transients are produced and how they are influenced by various circuit breaker characteristics. A test for detecting the likelihood of destructive transformer / breaker interaction is described. Methods for mitigating the influence of breaker reignitions are also described.

 
** Detailed and Reduced Transformers Models in Fast Front Transient Simulations
 

Transformer manufacturers have developed detailed transformer modes for their internal use. This paper investigates the use of such detailed models for Fast Front Transientes (FFT) simulation. Precisely, the response of detailed and reduced order models of transformers are compared in case of a lightning stroke in an overhead power line present in a number of typical power installations. Recommendations are provided concerning the use of reduced order models of transformers

 

** The Effect of The Transformer Model on the Accuracy of the Computed Transient Voltage and Frequency Response

 

Lumped parameter models are used extensively by manufactures in the computation of the transient response of the transformer to establish an adequate and economical insulation structure.  Additionally, these models are routinely used by consultants, utilities, and manufactures in system studies to determine the transient response of the system and transformer to some event on the system.  For both the accuracy of the result is critically important. 

 

There has been an extensive body of literature written addressing the modeling of the transformer.  The vast majority of this work  has focused on the building of an accurate inductance, capacitance, and loss model of the transformer winding and core of interest. Additionally, much work has been conducted on the formation of general solution methods to solve the resultant set of differential equations.  

 

Traditionally, the model used for transformer transient studies will be a single phase model of the transformer.  Or, if the representation is three phase the model is simplified considerabley, Additionally, the load will be ignored and the transient study will be performed with the secondary shorted or open circuited.  In the last decade much work has been done in examining the interaction of the breaker (and its reignition characteristic) and the natural frequency of the transformer. This paper will show it is important to consider the transformer as a three phase device and that the load has an effect on the transient and frequency response.  Additionally, what has been addressed only in passing is the effect on the way the model is subdivided. This paper will explore the effect on the transient voltage and impedance versus frequency of the model as a function of how the model is constructed.  

 

This paper demonstrates that in number of case it is inaccurate to explore the natural frequency characteristic of a three phase transformer with a single phase model.  Additionally, this paper demonstrates that even if the inductance, capacitance, and loss representation is accurate and an appropriate solution method employed it is possible to compute results that are in error.  Guide lines are provided to ensure an accurate response.

 
** Electrical Transient Interaction between Transformer and the Power System
 

The importance of assessing and discussing the different types of electrical transient interaction between transformers and other components of the T&D power system has been well addressed recently. This has been motivated by reported transformer dielectric failures, some of them with no specific cause.

 Although it is well acknowledged  that fast transient system ‘sources’ do exist and can cause damage ton transformer windings, a lot of unknowns remain regarding this issue, with reference to transformer design and testing – concerning in particular its insulation –   and to interactions between transformers and fast transient phenomena that may occur due to equipment switching, short –circuits and power electronics.

 In this context, a joint working group (JWG) was set up by Cigre A2 transformer and C4 system reliability study committees to pursue an improvement of transformer reliability, based on recommendations regarding equipment specifications, design review, system planning and operation. It is worth mentioning that a significant activity on this subject was carried out by a Brazilian Cigre group with the support of utilities, manufacturers and third parties like research institutes. Now the scope is being addressed under a wider international context.

 In this lecture, the JWG work in progress will be presented which includes  different case studies to represent typical system and transformer interaction. In addition, the main conclusion obtained by the Brazilian group will also be addressed.

 
** Transformer Model for FRA Traces Interpretation
 

Frequency Response Analysis is a commonly used technique applied with other electrical tests in order to discover possible failures inside the transformer, especially displacements of the internal elements. However, a complete understanding and interpretation of the physical phenomena through inspection of FRA traces is not a reality. Therefore FRA measurements interpretation constitutes an important research activity in the transformer diagnosis field. Transformer modeling is a research task almost as old as transformer construction itself. It has been applied in many different process related with the transformer design, construction, study and so on. Regarding FRA analysis, transformer behavior modeling has become one of the most used tools intending the FRA traces analysis. The main idea is trying to relate the observed changes on the responses with variations in different features of the model. However, due to different aspects, a complete model that can be used as a definitive tool for a diagnosis based on FRA measurements is not available yet. 

In this lecture, a transformer model for FRA traces interpretation and based on physical phenomena is presented. Due to its implementation process and the test complied for the time being, the model is able to establish the internal phenomena happening inside the transformer and distinguish the core phase causing the supposed problem.

 
** Solutions to Overvoltages in the Reconnection of the Lines with Inductive Voltage Transformers
 

One of the causes of the accelerated ageing or the insulations failure of the transformers are the frequent overvoltages and one of the more frequent overvoltage is the reconnection of the lines with an added DC component. 

 

The trapped DC voltage can cause overvoltages during the reconnection of the line. It can also cause insulation problems due to the polarization of insulating materials (for example the SF6).

 

One of the most practical ways to eliminate these trapped charges in the line is to place an inductive voltage transformer. These inductive voltage transformers must be sized properly to withstand the mechanical stresses caused by the discharge current of the line through the primary winding of the transformer. We must also take into account the increase in the temperature of the primary coil when the discharge of the line occurs, because all the energy trapped in the line will be dissipated by the primary winding of the transformer, causing a substantial increase in the temperature of the winding.

 

With the increased needs for Power Quality and Distributed Generation has been a big proliferation of capacitor banks. Those capacitor banks have the same problems.

 

In the same way as with the lines, when a capacitor bank is disconnected, electric charges are trapped in the capacitor bank, causing a big accumulation of energy. This trapped DC voltage in the capacitor bank can cause overvoltage problems on high voltage equipment when reconnecting the capacitor bank. This can be easily avoided by using an inductive voltage transformer to discharge the capacitor bank.

 

 Inductive voltage transformers are built specifically to comply with these requirements. Therefore, they can dissipate the energy stored in HV lines and capacitor banks, thus protecting the insulation of HV equipment against overvoltages caused by the reconnection of these lines or capacitor banks with trapped charges.

 
** Mineral Insulation Oil, Production, Supply and its Management
 

The lecture describes, insulating oil production, supply and  guidelines, a code of practice for in-service insulating oil based on the results of research on insulation ageing.  The paper also seeks to show the best compromise between technical requirements and economic considerations.

 
** Mineral Insulation Oil Comparation Study Between Gas Cromatography and Photo-Acoustic Infrafred Spectroscopy

 

It is well known that Dissolved Gas Analysis (DGA) is probably the most powerful tool for transformer condition monitoring. Application of Gas Chromatography (GC) to this purpose requires several steps: calibration of the gas chromatograph, extraction of gases and analysis of the extracted material by Gas Chromatography. 

 

The lecture presents the results of a comparative study between laboratory gas chromatography and a different analytical technique, Photo Acoustic Infrared Spectroscopy (PAS).

 
** Transformer Insulation Design based on the Critically-Stressed Oil-Volume and on the Accumulated-Field Reference-Curve
 

Although initially proposed as calculation methods of oil gap strength at power frequency, but over the years the lightning and switching impulse calculations have been included.

 

The lecture presents oil-insulation desigh methods, their theoretical base, advantages and limitations, as well as an assessment of the effect of oil gap geometry, of bare of insulated electrodes and transformer-oil quality.

 
** Assessing the Condition of Power Transformer Insulation
 

Due to the physical impracticality of accessing conductor paper and of taking samples from the hot spot of oil cooled power transformers in service, it is impossible to determine the condition of the insulation of aged transformers with adequate precision.

By means of measuring a multitude of samples from the various parts of the windings as well as from the clamping structures a comprehensive aging replica of the whole cellulose insulation of different transformers will be presented.

 
** Dielectric Frequency Response and Temperature Dependence of Dissipation Factor
 

Modern technology and developments in signal acquisition and analysis techniques have provided new tools for transformer diagnostics. Of particular interest are dielectric response measurements where insulation properties of oil-paper systems can be investigated. Dielectric Frequency Response, DFR (also known as Frequency Domain Spectroscopy, FDS), was introduced more than a decade ago and has been thoroughly evaluated in a number of research projects and field tests with good results. DFR data in combination with mathematical modeling of the oil-paper insulation is proven as an excellent tool for moisture assessment. Since the modeling theory contains influence of temperature, DFR and modeling can be used to calculate the temperature dependence of the insulation system. This paper gives a background to DFR, insulation modeling and how these tools can be utilized to improve understanding of dissipation factor temperature dependence and how this can be used for decisions on maintenance and/or replacement.

 
** Frequency Response Analysis Testing for Transformers
 

The tutorial will first discuss the purpose and objectives of diagnostic testing – to diagnose / dentify problems detected by monitoring, or suspected as a result of events affecting the transformer.

 

The possible damaging effects of events such as short circuits and tapchanger faults will be discussed, in particular typical failure modes.

 

The range of techniques that have been used to try to detect winding movement will be reviewed, concentrating on Frequency Response Analysis (FRA) measurements, which are now accepted as he

most sensitive means of detecting winding movement.

 

The practicalities of carrying out FRA measurements will be described, together with interpretation

methodology, particularly when no previous reference results are available, as is often the case.

 

Typical FRA results for various winding types and arrangements will be described.

 

Lastly, case examples of winding movement faults diagnosed by FRA will be described.

 
** On-Load Tap-Changers with Vacuum Switching Technology for Increased Fire Safety, Reliability and Enviromental Performace
 

Conventional arc-breaking-in-oil tap-changers are optimized for reliable operation in mineral oil. The switching arcs are responsible for severe oil deterioration, leading to frequent service and oil exchange. A new generation of tap-changers with vacuum switching technology encapsulates the switching arcs inside vacuum interrupters and so prevents the oil from excessive deterioration. As a result, tap-changer maintenance is minimized. In combination with alternative insulating liquids like High Molecular Weight Hydrocarbons (HMWH), synthetic and natural esters as well as silicone oils, additional benefits are achieved in terms of high fire safety and environmental friendliness.

 

Selected types of the MR vacuum tap-changer range have been tested extensively with common alternative liquids, such as R-TEMP Fluid, MIDEL 7131 and FR3. The tests included dielectric strength, lubricating capabilities, arcing behaviour of the change-over selector, mechanical function over a wide oil temperature range, cooling behaviour and compatibility with all insulating materials used.

 

The lecture describes the tests which have been carried out and the test results.

 

** New Products, Innovation and Concepts in Transformers: Dry type transformer 72.5 kV, 220kV Transformer with Vegetal Oil and HV Fast Deployable Mobile Transformer

 

The lecture will present three examples of innovation, new concepts and products covering a broad range of transformer applications:

- Development of dry type distribution transformers for higher voltages (up to 72.5kV).

 - Use of vegetal oil in power transformers up to 220kV addressing the technology and challenges to make them compatible with standardized existing installations in urban substations. 

- Fast deployable mobile transformers for contingency in HV transmission from 400kV. A mobile transformer concept for quick restoration of service in critical high voltage transmission substations during contingencies, supporting system stability and helping utilities to guarantee the continuity of the supply

The lecture will discuss the technical challenges which had to be solved during the development of the transformer. Especially the dielectric requirements become very demanding. Experimental and computational simulation methods have been applied. They finally allowed to achieve a compact and reliable transformer design. Intensive testing of the prototype transformers has shown that all requirements have been met, including the requirements for an insulation system free of partial discharge and the lightning impulse testing at 325 kV.

 

** Non-Conventional Instrument Transformers Application of Rogowski Coils Current Sensors in New Protection Solutions

 

Rogowski Coils may be designed with different shapes such as round and oval. The coils may be made of rigid or flexible materials. Coils can be constructed as non split-core style; but, the design required the split-core style that can be opened to assemble around an in-service conductor. High-precision Rogowski Coils may be designed using printed circuit boards (PCB). In addition, PCB Rogowski Coils have compact size and light weight. Rogowski Coils make protection schemes possible that were not achievable by conventional CTs because of saturation, size, and weight.

 
** Shunt Reactor Cores up to 765-300 MVAr
 

Long high voltage energy transmission lines, particularly when high voltage cable lines are operating at no load or subjected to any load suddenly due failure etc., huge voltage increases could take place on the transmission line due to their big operating capacities. In such cases, the shunt reactors are installed in order to prevent excessive voltage increase by compensating the capacitive reactive power of operating capacity of the transmission line with the inductive reactive power of the shunt reactor.

The concerned magnetic induction is provided by the magnetic energy in the magnetic circuit of the shunt reactor. The aforementioned energy developed in 4 places;

     1- Air gaps on the legs

     2- Air gaps between legs and yokes

     3- Volume between the core and winding

     4- Volume of winding

 The biggest portion of the energy occurs in the air-gaps of legs and the rest in the other sections.

The core packages and ceramics supports are glued to each other under the pressure. In this way, a robust unit is achieved.

Due to different magnetic permeabilities of core packages and air gaps, a tensile strength occurs as between the magnetic poles. Those strengths which affect on the air gap, try to reduce the air gap by changing between 0 and a maximum value and with frequency value of 2 times of network frequency. The pressure onto the ceramic supports is inversely proportional by the elasticity modulus of ceramics.

Three phase shunt reactors can be produced as three or five limbs. Production of five-limb reactors is expensive however it has below advantages.

There are also wounded yoke applications on Reactors up to 50 MVAr power level. In a case of wounded yokes there is no need to use fixing metal parts which can cause fluxes. These yokes help to minimize heat and to prevent fluxes which are obtained on outside of active part coils.

 

** Uptower Wind Turbine Transformers. Main Features

 

Although wind turbine transformers have the same overall features than regular ones, wind application forces to some peculiarities.

 

Related to the design, wind turbine manufacturers usually specify special vibration requirements in order to avoid failures in the fastening system of the transformer. Dimensions, weight and cooling system are very often limited by the anufacturer’s specification. Furthermore, cooling system in transformers placed in a platform inside the tower is not trivial because airflow in the tower is not always upward and tower air inlets are not allowed for structural reasons.

 

On the other hand, the transformer assembly should be done very carefully to avoid vibration coupling in electrical connections as well as to allow cable displacements due to the rotary motion of the nacelle.

 

Finally, dealing with the maintenance, oil transformers are avoided because oil replacement and potential oil leakages are difficult and expensive to manage.

 

** High-Temperature Insulation Systems

 

Introduction; High-Temperature; Insulation; Applicable Liquid-Immersed Standards; Key Definitions; IEC Insulation Systems; Thermal Testing; Applications.

 

Transformers with high-temperature insulation systems, operating at temperature rises above the 65K limit found in the standards are now quite common around the world.  High-temperature insulation such as wire wrap or wire enamel, layer insulation and board for barriers and spacers are commonly used in transformers for many varied applications.  Common applications include mobile, locomotive traction, wind turbine step-up, furnace and rectifier transformers.  For many years these materials have allowed manufacturers to develop weight or size optimized designs.  More recently, high-temperature insulation has been used to enhance the life of generator step-up transformers and to reduce gassing due to hot spots on the core and at lead exits.

 

The first attempt to standardize the design and application of high temperature liquid-immersed transformers began in the late 1980’s with an application guide published by IEEE.  The document was limited in scope to mineral oil-immersed power transformers.  However, more recently, applications in pole-type distribution transformers and wind turbine transformers have become increasingly more important and have shown substantial growth in the marketplace.  These units typically use alternate fluids that are not addressed by this IEEE document.

 

In response to this growing market, an IEC Technical Specification was developed to meet the international need for additional guidance in specification, design, testing and loading of high-temperature liquid-immersed power transformers and also considers many different dielectric coolants.  A key accomplishment of the document was the definition of new terms, including four new insulation systems.  These insulation systems are defined as a means of standardizing the technical content of the document for design guidance and to improve communication between the manufacturer and the user. 

 

This lecture will discuss the historical progress of high-temperature liquid-filled transformers, tracing the standards development and illustrating the intertwined relationship of the IEEE and IEC documents.  Current applicable standards will be explored by highlighting key definitions and the newly defined insulation systems.  Activities for a new IEEE standard and future upgrade work on the IEC document will be presented.  Issues concerning thermal testing of these insulations and systems will be presented and finally, typical applications will be described.

 

---> The list will be completed with the 22 involved lectures
 
 
 

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