My Transfo 2002

Turin, the 15th and 16th October 2002

Interventions and abstracts

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[toggle title=”Life Cycle Assessment of power transformer: an introduction” state=”opened”]

B. De Benedetti, G.L. Baldo, L. Maffia – Materials Science and Chemical Engineering Dept. –Politecnico di Torino

Power transformers are electrical equipment with a strategic role in the production, distribution and electricity use. The useful life of a transformer is about 40 years and an analysis of the manufacturing, installation, operation and maintenance, end of life management seems to be a right approach to develop new apparatus with a lower environmental load especially to better control eventual accidents, with particular regard to emissions from the insulating substances, and the end of life of all components.

Life Cycle Assessment (LCA) provides a physical description of the system in a quantitative indication of all flows of materials and energy across the system boundary either into or out of the system itself and is able to calculate the environmental burden of a process and its products. It was thought helpful therefore to separate this type of work into four distinct stages

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[toggle title=”Degradation and chemiometryc models”]

G.Camino, Politecnico di Torino, sede di Alessandria, viale T. Michel 5, 15100 Alessandria Italia
W. Tumiatti, O. Charron, F. Quagliotti, R. Maina, Sea Marconi Technologies, Via Crimea 4, 10093, Torino, Italia

Considering the difficulty in taking samples of insulating paper of transformers, the evaluation of the degradation of cellulose through the analysis of the products of its degradation (furans) dissolved in the oil has been pursued. The furans are formed by the ends of the polymeric chain of cellulose.

Insulating materials in transformers are of two types:
– Fluid insulation: oil
– Solid insulation: Kraft paper (cellulose)
This two materials of organic nature are able to provide their function correctly only when they maintain their chemical integrity when the transformer is in operation. For this reason, analytical methods have been developed to establish the rate of degradation of the oil by sampling the transformer in operation as well as methods of treatment to re-establish the chemical/physical features of the oil.
For what the paper is concerned, sampling is very complicated due to the unacessibility of the cellulose inside the transformer. This type of sampling is performed only when extremely complex maintenance operations are carried out, involving the full dismantling of the transformer. Thus, samplings of paper are extremely rare in comparison with oil sampling. Consequently, studies have been made to correlate the level of degradation of the paper with the products of its degradation (essentially thermal) dissolved in the oil.

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[toggle title=”Diagnostics”]

(A. de Pablo)

Electrical transformers are key equipment on generation, transportation, distribution and use of electricity. Its capillary use makes necessary to maintain a tight condition monitoring control to minimise the risks of faults and unplanned outages with corresponding lost of direct (price of equipment) and indirect (lost of production) assets, as well as the increase of unreasonable risks to the workers health (risks of fire, explosions) and to the environment (risk of spills).

From an industrial point of view, maintenance can be implemented in three levels:
·                Predictive maintenance
·                Preventive maintenance
·                Corrective maintenance
Thus, predictive maintenance is the first level, normally is the cheapest one and the information obtained is critical to avoid undesirable faults.
Large majority of industrial transformers are insulated by a so call “Impregnated insulation system”, that is a solid insulation (normally kraft paper) wrapped around winding conductors and an insulating liquid (mainly mineral insulating oil). From a point of view of predictive maintenance, the insulating liquid offers a number of advantages:
     it flows throughout all transformer components and accessories;
–      it can dissolve almost any decomposition product;
–      sampling is quite easy, even for not experienced personnel;
–      Under abnormal operating conditions (failure or fault), insulating materials degrade giving by-products which can be analysed dissolved on the fluid or can be inferred due to the modifications they provoke on physical properties of the insulating liquid.
More over, recent studies carried out by CIGRE (International Council on Large Electric Systems) Study Committee 12 (Transformers), stated that the insulating liquid may contain as much as 70 % of the information which can be obtained from a transformer in service.

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[toggle title=”I liquidi isolanti – Requisiti e Tipologie”]

(Roberto Campi)

La tipologia dei fluidi adottati da parte dell’industria elettrotecnica con funzioni di liquidi isolanti mette in evidenza come questi prodotti derivino quasi totalmente dalla raffinazione del petrolio o dall’industria petrolchimica .
Questa nota prende pertanto principalmente in considerazione i diversi tipi di oli minerali “isolanti” messi a punto da parte della industria petrolifera, nell’arco di 120 anni di evoluzione, per rispondere alle esigenze di alcune macchine elettriche tra le quali, principalmente, i trasformatori.
 Nei vari paragrafi vengono dati riferimenti storici, informazioni sulle normative nazionali, una panoramica delle tipologie attualmente disponibili sul mercato ed alcuni dati statistici.
In un ultimo breve paragrafo vengono infine citati gli altri principali fluidi di natura petrolchimica o “sintetici” che, durante il secolo scorso, hanno affiancato in tempi successivi gli oli minerali. Tale richiamo non ha soltanto la funzione di citazione storica, per ricordare quali specifiche soluzioni si siano trovate per soddisfare particolari esigenze, ma altresì quella di richiamare l’attenzione su un problema di viva attualità in quanto alcuni di essi, quali i fluidi a base di poli-cloro-bifenili (PCB), per problemi di carattere ambientale e tossicologico, stanno ormai concludendo il loro ciclo di utilizzo.
Viene infine riportato in due tabelle un riepilogo delle caratteristiche chimico-fisiche dei vari liquidi isolanti sopra citati per rendere più agevole il confronto tra le varie tipologie e mettere in evidenza quali specifiche soluzioni si siano ricercate, quando necessario, per superare l’unico significativo limite d’impiego presentato dagli oli minerali petroliferi : l’infiammabilità

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[toggle title=”Insulating oil regeneration and PCB destruction”]

Prof. B Pahlavanpour & Dr M Eklund, Nynas Naphthenics AB, SE-149 82 Nynashamn, Sweden

Insulating mineral liquids can be regenerated to prolong their lifetime and avoid failure of the transformer. The regeneration removes unwanted degradation products from the oil. This paper gives a background to the effects of degradation products, transformer monitoring and ways of removing of unwanted products.  PCB is discussed as a special case with a background to the legislation and health aspects. Oil management is considered from both legislative and health and safety view points.

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[toggle title=”Oil, a critical part of Transformer Asset Management”]

M. J. Meddins, National Grid, UK

Transformers are a significant proportion of the assets, monetary capital value, on the financial books of any Transmission company. The oil elemental cost is approximately 3 % of the total asset value. Oil acts as primarily as an insulator and coolant. The viscosity of the oil and how it reacts over time to the various component materials used in the manufacturing of a transformer, may either accelerate or defer ageing and deterioration of the transformer.

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[toggle title=”Transformer maintenance”]

Victor Sokolov, ZTZ-Service Co., Ukraine, Convenor of CIGRE WG 12.18 “Life Management”

The life of a transformer consists of many steps from initial specification, design and manufacture through installation, operation, maintenance, and possible change of state with reconditioning and, eventually, replacement. A model of the life of a transformer may be presented as a change of its condition, namely as reduction of safety margin with time under impact of thermal, electric, electromagnetic and electrodynamic stresses and contamination.

Economic as well as technical and strategic factors determine the effective end of life of equipment. A technical life may be still continue until a transformer retains its functional serviceability that may be determined by its four key properties:

  • Electromagnetic ability and integrity- an ability to transfer electromagnetic energy at specified conditions, without general overheating and localized hot spots, excessive losses, gassing, excessive vibration and sound.
  • Integrity of current carrying circuit.
  • Dielectric withstand strength under the influence of the specified operational stresses, considering a permissible level of deterioration.
  • Mechanical withstand strength under the effect of specified through-fault currents.

A failure occurs when the withstand strength of the transformer with respect to one of its key properties is exceeded by operating stresses

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[toggle title=”Transformer Manufacturing”]

A. C. Hall

The manufacture of transformers requires engineering knowledge and skills derived from experience and from other disciplines such as chemistry, economics and user practices just to mention a few. The manufacturer’s aim is to produce equipment that is fit for purpose; that meets the purchaser’s specification and applicable Standards; that will be competitive and will enhance the business and promote further orders.

The process of manufacture begins with a purchaser’s enquiry. It ends when the product is dispatched. This is not necessarily the contract end point. That usually occurs when the in-service guarantee period ends. Thereafter, issues relating to the performance and operation of the transformer in service are the responsibility of the purchaser. The supplier is only likely to be involved when the equipment requires some special resource for maintenance or to rectify some latent problem or to make repairs following a technical failure of the equipment.

There are factors throughout the whole of these activities and the purpose of this presentation is to examine some of these to see how they affect transformer design and manufacture. The factors chosen are: Standards, specifications, design and manufacture, asset management and economics.

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[toggle title=”Case histories”]

A. de Pablo

Oil analysis is one important tool for predictive maintenance of oil-filled electrical transformers but, sometimes, is a potential matter of concern during transformer life. In this report we would like to show some examples of both situations.

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[toggle title=”In-field Screening Techniques for PCBs in Transformer Oil:US-EPA Field Trial Results for the L2000DX Analyzer”]

J.D. Mahon, M.S., D. Balog, A.C. Lynn, T.B. Lynn, Ph.D., Dexsil Corporation, Hamden, CT, USA

The US-EPA, through the ETV, SITE and other programs, routinely evaluates innovative field testing technologies for measuring environmental contaminants. In August of 2000 Oak Ridge National Laboratory (ORNL), through the ETV program, investigated technologies for measuring PCB contamination in transformer oil. During the field trials the Dexsil L2000DX analyzer successfully analyzed 152 oil samples — 52 performance evaluation (PE) samples and 100 environmental samples. In comparison with laboratory results for all environmental samples, the L2000DX generated only one false positive and no false negatives. The mean relative percent standard deviation (RPSD) was 11% and the average recovery for PE samples was 112%. The overall comparison with the laboratory resulted in a correlation coefficient (R2) of 0.87, for single Aroclor samples the correlation with the lab was 0.92. Unlike the laboratory, the L2000DX was determined to be unbiased for both single Aroclor and mixed Aroclor samples.

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[toggle title=”Maintenance, repaires, refurbishment of power transformers and feedback”]

P. Voorspoels, Pauwels Trafo Service

After describing the different stages in the life of reparable systems, we will examine how a power transformer can be likened to a system of this type.  We will then look at the difference between repairs and reconditioning.  The second part of this report will attempt to highlight the criteria used to decide whether to repair or recondition.

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[toggle title=”State of the art for the inventory, decontamination and asset management of transformer and electrical equipment with PCBs”]

Tumiatti Vander, Actis Riccardo, Maina Riccardo, Tumiatti Cristina, Roggero Carlo, Boasso Giovanni, Luc Van den Bogaert, SEA MARCONI TECHNOLOGIES sas –
Prof. Shubender Kapila, University of Missouri

The PCBs (polychlorinated biphenyls) in insulating oils and liquids used in electrical equipment for the generation, transmission and distribution of electricity can determine an unreasonable risk for human health and the environment caused by their persistency and bio-accumulation and are included in the POPs (Persistent Organic Pollutants) listed in the UN/ECE Protocol signed in Stockholm in May 2001.

In order to mitigate and prevent the “PCBs risk” their use is subject to European legislation since 1976. With the last Directive 96/59EC of 16 September 1996, defines new and stricter regulations relative to the inventory (art. 4) the decontamination and/or disposal of the PCBs and equipment within 2010 (art. 3).

Also, it becomes important to diagnose the functional degradation and the residual life of the equipment, focalised on the reduction of damages and malfunctions, based upon the results of analytical and inspective parameters, to maximise the proper management of assets.

In the last 20 years several methods for the disposal and of PCBs have been implemented, such as controlled incineration, underground storage, bio-chemical transformation and chemical dehalogenation.

This paper presents real application cases for the inventory and asset management of power and distribution transformers focusing on the project implemented by the Electricity Authority of Cyprus for the decontamination of its fleet of distribution transformers and the results of the inventory performed in France during 2002.

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[toggle title=”Premature Insulating Oil Ageing and Remedial Action”]

(Mr M Meddins, National Grid, UK; Prof. B Pahlavanpour, Nynas Naphthenics AB, Sweden

The prime function of insulating oil is cooling and insulation. Specifications, standards are used for purchasing insulating oil. In service the oil is subjected to heat and electrical stress in which the oil is oxidised acid and sludge are produced. Recent experience shows that some oil age faster in service than others in a similar condition

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[toggle title=”Vibro-acoustic techniques to diagnose power transformers”]

(Victor Sokolov; Valery Rusov; C. Bartoletti, M. Desiderio, D. Di Carlo, G. Fazio, F. Muzi , G. Sacerdoti, F. Salvatori)

The presented paper is certainly timely in today’s needs in efficient On-Line continuous monitoring technique for Power Transformers. This paper contributes significantly to the condition assessment techniquesbased on vibro-acoustic procedures

The authors have done an excellent job of experimental tests in laboratory and directly in the field on transformers in normal operating conditions. They have studied a lot of related factors and suggested monitoring and diagnostic system including an elegant mathematical model allowing to relate vibrations to the main transformer anomalies

The paper raises a series of questions, which are very interesting, and we would like to comment on some of them and share some experiences with utilizing the vibro-acoustic techniques for the transformer condition assessment.

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