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Energies
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Experimental and Numerical Analysis of Thermal Ageing in Power Transformers
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Experimental and Numerical Analysis of Thermal Ageing in Power Transformers

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "F: Electrical Engineering".

Deadline for manuscript submissions: closed (31 December 2021) | Viewed by 19118

Special Issue Editor

Dr. Inmaculada Fernandez

E-Mail Website
Guest Editor
Department of Electrical and Energy Engineering, University of Cantabria, Santander, 39005 Cantabria, Spain
Interests: thermal ageing; biodegradable oils; power transformers; cooling behaviour; oil-paper insulation

Special Issue Information

Dear Colleagues,

The Guest Editor is inviting submissions to a Special Issue of Energies on the subject area of “Experimental and Numerical Analysis of Thermal Ageing in Power Transformers”. Due to continuous exposure to thermal, mechanical and electrical stresses, the oil-paper insulation system deteriorates causing the reduction of the overall useful life of transformers. Although many techniques have been developed for the measurement of insulation degradation, continued analysis of transformer insulation is required, using existing and new methods to provide useful tools that support decision-making in power systems. Moreover, the introduction of new liquids as natural and synthetic esters demands the study of the feasibility of the proposed methods until now for mineral oil.

This Special Issue will deal with different techniques for the assessment of insulation degradation in power transformers. Topics of interest for publication include, but are not limited to the following:

  • Power transformer
  • Insulation
  • Thermal stress
  • Moisture variation
  • Cooling performance
  • Breakdown voltage
  • Partial discharges
  • Dissipation factor
  • Dielectric permittivity
  • Resistivity
  • Viscosity
  • Thermal conductivity
  • Flash and fire point
  • Natural esters
  • Synthetic esters
  • Mineral oil
  • Acidity
  • Degree of polymerization
  • Tensile strength
  • Fourier transform infrared spectroscopy (FTIR)
  • Dissolved gases
  • Scanning electron microscope (SEM)
  • Refractive index (RI)
  • Frequency domain spectroscopy (FDS)
  • Computational fluid dynamics (CFD) modelling

Dr. Inmaculada Fernandez
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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Published Papers (5 papers)

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Editorial

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4 pages, 199 KiB  
Editorial
The Need for Experimental and Numerical Analyses of Thermal Ageing in Power Transformers
by Inmaculada Fernández
Energies 2022, 15(17), 6393; https://doi.org/10.3390/en15176393 - 1 Sep 2022
Cited by 3 | Viewed by 1388
Abstract
Most power transformers are oil-immersed transformers for which its insulation system consists of oil and cellulosic solid. The insulation liquid impregnates the solid-covering air spaces, which improves the efficiency of the insulation system. Not only does the oil ensure electrical insulation but it [...] Read more.
Most power transformers are oil-immersed transformers for which its insulation system consists of oil and cellulosic solid. The insulation liquid impregnates the solid-covering air spaces, which improves the efficiency of the insulation system. Not only does the oil ensure electrical insulation but it also works as coolants transferring the heat generated during transformer operation to the exterior of the transformer. Throughout normal operation conditions, transformers experience multiple stresses that degrade their insulation. Since the lifetime of oil-immersed transformers is defined mainly by the state of the insulation paper, it is critical to understand the behavior and degradation mechanisms of new insulation systems that try to overcome the drawbacks of mineral oil as well as to improve power transformer performances. The current increased prevalence of the nonlinear loads additionally stresses power transformers, which generates their premature ageing or even failure. Consequently, new materials and assessment methods are required to guarantee the suitable management of power transformer populations. In this Special Issue “Experimental and Numerical Analysis of Thermal Ageing in Power Transformers”, four papers have been published. The guest editor also describes briefly some challenges involved beyond the coverage of this Special Issue. Full article
(This article belongs to the Special Issue Experimental and Numerical Analysis of Thermal Ageing in Power Transformers)

Research

Jump to: Editorial

13 pages, 2231 KiB  
Article
Influence of Nanoparticles on the Degradation Processes of Ester-Based Transformer Insulation Systems
by Daniel Pérez-Rosa, Belén García and Juan Carlos Burgos
Energies 2022, 15(4), 1520; https://doi.org/10.3390/en15041520 - 18 Feb 2022
Cited by 6 | Viewed by 1819
Abstract
The use of nanofluids as dielectric liquids for transformer insulation has been widely investigated during the last decade. A number of authors have performed extensive studies on liquids produced from different types of nanoparticles and base fluids, providing evidence of their good dielectric [...] Read more.
The use of nanofluids as dielectric liquids for transformer insulation has been widely investigated during the last decade. A number of authors have performed extensive studies on liquids produced from different types of nanoparticles and base fluids, providing evidence of their good dielectric properties. Nevertheless, nanodielectric fluids are still at the research stage, and they are far from being a solution that can be applied to real transformers. One of the aspects that might be clarified is their compatibility with the rest of the materials present in the transformer and their behavior throughout the life of the equipment. This paper studies the aging process of cellulose impregnated with an ester-based nanofluid and compares it with the process that takes place when the impregnation liquid is a natural ester. Accelerated aging experiments were performed, and physical and chemical characterization of the process with several analytical techniques was carried out. The mechanical degradation of the cellulose was studied in terms of tensile strength, and the evolution of moisture in the paper and oil was monitored throughout the aging process. The study was completed with FTIR and XPS tests aimed at studying the chemical changes of the materials during the aging process. The experimental results suggest that the degradation rate of the cellulose is not significantly affected by the presence of nanoparticles. However, the XPS study revealed that the chemical reactions involved in the degradation processes of both types of insulation might differ. Several mechanisms are proposed in this work. Full article
(This article belongs to the Special Issue Experimental and Numerical Analysis of Thermal Ageing in Power Transformers)
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18 pages, 3336 KiB  
Article
Compatibility Study of Silicone Rubber and Mineral Oil
by Smitha Karambar and Stefan Tenbohlen
Energies 2021, 14(18), 5899; https://doi.org/10.3390/en14185899 - 17 Sep 2021
Cited by 13 | Viewed by 7349
Abstract
In this study, three types of silicone rubbers, namely, insulative silicone rubber, conductive silicone rubber and silicone rubber with conductive as well as insulative layers are investigated for their compatibility with mineral oil. Mineral oil with different silicone rubber samples is thermally aged [...] Read more.
In this study, three types of silicone rubbers, namely, insulative silicone rubber, conductive silicone rubber and silicone rubber with conductive as well as insulative layers are investigated for their compatibility with mineral oil. Mineral oil with different silicone rubber samples is thermally aged at 130 °C for 360 h, 720 h and 1080 h and at 23 °C, 98 °C and 130 °C for 360 h. At the end of each ageing interval, mineral oil and oil-impregnated silicone rubbers are investigated for their dielectric properties. Aged mineral oil samples are investigated for their moisture content, breakdown voltage, colour number, dissolved gases and total acid number, whereas solid insulation samples are investigated for their moisture content. Additionally, pressboard samples in mineral oil and mineral oil without any solid insulation materials are also aged under the same conditions and are investigated for their dielectric properties. From the obtained results, it can be assessed that the presence of carbon particles in conductive silicone rubber negatively impacts the dielectric properties of mineral oil. Among the investigated silicone rubbers, the insulative silicone rubber exhibits good compatibility with mineral oil and a strong potential for being used in mineral oil. Full article
(This article belongs to the Special Issue Experimental and Numerical Analysis of Thermal Ageing in Power Transformers)
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14 pages, 1728 KiB  
Article
The Analysis of Power Transformer Population Working in Different Operating Conditions with the Use of Health Index
by Patryk Bohatyrewicz and Andrzej Mrozik
Energies 2021, 14(16), 5213; https://doi.org/10.3390/en14165213 - 23 Aug 2021
Cited by 10 | Viewed by 2520
Abstract
The management of the power transformer population is a complex process, as the grid companies operate thousands of devices. For this issue, the health index method can be applied to facilitate asset management. The algorithm can be used not only in the technical [...] Read more.
The management of the power transformer population is a complex process, as the grid companies operate thousands of devices. For this issue, the health index method can be applied to facilitate asset management. The algorithm can be used not only in the technical assessment of the individual units, but also to determine the relationships within the whole population. In this paper, the presented health index method consists of periodic oil diagnostics, including the physicochemical properties, dissolved gas analysis, and furfural content, and further assessment in terms of the criticality of the device to determine the technical condition. The algorithm was specifically designed to reflect even the smallest changes of the input parameters in the final score. The performance of the health index was tested on 620 oil analyses from 220 transformers divided into four subpopulations based on the service conditions. The results have proven to be largely dependent on the criticality level and the operating conditions of the device. The analysis of the study group has shown the influence of corrective maintenance on the mean value of the health index score. Full article
(This article belongs to the Special Issue Experimental and Numerical Analysis of Thermal Ageing in Power Transformers)
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28 pages, 8300 KiB  
Article
Thermally Accelerated Aging of Insulation Paper for Transformers with Different Insulating Liquids
by Tobias Münster, Peter Werle, Kai Hämel and Jörg Preusel
Energies 2021, 14(11), 3036; https://doi.org/10.3390/en14113036 - 24 May 2021
Cited by 24 | Viewed by 4974
Abstract
The article presents issues related to the aging behavior of oil-paper insulations in transformers using different oil- and ester-based insulating fluids. Despite numerous conducted studies on the subject of oil-paper aging, the use of new insulating fluids is creating open questions. In addition, [...] Read more.
The article presents issues related to the aging behavior of oil-paper insulations in transformers using different oil- and ester-based insulating fluids. Despite numerous conducted studies on the subject of oil-paper aging, the use of new insulating fluids is creating open questions. In addition, new liquids such as synthetic and natural esters, as well as oil of the newest generation, are being used. Furthermore, there is still little research on the formation of aging markers with this form of the dielectric. For this reason, in this contribution, oil-paper insulations with mineral oil-based insulating fluids, natural and synthetic esters, as well as oil from natural gas, are aged thermally accelerated at 130 °C over a duration of 15 weeks, by considering two cases of free-breathing and hermetically sealed transformers. Therefore, various aging markers are investigated to allow a condition assessment. The results show that differences exist between the fluids and design of the transformer, as in the aging rate of the paper and the formation of aging markers in the insulating liquid such as acids. These findings can be used to improve asset management strategies by a more precise determination of the aging state depending on the transformer type as well as the type of insulating fluid. Full article
(This article belongs to the Special Issue Experimental and Numerical Analysis of Thermal Ageing in Power Transformers)
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