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Design and Optimization of Power Transformer Diagnostics: 3rd Edition
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Design and Optimization of Power Transformer Diagnostics: 3rd Edition

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

Deadline for manuscript submissions: 20 August 2025 | Viewed by 3345

Special Issue Editor

Prof. Dr. Zbigniew Nadolny

E-Mail Website
Guest Editor
Department of High Voltage and Electrotechnical Materials, Faculty of Environmental Engineering and Energy, Institute of Electrical Power Engineering, Poznan University of Technology, 60-965 Poznan, Poland
Interests: high voltage; insulation materials; transformer; electric and magnetic fields; insulation oil; heat transfer; thermal properties; thermal conductivity
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Special Issue Information

Dear Colleagues,

Power transformers play a significant role in the electric power system. All over the world, there is a tendency for transformers to work as long as possible, far beyond their technical lifetime. This is certainly due to the high price of the new units. It is not surprising, therefore, that many offline diagnostic methods have developed in recent decades. The use of these methods is associated with the frequent shutdown of transformers from the system. This is an undesirable situation by system operators because it causes a decrease in system stability. For this reason, an important aspect is skillful design and optimization of diagnostic methods of transformers in offline mode and the development of diagnostic methods that can be used online, which is what this Special Issue is devoted to.

Prof. Dr. Zbigniew Nadolny
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.

Keywords

  • power transformers
  • diagnostic methods
  • offline, online methods
  • transformer insulation system
  • transformer tap changer

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Related Special Issue

Published Papers (4 papers)

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Research

19 pages, 10300 KiB  
Article
Research on Simulation Analysis and Joint Diagnosis Algorithm of Transformer Core-Loosening Faults Based on Vibration Characteristics
by Chen Cao, Zheng Li, Jialin Wang, Jiayu Zhang, Ying Li and Qingli Wang
Energies 2025, 18(4), 914; https://doi.org/10.3390/en18040914 - 13 Feb 2025
Cited by 1 | Viewed by 664
Abstract
The existing methods for transformer core-loosening fault diagnosis primarily focus on fundamental frequency analysis, neglecting higher-frequency components, which limits early detection accuracy. This study proposes a comprehensive approach integrating full-band vibration analysis, including high-order harmonics, to enhance diagnostic precision. A theoretical model coupling [...] Read more.
The existing methods for transformer core-loosening fault diagnosis primarily focus on fundamental frequency analysis, neglecting higher-frequency components, which limits early detection accuracy. This study proposes a comprehensive approach integrating full-band vibration analysis, including high-order harmonics, to enhance diagnostic precision. A theoretical model coupling magnetostriction and thermodynamics was developed, combined with empirical mode decomposition (EMD) and Pearson’s correlation coefficient for fault characterization. A 10 kV transformer core vibration test platform was constructed, capturing signals under normal, partially loose, and completely loose states. The simulation results aligned with the experimental data, showing vibration accelerations of 0.01 m/s2 (Phase A) and 0.023 m/s2 (Phase B). A multi-physics coupling model incorporating Young’s modulus variations simulated core loosening, revealing increased high-frequency components (up to 1000 Hz) and vibration amplitudes (0.2757 m/s2 for complete loosening). The joint EMD–Pearson method quantified fault severity, yielding correlation values of 0.0007 (normal), 0.0044 (partial loosening), and 0.0116 (complete loosening), demonstrating a clear positive correlation with fault progression. Experimental validation confirmed the model’s reliability, with the simulations matching the test results. This approach addresses the limitations of traditional methods by incorporating high-frequency analysis and multi-physics modeling, significantly improving early fault detection accuracy and providing a quantifiable diagnostic framework for transformer core health monitoring. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics: 3rd Edition)
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13 pages, 3315 KiB  
Article
A Particularly Dangerous Case of the Bubble Effect in Transformers That Appeared in a Large Mass of Pressboard Heated by Mineral Oil
by Hubert Moranda and Hanna Moscicka-Grzesiak
Energies 2025, 18(2), 380; https://doi.org/10.3390/en18020380 - 17 Jan 2025
Viewed by 589
Abstract
The topic concerns the so-far-unknown mechanism of the bubble effect (b.e.) in a large mass of moist cellulose heated with mineral oil. The well-known b.e. occurs in the Hot Spot area, i.e., in the place where the hot metal of the windings is [...] Read more.
The topic concerns the so-far-unknown mechanism of the bubble effect (b.e.) in a large mass of moist cellulose heated with mineral oil. The well-known b.e. occurs in the Hot Spot area, i.e., in the place where the hot metal of the windings is in contact with the insulation paper. The authors first showed that cyclic heating of a windings model causes the drying of both the insulation paper and pressboard, but the paper dries faster. For this reason, the bubble effect inception temperature can be lower in the pressboard than in the paper. Next, the authors showed that the bubble effect in the pressboard is very intense and causes a sudden and very large increase in pressure in the tank. Moreover, if the tank seal is suddenly damaged because of this, the number and volume of bubbles will increase dramatically. Next, the influence of the mass of cellulose to the mass of oil ratio on the pressure increase dynamics was tested. This experiment showed that the greater the mass of cellulose to the mass of oil, the greater the increase in pressure in the test chamber. The authors also determined that the characteristics of the bubble effect initiation temperature in the pressboard samples, depending on their moisture content, ranged from 2.0 to 4.8%. The experiment showed that the b.e. in the pressboard proceeds in the same way as in paper insulation. The research results showed that, in addition to the well-known b.e. in the winding paper in the Hot Spot area, the b.e. can occur in a large mass of pressboard cellulose, which can be much more dangerous for the transformer. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics: 3rd Edition)
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12 pages, 6313 KiB  
Article
A New Method for Complex Impedance Measurement of Power Transformers via a Continuous Wavelet Transform
by Eduardo Gómez-Luna, John E. Candelo-Becerra and Juan C. Vasquez
Energies 2024, 17(23), 6056; https://doi.org/10.3390/en17236056 - 2 Dec 2024
Viewed by 724
Abstract
The Fourier transform is widely accepted as the time-to-frequency conversion procedure, although it has some limitations. Currently, measurements in the time domain are usually transient (non-periodic waveforms) within a finite window time and discrete (non-continuous) sampled signals. The accuracy of the Fourier transform [...] Read more.
The Fourier transform is widely accepted as the time-to-frequency conversion procedure, although it has some limitations. Currently, measurements in the time domain are usually transient (non-periodic waveforms) within a finite window time and discrete (non-continuous) sampled signals. The accuracy of the Fourier transform decreases as the window time and sampling frequency decrease. This is where the wavelet transform proves to be a valuable tool in this analysis. This paper presents a novel method for estimating the complex electrical impedance of power transformers by analyzing transient electrical signals with the continuous wavelet transform. The great importance of knowing the complex electrical impedance of the transformer is that it allows knowing the state and condition of the internal parts, such as the core and the windings, whose behavior depends on the frequency with which the transformer is fed. The wavelet transform is employed in the proposed method to improve the analysis of the frequency response (FRA), following the same procedure commonly used with the Fourier transform. The proposed method is validated by performing an experimental test on a 28 MVA power transformer. The results show that the new method using the continuous wavelet transform is a power tool that enhances the extraction of the total electrical impedance curve (magnitude–phase) compared to the Fourier transform. This enables real-time frequency response analysis in transformers, facilitating accurate diagnosis. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics: 3rd Edition)
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15 pages, 3388 KiB  
Article
Methanol Equilibrium Curves of Power Transformer Oil–Paper Insulation
by Piotr Przybylek
Energies 2024, 17(21), 5333; https://doi.org/10.3390/en17215333 - 26 Oct 2024
Viewed by 909
Abstract
To eliminate the problem of the aging of cellulose insulation in the manufacturing stage, a new drying method is being developed based on the use of methanol vapors. Previous studies have shown that the complete removal of methanol from the cellulose insulation after [...] Read more.
To eliminate the problem of the aging of cellulose insulation in the manufacturing stage, a new drying method is being developed based on the use of methanol vapors. Previous studies have shown that the complete removal of methanol from the cellulose insulation after the drying process is very difficult. Therefore, it is necessary to check how the remaining methanol after drying affects the properties of both the cellulose materials and mineral oil. To conduct such studies, it is necessary to know the methanol content in oil that can be expected depending on its initial content in the cellulose materials and the temperature of the insulation system. Therefore, the main goal of this work is to develop methanol equilibrium curves for oil–paper insulation. To achieve the assumed goal, three-stage studies were conducted. A gas chromatograph equipped with a flame ionization detector was used in all stages of these studies. The gas partition coefficient between oil and air was determined for a temperature of 70 °C. The key experimental finding was the development of methanol equilibrium curves for oil–paper insulation. Thanks to this achievement, it is possible to estimate the methanol content in cellulose materials and mineral oil depending on the insulation temperature. Such data are necessary, among others, to plan appropriate studies aimed at assessing the impact of methanol content on the dielectric and physicochemical properties of these materials, important from the point of view of the operation of power transformers. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics: 3rd Edition)
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