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Energies
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6th International Colloquium "Transformer Research and Asset Management"
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6th International Colloquium "Transformer Research and Asset Management"

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

Deadline for manuscript submissions: closed (2 June 2024) | Viewed by 10502

Special Issue Editors

Dr. Bojan Trkulja

E-Mail Website
Guest Editor
Department of Electrical Engineering Fundamentals and Measurements, University of Zagreb, 10000 Zagreb, Croatia
Interests: computational electromagnetics; FEM; BEM; multiphysics; transformers
Dr. Žarko Janić

E-Mail Website
Guest Editor
Končar Power Transformers, A joint Venture of Siemens Energy and Končar, 10090 Zagreb, Croatia
Interests: electromagnetics; FEM; optimization; power efficiency; Lean
Dr. Bruno Jurišić

E-Mail Website
Guest Editor
KONČAR - Electrical Engineering Institute Ltd., BU Laboratory Center, Transformers Department, 10000 Zagreb, Croatia
Interests: transformers, transients, EMTP, modelling, measurements, FEM, electromagnetics
Dr. Tomislav Župan

E-Mail Website
Guest Editor
KONČAR - Electrical Engineering Institute Ltd., BU Laboratory Center, Transformers Department, 10000 Zagreb, Croatia
Interests: numerical modelling; electromagnetics; FEM; multiphysics; insulation, transients; transformers; measurements

Special Issue Information

Dear Colleagues,

Transformers are a vital part of the electrical transmission network, without which today's life is unthinkable. A demanding task is the development of transformers that, with minimal maintenance, can work for several decades. The scope of the Special Issue is not limited to the knowledge of the most critical aspects of power and instruments transformers and its components, such as: transformer insulating and magnetic materials, transformers oils, load tap changers, bushings and cooling system, but also includes transformer failures, loading, diagnostic testing, and on-line monitoring.

The theme of this Special Issue is, therefore, all aspects of interest to both manufacturers and power system operators.

Topics of interest for publication include, but are not limited to:

  • Power transformers technologies;
  • Instrument transformers technologies;
  • Numerical modelling in transformer design;
  • Properties and behaviours of insulating and magnetic materials and components;
  • Digitalization and smart-grid;
  • Transformer in-service experience;
  • Transformer failures, diagnostics;
  • Transformer monitoring, asset management and resilience.

Dr. Bojan Trkulja
Dr. Žarko Janić
Dr. Bruno Jurišić
Dr. Tomislav Župan
Guest Editors

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
  • instrument transformers
  • modelling
  • smart-grid
  • insulating and magnetic materials
  • diagnostics
  • failures

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Further information on MDPI's Special Issue policies can be found here.

Published Papers (6 papers)

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Research

12 pages, 3773 KiB  
Article
Experimental Study of Clamping Pressure during Step Loading of Power Transformer with and without Prior Energisation
by Inge Madshaven, Henrik Enoksen, Lars E. Lundgaard, Stefan Jaufer, Christoph Krause, Borut Prašnikar and Asgeir Mjelve
Energies 2024, 17(12), 2898; https://doi.org/10.3390/en17122898 - 13 Jun 2024
Cited by 1 | Viewed by 1256
Abstract
The electrification of society, increasing renewable energy sources and mobility charging lead to new loading patterns for power transformers. Dynamic load conditions induce enhanced mechanical stress on the transformers’ windings, potentially causing degradation of the solid insulation over time and compromising the transformer’s [...] Read more.
The electrification of society, increasing renewable energy sources and mobility charging lead to new loading patterns for power transformers. Dynamic load conditions induce enhanced mechanical stress on the transformers’ windings, potentially causing degradation of the solid insulation over time and compromising the transformer’s short-circuit withstand capability. Thermal expansion of the windings, caused by losses in the copper conductors, occurring as the transformer is loaded, increases the stress. Conversely, magnetic losses in the core and tie plate expansion contribute to a reduction in stress. This paper presents the effect of step changes in core losses and copper losses by on-line measurements of the clamping pressure, to better understand the mechanical stresses acting upon the solid insulation cellulose materials. Energisation is found to decrease the clamping pressure following warming up of the transformer, and loading the transformer increased the pressure as the windings increased in temperature. The converse effect was found when unloading and de-energising. The on-line monitoring system provides a new and important step towards ensuring the short-circuit performance of power transformers. Full article
(This article belongs to the Special Issue 6th International Colloquium "Transformer Research and Asset Management")
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14 pages, 1585 KiB  
Article
A Combined Computational Fluid Dynamics and Thermal–Hydraulic Modeling Approach for Improving the Thermal Performance of Corrugated Tank Transformers: A Comparative Study
by Chunping Wang, Qingjun Sun, Ali Al-Abadi and Wei Wu
Energies 2024, 17(8), 1802; https://doi.org/10.3390/en17081802 - 9 Apr 2024
Cited by 1 | Viewed by 1752
Abstract
In this study, we present a complete analysis of the thermal behavior of an oil-filled distribution transformer using two different approaches: numerically, by applying computational fluid dynamics (CFD) simulations; and analytically, by using thermal–hydraulic modelling (THM). The THM method becomes challenging when the [...] Read more.
In this study, we present a complete analysis of the thermal behavior of an oil-filled distribution transformer using two different approaches: numerically, by applying computational fluid dynamics (CFD) simulations; and analytically, by using thermal–hydraulic modelling (THM). The THM method becomes challenging when the corrugated transformer tank wall structures are complex, and therefore CFD simulations are required to provide in-depth details of the winding oil thermal–hydraulic behavior and to generate parameters for improving the THM calculation. The numerical and analytical thermal performance results were then compared with heat-run measurements of a case study transformer and the accuracy of both approaches on different thermal performance parameters was validated. This study has certain reference value for improving the thermal performance and operation efficiency of distribution transformers, and eventually aims to provide engineers with an effective tool to design the most efficient and reliable distribution transformers with corrugated tank walls for various applications. Full article
(This article belongs to the Special Issue 6th International Colloquium "Transformer Research and Asset Management")
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14 pages, 5991 KiB  
Article
Test Methods for Validating Inductive Transformer Performance during Cable Discharge: Main Principles, Parameters and Testing Procedures
by Andrea Grđan, Igor Žiger, Zlatko Hanić, Imre Tannemaat, Ralf Huth and Ivan Novko
Energies 2024, 17(4), 799; https://doi.org/10.3390/en17040799 - 7 Feb 2024
Viewed by 1289
Abstract
High voltage connections will discharge through inductive voltage and combined transformers when they are switched off. In the past, there was a wide margin between the required capabilities and the actual capabilities of these components. Nowadays, however, this aspect is becoming more prominent [...] Read more.
High voltage connections will discharge through inductive voltage and combined transformers when they are switched off. In the past, there was a wide margin between the required capabilities and the actual capabilities of these components. Nowadays, however, this aspect is becoming more prominent due to a higher penetration by cable systems into the grid. Currently, none of the relevant international standards contain any definitions or requirements for line discharge, nor test methods which would validate the ability of the transformer to discharge a line of certain capacitance at a certain voltage. This is why the aim of this paper is to provide a foundation for how to specify, assess and verify the capacitive discharge performance of instrument transformers. This paper will present the basic theory, influencing parameters, multiple test sequences and acceptance criteria for cable discharge. It is clear that capacitive discharges present both thermal and mechanical stress to the unit, which is why this paper will detail how to guarantee both aspects. The idea is that this paper serves as a literal blueprint which can then be transferred to the relevant clauses in upcoming international standards. All conclusions within this paper are achieved through calculations and testing on actual 123 kV inductive voltage transformers and combined units. Full article
(This article belongs to the Special Issue 6th International Colloquium "Transformer Research and Asset Management")
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15 pages, 23011 KiB  
Article
Comparison of Empty and Oil-Filled Transformer Tank Mode Shapes Using Experimental and FEM Modal Analysis
by Karlo Petrović, Danilo Dobrić, Ivan Gotić and Tomislav Župan
Energies 2024, 17(3), 589; https://doi.org/10.3390/en17030589 - 25 Jan 2024
Viewed by 1579
Abstract
In this paper, the mode shapes of an empty and oil-filled transformer experimental model tank are obtained using 3D finite element method (FEM) modal analysis. For verification of the FEM analysis results, experimental modal analysis (EMA) is carried out in both cases using [...] Read more.
In this paper, the mode shapes of an empty and oil-filled transformer experimental model tank are obtained using 3D finite element method (FEM) modal analysis. For verification of the FEM analysis results, experimental modal analysis (EMA) is carried out in both cases using appropriate impact hammers and accelerometers. Simulated and measured results are visualized and compared for mode shapes in a frequency range of interest for both empty and oil-filled tanks. In order to avoid overly stiff FEM models of transformer tanks, the welded joint modeling technique is presented and analyzed in detail. For an oil-filled tank, the most accurate results are calculated in the model where the welded joint is modeled as half the tank wall’s thickness. In that case, the mean absolute error for the given ten-mode shapes is 1.7 Hz. Also, mesh sensitivity analysis is performed. It is concluded that a 10 mm maximum element size is an optimal solid (3D) mesh. However, shell mesh can be used to reduce computing requirements. Full article
(This article belongs to the Special Issue 6th International Colloquium "Transformer Research and Asset Management")
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Graphical abstract

14 pages, 30436 KiB  
Article
Theoretical Study of Liquid Flow and Temperature Distribution in OF-Cooled Power Transformers
by Uroš Plaznik, Blaž Breznik and Borut Prašnikar
Energies 2024, 17(3), 571; https://doi.org/10.3390/en17030571 - 24 Jan 2024
Cited by 1 | Viewed by 1374
Abstract
The objective of the paper is to analyse the effects of various geometrical and operating parameters on the liquid flow distribution in OF-cooled power transformers. Our investigation includes two cases: one with a simplified winding geometry and another that closely resembles the actual [...] Read more.
The objective of the paper is to analyse the effects of various geometrical and operating parameters on the liquid flow distribution in OF-cooled power transformers. Our investigation includes two cases: one with a simplified winding geometry and another that closely resembles the actual winding geometry. The analyses were carried out using computational fluid dynamics (CFD) and custom, internally developed thermo-hydraulic models. Our findings confirm that buoyancy forces rather than the pump drive the liquid flow within the windings of an OF-cooled power transformer. The results also show that the liquid flow distribution, which is influenced by the winding geometrical properties and liquid properties, has a significant impact on the hot-spot temperatures of the windings. The comparison between the results of the CFD simulations and the results of the simple model demonstrates a high level of agreement in calculating both the mass flow rates and temperatures. Full article
(This article belongs to the Special Issue 6th International Colloquium "Transformer Research and Asset Management")
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15 pages, 5167 KiB  
Article
Internal Arc Performance of Instrument Transformers Filled with Different Dielectric Liquids
by Ivan Mihoković, Anton Rački, Igor Žiger and Eduard Plavec
Energies 2024, 17(2), 493; https://doi.org/10.3390/en17020493 - 19 Jan 2024
Viewed by 1838
Abstract
Internal arc testing is still a controversial topic in the instrument transformer world. The main reason for that is the fact that even a fully successful test guarantees only a certain degree of transformer safety. Furthermore, the test does not cover a plethora [...] Read more.
Internal arc testing is still a controversial topic in the instrument transformer world. The main reason for that is the fact that even a fully successful test guarantees only a certain degree of transformer safety. Furthermore, the test does not cover a plethora of operational fault scenarios and has requirements which are not defined clearly enough. In addition, there are very few data available in the literature on the internal arc performance of alternative, biodegradable dielectric liquids. Some liquids (such as natural and synthetic esters) do inherently come with higher flash and fire points compared to conventional mineral oil, but there is insufficient test experience to corroborate the influence this high fire point has on the actual operation. Specifically, to the authors’ knowledge, internal arc tests on instrument transformers were never performed with biodegradable dielectric liquids, making the contributions of this paper a true world premiere. In short, this paper is intended to augment the existing standards, thus providing additional insight into how to test internal arc performance, what to look out for and what level of performance to expect, which is of broad interest to researchers, utility engineers and public alike. Full article
(This article belongs to the Special Issue 6th International Colloquium "Transformer Research and Asset Management")
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