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Design and Optimization of Power Transformer Diagnostics II

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

Deadline for manuscript submissions: 19 June 2024 | Viewed by 5920

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Special Issue Editor

Prof. Dr. Zbigniew Nadolny

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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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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.

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Keywords

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

Related Special Issue

Design and Optimization of Power Transformer Diagnostics in Energies (18 articles)

Published Papers (7 papers)

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Research

17 pages, 4651 KiB

Open AccessArticle

Thermal Ageing of Dry Cellulose Paper Impregnated with Different Insulating Liquids—Comparative Studies of Materials Properties

by Piotr Przybylek

Energies 2024, 17(4), 784; https://doi.org/10.3390/en17040784 - 6 Feb 2024

Cited by 1 | Viewed by 649

Abstract

Natural and synthetic esters are increasingly being chosen instead of mineral oil for environmental and fire safety reasons. However, their use in power transformers is limited due to insufficiently well-understood ageing processes affecting their properties and the properties of cellulosic materials impregnated with them. The research results presented in many scientific papers prove that the use of esters slows the ageing process of cellulosic materials. This article presents the results of research aimed at answering the question of whether the effect of slowing the ageing process will also occur in the case of insulation with very low initial moisture. The answer to this question will allow us to better understand the role of water in the ageing process of the transformer’s insulation system. The thermal ageing process was carried out at a temperature of 150 °C in closed systems. The degree of cellulose polymerisation was taken as a measure of the degree of paper ageing. Great attention was paid to measuring the water content in both paper and electro-insulating liquids at various stages of their ageing. Furthermore, measurements of the properties of electro-insulating liquids were made, which are considered markers of ageing. The test results obtained indicate that in the case of a dry insulation system, corresponding to the initial moisture of the new units, the type of liquid used to impregnate the cellulosic material does not significantly affect its depolymerisation process. However, in the case of paper impregnated with natural esters, a lower dynamic of moisture increase in insulation was observed. Full article

(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics II)

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18 pages, 7069 KiB

Open AccessArticle

Impact of Electrode Distance in a Quasi-Uniform Model Electrode System on Lightning Impulse Breakdown Voltage in Various Insulating Liquids

by Wiktor Kunikowski, Pawel Rozga, Bartlomiej Pasternak, Jakub Staniewski, Filip Stuchala and Konrad Strzelecki

Energies 2024, 17(4), 782; https://doi.org/10.3390/en17040782 - 6 Feb 2024

Viewed by 589

Abstract

This study presents findings on the influence of gap length distance on the lightning impulse breakdown voltage of three dielectric liquids of different chemical origins. The liquids were tested in a model electrode system with a quasi-uniform electric field distribution and a pressboard plate placed on the grounded electrode. The experimental studies were supported using calculations and simulations to show the individual relationships between the lightning impulse breakdown voltage and gap distance, which represent the so-called volume effect of the most stressed liquid. The results of the experiment, which involved four considered gap distances of 2, 4, 6, and 8 mm, show that a dynamic increase in lightning impulse breakdown voltage with an increase in gap distance is associated with mineral oil and bio-based hydrocarbons. However, similar trends were not observed for synthetic ester. Calculations that allowed us to assess the impact of gap length distance on lightning impulse breakdown voltage support the observations from the experimental studies. The curves obtained in this field can be considered in the process of designing insulating systems for transformers. Full article

(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics II)

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21 pages, 2266 KiB

Open AccessArticle

Application of Under-Impedance Criterion to Protect against Effects of Phase-to-Phase Short Circuits in Medium-Voltage Networks

by Beata Zięba, Bartosz Olejnik and Iwona Grobelna

Energies 2024, 17(2), 505; https://doi.org/10.3390/en17020505 - 20 Jan 2024

Viewed by 535

Abstract

Common overcurrent criteria used to detect phase-to-phase short circuits in medium-voltage (MV) networks in some cases do not bring the expected results. In particular, this applies to instantaneous overcurrent protections in lines with variable ranges and lines leading to local power plants (LPP), which generate a short-circuit current slightly greater than the rated current. When using overcurrent protections, there are some problems with ensuring the appropriate sensitivity and selectivity. This article proposes a protection based on impedance measurement against the effects of phase-to-phase short circuits in MV lines. The protection can be used at switchgears and also at protection points (PP) located deep in the network. The under-impedance criterion has a range independent of the value of the short-circuit current, and it can be alternative or complement to classic overcurrent protection. The introduction of these criteria allows the protection range to be independent of the type of short circuit and the short-circuit power on the busbar, and to determine this range more precisely. The under-impedance protection is particularly useful in conditions of a growing number of energy sources deep inside the networks and its automation. The main idea was to develop a uncomplicated characteristic that would ensure the possibility of setting the under-impedance protection by people who are not specialists in the field of distance protections. The characteristics have been optimally developed both in terms of the area of detected impedances and easy implementation, operation, and configuration. Full article

(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics II)

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14 pages, 6572 KiB

Open AccessArticle

Method of Reducing the Effects of Repeated Ignition during Earth Faults in Compensated Medium Voltage Networks

by Jerzy Andruszkiewicz, Józef Lorenc, Bartosz Olejnik, Agnieszka Weychan and Bogdan Staszak

Energies 2024, 17(1), 93; https://doi.org/10.3390/en17010093 - 23 Dec 2023

Viewed by 648

Abstract

The article presents the results of research in the field of limiting the effects of overvoltages and improving the conditions for the self-extinguishing of transient faults in medium voltage networks with earth fault current compensation. The aim of the research was to estimate the level of overvoltages generated by an earth fault during re-ignition of the electric arc and to assess the possibility of reducing them by increasing the attenuation of the earth fault circuit. The results of the conducted tests show that to increase the attenuation, which ensures a significant effect of limiting such overvoltages, it is enough to change the way of operation of the devices forcing an additional active component of the earth fault current (AWSCz/ACFA). In Poland, such devices are commonly used to improve the effectiveness of earth fault protection. It was also found that the proposed solution enables accurate tuning of the Petersen coil in networks with natural asymmetry of earth capacitances. Therefore, changes in the operation of AWSCz/ACFA devices may have a beneficial effect on the limiting the effects of repeated ignitions during earth faults and, at the same time, enable the accurate tuning of the Petersen coil and increase its ability to extinguish arc-fed faults. Research and theoretical analysis of the issue were carried out on the basis of data characterizing the parameters of the earth fault circuits of the real 15 kV network. Full article

(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics II)

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17 pages, 3231 KiB

Open AccessArticle

The Tools and Parameters to Consider in the Design of Power Transformer Cooling Systems

by Przemyslaw Goscinski, Zbigniew Nadolny, Ryszard Nawrowski and Tomasz Boczar

Energies 2023, 16(24), 8000; https://doi.org/10.3390/en16248000 - 10 Dec 2023

Viewed by 955

Abstract

Transformers are the most important elements of electric power systems. Many conditions must be met for power transformers to work properly. One of them is a low operating temperature. This condition will be met if the transformer cooling system is properly designed. One of the components of a cooling system is insulating liquid. The heat transfer coefficient α of liquid determines its ability to cool the transformer. The higher its value, the more effectively the liquid transfers heat to the environment. This article describes the influence of the position of the heat source, which is usually in the windings of the transformer, on the coefficient α value of the insulating liquid. The vertical and horizontal positions of the heat source were analyzed. The coefficient α was analyzed at different points of the heat source. The tests were carried out for mineral oil and various esters. Heat transfer coefficient measurements were carried out for various surface heat loads of the heat source. It has been proven that, in the case of a horizontal heat source, the coefficient α has a value several dozen percent higher than in the case of a vertical source. It has been proven that the coefficient α has different values in different places of the heat source. Regardless of the location, the highest value of the coefficient α occurred in the lower part of the heat source. Full article

(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics II)

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12 pages, 4427 KiB

Open AccessArticle

Determination of Mineral Oil Concentration in the Mixture with Synthetic Ester Using Near-Infrared Spectroscopy

by Piotr Przybylek

Energies 2023, 16(17), 6381; https://doi.org/10.3390/en16176381 - 3 Sep 2023

Cited by 1 | Viewed by 922

Abstract

Currently, synthetic ester is gaining a bigger share in the market. This type of insulating liquid is used both in new and operated transformers filled with mineral oil. In the case of transformers in operation, the synthetic ester is used in the retrofilling procedure, drying the cellulose insulation, or as a blend with oil, the properties of which are better than those of base liquids. In all these three cases, we are dealing with a mixture of synthetic ester and mineral oil. The concentration of both of these liquids in the mixture has a significant impact on its properties; therefore, methods are necessary to determine the content of individual mixture components. The article presents a method for determining the concentration of mineral oil in a mixture with synthetic ester using near-infrared spectroscopy. Based on the conducted tests, an absorption band was determined that can be used for this purpose. This band is centered at 2126 nm. The determined dependence of the absorbance on mineral oil concentration in the mixture with synthetic ester confirmed the linear nature of this relationship. The conducted research confirmed the possibility of using the method based on near-infrared spectroscopy to determine the concentration of individual components of a mixture of mineral oil and synthetic ester. The proposed method can be used both for a mixture of new liquids and mixtures of new synthetic ester with mineral oils of different degrees of aging. The method of determining the concentration of mineral oil in a mixture with synthetic ester based on near-infrared spectroscopy is new and is characterized by a higher accuracy in relation to the methods previously described in the literature. Full article

(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics II)

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11 pages, 1730 KiB

Open AccessArticle

The Use of Methanol Vapour for Effective Drying of Cellulose Insulation

by Piotr Przybylek and Jaroslaw Gielniak

Energies 2023, 16(11), 4465; https://doi.org/10.3390/en16114465 - 31 May 2023

Cited by 1 | Viewed by 1015

Abstract

The paper deals with a new method of drying cellulose insulation, which uses methanol vapour present in nitrogen as a drying medium. Compared to the insulation drying methods currently used in the industry, the method presented in the article has the following advantages: there is no cellulose depolymerization because there is no need to heat the insulation, there is no need to use large-size and energy-intensive dryers because the whole process takes place in the tank of the transformer. Important parameters of the drying process, such as methanol concentration in the nitrogen, flow rate, and process duration, were determined in four separate experiments. For the purposes of these experiments, a special system was constructed to control and measure the flow of drying medium. Controlling the flow rate of the carrier gas (nitrogen) made it possible to obtain different concentrations of methanol in nitrogen. Such values of concentration and flow rate were determined that allow drying of pressboard and paper in less than 144 h to a level lower than 1%. Full article

(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics II)

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