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Design and Optimization of Power Transformer Diagnostics
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Design and Optimization of Power Transformer Diagnostics

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

Deadline for manuscript submissions: closed (28 February 2023) | Viewed by 30016

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
Special Issues, Collections and Topics in MDPI journals

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

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Keywords

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

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Published Papers (18 papers)

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Editorial

Jump to: Research, Review

7 pages, 208 KiB  
Editorial
Design and Optimization of Power Transformer Diagnostics
by Zbigniew Nadolny
Energies 2023, 16(18), 6466; https://0-doi-org.brum.beds.ac.uk/10.3390/en16186466 - 07 Sep 2023
Cited by 2 | Viewed by 626
Abstract
From year to year, humanity’s dependence on electricity supplies is growing, which affects virtually all areas that improve the comfort of people’s lives [...] Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)

Research

Jump to: Editorial, Review

14 pages, 3013 KiB  
Article
Dielectric Properties and Fire Safety of Mineral Oil and Low-Viscosity Natural Ester Mixtures in Various Concentrations
by Grzegorz Dombek and Jarosław Gielniak
Energies 2023, 16(10), 4195; https://0-doi-org.brum.beds.ac.uk/10.3390/en16104195 - 19 May 2023
Cited by 1 | Viewed by 1178
Abstract
This paper presents the results of testing the electrical and fire properties of mineral oil and low-viscosity natural ester mixtures. Properties such as breakdown voltage, relative permeability, dispersion coefficient, conductivity, flash and burn point, and lower heating values were investigated in different concentrations [...] Read more.
This paper presents the results of testing the electrical and fire properties of mineral oil and low-viscosity natural ester mixtures. Properties such as breakdown voltage, relative permeability, dispersion coefficient, conductivity, flash and burn point, and lower heating values were investigated in different concentrations of mixtures of the two liquids, as well as for the base liquids. To ensure equal humidity levels, the prepared samples of mixtures and base liquids were conditioned under identical climatic conditions, resulting in samples with similar relative humidity (9 ± 3)%. The obtained measurement results for mixtures of the two fluids were related to the values obtained for the base liquids and analyzed in terms of changes in electrical properties and fire safety when used as insulating liquids in transformers. The presented results are useful for supplementing knowledge on the possibilities of using dielectric liquid mixtures in high-voltage power devices, with to the aim of using mixtures as alternatives to mineral oil. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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16 pages, 8277 KiB  
Article
Transformer Winding Fault Classification and Condition Assessment Based on Random Forest Using FRA
by Mehran Tahir and Stefan Tenbohlen
Energies 2023, 16(9), 3714; https://0-doi-org.brum.beds.ac.uk/10.3390/en16093714 - 26 Apr 2023
Cited by 2 | Viewed by 1300
Abstract
At present, the condition assessment of transformer winding based on frequency response analysis (FRA) measurements demands skilled personnel. Despite many research efforts in the last decade, there is still no definitive methodology for the interpretation and condition assessment of transformer winding based on [...] Read more.
At present, the condition assessment of transformer winding based on frequency response analysis (FRA) measurements demands skilled personnel. Despite many research efforts in the last decade, there is still no definitive methodology for the interpretation and condition assessment of transformer winding based on FRA results, and this is a major challenge for the industrial application of the FRA method. To overcome this challenge, this paper proposes a transformer condition assessment (TCA) algorithm, which is based on numerical indices, and a supervised machine learning technique to develop a method for the automatic interpretation of FRA results. For this purpose, random forest (RF) classifiers were developed for the first time to identify the condition of transformer winding and classify different faults in the transformer windings. Mainly, six common states of the transformer were classified in this research, i.e., healthy transformer, healthy transformer with saturated core, mechanically damaged winding, short-circuited winding, open-circuited winding, and repeatability issues. In this research, the data from 139 FRA measurements performed in more than 80 power transformers were used. The database belongs to the transformers having different ratings, sizes, designs, and manufacturers. The results reveal that the proposed TCA algorithm can effectively assess the transformer winding condition with up to 93% accuracy without much human intervention. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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15 pages, 11793 KiB  
Article
Quantitative Analysis of Surface Partial Discharges through Radio Frequency and Ultraviolet Signal Measurements
by Michał Kozioł, Łukasz Nagi, Tomasz Boczar and Zbigniew Nadolny
Energies 2023, 16(9), 3641; https://0-doi-org.brum.beds.ac.uk/10.3390/en16093641 - 24 Apr 2023
Cited by 3 | Viewed by 1152
Abstract
In high voltage insulation systems, dielectric materials may be exposed to partial discharges (PD), which can lead to equipment failures and safety hazards. Therefore, it is crucial to detect and characterize PD activity on the surface of insulation systems. Techniques such as radio [...] Read more.
In high voltage insulation systems, dielectric materials may be exposed to partial discharges (PD), which can lead to equipment failures and safety hazards. Therefore, it is crucial to detect and characterize PD activity on the surface of insulation systems. Techniques such as radio frequency signal analysis and ultraviolet radiation emission detection are commonly used for this purpose. In this research study, an analysis was conducted on the signals emitted by surface PD in the radio frequency and ultraviolet radiation emission ranges. The goal was to indicate possible directions for further basic research aimed at building a knowledge base and improving measurement methods. The analysis confirmed that radio frequency and ultraviolet signal analysis can provide important information about the activity and location of PD on the surface, including the intensity and nature of PD. The experimental investigation presented in this paper provides valuable insights into the potential for using radio frequency and ultraviolet signals to enhance diagnostic techniques for monitoring the condition of insulation systems in high-voltage equipment. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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18 pages, 10742 KiB  
Article
Discharge Characteristics and Numerical Simulation of the Oil–Gas Surface under DC Voltage
by Yuanxiang Zhou, Xiaojing Yang, Yuhang Li, Guiming Jiang and Jianning Chen
Energies 2023, 16(8), 3558; https://0-doi-org.brum.beds.ac.uk/10.3390/en16083558 - 20 Apr 2023
Cited by 2 | Viewed by 944
Abstract
Low insulation strength at the oil–gas surface due to oil leakage and partial discharge of oil-immersed power equipment is a major threat to the safe and reliable operation of power systems. This paper investigates the initiation and development of the oil–gas surface discharge. [...] Read more.
Low insulation strength at the oil–gas surface due to oil leakage and partial discharge of oil-immersed power equipment is a major threat to the safe and reliable operation of power systems. This paper investigates the initiation and development of the oil–gas surface discharge. The oil–gas surface discharge test platform was established, and discharge tests were carried out at different gap distances (1–2.5 mm). By coupling the electric field and flow field, the multi-layer dielectric discharge streamer model was built, and the characteristics of charge and electric field distribution at different gap distances were studied. The test results show that the liquid surface between the electrodes rises during the discharge process. Furthermore, the surface discharge voltage exceeds the air gap discharge voltage. With the simulation analysis, the oil–gas surface discharge is a typical streamer development process. Under 50 kV applied voltage and 2.5 mm gap distance, the average development speed of the streamer is 12.5 km/s. The larger the gap distance is, the greater the average streamer development speed is. The recording and numerical simulation of the discharge process are of great significance for exploring the mechanism of oil–gas surface discharge, optimizing the discharge process, and diagnosing partial discharges. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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15 pages, 3230 KiB  
Article
The Influence of Heat Transfer Coefficient α of Insulating Liquids on Power Transformer Cooling Systems
by Przemyslaw Goscinski, Zbigniew Nadolny, Andrzej Tomczewski, Ryszard Nawrowski and Tomasz Boczar
Energies 2023, 16(6), 2627; https://0-doi-org.brum.beds.ac.uk/10.3390/en16062627 - 10 Mar 2023
Cited by 3 | Viewed by 1466
Abstract
The power transformer plays an important role in electric power systems. One of the conditions for the proper operation of the transformer is to ensure a sufficiently low temperature. This condition can be met if the heat exchange is effective. Heat transfer depends, [...] Read more.
The power transformer plays an important role in electric power systems. One of the conditions for the proper operation of the transformer is to ensure a sufficiently low temperature. This condition can be met if the heat exchange is effective. Heat transfer depends, among other things, on the electrically insulating liquid. The thermal property describing the ability of a liquid to transfer heat is the heat transfer coefficient α. At the design stage of the transformers, it is most often assumed that the value of the α coefficient is constant and equal to 100 W·m−2·K−1. Such simplifications can lead to the improper design of the transformer since this factor depends on many factors. The article presents the results of research on the dependence of the heat transfer coefficient α on the type of electrical insulation liquid, the thermal load of the cooled surface, and the length of the heating element. Four types of electrical insulating liquids were considered: mineral oil, synthetic ester, natural ester, and natural ester with reduced viscosity. The obtained results prove that the type of electrical insulating liquid and the thermal surface load value affect the α coefficient. The length of the heating element did not affect the α factor. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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15 pages, 4944 KiB  
Article
Localization of HV Insulation Defects Using a System of Associated Capacitive Sensors
by Krzysztof Walczak
Energies 2023, 16(5), 2297; https://0-doi-org.brum.beds.ac.uk/10.3390/en16052297 - 27 Feb 2023
Cited by 1 | Viewed by 939
Abstract
The issue of detecting and locating defects generating partial discharges (PDs) is very important for the proper functioning of power grids. Despite the existence of many localization methods, both very large and relatively small objects are still a challenge due to the problem [...] Read more.
The issue of detecting and locating defects generating partial discharges (PDs) is very important for the proper functioning of power grids. Despite the existence of many localization methods, both very large and relatively small objects are still a challenge due to the problem of obtaining the required measurement accuracy. This article presents the idea of the method of PD localization in small objects of simple structure with the use of a system of four capacitive probes. Based on the relative difference in the amplitudes of the signals recorded by the pair of capacitive sensors and considering their distance characteristics, it is possible to determine the place where the PD pulses are generated. In the example of measurements made on a support insulator, it was shown that the location of a defect using the proposed method allows for an indication accuracy of up to 0.5 cm. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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25 pages, 11101 KiB  
Article
Investigation of Effects of Different High Voltage Types on Dielectric Strength of Insulating Liquids
by Fatih Atalar, Aysel Ersoy and Pawel Rozga
Energies 2022, 15(21), 8116; https://0-doi-org.brum.beds.ac.uk/10.3390/en15218116 - 31 Oct 2022
Cited by 11 | Viewed by 1555
Abstract
Liquid dielectrics are different from each other, but are used to perform the same tasks in high-voltage electrical equipment, especially transformers. In similar conditions, the insulation performance of transformer oils under different types of voltage will provide dielectric resistance. In this study, three [...] Read more.
Liquid dielectrics are different from each other, but are used to perform the same tasks in high-voltage electrical equipment, especially transformers. In similar conditions, the insulation performance of transformer oils under different types of voltage will provide dielectric resistance. In this study, three different dielectric liquids applied in transformers, namely mineral oil, natural ester and synthetic ester, were tested. Tests under AC and negative DC voltage were performed at electrode gaps of 2.5 mm, 2 mm and 1 mm using disk and VDE type electrodes as per ASTM D1816-84A and ASTM D877-87 standards, respectively. In turn, the impulse voltage tests were performed under an electrode configuration suggested by the IEC 60897 standard. The current data of 500 ms prior to breakdown under AC electrical field stress was decomposed using the empirical mode decomposition (EMD) and variational mode decomposition (VMD) methods. These analyses were conducted before the full electrical breakdown. Although synthetic ester has the highest dielectric strength under AC and negative DC electrical field stress, mineral oil has been assessed to be the most resistant liquid dielectric at lightning impulse voltages. In addition, stabilization of mineral oil under AC and negative DC voltage was also seen to be good with the help of calculated standard deviation values. However, synthetic ester has a significant advantage, especially in terms of dielectric performance, over mineral oil in spite of the stability of mineral oil. This indicates that liquid dielectric selection for transformers must be carried out as a combined evaluation of multiple parameters. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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15 pages, 3033 KiB  
Article
Research on the Influence of Moisture Exchange between Oil and Cellulose on the Electrical Parameters of the Insulating Oil in Power Transformers
by Konrad Kierczynski, Przemyslaw Rogalski, Vitalii Bondariev, Pawel Okal and Daniel Korenciak
Energies 2022, 15(20), 7681; https://0-doi-org.brum.beds.ac.uk/10.3390/en15207681 - 18 Oct 2022
Cited by 2 | Viewed by 998
Abstract
The article presents an oil moistening method, identical to the oil moistening in power transformers. Moistening took place through the migration of moisture from the moistened pressboard to the brand new oil. The AC electrical parameters (admittance, phase shift angle, permittivity, loss tangent [...] Read more.
The article presents an oil moistening method, identical to the oil moistening in power transformers. Moistening took place through the migration of moisture from the moistened pressboard to the brand new oil. The AC electrical parameters (admittance, phase shift angle, permittivity, loss tangent and conductivity) of the brand new and moistened insulating oil were tested. All measured parameters were found to be affected by the oil moistening. The greatest changes were observed in the loss tangent and conductivity. Moisturization increases the value of tanδ at a frequency of 10−4 Hz from about 20 to about 70. With an increase in frequency to about 400–1000 Hz, a minimum is observed, the position of which depends on the temperature. Its value for moistened oil is about six times lower than for brand new oil. This moisturizing increased the activation energy of the conductivity from 0.466 ± 0.0265 eV to 0.890 ± 0.0115 eV. This is likely due to the acceleration of water molecules diffusion from the pressboard into the oil with increasing temperatures. The observed changes in the oil parameters caused by moistening should be taken into account while analyzing the power transformers insulation condition using the FDS method. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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15 pages, 3228 KiB  
Article
A Novel Multi-Objective Optimal Design Method for Dry Iron Core Reactor by Incorporating NSGA-II, TOPSIS and Entropy Weight Method
by Yan Li, Yifan Liu, Shasha Li, Leijie Qi, Jun Xie and Qing Xie
Energies 2022, 15(19), 7344; https://0-doi-org.brum.beds.ac.uk/10.3390/en15197344 - 06 Oct 2022
Cited by 3 | Viewed by 1091
Abstract
Dry iron core reactors are widely used in various power quality applications. Manufacturers want to optimize the cost and loss simultaneously, which is normally achieved by the designers’ experience. This approach is highly subjective and can lead to a non-ideal product. Thus, an [...] Read more.
Dry iron core reactors are widely used in various power quality applications. Manufacturers want to optimize the cost and loss simultaneously, which is normally achieved by the designers’ experience. This approach is highly subjective and can lead to a non-ideal product. Thus, an objective dry iron core reactor design approach to balance the cost and loss with a scientific basis is desired. In this paper, a multi-objective optimal design method is proposed to optimize both the cost and loss of the reactor, which provides an automatic and scientific design method. Specifically, a three-dimensional finite element model of dry iron core reactor is established, based on which the dependency of cost and loss upon the wire size of the reactor’s winding is studied by using joint Matlab-finite element method (FEM) simulation. The Non-dominated Sorting Genetic Algorithm II (NSGA-II) is used to search for the Pareto optimal solution set, out of which the optimal wire size of the reactor is determined by using the fusion of the technique for order preference by similarity to ideal solution (TOPSIS) method and the entropy weight method. TOPSIS helps the designer to balance the concern between cost and loss, while the entropy weight method can determine the weight information through the dispersion degree of cost and loss. This methodology can avoid personal random subjective opinion when selecting the design solution out of the Pareto set. The calculation shows that the cost and loss can be reduced by up to 17.85% and 19.45%, respectively, with the proposed method. Furthermore, the obtained optimal design is approved by experimental tests. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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15 pages, 1923 KiB  
Article
Impact of Changes in Limit Values of Electric and Magnetic Field on Personnel Performing Diagnostics of Transformers
by Zbigniew Nadolny
Energies 2022, 15(19), 7230; https://0-doi-org.brum.beds.ac.uk/10.3390/en15197230 - 01 Oct 2022
Cited by 4 | Viewed by 1152
Abstract
Electric and magnetic fields accompany technical personnel in their working environment (work exposure). That is why many countries have the appropriate regulations. The impact of electric and magnetic fields on humans is still not fully recognized. This is the reason why the limit [...] Read more.
Electric and magnetic fields accompany technical personnel in their working environment (work exposure). That is why many countries have the appropriate regulations. The impact of electric and magnetic fields on humans is still not fully recognized. This is the reason why the limit values of its intensity in many countries differs significantly. The article presents changes in the stress limits of the electric and magnetic fields in Poland at the turn of the last dozen years. The last such change was the result of a Directive of the European Union (2013/35/EU). The effects of changes in limit values on the working conditions of technical personnel performing diagnostics of high voltage transformers or working in the immediate vicinity of such transformers are presented. The article shows that recent changes have improved the working conditions of technical personnel in relation to the electric field and worsened the conditions taking into account the magnetic field. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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28 pages, 6981 KiB  
Article
An AI-Layered with Multi-Agent Systems Architecture for Prognostics Health Management of Smart Transformers: A Novel Approach for Smart Grid-Ready Energy Management Systems
by Oussama Laayati, Hicham El Hadraoui, Adila El Magharaoui, Nabil El-Bazi, Mostafa Bouzi, Ahmed Chebak and Josep M. Guerrero
Energies 2022, 15(19), 7217; https://0-doi-org.brum.beds.ac.uk/10.3390/en15197217 - 01 Oct 2022
Cited by 16 | Viewed by 2875
Abstract
After the massive integration of distributed energy resources, energy storage systems and the charging stations of electric vehicles, it has become very difficult to implement an efficient grid energy management system regarding the unmanageable behavior of the power flow within the grid, which [...] Read more.
After the massive integration of distributed energy resources, energy storage systems and the charging stations of electric vehicles, it has become very difficult to implement an efficient grid energy management system regarding the unmanageable behavior of the power flow within the grid, which can cause many critical problems in different grid stages, typically in the substations, such as failures, blackouts, and power transformer explosions. However, the current digital transition toward Energy 4.0 in Smart Grids allows the integration of smart solutions to substations by integrating smart sensors and implementing new control and monitoring techniques. This paper is proposing a hybrid artificial intelligence multilayer for power transformers, integrating different diagnostic algorithms, Health Index, and life-loss estimation approaches. After gathering different datasets, this paper presents an exhaustive algorithm comparative study to select the best fit models. This developed architecture for prognostic (PHM) health management is a hybrid interaction between evolutionary support vector machine, random forest, k-nearest neighbor, and linear regression-based models connected to an online monitoring system of the power transformer; these interactions are calculating the important key performance indicators which are related to alarms and a smart energy management system that gives decisions on the load management, the power factor control, and the maintenance schedule planning. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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11 pages, 4082 KiB  
Article
Application of Near-Infrared Spectroscopy to Measure the Water Content in Liquid Dielectrics
by Piotr Przybylek
Energies 2022, 15(16), 5907; https://0-doi-org.brum.beds.ac.uk/10.3390/en15165907 - 15 Aug 2022
Cited by 4 | Viewed by 1781
Abstract
The article discusses the methods used to measure the water content in liquid dielectrics. The pros and cons of currently used methods are presented. The main aim of the research was to check the possibility of using near-infrared spectroscopy to measure the water [...] Read more.
The article discusses the methods used to measure the water content in liquid dielectrics. The pros and cons of currently used methods are presented. The main aim of the research was to check the possibility of using near-infrared spectroscopy to measure the water content in liquid dielectrics. On the basis of the conducted research, the absorbance bands are indicated that can be used to determine the water content in synthetic and natural esters. These bands are centered at 1901 and 1904 nm for natural and synthetic esters, respectively. The determined dependence of the absorbance on the water content in liquid dielectrics confirmed the linear nature of this relationship. Moreover, the influence of liquid aging degree on the result of absorbance measurements was checked. The verification of the method allowed for confirming the possibility of using near-infrared spectroscopy for the reliable quantitative analysis of water content in synthetic and natural esters. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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15 pages, 4570 KiB  
Article
Analysis of Polarization and Depolarization Currents of Samples of NOMEX®910 Cellulose–Aramid Insulation Impregnated with Synthetic Ester
by Adam Krotowski and Stefan Wolny
Energies 2022, 15(9), 3107; https://0-doi-org.brum.beds.ac.uk/10.3390/en15093107 - 24 Apr 2022
Cited by 5 | Viewed by 1537
Abstract
The paper presents the results of laboratory tests regarding the impact of accelerated thermal ageing of cellulose–aramid insulation samples saturated with electrical-insulating synthetic ester on the polarization and depolarization current characteristics being analyzed in the time domain. In the tests, electro-technical paper from [...] Read more.
The paper presents the results of laboratory tests regarding the impact of accelerated thermal ageing of cellulose–aramid insulation samples saturated with electrical-insulating synthetic ester on the polarization and depolarization current characteristics being analyzed in the time domain. In the tests, electro-technical paper from DuPontTM was used, commercially designated as NOMEX®910. Laboratory-accelerated ageing consisted of heating with air a supply of samples of not-impregnated cellulose–aramid insulation for a specified time at specified temperatures. The temperatures and the warming time were selected so as to faithfully represent the degree of the thermal degradation of the cellulose fibers that takes place during normal operation of the material in power transformers. To determine the described impact of the ageing process in the insulation samples on the dielectric properties, the Polarization and Depolarization Method was applied. In the measurements, the MIC-15k1 high resistance meter from SONEL S.A. was used. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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14 pages, 835 KiB  
Article
Determination of Dielectric Losses in a Power Transformer
by Zbigniew Nadolny
Energies 2022, 15(3), 993; https://0-doi-org.brum.beds.ac.uk/10.3390/en15030993 - 28 Jan 2022
Cited by 8 | Viewed by 2354
Abstract
The article presents a method of determining dielectric losses that occur in insulating materials in a power transformer. These losses depend mainly on the electric field stress, pulsation, dielectric loss coefficient, and electrical permittivity of insulating materials. These losses were determined by integrating [...] Read more.
The article presents a method of determining dielectric losses that occur in insulating materials in a power transformer. These losses depend mainly on the electric field stress, pulsation, dielectric loss coefficient, and electrical permittivity of insulating materials. These losses were determined by integrating an expression describing unit losses. The determined dielectric losses were compared with the total losses of the transformer. It turned out that dielectric losses are a fraction of a percent of the total losses. The influence of the electrical permittivity of the insulating liquid and paper insulation on the value of dielectric losses was investigated. This influence was ambiguous, which is characteristic of stratified systems made of materials with different permittivity. An analysis of the influence of the dielectric loss coefficient tan(delta) on the value of dielectric losses in the transformer was carried out. The impact of this coefficient on the amount of dielectric losses turned out to be directly proportional. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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Review

Jump to: Editorial, Research

21 pages, 7810 KiB  
Review
Frequency Range of UHF PD Measurements in Power Transformers
by Stefan Tenbohlen, Chandra Prakash Beura, Wojciech Sikorski, Ricardo Albarracín Sánchez, Bruno Albuquerque de Castro, Michael Beltle, Pascal Fehlmann, Martin Judd, Falk Werner and Martin Siegel
Energies 2023, 16(3), 1395; https://0-doi-org.brum.beds.ac.uk/10.3390/en16031395 - 30 Jan 2023
Cited by 10 | Viewed by 2837
Abstract
Although partial discharge (PD) measurement is a well-accepted technology to assess the quality of the insulation system of power transformers, there are still uncertainties about which frequency range PDs radiate and which frequency range should be evaluated in a measurement. This paper discusses [...] Read more.
Although partial discharge (PD) measurement is a well-accepted technology to assess the quality of the insulation system of power transformers, there are still uncertainties about which frequency range PDs radiate and which frequency range should be evaluated in a measurement. This paper discusses both a UHF PD frequency range obtained from studies investigating laboratory experiments and a frequency range from numerous practical use cases with online and on-site measurements. The literature review reveals a frequency spectrum of ultrahigh-frequency (UHF) PD measurements in the range of 200 MHz to 1 GHz for most publications. Newer publications extend this range from 3 to 6 GHz. The use cases present UHF PD measurements at transformers with power ratings up to 1000 MVA to determine frequency ranges which are considered effective for practical applications. The “common” frequency range, where measurements from all use cases provide signal power, is from approximately 400 MHz to 900 MHz, but it is noted that the individual frequency range, as well as the peak UHF signal power, strongly varies from case to case. We conclude from the discussed laboratory experiments and practical observations that UHF PD measurements in power transformers using either valve or window antennas, according to Cigré, are feasible methods to detect PD. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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15 pages, 318 KiB  
Review
Review on Gassing Tendency of Different Insulating Fluids towards Transformer Applications
by Arputhasamy Joseph Amalanathan, Ramanujam Sarathi, Maciej Zdanowski, Ravikrishnan Vinu and Zbigniew Nadolny
Energies 2023, 16(1), 488; https://0-doi-org.brum.beds.ac.uk/10.3390/en16010488 - 02 Jan 2023
Cited by 3 | Viewed by 2464
Abstract
This paper reports the critical reviews on the gassing tendency of different insulating fluids along with the precautionary measures to be considered during their fault diagnosis in transformer insulation. The experimental techniques and procedures for identifying the gassing due to electrical and thermal [...] Read more.
This paper reports the critical reviews on the gassing tendency of different insulating fluids along with the precautionary measures to be considered during their fault diagnosis in transformer insulation. The experimental techniques and procedures for identifying the gassing due to electrical and thermal stress along with the stray gassing phenomenon has been elucidated. The different interpretation schemes used for determining the faults in transformers results in unexpected errors when the historical data relating to mineral oil is used for the other alternative fluids. Mineral oil and natural ester show a positive gassing tendency compared to synthetic ester which exhibit a negative gassing tendency. The stray gases are mostly due to breakage of C-C bonds under normal operating temperature of transformer. Among the different hydrocarbons, hydrogen and ethylene are more predominantly formed under lower temperatures. The silicone oil and ester fluids are more stable even under localised hot spots simulated observing a lesser gassing compared to the mineral oil. The impact of additives along with the oxygen and water content in the insulating fluids can lead to the stray gas’s causing confusion towards the identification of actual faults occurring in transformers. Furthermore, the regeneration of insulating fluids using different adsorbents reduces the gassing tendency depending on the number of cycles used for its reclamation. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
20 pages, 347 KiB  
Review
Streaming Electrification of Different Insulating Fluids in Power Transformers
by Arputhasamy Joseph Amalanathan, Maciej Zdanowski and Ramanujam Sarathi
Energies 2022, 15(21), 8121; https://0-doi-org.brum.beds.ac.uk/10.3390/en15218121 - 31 Oct 2022
Cited by 6 | Viewed by 2194
Abstract
This paper presents a detailed review of the streaming electrification phenomena of different insulating fluids for power transformers. The comparison of different techniques used to assess the charging tendency of fluids is discussed depending on the flow type (planar or centrifugal), volume of [...] Read more.
This paper presents a detailed review of the streaming electrification phenomena of different insulating fluids for power transformers. The comparison of different techniques used to assess the charging tendency of fluids is discussed depending on the flow type (planar or centrifugal), volume of oil, and interface material. The charge separation between the insulating fluid and metallic/pressboard interfaces is explained in terms of the electrical double layer formation involving a fixed layer and diffuse layer. Based on the experimental results, the streaming electrification is observed to be a function of various factors such as speed, temperature, electric field, and surface roughness. Depending on the molecular structure of insulating liquids that come into contact with solid insulation at the interface, the streaming current can increase; hence, a suitable additive (benzotriazole, fullerene, Irgamet 39) is selected based on the type of fluid and charge polarity. The degradation of the insulating liquid upon ageing, which increases the streaming current and reclamation of such aged fluids using adsorbents (Fuller’s earth, activated carbon, bentonite, and alumina), is a possible method to suppress the static current through improving its dielectric properties. The nanofluids show a higher streaming current compared to base fluid with no change observed even after the reclamation process. The energization process using alternating current (AC) and direct current (DC) impacts the streaming phenomenon depending on its magnitude and polarity. The diffusion of sulfur compounds in the insulating liquid is another major hazard to transformers because the sulfide ions affect the physio-chemical reaction at the interface material, which is responsible for the formation of streaming current. Full article
(This article belongs to the Special Issue Design and Optimization of Power Transformer Diagnostics)
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