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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: closed (20 September 2021) | Viewed by 36816

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Special Issue Editor

Prof. Dr. Huseyin Hiziroglu

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Guest Editor

Department of Electrical & Computer Engineering, Kettering University, Flint, MI 48504, USA
Interests: transformer design; induction motor design; brushless DC motor design; synchronous machine design; gaseous, solid, and nanocomposite insulating materials used in electric machines and transformers; partial discharges in electric machine insulation; inrush current in transformers
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Special Issue Information

Dear Colleagues,

With rapid developments in materials and semiconductor devices, electric machines and transformers have evolved considerably over the past 10 years and have found new applications such as e-mobility, aerospace, renewable energy production, etc., where such stringent requirements as high power density, low weight, compact size, and low cost should be met. Thus, it is a necessity to establish new paradigms to design, construct, select materials and drive systems for electric machines and transformers. Therefore, the purpose of this Special Issue is to facilitate a platform for disseminating new findings on any aspect of electric machines and transformers.

Topics of interest for publication may include but not be limited to:

New materials used in electric machines and transformers;
Novel design of electric machines (synchronous motors and generators, brushless DC motors, induction motors and conventional DC motors) for such applications as drive-by-wire, fly-by-wire, renewable energy production from wind farms, precision control systems, etc.;
Design of low-frequency, high-frequency, and pulse transformers for various applications;
Development of mathematical models to investigate the performance of electric machines and transformers at dynamic as well as steady state;
Discussion of new methods for design optimization of electric machines and transformers;
Novel drive systems to increase the performance of electric machine operation;
Prediction of time-to-failure of the insulation in large electric machines and transformers;
Study of thermal behavior of electric machines and transformers for various applications;
Acoustic analysis of electric machines and transformers due to vibrations;
Continuous monitoring of the state of magnetic as well as insulating materials in electric machine and transformers during operation.

Prof. Dr. Huseyin Hiziroglu
Guest Editor

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Keywords

electric machines
transformers
synchronous machines
brushless DC motors
induction motors
materials for electric machines and transformers

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Published Papers (12 papers)

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Editorial

Jump to: Research

3 pages, 151 KiB

Open AccessEditorial

A Special Issue: Electric Machinery and Transformers

by Huseyin R. Hiziroglu

Energies 2023, 16(15), 5707; https://doi.org/10.3390/en16155707 - 31 Jul 2023

Viewed by 966

Abstract

As the demand for electrical energy increases worldwide, engineers and scientists have been investigating new electrical systems and materials to meet this demand economically, having large-scale planning and employing environmentally friendly energy production and energy-efficient systems for consumption to minimize adverse environmental effects [...] Read more.

(This article belongs to the Special Issue Electric Machinery and Transformers)

Research

Jump to: Editorial

14 pages, 5938 KiB

Open AccessArticle

Acoustic Signature Analysis and Sound Source Localization for a Three-Phase AC Induction Motor

by Anand Krishnasarma, Seyed Jamaleddin Mostafavi Yazdi, Allan Taylor, Daniel Ludwigsen and Javad Baqersad

Energies 2021, 14(21), 7182; https://doi.org/10.3390/en14217182 - 2 Nov 2021

Cited by 7 | Viewed by 4334

Abstract

As part of the recent electrification of the transportation industry, internal combustion engines are being coupled with or replaced by electric motors. This movement towards an electrified drivetrain poses new noise, vibration, and harshness (NVH) challenges related to electric motors. In this paper, the acoustic signature of an electric motor was analyzed to obtain a better understanding of the sound generated by these motors. This work provides an insight into an acoustic measurement technique that can be used to identify certain frequency bands that significantly contribute to the perceived sound. In the first part, the structural response of the motor was correlated with its acoustic spectra. Furthermore, data from acoustic and structural measurements were used to analyze the order content of the signal and identify critical contributors to the overall perceived sound. The differences between data captured by microphones in different positions around the motor helped to localize components of the overall sound. The results provide some discussion about techniques to decrease the overall sound. The technique described in this paper can be extended to fan-cooled motors that are used in vehicles such as golf carts or as auxiliary motors in electric/hybrid vehicles, as well as across a wide range of industrial applications. Full article

(This article belongs to the Special Issue Electric Machinery and Transformers)

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15 pages, 13372 KiB

Open AccessArticle

Evaluation of Methodology for Lightning Impulse Voltage Distribution over High-Voltage Windings of Inductive Voltage Transformers

by Bojan Trkulja, Ana Drandić, Viktor Milardić and Igor Žiger

Energies 2021, 14(16), 5144; https://doi.org/10.3390/en14165144 - 20 Aug 2021

Cited by 8 | Viewed by 2614

Abstract

Knowledge of lightning impulse (LI) voltage distribution over transformer windings during the design stage of the transformer is very important. Specific design differences in inductive voltage transformers make the transient analysis approach different to the approach to the power transformers. In this paper, a methodology for acquiring lightning impulse voltage distribution over high-voltage (HV) winding of inductive voltage transformers is presented and evaluated. Resistance, inductance, and capacitance matrices are calculated using the integral and boundary element methods (BEM) approach. Additionally, in order to improve the capacitance matrix solver, adaptive cross approximation (ACA) is applied. These parameters are then used to solve the equivalent circuit model in time domain. In order to evaluate the methodology, an experimental and numerical investigation of the layer discretisation, iron core influence, and accuracy of the proposed methodology is performed. The comparison of numerical results with measurements confirms the validity of the methodology. Full article

(This article belongs to the Special Issue Electric Machinery and Transformers)

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10 pages, 1559 KiB

Open AccessArticle

High-Frequency Modeling of a Three-Winding Power Transformer Using Sweep Frequency Response Analysis

by Yeunggurl Yoon, Yongju Son, Jintae Cho, SuHyeong Jang, Young-Geun Kim and Sungyun Choi

Energies 2021, 14(13), 4009; https://doi.org/10.3390/en14134009 - 3 Jul 2021

Cited by 15 | Viewed by 3674

Abstract

A power transformer is an essential device for stable and reliable power transfer to customers. Therefore, accurate modeling of transformers is required for simulation-based analysis with the model. The paper proposes an efficient and straightforward parameter estimation of power transformers based on sweep frequency response analysis (SFRA) test data. The method first develops a transformer model consisting of repetitive RLC sections and mutual inductances and then aligns the simulated SFRA curve with the measured one by adjusting parameters. Note that this adjustment is based on individual parameter impacts on the SFRA curve. After aligning the two curves, the final transformer model can be obtained. In this paper, actual single-phase, three-winding transformer model parameters were estimated based on field SFRA data, showing that SFRA curves simulated from the estimated model are consistent with the measured data. Full article

(This article belongs to the Special Issue Electric Machinery and Transformers)

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19 pages, 18910 KiB

Open AccessArticle

Magneto-Thermo-Structural Analysis of Power Transformers under Inrush and Short Circuit Conditions

by Antonio Roniel Marques de Sousa, Marcus Vinicius Alves Nunes, Wellington da Silva Fonseca, Ramon Cristian Fernandes Araujo and Diorge de Souza Lima

Energies 2021, 14(11), 3266; https://doi.org/10.3390/en14113266 - 3 Jun 2021

Cited by 5 | Viewed by 3657

Abstract

The main equipment responsible for connection and transmission of electric power from generating centers to consumers are power transformers. This type of equipment is subject to various types of faults that can affect its components, in some cases also compromising its operation and, consequently, the electric power supply. Thus, in this paper, electromagnetic, thermal, and structural analysis of power transformers was carried out with the objective of providing the operator with information on the ideal moment for performing predictive maintenance, avoiding unplanned shutdowns. For this, computational simulations were performed using the finite element method (FEM) and, from that, the different transformer operation ways, nominal currents, inrush current, and short-circuit current were analyzed. In this perspective, analyses of the effects that thermal expansion, axial forces, and radial forces exerted were carried out, contributing to possible defects in this type of equipment. As a study object, simulations were carried out on a 50 MVA single-phase transformer. It is important to emphasize that the simulations were validated with real data of measurements and with results presented in the current literature. Full article

(This article belongs to the Special Issue Electric Machinery and Transformers)

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19 pages, 7236 KiB

Open AccessArticle

Analysis and Pareto Frontier Based Tradeoff Design of an Integrated Magnetic Structure for a CLLC Resonant Converter

by Gang Wang, Qiyu Hu, Chunyu Xu, Bin Zhao and Xiaobao Su

Energies 2021, 14(6), 1756; https://doi.org/10.3390/en14061756 - 22 Mar 2021

Cited by 7 | Viewed by 2326

Abstract

This paper proposes an integrated magnetic structure for a CLLC resonant converter. With the proposed integrated magnetic structure, two resonant inductances and the transformer are integrated into one magnetic core, which improves the power density of the CLLC resonant converter. In the proposed integrated magnetic structure, two resonant inductances are decoupled with the transformer and can be adjusted by the number of turns in each inductance. Furthermore, two resonant inductances are coupled to reduce the number of turns in each inductance. As a result, the conduction loss can be reduced. The trade-off design of the integrated magnetic structure is carried out based on the Pareto optimization procedure. With the Pareto optimization procedure, both high efficiency and high-power density can be achieved. The proposed integrated magnetic structure is validated by theoretical analysis, simulations, and experiments. Full article

(This article belongs to the Special Issue Electric Machinery and Transformers)

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15 pages, 2967 KiB

Open AccessArticle

Influence of Molecule Structure on Lightning Impulse Breakdown of Ester Liquids

by Huaqiang Li, Linfeng Xia, Shengwei Cai, Zhiqiang Huang, Jiaqi Li and Lisheng Zhong

Energies 2021, 14(4), 1061; https://doi.org/10.3390/en14041061 - 18 Feb 2021

Cited by 12 | Viewed by 2066

Abstract

Ester liquids are environmentally friendly insulating oils, and they can be used as an alternative to mineral oil in transformers, even though in most countries spills of ester oils must be treated like spills of mineral oil. Furthermore, the breakdown characteristics of ester liquids are worse than those of mineral oils in heterogeneous electric fields. In this paper, we present a comprehensive experimental research on both positive and negative lightning impulse breakdown properties in point-plane geometries with gaps varying from 1 mm to 50 mm. The breakdown voltages and streamer velocities of five kinds of ester liquids, including natural ester, synthetic ester, and three kinds of single component esters have been measured. The results show that the double bonds have no effect on the breakdown voltage of ester liquids. The average streamer velocities of mono-esters are faster than that of other esters under positive polarity, and the breakdown voltages of all esters are close. Full article

(This article belongs to the Special Issue Electric Machinery and Transformers)

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14 pages, 5878 KiB

Open AccessArticle

Overvoltage Impact on Internal Insulation Systems of Transformers in Electrical Networks with Vacuum Circuit Breakers

by Marek Florkowski, Jakub Furgał, Maciej Kuniewski and Piotr Pająk

Energies 2020, 13(23), 6380; https://doi.org/10.3390/en13236380 - 2 Dec 2020

Cited by 11 | Viewed by 3648

Abstract

Vacuum circuit breakers are increasingly used as switching apparatus in electric power systems. The vacuum circuit breakers (VCBs) have very good operating properties. VCBs are characterized by specific physical phenomena that affect overvoltage exposure of the insulation systems of other devices. The most important phenomena are the ability to chop the current before the natural zero crossing, the ability to switch off high-frequency currents, and the rapid increase in dielectric strength recovery. One of the devices connected directly to vacuum circuit breakers is the distribution transformer. Overvoltages generated in electrical systems during switching off the transformers are a source of internal overvoltages in the windings. The analysis of the exposure of transformers operating in electrical networks equipped with vacuum circuit breakers is of great importance because of the impact on the insulation systems of switching overvoltages (SO). These types of overvoltages can be characterized by high maximum values and atypical waveforms, depending on the phenomena in the circuit breaker chambers, system configuration, parameters of electrical devices, and overvoltage protection. Overvoltages that stress the internal insulation systems are the result of the windings response to overvoltages at transformer terminals. This article presents an analysis of overvoltages that stress the transformer insulation systems, which occur while switching off transformers in systems with vacuum circuit breakers. The analysis was based on the results of laboratory measurements of switching overvoltages at transformer terminals and inside the winding, in a model medium-voltage electrical network with a vacuum circuit breaker. Full article

(This article belongs to the Special Issue Electric Machinery and Transformers)

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19 pages, 8866 KiB

Open AccessArticle

Effective Simulation Approach for Lightning Impulse Voltage Tests of Reactor and Transformer Windings

by Piyapon Tuethong, Peerawut Yutthagowith and Anantawat Kunakorn

Energies 2020, 13(20), 5399; https://doi.org/10.3390/en13205399 - 16 Oct 2020

Cited by 4 | Viewed by 3836

Abstract

In this paper, an effective simulation method for lightning impulse voltage tests of reactor and transformer windings is presented. The method is started from the determination of the realized equivalent circuit of the considered winding in the wide frequency range from 10 Hz to 10 MHz. From the determined equivalent circuit and with the use of the circuit simulator, the circuit parameters in the impulse generator circuit are adjusted to obtain the waveform parameters according to the standard requirement. The realized equivalent circuits of windings for impulse voltage tests have been identified. The identification approach starts from equivalent circuit determination based on a vector fitting algorithm. However, the vector fitting algorithm with the equivalent circuit extraction is not guaranteed to obtain the realized equivalent circuit. From the equivalent circuit, it is possible that there are some negative parameters of resistance, inductance, and capacitance. Using such circuit parameters from the vector fitting approach as the beginning circuit parameters, a genetic algorithm is employed for searching equivalent circuit parameters with the constraints of positive values. The realized equivalent circuits of the windings can be determined. The validity of the combined algorithm is confirmed by comparison of the simulated results by the determined circuit model and the experimental results, and good agreement is observed. The proposed approach is very useful in lightning impulse tests on the reactor and transformer windings. Full article

(This article belongs to the Special Issue Electric Machinery and Transformers)

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13 pages, 2450 KiB

Open AccessArticle

On Simplified Calculations of Leakage Inductances of Power Transformers

by Tadeusz Sobczyk and Marcin Jaraczewski

Energies 2020, 13(18), 4952; https://doi.org/10.3390/en13184952 - 21 Sep 2020

Cited by 14 | Viewed by 3178

Abstract

This paper deals with the problem of the leakage inductance calculations in power transformers. Commonly, the leakage flux in the air zone is represented by short-circuit inductance, which determines the short-circuit voltage, which is a very important factor for power transformers. That inductance is a good representation of the typical power transformer windings, but it is insufficient for multi-winding ones. This paper presents simple formulae for self- and mutual leakage inductance calculations for an arbitrary pair of windings. It follows from a simple 1D approach to analyzing the stray field using a discrete differential operator, and it was verified by the finite element method (FEM) calculation results. Full article

(This article belongs to the Special Issue Electric Machinery and Transformers)

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14 pages, 2975 KiB

Open AccessArticle

Performance Assessment of Oil-Immersed Cellulose Insulator Materials Using Time–Domain Spectroscopy under Varying Temperature and Humidity Conditions

by Benhui Lai, Shichang Yang, Heng Zhang, Yiyi Zhang, Xianhao Fan and Jiefeng Liu

Energies 2020, 13(17), 4426; https://doi.org/10.3390/en13174426 - 27 Aug 2020

Cited by 1 | Viewed by 2039

Abstract

The measurement of polarization and depolarization currents (PDC) based on time–domain response is an effective method for state assessment of cellulose insulation material in oil-immersed electrical equipment. However, the versatility of the data obtained at different temperatures is limited because of the temperature dependence of the PDC. In this respect, the universal conversion of PDC data at different temperatures is an essential aspect to improve the accuracy of the determination of insulating properties of cellulose materials immersed in the oil. Thus, an innovative temperature conversion method based on polarization time-varying current (PTC, obtained by multiplying the polarization current and time) is proposed in this article. In the current work, the PTC data at different temperatures are obtained from the oil-immersed cellulose pressboards with different moisture. Afterwards, the functional model based on the power series theory is used to simulate the PTC data, through which the coefficients of the power series are found related to the test temperature of the PTC and the moisture content (mc%) of the oil-immersed cellulose pressboards. Furthermore, the functional relationship among moisture, test temperatures, and the feature parameter calculated by these coefficients is established. Thus, the PTC data at various temperatures can be calculated by the established function. The potential application ability of the proposed method is verified by comparing the calculated results with the measured results obtained from the various samples. Full article

(This article belongs to the Special Issue Electric Machinery and Transformers)

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23 pages, 11121 KiB

Open AccessArticle

FRA Diagnostics Measurement of Winding Deformation in Model Single-Phase Transformers Made with Silicon-Steel, Amorphous and Nanocrystalline Magnetic Cores

by Maciej Kuniewski

Energies 2020, 13(10), 2424; https://doi.org/10.3390/en13102424 - 12 May 2020

Cited by 4 | Viewed by 2597

Abstract

The power transformer is a key object in the electrical power system. The working principle hasn’t changed since its discovery. The main work nowadays is focused on the rising of the reliability of transformers and lowering power losses. The replacement of new materials instead of conventionally used ones can provide a solution. This procedure can improve factors, like a reduction of power losses, but also influence others normally neglected, like proper work in higher frequencies. The article presents the measurement results of the frequency characteristics of model test coils made with different magnetic materials cores (silicon steel, amorphous material, and nanocrystalline material), the measurements based on the sweep frequency response analysis (SFRA) method used for the determination of chosen frequency characteristics. The analysis presents the impact of different coil deformation levels on frequency characteristics. Results show that the replacement of conventional silicon steel with thinner high permeability materials can modify the state-of-the-art frequency response analysis (FRA) interpretation guidelines. The replacement of a new type of magnetic material as a magnetic core in the existing design of power transformer should lead to a full analysis of its behavior in the high-frequency domain. Full article

(This article belongs to the Special Issue Electric Machinery and Transformers)

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