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1. Meron-mediated phase transitions in quasi-two-dimensional chiral magnets with easy-plane anisotropy: successive transformation of the hexagonal skyrmion lattice into the square lattice and into the tilted FM state

Author

Leonov, Andrey O.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Strongly Correlated Electrons
Abstract

I revisit the well-known structural transition between hexagonal and square skyrmion lattices induced by increasing easy-plane anisotropy in quasi-two-dimensional chiral magnets. I show that the hexagonal skyrmion order, by the first-order phase transition, transforms into a distorted (rhombic) skyrmion lattice. The transition is mediated by merons and anti-merons emerging within the boundaries between skyrmion cells. Since the energy density associated with anti-merons is highly positive owing to the wrong rotational sense, one anti-meron per unit cell annihilates: anti-merons are squeezed by the pairs of approaching merons at the opposite sides of the hexagonal unit cell. Further, in a narrow range of anisotropy values, the distorted skyrmion lattice gradually transforms into a perfect square order of skyrmions (alternatively called "a square meron-antimeron crystal") when two merons eventually merge into one. Thus, within the square skyrmion lattice, there is one meron and two anti-merons per unit cell, which underlie the subsequent first-order phase transition into the tilted ferromagnetic state. A pair of oppositely charged merons mutually annihilates, whereas a remaining anti-meron couples with an anti-meron occupying the center of the unit cell. As an outcome, the tilted ferromagnetic state contains bimeron clusters (chains) with the attracting inter-soliton potential. Moreover, domain-wall merons are actively involved in dynamic responses of the square skyrmion lattices. As an example, I theoretically study spin-wave modes and their excitations by ac magnetic fields. Two found resonance peaks are the result of the complex dynamics of domain-wall merons: whereas in the high-frequency mode, merons rotate counterclockwise as one might expect, in the low-frequency mode, merons are created and annihilated consistently with the rotational motion of the domain boundaries., Comment: 11 pages

Published
2024

2. Reorientation transition between square and hexagonal skyrmion lattices near the saturation into the homogeneous state in quasi-two-dimensional chiral magnets

Author

Leonov, Andrey O.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

I revisit the well-known phase transition between the hexagonal skyrmion lattice and the homogeneous state within the phenomenological Dzyaloshinskii theory for chiral magnets which includes only the exchange, Dzyaloshinskii-Moriya and Zeeman energy contributions. I show that, in a narrow field range near the saturation field, the hexagonal skyrmion order gradually transforms into a square arrangement of skyrmions. Then, by the second-order phase transition during which the lattice period diverges, the square skyrmion lattice releases a set of repulsive isolated skyrmions. On decreasing magnetic field, isolated skyrmions re-condense into the square lattice at the same critical field as soon as their eigen-energy becomes negative with respect to the field-aligned state. The underlying reason of the reorientation transition between two skyrmion orders can be deduced from the energy density distribution within isolated skyrmions surrounded by the homogeneous state. When the negative energy within the ring-shaped area at the skyrmion outskirt outweighs the positive energy amount around the skyrmion axis, skyrmions tend to form the square lattice, in which the overlap of skyrmion profiles results in smaller energy losses as compared with the hexagonal crystal. With the further decreasing field, the hexagonal lattice achieves smaller energy density in comparison with the square one due to the denser packing of individual skyrmions., Comment: 8 pages, 6 figures

Published
2024

3. Communicating skyrmions as the main mechanism underlying skyrmionium (meta)stability in quasi-two-dimensional chiral magnets

Author

Nakamura, Kaito and Leonov, Andrey O.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Mathematical Physics
Abstract

We re-examine the internal structure of skyrmioniums stabilized in quasi-two-dimensional chiral magnets with easy-axis uniaxial anisotropy. Skyrmioniums are particle-like states of two nested skyrmions with opposite polarities contributing to zero topological charge. The physical principles of skyrmionium stability are drawn from both the analytical analysis with a trial function and from numerical simulations within the framework of micromagnetism. We deduce that the radii of the internal skyrmion with the positive polarity and the ring-shaped external skyrmion with the negative polarity are mutually dependent, which constitutes the paradigm of communicating skyrmions. For large central skyrmions, the skyrmionium transforms into a narrow circular domain wall, whereas for small internal radii, the ring expands, which occurs at the verge of collapsing into an ordinary isolated skyrmion. We show that skyrmioniums may form lattices of two varieties depending on the polarity of the internal skyrmion. At the phase diagram (magnetic field)-(uniaxial anisotropy), both skyrmionium lattices share the same area with one-dimensional spiral states and remain metastable solutions for the whole range of control parameters. By expanding at the critical line, skyrmionium lattices do not release isolated skyrmioniums. Isolated skyrmioniums of just one type exist apart from the corresponding lattice in a narrow field region restricted by the critical line of expansion from below and by the line of collapse above.

Published
2024

4. Field-driven metamorphoses of isolated skyrmions within the conical state of cubic helimagnets

Author

Leonov, Andrey O., Pappas, Catherine, and Smalyukh, Ivan I.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics, Physics - Computational Physics
Abstract

Topologically stable field configurations appear in many fields of physics, from elementary particles to condensed matter and cosmology. During the last decade, chiral liquid crystals and chiral magnets took on the role of model objects for experimental investigation of topological solitons and understanding of their nonsingular field configurations. Here we introduce a paradigm of facile skyrmionic networks with mutually-orthogonal orientations of constituent isolated skyrmions. Such networks are envisioned as a novel concept of spintronic devices and are presumably responsible for precursor phenomena near the ordering temperatures of bulk cubic helimagnets. In particular, we demonstrate an interconversion between mutually orthogonal skyrmions: horizontal skyrmions swirl into an intermediate spring-like states and subsequently squeeze into vertical skyrmions with both polarities. Skyrmion tubes are also considered as building blocks for particle-like states with more involved internal structure. A family of target-skyrmions, which includes an overlooked so far type with a multiple topological charge, is formed owing to the tendency to minimize the interaction energy between vertical and horizontal skyrmions. The conical phase serves as a suitable background for considered skyrmion evolution. It substantializes the attracting skyrmion-skyrmion interaction in the skyrmionic networks, shapes their internal structure and guides the nucleation processes. Alternatively, intricate textural changes of isolated skyrmions result not only in the structural deformations of a host conical state, but may lead to the formation of an exotic skyrmion order with pairs of merons being the core of the game. Generically, the fundamental insights provided by this work emphasize a three-dimensional character of skyrmion metamorphoses and can also be extended to three-dimensional solitons, such as hopfions., Comment: 12 pages, 6 figures

Published
2021
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5. Evolution of Helimagnetic Correlations when approaching the Quantum Critical Point of Mn$_{1-x}$Fe$_x$Si

Author

Pappas, Catherine, Leonov, Andrey O., Bannenberg, Lars J., Fouquet, Peter, Wolf, Thomas, and Weber, Frank

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We present a comprehensive investigation of the evolution of helimagnetic correlations in Mn$_{1-x}$Fe$_x$Si with increasing doping. By combining polarised neutron scattering and high resolution Neutron Spin Echo spectroscopy we investigate three samples with $x$=0.09, 0.11 and 0.14, i.e. with compositions on both sides of the concentration $x^* \sim 0.11$ where the helimagnetic Bragg peaks disappear and between $x^*$ and the quantum critical concentration $x_C \sim 0.17$, where $T_C$ vanishes. We find that the abrupt disappearance of the long range helical periodicity at $x^*$, does not affect the precursor fluctuating correlations. These build up with decreasing temperature in a similar way as for the parent compound MnSi. Also the dynamics bears strong similarities to MnSi. The analysis of our results indicates that frustration, possibly due to achiral RKKY interactions, increases with increasing Fe doping. We argue that this effect explains both the expansion of the precursor phase with increasing $x$ and the abrupt disappearance of long range helimagnetic periodicity at $x^*$.

Published
2020
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6. Field and anisotropy driven transformations of spin spirals in cubic skyrmion hosts

Author

Leonov, Andrey O., Pappas, Catherine, and Kézsmárki, Istvan

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We discuss distinctive features of spiral states in bulk chiral magnets such as MnSi and Cu$_2$OSeO$_3$ that stem from the effect of the cubic magneto-crystalline anisotropy. First of all, at both the helical-to-conical and the conical-to-ferromagnetic transitions, taking place at H$_{c1}$ and H$_{c2}$, respectively, the cubic anisotropy leads to reversible or irreversible jump-like reorientations of the spiral wavevectors. The subtle interplay between the easy and hard anisotropy axes gives rise to a phase transition between elliptically distorted conical states almost without any detectable change in the period. We show that the competition between on-site cubic and exchange anisotropy terms can also lead to oblique spiral states. Our work gives clear directions for further experimental studies to reveal theoretically predicted spiral states in cubic helimagnets beyond the aforementioned well-established states thus, can help to understand the magnetic phase diagram of these archetypal skyrmion hosts. In addition, we show that properties of isolated skyrmions such as inter-skyrmion attraction, orientation and/or nucleation are also rooted in the properties of host spirals states, in which skyrmions are stabilized.

Published
2020
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7. Stability of in-plane and out-of-plane chiral skyrmions in epitaxial MnSi(111)/Si(111) thin films: surface twists versus easy-plane anisotropy

Author

Leonov, Andrey O., Tambovtcev, Ivan M., Lobanov, Igor S., and Uzdin, Valery M.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

The revisited theoretical phase diagrams for thin films of cubic helimagnets with the easy-plane anisotropy are shown to have different topology as previously reported [Phys. Rev. B 85, 094429 (2012)]. For both in-plane and out-of-plane directions of an applied magnetic field, the phase diagrams exhibit extensive areas of stable skyrmions, which overlap for a wide range of anisotropy parameters. Although the existence of the out-of-plane skyrmions was contradicted within the previous theoretical models, we prove that additional surface twists lead to their stability, while the moderate easy-plane anisotropy increases the stability range of in-plane skyrmions. Moreover, the interplay between the anisotropy and the surface twists gives rise to a stable spiral state canted with respect to the surfaces. Being absent in bulk helimagnets, this oblique spiral occupies vast areas at the phase diagrams in thin-film nanosystems and serves as a connecting-link between cones and helicoids. Our theory gives clear directions for renewed experimental studies of in-plane and out-of-plane skyrmions in epitaxial MnSi(111)/Si(111) thin films.

Published
2020
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8. Skyrmions and spirals in MnSi under hydrostatic pressure

Author

Bannenberg, Lars J., Sadykov, Ravil, Dalgliesh, Robbert M., Goodway, Chris, Schlagel, Deborah L., Lograsso, Thomas A., Falus, Peter, Lelièvre-Berna, Eddy, Leonov, Andrey O., and Pappas, Catherine

Subjects
Condensed Matter - Materials Science, Condensed Matter - Strongly Correlated Electrons
Abstract

The archetype cubic chiral magnet MnSi is home to some of the most fascinating states in condensed matter such as skyrmions and a non-Fermi liquid behavior in conjunction with a topological Hall effect under hydrostatic pressure. Using small angle neutron scattering, we study the evolution of the helimagnetic, conical and skyrmionic correlations with increasing hydrostatic pressure. We show that the helical propagation vector smoothly reorients from $\langle 111 \rangle$ to $\langle100\rangle$ at intermediate pressures. At higher pressures, above the critical pressure, the long-range helimagnetic order disappears at zero magnetic field. Nevertheless, skyrmion lattices and conical spirals form under magnetic fields, in a part of the phase diagram where a topological Hall effect and a non-Fermi liquid behavior have been reported. These unexpected results shed light on the puzzling behavior of MnSi at high pressures and the mechanisms that destabilize the helimagnetic long-range order at the critical pressure.

Published
2019
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9. Real-space observation of skyrmion clusters with mutually orthogonal skyrmion tubes

Author

Sohn, Hayley. R. O., Vlasov, Sergei M., Uzdin, Valeriy M., Leonov, Andrey O., and Smalyukh, Ivan I.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We report the discovery and direct visualization of skyrmion clusters with mutually-orthogonal orientations of constituent isolated skyrmions in chiral liquid crystals and ferromagnets. We show that the nascent conical state underlies attracting inter-skyrmion potential, whereas an encompassing homogeneous state leads to the repulsive skyrmion-skyrmion interaction. The crossover between different regimes of skyrmion interaction could be identified upon changing layer thickness and/or the surface anchoring. We develop a phenomenological theory describing two types of skyrmions and the underlying mechanisms of their interaction. We show that isolated horizontal skyrmions with the same polarity may approach a vertical isolated skyrmion from both sides and thus constitute two energetically-different configurations which are also observed experimentally. In an extreme regime of mutual attraction, the skyrmions wind around each other forming compact superstructures with undulations. We also indicate that our numerical simulations on skyrmion clusters are valid in a parameter range corresponding to the A-phase region of cubic helimagnets.

Published
2019
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10. Skyrmion instabilities and distorted spiral states in a frustrated chiral magnet

Author

Mutter, Thomas T. J., Leonov, Andrey O., and Inoue, Katsuya

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Magnetic skyrmions are particle-like topological excitations that recently generated much interest as candidates for future spintronic devices based on skyrmion small size, enhanced topological stability, and/or mutual interaction. Here we examine the properties of isolated skyrmions in a frustrated chiral magnet with competing Dzyaloshinskii-Moriya and frustrated exchange interactions. We show that the skyrmion size drastically decreases even for small values of competing stabilization mechanisms. Skyrmion mutual interaction remains attracting as is inherent for frustrated skyrmions, but the value of the Dzyaloshinskii constant regulates the number of minima in the interaction potentials. Moreover, the constructed phase diagrams for a chiral helimagnet contain a distorted spiral state that can be considered as a buffer between the helicoidal and conical one-dimensional modulations. The formulated concepts may further enhance the functionalities of spintronic devices. In particular, the controlled instability of skyrmions with respect to the conical state allows to obtain bimeron-like structures. Moreover, our results provide physical insight into the chiral states in the magnetic systems, e.g., in MnSi$_{1-x}$Ge$_x$.

Published
2019
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11. Current-induced shuttlecock-like movement of non-axisymmetric chiral skyrmions

Author

Murooka, Remi, Leonov, Andrey O., Inoue, Katsuya, and Ohe, Jun-ichiro

Subjects
Condensed Matter - Materials Science
Abstract

Current-induced motion of non-axisymmetric skyrmions within angular phases of polar helimagnetis with the easy plane anisotropy is studied by micromagnetic simulations.Such non-axisymmetric skyrmions consist of a circular core and a crescent-shaped domain-wall region formed with respect to the tilted surrounding state. A current-driven motion of non-axisymmetric skyrmions exhibits two distinct time regimes: initially the skyrmions rotate towards the current flow direction and subsequently move along the current with the skyrmionic crescent first. According to the Thiele equation, the asymmetric distribution of the topological charge and the dissipative force tensor play an important role for giving the different velocities for the circular and the crescent-shaped constituent parts of the skyrmion what underlies such a shuttlecock-like movement. Moreover, the current-velocity relation depends on the tilt angle of the surrounding angular phase what makes in particular the transverse velocity of skyrmions sensitive to their field-driven configurational transformation., Comment: 5 pages, 5 figures

Published
2018

12. Toggle-switch-like crossover between two types of isolated skyrmions within the conical phase of cubic helimagnets

Author

Leonov, Andrey O., Bogdanov, Alex N., and Inoue, Katsuya

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We investigate the field-induced crossover between two types of isolated skyrmions that exist within the conical phase of cubic helimagnets and orient themselves either along or perpendicular to the field. Such a crossover takes place for the same value of the field, at which the closely packed skyrmion lattice was predicted to stabilize in the A-phase region. The clusters and a skyrmion lattice comprised by the skyrmions perpendicular to the field, however, are unfavorable and lose their stability as compared with the skyrmions parallel to the field. We also followed transformation of perpendicular skyrmions into pairs of merons that rupture the helical state. An attractive interactions between different types of isolated skyrmions make it feasible to construct complex cluster states with the cubic arrangement of skyrmions.

Published
2018
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13. Crossover of skyrmion and helical modulations in noncentrosymmetric ferromagnets

Author

Leonov, Andrey O. and Bogdanov, Alexei N.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

The coupling between angular (twisting) and longitudinal modulations arising near the ordering temperature of noncentrosymmetric ferromagnets strongly influences the structure of skyrmion states and their evolution in an applied magnetic field. In the precursor states of cubic helimagnets, a continuous transformation of skyrmion lattices into the saturated state is replaced by the first-order processes accompanied by the formation of multidomain states. Recently the effects imposed by dominant longitudinal modulations have been reported in bulk MnSi and FeGe. Similar phenomena can be observed in the precursor regions of cubic helimagnet epilayers and in easy-plane chiral ferromagnets (e.g. in the hexagonal helimagnet CrNb3S6).

Published
2018
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14. Helimagnon resonances in an intrinsic chiral magnonic crystal

Author

Weiler, Mathias, Aqeel, Aisha, Mostovoy, Maxim, Leonov, Andrey, Geprägs, Stephan, Gross, Rudolf, Huebl, Hans, Palstra, Thomas T. M., and Goennenwein, Sebastian T. B.

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

We experimentally study magnetic resonances in the helical and conical magnetic phases of the chiral magnetic insulator Cu$_2$OSeO$_3$ at the temperature $T$=5 K. Using a broadband microwave spectroscopy technique based on vector network analysis, we identify three distinct sets of helimagnon resonances in the frequency range 2 GHz $\leq f \leq$ 20 GHz. The extracted resonance frequencies are in accordance with calculations of the helimagnon bandstructure found in an intrinsic chiral magnonic crystal. The periodic modulation of the equilibrium spin direction that leads to the formation of the magnonic crystal is a direct consequence of the chiral magnetic ordering caused by the Dzyaloshinskii-Moriya interaction. The opening of magnon band-gaps allows for excitation of helimagnons with wave vectors that are multiples of the spiral wave vector., Comment: Accepted on November 9th, 2017 for publication at Physical Review Letters (https://journals.aps.org/prl/accepted/5607dY38Rcf14865a08e67543fa3d1c6d0df92c65)

Published
2017
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16. Magnetic Excitations in the Multiferroic N\'eel-type Skyrmion Host GaV$_4$S$_8$

Author

Ehlers, Dieter, Stasinopoulos, Ioannis, Tsurkan, Vladimir, von Nidda, Hans-Albrecht Krug, Fehér, Titusz, Leonov, Andrey, Kézsmárki, István, Grundler, Dirk, and Loidl, Alois

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

Broadband microwave spectroscopy has been performed on single-crystalline GaV$_4$S$_8$, which exhibits a complex magnetic phase diagram including cycloidal, N\'eel-type skyrmion lattice, as well as field-polarized ferromagnetic phases below 13 K. At zero and small magnetic fields two collective modes are found at 5 and 15 GHz, which are characteristic of the cycloidal state in this easy-axis magnet. In finite fields, entering the skyrmion lattice phase, the spectrum transforms into a multi-mode pattern with absorption peaks near 4, 8, and 15 GHz. The spin excitation spectra in GaV$_4$S$_8$ and their field dependencies are found to be in close relation to those observed in materials with Bloch-type skyrmions. Distinct differences arise from the strong uniaxial magnetic anisotropy of GaV4S8 not present in so-far known skyrmion hosts.

Published
2015
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20. Contributors

Author

Bonanno, Gabriele, primary, Büttner, Felix, additional, Carpentieri, Mario, additional, Chen, Xing, additional, Chubykalo-Fesenko, Oksana, additional, D’Aguì, Giuseppina, additional, Denisov, Konstantin, additional, Ezawa, Motohiko, additional, Fischer, Peter, additional, Hug, Hans J., additional, Kang, Wang, additional, Kläui, Mathias, additional, Legrand, William, additional, Lei, Na, additional, Leonov, Andrey O., additional, Li, Sai, additional, Litzius, Kai, additional, Liu, Xiaoxi, additional, Miltat, Jacques, additional, Pappas, Catherine, additional, Rohart, Stanislas, additional, Roy, Sujoy, additional, Rozhansky, Igor, additional, Sánchez-Tejerina, Luis, additional, Shen, Laichuan, additional, Thiaville, André, additional, Tomasello, Riccardo, additional, Tretiakov, Oleg A., additional, Woo, Seonghoon, additional, Xia, Jing, additional, Zhang, Xichao, additional, Zhang, Xueying, additional, Zhao, Weisheng, additional, Zhou, Yan, additional, Zhu, Daoqian, additional, and Zivieri, Roberto, additional

Published
2021
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22. ПЕРЕХОДНЫЕ ПРОЦЕССЫ В ЭЛЕКТРОТЕХНИЧЕСКОМ КОМПЛЕКСЕ ДОБЫВАЮЩЕЙ СКВАЖИНЫ С ВНУТРИСКВАЖИННЫМ КОМПЕНСАТОРОМ РЕАКТИВНОЙ МОЩНОСТИ

Author

Glazyrin, Aleksandr Saveljevich, Isaev, Yusup Niyazbekovich, Kopyrin, Vladimir Anatolievich, Timoshkin, Vadim Vladimirovich, Kladiev, Sergey Nikolaevich, Khamitov, Rustam Nurimanov, Kovalev, Vladimir Zakharovich, Losev, Fedor Alekseevich, Leonov, Andrey Petrovich, and Popov, Evgeny Igorevich

Subjects
погружные электродвигатели, внутрискважинные компенсаторы, Materials Science (miscellaneous), downhole compensator, submersible electric centrifugal pump, submersible induction motor, Management, Monitoring, Policy and Law, transient processes, Geotechnical Engineering and Engineering Geology, Fuel Technology, погружные электроцентробежные насосы, электротехнические комплексы, добывающие скважины, математические модели, Economic Geology, переходные процессы, Waste Management and Disposal, mathematical model
Abstract

Актуальность. В настоящее время при повсеместном усложнении технологических процессов для повышения эффективности производственных процессов за счет внедрения нового оборудования происходят конфликты между функциональными возможностями различных технических средств и их способностью функционировать с заданным качеством, в заданной электромагнитной обстановке и не создавать недопустимых электромагнитных помех другим техническим средствам. В состав электротехнического комплекса для добычи нефти, под которым понимается совокупность наземного и погружного электрооборудования, скомпонованного для приема, трансформации, управления, преобразования электрической энергии в механическую и передачи её погружному насосу, входят различные электротехнические и электронные устройства: станция управления с преобразователем частоты, повышающий трансформатор, кабельная линия, погружной электродвигатель, внутрискважинный компенсатор реактивной мощности и другие устройства. Любое изменение компоновки электротехнических комплексов для добычи нефти или технических характеристик используемого оборудования требует тщательного исследования переходных процессов между режимами работы электрооборудования для предотвращения рисков ложного срабатывания устройств защиты электротехнического оборудования. Цель: анализ переходных процессов в электротехническом комплексе добывающей скважины с внутрискважинным компенсатором реактивной мощности при отключении источника питания с целью предупреждения рисков ложного срабатывания устройств защиты компенсатора. Объект: участок системы электроснабжения куста нефтедобывающих скважин, оснащенных установками электроцентробежных насосов с внутрискважинными компенсаторами реактивной мощности. Методы: использованы положения теоретических основ электротехники, теории электропривода, теория дифференциальных уравнений, численные методы. Результаты. Разработана математическая модель электротехнического комплекса установки электроприводного центробежного насоса с внутрискважинным компенсатором реактивной мощности, позволяющая исследовать переходные процессы в режиме пуска и остановки погружного асинхронного электродвигателя. Получены характеристики переходных процессов в элементах электротехнического комплекса установки электроприводного центробежного насоса при включении и отключении источника питания. Установлено, что максимальный бросок тока во внутрискважинном компенсаторе реактивной мощности составляет 2,56 раза при принятых в исследовании параметрах электротехнического комплекса добывающей скважины. Предложены мероприятия по снижению количества ложных срабатываний устройств защиты. The relevance. At the present time at routine complication of technological processes to increase efficiency of production processes due to introduction of new equipment the conflicts between functional capabilities of various technical means and their ability to function with specified quality, in specified electromagnetic environment and do not create inadmissible electromagnetic interference to other technical means occur. The electrical engineering complex for oil production includes a combination of ground and submersible electrical equipment assembled for receiving, transforming electrical energy, controlling its flow, converting electrical energy into mechanical energy and transmitting it to a submersible pump, including various electrical and electronic devices: a control station with a frequency converter, a step-up transformer, a cable line, a submersible electric motor, a downhole reactive power compensator and other devices. Any change in the layout of electrical systems for extracting oil or technical characteristics of the equipment used requires careful analysis of transient processes between the operating modes of electrical equipment in order to prevent the risks of false triggering of electrical equipment protection devices. The purpose: analysis of transient processes in the electrical system of the production well with the downhole reactive power compensator when the power supply is disconnected in order to prevent the risks of false operation of the compensator protection devices. The object: section of a power supply system for a cluster of oil producing wells equipped with electric centrifugal pump installations with downhole reactive power compensators. Methods: positions of theoretical bases of electrical engineering, theory of electric drive, theory of differential equations, numerical methods. Results. The authors developed the mathematical model of the electrical system of the submersible unit for oil production with a downhole reactive power compensator, which enables to investigate transient processes in start-up and shutdown mode of the submersible induction motor. Characteristics of transient processes are obtained in elements of electrical complex of submersible plant for oil production when power supply is switched on and disconnected. It is established that the maximum current surge in the downhole reactive power compensator is 2,56 times with the parameters of the electrical system of the production well accepted in the study. The inventive measures for reducing the number of false actuations of the protection devices are also disclosed.

Published
2023
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24. Macroscopic manifestation of domain-wall magnetism and magnetoelectric effect in a Néel-type skyrmion host

Author

Geirhos, Korbinian, Gross, Boris, Szigeti, Bertalan G., Mehlin, Andrea, Philipp, Simon, White, Jonathan S., Cubitt, Robert, Widmann, Sebastian, Ghara, Somnath, Lunkenheimer, Peter, Tsurkan, Vladimir, Neuber, Erik, Ivaneyko, Dmytro, Milde, Peter, Eng, Lukas M., Leonov, Andrey O., Bordács, Sándor, Poggio, Martino, and Kézsmárki, István

Published
2020
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25. "Polymerization" of Bimerons in Quasi-Two-Dimensional Chiral Magnets with Easy-Plane Anisotropy.

Author

Mukai, Natsuki and Leonov, Andrey O.

Subjects
*SKYRME model, *POLYMER networks, *UNIT cell, *MAGNETS, *ANISOTROPY, *POLYMERIZATION, *SKYRMIONS
Abstract

We re-examine the internal structure of bimerons, which are stabilized in easy-plane chiral magnets and represent coupled states of two merons with the same topological charge | 1 / 2 | but with opposite vorticity and the polarity. We find that, in addition to the vortices and antivortices, bimerons feature circular regions which are located behind the anti-vortices and bear the rotational sense opposite to the rotational sense chosen by the Dzyaloshinskii–Moriya interaction. In an attempt to eliminate these wrong-twist regions with an excess of positive energy density, bimerons assemble into chains, and as such exhibit an attracting interaction potential. As an alternative to chains, we demonstrate the existence of ring-shaped bimeron clusters of several varieties. In some rings, bimeron dipoles are oriented along the circle and swirl clockwise and/or counterclockwise (dubbed "roundabouts"). Moreover, a central meron encircled by the outer bimerons may possess either positive or negative polarity. In other rings, the bimeron dipoles point towards the center of a ring and consequently couple to the central meron (dubbed "crossings"). We point out that the ringlike solutions for baryons obtained within the Skyrme model of pions, although driven by the same tendency of the energy reduction, yield only one type of bimeron rings. The conditions of stability applied to the described bimeron rings are additionally extended to bimeron networks when bimerons fill the whole space of two-dimensional samples and exhibit combinations of rings and chains dispersed with different spatial density (dubbed bimeron "polymers"). In particular, bimeron crystals with hexagonal and the square bimeron orderings are possible when the sides of the unit cells represent chains of bimerons joined in intersections with three or four bimerons, respectively; otherwise, bimeron networks represent disordered bimeron structures. Moreover, we scrutinize the inter-transformations between hexagonal Skyrmion lattices and disordered bimeron polymers occuring via nucleation and mutual annihilation of merons within the cell boundaries. Our theory provides clear directions for experimental studies of bimeron orderings in different condensed-matter systems with quasi-two-dimensional geometries. [ABSTRACT FROM AUTHOR]

Published
2024
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30. Reorientation processes of tilted skyrmion and spiral states in a bulk cubic helimagnet Cu2OSeO3

Author

Leonov, Andrey O. (author), Pappas, C. (author), Leonov, Andrey O. (author), and Pappas, C. (author)

Abstract

We present a systematic study of tilted spiral states obtained theoretically within the classical Dzyaloshinskii model for magnetic states in cubic non-centrosymmetric ferromagnets. Such tilted spirals are shown to stabilize under the competing effect of cubic and exchange anisotropies inherent to cubic helimagnets. By focusing on the internal structure of these spirals and their field-driven behaviour for different aspect ratios of the anisotropy coefficients, we are able to capture the main features of the experimental findings in a bulk cubic helimagnet Cu2OSeO3 and to make a step further towards a complete quantitative model of this chiral magnet. In particular, we show that for strong anisotropy values (which experimentally correspond to low temperatures near zero) there exist an angular separation between the conical and tilted spirals, i.e., the conical spiral flips into a tilted state and immediately composes some finite angle with respect to the field direction. As the anisotropy ratio decreases, such a transition between two spiral states becomes almost continuous and corresponds to higher temperatures at the experiments. In addition, we investigate the field-driven reorientation of metastable skyrmion lattices induced by the competing anisotropies, which may be responsible for some peculiarities at the experimental phase diagrams of Cu2OSeO3., RST/Neutron and Positron Methods in Materials

Published
2023
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31. Swirling of Horizontal Skyrmions into Hopfions in Bulk Cubic Helimagnets.

Author

Leonov, Andrey O.

Subjects
SKYRMIONS, SWIRLING flow, CHIRALITY, MAGNETIC fields, ELECTROMAGNETISM
Abstract

Magnetic hopfions are three-dimensional topological solitons embedded into a homogeneously magnetized background. The internal structure of hopfions is distinguished by the linked preimages—closed loops with a single orientation of the magnetization on the target space  S 2 —and is thus characterized by the integer Hopf index  Q H . Alternatively, hopfions can be visualized as a result of the swirling of two-dimensional bimerons around the direction of an applied magnetic field. Since the bimeron consists of a circular core and an anti-skyrmion crescent, two hopfion varieties can be achieved with either bimeron constituent facing the hopfion interior. In bulk cubic helimagnets, however, the applied magnetic field leads to a spontaneous collapse of hopfions, i.e., the eigen-energy of hopfions has the minimum for zero hopfion radius R. Anti-hopfions with  Q H = − 1 , in this case, pass through the intermediate toron state with two-point defects. Here, we demonstrate that the competing cubic and exchange anisotropies inherent in cubic non-centrosymmetric magnets (e.g., in the Mott insulator Cu 2 OSeO 3 ) as a third level of the hierarchy of energy scales following the exchange and Dzyaloshinskii–Moriya interactions, may shift the energy minimum into the region of finite hopfion radii. [ABSTRACT FROM AUTHOR]

Published
2023
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32. Precursor skyrmion states near the ordering temperatures of chiral magnets.

Author

Leonov, Andrey O.

Abstract

In noncentrosymmetric magnets, chiral Dzyaloshinskii–Moriya interactions (DMI) provide a distinctive mechanism for the stabilization of localized skyrmion states in two and three dimensions with a fixed sense of rotation. Near the ordering transition, the skyrmion strings develop attractive skyrmion–skyrmion interactions and ultimately become confined in extended clusters or textures [A. O. Leonov and U. K. Rößler, Nanomaterials, 2023, 13, 891], which is a consequence of the coupling between the magnitude and the angular part of the order parameter. Multi-skyrmionic states built from isolated skyrmions (IS) can form multiple modulated magnetic phases that may underlie the exotic magnetic phenomena of "partial order" or the field-driven "A-phase" observed in MnSi and other cubic helimagnets. Based on the standard phenomenological Dzyaloshinskii model, we obtain numerically exact solutions for skyrmion lattices (SkL), formulate their basic properties, and elucidate physical mechanisms of their formation and stability. Our detailed numerical studies show that the bound skyrmion states arise as hexagonal lattices of ±π-skyrmions (with the magnetization in the center along or opposite to the magnetic field) or square staggered lattices of π/2-skyrmions, which contain defect lines with zero modulus value and thus may form thermodynamically stable states only near the ordering temperature. In the simplest case of a two-dimensional (2D) skyrmionic texture, the structure is homogeneous in the third dimension (3D). The skyrmions preserve an ideal axisymmetric "double twist" core in condensed phases, while continuation into a space-filling texture is frustrated. The evolution of skyrmion lattices in an increasing magnetic field leads to a succession of phase transitions of first or second kind between diverse textures and finally ends due to the formation of isolated skyrmion-filaments with fixed radius and shape embedded in a homogeneously magnetized matrix. In the framework of the phenomenological model including only isotropic interactions (exchange, Zeeman, and DM energy contributions), the considered skyrmion lattices are only metastable states as the competing conical one-dimensional spiral forms the equilibrium state. But due to the weak couplings between skyrmions, secondary effects like anisotropies can stabilize skyrmionic textures as compared to simple helices. Also the topological nature of skyrmion condensates makes the magnetization processes in chiral magnets history-dependent and hysteretic. [ABSTRACT FROM AUTHOR]

Published
2023
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33. Supplementary Figures 1-2, Tables 1-4 from Prevention of Colorectal Carcinogenesis by DNA-Binding Small-Molecule Curaxin CBL0137 Involves Suppression of Wnt Signaling

Author

Kirsanov, Kirill, primary, Fetisov, Timur, primary, Lesovaya, Ekaterina A., primary, Maksimova, Varvara, primary, Trukhanova, Lubov, primary, Antoshina, Elena, primary, Gor'kova, Tatiana, primary, Morozova, Olga, primary, Safina, Alfiya, primary, Fleyshman, Daria, primary, Salimov, Ramiz, primary, Shipaeva, Elena, primary, Ivanov, Roman, primary, Leonov, Andrey, primary, Purmal, Andrei A., primary, Belitsky, Gennady A., primary, Gudkov, Andrei V., primary, Gurova, Katerina V., primary, and Yakubovskaya, Marianna G., primary

Published
2023
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34. Data from Prevention of Colorectal Carcinogenesis by DNA-Binding Small-Molecule Curaxin CBL0137 Involves Suppression of Wnt Signaling

Author

Kirsanov, Kirill, primary, Fetisov, Timur, primary, Lesovaya, Ekaterina A., primary, Maksimova, Varvara, primary, Trukhanova, Lubov, primary, Antoshina, Elena, primary, Gor'kova, Tatiana, primary, Morozova, Olga, primary, Safina, Alfiya, primary, Fleyshman, Daria, primary, Salimov, Ramiz, primary, Shipaeva, Elena, primary, Ivanov, Roman, primary, Leonov, Andrey, primary, Purmal, Andrei A., primary, Belitsky, Gennady A., primary, Gudkov, Andrei V., primary, Gurova, Katerina V., primary, and Yakubovskaya, Marianna G., primary

Published
2023
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35. Supplementary Table 5 from Prevention of Colorectal Carcinogenesis by DNA-Binding Small-Molecule Curaxin CBL0137 Involves Suppression of Wnt Signaling

Author

Kirsanov, Kirill, primary, Fetisov, Timur, primary, Lesovaya, Ekaterina A., primary, Maksimova, Varvara, primary, Trukhanova, Lubov, primary, Antoshina, Elena, primary, Gor'kova, Tatiana, primary, Morozova, Olga, primary, Safina, Alfiya, primary, Fleyshman, Daria, primary, Salimov, Ramiz, primary, Shipaeva, Elena, primary, Ivanov, Roman, primary, Leonov, Andrey, primary, Purmal, Andrei A., primary, Belitsky, Gennady A., primary, Gudkov, Andrei V., primary, Gurova, Katerina V., primary, and Yakubovskaya, Marianna G., primary

Published
2023
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40. ОЦЕНКА СРОКА СЛУЖБЫ ИЗОЛЯЦИИ КАБЕЛЬНЫХ ИЗДЕЛИЙ ДЛЯ СИСТЕМ ПИТАНИЯ И УПРАВЛЕНИЯ ГОРНОШАХТНОГО ЭЛЕКТРООБОРУДОВАНИЯ

Author

Leonov, Andrey Petrovich and Soldatenko, Evgeniy Yurievich

Subjects
ethylene-propylene rubber, insulation, Materials Science (miscellaneous), шахтные кабели, mining electrical equipment, Management, Monitoring, Policy and Law, Geotechnical Engineering and Engineering Geology, кабельные изделия, изоляция, срок службы, flexible mining cables, elongation at break, Fuel Technology, activation energy, этиленпропиленовая резина, горношахтное электрооборудование, Economic Geology, thermal aging, энергия активации, service life, Waste Management and Disposal, тепловое старение, относительное удлинение, разрывы
Abstract

Актуальность исследования обусловлена повышением требований к эксплуатационным свойствам гибких кабелей, применяемых в системах питания и управления горношахтного электрооборудования. Основным направлением, обеспечивающим улучшение свойств, является применение новых электроизоляционных материалов. На сегодняшний день шахтные кабели изготавливаются преимущественно с изоляцией из резины. Перспективным решением в плане совершенствования конструкций гибких шахтных кабелей является применение этиленпропиленовой резины, обладающей более высокой нагревостойкостью по сравнению с применяемыми резинами на основе хлоропренового и бутилкаучука. Повышение допустимой температуры нагрева токопроводящих жил позволит повысить передаваемую мощность, высокие значения тока термической устойчивости при коротком замыкании с обеспечением требуемой гибкости. Практическое применение кабелей нового типа в системах горношахтного электрооборудования невозможно без экспериментального подтверждения ресурсных характеристик. Отсутствие в технической литературе рекомендаций по проведению подобных испытаний определяет необходимость исследований, позволяющих прогнозировать срок службы гибких кабелей с учетом изменения физико-механических свойств этиленпропиленовой резины. Цель: разработать методику и определить срок службы гибких кабельных изделий с изоляцией из этиленпропиленовой резины для систем питания и управления горношахтного электрооборудования. Объект: гибкий шахтный кабель, изоляция, этиленпропиленовая резина, физико-механические свойства, энергия активации, срок службы. Методы: экспериментальные методы оценки физико-механических свойств и теплостойкости полимерных материалов; математические методы решения нелинейных систем уравнений и статистический анализ результатов испытаний. Результаты. Разработана методика определения срока службы кабелей с изоляцией из этиленпропиленовой резины, основанная на методе прогнозирования изменения физико-механических свойств с учетом энергии активации Ea процессов термической деструкции. Определен срок службы гибких шахтных кабелей с учетом температуры. The relevance of the research is provided by flexible cables design perfection for power and control systems of mining electrical equipment. The application of modern insulation materials is the main way for improving flexible cables properties. Currently, mining cables are produced with the rubber insulation. Advanced solution for improving the design of flexible mining cable is application of ethylenepropylene rubber, which has a higher heat resistance as compered to chloroprene and butyl rubber. The transmitted power is increased and a high values of thermal stability current at a short current with the requiring cycle flexibility is provided. The practical application of brand-new cables in the mining electrical equipment is impossible without lifetime characteristics testing. The lack of recommendations in the technical literature on the methodology of such tests requires studies to predict the service life, taking into account changes in the physical and mechanical properties of the ethylene-propylene rubber. The main aim of the research is to develop the method and to determine the service life of flexible cables with ethylene-propylene rubber insulation for power and control systems of mining electrical equipment. Objects: flexible mining cable, insulation, ethylene-propylene rubber, physical and mechanical properties, activation energy, service life. Methods: experimental methods for evaluating the physical and mechanical properties, and heat resistance of polymeric materials; mathematical methods for solving nonlinear systems of equations and test results statistical analysis. Results. The method for determining the service life of cables with ethylene-propylene rubber insulation was developed. This method is based on the physical and mechanical properties prediction considering the activation energy of thermal destruction processes. The service life of flexible mine cables is determined taking into account temperature.

Published
2022
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42. ОПРЕДЕЛЕНИЕ ПОГОННЫХ ЭЛЕКТРОТЕХНИЧЕСКИХ ПАРАМЕТРОВ НЕФТЕПОГРУЖНОГО КАБЕЛЯ

Author

Glazyrin, Aleksandr Saveljevich, Isaev, Yusup Niyazbekovich, Kladiev, Sergey Nikolaevich, Leonov, Andrey Petrovich, Rakov, Ivan Vitalievich, Kolesnikov, Stanislav Vyacheslavovich, Langraf, Sergey Vladimirovich, Philipas, Alexander Alexandrovich, Kopyrin, Vladimir Anatolyevich, Khamitov, Rustam Nurimanovich, Kovalev, Vladimir Zakharovich, and Lavrinovich, Alexey Valerievich

Subjects
электрические поля, Electric motor, Computer science, Stator, Differential equation, Materials Science (miscellaneous), Automatic frequency control, нефтепогружные кабели, Mechanical engineering, magnetic field, Management, Monitoring, Policy and Law, skin effect, law.invention, скин-эффект, law, магнитные поля, electric potential, нефти, электротехнические параметры, Waste Management and Disposal, электрический потенциал, Mathematical model, векторный потенциал, Maxwell's equation, Geotechnical Engineering and Engineering Geology, Finite element method, electric field, submersible electric motor, механизированная добыча, Fuel Technology, уравнение Максвелла, Electromagnetic coil, Control system, оil submersible cable, mechanized oil production, Economic Geology, vector magnetic potential, магнитный потенциал
Abstract

Актуальность. Определение основных электрических параметров нефтепогружных кабелей связано с необходимостью создания точных математических моделей станции управления системами - нефтепогружной кабель - погружной электродвигатель, в которых необходимо учитывать волновые процессы в протяженной кабельной линии, возникающие в связи с формой импульсов, генерируемых преобразователями частоты, входящими в состав современных пультов управления. Электрические параметры, такие как линейная емкость и индуктивность, не стандартизированы в технической литературе и не указываются в технических характеристиках производителями кабелей. Однако, очевидно, что создание систем управления и идентификация режимов работы ПЭД требует решения систем дифференциальных уравнений, включающих в качестве параметров заданные характеристики. Кроме того, современные концепции частотного регулирования электродвигателей, в частности погружных, указывают на то, что при работе преобразователей частоты на базе IGBTтранзисторов в сигнале питания ПЭД возникают высокочастотные перенапряжения, приводящие к появлению частичных разрядов в обмотках статора моторов. Этот факт будет усугубляться развитием более cильных полей с увеличением длины кабеля и, соответственно, большим влиянием волновых процессов на форму сигнала, подаваемого на ПЭД. Цель исследования заключается в разработке методики определения погонных электротехнических параметров нефтепогружного кабеля любых конструкций и используемых материалов. Методы: методы решения дифференциальных уравнений, полевых задач, численное конечно-элементное моделирование. Результаты. Разработана методика определения погонных ёмкостей и погонных индуктивностей жил и брони нефтепогружного кабеля, основанная на решении дифференциальных уравнений для эталонной «справочной» модели и численном моделировании идентичной конструкции в COMSOL Multiphysics® Version 5.5a. Указано, что конечно-элементное моделирование в COMSOL Multiphysics® Version 5.5a корректно и с достаточной точностью (ошибка менее 5 %) совпадает с результатами решения уравнений, приведённых в справочной литературе. Определены погонные значения ёмкостей и индуктивностей для наиболее распространённых конструкций нефтепогружных кабелей. The relevance. Determination of the main electrical parameters of oil submersible cables is associated with the need to create accurate mathematical models of the systems control station - oil submersible cable - submersible motor, in which it is necessary to take into account wave processes in a long cable line arising in connection with the shape pulses generated by frequency converters included in the set of modern control stations. Electrical parameters such as linear capacities and inductances are not standardized in the technical literature and are not indicated in the technical specifications by cable manufacturers. However, it is obvious that the creation of control systems and identification of the SEM operation modes requires the solution of systems of differential equations, which include the specified characteristics as parameters. In addition, modern concepts of frequency control of electric motors, in particular submersible, indicate that during operation of frequency converters based on IGBT transistors, high-frequency overvoltages arise in the SEM supply signal, leading to the appearance of partial discharges in the stator windings of the motors. This fact will be aggravated by the development of deeper fields, with a longer cable length and, accordingly, a greater influence of wave processes on the shape of the signal supplied to the SEM. The main aim of the research consists in development of a method for determining the linear electrical parameters of the submersible cable of any designs and materials used. Methods: methods for solving differential equations, field problems, numerical finite element modeling, and a physical experiment. Results. A method was developed for determining the linear capacities and inductances of conductors and armor of an oil-submersible cable, based on solving differential equations for a «reference» model, numerical modeling of an identical design in COMSOL Multiphysics® Version 5.5a, comparison of the obtained values with experimental data. It is indicated that the finite element modeling in COMSOL Multiphysics® Version 5.5a is correct and with sufficient accuracy (error less than 5 %) coincides with the results of solving the equations given in the reference literature. The linear values of capacities and inductances have been determined for the most common designs of oil-submersible cables.

Published
2021
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43. ИССЛЕДОВАНИЕ АСИНХРОННОЙ ЭЛЕКТРИЧЕСКОЙ МАШИНЫ С КОРОТКОЗАМКНУТЫМ РОТОРОМ ДЛЯ ВОЗОБНОВЛЯЕМОЙ ЭНЕРГЕТИКИ ПРИ НЕСТАЦИОНАРНОМ КОНДЕНСАТОРНОМ ВОЗБУЖДЕНИИ

Author

Bunkov, Dmitriy Sergeevich, Glazyrin, Aleksandr Saveljevich, Bolovin, Evgeny Vladimirovich, Krokhta, Yuri Vladimirovich, Bannov, Dmitry Mikhailovich, Kovalev, Vladimir Zakharovich, Khamitov, Rustam Nurimanovich, Kladiev, Sergey Nikolaevich, Langraf, Sergey Vladimirovich, and Leonov, Andrey Petrovich

Subjects
Computer science, Stator, генераторные установки, Materials Science (miscellaneous), Management, Monitoring, Policy and Law, возобновляемые источники энергии, децентрализованное электроснабжение, squirrel-cage rotor, law.invention, Generator (circuit theory), law, короткозамкнутые роторы, renewable energy sources, Waste Management and Disposal, non-stationary capacitor excitation, асинхронные машины, decentralized power supply, электромеханические преобразователи, business.industry, Squirrel-cage rotor, Rotor (electric), турбины, Induction generator, Electrical engineering, induction generator, Geotechnical Engineering and Engineering Geology, нестационарное конденсаторное возбуждение, Capacitor, Fuel Technology, Electricity generation, Economic Geology, business, Alternating current
Abstract

Актуальность. Доля электроэнергии, вырабатываемой установками на основе возобновляемой энергии, постоянно растет, в связи с чем потребность в развитии систем питания и автоматического управления электрическими машинами, лежащими в основе ветро- и гидрогенераторов, не теряет актуальности. В составе таких генераторных установок переменного тока применяют синхронные электрические машины, асинхронные машины с фазным и короткозамкнутым ротором. Преобразователи частоты, устанавливаемые в статорные и роторные цепи асинхронных машин переменного тока, позволяют управлять процессами их возбуждения, однако для начала генерации требуется использовать дополнительные внешние источники питания. Благодаря остаточному намагничиванию в магнитопроводе можно обеспечить процесс гарантированного самовозбуждения асинхронной машины c короткозамкнутым ротором с помощью подключения батарей конденсаторов к ее статорным обмоткам без применения дополнительного внешнего источника питания. Предложенный способ нестационарного конденсаторного возбуждения позволяет обеспечить адаптацию генераторной установки к изменению режимов работы в условиях децентрализованного электроснабжения. Цель: исследовать предложенную систему стабилизации напряжения асинхронной машины с короткозамкнутым ротором с варьируемым конденсаторным возбуждением в составе источника возобновляемой энергии. Методы: теоретические - теория дифференциальных уравнений, методы численного решения обыкновенных дифференциальных уравнений, теория электропривода, теория электрических машин, численные методы аппроксимации данных, и экспериментальные - проведение испытаний асинхронной электрической машины с нестационарным конденсаторным возбуждением на разработанном испытательном стенде с целью получения нагрузочных характеристик и осциллограмм напряжений на обмотках статора асинхронных машин с короткозамкнутым ротором в различных режимах работы, методы исследования. Результаты. Разработана и изготовлена оригинальная экспериментальная установка с узлом, имитирующим работу турбины. Электромеханический преобразователь энергии выполнен в виде асинхронной машины с короткозамкнутым ротором с нестационарным конденсаторным возбуждением. Блок управления установкой выполнен в виде интегрированного с силовым блоком гальванически развязанного модуля во влагостойком исполнении с применением беспроводного интерфейса связи Bluetooth. Описан и протестирован способ коммутации батарей конденсаторов с применением тиристоров в качестве управляемого ключа с двухсторонней проводимостью. Анализ полученных нагрузочных характеристик показывает принципиальную возможность обеспечить гарантированную выработку электроэнергии со стабилизацией напряжения в допустимых пределах изменения мощности нагрузки. Примененная в составе экспериментальной установки система автоматической коммутации конденсаторов с варьируемой в зависимости от потребляемой мощности емкостью позволила обеспечить приемлемое время динамической реакции на возмущающее воздействие при нестационарной нагрузке. The relevance. The share of electricity generated by installations based on renewable energy is constantly growing, and therefore the need for the development of power supply systems and automatic control of electrical machines underlying wind and hydro generators is still relevant. As part of such alternating current generator sets, synchronous electric machines, induction generator with phase and squirrel-cage rotor are used. Frequency converters installed in the stator and rotor circuits of induction generators make it possible to control their excitation, however, to start generation, additional external power sources must be used. Due to the residual magnetization in the magnetic circuit, it is possible to ensure the process of guaranteed self-excitation of the induction generator by connecting the capacitor banks to the electrical circuit of its stator without using an additional external power source. The proposed method of non-stationary capacitor excitation makes it possible to ensure the adaptation of the generator set to the change in operating modes under conditions of decentralized power supply. The main aim of the research is to study the proposed voltage stabilization system of squirrel-cage induction generator with a short-circuit rotor with variable capacitor excitation as part of a renewable energy source. Methods. To achieve the goal of the study, theoretical and experimental research methods were used. Theoretical research methods include the theory of differential equations, methods for the numerical solution of ordinary differential equations, the theory of electric drives, the theory of electrical machines, numerical methods for approximating data. The basis of experimental research is testing an induction generator with non-stationary capacitor excitation on a developed test bench in order to obtain load characteristics and oscillograms of voltages on the stator windings self-excitation of squirrel-cage induction generator rotor in different operating modes. Results. An original experimental setup with a unit imitating the operation of a turbine, an electromechanical energy converter in the form of squirrel-cage induction generator with non-stationary capacitor excitation has been developed and manufactured. The control system is made in the form of a galvanically isolated module integrated with the power unit in a moisture-resistant design using a wireless Bluetooth communication interface. A method for switching capacitor banks using thyristors as a controlled switch with two-way conduction is described and tested. The analysis of the obtained load characteristics shows the fundamental possibility of ensuring a guaranteed generation of electricity with voltage stabilization within the limits of load power variation. The system of automatic switching of capacitors with a capacitance varying depending on the power consumption applied as part of the experimental setup made it possible to provide an acceptable time for dynamic response to a disturbing effect under nonstationary load.

Published
2020
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45. Providing a minimum defectiveness of inter-turn insulation at the manufacturing stage and during the exploitation

Author

Leonov, Andrey Petrovich and Supueva, A.

Subjects
reliability, enameled wire, низковольтные обмотки, частотно-регулируемые электроприводы, asynchronous motor, надежность, low-voltage winding, асинхронные двигатели, frequency-controlled drive, межвитковая изоляция, inter-turn insulation, эмалированные провода, дефектность, defectiveness
Abstract

The reliability of a low-voltage asynchronous electric motor is primarily determined by the reliability of the stator winding insulation. Common reasons for the failure of the insulation system are the unsatisfactory quality of the enameled wires and electrical insulating materials used for imperfection and violation of the technological process of winding and insulating work, and the discrepancy between operating modes. In the vast majority of cases, failures occur due to damage to the inter-turn insulation as the weakest element. This causes the need to study the insulation system resistance to the formation of defects. The results of assessing the stability of the insulation of winding wires to defect formation are obtained, taking into account the features o f the operational loads characteristic of frequency-controlled drives with pulse-width modulation of the output voltage and the influence of the inter-turn insulation defectiveness level on its reliability indicators is also studied. The authors have developed the measures to reduce the defectiveness of inter-turn insulation at the manufacturing stage and during operation. This will ensure a minimum level of insulation defects and increase the resource of asynchronous electric motors by reducing the number of failures.

Published
2022

46. Tribotechnical and mechanical properties of CrN/TiN multi-layer coatings deposited on the surface of die steel.

Author

Leonov, Andrey, Denisova, Yulia, Denisov, Vladimir, Savchuk, Mikhail, and Tishchenko, Vasiliy

Subjects
*ELECTRIC arc, *COLD working of steel, *TITANIUM nitride, *SURFACE coatings
Abstract

The paper presents the results of studies of CrN/TiN multi-layer coatings on Cr12MoV cold work die steel deposited by vacuum-arc plasma-assisted method. All coatings were deposited at electric arc evaporator currents of 80 A for Ti and 90 A for Cr, substrate bias voltage (-) 150 V, substrate temperature 390-400 °C in a nitrogen-argon gas mixture (90 % (N2) and 10 % (Ar)) at a pressure of 0.6 Pa. The thickness of investigated coatings was about 4 µm. 8-, 16-, 32- and 64-layer CrN/TiN coatings were deposited, in which the thickness of each layer was 500 nm, 250 nm, 125 nm and 63 nm, respectively. The tribotechnical and mechanical properties of the deposited coatings were investigated. The microhardness of the CrN/TiN multi-layer coatings ranged from 16.4 GPa to 19.9 GPa, which was higher than the values for CrN and TiN single-layer coatings. Maximum microhardness was achieved for 16-layer CrN/TiN coating and amounted to 19.9 GPa. Changing the architecture of CrN/TiN multi-layer coatings by reducing the thickness of the CrN and TiN layers from 500 nm to 63 nm promotes a smooth decrease in both the wear parameter and the coefficient of friction. The minimum values of the wear parameter and the coefficient of friction were observed for the 64-layer CrN/TiN coating, which is 11 times and 2 times lower, respectively, than the average values for TiN and CrN single-layer coatings. [ABSTRACT FROM AUTHOR]

Published
2022
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