Short-circuited Coil Research Articles

Enhancing Magnetic Coupling Using Auxiliary Short-Circuited Coils

The efficiency of Dynamic Inductive Power Transfer (DIPT) depends mainly on the coupling coefficient within the coupler. In order to improve this parameter, a novel approach has been introduced that results in a significant increase of between 25% and 36% at minimal additional cost in the case of juxtaposed rectangular coil configuration on the road. This method involves the incorporation of a passive additional short-circuit coil adjacent to the primary coil for obtaining a higher coupling coefficient, as has been theoretically demonstrated. Simulations carried out on Comsol have optimized the dimensions of this additional coil, not only for cost effectiveness and minimal space utilization, but also for optimal efficiency. Experimental validation was performed at reduced power, using a 2 kW test bench, and confirmed the estimation. The efficiency improvement proposed in this paper is crucial for improving the global DIPT efficiency and then facilitating its social acceptance.

HTS-Tape Magnetic Bearing for Ultra High-Speed Turbo Motor

This paper aims to design superconducting mag-netic bearing using HTS tape for a ultra high-speed turbo motor operating up to 120000rpm. Despite being a recent technology compared to conventional magnetic bearings, HTS passive bearings have many interesting features, such as re-duced dimensions, easy implementation and excellent dynamic response at high speed. The results of the finite element simulation are promising as the levitation forces and the stiffness of the superconductor bearing are compatible with the design requirements. The main contribution of this paper lies in the use of short-circuited HTS coils, unlike previous systems that used HTS bulk.

Modeling, Analysis, and Identification of Armature Winding Interturn Fault in Multiphase Brushless Exciters

As the core of large-capacity nuclear power generation system, the multiphase annular brushless exciter (MPABE) may cause a serious catastrophe to the nuclear power plant if it fails. In order to effectively protect the armature winding of MPABE, a rapid simulation model and a sensitive diagnosis method of armature winding short-circuit (AWSC) fault are studied systematically in this article. First, this article proposes a general and rapid simulation model of MPABE with AWSC fault. To verify the correctness of this model, corresponding simulations and experiments of AWSC faults are carried out, respectively, through which the fault characteristics are obtained. Then, a detailed mechanism analysis is presented, which explains the induction process of the related harmonics in the stator and rotor currents. The variation law of the characteristics value when the number of short-circuited coils changes is also analyzed. Finally, a new method to diagnose AWSC fault of the MPABE is proposed and then optimized. The test results on the prototype show that this method can sensitively diagnose even the slightest AWSC fault. Therefore, it can provide a reliable basis for the monitoring and protection of MPABE in nuclear power plants.

Principle and Performance of a New Brushless Doubly Fed Reluctance Machine With Asymmetrical Composite Modulator

For the brushless doubly fed reluctance machine (BDFRM), a composite rotor featuring salient pole reluctance and short-circuited coils (SCC) is applied to efficiently improve the cross-coupling capability and magnetic field modulation effects, where the SCCs induce symmetrical multiphase current and then establish the corresponding additional magnetizing magnetomotive force to modulate the source one. This article investigates the modulation behavior and evaluates the modulation capability of the composite modulator from the perspective of the magnetic field conversion mechanism. The modulated airgap harmonic phase-shift phenomenon in space caused by the SCC modulator is first observed, resulting in the reduction on the effective magnetic field conversion factors in the BDFRM with conventional symmetrical composite rotor. The phase-shift mechanism is revealed for the first time, then an asymmetrical composite modulator configuration is proposed to eliminate the phase shift so as to enhance the rotor cross-coupling capability and improve torque performance. A BDFRM prototype with the asymmetrical composite modulator is designed and manufactured for experimentation. Theoretical predictions are verified by two-dimensional finite-element analysis together with experiments.

On Estimating the No-Load Current of High-Capacity Moving Coil Voltage Regulators

Moving coil voltage regulators are intended for smooth variation of voltage in a wide range. In the 20th century, various design versions of such devices were developed, and their production was mastered around the world, including in Russia. The type of voltage regulators with a moving short-circuited (SC) coil has been most widely used. Today, the production of such regulators in Russia has been stopped, although the need for them in specialized fields of application, in particular, at research and testing laboratories, still remains quite high. Currently, the Ramensky Electrotechnical Plant Energiya conducts research and development works for constructing a new lineage of high-capacity moving SC coil voltage regulators in single-phase and three-phase versions. In view of the specific features relating to operating principle of moving SC coil voltage regulators, one of the key parameters of their design, which in many respects determines their characteristics, is the no-load current, which can make tens of percent of the rated current. Accordingly, effective designing of voltage regulators that would comply with target indicators and characteristics is only possible if there are tools for estimating the device no-load current with acceptable accuracy. The article describes the operating principle of a moving SC coil voltage regulator and reveals the relationship between its main characteristics and the no-load current. The well-known analytical approach to estimating the no-load current of the considered regulator type is briefly outlined. An interpretation of this approach for application to the prototype design of the regulator that is under development is described. Based on the regulator magnetic field 3D modeling by the finite element method using up-to-date dedicated software tools, a numerical method for estimating the device no-load current is proposed, the accuracy of which is several times better than that provided by the known methods. A comparison between the estimated and measured values of the no-load current of the prototype 100 kVA single-phase moving coil voltage regulator is given.

HTS Dipole Magnet Model for the Persistent Current Operation

Recent advances in the fabrication of high-temperature superconducting (HTS) coils allow the design of superconducting accelerator magnets that work in a persistent current mode. Many various, rather low-field magnets in particle accelerators operate in the DC current mode. Fermilab designed, fabricated, and tested an HTS dipole magnet model that has 20-mm air gap and a magnetic field up to 0.5 T. The magnet has a primary copper coil that for a short period pumps the energy in the short-circuited secondary HTS coil. The current paper presents the design, fabrication, and testing of this magnet at liquid-nitrogen temperature.

Optimized Shape of Short-Circuited HTS Coils by Cutting Process for Superconducting Fault Current Limiters

This article presents an optimization of short-circuited superconducting coils to be used in superconducting fault current limiter devices. The optimized shape reduces losses, eliminates overheating points, improves current distribution, uniforms the voltage drop over the tape length, and ensures uniform resistivity. The geometric analysis and its optimization are presented in this article. The results of computational simulation by finite element method are also presented. Superconducting tape cutting methods and coil welding are investigated. The influence of geometry and cutting technique on the critical current are evaluated based on the experimental tests results. Cutting high-temperature superconductor tapes by punching or laser process showed excellent results using <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta ={7.5}^{\circ }$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${30}^{\circ }$</tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta$</tex-math></inline-formula> is a characteristic angle of the geometry of the coil. There was no excessive degradation of the critical current or delamination, which is common due to the cutting. The laser process led to higher critical current values per unit width ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$I_c-{\rm mm}$</tex-math></inline-formula> ) to angle cut <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\theta ={30}^{\circ }$</tex-math></inline-formula> , a characteristic that has its origin in two factors: 1) temperature increase in a larger area when the adopted cutting angle is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${7.5}^{\circ }$</tex-math></inline-formula> and 2) higher cutting precision, which imposes a slightly different cross section when compared to the punching process.

Dynamic stability of wind farm multi-machine power system

Since it is difficult to store electrical energy, production, and consumption must be in equilibrium under constant voltage and frequency. The producers, the receivers, and the electrical networks that connect them, have mechanical and electrical inertias which disturb this balance. Faced with a variation in power, the electrical system, after oscillations, returns to a stable state. In some cases, the oscillatory regime may diverge. Studies are being carried out to remedy this problem and ensure the stability of the electricity network. This manuscript focuses on FACTS regulation which helps electrical systems, subjected to strong disturbances, to maintain their stability. Magnetic Energy Storage Superconductor (SMES) contains a short-circuited superconducting coil on itself, which injects or absorbs active and reactive power into the system, thereby improving the stability of electrical systems.

Study of the influence of magnetic properties of amorphic alloys on the electromagnetic field of current transformers with a short-closed circuit

The optimal functioning of the electric power industry can be ensured only if the important problem is successfully resolved by reliable measurement of electrical quantities, such as voltage, current, and power. In industry, a current transformer is often used as a current meter, which makes it possible to obtain an AC current measurement result with high accuracy. Structurally, the current transformer has a significant drawback, which is that the opening of the secondary measuring winding leads to an emergency. To solve this problem, you can apply the improved design of the current transformer squirrel-cage current transformer (in the form of a cylinder or ring). This article presents the results of two-dimensional modeling of the electromagnetic field of current transformers with a short-circuited coil, with cores made of different grades of amorphous iron in the ELCUT software package. In addition, the results of experimental studies of the improved design of the current transformer are presented. An analysis of the results allows us to conclude that the use of a core made of amorphous iron with a higher magnetic permeability will lead to economic benefits and make the measurement process more energy efficient.

FEM Model of Oscillating Ferromagnetic Yoke in the Magnetic Field of a Permanent Magnet With and Without a Short-Circuited Coil

Numerical simulation of the oscillating ferromagnetic yoke in the magnetic field of a cylindrical permanent magnet without and with a short-circuited multi-turn coil was performed. Finite-element method (FEM) analysis based on the fundamental Maxwell equations and the Maxwell stress tensor approach was used. Due to induction of eddy currents in the volume of the conducting yoke, as well as in the other parts of the magnetic circuit, eddy current damping (ECD) occurs. There is some influence of the current circulating in the short-circuited coil. The shift of resonance frequency of studied systems to the lower values in comparison to the solely mechanical system was more significant for mechano-electromagnetic systems without the short-circuited coil than for the same system with the short-circuited coil. Also, the damping was higher without the short-circuited coil than with the coil. Good agreement with results obtained from experiments, as well as from the simplified analytic model, was observed. It follows that the addition of short-circuited coil deteriorates the vibration control properties of the system based solely on the ECD.

Numerical investigation of stent designs for wireless access to integrated sensors

Abstract In recent years, a progressive interest in the implementation of wireless access to cardiovascular implants has been established. This manifests in new devices, such as arterial pressure sensors, or additional functionalities added to established implants like stents. However, common stent designs, possessing highly optimized mechanical properties, often consist of cylindrically arranged struts with connections in-between which can be considered as short-circuited inductive coils. As a consequence, the small inductance raises the resonance frequency, which may decrease the in vivo performance of the wireless connection between the stent and the external readout device. Thus, new designs were developed to overcome this limitation, for example by avoiding the short-circuit due to a helical arrangement of the struts. Within this work we compare the performance of a common stent design and a helical design by means of numerical simulations. We are using two designs which only differ in the arrangement of the struts. The electromagnetic and mechanical properties are investigated using a finitedifference time-domain algorithm and finite element method, respectively. We will show that a common stent design exhibits resonance frequencies in the gigahertz regime, much higher than the frequencies of comparable helical designs. Furthermore, we compare the mechanical performance of the two designs and reveal individual distinctions in the radial stiffness, bending stiffness, and the von Mises stress.

Pulsed Magnetization of a Short-Circuited HTSC Coil

We have studied trapped magnetic fields and their relaxation during pulsed magnetization of a 20-turn short-circuited coil made of a stabilized HTSC-2G tape at liquid nitrogen temperature. The highest trapped field is close to the value obtained during field cooling (FC process) and varies insignificantly upon a five-fold increase of the magnetizing pulse amplitude. Copper coating of the tape considerably suppresses pulsed heating effects. Current relaxation at the initial segment is determined by the current passing between superconducting and normal layers and by the form of the current–voltage characteristic. Over long time intervals (t > 100 s), relaxation is determined by the contact resistance of the soldered junction.

Stable Levitation of Superconducting Myxines of Galathea Plasma Traps

Designing magnetic systems of Galathea plasma traps on the basis of levitating superconducting magnetic coils requires searching for their stable levitating states. For this purpose, proceeding from the property of superconductors to preserve the trapped magnetic flux, the potential energy of a system of several coaxial superconducting rings (one of the rings is fixed) with given trapped magnetic fluxes is obtained as an analytic function of the coordinates of the free rings along the system axis and angular deviations of their axes from the common axis of the system in a uniform gravity field in the thin-ring approximation. Computations demonstrate that, under certain values of physical parameters (the trapped magnetic flux and the dimensions and masses of the rings), this dependence has local minima, which correspond to stable equilibrium states of the levitating rings. For high-temperature superconducting (HTSC) rings and short-circuited HTSC coils manufactured for experiments on levitation, equilibrium states are found in different cases by calculating the aforementioned dependence of the potential energy. In the case where the magnetic fluxes trapped by the rings have the same signs, the calculated equilibrium levitating states of an HTSC ring in the field of a short-circuited HTSC coil (or an HTSC ring), namely, states that are stable against vertical displacements and angular deviations of the axis from the vertical, are implemented experimentally.

Импульсное намагничивание короткозамкнутой катушки из ВТСП

In this paper is described the pulsed magnetization of a 20-turn short-circuited coil from a stabilized HTSC-2G tape. The trapped field in the coil is close to the value obtained at the field cooling (FC) process and varies only slightly with a 5-fold increase in the amplitude of the magnetizing pulse. The copper coating of the tape significantly reduces the effects of pulsed heating. The relaxation of the current in the initial stage is determined by the flow of current between the superconducting and normal layer and the type of the current-voltage characteristic. At large times (t&gt; 100 s), attenuation is determined by the contact resistance of the junction.

Magnetic coupling enhancement using a flux transformer

We explore the possibility of improving the magnetic coupling between two distant coils by using a flux transformer. A flux transformer is a short-circuited coil operating in constant flux mode. It could be an alternative for applications where it would not be suitable to use a magnetic core. From the circuit model of an air-cored inductive power transfer (IPT) system, we show that the flux transformer allows for magnetic coupling of systems separated by a large distance, even at low frequencies. A flux transformer can be practically obtained with a joint-free superconducting (SC) coil. We demonstrate here how this can be done using a laser-cut high temperature SC ReBCO coated conductor. Experimental results confirm the prediction of the circuit model and the corresponding finite element (FE) model. The flux transformer opens the door to new kinds of IPT systems.

Preliminary Design and Test of Low-Resistance High Temperature Superconducting Short-Circuited Coils

Despite their relatively high volume and weight, inductive fault current limiters with high temperature supercon-ducting (HTS) secondaries have already proven their viability, especially the transformer topology. Volume and weight make them inappropriate for transmission grids, but they can, e.g., promote the advent of renewable energy sources in medium voltage electric distribution networks while maintaining short-circuit current levels consistent with existing protections ratings. These devices make use of a short-circuited HTS secondary, which typically requires nonsuperconducting joints. Although jointless HTS secondaries have already been built (by means of, e.g., opening slits in the tapes), these have no application in real-scale devices. In this paper, a new engineering design of low-resistance HTS short-circuited coils, intending applications in distribution grid fault current limiters, is proposed. This design allows building coils with an arbitrary number of turns and a single joint only, thus providing an effective way of adjusting the parameters of limiters (e.g., activating current). A prototype coil is built, and the manufacturing process is described. The proposed concept is experimentally validated by measurements of contact resistance and induced superconducting currents.

Minimization of the Electromagnetic Torque Ripple Caused by the Coils Inter-Turn Short Circuit Fault in Dual-Redundancy Permanent Magnet Synchronous Motors

With the development of electric vehicles and More-Electric/All-Electric aircraft, high reliability is required in motor servo systems. The redundancy technique is one of the most effective methods to improve the reliability of motor servo systems. In this paper, the structure of dual-redundancy permanent magnet synchronous motor (DRPMSM) with weak thermal coupling and no electromagnetic coupling is analyzed and the mathematical model of this motor is established. However, there is little research on how to suppress the torque ripple caused by short-circuited coils in the DRPMSM. The main contribution of this paper is to present the advantages of DRPMSM and to find a way to suppress the torque ripple caused by the short circuit fault in DRPMSM. In order to improve operation quality and enhance the reliability of DRPMSM after a short circuit occurs, the torque ripple caused by the coils inter-turn short circuit fault in DRPMSM is analyzed in detail. Then, a control method for suppressing the electromagnetic torque ripple of a short-circuited coil is proposed for the first time by using an improved adaptive proportional resonant (PR) controller and a proportional integral (PI) controller in parallel. PR control is a method of controlling alternating components without steady-state error, and it can be used to suppress torque ripple. DRPMSM adopts speed and current double closed-loop control strategies. An improved adaptive PR controller and a PI controller are employed in parallel for the speed loop, while traditional PI control is adopted in current loop. From the simulation and experimental results, the torque ripple is reduced from 45.4 to 5.6% when the torque ripple suppression strategy proposed in this paper is adopted, in the case that the speed is 600 r/min. The torque ripple suppression strategy based on the PR controller can quickly and effectively suppress the torque ripple caused by the short-circuited coils, which makes the motor speed more stable.

Investigation and Analysis of a New Shaded-Pole Main Exciter for Aircraft Starter–Generator

In this paper, a new shaded-pole main exciter (ME) with additional short-circuited coils for aircraft three-stage starter–generator (SG) is proposed and investigated. The basic structure, winding configurations, operating principle, and start system structure of the presented shaded-pole ME are illustrated in detail. The comparative study between the original ME and the shaded-pole ME with respect to the starting mode performances is conducted by 2-D finite-element method (FEM). A prototype SG with original ME has been developed, and the experimental results are essentially consistent with the simulation results by the FEM utilized in the predictions in this paper. Simulation data and waveforms verify that the proposed shaded-pole ME is a good candidate for aircraft machines to satisfy the dual function of starter and generator.

General Airgap Field Modulation Theory for Electrical Machines

This paper proposes a general field modulation theory for electrical machines by introducing magnetomotive force modulation operator to characterize the influence of short-circuited coil, variable reluctance, and flux guide on the primitive magnetizing magnetomotive force distribution established by field winding function multiplied by field current along the airgap peripheral. Magnetically anisotropic stator and rotor behave like modulators to produce a spectrum of field harmonics and the armature winding plays the role of a spatial filter to extract effective field harmonics to contribute the corresponding flux linkage and induce the electromotive force. The developed field modulation theory not only unifies the principle analysis of a large variety of electrical machines, including conventional dc machine, induction machine, and synchronous machine which are just special cases of the general field modulated machines, thus eliminating the problem of the machine theory fragmentation, but also provides a powerful guidance for inventing new machine topologies.

Current-carrying capability of the 100 kA-class HTS STARS conductor for the helical fusion reactor FFHR-d1

A 100-kA-class conductor using REBCO high-temperature superconductor (HTS) is proposed as one of the conductor options for the helical coils of the LHD-type helical fusion reactor FFHR-d1. We named it STARS (Stacked Tapes Assembled in Rigid Structure) conductor. Current carrying capability of such a simply-stacked tape conductor is an important issue. We fabricated and tested a 100-kA class STARS prototype conductor sample to verify whether a premature quench occurs. The conductor sample is a one-turn short-circuit coil with a race-track shape having a bridge-type mechanical lap joint. The transport current of the sample was induced by changing the external magnetic field, and the critical current of the sample was measured. A numerical analysis of the critical current is being performed by self-consistently solving the spatial distributions of the current density and magnetic field among the tapes to verify the measured critical current of the samples.