40 research outputs found
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Frequency-dependent demagnetisation rate of a shielded HTS tape stack
Abstract
This work presents results of investigation of crossed-field demagnetization in 2G high temperature superconducting stacks at temperatures in the range of 77 - 20 K and in a variable frequency, corresponding to the particular rotor application.
We propose a method to reduce the demagnetization rate for a given stack configuration necessary for the superconducting rotor operating at a cryogenic temperature. This technique involves 3-D wrapping the stack of tapes with perpendicular layers of similar superconducting properties.
Previous ‘proof of concept’ studies documented some improvements in flux demagnetisation reduction for basic configuration. In the present study a more advanced approach based on magnetic flux shielding is adopted. The presented results provide an important contribution to development for design solutions that aim to increase the operational time before remagnetisation of the stacks would be required.</jats:p
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Superconducting Magnetic Heterostructured Components for Electric Motor Applications
Trapped flux magnets made by stacking high temperature superconducting tape portray an easy assembly with already available materials, high mechanical resistance, provided by the substrate and improved thermal stability, which enhances the trapped flux compared to bulks. This allowed reaching the world record of 17.7 T. The presented analysis expands previous work with wide superconducting tapes showing further pos-sible improvements in this kind of devices in order to be used as source of magnetic flux in electrical motors, substituting permanent magnets. The aims are to increase the trapped magnetic flux during magnetization and decrease the leakage flux at the edges of the magnet during the operation of the machine. This is expected to be achieved by either introducing new materials in-between the individual tapes, such as ferromagnetic layers, or modifying the composition of the substrate. The results of simulations using the H-formulation as well as experimental measurements are presented.EPSRC grant EP/P000738/
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Testing of Surface Mounted Superconducting Stacks as Trapped-Flux Magnets in a Synchronous Machine
Stacks of high temperature superconducting tapes may offer a technically affordable solution for the application of superconducting materials as trapped-flux magnets in the rotor of synchronous electrical machines. Nevertheless, several concerns must be first addressed, among others, the optimal procedure to induce the current vortexes previously to operation (magnetization), the survivability of these vortexes in the electromagnetic environment present in an electrical machine and the accuracy of recently developed numerical models. With the aim of exploring such practicalities, this paper presents a modified synchronous machine to test under liquid nitrogen conditions thin stacks of superconducting tapes. The machine is run under realistic conditions: currents in the stacks are induced from the stator, then the shaft is rotated and finally the machine is connected to a load, working as a generator. The results confirm previous numerical and experimental studies and establish a procedure for assessing the behavior of stacks in their actual operational environment.Also EPSRC EP/P000738/
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Heat extraction from HTS tape stacks applied in a superconducting motor in different cooling conditions
Abstract
The heat is generated inside the stack of superconducting tapes mounted on the surface of the electrical machine rotor during its operation and magnetization. Cooling of such stack presents challenges because of the layered structure of both tape, and stack. Moreover, the tapes should be electrically isolated to minimize the AC losses, that assumes gluing them, rather than soldering. The calculations consider a conductive heat dissipation also through the rotor iron.
Results show that: liquid nitrogen provides an effective cooling; the temperature of the stack shows complex distribution patterns with the gaseous coolant. Additional preventive measures were analyzed to keep the stack operational in vacuum conditions.</jats:p
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Experimental system for testing a superconducting motor at temperatures close to 15 K
Integrating superconducting elements in an electric motor can greatly increase its power density. By doing so,
lighter and more powerful machines can be produced for applications such as aviation, wind turbines and marine
propulsion. Superconducting tapes can be stacked and magnetised to produce powerful trapped-flux magnets.
The experimental setup was designed to allow measurements in a low temperature environment, providing
tightness for the rotating part.
We report on the design and construction of the setup and results from its first operation. The temperatures
achieved during the experimental measurements reached 15 K, close to the actual operational temperatures of a
liquid hydrogen cooled motor. The application of hydrogen onboard an aircraft is highly advantageous due to the
possibility of its application as both coolant and fuel. Examination of the operation of the trapped-flux magnets at
such temperatures is crucial for the understanding of the behavior of fully superconducting motors for future
applications
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Distribution of Trapped Magnetic Flux in Superconducting Stacks Magnetised by Angled Field
Abstract: Some novel energy applications require the use of complex shapes of stacks of superconducting tapes as trapped-flux magnets. A trapped-flux magnet magnetised in a superconducting motor may experience an angled magnetising field rather than a field normal to its surface. This will affect the trapped magnetic flux distribution. This work presents the results of the numerical and experimental analyses of the stacks magnetised in an angled magnetic field. The finite element model using H-formulation is developed to compute the induced superconducting currents. The measurements are performed on stacks with different thicknesses and with different orientations against a magnetising field. The resulting distribution of the magnetic flux as well as the electric currents is computed, presented and discussed in details. The importance of the observed distribution patterns is assessed in the context of the implementation of such stacks in a fully superconducting electric motor
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Magnetization and losses for an improved architecture of trapped-flux superconducting rotor
A hybrid electric configuration for aircraft propulsion yields several advantages, such as reducing the fuel consumption and take-off distance, improving control, and decreasing emissions. For such a scenario to occur, advances designed to increase the power-to-weight ratio of actual electric motors must be developed. Superconducting technologies offer the prospect of achieving such performances but at a cost of increased design and construction complexities. In that sense, stacks of high temperature superconductors have proven to trap high-current vortexes that provide a source of magnetic flux density for torque production without the need of current leads or other equipment in the rotor. However, these macroscopic currents must be induced prior to operation and remain undisturbed by variations in the magnetic flux density of the airgap, such as the ones caused by heating and demagnetization. This work presents the results of numerical computations on a new rotor architecture designed to facilitate the magnetization of stacks from a superconducting stator and prevent their demagnetization during torque production. The machine performance is assessed, and the expected survivability of the trapped-flux in stacks is compared to laboratory measurements.This research is financially supported by the European Union’s Horizon 2020 research innovation programme under grant agreement No 7231119 (ASuMED consortium) and EPSRC grant EP/P000738/1
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Effect of HTS stack sectioning on pulse magnetization efficiency in a motor
Abstract
Stacks of HTS superconductors can be magnetized and used as a surface mounted magnet for electrical machines. Pulse field magnetization is considered as a practical method; however, the amplitude of the pulse can be limited in an electrical motor which results in an under-saturated stack with the superconducting currents penetrating only a part of it making the magnetization less efficient. A solution to this problem could be sectioning the stack along its width enabling effective penetration of the superconducting currents. In this paper we investigate the effect of sectioning of HTS surface mounted stacks on the efficiency of pulse magnetization method in trapping the flux using low pulsing field. It is shown that the sectioning of wide stacks into several narrower parts results in a higher trapped flux at low pulses. Experimental measurements are performed on a lab-scale motor to validate the theoretical analysis.</jats:p
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Heat extraction from HTS tape stacks applied in a superconducting motor in different cooling conditions
Abstract
The heat is generated inside the stack of superconducting tapes mounted on the surface of the electrical machine rotor during its operation and magnetization. Cooling of such stack presents challenges because of the layered structure of both tape, and stack. Moreover, the tapes should be electrically isolated to minimize the AC losses, that assumes gluing them, rather than soldering. The calculations consider a conductive heat dissipation also through the rotor iron.
Results show that: liquid nitrogen provides an effective cooling; the temperature of the stack shows complex distribution patterns with the gaseous coolant. Additional preventive measures were analyzed to keep the stack operational in vacuum conditions.</jats:p
Recommended from our members
Frequency-dependent demagnetisation rate of a shielded HTS tape stack
Abstract
This work presents results of investigation of crossed-field demagnetization in 2G high temperature superconducting stacks at temperatures in the range of 77 - 20 K and in a variable frequency, corresponding to the particular rotor application.
We propose a method to reduce the demagnetization rate for a given stack configuration necessary for the superconducting rotor operating at a cryogenic temperature. This technique involves 3-D wrapping the stack of tapes with perpendicular layers of similar superconducting properties.
Previous ‘proof of concept’ studies documented some improvements in flux demagnetisation reduction for basic configuration. In the present study a more advanced approach based on magnetic flux shielding is adopted. The presented results provide an important contribution to development for design solutions that aim to increase the operational time before remagnetisation of the stacks would be required.</jats:p