1,721,113 research outputs found
Numerical Investigation on Induced Current Distribution and AC Losses in a Prototype Cable for the European DEMO TF Coils
No full textA new geometrical model has been implemented in the THELMA code, aiming at permitting the study of multistage, forced-flow cable-in-conduit conductors with rectangular cross-section, like that proposed for the toroidal field (TF) magnets of the future fusion reactor DEMO. This model gives verisimilar strand trajectories which should enable the adoption of a more detailed interstrand electrical contact model. This paper shows the results of the first application of these new code features to a set of contact resistance and ac loss experiments carried out by Twente University on a DEMO TF prototype conductor. The results of this analysis present some unforeseen aspects that need further work to be fully understood, to improve and validate the model
Numerical Investigation on Induced Current Distribution and AC Losses in a Prototype Cable for the European DEMO TF Coils
No full textDevelopment of a Small Cryogen-Free MgB2 Test Coil for SMES Application
No full textMgB2 material operating at moderate field can conveniently be considered for short-term cost-effective implementation of superconducting magnetic energy storage (SMES). Due to the intrinsic performance of this material, moderate field operation and cryogen free cooling in the range 10-20 K need to be considered. For investigating the feasibility of MgB2 based SMES technology a 10 kW - 2 s system is under development. A small MgB2 coil was developed and tested as the first step of this study. The cooling was obtained by means of a cryogen-free test facility based on a two-stages Gifford-McMahon regenerative heat exchanger. A power conditioning system (PCS) was also developed in order to connect the coil with the power grid. The PCS is based on power mosfet components and consists of two parallel dc/dc boost converters and an inverter connected to a common dc bus at 100 V. Continuous operation of the coil at a charge/discharge rate up to 24 kW can be achieved by means of the PCS. Details of the layout of the coil and the thermal connection with the cryocooler are discussed in this paper. Results of cooling test are reported. Possible SMES operation is also discussed
A Comprehensive Investigation on the Accuracy of Electrical Measurement of Transport Current AC Losses in HTS Tapes
Full text linkThe measurement of transport current ac losses in high-temperature superconductor tapes with the electric method has been extensively discussed in the literature. It is well known that the configuration of the circuit used to acquire the voltage signal can affect the measured losses, potentially leading to inaccurate results. To reduce this undesired effect, the rectangular circuit arrangement, which is widely adopted, involves twisting the pair of voltage taps at a given distance from the tape middle axis. However, the explanations reported in the literature to identify the correct distance are not fully exhaustive, and an alternative interpretation is described here. Moreover, given that the conventional voltage taps arrangement creates a significant circuit area to which electromagnetic noise can be linked, an alternative configuration is proposed, aiming to reduce the linked flux. This article presents a theoretical analysis to quantify the impact of the measurement circuit configuration on the losses. To ensure clarity, the model equations involved are derived step by step. The numerical results are applied to a thorough investigation on the accuracy of the ac losses measured on a sample tape, at different frequencies and current amplitudes. Both the conventional and the alternative arrangements are studied, varying their main geometrical parameters, at the same operating conditions. The correction terms are then applied to the measurement results, highlighting the advantages and drawbacks of the different configurations
Improvement of the Circuit Analyzer Problem Solver CALYPSO
No full textThe no-insulation high-temperature superconducting (NI-HTS) coil technology is a promising field of application of HTS tapes, which has gained popularity in recent years. Compared to conventional insulated coils, NI-HTS coils have a better ability to cope with quenches, given the possibility for current and heat to redistribute towards adjacent turns in presence of a hot-spot. In recent years, the authors developed a nonlinear circuit model to compute current distribution and AC losses in NI-HTS coils (named CALYPSO). This model describes the currents flowing from turn to turn due to the NI configuration, as well as the magnetization currents arising in each tape. However, applying this model to coils composed of a large number of turns results in a high computational burden. This work presents an in-depth discussion of the reasons for the long computation time and the solutions and code improvements implemented to tackle this issue. Additionally, a comparison between the losses predicted by the code and those measured on straight REBCO tapes is presented. The model is then applied to investigate the electrodynamics of a NI pancake coil including both magnetization currents and radial currents. The impact of surface contact resistivity between turns on the delay between the magnetic field along the coil axis and the transport current is analyzed, showing the details of the current distribution between turns and inside individual tapes
Modeling of AC Losses in DEMO RW2rutstab Conductor
No full textThe AC loss in the react&wind DEMO TF prototype conductor RW2rutstab were measured in SULTAN at the end of 2019. These tests were modelled with the THELMA code, making use of a detailed geometric cable description. The inter-strand contact conductances are computed starting from the strand trajectories, their diameters and a set of contact specific conductivities individually assigned to the strands. Different criteria to assign these conductivities have been considered. Starting from the model parameters identified through the simulation of AC loss tests performed with a sinusoidal field perpendicular to the cable broad face, tests performed with the cable rotated by 90(degrees), sinusoidal field were also modelled. The AC losses in the presence of a magnetic field varying in time with a trapezoidal cycle were studied as well. The article describes the utilized models and discusses in detail the obtained results
AC Loss Investigation in MgB2 Multifilamentary Wires: A Numerical Study
No full textThe discovery of superconductivity in magnesium diboride ( MgB2 ) in 2001 generated significant interest due to its relatively high critical temperature and cost-effectiveness. While MgB2 has shown promise in direct current (DC) applications, its utilization in alternating current (AC) devices is hindered by dissipative phenomena. Consequently, research and development efforts have been devoted to understanding the factors influencing losses in MgB2 conductors and exploring novel designs aimed at reducing AC losses. This study presents an efficient computational tool based on a three-dimensional integral formulation of Maxwell's equations, enabling the calculation of losses in multi-filamentary MgB2 wires. By employing numerical simulations under various operating conditions and comparing the results with existing analytical formul ae, the study primarily focuses on simplified scenarios. Essential design criteria are identified, providing insights on how to effectively minimize coupling losses for specific operating conditions
Experimental validation of magnetic shield type fault current limiter circuit model
No full textA circuit scheme of a Magnetic Shield Type Superconducting Fault Current Limiter is developed. The circuit parameters are determined by means of the energy conservation law after the discretized field problem inside the device is solved. In order to validate the model a basic prototype of the limiter is tested. Experimental and numerical waveforms of current and voltage across the device under different operating conditions are compared. The equivalent circuit obtained can be introduced in a power system simulator to evaluate how a Magnetic Shield Type SCFCL interacts with a power network
Quench in a pancake coil wound with REBCO Roebel cable: model and validation
No full textRoebel cables assembled with high temperature superconducting tapes are a promising technology for several AC and DC applications. Their mechanical flexibility and compact design, combined with the capability of REBCO tapes to carry high transport currents in intense magnetic fields make them suitable for the application both in power devices and high field magnets. In this paper, an electro-thermal finite-element model developed at the University ofBologna (Italy) is described. The model allows computing the current and heat redistribution between the strands of the cable and from turn to turn inside a winding through non-uniform distributed thermal and electrical resistances between strands. The tape is ‘homogenized’ so as to create an anisotropic continuum model through a previously developed homogenizationtechnique. The model is validated by comparison with quench tests performed on a well instrumented 7-turn pancake coil wound with a 2 m long Roebel cable composed of 15 REBCO tapes. The experiments were performed at the University of Southampton (UK) in the frame of the R&D activities of the EuCARD-2 project. The quench decision time, the temperature and electric potential evolution, the current and heat redistribution between strands in the event of a quench are analysed and discussed in the present study
A Numerical Study of Quench in the NHMFL 32 T Magnet
No full textThe National High Magnetic Field Laboratory (NHMFL), Tallahassee, FL, USA, has developed, built, tested, and commissioned a 32 T all-superconducting user magnet system combining two series-connected high-field high-temperature superconductor (HTS) nested inner coils (insert) wound with SuperPower, Inc. REBCO tapes and a low temperature superconducting (LTS) outer magnet (outsert) composed of five coils (subdivided into 17 electrical sections). Protected-quench tests were performed at the NHMFL to analyze the reliability of the 32 T magnet during the superconducting-to-normal transition. The quench tests were performed at different values of transport current both in the HTS insert and in the LTS outsert. The University of Bologna, in collaboration with the NHMFL, has developed a quasi-3-D FE model suited for the analysis of quench in HTS magnets. The model was previously applied to the analysis of the experimental results of the quench tests carried out on the prototype coils, manufactured in the framework of the 32 T magnet R&D activities. In this paper, the numerical model is applied to analyze the quench initiation and propagation in the 32 T HTS insert. The dump of the transport current during quench is computed and compared with the experimental result. The most stressed regions within the insert windings are identified
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