130,910 research outputs found
Fast 3-D Analysis of Eddy Current in Litz Wire Using Integral Equation
No full textEddy current loss in a litz wire which has 3-D structure is analyzed using the integral equation method considering the proximity effect. In the present method, each wire is modeled as a polygonal line. 1-D integral equation is solved for the dipole magnetization generated by the anti-parallel eddy currents in the wire. The discretized integral equation can effectively be solved using an iterative method solver to compute the eddy current distribution in the wire due to the proximity effect
Electromagnetic Characterization of Hyperconducting Aluminum Litz Wires at Cryogenic Temperatures
No full textCryogenic electric machines (CEMs) offer significant potential for highly power-dense and ultra-efficient net-zero aircraft. Aluminum (Al) displays superior conductivity to copper (Cu) at cryo-temperatures, making Al Litz wires an attractive option for CEM windings to minimize DC and eddy losses. However, accurately quantifying Al Litz wire losses remains challenging, particularly considering their unknown electromagnetic behavior at different cryo-temperatures and frequencies when embedded in iron cores. To address this, a specialized test setup was developed to measure the losses of two customized Al Litz coils, alongside a Cu Litz coil, under varying cryo-temperatures (25 to 77 K) and frequencies (50 to 1000 Hz). A numerical model was also developed using COMSOL, incorporating a temperature-dependent electrical conductivity and a homogenization model for Litz wires with rectangular cross-sections. The model was incorporated into an analytic design procedure to maximize the test-rig loss ratio within the tight space and maximum heat rejection constraints of the cryostat, to allow accurate loss separation. The experimental data aligns closely with the numerical simulations, enabling a comprehensive analysis of the loss characteristics of Al Litz wires. This study provides a detailed design methodology and serves as a valuable resource for developing CEMs for zero-emission electric aircraft
Frequency-Domain Homogenization for Impedance Characterization of Litz-Wire Transformers in 2-D Finite Element Models
No full textThis work deals with a frequency-domain homogenization technique for litz-wire bundles in transformers. The approach consists in adopting a frequency-dependent complex reluctivity in the litz-wire bundles and a frequency-dependent complex impedance in the electrical circuit. The litz-wire bundles become homogeneous conductors which are easy to integrate into a finite element model of a transformer. The magnetic flux and the impedance of the litz-wire transformer computed from the homogenized model agree well with the reference fine model in which each litz-wire turn is finely discretized. The errors of the computed resistance and inductance values are less than 3% and 0.03% respectively with several times faster calculation.status: Publishe
Mr. and Mrs. Amon Carter with Sammy Baugh and Helen Elizabeth Litz
No full textMr. and Mrs. Amon Carter (left) with Sammy Baugh, formerly of TCU who plays for Washington Redskins, in Washington, D. C. for Texas Day at the football game; Helen Elizabeth Litz puts pin on Baugh\u27s jersey.https://mavmatrix.uta.edu/specialcollections_startelegram1930s/6779/thumbnail.jp
Time-Domain Homogenization of Litz-Wire Bundles in FE Calculations
No full textThis paper deals with a time-domain homogenization technique for Litz-wire bundles embedded in a finite element (FE) model. An elementary FE model is used to determine dimensionless frequency- and time-domain coefficients regarding the skin and proximity effects in Litz-wire bundles. Thanks to these coefficients, Litz-wire bundles become homogeneous conductors which are easy to integrate into a FE model of a complete device. The method is validated with the reference solution of the 2-D FE transformer model, which is computed by finely discretizing each conductor. The results agree well with the accurate reference solution.sponsorship: This paper is supported by the Advanced Electric Powertrain Technology (ADEPT) project which is an EU funded Marie Curie ITN project, grant number 607361. (Advanced Electric Powertrain Technology (ADEPT) project, EU|607361)status: Publishe
Recursive Domain Decomposition Approach in 2-D Time-Harmonic Wireless Power Transfer Simulations Considering Litz Wires
No full textA recursive domain decomposition approach based on 2-D time-harmonic finite element (FE) model with AVI formulation is used to model a wireless power transfer (WPT) unit with litz wires. Similar techniques exist in the literature but they haven’t yet been applied to WPT units. The approach produces a model which is significantly faster to update and re-solve than a traditional FE model and hence it is suitable for performing parametric sweeps where the positioning of the coils is varied. Using the technique it is possible to study losses emerging in individual strands even with extremely high number of strands. The loss distribution between the litz wire strands is studied, varying the number of strands from 7 to 925. The results and speed are compared to a traditional FE AVI model. The method yields results up to a 1 % relative error compared to the traditional model with a significantly faster simulation time.Peer reviewe
Infra-red imaging of Litz wires with and without enamel
No full textInfra-red imaging of Litz wires with and without enamel.
Data supporting Tiwari, D. et al. Inspection of Enamel Removal Using Infrared Thermal Imaging and Machine Learning Techniques. Sensors 2023, 23, 3977.</p
Litz wire loss performance and optimization for cryogenic windings
No full textLitz wires operating in a cryogenic environment can potentially improve both the efficiency and power density of electrical machines and passive components. However, due to the low resistivity and high magnetic fields, eddy-current losses may become significant in cryogenically cooled windings, especially in airgap winding arrangements or in the case of significant slot leakage fields, unless the litz wire parameters are carefully chosen. A framework for litz wire loss performance optimization and experimental characterisation at cryogenic temperatures is provided. An optimum operating temperature for minimum loss is derived based on analytical expressions, which highlights the role of litz wire parameters, current density and external field. The proximity loss model, used to calculate the optimum operating temperature, is validated experimentally. Two test rigs with different magnetic cores were designed and built. Copper and aluminium litz wires with a strand diameter down to 0.1 mm were tested in a liquid nitrogen bath with a uniform harmonic external magnetic field up to 0.5 T peak and a frequency up to 1 kHz. Measurements show good agreement with the theoretical results and confirm that the proposed model can be confidently used during the preliminary design of cryogenic windings.</p
Utilizing Helicoidal and Translational Symmetries Together in 2-D Models of Twisted Litz Wire Strand Bundles
No full textIn this article, a helicoidally symmetric 2-D model of a twisted litz wire strand bundle is studied. Suitable foundations for compatibility tools are presented to use such a model as a part of a larger system which does not follow a helicoidal symmetry. A measure for the symmetricity of a field is proposed. This provides the foundations for the coupling of helicoidally symmetric and translationally symmetric models with good understanding of the introduced approximation error.Peer reviewe
Frequency-domain homogenization for litz-wire bundles in finite element calculations
No full textThis work deals with a frequency-domain homogenization method for litz-wire bundles embedded in a finite element (FE) model. The approach consists in adopting a frequency-dependent complex reluctivity in the litz-wire bundles and a frequency-dependent complex impedance in the electrical circuit in terms of dimensionless coefficients. The litz-wire bundles become homogeneous conductors which are easy to integrate into a finite element model. The homogenization methods in previous works are also reviewed. The complex permeability achieved with our model is compared to the most accurate expression found in literature. The agreement is very good despite the different elementary cell and condition setting. Moreover, the homogenization method in this paper is validated for both 2-D and 3-D FE calculations with the translational-symmetry transformer model and the axisymmetric inductor model respectively. The reference solutions of those models are computed by finely discretizing each conductor inside the litz-wire bundle. The results of the computed resistance and inductance agree well with those computed by the reference fine model, resulting in less than 3% and 0.05% maximum errors respectively in 2-D FE model, and 4% and 1.8% respectively in 3-D FE model with several times less computational cost.status: Publishe
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