A 2 kW/28.5 kJ superconducting flywheel energy storage system (SFESS) with a radial-type high-temperature superconducting (HTS) bearing was set up to study the electromagnetic and rotational characteristics. The structure of the SFESS as well as the design of its main parts was reported. A mathematical model based on the finite element method (FEM) was established to research the electromagnetic characteristics of the HTS bearing during the levitation process, which show that a part of the magnetic flux penetrates into the edge of the HTS bulks and then goes back to the opposite pole of the permanent magnet rotor (PMR). The induced current mainly distributes in the edge of the HTS bulks, indicating that larger force acts on the edge part of the HTS bulks and probably causes them to crack. The free rotations of the rotor at different steady-state speeds of 2500–5000 rpm and its radial vibration were displayed. The induced voltage of the stator winding of the motor in this process was analyzed. The rotational characteristics are related to the vibration of the rotor. Below the resonant frequency, the vibration increases significantly with the speed. Enhancing the radial stiffness to limit the vibration amplitude of the rotor is an effective approach to improve the speed.

Electromagnetic and Rotational Characteristics of a Superconducting Flywheel Energy Storage System Utilizing a Radial-Type High-Temperature Superconducting Bearing

High-temperature superconducting (HTS) transformers have remarkable appealing advantages over conventional ones. But higher brittleness of HTS windings with respect to copper windings makes HTS transformers more vulnerable in short circuit and inrush current situations. During tap changer operation, appreciable asymmetry and non-uniform distribution of ampere-turn along the windings causes high axial component of short circuit forces and makes the situation more severe. In this paper, multi-segment winding method is employed for reduction of axial short circuit forces. An analytical method is presented for calculation of axial component of short circuit forces under tap changer operation. Analytical method shows that with utilizing HLHLHLH asymmetrical multi-segment windings, during tap changer operation, the axial component of short circuit forces reduces significantly. The results of the analytical method are compared with the results of finite element method (FEM) model simulations, and the consistency is demonstrated.

Multi-segment Winding Application for Axial Short Circuit Force Reduction Under Tap Changer Operation in HTS Transformers

Fermi National Accelerator Laboratory, together with Lawrence Berkeley National Laboratory, is building a new High Field Vertical Magnet Test Facility (HFVMTF) to be situated in the Magnet Test Facility at Fermilab. The HFVMTF is jointly funded by the US DOE Offices of Science, High Energy Physics, and Fusion Energy Sciences, and will serve as a superconducting cable test facility for both communities. The background magnetic field for test samples is 15 T and will be produced by a magnet provided by LBNL operating at 1.9 K in superfluid helium. The samples will be placed in the background magnetic field, cooled to between 4.5 K and a user-specified upper limit, and will be powered with a superconducting transformer at up to 100 kA. Additionally, this facility will be used to test high-field superconducting magnet models and demonstrators, including hybrid magnets, produced by the US Magnet Development Program. Currently, the various tasks of the project are at different stages of execution, from conceptual to ready-for-construction designs. This paper describes the parameters and design status of the pit construction, cryostat, heat exchanger, lambda plate, power system, and quench protection and monitoring systems of the facility.

Design and Construction of a High Field Cable Test Facility at Fermilab

On the Evolution of Passive Magnetic Bearings

In this paper, a 3D numerical model, which was theoretically established and experimentally validated, was utilized to investigate the dynamic electromagnetic behaviors of a high-temperature superconductor (HTS) levitation system consisting of a cylindrical permanent magnet (PM) and an HTS fabricated by the YBCO material. The effects of critical current, cooling temperature, multiseeded material, and thickness of the HTS on electromagnetic behaviors were discussed from a 3D perspective. The dynamic electromagnetic behaviors indicate the induced current is mainly distributed near the top surface and edges of the HTS. As the PM approaches the HTS, the induced current density increases gradually. As the PM withdraws, it reduces initially and is then induced in the opposite direction. The levitation force increases with critical current but exhibits saturation. The lower the temperature, the larger the levitation force and the smaller the hysteresis. The induced current of the multiseeded HTS is characterized by a symmetrical distribution with the seed domain boundary or central axis. Its maximum value increases with the number of seeds but the levitation force significantly reduces. The induced current on the cross section is symmetrically distributed. As the thickness of the HTS decreases, the levitation force reduces drastically but the maximum value of the induced current increases. The reason was explained. Finally, the dynamic electromagnetic behaviors of a radial-type HTS bearing were investigated from a 3D perspective.

Dynamic Electromagnetic Behaviors of High-Temperature Superconductor Levitation System Based on YBCO Material from 3D Perspective

The Solenoid Test Facility at Fermilab was built using a large vacuum vessel for testing of conduction-cooled superconducting solenoid magnets, and was first used to determine the performance of the MICE Coupling Coil [1, 2] The facility was modified recently to enable testing of solenoid magnets for the Mu2e experiment, which operate at much higher current than the Coupling Coil One pair of low current conduction-cooled copper and NbTi leads was replaced with two pairs of 10 kA HTS leads cooled by heat exchange with liquid nitrogen and liquid helium The new design, with additional control and monitoring capability, also provides helium cooling of the superconducting magnet leads by conduction A high current power supply with energy extraction was added, and several improvements to the quench protection and characterization system were made Here we present details of these changes and report on performance results from a test of the Mu2e prototype Transport Solenoid (TS) module Progress on additional improvements in preparation for production TS module testing will be presented

James A. Hocker

Papers

Improvements and Performance of the Fermilab Solenoid Test Facility