Abstract
Bulk high temperature superconductor magnets (HTSMs) have a higher flux-generating capability compared to conventional permanent magnets (PMs). These materials potentially can be used in high temperature superconducting (HTS) linear synchronous motors (LSMs) as superconducting secondary magnets, what will result in a reduced volume and weight as well as in higher force density and efficiency of these devices when compared to conventional PMs. The focus of this paper is on the effect of size of the secondary HTSM on the static performance (thrust force and normal force) of a LSM. In order to obtain high-field HTSM as the secondary, single grain bulk GdBCO-Ag superconductors of diameter 20 mm, 30 mm and 40 mm, which have higher Jc and trapped fields than YBCO superconductors, were used in this device for the first time following application by the same optimized magnetization condition. It was found that both thrust and normal forces increase and saturate with the increasing size of the HTSM secondary at the small size range, and then potentially distort when the physical size of the HTSM secondary approaches the pole pitch of the linear three-phase primary windings of the LSM. Furthermore, more experiments of a larger-sized multi-seeded HTSM secondary, confirmed that the relationship between the HTSM secondary size and the pole pitch of the primary is an important factor for achieving higher thrust and normal forces. It is suggested that the multi-pole HTSM secondary will be more beneficial to future HTS LSM designs since the single-pole HTSM secondary size should be equal to or smaller than the stator pole pitch in the paper.
Highlights
Linear motors are employed widely in various types of Maglev transportation systems
We focus on the effect of size of the premagnetized bulk high temperature superconductors (HTSCs) on thrust and normal forces of an experimental high temperature superconducting (HTS) linear synchronous motors (LSMs) prototype over a flat, single-sided three-phase copper-wound stator
The space phases, 2πx/λ and 2πz/λ, are constants in this case, since the HTSC magnet secondary was fixed above the HTS LSM primary in the static studies performed here
Summary
Linear motors are employed widely in various types of Maglev transportation systems. These motors, which form the basis of a contact-free translational propulsion system, have the advantage of producing a direct thrust that is independent on the levitation/suspension interaction between vehicles and rails [1]. The unique flux trapping properties of bulk HTSCs on board a Maglev transportation system enable them to provide both stable levitation/guidance via an interaction with the ground-based permanent magnet rail (PMR) and propulsion and breaking of the vehicle via the linear motor subsystem. These two key subsystems are separated physically in conventional designs, due partly to the different working temperatures for the different components (liquid nitrogen temperatures for HTSCs and room temperature for linear motor), and to prevent magnetic interference. Additional complementary experiments were performed on a larger-sized, three-seeded YBCO bulk to verify the size effect of the HTS magnet secondary on the total force characteristics with a view to developing an effective HTS LSM design
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