Low-power superconducting motors

Abstract

Since the discovery and development of adequate superconducting materials, the development of motors has been a challenge for applications. The basis of design, however, has been the substitution of copper wires by superconducting tapes in coils in order to obtain a higher working field, thus improving power density and efficiency.In the case of high-power motors, the benefit is clear. The cost of the materials, cryogenics and building procedures could be assumed by the clear benefit in size, weight, efficiency, and, in some cases, reliability. Otherwise, low-power motors require a different treatment. Superconducting wires are insufficiently developed to produce small coils for a high field with the adequate shape. Air gaps are more critical than in large motors and cost has a major impact. Only very specific applications, in which standard technology cannot give a reliable and satisfactory solution, could benefit from superconductivity. This paper summarizes our work realized by applying superconducting pellets in low-power motors, thus improving their power density, reliability, dynamics and regularity. Applications to cryogenics, control and high speed have been our focus.

Mitigation of Demagnetization of Bulk Superconductors by Time-Varying External Magnetic Fields

“…6. It is shown that the mitigation effect during the applied timevarying field stage (second stage) contributed by the ferromagnetic surface shield is relatively large when B ex = 0.1 T, compared with the case where B ex = 0.3 T. The mitigation performance of the ferromagnetic surface shield is a passive effect, which means if the magnitude of applied field is below the saturation field and the final trapped field near the ferromagnetic surface is relatively high, the enhancement performance will be also high as shown in equation (5):…”

“…arge, single-grain (RE)BCO high-temperature superconducting (HTS) bulk materials have great potential to trap high magnetic fields of over 17 T below 30 K [1], [2] and up to3 T at 77 K [3]. More compact and high-performance applications can be realized by using HTS bulks [4][5][6][7][8][9][10][11], but in practical applications these can be exposed to time-varying magnetic field perturbations. Since this phenomenon affects the magnetic field trapped in the bulks to a large extent, the overall efficiency and performance can be limited.…”

Measurements on magnetized GdBCO pellets subjected to small transverse ac magnetic fields at very low frequency: Evidence for a slowdown of the magnetization decay

“…The common point of the investigations mentioned above is that they refer usually to a relatively "low" number of transverse ac cycles (typically up to 100-1000) with a "large" amplitude (typically from 0.1 Hp to several times Hp, where Hp denotes the full-penetration field). In applications such as magnetic bearings and brushless ac machines [46][47][48][49][50][51][52], however, the transverse fields of small amplitude are applied repeatedly for a long time. This is precisely the regime studied in the present work.…”

Numerical simulation of the magnetization of high-temperature superconductors: a 3D finite element method using a single time-step iteration

“…Highly sensitive magnetic measurement systems, such as in a biomagnetic imaging device, need efficient magnetic shields for reducing the effects of the external magnetic disturbances [4,5,6]. Powerful magnets are required in magnetic bearing systems, where they produce large levitation forces [7,8], or in rotating machines, where they produce a large torque on the shaft [9,10,11].…”