A superconducting magnetic gear

Abstract

A comparison is made between a magnetic gear using permanent magnets and superconductors. The objective is to see if there are any fundamental reasons why superconducting magnets should not provide higher power densities than permanent magnets. The gear is based on the variable permeability design of Attilah and Howe [1] in which a ring of permanent magnets surrounding a ring of permeable pole pieces with a different spacing gives an internal field component at the beat frequency. Superconductors can provide much larger fields and forces but will saturate the pole pieces. However the gear mechanism still operates, but in a different way. The magnetisation of the pole pieces is now constant but rotates with angle at the beat frequency. The result is a cylindrical Halbach array which produces an internal field with the same symmetry as in the linear regime, but has an analytic solution. In this paper a typical gear system is analysed with finite elements using FlexPDE. It is shown that the gear can work well into the saturation regime and that the Halbach array gives a good approximation to the results. Replacing the permanent magnets with superconducting tapes can give large increases in torque density, and for something like a wind turbine a combined gear and generator is possible. However there are major practical problems. Perhaps the most fundamental is the large high frequency field which is inevitably present and which will cause AC losses. Also large magnetic fields are required, with all the practical problems of high field superconducting magnets in rotating machines. Nevertheless there are ways of mitigating these difficulties and it seems worthwhile to explore the possibilities of this technology further.

A New Structure for the Coaxial Magnetic Gear With HTS Bulks for Fitness Car

“…The linear MG with HTS bulks is presented in [10], and magnetic flux density and thrust force transmission capacity are higher than the conventional MG. In [11], a CMG topology using superconductors instead of PMs is proposed, which can produce a large torque density. A novel single PM array stationary CMG with flux modulation teeth made of HTS material is proposed in [12].…”

HTS Motor Performance Evaluation by Different Pulsed Field Magnetization Strategies

“…Nevertheless, more studies are still required to understand the complex magnetic response of SC materials in rotary machines like motors and generators, where a strong reduction on the total weight of the machine together with a significant increase on its rated power, are both expected by the replacement of the copper windings and/or permanent neodymium-based magnets by SC materials [1]. Some of these technologies have been demonstrated in the past by different groups either by using Gd-based superconducting bulks on the designing of an axial-gap type synchronous propulsion motor [2], or by using 2G-HTS wires for the prototyping of synchronous induction motors [3].…”

Recent advances in superconducting rotating machines: an introduction to the ‘Focus on Superconducting Rotating Machines’

“…In [11], Radyjowski et al report on an initial prototype claw-pole superconducting machine that has a modular design, as well as a stationary superconducting field winding, eliminating the need for cryocouplers, brushes and so on. Campbell analyses the possibility and performance of a superconducting magnetic gear using HTS conductors in [12], which could replace a conventional gearbox in an electric machine and offer reduced acoustic noise and vibration, as well as improved reliability and significantly reduced maintenance.…”