High Temperature Characterization of a Radial Magnetic Bearing for Turbomachinery

Abstract

Open loop, experimental force and power measurements of a radial, redundant-axis, magnetic bearing at temperatures to 1000°F (538°C) and rotor speeds to 15,000 rpm along with theoretical temperature and force models are presented in this paper. The experimentally measured force produced by a single C-core circuit using 22A was 600 lb (2.67 kN) at room temperature and 380 lb (1.69 kN) at 538°C. These values were compared with force predictions based on a one-dimensional magnetic circuit analysis and a thermal analysis of gap growth as a function of temperature. The analysis showed that the reduction of force at high temperature is mostly due to an increase in radial gap due to test conditions, rather than to reduced core permeability. Tests under rotating conditions showed that rotor speed has a negligible effect on the bearing’s static force capacity. One C-core required approximately 340 W of power to generate 190 lb (845 N) of magnetic force at 538°C, however the magnetic air gap was much larger than at room temperature. The data presented are after bearing operation for eleven total hours at 538°C and six thermal cycles.

Theoretical characterization of the temperature-dependent saturation magnetization of magnetic metallic materials

“…By combining Eqs. (11) and (12) with Eq. ( 17), the temperature-dependent saturation magnetization model of the final model can be obtained…”

“…[2][3][4] In addition, magnetic metallic materials make substantial contributions to diverse domains, including rail transport (electric motors in automobiles [5] ), aerospace (permanent magnet machines [6] ), medicine (magnetic resonance imaging (MRI) scanners [7] ), and beyond. [8][9][10][11][12][13][14] Nevertheless, magnetic metallic materials frequently experience temperature variations in these aforementioned applications. This becomes particularly critical when the material reaches its critical temperature, as the magnetic metallic material will then cease to function effectively.…”

Embedded Sensors and Controls to Improve Component Performance and Reliability Conceptual Design Report

“…In addition, a high-temperature magnetic bearing was operated at 1000°F (540ºC). The design and fabrication, including the development of high temperature wire, and a coil fabrication process, were reported by Montague et al 23 Test data acquired during and after 11 hours of operation at 1000°F, and multiple (six) thermal cycles, was described by Provenza et al 24 A high-temperature switched reluctance motor capable of speeds up to 8,000 rpm was operated at 1000°F (540ºC), for >27.5 hours, including 14 thermal cycles. 25…”

Internal Rotor Actuation and Magnetic Bearings for the Active Control of Rotating Machines

“…Combining the actuation and rotor support, Active Magnetic Bearings (AMBs) can be used to mitigate vibrations for high speed machines, offering improved performance, even though they require the inclusion of amplifiers and sensors to control the rotor levitation. Indeed, AMBs have a much higher life expectancy compared to rolling element bearings, together with having a lubrication-free architecture particularly well suited to wide temperature ranges [22], operation in a vacuum and very high speed applications, such as flywheels [23,24]. The closed loop nature of AMB levitation allows tailoring of the controller to suit a given application, for example, with custom stiffness, damping and unbalance rejection [25,26].…”