An active homopolar magnetic bearing with high temperature superconductor coils and ferromagnetic cores
- NASA Lewis Research Center, Cleveland, OH (United States)
A proof-of-feasibility demonstration showed that high temperature superconductor (HTS) coils can be used in a high-load, active magnetic bearing in liquid nitrogen. A homopolar radial bearing with commercially wound HTS (Bi 2223) bias and control coils produced over 200 lb (890 N) radial load capacity (measured nonrotating) and supported a shaft to 14000 rpm. The goal was to show that HTS coils can operate stably with ferromagnetic cores in a feedback controlled system at a current density similar to that in Cu in liquid nitrogen. Design compromises permitted use of circular coils with rectangular cross section. Conductor improvements will eventually permit coil shape optimization, higher current density and higher bearing load capacity. The bias coil, wound with nontwisted, multifilament HTS conductor, required negligible power to carry its direct current. The control coils were wound with monofilament HTS sheathed in Ag. These dissipated negligible power for direct current (i.e., for steady radial load components). When an alternating current (AC) was added, the AC component dissipated power which increased rapidly with frequency and quadratically with AC amplitude. In fact at frequencies above about 2 Hz, the effective resistance of the control coil conductor actually exceeds that of the silver which is in electrical parallel with the oxide superconductor. This is at least qualitatively understandable in the context of a Bean-type model of flux and current penetration into a Type II superconductor. Fortunately the dynamic currents required for bearing stability are of small amplitude. These results show that while twisted multifilament conductor is not needed for stable levitation, twisted multifilaments will be required to reduce control power for sizable dynamic loads, such as those due to unbalance.
- OSTI ID:
- 390766
- Report Number(s):
- CONF-950852-; TRN: 96:005769-0024
- Resource Relation:
- Conference: 4. industrial conference and exhibition on applications of magnetic bearings, magnetic drives, and dry gas seals, Alexandria, VA (United States), 10-11 Aug 1995; Other Information: PBD: 1995; Related Information: Is Part Of Proceedings of the MAG `95 magnetic bearings, magnetic drives and dry gas seals conference & exhibition; PB: 384 p.
- Country of Publication:
- United States
- Language:
- English
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