Siemens and Nexans SuperConductors (NSC) are to exhibit the first superconducting bearing for industrial applications jointly at the “SuperConductingCity,” a forum on superconductivity at the Hannover Fair 2006.
Siemens commissioned NSC to build a prototype suitable for industrial purposes for practical testing. This cooperative venture was part of a 4-MVA HTS generator project supported by BMBF.
The HTS bearing is based on High-Temperature Superconductors (HTS), which support a rotating shaft in a magnetic field through contactless suspension. The shaft is held centrally as a prerequisite for optimum application in high-speed generators and motors.
According to Siemens, HTS bearings can open up a host of new applications or improve existing systems, for example for high-speed drives, generators or turbines. Increasingly flexible high-performance drives are required in the chemical and processing industry.
HTS bearings can be applied is in flywheel power storage systems used in power supplies, in which electrical energy is temporarily stored in the form of rotational energy. When required, the rotating mass is used to drive a generator for feeding current into the power supply system again. High performances are achieved by means of large masses or high speeds. A contactless HTS bearing extends the range of usable speeds upwards and thus increases the power density. In addition, energy losses due to bearing friction can be avoided. NSC is expected to have a bearing of this kind ready before the end of the year.
The HTS bearing built by NSC can carry a radial load of up to 690 kg and is suitable for speeds of up to 3,600 rpm, which is appropriate for the 60-Hz current frequency. The bearing is accommodated in a welded cryogenic housing made of VA steel, which guarantees that a vacuum can be maintained over a long period.
A refrigerating machine cools the superconductor directly without additional refrigerants down to the operating temperature of minus 210 °C to minus 245 °C. An integrated backup bearing ensures safety in extreme load situations. Shaft vibrations induced by resonant frequencies are attenuated by an electrodynamic damping unit.
The rotor, equipped with permanent magnets, runs in the bore at room temperature in a gap 1 mm wide. There is also 1 mm distance between the insulating cryostat wall and the HTS material at a temperature of minus 210 °C. Differential temperatures of up to 270°C are insulated over this short distance and the insulated stator is protected from the ambient heat.