Siemens and Nexans present the first superconducting bearing for industrial
applications
Munich, Germany, Apr. 20:
Siemens AG
and Nexans SuperConductors GmbH (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, which has been long involved in the field of
HTS magnetic bearings, 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. The bearing meets the requirements for industrial use. It is of
fail-safe design, maintenance and wear-free and has a high degree of
availability. HTS bearings are also inherently safe and require no
additional monitoring by sensors or software, which is what distinguishes
them from actively regulated magnetic bearings.
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. Adapting the speed of high-speed compressors can
play an important role in optimizing processes, and rugged, fail-safe
bearings are an essential requirement for this.
An interesting area of application for HTS bearings 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 (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 Nexans engineers have performed an outstanding achievement. The rotor
equipped with permanent magnets runs in the bore at room temperature in a
gap just 1 mm wide. There is also only 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.
The HTS bearing cooled by a small refrigerating unit will be on show during
the SuperConductingCity for inspection by interested visitors, who can even
try turning it by hand. A cutaway functional model showing all the
components that are important for the system illustrates how the bearing
works.
