100 Ë 4 Superconducting magnetic levitation
Fig. 4.8:Merits of applying HTS 2G wires to a superconducting magnet for the Maglev train. The
original figure is a schematic view of the LTS magnet which installed Nb-Ti coils, and symbol “>>”
shows merits of applying HTS 2G wires [77].
HTS over 40 K. The distance between the superconducting coil and the outer surface
of the cryostat is only 20 mm, which increases interlinkage magnetic flux to the
ground coil and improves efficiency of Maglev applications. The eddy current in the
ground conductor is proportional to flux linkage, and the levitation force is directly
proportional to the eddy current value.
With further improvement of the performance of 2G wire, HTS 2G coil magnets can
replace LTS magnets and greatly improve the performance of the EDS Maglev system.
The levitation characteristics of the HTS EDS system were investigated by the
relative motion between the HTS levitation magnet of 279.4 mH and the aluminum
ground conductor in a rotating state [79]. The experimental results showed that the
levitation force saturated after 20 m/s. The measured levitation forces with 20 and 30 A
at relative speed of 30 m/s were about 265 and 618 N, respectively. These results can be
used in the design of HTS levitation magnets mounted on the very-high-speed Maglev.
There was an interesting experiment using 2G wires as a passive levitator for
Maglev vehicles [80]. For that purpose, a superconducting 2G block was built by
stacking more than 500 pieces of coated conductors. The 2G block showed good
resistance to humidity, which made their storage easier. Also, the 2G wire can be
stacked in many different ways, enabling the design of a HTS sample optimized for
the magnetic field profile. The levitation and lateral forces between the 2G block and
a PM guideway were measured and compared with the results of an YBCO bulk with
the approximately same dimensions. The 2G block was conceived to replace a YBCO
bulk in the Maglev prototype, but the force between the 2G block and a PM was lower
than that for ordinary YBCO bulks. The experiment results may herald the 2G block’s
potential to be applied in a Maglev bearing and vehicle application.