290 Ë 8 New progress of HTS Maglev vehicle
Fig. 8.31:Levitation (a) and guidance forces (b) of the bulk levitation unit above the PMG at different
re-magnetization heights after ZFC.
cases. By adding the re-magnetization process after ZFC, the levitation force curves
are very close to each other and show a slight decrease with the decrease of the re-
magnetization height between bulks and the PMG. The guidance performance of the
HTS bulk levitation unit shows an obvious improvement with the decrease of the re-
magnetization height. It is worth noting that such stability partly benefited from the
double-pole magnetic field distribution of the experimental Halbach PMG [25].
With the decrease of the re-magnetization height from 30 to 6 mm, the maximum
levitation forces decreased from 695 to 658 N, corresponding to a decrease ratio
of 5.3%. At the case of 6 mm re-magnetization height, the maximum levitation force of
658 N was still bigger than the biggest levitation force of 627 N in the direct 30-mm
FCH case. It indicated that by employing the re-magnetization process after ZFC,
bulks had inherited the advantage of the ZFC activation with a big levitation force.
Meanwhile, the maximum guidance forces increased from 70.8 to 123.2 N with the de-
crease of the re-magnetization height from 30 to 6 mm. Although the guidance forces
had increased greatly with an increase ratio of 74%, the maximum guidance force of
123.2 N was only about two thirds of the largest one of 181.0 N in the 6-mm FCH case.
On one hand, the increased guidance forces indicated HTS bulks can indeed re-trap
certain flux in the re-magnetization process after the first ZFC activation. On the other
hand, the smaller guidance forces indicated the re-trap ability of HTS bulk is limited
in the present PMG field condition. In other words, the re-trap ability is not as effective
as the one in the direct FC case.
As indicated in Section 8.2.1, 30-mm FCH is regarded as an interesting FCH for the
present HTS Maglev vehicle system. It was chosen to verify the effectiveness of this
re-magnetization process after ZFC by comparing the magnetic force results with the
30-mm FCH case. Figure 8.32a and b show comparisons of the levitation forces and
guidance forces of the bulk levitation unit above the PMG. The two levitation force
curves are very close to each other, and the inset shows an enlargement from the gap