8.3 Methods to improve Maglev performances Ë 289capability) but poor stability when interacting with an applied field. While with
FC processes, the HTS bulk can have a good guidance forces (stability) due to the
trapped flux, but a reduced levitation force. Hence, the FC way seems more suitable
for practical applications. In FC cases, the bigger levitation force can be obtained by
increasing the FCH between the HTS bulks and the applied field at the price of some
stability, and vice versa [36–38]. The two forces in a levitation system act more like
a contradictory couple. Under this rule, it is very difficult to improve the levitation
forces (load capability) and guidance forces (stability) at the same time with the
given HTS bulks and applied field in practice. Referring to the recent reports about
the re-magnetization ability of HTS bulks [39, 40], the HTS bulks after the first ZFC
process are considered to be able to trap some flux in the following re-magnetization
process, thus creating stable levitation. This characteristic implies a possible way to
improve both the levitation and guidance forces. Thus, the optimization method with
an additional re-magnetization process after ZFC is proposed and examined in this
section.
As shown in Fig. 8.30, the levitation unit was composed of four three-seeded bulk
samples. The magnetic forces between the levitation unit and the Halbach PMG under
different excitation ways were measured by the SCML-01 [26] (see Section 5.3). For the
re-magnetization process after ZFC, the typical pre-load execution steps include
- The HTS bulk levitation unit was first cooled by liquid nitrogen far away the PMG
in the ZFC process. - After about 20 minutes when the bulks have been cooled completely, the bulk
levitation unit was lowered and stopped above the PMG with a smaller gap to
experience the PMG field thus being magnetized again. - This re-magnetization process also lasted about 20 minutes to make the bulks trap
as much flux as they can in the PMG field.
After that, the force measurements were performed to verify the Maglev performance
obtained for HTS Maglev vehicle application.
Figure 8.31a and b shows the levitation and guidance force curves of the bulk levi-
tation unit above the PMG at different re-magnetization heights after ZFC, respectively.
All the levitation and guidance force curves have the similar profiles to the normal FC
Fig. 8.30:Schematic illustration of working process of the bulk levitation unit with a
re-magnetization process after zero-field cooling.