164 Ë 6 First manned HTS Maglev vehicle in the world
Fig. 6.14:Relationship between the levitation force and
the temperature [30].Fig. 6.15:Levitation forces vs. gap at the temperature
of 16, 50, 70, and 77 K [31].deep cryogenic measurement system, ranging from 77 to 16 K. A single-NdFeB PM
disk (휙 30 ×15 mm) could be lifted vertically above the HTS YBCO bulk with the gap
between 100 and 5 mm. Levitation forces of YBCO bulk at different gaps were obtained
at different temperatures under the control of the HTS Maglev measurement system
(see Section 5.3).
Figure 6.15 shows the levitation forces of a single YBCO bulk under a single
permanent magnet disk at 16, 50, 70, and 77 K, respectively. It is clear that temperature
has a notable effect on the levitation force at small levitation gaps, for example, 22.3 N
at 16 K and 15.2 N at 77 K for the same gap of 5 mm. However, the effect of temperature
on the levitation force is not obvious at larger levitation gaps. Therefore in practical
applications, if the levitation gap is larger, it is not economic to have a cryogenic
temperature lower than 77 K.
Song et al. [32] reported the temperature dependence of the HTS YBCO bulk
at different levitation gaps. Results showed that the levitation force at lower tem-
perature was larger than that at higher temperature near the critical temperature
of the YBCO. Figure 6.16 shows that the levitation force at a gap of 5 mm incre-
ased with decreasing temperature. The levitation performance of the YBCO below
35 K was stable with maximum levitation force of 22.3 N (16 K). When the gap was
10 mm, improvement of the levitation performance versus the temperature was not
notable.