144 Ë 5 HTS Maglev experimental methods and set-up
Fig. 5.35:Measurement results of the levitation
forces of YBCO bulk in zero field cooling (ZFC)
[12].Fig. 5.36:Measurement results of the guidance
forces of YBCO bulk at a 15 mm levitation gap for
the field cooling (FC) [12].measuring times and different rotational speeds were investigated experimentally.
Rotational speeds of 50 rpm, 100 rpm, 200 rpm, 300 rpm, and 400 rpm, with time
intervals of 12 s were tested and shown in Fig. 5.37. The experimental results were
measured with a levitation gap of 10 mm.
Figure 5.37 shows that the changes of the measured levitation forces are small,
especially at the 300 and 400 rpm speeds. The higher the PMG rotation speed, the
smaller the levitation force changes. At a levitation gap of 10 mm the observed changes
of the measured levitation forces in a 48 s period were 0.54 N at 300 rpm and 0.10 N at
400 rpm.
The levitation force decreased with increased rotational speed. The decrease in
value of the levitation forces was 22.98 N when the rotation speed increased from 50
to 400 rpm at time intervals of 12 s, which a decrease of the levitation force of 7.4% from
the original value. The reason for the decrease of the levitation force can be attributed
to some subtle changes in the uniformity of the circular PMG’s magnet field along the
circumferential direction which at high speed is equivalent to subjecting the HTS to
an AC magnetic field.
The experimental results of the guidance forces on field cooling YBCO supercon-
ductor bulks at time intervals of 12 s, levitation gap of 15 mm, and special rotation