294 Ë 8 New progress of HTS Maglev vehicle
PMG at the smallest gap of 6 mm. In the ZFC case, the maximum levitation forces were
239 N, 690 N, and 870 N, respectively for the upper, lower, and double-layer HTS bulk.
By adding the upper-layer HTS bulk, the levitation forces of the double-layer HTS bulk
increased by 26.1% compared to the lower layer. However, the maximum levitation
force of the double-layer of 870 N was smaller than the sum of the upper and lower
HTS bulk’s levitation force of 929 N, 75.3% of levitation capability of the upper-layer
HTS bulk was excited. This decrease of levitation forces between the sum of the upper
and lower layer and the double-layer HTS bulk can be explained by the shielding of
the HTS bulks in the lower layer [45]. In the FC case, the maximum levitation force of
the double-layer HTS bulk increased by 19.4% compared to the lower layer and 57%
of levitation capability of the upper-layer HTS bulk was excited. It was implied that
adding the upper-layer HTS bulk is not as effective in FC case as in ZFC case.
In practice, the levitation performance of the on-board HTS bulk at the working
gap is more useful than the maximum forces at the smallest gap. Table 8.4 shows the
levitation forces and guidance forces of the individual and double-layer of HTS bulk
levitation unit above the PMG at a typical working gap of 15 mm. The levitation forces
of the double-layer HTS bulk were still smaller than the sum of that of the upper and
lower layer in both ZFC and FC cases. Moreover, the increased ratio of the double-
layer to the lower layer and the efficiency of the upper layer at the working gap of
15 mm were close to the corresponding values at the smallest gap, shown in Tab. 8.3.
An increase of 24.9% in levitation force was obtained by the double-layer HTS bulk
in the ZFC case, which means 79.8% of levitation capability of the upper-layer HTS
bulk was excited at the working gap, while, in the FC case, the increase in the ratio
of the double-layer was only 16.9% and the efficiency of the upper layer was 53.5%.
The improvement of performance by adding the upper HTS bulk layer was still not
as effective in the FC case as it was in the ZFC case. As for the guidance forces, the
efficiency of adding the upper-layer HTS bulk was lower than that of the levitation
forces. Only an increase of 8.8% was obtained by the double-layer HTS bulk, which
means 27.3% of guidance performance of the upper-layer HTS bulk was excited. Hence,
the performance improvement in guidance forces was not increased much by adding
the upper-layer HTS bulk.
Tab. 8.4:Levitation forces and guidance forces of the individual and double-layer of HTS bulk
levitation unit above the PMG at the working gap of 15 mm.
Conditions Upper Lower Sum Double- Double Upper
layer layer layer increase eflciency
ZFC FLev(N) 109 349 458 436 24.9% 79.8%
FC FFLev(N)^68215283252 16.9% 53.5%
Guie(N) 30.0 93.6 123.6 101.8 8.8% 27.3%
eFGuiis the guidance force.