8.3 Methods to improve Maglev performances Ë 2998.3.5Introduction of ferromagnetic materials
As described in Eqs. (8.6)–(8.8), the electromagnetic forces (levitation forces and
guidance forces) obtained by HTS bulks is closely dependent on the magnetic field
at the bulk position. If the magnetic field at the bulk position is enhanced, corre-
spondingly, the levitation forces of the bulk can be improved [48]. A ferromagnetic
material like iron with a high permeability is used to guide the flux distribution
of the PMG in order to enhance the magnetic field at the bulk-laying position. The
principle of this method is similar to the PMG design, in which the ferromagnetic
materials are usually employed as flux collectors to increase the intensity and gradient
of the generated magnetic field of the PMG. The key question is how and where to
add the iron plates. Figure 8.39 presents an example in which an optimized 1-mm-
thick iron plate was added on the surface of the bulk unit. It was observed that after
adding the iron plate, the magnetic field distribution was obviously changed at the
bulk position.
In the confirmatory experiments, a single iron plate was employed just covering
the upper surface of the bulk unit. Since there would be an obvious attractive force
between the iron plate and the PMG, the added iron plate should be thin. After
magnetic field simulations by FEMM software, a 1-mm-thick iron plate was chosen
by optimization. To check the effectiveness, the influence of the added iron plate on
the magnetic forces in the typical FC condition was examined with the SCML-01 [26]
(see Section 5.3).
Figure 8.40a and b shows the levitation force and guidance force curves of the
bulk levitation unit with and without adding the iron plate on its surface, respectively.
It is found that the added iron plate will weaken the levitation forces and that the
levitation forces decrease more with increased size of the iron plate (see Fig. 8.40a).
The maximum levitation force of the bulk unit is 474, 396, and 433 N, respectively, for
the cases of a full iron plate, no iron plate and partial iron plate on the bulk surface.
This result is thought to result from the attractive forces between the iron plate and
Fig. 8.39:Magnetic field distribution of the Halbach PMG at the HTS bulk position. (a) Without iron,
(b) with a 1-mm-thick iron plate added on the HTS bulk surface.