166 Ë 6 First manned HTS Maglev vehicle in the world
6.7 Guidance forces of HTS bulks over PMG
6.7.1Guidance forces of HTS bulks over single PMG [34]
The guidance forces refer to the forces that compels the carrier to return to its original
location of magnetic balance, after a lateral displacement. These forces are from the
pinning forces caused by trapped flux. Maglev guidance forces are measured with the
relative translational motion between a Maglev carrier and the external magnetic field
(PMG or PM). The moving element of the relative motion can be the Maglev carrier or
also the external magnetic field. The test process of guidance forces is similar to the
levitation force measurements.
The difference is that the PMG moves in the horizontal plane while the guidance
force (lateral force) is measured.
In order to test guidance forces over a PM guideway, Wang et al. [34] designed and
produced two types of special test apparatus. One was the special test apparatus of
the HTS Maglev measurement system SCML-01 (see Fig. 5.7). The PMG was composed
of NdFeB PMs and iron plate whose concentrating field in the center the surface was
up to 1.2 T and remains 0.4 T at the position of 20 mm above it. The length of the PMG
was 920 mm (see Section 6.14).
A sketch of the apparatus measuring the guidance forces is shown in Fig. 6.18. The
guidance forces of the YBCO bulk above the PMG were measured with the SCML-01.
A circular liquid nitrogen vessel (see Section 5.2.2) with the HTS bulks fixed inside
was hung over the PMG. The vessel could only swing freely around the point O in the
x-zplane (see Fig. 6.18a). The bottom center of the liquid nitrogen container was taken
as the origin of the Cartesian coordinate.
Fig. 6.18:(a) Sketch of the guidance force test apparatus of the HTS bulk over the single PM
guideway. (b) Overview of the epoxy ring and the cryogenic vessel [34]. (1) Liquid nitrogen vessel.
(2) Epoxy ring. (3) Single HTS bulk. (4) PM guideway. (5) Step motor. (6) Force transducer. (7) Epoxy
wedges.