384 Ë 10 HTS Maglev launch technology
Fig. 10.10:The superconducting secondary of the LIM
system [33].The secondary conducting plate can be replaced by coils made of copper wire that are
shorted at the ends, so current can be induced when there is a change in the magnetic
flux and a thrust force will also be generated in this way.
The superconducting secondary (Fig. 10.10) of the LIM system consisted of four
racetrack coils made of YBCO-coated conductor wire with a copper stabilizer acquired
from SuperPower. The dimensions of the CC by itself (not in coil form) were 0.09 mm
in thickness and 4.2 mm in width, the rated critical current at 77 K and self-field
was 92 A. The coil was designed to be a double-pancake coil so the two ends of the
coil were easily soldered together. The upper pancake coil for both sample coils was
made to consist only of 0.5 turns while the lower pancake coil consisted of 17.5 turns.
This design was chosen for the purpose of achieving a higher thrust since the lower
pancake coil was closer to the primary so the average magnetic field density along the
z-direction (Bz) was stronger. A superconducting double lap joint connection linked
the two ends of each coil, also referred to as a bridge joint. Kapton tape was used as
the insulation layer between subsequent turns of CC wire, which served as the buffer
layer between the upper and lower pancakes. No insulation layer was applied between
the first layer of the CC wire and the coil form made of paramagnetic stainless steel.
Stycast epoxy was used to secure the CC turn layers onto the coil form.
The primary was a three-phase, flat, single-sided copper wire wound on a slotted
armature with a coil pitch of 42 mm acquired from Han’s motor. The width and length
of the armature stator was 215 and 640 mm, respectively. The primary was secured on
the ground and connected to a variable voltage variable frequency converter made by
Han’s motor for the sourcing of alternating current up toIAC=8 A and 46.9 Hz.
Larger thrust densities may thus be generated if a superconducting wire is used
to replace the copper wound racetrack coils in the secondary of an LIM system
since the superconducting wires have much higher current capacities. At the same
time, the supercurrents will be more easily generated since the resistance of the
superconducting coil is still relatively small at low-frequency alternating currents
compared to copper wound coils. As a result, high-current values are easily obtained
at low frequencies.
Furthermore, there are other methods to improve the performance of HTS LSM.
The research of Zheng indicates that a multi-pole YBCO bulk could acquire almost
two times the peak thrust force compared with the HTS coil magnets, from 54 to 102 N
based on the same motor stator platform for an armature current of 8 A [34]. This
study indicates clearly that the bulk-type HTS LSM has much potential advantages of