High Temperature Superconducting Magnetic Levitation

9.2 Characteristics of HTSB Ë 333

Fig. 9.5:Schematic diagrams of the interaction between the PM rotor and HTS bulks. (a) The PM
rotor and four HTS bulks. (b) The HTS bulk with a position angle of휙. (c) Decomposition of radial
displacement of the PM rotor in (b).

HTS bulkAand the PM rotor is reduced and their mutual radial stiffness is marked as
k⊥ 1. For the HTS bulkC, the distance is increased and the radial stiffness is marked as
k⊥ 2. For HTS bulksBorD, the distance to the PM rotor almost doesn’t change and the
radial stiffness is marked ask//. In Fig. 9.5b, the position angle of a HTS bulkEis휙.
As shown in Fig. 9.5c, the radial displacement of PM rotor,l, can be decomposed into
a vertical component and a parallel component relative to the HTS bulkE:lsin휙and
lcos휙. Thus, the radial stiffness between the HTS bulkEand PM rotor is

kR,휙=k//cos^2 휙+k⊥ 1 sin^2 휙 (if 0⩽휙<휋). (9.1)

If the position angle휙is larger than휋, the radial stiffness is

kR,휙=k//cos^2 휙+k⊥ 2 sin^2 휙 (if휋⩽휙< 2 휋). (9.2)

The calculation precision of Eqs. (9.1) and (9.2) are discussed basing on the experi-
mental data from Ref. 21. The HTS stator is made up of 8 HTS bulksA∼H. The position
angle of the HTS bulkAis휋
2

and its radial stiffnessk⊥ 1 is 32.5 N/mm. The position

angle of the HTS bulkEis^3 휋
2

and its radial stiffnessk⊥ 2 is also 32.5 N/mm. For the

HTS bulkCorG, the radial stiffnessk//is 3.5 N/mm. The position angle of the HTS

bulkBis휋
4

and its radial stiffness can be calculated by Eq. (9.1):

kR,휙=k//cos^2 휙+k⊥ 1 sin^2 휙= 3. 5 ×cos^2

휋

4 +^32.^5 ×sin

22

4 =^18 (N⋅m). (9.3)

The practical value for HTS bulkBis 17.5 N/mm, while the calculated result of the
former method is 23 N/mm [22]. The calculated result of 18 N/mm obtained with Eqs.
(9.1) and (9.2) indicate that the calculation precision has been improved.