Niobium-tin superconducting inductor for levitated vehicles

ICEC 14 Proceedings

NIOBIUM-TIN

SUPERCONDUCTING

INDUCTOR

FOR L E V I T A T E D

VEHICLES

E.Yu.Klimenko* N.N.Martovetsky* A.M.Malofeev* V.A.Mokhnatuk* S.I.Novikov* N . M . R o d i n a * V . I . O m e l y a n e n k o * * R . N . P o k h o d e n k o * * S.A.Sergeev** * K u r c h a t o v Institute for Atomic Energy, Moscow, 123182, Russia ** Kharkov P o l y t e c h n i c Institute, Kharkov, 310002, U k r a i n e

The design of a full-scale niobium-tin coil intended for g e n e r a t i n g propulsion, levitation and g u i d a n c e of a vehicle is given. A compact cryostat m a k i n g it possible to test the coil as a part of a dynamic laboratory installation is described. The results of stress and d i s p l a c e m e n t calculations for winding components as well as the results of p r e l i m i n a r y tests of the coil in the p e r s i s t e n t current mode are presented.

INTRODUCTION O b t a i n i n g of high efficiency of the vehicle p r o p u l s i o n and levitation systems is closely related with the improvement of the c h a r a c t e r i s t i c s of the s u p e r c o n d u c t i n g magnet [i]. One of the ways of solving this p r o b l e m is to use n i o b i u m - t i n wire t o g e t h e r with the novel, d e s i g n e d by the authors technique of securing the winding turns by glueing them to the structural sheets [2]. In order to investigate the influence of mechanical loads and alternating electromagnetic fields on such a winding we have created the laboratory i n s t a l l a t i o n which would enable us to accelerate the coil being tested to the v e l o c i t y of ca. 30m/s [3]. The i n s t a l l a t i o n consists of a stator whose length exceeds 14 m and a m o v a b l e inductor. The stator is split along the installation length into three fragments. The first fragment intended for a c c e l e r a t i n g the inductor to the required v e l o c i t y is a double-sided direct current linear m o t o r (DCLM). At the second fragment the inductor moves with a constant speed. At the last fragment the catcher with inductor travelling along guideways is d e c e l e r a t e d due to friction of b u s h i n g s against the rest pipes. In order to use the s u p e r c o n d u c t i n g coil as a DCLM inductor, we had to design a flat cryostat only 52mm thick. Rather small apparatus thickness favours high effective operation of the DCLM. The cryostat design, methods and results of calculations of the mechanical stresses in the s u p e r c o n d u c t i n g w i n d i n g caused by the ponderomotive forces, as well as the results of p r e l i m i n a r y tests are given below.

INDUCTOR

DESIGN

The inductor design should guarantee its serviceability under repeated s h o r t - t e r m mechanical overloads. The absence of power and cryogenic supply of the inductor in the course of the tests stipulates also the requirement of m i n i m u m heat leak. The inductor (Fig.l) consists of the following main assemblies: s u p e r c o n d u c t i n g coil together with a helium vessel, load-transmitting system, radiation shield, external vessel, removable current leads. R e c t a n g u l a r winding of the coil consists of two double pancakes made of wire MPNOS-4.5xI-14641. The pancakes are adhesive bonded to 328

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ICEC 14 Proceedings the central s t r u c t u r a l sheets made of stainless steel and to the c o p p e r p l a t e s inserted b e t w e e n the p a n c a k e halves. Plane walls of h e l i u m vessel w e l d e d over their p e r i m e t e r to the r e c t a n g u l a r power frame are b o n d e d also to the winding. The coil o p e r a t i o n in the a u t o n o m o u s mode is e n s u r e d by a thermal p e r s i s t e n t current switch made of h e a t - i n s u l a t e d n i o b i u m - t i n t w i s t e d wires P S T - I I x 0 . 5 mounted on the coil terminals. S i m i l a r to the h e l i u m vessel, the external v a c u u m vessel is p r o v i d e d w i t h a power frame with side covers w e l d e d thereon. Inside the v e s s e l there are rests r e c e i v i n g the a t m o s p h e r i c pressure. M e e t i n g the r e q u i r e m e n t s to the design of the inductor under discussion, the system for t r a n s m i t t i n g m e c h a n i c a l forces has been d i v i d e d into a s t a t i o n a r y and d i s e n g a g e a b l e parts. The s t a t i o n a r y system is loaded by the mass of the h e l i u m vessel only and therefore is made of glass fiber. E l e c t r o m a g n e t i c and inertial m e c h a n i c a l loads are t r a n s m i t t e d from the s u p e r c o n d u c t i n g coil to the v a c u u m vessel t h r o u g h d i s e n g a g e a b l e supports. These supports w o r k only d u r i n g the acceleration, m o t i o n and d e c e l e r a t i o n of the inductor. They are a set of fiber glass plates m o u n t e d on the p o w e r frame of the helium vessel, m o v a b l e part of the r a d i a t i o n shield and internal surface of the v a c u u m vessel power frame. The power frames of the h e l i u m and external v e s s e l s are m e c h a n i c a l l y e n g a g e d or d i s e n g a g e d by a wedge m o v e d by a s p e c i a l - p u r p o s e drive. Disengaged, the fiber glass plates have the t e m p e r a t u r e of the cryostat a s s e m b l i e s they are m o u n t e d on. In the e n g a g e d state, due to a low thermal c o n d u c t i v i t y of fiber glass and insignificant duration of the inductor accelerationd e c e l e r a t i o n p r o c e s s (ca. 0.2s) the heat leak to the h e l i u m vessel is insignificant. Our d e s i g n w o r k has resulted in the s u p e r c o n d u c t i n g magnetic system the s p e c i f i c a t i o n s of which are given in Table i. Table

1

Inductor characteristics

Parameter

Value

I n d u c t o r d i m e n s i o n s (m) I n d u c t o r mass (kg) Coil m i d d l e - t u r n d i m e n s i o n s (m) N u m b e r of turns W i n d i n g mass with structural sheets O p e r a t i n g c u r r e n t (kA) Stored energy (kJ)

CALCULATION

(kg)

OF STRESSES AND D I S P L A C E M E N T S

1.3 x 0.75 x 0.052 114 0.77 x 0.3 184 25 1.2 40

IN THE S U P E R C O N D U C T I N G

COIL

As we are interested in stresses and deformations caused by p o n d e r o m o t i v e forces in the plane of the s u p e r c o n d u c t i n g winding, the p r o b l e m of the t h e o r y of e l a s t i c i t y was solved for p o s i t i n g of two dimensions. S t r e s s e s and d i s p l a c e m e n t s of the a s s e m b l y c o n t a i n i n g the winding, s t r u c t u r a l sheets and power frame of the h e l i u m vessel were c a l c u l a t e d by the m e t h o d of finite elements reduced to the solution of the f o l l o w i n g set: Ku

= R,

(i)

where K is the global m a t r i x of rigidity, u is the d i s p l a c e m e n t s of the e l e m e n t nouds, R are the g e n e r a l i z e d forces. The global m a t r i x of r i g i d i t y is formed by s u m m i n g the rigidity m a t r i c e s of flat q u a d r a n g u l a r elements of v a r i o u s t h i c k n e s s according to the actual coil t h i c k n e s s in the place of e l e m e n t location. The spatial a n i s o t r o p y was d i s c r i b e d by a c c o u n t i n g for d i f f e r e n c e s in the

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ICEC 14 Proceedings values of moduli of elasticity and coefficients of transverse d e f o r m a t i o n along the axes of the spatial s y s t e m of coordinates. The fields of linear displacements u and v for each element were s p e c i f i e d by L a g r a n g e ' s t w o - p o i n t i n t e r p o l a t i o n function. We u s e d two kinds of b o u n d a r y conditions. The k i n e m a t i c one limited the degrees of freedom of two extreme points at the horisontal axis of symmetry. The force b o u n d a r y conditions were s p e c i f i e d in the form of c o n c e n t r a t e d loads a p p l i e d to the nodes. The p r o g r a m for s o l v i n g the set (i) was b a s e d on Gauss m e t h o d of elimination. U s i n g the LTDL d e c o m p o s i t i o n of m a t r i x K, the set (i) can be w r i t t e n as two equations: LT V = R;

V = D L u

(2)

w h e r e s o l u t i o n v is o b t a i n e d by the load v e c t o r t r a n s f o r m a t i o n and d i s p l a c e m e n t u is c a l c u l a t e d then by the r e v e r s e substitution. The c a l c u l a t e d v a l u e of m e c h a n i c a l stress over the sheet plane is equal to 244 MPa, w h i c h indicates an a p p r o x i m a t e l y fivefold safety margin. A s u b s t a n t i a l c o n t r i b u t i o n to the s t u r c t u r e r i g i d i t y is made by the p o w e r frame. W i t h o u t the frame the stress in the sheets is increased f o u r f o l d w i t h respect to the above value.

PRELIMINARY

TEST R E S U L T S

In order to c h e c k up the wire current c a r r y i n g a b i l i t y after wire r e a c t i n g and p a n c a k e s g l u e i n g to the c o p p e r p l a t e s and stainless steel sheet, we p l a n e d to test the s u p e r c o n d u c t i n g coil w i t h o u t the power frame of the h e l i u m vessel. As the c o n s t r u c t i o n rigidity in this case is s u b s t a n t i a l l y reduced, i r r e v e r s i b l e w i n d i n g d e f o r m a t i o n s can occur as the c u r r e n t is lead in the coil. To avoid this, the external faces of the w i n d i n g were p r o v i d e d w i t h steel strips 0.15 m wide b o n d e d thereon. We did not d e t e r m i n e the critical c u r r e n t for the same reason. The f o l l o w i n g p a r a m e t e r s were r e c o r d e d in the course of the tests: w i n d i n g current; d e f o r m a t i o n of v a r i o u s coil regions; m a g n e t i c field i n d u c t i o n in the p o i n t r e m o t e d by 10mm from the most stressed one; c u r r e n t lead-ins t e m p e r a t u r e in the place of s o l d e r i n g w i t h the winding; mechanical noise; electrical voltage across the w i n d i n g p a n c a k e s and s u p e r c o n d u c t i n g switch. The test c o m p r i s e d several cycles, including: c u r r e n t lead into the coil up to a s p e c i f i e d value; coil t r a n s f e r into the p e r s i s t e n t c u r r e n t mode; c u r r e n t lead-out from the coil. These cycles have been c a r r i e d out at t h e c u r r e n t s of 120, 300, 500 and 800A. The fully h e l i u m - i m m e r s e d switch t r a n s i t s to the normal state w i t h the s u p p l i e d power of 1.5W. At 800A c u r r e n t the m a g n e t i c field i n d u c t i o n at the sensor's place was 1.4T, and the t e m p e r a t u r e at the c u r r e n t lead-ins had r e a c h e d 6.8K. The m a g n e t i c system was t h e r e a t stable. The c u r r e n t decay time in the p e r s i s t e n t current mode was above 70 hours. We have not r e c o r d e d s u b s t a n t i a l splashes of a c o u s t i c signals. This p r o v e s the a b s e n c e of the w i n d i n g cracking, u s u a l l y o b s e r v e d at l a b o r a t o r y testing. The coil d e f o r m a t i o n along the small axis was ca. i00 URD.

CONCLUSION Our investigations have demonstrated the feasibility of the s u p e r c o n d u c t i n g coil d e s i g n based on d o u b l e n i o b i u m - t i n p a n c a k e s with c o p p e r p l a t e s and s t a i n l e s s steel s t r u c t u r a l sheets b o n d e d b e t w e e n the p a n c a k e halves. This structure, being h i g h l y rigid, is light, w h i c h makes it a t t r a c t i v e to m a g l e v vehicles. S u c c e s s f u l m a n u f a c t u r i n g of the inductor as a w h o l e will enable us to test d y n a m i c a l l y the w i n d i n g at the w o r k i n g i n s t a l l a t i o n with the a c c e l e r a t i o n s of up to 50 g. 330

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ICEC 14 Proceedings

REFERENCES 1

Mine, S. et al. Highly efficient superconducting magnet for magnetically levitated train Proc. 9 Int. Cryoq. Eng. Conf. Kobe (1982)

198-201

2

Klimenko, E.Yu. Novikov, S.I. Omelyanenko, V.I. Sergeev, S.A. Superconducting magnet for high speed ground transportation Cryoqenics (1990) 30 41-45

3

Klimenko, E.Yu. et al. Laboratory installation for testing fullscale magnetic levitation modules Proc._ist_Japan-CIS joint seminar on electromaqnetomechanics in structures Tokyo (1992) 122-125

_A_

--'SUPPORT DRIVE

STRETCHER

SUPERCONDUC~NG INTERNAL

GUIDING WHEEL

STAINLESS STEEL PLATE

SUPERCONDUC~NGCOIL COPPER P L A T E

OUTER V E S S E L STAINLEss STEEL PLATE

RADIATION SHIELD

t

D~ENGAGF~BLE SUPPORT

STRETCHER INNER VESSEL

Figure 1

Figure 2

Lay-out of the inductor

The supercoducting

coil with the power frame

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