EXPERIENCES IN DEVELOPING THE HIGH CURRENT DENSITY WAX-FILLED SUPERCONDUCTING SADDLE MAGNETS

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EXPERIENCES IN DEVELOPING THE HIGH CURRENT DENSITY WAX-FILLED

SUPERCONDUCTING SADDLE MAGNETS

Yan Luguang, Yu Yunjia, Ye Zuxian, Jing Bohong, Li Huidong, Wang Silian, Yi Changlian, Chen Haoshu, Ma Hongda

To cite this version:

Yan Luguang, Yu Yunjia, Ye Zuxian, Jing Bohong, Li Huidong, et al.. EXPERIENCES IN DEVEL- OPING THE HIGH CURRENT DENSITY WAX-FILLED SUPERCONDUCTING SADDLE MAG- NETS. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-837-C1-840. �10.1051/jphyscol:19841171�.

�jpa-00223646�

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JOURNAL DE PHYSIQUE

Colloque C1, supplement a u no 1, Tome 45, janvier 1984 page C1-837

EXPERIENCES I N DEVELOPING THE HIGH CURRENT DENSITY WAX-FILLED SUPERCONDUCTING SADDLE MAGNETS

Yan Luguangf, Yu Yunjia, Ye Zuxian, Jing Bohong, Li Huidong, Wang Silian, Yi Changlian, Chen Haoshu and Ma Hongda

I n s t i t u t e of EZectricaZ Engineering, Academia Sinica, Beijing, China ResumP

-

La conception, l a f a b r i c a t i o n e t l e s r 6 s u l t a t s experimentaux de t r o i s aimants ("saddle magnets") sont d @ c r i t ( e ) s . Les experiences pendant 1 e devel oppement sont rPsumPes.

A b s t r a c t

-

The design, c o n s t r u c t i o n technology and t e s t r e s u l t s o f t h r e e model saddle magnets a r e described. The main research and development experiences are summarized.

Several years ago we i n i t i a t e d a program t o b u i l d a 5Mj, 35cm bore, 4T a d i a b a t i c a l l y s t a b l e saddle magnet f o r our experimental MHD generator. To solve t h e problems asso- c i a t e d w i t h such middle s i z e h i g h c u r r e n t d e n s i t y magnet, a s e r i e o f t h r e e model saddle magnets SSM-1, SSM-2 and SSM-3 has been designed, c o n s t r u c t e d and t e s t e d i n sequence. F i n a l l y , t h e SSM-3 magnet achieved "short-sample" performance. The present paper describes these mode? magnets and t h e i r t e s t r e s u l t s , summarizes t h e main research and development experiences. These model magnets used m u l t i f i l a m e n t a r y t w i s t e d r e c t a n g u l a r NbTi conductor w i t h Cu/s.c=2 and 40p polyimide tape i n s u l a t i o n . D i f f e r e n t winding shape, c o n s t r u c t i o n technology, support s t r u c t u r e design and f i l - l i n g m a t e r i a l s were i n v e s t i g a t e d on them. Main parameters o f these model magnets are l i s t e d i n Tab. 1. Fig. 1 presents t h e i r p i c t u r e s .

Table 1 Main parameters o f model saddle magnets

NO. SSM- 1 SSM-2 SSM-3

"Whole" " I n n e r "

Conductor Cross s e c t i o n 1.54x2.09 1.54x2.09 1.81x3.28

mm2

Weight kg 47 -8 2 7 2 7 64.6

Winding Cross s e c t i o n I n t e r s e c t i n g e l l i p s e I n t e r s e c t i n g 450 segmet e l 1 io s e

Shape Constant perimeter constant Double-

perimeter pancake

I.D. mm 148 148 150 215

O.D. mm 310 230 230 302

Length mm 565 565 560 625

No. o f l a y e r s 41 arge/ 21 arge/ 21 arge/ 10

28small 14small 14small

No. o f t u r n s 171 1 1087 1058 932

Fiagnet

L

H 0.543 0.2 0.2 0.297

Bo/I G/A 54.8 36.4 36.4 27.9

Bm/I G/A 63.9 43.4 43.7 38.6

"Short- Ic0 k A 1.03 1.30 1.69

sample" Boco T 5.64 4.73

::::

^4.72

p e r f o r - Bmco T 6.58 5.64 5.64 6.52

mance W M ~ ~k j 288 169 169 424

on leave at Kernforschungszentrum Karlsruhe, F.R.G.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841171

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Cl-838 JOURNAL DE PHYSIQUE

a ) SSM-1 magnet b) SSM-2 magnet c ) SSM-3 magnet

F i g . 1 The model saddle magnets 1

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SSM-1 MAGNET

The SSM-1 magnet i s a 1/3 model o f t h e magnet f o r experimental MHO generatar. It has f o u r l a r g e l a y e r s designed as constant perimeter winding t o approximate t h e i n t e r - s e c t i n g e l l i p s e cross s e c t i o n , each l a r g e l a y e r c o n s i s t s o f seven small l a y e r s . The winding i s wound d i r e c t l y on t h e 12.5mm t h i c k s t a i n l e s s s t e e l bore tube, d u r i n g winding a f t e r each small r a d i a l l a y e r ( 7 t u r n s ) the gaps are f i l l e d w i t h melted p a r a f - fin-wax by brushes. A f t e r every l a r g e l a y e r a banding i s made w i t h 25mm wide, 0.5mm t h i c k s i l k tape, a f t e r a p p l y i n g epoxy w i t h brushes t h e banding i s cured a t room temperature. The magnet r a d i a l electromagnetic f o r c e i s supported by 12 p a i r s aluminium a1 l o y I-beam r i n g g i r d e r s , each p a i r i s clamped t o g e t h e r by 16xM10 s t a i n l e s s s t e e l b o l t s . A x i a l f o r c e i s supported by aluminium a l l o y end flanges and 8 brass bars.

The magnet was t e s t e d t h r e e times i n a @ 600 mm v e r t i c a l dewar. The f i r s t (No. 1) t e s t was conducted w i t h magnet w a x - f i l l e d by brushes d u r i n g winding. Before t h e second (No. 2) t e s t t h e magnet was vacuum impregnated w i t h wax. The t h i r d (1'40. 3) t e s t was conducted a f t e r repeated vacuum impregnation o f wax. Test has been done both f o r t h e "whole1' winding ( a l l f o u r l a r g e l a y e r s i n s e r i e ) and t h e " i n n e r " winding ( t h e i n n e r two l a r g e l a y e r s ) . Fig. 2 presents t h e t e s t r e s u l t s .

From t h e t e s t r e s u l t s i t was observed:

( 1 ) A f t e r about 20 t r a i n i n g steps t h e h i g h e s t achieved performance o f wax- f i l l e d by brushes magnet i s 47% o f t h e

"short-sampl e" performance. Vacuum i m - pregnation reduced t r a i n i n g and i n c r e - ased t h e performance t o 60%, repeated impregnation f u r t h e r increased i t t o

68%. Degradation and t r a i n i n g are s t i l l serious.

(2) U n l i k e t h e solenoids, t h e quench c u r r e n t d u r i n g t r a i n i n g does n o t i n - crease monotonously, t h e r e were several undulations, t h e i r amp1 i tude reached 60A.

( 3 ) From t h e recorded b r i d g e s i g n a l i t

" ~ h o l e l ' I ⁴

0 . 8 -

- _{\ I}

---

"Inner,

^I, ^I

I 0.6 ^'

I I

I ^I

0 ' 10 20 30 40 50

F i g . 2 SSM-1 t e s t r e s u l t s

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was observed t h a t before quench there appeared repeatedly a l o t of 1-3mV amplitude and 1-2 sec. long small pulses.

( 4 ) Comparison between the "whole" winding and "inner" winding t e s t r e s u l t s shows t h a t f o r both cases the products of highest quench current and peak f i e l d ( I

B

)max are approximate1 y identical

.

That means the magnet performance i s 1 imi ted t o q t t e same electromagnetic force l e v e l .

During dissection of the magnet a f t e r t e s t s i t was observed t h a t the bandings on the inner two layers were broken in many places, the thickness of wax layer between the s t r a i g h t part of winding and bore tube reached 5-6mm.

2

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^SSM-2 ^MAGNET

Based on the t e s t r e s u l t s of SSM-1 magnet, i t was decided t o reduce the thickness of wax layer and t o improve the banding between layers. Using the bore tube, the coil forms and conductors of the

two

inner large layers of the SSM-1 magnet, the SSM-2 magnet has been constructed. I t has the same parameters and winding technology as the "inner" winding of SSW-1. The main differences are:

(1) an additional banding with

0

0.8mm s t a i n l e s s s t e e l wire i s made on the s i l k banding of the f i r s t large layer.

(2) wax-filling with brushes during winding i s avoided.

( 3 ) simpler support s t r u c t u r e consisting of 12 pairs of 20mm thick s t a i n l e s s s t e e l clamps and 24xM20 s t a i n l e s s steel bolts i s used (Fig. Ib).

The magnet was tested s i x times. The f i r s t four t e s t s were with vacuum wax-impregnated magnet, the e f f e c t of repeated impregnation and warming t o LN? temperature was investigated. The f i f t h t e s t was with magnet vacuum impregnated w i t h alcohol a f t e r removing wax. The l a s t t e s t was with unfilled magnet a f t e r removing alcohol. Fig. 3 presents the t e s t r e s u l t s . I t can be seen from the t e s t r e s u l t s that:

( 1 ) There i s no improvement in magnet performance in comparison with SSM-1 magnet.

( 2 ) As SSM-1, the f i r s t reimpregnation improved the magnet performance, but the second reimpregnation did

n o t

give f u r t h e r improvement.

( 3 ) In comparison with wax f i l l i n g , the impreg-

nation with alcohol a l s o 0.8 -

-

does not improve the mag-

net performance, a1 though Ic0=1 .3kA

in t h i s case t h e small pulses in bridge signal disappeared.

( 4 ) When magnet was

un-

f i l l e d , the magnet per-

Tormance decreased strong-

1

ly. The highest perfor- 2 0 4 0 6 0 80

mance droped from 67% t o

1

37% of the "short-sampl e"

performance. The SSM-2

t e s t r e s u l t s show c l e a r l y 0 . t h a t t o get good magnet

performance i t i s necess- 0.4 -

ary t o change the magnet impregnation I impregna- design and construction

o S 2

-

techno1 ogy.

I 0 I 1 1 1 I I N .

0 100 120 140 160 180 203

Fig. 3 SSM-2 t e s t r e s u l t s

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30URNAL DE PHYSIQUE

3

-

^SSM

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^{3 MAGNET}

A f t e r SSM-2 magnet t e s t i t was decided t o make a new design and t o improve t h e winding technology s e r i o u s l y . The SSM-3 magnet has been designed and constructed. I n comparison w i t h two previous models, the main changes are:

(1) I n s t e a d o f p r e v i o u s constant perimeter m u l t i l a y e r winding the double-pancake winding i s used.

(29 The winding cross s e c t i o n i s m o d i f i e d from i n t e r s e c t i n g e l l i p s e t o 45O segment.

( 3 ) The bore diameter and conductor cross s e c t i o n a r e l a r g e r .

(4) The w e f t l e s s epoxy-fiberglass tape i s used f o r i n t e r l a y e r bandings. A f t e r c u r i n g the bandings are machined t o given dimension.

(5) Many e f f o r t s have been p a i d t o improve t h e winding technology. The SSM-3 magnet used t h e same support s t r u c t u r e o f SSM-1. The design and c o n s t r u c t i o n technology o f SSM-3 a r e d e t a i l l y described i n /I/.

Fig. 4 presents t h e t e s t r e s u l t s

o f t h e SSM-3 magnet. The f i r s t I q Ic0=1 .69kA t e s t was w i t h u n f i l l e d magnet, t h e

second was conducted a f t e r vacuum kA

---

impregnation o f wax. During second

- G

1.5'

n L ^-

t e s t the b o l t s o f support s t r u c t u r e were damaged a t 1.525kA magnet c u r - r e n t . The t h i r d t e s t was w i t h t h e

magnet w i t h redesigned support 1.0 s t r u c t u r e . The improvement o f t h e

support s t r u c t u r e i s described i n

/2/. 0.5

From t h e t e s t r e s u l t s i t can be seen c l e a r l y t h a t t h e magnet performance has been improved s i g n i -

-

U n f i l l e d

I

Vacuum I A f t e r impreg-

1

s t r u c t u r e

- '

n a t i o n

I

improve-

I

o f wax

,

^ment

I

I 1 1 1

f i c a n t l y . Even the, u n f i l l e d mag- 0 10 20 30 40 50 n e t reached 77% o f "short-sample"

performance, t h e magnet w i t h i m - Fig. 4 SSM-3 t e s t r e s u l t s

!roved support s t r u c t u r e achieved short-sample" performance (97%!).

4

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MAIN EXPERIENCES AND CONCLUSION

The main experiences gained from these t h r e e model magnets are:

-

For MHD magnet, where t h e requirement o f magnetic f i e l d homogeneity i s low, t h e double-pancake segment winding i s b e t t e r i n t h e aspects o f f o r c e transmission and winding compactness.

-

Much a t t e n t i o n should be p a i d t o improve t h e winding technology, t o develop s u i t - able winding instruments.

-

The w e f t l e s s epoxy-fiberglass tape banding has been proved q u i t e good. The machin- i n g o f bandings a f t e r c u r i n g i s necessary f o r winding t h e succeeding pancake.

-

F i l l i n g seems t o be unavoidable. Wax f i l l i n g has several advantages, such as simpl- e r technoloqy, cheaper, magnet can be rewind and conductor can be reused.

-

Correct design o f support s t r u c t u r e i s a l s o important. Ring g i r d e r s w i t h p i n - p l a t e clamping a r e a good s o l u t i o n .

The,SSM-3 magnet demonstrated t h e f e a s i b i l i t y o f c o n s t r u c t i o n h i g h performance,close- packed, wax-f i 11 ed middle-si ze saddle magnets.

REFERENCES

/I/ Yan Luguang e t a l . IEEE Trans. on Magnetics, v o l . MAG-19, No.3, p. 1381 (May, 1983).

/2/ Yan Luguang e t a l . Paper 4P2-02 a t t h i s (MT-8) Conference, SeDt. 1983.