PROSPECTS OF MULTIFILAMENTARY SUPERCONDUCTOR AC 50 Hz APPLICATIONS

HAL Id: jpa-00223750

https://hal.archives-ouvertes.fr/jpa-00223750

Submitted on 1 Jan 1984

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

PROSPECTS OF MULTIFILAMENTARY

SUPERCONDUCTOR AC 50 Hz APPLICATIONS

I. Hlásnik

To cite this version:

I. Hlásnik. PROSPECTS OF MULTIFILAMENTARY SUPERCONDUCTOR AC 50 Hz APPLICA- TIONS. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-459-C1-466. �10.1051/jphyscol:1984194�.

�jpa-00223750�

PROSPECTS OF MULTIFILAMENTARY SUPERCONDUCTOR AC 50 Hz APPLICATIONS

EZectrotecXnical Institute CEFR, Slovak Academy of Sciences, 842 39 Bratislava, CzechosZovakia

&& - ^A p a r t i r d e s parambtres d e supraconducteurs m u l t i f i l a m e n t a i r e s mo- d e r n e s e t de l e u r s p o s s i b l e s a m 6 l i o r a t i o n s on montre que l e u r s a p p l i c a t i o n s aux bobinages & c o u r a n t a l t e r n a t i f 50 Hz avec B , autour de IT peuvent appor- t e r d e s Bconomies d ' 6 n e r g i e e t e n m6ne temps une diminution du p r i x de r e - v i e n t .

B b s t r a c t - ^It i s shown t h a t parameters o f modern m u l t i f i l a m e n t a r y supercon- d u c t o r s and t h e i r p o s s i b l e improvements a l l o w t h e i r a p p l i c a t i o n t o AC 50 Hz windings working a t Bm of about 1 T and g i v i n g energy and t o t a l c o s t savings.

AC l o s s e s which a r i s e i n t y p e I1 s u p e r c o n d u c t o r s i n t i n e v a r y i n g magnetic f i e l d s w i t h f l u x d e n s i t y amplitude B,higher t h a n t h e lower c r i t i c a l f l u x d e n s i t y

&, have two i n a u s p i c i o u s coneequences. F i r s t t h e y l e d through t h e superconductor warming u p t o a n e x c e s s i v e d e c r e a s e of quenching and working c u r r e n t s . Second i n concomitance w i t h needed r e f r i g e r a t o r energy consumption t h e y d i d t h e t o t a l energy b a l a n c e economically unfavourable.

Recent p r o g r e s s i n low l o s s m u l t i f i l a m e n t a r y superconductor technology t o g e t - h e r w i t h a b e t t e r u n d e r s t a n d i n g of t h e i r behaviour i n time v a r y i n g f i e l d s have evoked t h e d i s c u s s i o n a b o u t t h e p o s s i b i l i t y of b u i l d i n g AC 50 Hz superconducting equipment6 from m u l t i f i l a m e n t a r y composites [ l ] - ^{/ 5 ]} .

Following q u e s t i o n s a r i s e d :

1. Could t h e s e new composites work a t 50 Hz and i n 1 T range?

2. I f yes, could t h e t o t a l energy consumption i n windings from t h e s e composi- t e s be s m a l l e r t h a n t h a t i n c o n v e n t i o n a l windings?

3. If y e s , could t h e t o t a l c o s t s o f superconducting equipment b e s m a l l e r t h a n t h o s e o f a conventional one ?

4. I f y e s , what a r e t h e key problems t o b e s o l v e d on t h e way t o i n d u s t r i a l A C 50 Hz m u l t i f i l a m e n t a r y superconductor a p p l i c a t i o n s ?

The aim o f t h i s p a p e r i s t h e l o o k i n g f o r , a t l e a s t , p r e l i m i n a r y answers on t h e m q u e s t i o n s .

I. FIKE FILALlENT LOW LOSS SUPERCONDUCTORS. THEIR QUENCHIEC CURRENTS AND AC LOSSES The p r o g r e s s a t t a i n e d i n t h e m u l t i f i l a m e n t a r y superconductor technology 161- 19) h a s l e d t o a s u b s t a n t i a l f i l a m e n t diameter r e d u c t i o n i n t o t h e micrometer and submicrometer r a n g e ( d C l pm). Small w i r e d i a m e t e r s (Dz0.1 - 0.3 mm)which ha- ve been o b t a i n e d allowed t o reduce lp under 1 an t o o ( f o r mechanical r e a s o n s lp?. 5 D). I n t r o d u c i n g a p p r o p r i a t e , homogeneously d i s t r i b u t e d CuNi b a r r i e r s ( s e 8 Fig.1) around s u p e r c o n d u c t i n g f i l a m e n t s , between and around f i l a m e n t s t a c k s a s w e l l a s around s t a b i l i z i n g Cu f i l a m e n t s r e s u l t e d i n h i g h $ ( 1 6 " 10-%dsimultane- o u s l y c o n s e r v i n g low?, 6 1 ~ - 4 b m ) 1101 - ^[13] . Table I g i v e s a n overview o f t h e com- p o s i t e p a r a m e t e r s r e f l e c t i n g t h e p r e s e n t s t a t e o f t h e a r t a s w e l l a s t h e expected p r o g r e s s i n t h i s domaine.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984194

C1-460 JOURNAL DE PHYSIQUE

5 3 21

5 I 21

con 0-31 a o n 01, 0 n

, I 0 II 1.1

I- W A C ns nca

-

m M n

A l l t h e s e t e c h n o l o g i c a l achievemonts hove l e d t o a s u b s t a n t i a l r e d u c t i o n of A C l o s s power d e n s i t y p e r composite u n i t v o l u r ~ ~ e p, v ~ h i c h is t h e s-xm o f h y s t e r e s i s and eddy c u r r e n t l o s s power d e n s i t y p and pe r e s p e c t i v e l y . I n m u l t i f i l a m e n t a r y superconductors which come i n t o c o n s i k e r a t i o n f o r t h e u s e a t 50 Hz and B 2 0.5 T p, a t f i r s t approximation can b e expressed a s f o l l o w s [5]

8 nnl u loo or1 I I I C r O I lo o o l a 0 . 1 ~ 2 I IS :a 1 1.1 a,onrlr

OC( I ~n 11 I ,134 I W Y ~ O I I I

7 0% I 197 0-11 0 2 113 0 m l DW 304 155 ,01 I xm-"

where h i s r e l a t i v e superconductor volume i n t h e composite, J f B ) c r i t i c a l c m c u r r e n t d e n s i t y i n t h e superconductor a t Bm, f i s t h e frequency.

Y

8

I

0

r

Experimental d a t a o n quench c u r r e n t s and A C l o s s e s i n mixed m a t r i x f i n e f i - laments ( d = ¹ pm) c s p e c i s l l y a t f > 5 Hz a r e s c a r c e [12] , ^[13] . L a s t l y we heve un- d e r t a k e n a s y s t e m t i c s t u d y of quenching c u r r e n t s and AC l o s s e s on i n d u c t i v e c o i l s w i t h d i f f e r e n t c o o l i n g channels f r o n t h e conductor N09 of Table I which was u s k i n d l y made a v a i l a b l e i n a l e n g t h of-500 m by D r . J.Goyer from Alsthom A t l a n t i q u e . F i r s t s e r i e s o f c o i l s was wound from a sample of 30 m l e n g t h o n t o FRP bobbin w i t h diameter of 5 ma, l e n g t h o f 6 cm and w i t h maximum 7 l a y e r s (see Fig.2). The c o i l s d i f f e r e d by t h e t h i c k n e s s of s p a c e r s , which were i n s e r t e d a t each l a y e r t o form c o o l i n g channels. Analogous ' c o i l s h a s been made from Niomax TC 1045/ 20, ~ ' 6 4U.I.

OU I I41 OW1 111 123 615 '754 161

1.1 I . 1.39 I n 0 3 167 0.1 0 1 s 1 % I.= 8% '8 1 8

on I m o 149 n s 4 ‘~4 31.4 $41 ,.Fu-'~

I I I I S 115 0 3 10 0 2 m4 o 0 6 5 0 2 1 l o e 0 6 1 1 r h * s a .

OW 2 2.21 0 2 5 0.15 0.5 I6 2 S W m n t h l

The experjmental r o s u l t s a r e shown o n t h e F i g 3 whore t h e r a t i o o f Kim' s pa- r.-.neter += ^{Iq(B,,+ B,J f o r AC} and DC measurements i s p l o t t e d a g a i n s t frequency f , where B being maximum B a t I i n t h e coil.dcDcfast i n a l l c o i l s , exocpl; c o i l

'3 m q

work 10

! r

_--

f=50 H z G e q u a l a g a i n t o q x . A t t h e s e good c o o l i n g c o n d i t i o n s t h e A C amplitude o f megnetic f l u x d e n e i t y B, i s h i g h e r t h a n 1.5 T which correspond t o maximum ramp r a t e 8-475 T/s f o r hlsthom A t l a n t i q u e w i r e , a s s e l l a s B =1 T and B,=314 T/s f o r 1i.U wire. These r e s u l t s Fire i n accord w i t h t h o s e i n [1$[13]. A f t e r t h e e x p e r i - ments on s m a l l c o i l s a b i g s r one from about 450 m l o n g scmple with 1 2 l a y e r s end 0.55 mm t h i c k FRP s p a c e r s was wound onto a FW bobbin w i t h diameter o f 27 mm and l e n g t h of 11 cm. The e x t e r n a l c o i l diameter was 47 m ( s e e Fig. 2 ) t c o i l AAV).

Fig. 3 Fig. 4

Here a g a i n +was equal t o hk of t h e s h o r t samyle. :.laximum B,of 2.46 T has been reached. The c o i l was energized i n s t a t i o n a r y contlitione up t o a AC c u r r e n t amplitude equal t o 91.5 % + w i t h o u t quenching. To t h i s c u r r e n t corresponds Bm=2.25 T and maximum ramp r a t e B=707 T/s.

The r e s u l t s o f c a l o r i m e t r i c l o s s meesurements m d o on d i f f e r e n t c o i l s a r e r e p r e s e n t e d i n Fi8.4.

Xore d e t a i l s on t h e s e experimonts w i l l b e p u b l i s h e d elswhere.

Our r e s u l t s on A C l o s s measurements t o g e t h e r w i t h t h o s e of 1121 , 1131 and o t - h e r have shown t h a t t h e e x . ( l ) i s i n q u a l i t a t i v e agreements w i t h experimental re- s u l t s . Nevertheless i t must be pointed. a u t , t h a t t h e measured p v a l u e s were about 2.9 t i m e s h i g h e r t h a n t h o s e c a l c u l a t e d from m e a s u r e d o ~ c = f ( b ) u s i n g f o r m l a ( 1 ) f o r conductor h'O9 and about 2 times h i g h e r f o r conductor B 6. T h i s could be cau- sed by s h o r t c i r c u i t e between t h e f i l a m e n t s due t o a c c i d e n t a l m e t n l i c c o n t a c t s o r due t o proximity e f f e c t i n vory t h i n normal metal b a r r i e r s between them.

The r a t i o of t h e winding conductor volumes V /Vws/s denotes t h e supercon- d u c t i n g v a r i a n t and c t h e conventional onoh when Tfie same ampereturns and conduc- t o r l e n g t h for both v o r i m t s a r e supposed can be expressed a s

where J N and JS a r e t h e a d m i s s i b l e c u r r e n t d e n s i t i e s a t nominal regime i n t h e con- v e n t i o n a l and superconducting conductor r e s p e c t i v e l y , V i s t h e f a u l t c u r r e n t over- l o a d c o e f f i c i e n t and Jc(Bmma? i s t h e c r i t i c a l c u r r e n t d e n s i t y i n t h e superconduc- t o r a t t h e maximum f l u x d e n s l t y B i n t h e minding d u r i n g t h e f a u l t .

mmox

Using t h e r e l a t i o n s (1) and (2) we o b t a i n t h e r e t i o \ of t o t a l energy consump- t i o n

i n s u p e r c o n d u c t i ~ \,finding i n c l u d i n g r e f r i g e r a t i o n t o t h a t i n c l a s s i c a l one

where Q N _{i s} t h e r e s i s t i v i t y of t h e conventional conductor, < i s t h e r e f r i g e r a t o r

i n p u t n e c e s s a r y t o evacuate 1 _'N from working t e m p e r a t u r e t o room temperature.

C1-462 JOURNAL DE PHYSIQUE

can be expressed a s { '(T1 - ^{To) / qcTo /4/}

where '(lc- s o c a l l e d p e r c e n t Carnot depends on t h e r e f r i g e r a t o r c o o l i n g power P , on T b u t mainly on compressor and expander e f f i c i e n c i e s . The most c i t e d da-

t g ^on g r e t h o s e of S t r o b r i d g e 1171, b u t t h e y seem today t o be t o o optimistic~f8].

For f u t & e a p p l i c a t i o n s of m u l t i f i l a m e n t a r y superconductor and T ~ 4 . 2 K we can c a l c u l a t e w i t h !=328.for p r e c o o l e d r e f r i g e r a t o r s p l u s 0.3 1 L N ' / ~ and 1 W of PC, o r w i t h {=500 f o r r e f r l g e r e t o r w i t h o u t precooling. I n t h e f o l l o w ~ n g we c o n s i d e r r e f r i g e r a t o r s \*/ithout p r e c o o l i n g ,

7 2

~i 9,=2fiodnmi ~ ~ ~ 1 x 1 0 *jm ; > . J ~ (8-1) = 1 d 0 9 *h2 ^/5/

t h e n ps a t which .( ^{=1 is}

efdhJc( Bm) Bm ~ ~ f 212 QNJN Jc(B,& 14x10 8 W/m 3

+ A=-- /6/

pso =

3 T 2

Eu(i+C) v ( l + f )

F o r V = l and f = 5 0 0 , o r

=3 and { =lo00 zx. ( 6 ) i v e s

pso = 2 . 8 ~ 1 0 5 w/m3 /6a/ and pso = 4.7xI.O W/m3 /6b/ r e s p e c t i v e l y . From Table I and Fig.4 we s e e t h a t f o r Bm=l T t h e c o n d i t i o n /6a/ i s f u l f i l - l e d by today

c o n d c c t o r s ~ O 3 , 4 , 9 and c o n d i t i o n /6b/ w i l l be f u l f i l l e d only , b : f u t u r e g e n e r a t i o n conductors.

W e s e e t h a t

i s one o f t h e most d i f f i c u l t o b s t a c l e s t o A C superqonductor a p p l i c a t i o n s i n t h i s domaine and a l l must be made t o l o v e r i t by adequate d e s i g n o f power equipment i n t e r n a l impedances 151, [14] and/or by n s u i t a b l e c u r r e n t li- m i t e r (21, [15],[16].

11. EVALUATION OF OVERALL BEIXFITS OF AC 50 Hz SUPERCOh3UCTING iVIIIDIl~GS

O v e r a l l b e n e f i t s can be r e p r e s e n t - d by t h e t o t a l c o s t d i f f e r e n c e Ctc-Cts o f b o t h v a r i a n t s a s w e l l a s by t h e d i f f e r e n c e of t h e i r t e c h n i c a l parameters.

Ct can be expressed a s t h e sum of c a p i t a l c o s t s C which a r e a s s o c i a t e d w i t h t h e purchasse and , i n s t a l a t i o n of t h e d e v i c e and of c a p i ? a l i z e d o p e r a t i n g c o s t s K which a r e g i v e n by t h e f o l l o w i n g formula 1191

1 - [ ( l + i l / ( l + d ) ]

K ~ B ~ ~

( l + d j / ( l + i ) -1 = 'cok

/7/

Here Fco a r e t h e annual o p e r a t i n g c o s t s i n t h e lSt o p e r a t i n g y e a r , i i s in- f l a t i o n r a t e , d d i s c o u n t r a t e and n o p e r a t i n g l i f e time expressed i n y e a r s .

Because t h e c a p i t a l c o s t s o f t h e superconducting v a r i a n t a r e n o t y e t e x a c t l y known, t h e c a p i t a l c o s t d i f f c r e n c o w i l l be h e r e expressed a s 2 times t h e winding m a t e r i a l c o s t d i f f e r e n c e C - ^C minus t h e r e f r i g e r a t o r c a p i t a l c o s t s CRS.

For o p e r a t i n g c o s t s we sha!ff conzfder t h e winding t o t a l enercy consumption d i f f e - r e n c e and maintenance c o s t s f o r r e f r i g e r a t o r f a s w e l l a s c o s t s f o r U2 conaump- t i o n p e r hour C f o r r e f r i g e r e t o r s w i t h LN2 p&cooling. A 1 1 o t h e r c o s t s rill be c o n s i d e r e equalL!or both v a r i a n t s . Then f o r o v e r a l l b e n e f i t s we o b t a i n

where c and c a r e t h e p r i c e s p e r m3 of copper and superconductor respec- t i v g l y , ce i l c t h e prJcSe p e r 1 Wh. Following s e t of parameter w i l l be used f u r t h e r

S u b s t i t u i p g from ex. ( 2 ) a n d ( 9 ) e q r e s a i o n f o r winding p r i c e d i f f e r e n c e i s

t h e p r i c e of superconduting winding conductor would be s m a l l e r t h a n t h a t o f t h e copper. For c u r r e n t d e n s i t i e s i n d i c a t e d i n /5/ i t would b e t r u e f o r

2 .

F o r Y = l t h e p r i c e o f superconductor would r e p r e s e n t o n l y

% of t h a t o f copper.

The lower w i l l b e B t h e h i g h e r w i l l b e hJc(Bmma! and t h e h i g h e r could be win- d i n g conductor s a v i w :

It i s necessary t o p o i n t o u t , t h a t h i g h mean c u r r e n t d e n s i t y i n t h e AC super- conducting winding l e a d s t o s u b s t a n t i a l l y lower winding mass B4 a s w e l l a s t o l o - wer o v e r a l l dimensions and by t h i s t o f u r t h e r c a p i t a l c o s t s sg$ings. For t h e sa- k e of s i m p l i c i t y we s h a l l n o t a m l y s e t h i s a s p e c t h e r e .

R e f r i g e r a t o r p r i c e f o r PC> 100 f i s ~ i v e n by 1181

CRs = 5 M 0 P:*~~ A 2 a / %, ^{= 6500 P, 0.73 /12b/}

f o r r e f r i ~ e r e t o r s w i t h or without LN ₂ p r e c o o l i n g r e s p e c t i v e l y . The terme ma-

Ires t h a t f o r s m a l l e r equipment t h e r e f r i g e r a t o r c o s t s rill be more i m p o r t a 8 t t h a n f o r a b i g e r one. I t l e a d s a l s o t o ~ m a l l e r r e f r i g e r n t o r c c s t s when r e f r i c e r a t o r w i l l be used a l s o f o r o t h e r purposea t h a n f o r hC equipmect. I n such a c a s e a l s o l a b o r and meintenance c o s t s a r e s m a l l e r .

J o u l e l o s s e s i n b i g power t r a n s f o r m e r s and cryoturboe;enerators o f 1000 WfV r a - t i n g range a r e r e l a t i v e l y small, o f a b o u t 0.2 X o f nominal r a t i n g . N e v e r t h e l e s s i n a b s o l u t e v a l u e they r e p r e s e n t over 30 y e a r s o p e r a t i n g l i f e p e r i o d approximate- l y 400 m i l i o n s of kVh p e r machine. Expressed i n c a p i t a l i z e ? p r e s e n t v a l u e c o s t s t h e y amount t o 4.25 + 7.44 mil.$. T h i s i s about 24i40 % of t h e c a p i t a l c o s t s o f a c o n v e n t i o n a l 1000 UEI t u r b o g e n e r a t o r [19], [21]and 100-185 % o f t h o s e o f a con- v e n t i o n a l power t r a n s f o r m e r o f t h e same r a t i n g . If t h e y could be s u b s t a n t i a l l y r e - duced o r e l i m i n a t e d a n important economic s a v i n g could be gained.

:,!any s t u d i e s examined t h e p o s s i b i l i t y of b u i 1 d i . g superconducting t r a n s f o r - n e r s from 1961, but o n l y i n 1981 low l o s o multifilame..tary conductors have been considered f o r t h i s aim [2], [4]. I n r e f e r e n c e r 2 ) t h e i n s u l a t i o n and bushing pro- blems a s w e l l a s those?rnechanical and cryogenic d e s i g n were d i ~ c u s s o d i n d e t a i l s and f o l l o w i n g c o n c l u s i o n s , which a g r e e i n g e n w a l l i n e s w i t h t h o s e o f o t h e r a u t - h o r s , have been r e t a i n e d .

Tho i r o n c o r e should be p r e s e r v e d n e a r room temperature, owing t o i n ~ u l e t i o n r e q u i r e m e n t s a u p o r c r i t i c a l one phase helium should be used a s c o o l a n t , vecuuffi epoxy bushing w i t h c a p a c i t i v e l y g r ~ d e d c y l i n d r i c a l s h i e l d s have t o be developed, C-10 composite i n s u l a t i n g m a t e r i a l i s widely t o be used a s former and c r y o s t a t m a t e r i a l .

To reduce t h e i n f l u e n c e of f a u l t c u r r e n t overload on A C l o s s e s i n nominal c o n d i t i o n s two p a r a l l e l windings w i t h low and h i g h l e a k a g e impedances h a s been Fro- posod i n 121.

K e v e r t h e l e s s t h e problem of t h e i r c o r r e c t o p e r a t i o n a t f a u l t h a s n o t been solved. 1;o d e t a i l s on t h e m u l t i f i l a m e n t a r y composite parameters and t h e i r impact on A C l o s s e s have been given.

On t h e b a s i s o f our experimental r e s u l t s on A C 50 Hz l o s s e s and quenching c u r r e n t s and u s i n g t h e r e s u l t s o f t h e p r e c e e d i n g c h a p t e r wo have evaluate(! t h e c o s t d i f f e r e n c e of d i f f e r e n t components a s w e l l a s t h e o v e r a l l c o s t d i f f e r e n c e f o r 3 composite t y p e s and f o r v = 4 o r 1.3. Maximum f l u x d e n s i t y amplitude i n s t a - t i o n n r y c o n d i t i o n s was t a k e n e s in [2]%=0.56 T. Parameters of conductors a s w e l l a s t h e c a l c u l a t i o n r e s u l t s a r e i n Table 11.

3 3

Conventional winding par9meters a r e V =8.16 m , ¹ ~ 7 2 . 6 5 x 1 0 kg,

C =581000 $, JN=3.5 x 1 0 6 ~ / r n . We s e e t h a l c f o r Y=4 any$ w i t h conductor ~ ' 3 ~ o v e -

rxfl c o s t d i f f e r e n c e could be p o s i t i v e , w h i l e f o r ~ = 1 . 3 a l r e a d y conductor N 2,

v e r y s i m i l c r t o one which h a s been produced without r e a c h i n g t h e l i m i t s o f w i r e

drawing p o s s i b i l i t e s [14], g i v e s i m p o r t a n t o v e r a l l savings. Here a e a i n t h e neces-

CI-464 JOURNAL DE PHYSIQUE

s i t y of loworinl: v w i t h t h e u s e of s u i t a b l e c u r r e n t l i m i t e r appears, Conductpr nO1

does n o t g i v e y e t any b e n e f i t s .

Cor.dustor prraostsrsi bcdmotor ~'18 LW.3 n d.1.25 UI ;1 ? u &.2.10-~2 .e. . ~ ? ~ ~ d i y ? , + E =I. j T Condrtctor If21 W.1 m d.O.41'hu 1 e . 5

=

CondDetor ~ ~ 3'3-C.1 8 pm ?,-13-'~n o t h k ss for x02

The superconducting winding mass i s s u b s t a n t i a l l y s m a l l e r t h a n t h a t o f conven- t i o n a l one which l e a d s t o a c o n s i d e r a b l e overs11 weight r e d u c t i o n of a b o u t 70 tons.

The n e c e s s i t y of improving t h e c r y o t u r b o g e n e r e t o r a r m a t u r e windinc i s vie11 r e - cognized. J .L. Smith i n 122) c h a r a c t e r i z e s t h e p r e s e n t s i t u a t i o n a 8 follows.

The c r y o t u r b o g e n e r a t o r p r o t o t y p e e f f o r t s have c o n c e n t r a t e 2 on r o t o r develop- ment s o t h a t a r n a t u r e development

behind. T h i s is a d e f i c i e n c y s i n c e a super- conducting r o t o r i n a more or l e s s c o n v e n t i o n a l s t a t o r is j u s t a conventional ma- chine w i t h a conplex r o t o r . A f i l l y developed s t a t o r i s r e q u i r e d t o r e a l i z e t h e po- t e n t i a l o f tho superconducting r o t o r .

I n o u r p r e v i o u s s t u d i e s :4]-[5] i t h a s been shown, t h a t t h e u s e o f some a l r e a - dy produced m u l t i f i l a m e n t a r y compo-itea p r o m i s e s i n t e r e s t i n g s a v i n g s i n t o t a l ener- gy consumption / s e e f v a l u e s i n Table I / .

Moreover h i g h e r moan c u r r e n t d e n s i t y expected i n superconducting winding to- e e t h e r w i t h s m a l l synchronous r e a t e n c e r r o v i d e t h e i n h e r e n t p o s s i b i l i t y of a f u r t - h e r d e c r e a s e i n weight and dimenoicns of t h e machine. Using t h e seme r e f r i g e r a t o r f o r both t h e e x c i t i n g and armature windings a s w e l l a s f o r o t h e r s u p e r c o n t u c t i n g d e v i c e s / c u r r e n t l i m i t e r , p o w e r t r a n s f o r m e r / w i l l reduce t h e r e f r i g e r a t o r c a p i t a l

costs.

Due t o t h e r o t a t i n & magnetic f i e l d , t h e c r y o s t a t h a s t o be nonmetallic. Hoae- v e r , t h e p r o b l e n s r e l a t e d t o a s t a t i c d i e l e c t r i c c r y o s t a t w i l l probably be s m a l l e r t h e n t h o s e encountered a t t h e r o t a t i n e one f o r e x c i t i n g winding.

'!ie can conclude t h a t t h e p r o s p e c t s o f u s i n g m l t i f i l a m e n t a r y composites f o r c r y o t u r b o g o n e r a t o r armature winding a r e b e t t e r t h a n f o r power t r a n s f o r m e r s , b u t t h e y seem t o b e s u f f i c i e n t t o s u b s t a n t i a t e t h e development work i n b o t h t h e s e do- maincs.

D e ~ i d e s t h e s e b i g poT::er equipments t h e r e a r e s t i l l o t h e r s m a l l e r d e v i c e s i n which AC superconducting windings could be a p p l i e d a s e.g. magnetic s;eten;s t o con- t r o l superconducting r e c t i f i e r s o r c u r r e n t t r a n s f o r m e r s f o r s u p e r c o n ~ u c t i n g l ~ a e n e t c u r r e n t s u p p l i e s .

From experimental r e s u l t s on quenching c u r r e n t s an5 E.C l o s s e s o f f i n e f i l a m e n t

mixed m a t r i x r n u l t i f i l a m e n t a r v c n n p o n i t e s a s w e l l a s from crri.-t:-- t h e o r y f o l l o v i n g

1. Modern m l t i f i l a m e n t a r y conductors e r e n b l e t o

50 Hz i n f i e l d s w i t h Bm a t l e a s t u p t o about 2 T w i t h o u t c u r r e n t d e g r a d a t i o n i f good c o o l i n g c o n d i t i o n s a r e provided.

2. Savings i n t o t a l energy consumption f o r a g i v e n conductor depend on B a s w e l l a s on c u r r e n t overload c o e f f i c i e n t v and r e f r i g e r a t o r consumption c o e f f i F i e n t

. ^{For V a l , {} =500 and Bmtl T, a t f = 0 I Hz energy s a v i n g s a r e a t t a i n a b l e w i t h a l r e a d y produced composites, while f o r V-3 and 5=1000 new composite g e n e r a t i o n x i t h f i l a m e n t d i a m e t e r d 5 O . l p m , w i r e d i a m e t e r D S 0.1 mm end t r e n s v e r s e r e s i k t i - v i t y 9,2 10-%,m i s needed.

3. O v e r a l l s a v i n g s i n c a p i t a l and o p e r e t i n g c o s t s depend b e s i d e s J N ? Bn, and f s t i l l on t h e r e f r i g e r a t o r c a p i t a l c o s t s and mean c u r r e n t d e n s i t y i n euper- conductinf: winding. Bectauae r e f r i g e r a t o r c a p i t o l c o s t s dependence a r e p r o p o r t i o - n a l t o pac3, h i g h e r machines and/or p l a n t s w i t h m u l t i p l e needs i n helium t e m p e r a t u r e s a r e n o r e a p p r o p r i a t e t o superconductor A C a p p l i c a t i o n s . Higher c u r r e n t d e n s i t y i n superconducting winding can i n c r e a s e o v e r a l l b e n e f i t s by weight and dimension r e - cluction of t h e windin& a s vie11 a s o f t h e i r o n core.

4. Inexpensive and r e l i a b l e c u r r e n t l i m i t e r s would s u b s t a n t i a l l y e n l a r g e su- perconductor AC a p p l i c a t i o n s .

5 . One of t h e most a c u t e q u e s t i o n s which i s t o be e l u c i d a t e d a r e t h e l i m i t s up t o which f i l a n - n t d i a m e t e r , b a r r i e r t h i c k n e s s and t w i s t p i t c h l e n g t h can b e re- duced without enhancing t h e e l e c t r i c c o u p l i n g between f i l a m e n t e .

6. Iiydroextrusion t e c h n i c s t o g e t h e r w i t h e x t e r n a l d i f f u s i o n p r o c e s s seem t o be t h e most a p p r o p r i a t e b o t h f o r NbTi and Nb3Sn s u p e r - f i n e f i l a m e n t composite tech- nology.

7. Development of h i g h c u r r e n t conductors from f i n e f i l a m e n t composites ~ r o - v i d i n g good c o o l i n g of each s t r a n d and small eddy and c i r c u l a t i n g c u r r e n t l o s s e s a s vrell a s of s u i t a b l e d i e l e c t r i c m a t e r i a l s f o r e l e c t r i c i n s u l a t i o n , winding s t r u c - t u r e and c r y o s t n t i s v e r y necessary.

8. I n c r e a s e d r e f r i g e r a t o r c a p i t s 1 c o s t s would be warranted by i n c r e a s e d r e - f r i g e r z t o r e f f i c i e n c y .

9. S y s t e m a t i c s t u d y of a l l f i n e f i l a m e n t composites i n A C c o n d i t i o n s a r e nee- ded t o a c q u i r e c so131 b a s i s f c r i n d u s t r i a l A C 50 Hz a p p l i c a t i o n s .

The a u t h o r wishes t o thank Dr. J.Goyer, Alsthom A t l a n t i q u e , f o r making a v a i - l a b l e e p e c i f i c m l t i f i l a m e n t a r y superconductor and t o D r , K r a j E i k f o r a s s i s t a n c e i n experimental work.

LITEHATURE

[I] Trusov N.B., Trudy V N I I e l e k C r o m e c h . ~ /1977/5; [?I Riemersna H. ,Barton M.L., L i t z D.C., E c k e l s P.W., Murphy J.H., Roach J.F., A p p l i c a t i o n o f superconducting technology t o povier t r a n s f o r m e r s , IEEE PES Winter Meeting, A l a n t a , Georgie, Februa- r y 1-6, 1981; [3] H l b n i k I., IEEE Trans. on MR n e t i c s . , Vo1. MAG-17 /1981/ 2261; [4]

Hlasnik I., Elektrotech.Casopis 2 /l9t32/ 249; 75) H l s s n i k I., Could cryoturboge- n e r a t o r armature winding be superconducting? T r i m h b e r i c h t 03.05.01 POlC, June 1982, Kernforschungazentrua K a r l s r u h e j H l h n i k I, Cryogenics a /1983/ 508 ; (61 Rosner C.H., Z e i t l i n B.A., Schwa11 R.E., Walker M.S., Ozeryansky G.M., Filamentary A-15 Superconductors, Suenaga M. Clark A.F., Ed8 Plenum P r e s s New York /1980/ 6 9 ;

[7] K l e i h J.D. Cogan S.F., Warshaw G., h d z i a k h'., Rose R.M., IEEE Trans. on Ma- gnetism, Vol.MAC-17 /l981/ 378 an& 380; C81 Dvkots p., Maldy J., Renard J.C., Goyer J., N i t h a r t H., S a b r i 6 J.L. Proc. o f t h e 8 ICEC, Genova /1980/ 505; [9]

Buryak V.P., Matrosov N.I., Yerrjemenko TA., Mironova O.N., ~ o r o f l a j V.I., Paper

FP-10, CEC/ICEC, Colorado Springs, August 19831 (107 bftildy J., F Q v r i e r A., Du-

b o t s P., Rcnard J.C., Coyer J., N i t h a r t I!., Duchateau J.L., IEEE Trans. on blagne-

t i c s , Vo1. MAG-17 /l98l/ 119; [ll] Cr:logenics Newsletter 1'47, /1983/ 4 ; 1121

Ogasawara T., Kubota Y., ldakiura T., Akachi T., H i s a n a r i T., Oda Y., Yasukochi K.,

IEEE Trans. on Magnetics, Vol. MAG-19 /1983/ 248; D 3 j Hldsnik I., S e i b t E.W.,

t o be published i n J.A?yl* Ph:~s. [14) S e b r i e J.L., Goyer T., IEEE Trans. on !"fag-

CI-466 JOURNAL DE PHYSIQUE

n e t i c s , Vol. ;.KC-19 /1983/ 529; ['lq ,Ipylctcn X.D., Cryo,:anic: 2 /19C?/ 435;

116) Rogers J.D., Boerie; H.J., Choerthuri P., S c h c ~ n e r X.I., Woll?n J.J., Vcldon D.M., I E E E Tmm, on Uagnotice Vol. L3.G-19 /19e3/ 1054; [17] S t r o b r i d g e T.R., k y o g e n i c r e f r i g c r a t o r a a n updated zurve;!,

T e c h n i c ~ l h'ote 655 /1975/, Bouldnr, Zolorado; [18] Robinoon G.Y., Jr. hdvences in Cryogenic ~ n c i n e e r i n g 3 /1979/

142; [lq Bzura J.J., Abtahi F., S t r a t t o n L.J., 1 5 3 Tr::ns.on h!ngnetics, Vol.

.LAG-17 /1981/ 880; [26J Feldman J.C., C o g b i l l B.1.. , S::rma X.S., Suporconductin(:

s i n d i n g s i n a power trnnsformcr, a n o l d q u e s t i o n .iti.th a nsyr ansncr, I ' a r t 11: S o r e ,,f t h e p r a c t i c a l problems, Peper A 77 019-3 presente:: a t t h e I E 3 PES :'/inter mee- t i n g , Nett Yurk, January 1977; [25 EdnonZs J.L., IEEE Tran:.. on Eapnoticc Vol.

.dAG-15 /1979/ 673) ²² S h t h J.L. Jr., I L Z Trnns. on !.:r:gnctics ~ o l : ~ h C - 1 9 ' /19~3/

529 .