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DESIGN CURRENT DENSITY IMPACT ON COST AND RELIABILITY OF SUPERCONDUCTING MAGNET SYSTEMS FOR EARLY COMMERCIAL
MHD POWER PLANTS
A. Hatch, P. Marston, R. Thome, A. Dawson, W. Langton, W. Mann
To cite this version:
A. Hatch, P. Marston, R. Thome, A. Dawson, W. Langton, et al.. DESIGN CURRENT DENSITY
IMPACT ON COST AND RELIABILITY OF SUPERCONDUCTING MAGNET SYSTEMS FOR
EARLY COMMERCIAL MHD POWER PLANTS. Journal de Physique Colloques, 1984, 45 (C1),
pp.C1-867-C1-870. �10.1051/jphyscol:19841176�. �jpa-00223651�
JOURNAL DE PHYSIQUE
Colloque C l , supplCrnent au n o 1 , Tome 45, janvier 1984 page C1-867
DESIGN CURRENT DENSITY IMPACT ON CO$T AND RELIABILITY OF
S U P E R C O N D U C T I N G M A G N E T SYSTEMS F O R E A R L Y C O M M E R C I A L M H D P O W E R PLANTS*
A.M. Hatch, P.G. Marston, R . J . Thome, A.M. Dawson, W.G. Langton and W.R. Mann
PZasma Fusion Center, Massachusetts I n s t i t u t e of TechnoZogy, Cambridge, Massachusetts 02139, U.S.A.
Rdsum6
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Ce r a p p o r t 6 t u d i e l e s consEquences du c h o i x d e l a d e n s i t 6 d e c o u r a n t s u r l e c o Q t de g r a n d s s y s t s m e s d ' a i m a n t s s u p r a c o n d u c t e u r s MHD, e n u t i l i s a n t l e s i n d i c e s d ' e s t i m a t i o n d e coDt f o u r n i s p a r o r d i n a t e u r . I1 y e s t dBmontrE que l a d e n s i t d d e c o u r a n t c h o i s i e a f f e c t e de f a ~ o n s i g n i f i c a t i v e l e c o 6 t du s y s t s m e , e n p a r t i c u l i e r l e s s y s t s m e s B p l u s f a i b l e p u i s s a n c e p r i s e n c o n s i - d d r a t i o n , c e q u i i n d i q u e que l e s d e n s i t e s d e c o u r a n t moyennes s E l e c t i o n n 6 e s pour l e s a i m a n t s MHD d o i v e n t C t r e c h o i s i e s s u r l a b a s e d e s e f f e t s a f f e c t a n t a u s s i b i e n l e coGt que l a f i a b i l i t d d e s s y s t s m e s .A b s t r a c t
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The impact of d e s i g n c u r r e n t d e n s i t y on t h e c o s t of l a r g e s u p e r - c o n d u c t i n g MHD magnet systems was s t u d i e d u s i n g c o s t e s t i m a t i n g computer codes. Design c u r r e n t d e n s i t y was shown t o a f f e c t system c o s t s i g n i f i c a n t l y , p a r t i c u l a r l y f o r t h e lower-power s y s t e m s c o n s i d e r e d , i n d i c a t i n g t h a t aver- a g e c u r r e n t d e n s i t i e s s e l e c t e d f o r f i n a l MHD magnet d e s i g n s s h o u l d b e chosen based on e f f e c t s on b o t h c o s t and system r e l i a b i l i t y .INTRODUCTION AND APPROACH
High r e l i a b i l i t y and l o n g s e r v i c e l i f e , p r e r e q u i s i t e s f o r s u p e r c o n d u c t i n g magnets f o r commercial MHD power p l a n t s , d i c t a t e c o n s e r v a t i v e magnet d e s i g n a c h i e v e d most e a s i l y i f d e s i g n c u r r e n t d e n s i t i e s a r e k e p t low. Low c a p i t a l c o s t i s a l s o a n i m - p o r t a n t c o n s i d e r a t i o n f o r commercial s i z e MHD magnets, b e c a u s e magnet system c o s t r e p r e s e n t s one of t h e l a r g e s t component c o s t s i n t h e MHD t o p p i n g c y c l e . I n de- v e l o p i n g d e s i g n s f o r commercial MHD magnets, t r a d e o f f s must b e made between t h e c o s t a d v a n t a g e s of h i g h e r d e s i g n c u r r e n t d e n s i t i e s and t h e r e s u l t i n g g r e a t e r r i s k s a n d / o r s p e c i a l d e s i g n p r o v i s i o n s a s s o c i a t e d w i t h t h e h i g h e r c u r r e n t d e n s i t i e s . The main p u r p o s e of t h i s s t u d y was t o o b t a i n q u a n t i t a t i v e i n f o r m a t i o n on t h e e f f e c t of d e s i g n c u r r e n t d e n s i t y on magnet c o s t . The r e s u l t s may b e u s e f u l i n d e s i g n i n g commercial-size MHD magnets. The d e s i g n s s t u d i e d were c o n s i d e r e d s u f f i c i e n t l y r e p r e s e n t a t i v e t o s e r v e a s a b a s i s f o r d e t e r m i n i n g t r e n d s , b u t were n o t o p t i m i z e d . The f a c t t h a t computer-generated d e s i g n c h a r a c t e r i s t i c s f o r some of t h e d e s i g n s d e p a r t s u b s t a n t i a l l y from good d e s i g n p r a c t i c e emphasizes t h e importance of c a r e - f u l c o s t / r i s k a s s e s s m e n t when f i n a l d e s i g n s a r e developed.
MHD magnet r e f e r e n c e d e s i g n s from component t e s t s i z e t o t h e s i z e r e q u i r e d f o r a 1100 MWe c h a n n e l , a l l embodying t h e same d e s i g n c o n c e p t s , were used a s a b a s i s f o r t h e s t u d y . I n r e v i e w i n g d e s i g n s developed i n t h e p a s t , / 2 / i t i s n o t e d t h a t winding
* s u p p o r t e d i n p a r t by t h e O f f i c e of F o s s i l Energy, MHD D i v i s i o n , U.S. Department of Energy.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841176
C1-868 JOURNAL
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PHYSIQUEd e s i g n ( a v e r a g e ) c u r r e n t d e n s i t i e s a r e i n t h e r a n g e of 1 . 0 t o 2.5 x
lo7
~ / m * and t e n d t o d e c r e a s e a s magnet s i z e i n c r e a s e s . V a r i o u s c u r r e n t d e n s i t i e s s p a n n i n g t h i s r a n g e were c o n s i d e r e d f o r each s i z e magnet s t u d i e d . Using computer programs and s c a l i n g t e c h n i q u e s , t h e c h a r a c t e r i s t i c s and e s t i m a t e d c o s t s of e a c h magnet a l t e r n - a t i v e were c a l c u l a t e d and c u r v e s p l o t t e d t o show how c o s t and o t h e r c h a r a c t e r i s t i c s v a r i e d w i t h d e s i g n c u r r e n t d e n s i t y . P a r t i c u l a r a t t e n t i o n was g i v e n t o c h a r a c t e r -i s t i c s r e l a t i n g t o r e l i a b i l i t y and s a f e t y .
To cover t h e 100-1100 MWe MHT, c h a n n e l s i z e r a n g e , t h r e e magnet s i z e s were chosen, d e s i g n a t e d ETF, CSM and LBL. I n a d d i t i o n , a s m a l l e r magnet s i z e , d e s i g n a t e d CDIF, was i n c l u d e d i n t h e s t u d y f o r c o m p a r a t i v e purposes. B a s i c c h a r a c t e r i s t i c s of t h e s e magnets a r e l i s t e d i n Table I. A l l magnets were 6 T d e s i g n s and t h e i n t e r n a l d i - mensions o f t h e CDIF, ETF and CSM s i z e s were d e r i v e d from a v a i l a b l e c o n c e p t u a l de- s i g n s . / 1 , 2 / For c o n s i s t e n c y , a l l d e s i g n s a r e of t h e r e c t a n g u l a r s a d d l e - c o i l t y p e w i t h r e c t a n g u l a r warm b o r e s , c o p p e r - s t a b i l i z e d NbTi c o n d u c t o r and r e c t a n g u l a r frame winding s u p p o r t s t r u c t u r e s of s t a i n l e s s s t e e l . Designs of o t h e r t y p e s would b e expected t o show t h e same t r e n d s w i t h r e g a r d t o c u r r e n t d e n s i t y impact o n magnet c o s t , e t c . The f o u r p r i n c i p a l magnet d e s i g n s a l l i n c o r p o r a t e d round c a b l e con- d u c t o r s and i n s u l a t i n g ( f i b e r g l a s s ) s u b s t r u c t u r e s .
A f i f t h magnet d e s i g n was i n t r o d u c e d a t t h e end of t h e s t u d y t o show how modifi- c a t i o n s i n t h e winding d e s i g n might minimize t h e a d v e r s e e f f e c t s of h i g h winding c u r r e n t d e n s i t y . T h i s d e s i g n , CSM-MOD, was t h e same s i z e and c o n f i g u r a t i o n a s Design CSM (450 MWe) b u t i n c o r p o r a t e d h i g h s t r e n g t h aluminum a l l o y s u b s t r u c t u r e and b u i l t - u p b a r c o n d u c t o r t o i n c r e a s e t h e amount of copper s t a b i l i z e r i n t h e winding c r o s s s e c t i o n by a f a c t o r of 2 . 5 .
A l l magnet d e s i g n s used i n t h e s t u d y i n c o r p o r a t e d s u b s t r u c t u r e s ~ r o v i d i n g i n d i v i d u a l s u p p o r t f o r t h e c o n d u c t o r s and t r a n s m i t t i n g magnetic l o a d s from c o n d u c t o r s t o con- t a i n m e n t v e s s e l s ( s u p e r s t r u c t u r e ) w i t h o u t a c c u m u l a t i o n of l o a d i n g on c o n d u c t o r s themselves. S u b s t r u c t u r e d e s i g n s t r e s s ranged from 1 0 3 MPa f o r t h e s m a l l e s t t o 125 MPa f o r t h e l a r g e s t p r i n c i p a l d e s i g n , and was 172 MPa f o r t h e m o d i f i e d d e s i g n , where h i g h - s t r e n g t h aluminum a l l o y r e p l a c e d g l a s s - r e i n f o r c e d - p l a s t i c .
Computer programs were developed t o c a l c u l a t e t h e dimensions, component w e i g h t s , c o s t s and o t h e r c h a r a c t e r i s t i c s of t h i s s e r i e s of magnets. S c a l i n g t e c h n i q u e s were employed, t o g e t h e r w i t h u n i t c o s t s and e m p i r i c a l f a c t o r s d e r i v e d from p a s t exper- i e n c e . Curves of v a r i o u s c h a r a c t e r i s t i c s v s winding ( d e s i g n ) c u r r e n t d e n s i t y w e r e t h e n p l o t t e d t o show t r e n d s .
RESULTS
Curves of n o r m a l i z e d magnet c o s t v s c u r r e n t d e n s i t y a r e shown i n F i g . 1. Normal- i z i n g i s b a s e d on t h e 1 . 0 x
l o 7
A/m2 d e s i g n . The d e c r e a s e s i n t o t a l magnet c o s t a s c u r r e n t d e n s i t y i n c r e a s e s a r e a s i g n i f i c a n t r e s u l t of accumulated d e c r e a s e s i n weight and c o s t o f a l l major components and a s s o c i a t e d d e c r e a s e s i n winding and assembly c o s t s . Higher c u r r e n t d e n s i t y i m p l i e s a more compact winding, fewer ampere t u r n s , d e c r e a s e d s t o r e d e n e r g y and t o t a l f o r c e , d e c r e a s e d volume of con- d u c t o r and s u b s t r u c t u r e and s m a l l e r helium containment v e s s e l , s u p e r s t r u c t u r e and vacuum v e s s e l . These t r e n d s f o r a p a r t i c u l a r magnet s i z e a r e shown i n T a b l e I1 which l i s t s c a l c u l a t e d c h a r a c t e r i s t i c s f o r two c u r r e n t d e n s i t y l e v e l s i n t h e CSMs i z e magnet.
The e f f e c t of i n c r e a s i n g d e s i g n c u r r e n t d e n s i t y on s t a b i l i z e r c u r r e n t d e n s i t y and copper-to-superconductor r a t i o , b o t h of which a r e s t a b i l i t y c r i t e r i a , i s shown i n F i g . 2. Above 1 . 5 x
lo7
A/m2 d e s i g n c u r r e n t d e n s i t y , t h e copper-to-superconductor r a t i o i n t h e l a r g e r cable-wound magnets becomes lower t h a n i s u s u a l l y c o n s i d e r e d a c c e p t a b l e . The c u r v e s of F i g . 3 show h e a t f l u x a t a c o n s e r v a t i v e l e v e l f o r t h e lower d e s i g n c u r r e n t d e n s i t i e s b u t r i s i n g r a p i d l y i n l a r g e r magnets and becoming e x c e s s i v e a t h i g h d e s i g n c u r r e n t d e n s i t y . Helium-to-c-onductor m e t a l volume r a t i o does n o t v a r y w i t h c u r r e n t d e n s i t y i n t h e p r i n c i p a l d e s i g n s , b e c a u s e a c a b l e con- d u c t o r w i t h a c o n s t a n t metal-to-void r a t i o i s u s e d . The helium-to-conductor volume r a t i o i s a c o n s e r v a t i v e 0.43.The c h a r a c t e r i s t i c s of t h e CSM-MOD a r e shown by dashed l i n e s i n F i g s . 1 t h r o u g h 4 . Because t h e amount of s u r f a c e exposed t o l i q u i d h e l i u m i s l e s s w i t h t h e CSM-MOD b a r c o n d u c t o r t h a n w i t h t h e CSM c a b l e c o n d u c t o r , t h e h e a t f l u x e s f o r t h e two de- s i g n s a r e r o u g h l y s i m i l a r , even though t h e l o s s e s i n t h e m o d i f i e d d e s i g n a r e sub- s t a n t i a l l y lower. The r a t i o of helium t o conductor volume, 0 . 1 i n t h e m o d i f i e d d e s i g n , i s l e s s f a v o r a b l e t h a n t h a t i n t h e p r i n c i p a l d e s i g n . The emergency d i s - c h a r g e c h a r a c t e r i s t i c s of t h e m o d i f i e d d e s i g n a r e much more f a v o r a b l e t h a n t h o s e o f t h e p r i n c i p a l d e s i g n , remaining w i t h i n a c c e p t a b l e l i m i t s even a t h i g h d e s i g n c u r r e n t d e n s i t i e s . Comparison of t h e two d e s i g n s c a l l s a t t e n t i o n t o t h e t r a d e o f f s t h a t must b e c o n s i d e r e d .
CONCLUSIONS
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1. I n c r e a s i n g d e s i g n c u r r e n t d e n s i t y c a u s e s a s i g n i f i c a n t d e c r e a s e i n t h e c o s t of s u p e r c o n d u c t i n g MHD magnets, a l t h o u g h t h e e f f e c t i s n o t a s g r e a t i n l a r g e magnets a s i n s m a l l e r ones. F o r a s p e c i f i c d e s i g n s t u d i e d , t h e e s t i m a t e d c o s t of a 1100 MWe s i z e MHD magnet system was reduced by a b o u t 30% ( r o u g h l y $20 x l o 6 ) when d e s i g n
c u r r e n t d e n s i t y was i n c r e a s e d from 1 . 0 x
lo7
~ / t o 2 . 0 m ~ xl o 7
A/m2.2. I n c r e a s i n g d e s i g n c u r r e n t d e n s i t y from 1 . 0 x
l o 7
A/m2 t o 2.0 xl o 7
A/m2 h a s a s i g n i f i c a n t a d v e r s e e f f e c t on t h e a b i l i t y t o a c h i e v e winding s t a b i l i t y and s a f e t y . T h i s e f f e c t i s p a r t i c u l a r l y pronounced i n t h e l a r g e r s i z e magnet d e s i g n s .3. I n a n t i c i p a t i o n of f u t u r e l a r g e MHD magnet c o n s t r u c t i o n , i t i s i m p o r t a n t t h a t a n a l y s i s , development t e s t i n g and d e s i g n s t u d i e s b e performed t o e n a b l e t h e u s e of h i g h e r winding c u r r e n t d e n s i t i e s w i t h a c c e p t a b l e s t a b i l i t y and s a f e t y , s o t h a t mag- n e t d e s i g n s w i l l b e more c o s t e f f e c t i v e .
REFERENCES
1. Conceptual Design E n g i n e e r i n g Report MHD E n g i n e e r i n g T e s t F a c i l i t y 200 m e
Power P l a n t , p r e p a r e d f o r NASA/LeRC f o r DOE by Gilbert/Commonwealth, DoE/N~sA/0224-1, Vol. l - V , S e p t . 1981.
2. MHD Magnet Technology Development
Program Summary, p r e p a r e d f o r DOE by Plasma Fusion C e n t e r , MIT, 1982,
( t o b e i s s u e d ) .
TABLE I
BASIC CHARACTERISTICS OF MAGNET REFERENCE DESIGNS
MAGNET MHD CHANNEL WARN BORE SIZE ACTIVE
SIZE POWER INLET EXIT LENGTE
MWe H M M
CDIF 4 0.78 x 0.97 0.97 x 0.97 3.4 ETP 100 1.5 x 1.9 2.2 x 2.8 11.7 CSM 450 2.2 x 2.8 4.0 x 4.2 14.5 LBL 1100 3.3 x 4.2 6.1 x 6.4 16.0
FIELD STRENGTHS FOR ALL MAGNETS ARE TAKEN AS 6 T PEAK ON-AXIS. 4.8 T INLET, 3.6 T EXIT.
JOURNAL DE PHYSIQUE
TABLE I1
MAJOR CHARACTERISTICS OF CSM MAGNET DESIGNS, L 5 0 MUe S l Z E
DESIGN REFERENCE csn CSM csn-MOD
-
DESIGN CURRENT DENSITY (10' A/m2) 1 . 2 2 . 0 2 . 0
AMPERE TURNS ( l o 6 A) 3 8 . 6 3 4 . 8 3 4 . 8
STORED ENERGY ( l o 6 J) 7 5 6 0 6 1 0 0 6 1 0 0
WEIGHT OF CONDUCTOR ( l o 3 KG) 2 7 4 9 6 2 3 5
WEIGHT OF SUPERSTRUCTURE ( l o 3 KG) 7 0 4 5 6 7 5 6 7 TOTAL. WEIGHT, MAGNET ASSPIBLY ( l o 3 KG) 2 2 2 0 1 5 8 0 1 7 8 0 TOTAL. COST OF MAGNET SYSTEM
INCLUDING DESIGN, ACCESSORIES lo6 $ 91.3 6 8 . 2 81.4 MARK-UP. ETC.
A COIF Sire ( 4 M W e ) B E T F S i r e (100 M W e l C CSM S i z e ( 4 5 0 M W e l D L B L S i z e I1100 M W e ) CMOD CSM S12e ( 4 5 0 M W e )
M o d t t m d Design
U
0.4
-
I I I
10 15 2.0
C u r r e n t D e n s i t y ( l o 7 A / r n 2 )
F i g , 1 Normalized magnet c o s t v s d e s i g n c u r r e n t d e n s i t y
A C D l F Size ( 4 M W e ) B E T F S l i e ( 1 0 0 M W e ) C CSM Srze I 4 5 0 M W e ) D L B L Srze ( 1 1 0 0 M W e ) CMODCSM S n e ( 4 5 0 MWe)
M ~ d l f t e d Design
Cable sondustor cooled surface taken or outside surface of a l l
7 elements of cobie
I'
BulIt-up canduetor cooled
10 15 2 0
C u r r e n t D e n s ~ t y ( 1 0 ' ~ / m ' )
F i g . 3 Heat f l u x v s d e s i g n c u r r e n t d e n s i t y .
A C D l F S l r e ( 4 M W e l 8 E T F Size I I O O M W e ) C C S M Slze ( 4 5 0 M W e l D L B L Size ( 1 1 0 0 M W e ) ,,
W i n d ~ n g C u r r e n t D e n s i t y ( I O ' A / ~ ~ ) X A L I Y ~ ~ ~ 011 c u r r e n t 80 coppel
F i g . 2 C u r r e n t d e n s i t y i n copper and copper-to-superconductor r a t i o v s d e s i g n c u r r e n t d e n s i t y
A C D l F Size ( 4 M W e l C CSM S u e ( 4 5 0 MWe) C.,,DCSM Size ( 4 5 0 M W e l
D
>
_/--
O 1.0
I I
1.5 2.0
C u r r e n t D e n s ~ t y ( l o 7 ~ / r n ' )
F i g . 4 Emergency d i s c h a r g e v o l t a g e ( i n i t i a l ) vs d e s i g n c u r r e n t d e n s i t y .
