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FEASIBILITY STUDY OF A 10-GWh TOROIDAL SUPERCONDUCTIVE MAGNETIC ENERGY STORAGE SYSTEM2. CONCEPTUAL DESIGN OF
COIL SYSTEM
M. Shimizu, T. Yoshioka, Y. Morita, Y. Tanabe, T. Hamajima, N. Fujiwara, N. Miki, M. Yamaguchi, T. Horiuchi, N. Takeda, et al.
To cite this version:
M. Shimizu, T. Yoshioka, Y. Morita, Y. Tanabe, T. Hamajima, et al.. FEASIBILITY STUDY OF A
10-GWh TOROIDAL SUPERCONDUCTIVE MAGNETIC ENERGY STORAGE SYSTEM2. CON-
CEPTUAL DESIGN OF COIL SYSTEM. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-587-
C1-590. �10.1051/jphyscol:19841118�. �jpa-00223587�
JOURNAL DE PHYSIQUE
Colloque C1, suppl6ment au no I , Tome 45, janvier 1984 page C1-587
F E A S I B I L I T Y STUDY OF A 10-GWh TOROIDAL SUPERCONDUCTIVE MAGNETIC ENERGY STORAGE SYSTEM
2 , CONCEPTUAL DESIGN OF C O I L SYSTEM
M. Shimizu, T . ~ o s h i o k a * , Y. ~ o r i t a * , Y. ~ a n a b e * , T, ~ a m a j imar*, N. ~ u j i w a r a * ' , N . Mikir*, M . yamaguchir*, T . ~ o r i u c h i * ~ , N. ~akeda***, H. Miyazakirrr and K . ~amemura***
!The Kansai EZectric Power Company, Inc., Japan
*
l'he I n s t i t u t e of Applied Ene~gy, Japani* Toshiba Corpora t i o n , Japan
***
T a i s e i Corpora t i o n , JapanRBsume
-
On p r 6 s e n t e l e p l a n d ' u n systgme d e s t i n e 21 l ' a c c u m u l a t i o n d'une Bner- g i e de 10 GWh p a r aimant supraconducteur. On p r e f e r e a d o p t e r un arrangement d'aimant t o r o ' i d a l . Le p r i n c i p a l avantage de c e systeme r e s i d e dans l a f a i t que l a f u i t e du champ magnetique e s t t r e s f a i b l e , l a r e a l i s a t i o n e t l ' e n t r e t i e n p l u s s i m p l e s . En consdquence, l e s charges pour l e s i t e de c o n s t r u c t i o n s o n t r e d u i t e s.
A b s t r a c t - A conceptual design of a 10 GWh superconductive magnetic energy s t o r a g e (SMES) f o r d i u r n a l energy s t o r a g e u s e i s p r e s e n t e d . A t o r o i d a l f i e l d c o i l arrangement i s p r e f e r a b l y adopted. The main advantage of t h i s d e s i g n i s t h a t t h e s t r a y magnetic f i e l d is i n h e r e n t l y q u i t e s m a l l a n d m a n u f a c t u r a b i l i t y a s w e l l a s m a i n t a i n a b i l i t y i s more f e a s i b l e . T h e r e f o r e , requirements f o r a c o n s t r u c t i o n s i t e a r e r a t h e r small.
1. INTRODUCTION
A superconductive magnetic energy s t o r a g e i s worthy of m e r i t f o r d i u r n a l energy s t o r a g e use p r i m a r i l y from t h e p o i n t of view of h i g h e r e f f i c i e n c y and f a s t
c o n t r o l l a b i l i t y . The p r e s e n t e d SMES i n t h i s paper h a s t h e c a p a b i l i t y o f 10 GWh of which 75% of s t o r e d energy i s d e l i v e r e d t o t h e power system d u r i n g 8 hours with a c o n s t a n t power. This SMES would be a b l e t o be i n s t a l l e d i n l i e u of pumped s t o r a g e power s t a t i o n s . The SMES which h a s t h e t o r o i d a l f i e l d c o i l arrangement i s chosen i n p r e f e r e n c e t o s o l e n o i d a l c o i l type. The major advantages of t h e t o r o i d a l c o i l system a r e i t s extremely low s t r a y f i e l d and e a s i n e s s of c o i l manufacturing and maintenance.
The 10 GWh SMES with t h e t o r o i d a l f i e l d c o i l composed of 500 c o i l s i s p l a c e d a t t h e 30 m depth of underground. Major r a d i u s and minor r a d i u s a r e 272 m and 14.8 m r e s p e c t i v e l y . C o i l c u r r e n t i s 100 kA and c o i l maximum f i e l d i s 9.4 T, t h e r e f o r e b o t h Nb3Sn and NbTi superconductors a r e e f f e c t i v e l y a p p l i e d t o t h e c o i l . The pool b o i l i n g c o o l i n g s a t i s f i e s t h e cryogenic s t a b i l i t y of t h e c o i l . The t o r o i d a l f i e l d c o i l r e c e i v e s two k i n d s of electro-magnetic f o r c e : t h e . c e n t e r i n g f o r c e of
2.5 x l o 7 kg a c o i l and t h e hoop f o r c e of 9.2 x 10' kg a c o i l . Only t h e former i s supported with rock mass while t h e l a t t e r with s t a i n l e s s s t e e l m a t e r i a l . The s t r a y f i e l d r e g i o n i s very s m a l l , f o r i n s t a n c e t h e boundary of 200 G and 20 G from t h e t o r u s c e n t e r i s 320 m and 380 m i n r a d i u s r e s p e c t i v e l y , each considered a s t h e allowable f i e l d f o r e l e c t r i c a l machine and c o n t r o l equipment.
For c o n s t a n t power supply, 12-pulse number c o n v e r t e r s a r e p u t t o u s e , which have advantages with r e s p e c t t o t h e r e a c t i v e power requirement and harmonic c o n t e n t of t h e l i n e c u r r e n t . I n a d d i t i o n , bypass s w i t c h e s a r e used i n o r d e r t o decrease t h e peak v a l u e of t h e r e a c t i v e power, r e s u l t i n g i n t h e 60% decrease.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841118
JOURNAL DE PHYSIQUE
2. TOROIDAL COIL SYSTEM 2.1 Coil parameters
Toroidal coil parameters were studied to optimize the coil weight, volume and conductor length taking account of coil fabrication and maintenance under the condition of the stored energy of 10 GWH (3.6 x 1013 J)
.
Main results are as follows /I/: (1) aspect ratio (major radius/minor radius) is about 20, (2) the torus is placed at depth of 30 m under the ground in an open trench, (3) 500 toroidal coils are adequately chosen, (4) the rock mass supports only the centering force, a part of electro-magnetic forces, (5) the hoop forces are supported by the coil itself.Toroidal system and coil parameters on the basis of above optimization are listed in Tables 1 and 2, respectively. The maximum field is 9.4 T, which can make the coil compact. Therefore, Nb3Sn superconductor with copper matrix is used above 8 T. NbTi with mixed matrix below 8 T is chosen in order to reduce AC loss in the conductor /2/. Both type conductors are designed to satisfy the cryogenic
stabilization at the rated current of 100 kA. The coils are immersed in 4.2 K liquid helium, because of its matured technology.
The Heat conduction through the structures supporting the centering force and gravitational force will be the major one in the total heat load, and will be estimated to be about 29 kW at 4.2 K when the liquid nitrogen shield is employed.
The helium reservoir might consist of non-metalic materials such as FRP, which has been extensively developed, and therefore the eddy current loss should be-reduced below 1 kW. The satellite cooling systems, connected each other through coolant bus line, can be adopted for cooling down each divided sector of the torus.
The stray field distribution on radial and axial plane is shown in Fig. 1. The maximum field on the ground is about 1 KG, but the field rapidly decreases with the distance from the coil. The control equipment should be located outside the radial distance of 380 m from the torus center, where the field is less than 20 G, and the field at 800 m is the same order as the terrestrial magnetism of 0.3 G. Therefore, such weak stray field suggests that the SMES site could be arbitrarily selecfed.
und
/ Coil
Torus center Radial distance R (m) Fig. 1 Stray field distribution
Table 1- 10-GWh SMES System Parameters
Stored enerq-i 3.6 x loL3 5
Energy exchanged 2.7 x lox3 J
Mexlmum c u r r e n t 100 kA
Minimum c u r r e n t 50 kA
Discharge duration time 8 boors
Discharge power 940 MW
M a x i r n m f i e l d 9.4 T
Hoop f o r c e pee c o d 9 x 10' kg£
Centering f o r c e p e r c o i l 2.5 x 10' kgf
lteat load p e r c o ~ l 57 W a t 4.2-K
Cryogenic c o o l a n t pool boxling a t 4.2*K
Maximum s t r a y Eield on the ground 800 Gauss Cox1 l o c a t i o n i n t h e -pen trench 30 m Cross s e c t i o n of t h e open trench 40 x 80 m Table 2. 10-GWh T o r o i d a l C o i l C h a r a c t e r i s t i c s
Major r a d i u s Minor r a d i u s Aspect r a t i o C o i l t h i c k n e s s Number of c o i l s Number of t u r n s p e r c o i l Weight of one c o i l Windrng p a t t e r n
500 240 3000 tons pancake
2.2 C o i l S t r u c t u r e
There a r e s e v e r a l concepts concerning t h e s u p p o r t system of t h e e l e c t r o m a g n e t i c f o r c e . The o p t i o n s c o n s i d e r e d a r e :
(1) t h e u s e of an open t r e n c h i n rock a s a c e n t r a l compressive s t r u c t u r e which s u p p o r t s o n l y t h e r a d i a l c e n t e r i n g f o r c e ,
(2) t h e use of a t u n n e l i n rock which s u p p o r t s both t h e r a d i a l c e n t e r i n g f o r c e and t h e hoop f o r c e .
The o p t i o n 1 i s s e l e c t e d i n t h i s design.
The s t r u c t u r e of t h e t o r o i d a l f i e l d c o i l i s shown i n Fig. 2. The number of t h e c o i l s amounts t o 500. The o u t e r diameter of t h e helium v e s s e l i s 33.6 m and i t s c r o s s s e c t i o n i s 2.16 m x 2.7 m. The thermal i n s u l a t o r of f i b e r g l a s s r e i n f o r c e d p l a s t i c s i s provided t o t r a n s m i t t h e c e n t e r i n g f o r c e from c o i l t o rock. Thermal s h i e l d p l a t e (77K) is i n s t a l l e d i n t h e i n s u l a t o r i n o r d e r t o reduce t h e h e a t l e a k t o helium v e s s e l . The l e n g t h of t h e thermal i n s u l a t o r f o r 300K-77K r e g i o n i s 2 m and t h a t f o r 77K-4K r e g i o n is 1 m. The p r e s s u r e on t h e rock due t o t h e c e n t e r i n g f o r c e i s 3 MPa.
The e l e c t r o m a g n e t i c hoop f o r c e Intercoil
i s supported by t h e s t a i n l e s s s t e e l reinforcement around t h e conductor and n o t t r a n s m i t t e d t o t h e rock. The average t e n s i l e s t r e s s of t h e reinforcement i s 470 MPa which is below t h e allow- a b l e s t r e s s f o r SS316LN a s t h e reinforcement m a t e r i a l .
Another f e a t u r e of t h e s t r u c t u r a l c o n f i g u r a t i o n i s t h e g r a v i t y s u p p o r t system. The s u p p o r t i s p l a c e d a t t h e bottom of c o i l and between c o i l s . The i n t e r c o i l s u p p o r t beams a r e provided a s t h e
s u p p o r t i n g s t r u c t u r e f o r an ~ o c k mass
earthquake. F i g . 2 C o i l s t r u c t u r e c o n f i g u r a t i o p
3. POWER CONVERSION SYSTEM
The power conversion system f o r t h e SMES i s s t u d i e d h e r e on t h e b a s i s o f : (1) con- n e c t i o n t o t h e power l i n e of AC 275 kV o r AC 500 kV, (2) c o n s t a n t power of 940 MW
CI-590 JOURNAL DE PHYSIQUE
d u r i n g c h a r g i n g and d i s c h a r g i n g t h e c o i l , ( 3 ) p r e f e r a b l e c h o i c e of t h y r i s t o r con- v e r t e r i n i t s economy and r e l i a b i l i t y a s t h e power conversion equipment, (4) con- s i d e r a t i o n of r e a c t i v e power compensator, harmonic f i l t e r and a u x i l i a r y power supply.
A schematic main c i r c u i t diagram of t h e SMES power system i s shown i n F i g . 3 . The u l t r a - h i g h v o l t a g e i s stepped down t o t h e manageable v o l t a g e of 66 k V i n t h e con- v e r t e r equipment through t r a n s f o r m e r s . The c o n v e r t e r , r e a c t i v e power compensator and harmonics f i l t e r a r e connected t o t h e 66 k V bus l i n e . The a u x i l i a r y power i s s u p p l i e d from t h i s l i n e .
The t h y r i s t o r conversion equipment i s composed of 1 2 b r i d g e s (1.9 k V
-
100 kA f o r 8 b r i d g e s and 0.95 k V-
100 kA f o r 4 b r i d g e s ) connected i n s e r i e s , and o p e r a t e d a t 12 p u l s e number. The by-pass switch connected i n p a r a l l e l w i t h each p a i r b r i d g e( c o n s i s t e d of two 6-pulse Gretz b r i d g e s , which a r e connected i n s e r i e s ) i s employed i n o r d e r t o reduce b o t h t h e r e a c t i v e power and t h e j o u l e l o s s generated by c i r c u l a t - i n g c u r r e n t . The c e n t e r t a p of t h e c o i l i s grounded i n o r d e r t o reduce t h e c o i l v o l t a g e t o t h e ground.
The c o i l v o l t a g e is mainly c o n t r o l l e d by two p a i r b r i d g e s of 1.9 k V , w h i l e t h e o t h e r p a i r b r i d g e s a r e o p e r a t e d a t a c o n s t a n t phase angle. The r e a c t i v e power com- p e n s a t o r i s i n s t a l l e d t a k i n g account of s u p p r e s s i n g t h e a p p a r e n t power f l u c t u a t i o n of 200 MVA on t h e power l i n e , which may b e caused by t h e above o p e r a t i o n mode.
The two t r a n s f o r m e r s w i t h t a p changers a r e connected between two 1 . 9 k V p a i r b r i d g e s and t h e 6.6 k V bus l i n e t o minimize t h e r e a c t i v e power.
CONCLUSION
A SMES employing a t o r o i d a l f i e l d c o i l arrangement h a s t h e p o t e n t i a l of p r o v i d i n g an e f f i c i e n t energy s t o r a g e f o r d i u r n a l energy s t o r a g e u s e , because of i t s advantage t h a t t h e s t r a y magnetic f i e l d i s q u i t e small and it i s more f e a s i b l e from t h e stand- p o i n t of b o t h m a n u f a c t u r a b i l i t y and m a i n t a i n a b i l i t y .
F i g . 3 Schematic main c i r c u i t diagram of t h e SMES power system REFERENCES
(1) M. Shimizu, e t . a l : i n t h e proceedings of t h i s conference.
( 2 ) H. T s u j i , e t a l : 9 t h Symposium on Engineering Problems of Fusion Research (1981, Chicagp) p2035.
