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ELECTRODYNAMIC FORCE CHARACTERISTICS OF THE SPLIT-TRACK MAGLEV SYSTEM
J. Mahtani, R. Rhodes
To cite this version:
J. Mahtani, R. Rhodes. ELECTRODYNAMIC FORCE CHARACTERISTICS OF THE SPLIT- TRACK MAGLEV SYSTEM. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-747-C1-751.
�10.1051/jphyscol:19841152�. �jpa-00223625�
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Colloque C I , supplement a u n o 1, Tome 45, janvier 1984 page Cl-747
ELECTRODYNAF'IIC F3RCE CHARACTERISTICS OF THE SPLIT-TRACK MAGLEV SYSTEM
J . L . Mahtani and R.G. Rhodes
Departmsnt of Engineering, University o f Warnick, Coventry, CV4 7AL, U . K.
RQsumQ - Dans l e systsme Qlectrodynamique d e 1 Q v i t a t i o n magnstique, dsvelop- p6 5 l ' u n i v e r s i t s d e Warwick, l e s f o r c e s d e s u s t e n t a t i o n e t d e g u i d a g e l a t s - r a l s o n t p r o d u i t e s p a r l e s c o u r a n t s de F o u c a u l t e n g e n d r s s dans l e s bords d e s deux g u i d e s d'a1um;nium. Des e x p s r i e n c e s o n t Q t Q e n t r e p r i s e s pour mesurer l e s f o r c e s d e s u s t e n t a t i o n , de t r a c t i o n e t de g u i d a g e p r o d u i t e s p a r une bobine e n c u i v r e p u l s 6 e r e f r o i d i e dans un l i q u i d e cryoggnique e t montQe s u r une ba- l a n c e d e f o r c e au-dessus d ' u n d i s p o s i t i f t o u r n a n t de 3 m de diamPtre.
A b s t r a c t - I n t h e darwick s p l i t - t r a c k d e s i g n of an e l e c t r o d y n a m i c system of magnetic l e v i t a t i o n , b o t h v e r t i c a l l i f t and l a t e r a l guidance f o r c e s a r e produced by t h e g e n e r a t i o n of eddy c u r r e n t s i n t h e i n n e r edges of t h e two aluminium guideway s t r i p s . Experiments have been u n d e r t a k e n t o measure t h e l i f t , d r a g and g - ~ i d a n c e f o r c e s produced by a c r y o g e n i c a l l y - c o o l e d , p u l s e d copper c o i l , i r ~ u n t e d on a f o r c e b a l a n c e above a 3m-diameter, r o t a t i n g wheel r i g .
I n t r o d u c t i o n
The s p l i t - t r a c k e l e c t r o d y n a m i c l e v i t a t i o n (EDS) system a s developed a t t h e
U n i v e r s i t y of Warwick combines t h e f u n c t i o n s of l e v i t a t i o n , guidance and p r o p u l s i o n from a s i n g l e a r r a y of c o i l s on t h e v e h i c l e , o v e r a p a i r of aluminium c o n d u c t o r r a i l s spaced a p a r t by a n amount a p p r o x i m a t e l y e q u a l t o t h e c o i l width. The l e v i t a t i o n and g u i d a n c e f o r c e s a r e o b t a i n e d by f r i n g e e f f e c t s of t h e p r o p u l s i o n magnets. P r e v i o u s s i - u d i e s [ I ] have shown t h a t t h e s p l i t geometry h a s b e t t e r c h a r a c t e r i s t i c s th3n o t h e r EDS systems w i t h a n added advantage of p r o v i d i n g a v e r y f l e x i b l e d e s i g n .
T h i s paper p r e s e n t s some e x p e i m e n t a l r e s u l t s of t h e f o r c e c h a r a c t e r i s t i c s i . e . l i f t , l a t e r a l , d r a g and l i f t t o d r a g r a t i o s , f o r a f l a t , r e c t a n g u l a r c o i l o v e r a s p l i t guideway, u s i n g t h e 3 m e t r e d i a m e t e r t e s t f a c i l i t y , f o r speeds up t o 45 m/s.
,Comparison i s made w i t h 1:l s c a l e impedance model measurements throughout a s i m i l a r s p e e d r a n g e .
E x p e r i m e n t a l Measurements
An a . c . analogue of t h e EDS system can be r e p r e s e n t e d by t h e impedance m o d e l l i n g t e c h n i q u e [ Z ] , whereby t h e irapedance o f t h e c o i l , c a r r y i n g a . c . c u r r e n t s and p o s i t i o n e d above a n aluminium t r a c k , i s measured and hence, t h e f o r c e can be
o b t a i n e d f o r v a r i o u s positions 3f t h e c o i l . The f o r c e of t h e c o i l i s r e l a t e d t o i t s c u r r e n t and t o t h e g r a d i e n t of i h e i n d u c t a n c e and s o , by measuring impedance a s a f u n c t i o n of t h e d i s p l a c e m e n t -f t h e c o i l , t h e v e r t i c a l ( l i f t ) and l a t e r a l (guidance) components of t h e i n d u c t a n c e can be found.
The Warwick t e s t f a c i l i t y i s d e t a i l e d i n [2]. I t i n v e r t s t h e maglev system f o r e x p e r i m e n t a l convenience b ~ u s l n g a s t a t i o n a r y v e h i c l e component i n t e r a c t i n g w i t h t h e moving guideway mounted on t h e rim of a 3 m e t r e d i a m e t e r wheel. The t e s t wheel
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841152
C1-748 JOURNAL DE PHYSIQUE
r o t a t e s about a h o r i z o n t a l a x i s w i t h a maximum p e r i p h e r a l v e l o c i t y of 45 m/s. For the experimental EDS i n v e s t i g a t i o n anapproximately1/12 s c a l e d model was used. The guidance conductors a r e two aluminium s t r i p s 65mm wide, 6.35mm t h i c k , with a separa- t i o n of l l O m m from t h e i n n e r edges. The t r a c k t h i c k n e s s chosen e n s u r e s f u l l eddy c u r r e n t p e n e t r a t i o n a t t h e maximum v e l o c i t y of 45 m/s. A 546 t u r n , copper c o i l , 130mm square i s mounted on a 3 component f o r c e balance. The c o i l was open-bath, cooled w i t h l i q u i d n i t r o g e n and e n e r g i s e d w i t h a c o n s t a n t c u r r e n t of 20 amps, which gave a measurement time of 3 s e c s . b e f o r e t h e v o l t a g e of t h e power supply was exceeded. A 3 component, s t r a i n - g a u g e , f o r c e balance t o measure l i f t , d r a g , and l a t e r a l f o r c e s was designed and b u i l t with a maximum f o r c e of + 10 newtons and good l i n e a r i t y .
R e s u l t s
-- a ) I n f i n i t e width t r a c k :
For a f i x e d l e v i t a t i o n h e i g h t (22.5mm) t h e l i f t and drag f o r c e s and l i f t l d r a g r a t i o were measured f o r a square c o i l (130 x 130mm) p o s i t i o n e d over an i n f i n i t e s h e e t of t h i c k n e s s 6.35mm, f o r t h e speed range 0-45 m/s. The measurements show t h a t the l i f t f o r c e i n c r e a s e s r a p i d l y as a f u n c t i o n of speed up t o 10 m/s, then l e v e l s o f f
approaching t h e asymptotic l i m i t with i n c r e a s i n g v e l o c i t y . The drag f o r c e on t h e o t h e r hand r i s e s t o a peak v a l u e a t a r e l a t i v e l y low speed (7.6 m/s) and t h e n d e c r e a s e s with i n c r e a s i n g speed [ 2 ] . The l i f t l d r a g r a t i o i s l i n e a r l y p r o p o r t i o n a l t o speed w i t h a measured value of 6 a t 45 m/s. These measurements showed good agree- ment with t h i n t r a c k , t h e o r e t i c a l r e s u l t s based on Fourier Transform c a l c u l a t i o n s [2].
b) S p l i t t r a c k guideway
The f o r c e s determined from impedance modelling were a l s o measured f o r t h e s p l i t - t r a c k system Fig. ( I ) , over t h e same v e l o c i t y range (0-45 m/s) with t h e c o i l cent- r a l l y l o c a t e d and w i t h a l a t e r a l displacement of 5mm. These r e s u l t s d i f f e r e d from t h e t e s t wheel measurements, i n t h a t t h e l i f t , and drag were both l a r g e r b u t they confirmed t h e absence of t h e low speed drag peak. Regardless of t h i s discrepancy t h e impedance modelling does determine t h e e f f e c t of parameter v a r i a t i o n s of t h e c o i l and guideway on t h e magnetic f o r c e s .
A l l t h e measurements were made f o r a f i x e d l e v i t a t i o n h e i g h t of 22.7mm, and a f i x e d r a t i o of t r a c k gap'width t o c o i l width of 0.96 F i g . ( 1 ) . The r e s u l t s , shown i n F i g .
(2) a r e markedly d i f f e r e n t from t h e f o r c e c h a r a c t e r i s t i c s mentioned p r e v i o u s l y i n t h a t t h e drag curve does n o t show a pronounced low speed peak, b u t tends t o s a t u r a t e a t 45 m/s and t h e l i f t f o r c e , w i t h i n t h i s speed range, h a s no asymptotic l i m i t . However, t h e l i f t / d r a g r a t i o s t i l l remains l i n e a r w i t h speed. To i n v e s t i g a t e t h e e f f e c t of t h e l a t e r a l f o r c e s , experiments were conducted f o r l a t e r a l displacements of t h e c o i l e . g . 2.5mm t o 8 7 . 5 m from t h e c e n t r e of t h e s p l i t t r a c k . A displacement of 87.5mm corresponds t o a c o i l c e n t r a l l y p o s i t i o n e d over one of t h e guideway t r a c k s , and may be compared with t h a t of t h e impedance modelling measurements f o r t h e semi- i n £ in i t e t r a c k .
F i g . (3) shows t h e e f f e c t of l a t e r a l displacement of t h e magnet on l i f t , d r a g , and l a t e r a l f o r c e s and l i f t l d r a g r a t i o a t t h e maximum v e l o c i t y of 45 m / s . L i f t remains c o n s t a n t up t o 5mm displacement and a t lOmm i t i n c r e a s e s by 13%. Drag g r a d u a l l y r i s e s up t o 5 m displacement, t h e r e a f t e r r i s i n g s h a r p l y t o 64% a t 10mm. The l a t e r a l f o r c e i n c r e a s e s s t e e p l y with l a t e r a l displacement and a t 5mm displacement i t i s 67%
of t h e l i f t f o r c e , w h i l e a t 7.2mm i t i s e q u a l and a t lOmm i t i s 143% of t h e l i f t f.orce.
F i g . (4) shows the v a r i a t i o n s of the f o r c e s f o r l a r g e r displacements up t o 87.5mm.
Conclusions
The r e s u l t s p r e s e n t e d f o r t h e 1/12 s c a l e d model of t h e s p l i t t r a c k EDS systems, demonstrates t h e f e a s i b i l i t y of t h i s design f o r a p r a c t i c a l system. Guidance f o r c e s can b e generated which can exceed t h e l i f t f o r c e and t h e l i f t l d r a g r a t i o , when s c a l e d up f o r a f u l l s c a l e system, i s q u i t e a c c e p t a b l e from t h e energy p o i n t of view.
Furthermore, t h e absence of t h e low speed drag peak would appear t o be an added bonus.
Square coil: 1 l 5 x 1 l 5 m m X-sectlon: 1 6 x l 5 m m current: 2 0 A Turns: 6 4 6
I
Fig.1. Coil and guldeway configuration
Fig.2. Measurement of lift and drag forces and
1iftIdt.g ratio va. velocity for a coil over a split guideway
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lateral
1.0 -
-
I I I I I I I I I I
0 1 2 3 4 5 6 7 8 9 1 0
Lateral dlsplacernent Flg. 3. Mearurements of l1ft.drag.and lateral forces
and Iiftldrag ratio va. lateral dlsplacement a t vel. of 4 6 m l r
I
Lateral dlrplacement mm
Flg..4. Measurements of 1Ift.drag and lateral forces and lift/drag ratio vs. lateral dlsplacernent a t a vel. of 4 5
F u r t h e r i n v e s t i g a t i o n s a r e b e i n g conducted w i t h b o t h a s i n g l e and a p a i r of s q u a r e (115 x 115mm) r a r e - e a r t h permanent magnets. A one m e t r e d i a m e t e r wheel h a s a l s o been d e s i g n e d and b u i l t and w i l l be used f o r f u r t h e r i n v e s t i g a t i o n s a t h i g h e r s p e e d s t o a maximum of 135 m/s.
R e f e r e n c e s
1. J . Y . Wong e t a l , 'Performance S t a b i l i t y C h a r a c t e r i s t i c s of a n e l e c t r o d y n a m i c a l l y l e v i t a t e d v e h i c l e o v e r a s p l i t guideway', T r a n s . A S P E , Vol. 98, S e r i e s G, No. 3 , S e p t . 1976, pp. 277-285.
2. R.G. Rhodes e t a l , 'Magnetic l e v i t a t i o n and l i n e a r motor p r o p u l s i o n f o r AGT', Report t o SERC (London) March 1980.
