Ac Superconducting !

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IEEE Transact ions O h Magnetics , V O l . MAC-12, No. 6, November 1976SUPERCONDUCTING AC GENERATORS

J. H. Par k e r , J r .West inghouseResearchLabora to r ies ,P i t t sburgh ,Pennsy lvan ia15235

andR. A. T o m eWestinghouseLargeRotatingApparatusDivision, East Pi t t sburgh ,Pen n s y l v an i a1 5 1 1 2

ABSTRACTThe u t i l i z a t i o n o f s u p e r co n d uc t i n g f i e l d w i n d i n g s

i n a r g e a c g e n e r a t o r sg i v e sprom ise o f educed s i ze andw e i g h t , n c r e a s e d e f f i c i e n c y a n d b e t t e r e l e c t r i c a l c h a r -ac ter i s t ics over conven t ional copper - i ron mach ines .T h is new co n cep t n ap p l i c a t i o n o cen t r a l s t a t i o n powergenera t ion co u l d ead o m ach i n eswi th rat ings beyondt h e limits se t by pres ent echn ology andeven a t p r es en tday r at in gs may have conomic dvantage. Also the lowweigh t o power r a t i o o f th i s ypeofmachine makes i tat t r ac t i ve o r advanced i rborne ys tems .Becauseoft h e s e a t t r a c t i v e c h a r a c t e r i s t i c s , h e e n g i n e e r i n gschoo ls and the argeg en e r a t o rmanufactu rer s h roughoutt h ew o r l d h av e n i t i a t ed p r o g r am s o evalu ate h i s con-cept .Theseprograms ange rommachinedesign o ystems t u d i e s up t o c o n s t r u c t i o n a nd t es t of pr oto typ e demon-s t r a t i o n m ach i n es .conceptof a superc onduc t ing g en e r a t o r n co n t r a s t w i t ha presen tdaycopper - i ronmachineand henout l ine hep o t en t i a l advan tages o f th i s new conc ep t , b o t h ech n i ca land conomic. Based n de si gn tu di es and t es t r e s u l t sof thepro to typemachines ,cr i t i ca ldevelopmentprob lemst h a t c a n b e a n t i c i p a t e d f o r f u t u r e , a r g e r g e n e r a t o r sw i l l be r ev iewed wi th specia l emphas is on those aspec tsassocia ted wi th he superconduc t ing f ie ld wind ing .

The present paper w i l l f i r s t r e vi e w h e g e n er a l

INTRODUCTIONW ith t h e n t r o d u c t i o n n h e m i d . 6 0 ' ~ of s t a b l e

m u l t i f i l am en t a r y , y p e I1 superconducto r scapab le o fc a r r y i n g a r g e c u r r e n t s n h i g h d c m a g n e t i c f i e l d s , camet h e r ea l i za t i o n o f h e p o t e n t i a l i mp ro vement s t h a tco u l dr e s u l t fro m t h e i r a p p l i c a t i o n o h e f i e l d w i n d i n g o fh i g h power e l e c t r i ca l ac g en e r a t o r s .S i n ce h a t t ime,numerousprogramshaveb een i n i t i a t e d h r o u g h o u t h ewor ld o va luate h is oncep t .Theseprogramshaveranged romconceptualdesignsandeconomicevaluationsto p ro t o typ e mach ine cons t ruct ion and es t . '

The potentialad v an t ag es o beg a i n edf rom subs t i -t u t i n g a s u p e r co n d uc t o r o r a co p p e rconducto r n hef i e l d w i n d i n g stems f rom he fo l lowing ,

0 Loss lessu n d e rd c o n d i t i o n sH i g h e rc u r r e n td en s i t i e s b y a t l e a s ta no r d e rof magnitude, 2 l o 8 A/m2

0 High magne t ic ie ld c a p a b i l i t y 1. 5 t e s la a t4 K.

The losslessp e r f o r m an ce ead s oan n c r ea s e nm ach i n ee f f i c i en c y . The r e f r i g e r a t i o np e n a l t ymus t , o f cour se ,b e a k e n n t o a c c o u n t ,b u t o rgen era t o r s n he powersy s t em c l a s s a t 1.1000 MVA, t h e p en a l t y i s aboutano r d e r of magnitude ower han he emaining l os se s .The i n c r e a s e d m a g n e t i c f i e l d c a p a b i l i t y o a l e v e lb ey on d t h e s a t u r a t i o n . l e v e1 o f i r o n means t h a t h e r o ncanbe removed f rom th e ro to r eav in g more spa ce ava il-a b l e f o r h e w i n d i n g a nd r e s u l t i n g n a r e d u c t i o n nr o t o rd i am e t e r .Fo r h e same r e a s o n , h es t a t o r e e t hca nbe removed le ad in g o a f u l l a i r gapmachine.Botho f h e s e e s u l t n h e s eco n d advan tage o f r educ ed s i zeandweigh tover onven t ionalgenera to r s . The po te n t ia lof educed s i z e and weig htan d n c r ea s edef f ic iencymakes theseg e n e r a t o r s e s p e c i a l l ya t t r a c t i v e o r powers y s t em sap p l i ca t i o n s .The purp ose of the presen t p ap e r i s t o r ev i ew h epres en t ta t us of th i s new techno logy .This nvo lves adiscus s ion of the b a s i cc o n c e p t s , a review of t h e i r po-

t e n t i a l a d v a n t a g e s when a p p l i e d o c e n t r a l s t a t i o n ge ne -r a t i o n an4 to h i gh power a i rbonre sys tems , a coverage oft h e s ev e r a l o f h e p r o t o t y p e p ro gr am sa n d f i n a l l y a d i s -cuss ionof some of the ech nic al p r o b l em s ob es o l v edi n o r d e r h a t s u ch g en e r a t o r s becom ea commercialr e a l i t y .

GENERAL DESIGNFEATURESThe b as i c d e s i g n f ea t u r e s o f a two-polegenerator

u t i 1 i z i n g . a s u p e r c o n d u c t i n g f i e l d w i n d i n g are i l l u s -t r a t e d i n Figure 1.

,,/ ,/ [Damper Shield Liquid Helium SupplyAnd ReturnRadiation Shieldstator Shield

Armature Winding

'vacuum/ cdce VFkWinding

Radiation ShieldCollectar RingsFiem curre nt J

Fig. 1 Cross section of a AC generator lWo polelwith superconductlng ield winding

T he r o t o r co n s i s t s o fan i n t e r n a l l o w em per at ur es t r u c t u r e w h i c hsuppor t s hes u p e r co n d u c t i n gco i l san dloc ate s he power leads and He t r ans fer ys tem.Sur -r o u n d i n g h i s s t r u c t u r e i s a low empera tu re ad ia t ionsh ie ld and the n an out er room temperature damper ore l ec t r o m ag n e t i c h i e l d .T h i so u t e r h i e l d o n n ec t s h es h a f t s and s e r v e s a s h e o u t e r wall o f th e vacuum n-c l o s u r e . The lo w t em p er a t u r e n n e r t r u c t u r e i s con-n ec t ed o h e s t u b s h a f t s by h e l iu m - vap o rcooled orquet r ansmiss ion ubes a t each nd.These ubes are de -s i g n ed om i n i m i ze h eheat low nto he low empera-t u r e s t r u c t u r e and t o accomm odate t h e r e l a t i v e h e r m a lc o n t r a c t i o n b e t w e e n h e n t e r n a l f i e l d w i n d i n g s t r u c t u r eand theou te r room temp eratu re damper sh ie ld . The non-d r i v e nshaf t endaccommodates th e ro ta t i ng sea l systemf o r r an s f e r r i n g h e l i u m co o l an t n t o and o u t of t h er o t o r and t h e f i e l d c u r r e n t s l i p r i n g s .f u n c t i o n s .F i r s t i t s e r v e s h ec l a s s i c u n c t i o n ofdampingm echani ca l o s c i l l a t i o n s of t h e r o t o r d ue t osys temdis tu rbances .Second , i t s e r v es a f u n c t i o nun ique o a superconduct ingmachineofsh ie ld ing hef ie ldw i n d i n gand i t s s u p p o r t s t r u c t u r e f r o m time vary-in gm ag n e t i cf ie lds an d h e r eb y reducing h ea tgenera t ioni n h i s eg i o n . Under s t ea d y t a t ec o n d i t i o n s h e o t o ri s s u b j ec t ed o r o t a t i n g m ag n e t i c f i e l d s d u e o o ad un-b a l an ce and s t a t o r p ac i a lh a r m o n i c s .Fau l t and o t h e rt r a n s i e n t c o n d i t i o n s a l s o e a d o time varyingmagneticf i e l d s a t t h e o t o r . The s h i e l d serves t oa t t e n u a t ebo th of th ese e f f e c t s .

The armature i s ofa n a i r g a pdes ign , i . e . , nos t a t o r e e t h , and i s wound with a t r ansposed mul t i s t r andco p p e rco n d u c t o rw i t h n t e r n a l water coo l ing . Them u l t i s t r an dco n d u c t o r is r eq u i r ed no r d e r om i n i m i zet h e edd y cu r r en t h ea t i n g d u e o h e v e r y h i g h ac magne-t i c i e l d s h a t h ec o n d u c t o r i s exposed to . The arma-

The damper ore l ec t r o m ag n e t i c s h i e l dserves two

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t u r e w i n d i n g i s sur roundedwi th a l am i n a t ed r o n s h i e l dwhichserves as a magnet icenclosure .

APPLICATIONSOne of them o s tp r o m i s i n gapp l ica t ions i s t o h e

v e r y a r g e g e n e r a t o r s w i t h r a t i n g s of > 1000 MVA f o rc e n t r a l t a t i o n power g e n e r a t i ~ n . ~ , ~ T h i s c a s ea p p e a r soptimum because he r e f r i g e r a t i o n l o s s i s sm al l n com-p a r i s o n o o t h e r o s s e s a t h e s e r a t i n g s a nd t h ep r e -d i c t ed r ed u c t i o n of r o t o r d i am e t e r a t a g i v e n r a t i n gi m p l i e s h a t h e s u p e r c o n d u c t i n gg e n e r a t o rc a n c a r r y h er a t i n g o e v e l s h a t a p p e a r m p o s s i b l e w i t h p r e s e n t dayi ron-copper echno logy . n dd i t ion , as the upercon-d u c t i n gg en e r a t o r ech n o l o g yd ev e l o p s , i t may turn o u tt h a t h ead v an t ag es s u cha se f f i c i en cyan ds i ze w i l ll e a d obe t t er economics ven fo rp r e s e n t a t i n g s . I tmust beem p h as i zed h a t o r h i sap p l i ca t i o n h eo v e r -r id ing equ i r ementof ong- term e l iab i l i tyeq u a lo rb e t t e r h a np r e s en t d aymachines i s uppermost.

Anotherpromis ingapp l ica t ion i s f o r a i r b o r n e ,s h o r tmis s ion power supp l ies . Here, w h i l e h ep r e d i c t e dpower requirements are o n l y h eo r d e ro f en s of mega-w a t t s , theneed of very owspeci f icp o w er , . e . ,- 0.05 kg/kVA, and a b i l i ty to use s to re d hel iu m ra the rt h an a r ef r i gera t ion sys t em makes the superconduct inga l t e r n a t i v e v e r y a t t r a c t i v e .Turb ine Genera to r sT u r b i n eg en e r a t o r a t i n g sh av e n c r ea s eds i n ce h ef o r m a t i o n o f h e e l e c t r i c u t i l i t y n d u s t r y e a r l y n h i scen tu ry . Today s in g leg e n e r a t o r s a t e d a t 1200 MVA a r ei n s e r v i c e an d h i g h e r r a t ed u n i t s h av e b een o r d e r ed f o ri n s t a l l a t i o n i n a few years .weighthavebeenachieved by improvin g hecoo l ing oft h eh e a tge ne rat ing components f thegenera to r . Thecoo l ingsys temadvances ,a l lowing ncreasedgenera to rra ti ng s, ha ve moved from a i r c o o l i n g o Hp an d waterco o l i n g .T h es ead v an cesh av e e s u l t ed nan n c r ea s eo f r a t i n g s n o r m a l i zed o u n i t v ol um eof mat er ia l f romab o ut 5 t o 28 MVA/m3 over heper iod rom1940 o1975 .b e t t e r u t i l i z a t i o n o fm a t e r i a l s , h e r ehasb eenan n -c r e a s e n p h y s i c a l s i z e s , n o t o rd i a m e t e r s , e n g t h s ,andweigh ts, and in th e us e o fmore ne ar ly optimum de-s g n s .

Shippingw e i gh t and s i ze i m i t a t i o n s h av e b o t hbeen ncreased by thec o n s t r u c t i o no f s p e c i a lg e n e r a t o rsh ipmentcar swhich are cap ab l eo fhand l ing genera to r s4 m in d ia me ter and weigh ing550metr ic ons.f o r a t i n g s up t o h eor de r of 500 MVA. Such r a t ingsw i l l r eq u i r e h i g h co s t m a t e r i a l s , co m pl exshippingpro-cedu res, and expens ive esigns. Thus superconductingt u r b i n eg e n e r a t or s may b e f i r s t a p p l i e d a t r a t i n g sbeyond 2500 MVA t o ra i se t h e a t i n g l imit. They appeart o o f f e r e co nom ic b e n e f i t s n h e a r g e r r a t i n g s , b u top in ions vary as t o how low a ra t i ng w i l l someday bep r a c t i c a l a ndeconomical.crease as shown i n F i g u r e2 .t i v e p r a c t i c e h a n i s presen t ly b e i n gused and a muchl o w er a t eo f n c r ea s e h an n h ep as t .Fo rex am p l e ,between1944an d1970 thecu m u l a t i v ean n u a lg rowth a teof u n i t s i z e s was ov e r lo%, w h i l e h eg r o w t h a t e ofthepeak oad was 7 .5% or he same per iod .F i g u r e 2i n d i c a t e s a maximum un it s i z e ofapproximately 4000 MWwhereas a s i m p l eex t r apo la t ion ofp as tand cur ren tp r ac t ic es would sugges t a maximum un it ra t i ng n heyear 2000 between7000 MW and11,000 MW An ad di ti on alco n s i d e r a t i o n i s the she er number of un i t s h a t w i l l b er e q u i r e d o p r o v i d e h e pr o j e c t e d g e n e r a t i o n a d d i t i o n si f S.C. gener a to r sa ren o tap p l i ed .

E a r l i e r n c r e a s e s n r a t i n g p e r u n i t of s i z e o r

Concur ren t w i th he coo l ing sys tem advances and

I t ap p ea r s h a tp resen t echno logy w i l l prov ide

We a n t i c i p a t e h a t h e f u t u r e r a t i n g s w i l l i n -The s lop e o f t h i s band r ep rese n ts a more conserva-

350030002500

/

I Y /'

5001I I I I I 1 I L

19802 84 86 88 90 92468 20I n s t a l l a t i o n Y e a r

Fig. 2 -Growth of g e n e ra to r ra t i n g sTheband wid th shown w i l l accommodatewhat w e f

r ep r e s en t s h e eq u i r em en t so fo v e r 70% of t h e u t i l i ti n d u s t r y n h i s c o u n t r y .two-polesuperconducting1200 MVA gen era to r n compso n w i t h h o s e f o r a co n v en t i o n a l Hg cooledmachineoft h e same r a t i n g .F i g u r e 3 shows a s i z e compar ison ft h e s e same two machines.Th isdata w a s preparedas

T ab l e I shows the p r e d i c t e d c h a r a c t e r i s t i c s o f

p a r t o fan n-houseprogram.Table 1

Comparisono f C h a r ac t e r i s t i c s1200 MVA

~- ConventionalSynchronousReactance, %

13Length ,640,000otalWeight ,kg 91,000otorWeight,kg 550,000tatorWeigh t ,kg

98.7u l l Load Ef f ic ien cy , % 0.04u b t r an s i en t T i m e Cons tan t ,sec 0.8ran sie nt Time Constant , ec

26u b t r an s i en tR eac t an ce , % 32rans ien tReactance , %18 0

____.

sc522916230 -2

99.140,14,015 0,

7.

The t a b l e an d f i g u r e c l ea r l y p o i n t o u t m os to f techn ica ladvan tagesprom ise d by a supercondu ctinggee r a t o r . T he l a r g ew e i g h t ed u c t i o n e s u l t s r o m h eremoval of i ro n and rom th e smaller l en g t h of t h e mch ine . The in crease n f f ic iency o l lows rom educ-t i o n o f l o s s e s n h e i e l dw i n d i n g a n dwindage.Th el o n gs u b t r an s i en t time con s tan t ends o make th et r a n s i e n t s t a b i l i t y d e p e n d e n t on t h es u b t r an s i en t r eact a n c e r a t h e r h a n h e r a n s i e n t r e a c t a n c e as w i t h aconventionalmachine. Also the educed ynchronous nds u b t r an s i en t eac t an ces en d oco m p en s a t e o r h el o w e r n e r t i a o f h e r o t o r ,y i e l d i n g a c r i t i c a l f a u lc le ar in g ime equ al o r somewhat be t te r han conve n t ionmachines.

910


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I 4.7

Conventional

superconductingFig. 3 -Outli nes of hydrogencooled and superconducting wo pole,1200MVA generators. Dimensions are in meters

PROTOTYPE MACHINES AND DESIGNPROGRAMSOver the l a s t s ev e r a ly ea r s , h r eep r o t o t y p e ma-

c h i n e s n h e MW class have been des igned , cons t ructed ,a nd t e s t e d n h e U. S. MIT , through EPRI sponsorship,hascons t ructed and tes ted a 3 MVA g en e r a t o r .Westinghousehasconstructedand t es ted a 5 MVA,3600 rprn gene rator with n-ho use fundi ng andund er AFsponsor sh ip has cons t ructed and es ted a 5 MVA,12,000 rpm rotor and i s now com ple ti ng heentire gen-e r a t o r w i t h a p r o j ec t ed 10 MVA r a t i n g a t 12,000 rpm.In 1970 , Wes ting hous e nit iat ed a program whoseo b j e c t i v e was t o e v a l u a t e h e e c h n i c a l f e a s i b i l i t y ofapp ly ingsuperconduct ing ie ldwind ings o argeelec-t r i c a l genera to r s . This d ec i s i o n w asbased i n p a r t o nt h e e x c e l l e n t s t u d i e s a ndexperiments underway a t MITand , i n p a r t , on n-housestudies of th i s new area andi t s poten t ia l mpor tance oWest inghouseas a manufac-t u r e r o f l a r g e u r b i n eg en e r a t o r s . A m aj o rpar t o f th ee f f o r t d u r i n g h e f i r s t h r e e y e a r s was d ed i ca t ed othedes ign ,cons t ruct ion ,and t es t of a 5 MVA g en e r a t o ru t i l i z i n g a s u p e r co n d uc t i n g i e l dwind ing . This gene-r a t o r was b u i l t o d e m o n s t r a t e h e e c h n i c a l f e a s i b i l i t yof a s u b s t an t i a l l y r a t e d m achi neand t o d en t i f y ech -n i ca l p r o b l em s .s t r u c t i o n was completed i n he s p r i n g o f1972. Cryo-g e n i c r o t o r tests were carr iedo u t n J u n e1 9 7 2 ,w i t ht es t s on the comple te genera t o r ak ing p lace n Ju lyandSeptember1972 and Jul y1973 .4 ,5 Figure 4 showst h e 5 MVA genera to r on t es t .Themachine was designed as a 3600 rpm, 60 Hz( two-pole)genera to rwi th 4160 vo l t s ine- t o - l in e ,three-phaseou tpu t .i n g f i e l d w i n d i n g w i t h i n a s t a t i o n a r y , a i r gap woundarmaturesh ie lded by a l am i n a t ed r o n s t r u c t u r e .(nonmagnetic)polepiec e nd wedged.The machinet o r q u e i s t r ansmi t ted o he ie ldwind ing h rough al o n g , h i nw a l l ed o r q u e u b e .R ad i a t i o n h i e l d sw er ei n s t a l l e d a r o u n d t h e f i e l d w i n d i n g t o i n t e r c e p t r a d i a land a x i a l a d i a t i o n . The r a d i a l a d i a t i o n h i e l d i sa l s ou s e d as a ne l e c t r i ca l d am per s h i e l d . The s h i e l d sa r e m a i n t a i n ed a t ab o u t 50 K by exhaustheliumgas

The design was completed in ear ly 197 1 andcon-

The gene ra to r cons i s t s of a ro ta t ingsuperconduct -

The superconductor was wound on a s t a i n l e s s s t ee l

911

l e a v i n g h e i e l dwind i ng . The ro to rs t r u c t u r ea n ddewar wall was p l aced o v e r h e n t e r n a l f i e l d w i n d i n gs t ruc tu ra l asse mbly o p rov i de he r equ i r ed vacuum in -s u l a t i o n co n t a i n m en t v e s s e l .por tedwi th a r ad i a l s p o k e s t r u c t u r e h a t co n n ec t ed h eroom tempe ra tu r e ro to r shel l w i th he low empera tu reinner ie ldwind ingas s em b ly . The s t r u c t u r e i s de -s i g n e d f o r r a d i a l s t i f f n e s s , dyn am ic s t a b i l i t y , a nda x i a l f l e x i b i l i t y so t h a t h e r e l a t i v e h e r m a l co n t r ac -t ion o f he nner and ou ter s t ruc tu re cou l d be accommo-datedwith low s t r es s l e v e l s . A r o t a t i n gs e a ls y s t e m 'u t i l i z i n g r u b b i n g f a c e seals s e r v e d f o r r a n s f e r r i n gt h e i q u i d h e l i u m n t o h e r o t o r o c o o l h e f i e l dwind ing , o rque ube ,andelec t r ica l eads .The ar mat ure coi ls were f ab r i ca t ed f r o m f i n e l ys t r anded copper wi re- in o r i le r o min imize he eddycur-r e n t s . The c o i l s were wound andbonded on an epoxyg l a s sb o r e seal tube .The ron hield was f a b r i c a t e dfrom iron aminatio nss tackedand keyed to he arm atu rec o i l san d h e t a t o r r am e .Cool i ng o f thea r m a t u r ewas accompl ished by c i r cu la t i ng o i l on the ou ts i de o ft h e co n d u c t o r n s u l a t i o n .

The performance of th e 5 MVA genera to r was d e t e r -mined by anumberof bas ic tests co n s i d e r ed s u f f i c i en tt o p r e d i c t s t e a d y s t a t e and t r a n s i e n t e l e c t r i c a l per-formanceunder fu l l oad cond i t ion s :

The f r e e endof t h e n t e r n a l s t r u c t u r e was sup-

0 Open c i r cu i t t es t0 S h o r t i r c u i t t e s te Sudd en s h o r t c i r c u i t t es t ' f rom educedvol tage0 Harmonic wave a n a l y s i s0 Loss t e s t .The measuredopen c i r c u i t vo l t ag e was in good

agreementwith hedes ignvalue. The sh or tc i r c u i theat un tes t a t r a t eds t a t o rcu r r en td em o n s t r a t ed h a tt h e o o l i n g y s t em was adequate.The udden hor tc i r c u i t tests a t r e d u ce dexci ta t ion y ie lded hesub-t r an s i en t an d r an s i en t r eac t an ces an d time co n s t an t s .Numerous quenches of th e fi el d wi nd in g were purposelyi n i t i a t e d n o r d e r o e v a l u a t e h e b e h a v i o r of t h ef i e l dw i n d i n g e s u l t i n g f ro m t h esequenches. Subse-q u en t o th e above t e s t s , it was dem onstra ted hat th ef ie ld wind ing cou ld opera te a t a n e x c i t a t i o n l e v e l c o r -responding o a 1 5 MVA r a t i n g .AF/Westinghouse12,000 FS", 5 MVA Genera to r

As a r e s u l t of t h epred ic tedsav ings nweigh tandvolume offered by acg en e r a t o r su t i l i z i n gs u p e r co n d u c t -ing f ie ld win d ing s , the Aero Propuls ion Labora to ry oft h e U. S. A i r F o r c e , n i t i a t e d a technologyadvancementprogram i n 1971,d i r ec ted oward hedevelopment of a5 MVA, 12,000 r pm superconduct inggenera to r for a i r -


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borne ap p l i ca t i o n s . T h eWestinghouse El ec tr ic Corpora-t ion ece ived hepr imeco nt ra ct (F33615-71-C-1591) i nMay 1971.Pre l iminaryGenera to rDes ign ,andDes ignand Test ofC ri t i c a l Rot or Components; ( 11):Design ndConstruc-t i o n of CompleteGenerator ; 111) :Ful l Power Tes to fGenerator .The p re l imin ary des i gn s tud y r esu l ted n a genera-t o r w i t h h e b a s i c s p e c i f i c a t i o n s as g i ven i n T ab le 11.A pre l iminary des ign was a l so developed fo r a h igh vo l -tage 37 kV) opt ion .

The program w a s d i v i d ed n t o h r eep h a s e s : (I):

Table I1AF Gene rator Spec if ica t ions(Phase I )-~

Power Rating, 5 MVA (0.8 p f )Line-to-LineVoltage, 5000 vo lt s rmsFrequency, 400 Hzrpm, 12,000Po l e s , 4SynchronousReactance, 0.30 puMachineDiameter,0.45 mMachineWeight, 450 kgI r o n S t a t o rS h i e l dU t i l i z e dSpanbetweenBearingCenters,0.95 m

The main e ff o r t of Phase I was d i r e c ted owa rd hedes ign ,cons t ruct ion ,an d t e s t of a c o m p l e t e o t o r odemons t r a te ha t a four -po le , s u p e r co n d u c t i n g i e l dwindingcouldbe o ta ted a t 12 ,000 rpm under fu l l ex ci -t a t i o n . na d d i t i o n , a s e p a r a t e t e s t on c e r t a i nc r i t i -ca l ro to r components, uch as t h e r o t a t i n g sea l system,cryogenic power leads, and individualco i l s ,p r eced edt h e f u l l r o t o r e s t s n o r d e r o o b t a i n d a t a on r e l i a b i -l i t y andperformanceof hese omponents. A cutawayviewof hePhase I r o t o r i s shown in Figu re 5.

H e l i u m G a s v e n t sI

Fig. 5 -Cutaway Of A F o t o rPhase I was completed i n January1974 by succe ss-

f u l r u n s w i t h h e r o t o r a t 1 2 , 0 0 0 rpm a n dwi th hef i e l d e x c i t e d a t a l ev e lcor resp onding o a 5 .32 MVAg en e r a t o ro u t p u t .6 Figure 6 shows thePhase I r o t o r o ni t s t e s t s t an d .The desig n ask7 of Phase I1 w a s completed i nFebruary1975. The Phase I1 g en e r a t o r i s c u r r e n t l yp r o j e c t e d a t 1 0 W A ; o t h e rs p ec i f i ca t i o n s a r ec l o s e oth ev a l u esg i v en nT ab l e 11. The cons t ruct iono f h ecomple tegenera to r i s now underwayand i s s ch ed u l edfo rcom ple tio n by August1976.The f u l l power t es t s a r ep r e s en t l ys ch ed u l ed o rea r l y1 9 7 7 .

Superconducting Generator Research a t MITResearch on superconductingmachinesbegan a t MinJanuary1967 . * Fun di ng f o r h e e s ea r ch was i n i t

l y provide d by theE d i s o nE l ec t r i c n s t i t u t e ,and mr ecen t l y by t h e E l e c t r i c Power R es ea r ch I n s t i t u t e(EPRI).T h e p r o j ec t i s under he ontinuousguidanceof a s t eer in g comm ittee whose members are rep res ent at i v e s of p r i v a t e e l e c t r i c u t i l i t y com panie s.

The MIT r esearch ncludesbothexper imenta landan a l y t i ca l w or k. In t h ee x p e r i m e n t a le f f o r t , two an a t o r s , w i t h r o t a t i n g s u p e r co n d u c t i n g f i e l d w i n d i n g sh av eb eenb u i l tan d e s t ed .T h es ea l t e r n a t o r sh av eproven ob esuccess fu l andusefu lexper imenta l oo ls .

A f i r s t m ac hi ne ,which w a s u l t i m a t e l y r a t e d a t45 kVA, was con st ru ct ed o d e m o n s t r a t e h e f ea s i b i l i t yof theb as i cco n cep t . I t showed th at a fi eldw i n d i n gcould rema in supe rcondu cting while rotat ing at 3600It a ls o showed tha t he re were noproblems associatew i t h r o t a t i o n of l i q ui dhel iumwhichcou ldnotbeover -come by ca ref ul otord es i g n .T h i sm ach i n eh as aoomt em p er a t u r e r o n - f r ees t a t i o n a r yarmatu re , a gascootorque ube ,gascoo ledcur ren t eads ,and a r o t a t i nh e l i u m r an s f e r co u p l i n g , a l l com po nent swhich w i l lfound in uturemach ines .Th ism ach i n e w a s t h e f i r ss u p e r co n d u c t i n g a l t e r n a t o r o b e o p e r a t ed as a syncnouscondenserconnecte d t o a commercial power syste

The secondmachine,'whichha s a nominal at ing 3 MVA, was co n s t r u c t ed odem onst rate component deswhichmigh tbeuti l ized on ful l-s calemach ines . I ta ca r e f u l l ydesigned epoxyand glass-fibersupercondut o rs u p p o r ts t r u c t u r e ,s tage-c oo led o rque ubes , aan o i l co o l ed a r m a t u r e w i n d i n g w i t h ca r e f u l l y con-t r o l l edv o l t a g egrad ien t s . The hel ium ransfer coup l i n gc a r r i e s h r e eg a ss t r eam s , and a l l h e li um l ow scanbecon t ro l led nd iv idual ly .Th ism ach i n ehasalsobeenopera ted as a synchronouscondenser on t h eCambridge El e c tr ic power system.on to upp or t and guide he xper i menta l f for t . Ayseshavebeenm o ti v at ed by s p ec i f i ca t i o n s f o r ex p e r imenta ldes igns , nd by exper im enta l esu l t s .T h i sanalys i shascover ed a broad ange of top ics .Thesei n c l u d em ach i n e i e l d s , o r ce s , and e l ec t r i c a l pa ramt e r s ; machine- sys tem n terac t ions ; low t empera tu ret h e r m a lan a l y s i so f he o rque ubes , eads , and het r ans fersys tem;elec t romagnet icsh ie ldper fo rmance;and armaturee l ec t r i ca lp e r f o r m an ce .EPRI LargeMachineDesignProgramprogram i n September1975directed oward he ol lowingg o a l s :

An ex t e n s i v e an a l y t i ca l p r og r amha sbeencarr ied

The E l ec t r i c Power R es ea r ch I n s t i t u t e n i t i a t e d

To developconcep tualdes igns o r a 300 nd1200 MVA, 3600 rpm generator.

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0 To invest ig ate heeconomicsand ys tem n-t e r a c t i o n s o f these machines.

0 To layo u t a developmentprogram th at wouldl e a d o h e c o n s t r u c t i o na n d e s t u n d e ru t i l i t y c o n d i t i o n f o r a 300 MVA machine.

Wes t inghousehas ece ivedone9of he two co n t r ac tsth at EPRI has unded on t h i s work.The b a s i c n t e n t oft h i s two-yearprogram i s t o o b t a i n as f i r m a n o v e r a l lev a l u a t i o n as poss ib leo fsuperconduct ing genera to r sf o ru t i l i t ya p p l i c a t i o n s . Then i f h ee v a l u a t i o n i sj u d g e d s u f f i c i e n t l y p o s i t i v e w i t h r e s p e c t o e c h n i c a lan de con om ic b e n e f i t s , o n i t i a t e a secondphase t oc o n s t r u c t a n d e s t a l a r g e u t i l i t y d e m o n s t r a t i o n ma -ch ine .

SOME DESIGNASPECTSMany of h eg en e r a l e a t u r e san dch a r ac t e r i s t i c s o f

a cg en e r a t o r s u t i l i z i n gs u p e r co n d u c t i n g f i e l dw i n d i n g swere eviewed in hepre ce d in g ec t ion s . The purposeoft h e p r e s e n t s e c t i o n i s t o c o v e r a f ew c r i t i c a l a s p e c t sandproblems i n more det ai l .Sp ec i a lem p h as i s i s placedon f au l t co n d i t i o n s and t h e i r m p ac to ng en e r a t o rdes ign .Fau l t Fo r ces

A c r i t i c a l d e s i g n r e q u i r e m e n t f o r a superconductingt u r b i n eg en e r a t o r i s t o s u r v i v e s y s t e m f a u l t s w i t h o u tmech anica l damage o r iel dnormal iza t ion .Forex am p l e ,i f a s y s t e m f a u l t were t o o c c u r , it i s impor tan t ha tth egenera to r can m m ed i a t e l ydel iver power af te r hef a u l t i s cleared .D u r in g a f a u l to rs h o r tc i r c u i t , h er o t o r a n d a r m a t u r e c i r c u i t s a r e s u b j e c t e d o a r g e e l e c -t romagnet ic o rcesand o rqueswhicharemos tseverewhen t h e f au l t o ccu r s n ea r h e h i g h s i d e e r m i n a l s oft h eun i t r ans fo rm er . Under such ond i t io ns , he arma-t u r e c u r r e n t s c a n n c r e a s e o h r e e o f o u r times t h er a t e ds t e a d y s t a t e cur ren t and is s u s t a i n e d u n t i l h ef a u l t i s c l ea r ed n o m e t h i n g e s s h an a 0 . 1 s ec . Them ag n i t u d eo f h e au l tcu r r en t sd ep en d so ng en e r a t o r ,transformer nd ystem mpedances. The in te ra ct io n oft hearmature cur ren ts an d h ecor responding nducededdy c u r r e n t s n h e damper s h i e l d r e s u l t s n a r g e re-p u l s i v e o r c e s h a t e n d t o push hearmatureconducto rr ad i a l l y o u t w ar dand toc r u s h h ee l ec t r o m ag n e t i cs h i e l d .T h es ecu r r en t san d o r ce s en d ob e a r g e r o ra superconduct inggenera to rbecauseof i t s lows u b t r an s i en t r eac t an ce w h i ch p u t s h i g h e r s t r esses ont h ea r m a t u r e n s u l a t i o n h a n i s encountered nconven-t i o n a lg e n e r a t o r s .Fu r t h e r h e h i e l d m us tbedesignedn o t on ly o optimumly se rve i t s s h i e l d i n g an ddamperr o l e b u t b e s u f f i c i e n t l y s t r o n g o w i t hs t a n d h e c r u sh -ing o rceswi thou ty ie ld ing .Thes e two requirementsdemand sp eci a l ma ter ia l andconcep tcons idera t ion .c i l l a t i n g (6 0 an d120 Hz) to rqu esdur ing a good pa r t oft h e a u l tp e r i o d .T h i s i s d u e o h e n t e r a c t i o no ft h e o t o rcu r r en t s w i t h h e r a p p e d o r r a n s i e n t d c )f l u x n h ea r m a t u r e .T h i s o r q u e i s p r o p o r t i o n a l ot h e a r m a t u r e a u l t cu r r e n t s and can h e r e f o r e b e h r e et o f o u r times t h e a t e d s t e a d ys t a t em a c h i n e o r q u e .I n t h i s c a s e , s p e c i a l c o n s i d e r a t i o n m ust b e g i v e n ot h em ech an i ca l n t eg r i t yo f h es h i e l das well as t ohow th is orq ue i s t r an s m i t t ed o h epr ime mover sh af t .

Thedamper shield i s a l s o s u b j e c t e d o a r g e OS-

Fie ld Wind ingandSupportStructures t r u c t u r e i s s u b j ec t ed oq u i t es ev e r e h e r m a lco n d i -t i o n s d u r i n g a nd a f t e r a f a u l t p e r i o d .a t ed w i t h h e a r m a t u r e f au l t cu r r en t sd i f f u s e h r o u g hth e dam?er s h i e l d n a time e q u a l o h e s u b t r a n s i e n tt i m e o n s t a n t .T h i s e a d s o n x p o n e n t i a l l y a i s i ngm ag n e t i c i e l d a t t h e f i e l d w i n d i n g h a t h e a t s h ef ie ldwind ingand i t s s u p p o r t s t r u c t u r e .

The superco nduct ing ieldwindingand i t s suppor t

D u r i n g h e f a u l t , h e a r g e m a g n e t i c f i e l d s a s s o c i -

I n a d d i t i o n , h e c r u s h i n g f o r c e s d u r i n g a f a u l tc a u s e r a d i a l d e f l e c t i o n of t h e s h i e l d h a t n u r n p ro -d u ces i m e v a r y i n gf i e l d swi th in he damper sh i e ld .T h i s e f f e c t ag a i n ead s o h ea t i n g n h e low t em pera -t u r e r e g i o n .A f t e r h e f a u l t i s c l e a r e d , h e o t o ru n d e r g o e s adamped mech an ic a l osc i l la t ion wi th a f r equencyofabout1Hz and a decayper iod of abou t1 0cy c l e s .Thesero to rswings epresen t he e tu rnof hem ach i n e os t ead y s t a t e with he ys tem.Dur ing he wings , her o t o r i s s u b j e c t e d o a 1 Hz ma gne tic f i e l d h a t c a np e n e t r a t e n t o h e f i e l d r e g i o n a n d g e n e r a t e s h e a t .

Decis ions nsuperconducto r des ign ,coo l ingandc o i l c o n s t r uc t i o n and f i e l d s u p p o r t s t r u c t u r e a r e a l li n t e r r e l a t e d an d c r i t i c a l l y a f f e c t e d by t h es eev en t s .The primecons idera t ion i s t h a t h e a t i n g n h e s u p e r c o n -d u c t o ro r n h e s u p p o r ts t r u c t u r e . w i . 1 1n o t e a d o t em -p e r a t u r e e x c u r s i o n s h a t r e s u l t n n o r m a l i z a t i o n o f h ewind ing .There r edes ign r ade-of f sbetween he l imitsofgoingwith a ver y low loss cab ledconducto rand 100%p o t t i n g of t h e co i l o h e o t h e r ex t r e m e o f a m o n o l i t h icco n d uc t o r w i t h a h i g h r e s i s t an ce matrix and hav ing ap a r t i a l l y o pe nwinding in o r d e r o a k e ad v an t ag e of t h eh igh spec i f ic hea t o f he l ium.

m i l e a l l of hepro to typemachineshaveusedm e t a l l i c i e l ds u p p o r ts t r u c t u r e s ,c o n s i d e r a t i o n nf u t u r e d e s i g n s m ust b e g i v e n o h e p o s s i b i l i t y o f u t i -l i z i n g n o n - m e t a l l i c c o m p o s i t e s f o r h i s s t r u c t u r e a n dt h u se l i m i n a t i n g h i ss o u r ce o f heat . I t s h o u l da l s ob ee v i d e n t h a t s p e c i a l a t t e n t i o n m ust b e d i r e c t e d o h ehelium management i n t h e low te mper ature eg ion s o t h a tt h e s t o r e d h e a t r e s u l t i n g f r o m a f a u l t w i l l be removedas q u i ck l yasp o s s i b l e .SuperconductorsMul t i f i l amenta ry NbTi superconducto r s have beent h e o n l y c h o i c e , u p u n t i l v e r y r e c e n t l y , f o r u t i l i z a t i o ni n h ep r o t o t y p em ach i n es an d o rd es i g ns t u d i e s o rlargerm ach i n es . Wit5 t h e s eco n d u c t o r s , a workingcur-r e n tden s i ty o f abou t l o 8 A/m2 a t 5 T wit h a thermalmargin of abou t 1 K a t 4 K c a nbe ea l iz ed . Howeverconducto rdevelopmentprograms n i t ia ted by th e USAF'and ERDA on NbgSn mu lt ifi la me nt ar y co nd uc to rs are nowunderway.This ypeof onductorpromiseshigher ur-r e n t d e n s i t i e s a t h i g h e r m a g n e t i c s f i e l d w i t h g r e a t e rthermalmarg ins .Fu turegenera to rprogramsmust aket h i s a t t r a c t i v e o p t i o n n t o c o n s i d e r a t i o n .

CONCLUSIONSThe prototypemachinedesignand t e s t s havepro-v i d ed a f ea s i b i l i t y d e m o n s t r a t i o nf o ra c s u p e r c o n d u c t -

i nggenera to r s .Largegenera to rdes ign tud ies ndcommercialevaluationhavegiven a c l e a r n d i c a t i o n o ft h e p o t e n t i a l e c h n i c a l an d eco no mi c b en e f i t s o b erea l ized .Addi t ionaldevelopmentwork emains obec a r r i e d o u t b e f o r e h i s c o n c e p t i s demons t r a ted ober e l i a b l e a ndeconomical lycompet i t ivewi thconven t ionalmachines.

REFEWNCES1. For a briefoverv iew of theseprograms ee , J. L.

Smith, J r . , J . K. K i r t l e y , J r . , andP.Thul ler ,I E E E Trans. on Magnetics MAG-11 (2) ,128 1975) .

2 . M . S . Baldwin nd C . . S t e r r e t t ,P r o c . of t h eAmerican Power Conference, 3 6 , 1036 (1974).3. M J . J e f f e r i e s , e t a l . , I EEE Trans. Power Appara-tu s and Systems,Vol. PAS-92 ( 5 ) , 1659 1973).

4 . Y . S. Chung, e t a l . , I EEE Trans. Power Apparatusan dSyste ms. PAS-93 (2 ). 496 (19 74) .5. C . K . Jones nd D. C: Li tz , Advances i n Cryogen icEngineer ing 1 9 , 441974).

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6 . R. D. Blaugher, T . J . Fagan, J. H. Par k e r , J r . ,J . M . Wells,and J . L. McCabr ia ,Proc .Fif th nter-nationalCryogenicEngineer ingConf . , Kyoto, Japan,143 1974) ; J . H. Par k e r , J r . , R . D. Blaugher ,A . Pa t t e r s o n , P . D . Vecchio, nd J . L . McCabria,I EEE Trans. on Magnetics , 640 (1975) ,Techn ica lRep ort APAPL-TR-74-84.J r . , "SuperconductingGeneratorDevelopment,Proc.NationalAerospaceElectronicConference 1975) ,Dayton,Ohio.and H. H. Woodson, Proc. I EEE 61 (1 ) 112 (1973).

7 . J. L . McCabria, R. D . Blaugher, nd J . H . Parker ,

8 . J. L. Smith, J r . , J . K. K i r t l e y , J r . , P . Thul len ,9. EPRI Co nt ra ct RF 429-1.

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