The 65,000-kv-a. generator of the Niagara Falls power company

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  • The 65,000-Kv-a. Generator of the Niagara Falls Power Company

    By W. J. FOSTER Fellow, . I. . E.

    AND A. E. GLASS Both of the General Electric Co., Schenectady, . Y.

    AT the close of t h e 19th cen tu ry a no t ab l e even t occurred a t N iaga ra Fa l l s ,the deve lopment of a p lan t for t h e ut i l iza t ion electrically of N i a g a r a

    power. Then , as now, N iaga ra Fal ls was recognized as the finest wa te r power in t he world, a c a t a r a c t of great height, fed from, t h e five G r e a t Lakes , cons t i t u t ing a water s torage w i thou t a r ival . I t was in keeping with t he s i tuat ion t h a t t h e first p l a n t was developed with m a m m o t h un i t s , m u c h larger t h a n had been dreamed of u p t o t h a t t ime . T h e y were 5000 horse power each, or, t r ans la ted in to electrical t e rms , 3750 kw., eleven of these un i t s unde r one roof.

    Almost exact ly twenty-five years la ter a genera tor with nominal r a t i ng of 65,000 kv-a . or one capable of 50 per cent greater o u t p u t t h a n t h e en t i re row of un i t s in the original power house, was p u t in to service. Th i s la tes t generator is t h e p r o d u c t of t h e experience gained dur ing t h e in tervening years , I t is three-phase , instead of two-phase ; i t is 12,000 vol ts , ins tead of 2200; i t is 80 per cent power factor, ins tead of un i ty -power factor; i t has high in ternal reac tance , ins tead of low; it has losses a t full-rated load equal t o approx imate ly 2 per cent of i ts ou tpu t , whereas t h e original h a d from 7 per cent t o 8 per cen t ; i t is of t he ' ' c o n v e n t i o n a l / ' internal-revolving field type , whereas t h e original h a d its field revolving outs ide of t h e a r m a t u r e ; i t suppor t s on i ts s ta tor , b y means of t h r u s t bear ing m o u n t e d a t the top , t h e ent i re weight of i t s own ro tor and t h e runner of t h e tu rb ine , whereas t he original had i t s revolving p a r t suppor ted from an oil-pressure s t ep bear ing located u n d e r n e a t h ; i t is located so close t o t h e tu rb ine t h a t i t h a s no lower guide bear ing of i t s own, whereas t h e original was some 150 ft. above t h e t u r b i n e with several guide bear ings in te rvening; i t is equipped with brakes t o br ing i t t o res t quickly, whereas t h e original had no means provided for br inging i t t o res t , except t he shu t t i ng off of t h e wa te r t o t h e t u rb ine ; i t contains approximate ly twen ty - th ree pounds of m a terial per kv-a. o u t p u t , whereas t h e original conta ined nearly fifty pounds .

    Although t h e q u a n t i t y of mater ia l in th is large generator is less t h a n a half t h a t of t h e original per kv-a., i t is ve ry large a s compared wi th a modern 60-cycle generator of large capac i ty a t t h e higher speeds t h a t are now common in hydraul ic deve lopments . There a re th ree reasons for th is genera tor hav ing such great weight as one and one-half million pounds of mater ia l ; first, t h e fact t h a t i t is low speed; second, i t

    To be -presented at the Spring Convention of the A. I. E. E.t Birmingham, Ala., April 7-11, 1924-

    is low per iodic i ty ; th i rd , i t was designed for t he highest economic efficiency.

    Regard ing t h e effect of ro t a t i ve speed on weight, i t m a y be said, t h a t for t h e same electrical character is t ics t h e lower t h e per ipheral speed, t h e grea ter t h e weight of magne t i c mate r ia l and copper, and t h a t t h e lower r o t a t i v e speed a lways requires a lower per ipheral speed to ob ta in t h e proper a d j u s t m e n t be tween t h e mater ia l t h a t m u s t be used for mechanical s t ruc tu re and t h a t which m u s t be used for t h e electrical pa r t s . In t h e case of th i s generator , t h e per ipheral speed is only 8200 ft. per minu te , whereas m a n y 50 and 60-cycle hydraul ic genera tors t h a t have been bui l t a t speeds from 200 t o 600 rev . per min . h a v e per ipheral speeds of 12,000 ft. per min. , or h igher ,some of t h e m as high as 15,000 ft. per min .

    W i t h regard t o t h e effect of per iodici ty on q u a n t i t y of ma t e r i a l ; a s suming same o u t p u t , same character istics, s ame ro t a t i ve speed and same per ipheral veloci ty , t h e to t a l magne t i c flux in t h e a i rgap m u s t be the same a t all periodicit ies, b u t t h e lower periodici ty mach ine has fewer poles a n d t h e flux l inked th rough a r m a t u r e from pole t o pole is in inverse ra t io t o the per iodic i ty , a 25-cycle mach ine hav ing 2.4 t imes t h a t of a 60-cycle; hence, a cross section of a r m a t u r e core t h a t m a n y t imes grea ter m u s t be provided. Former ly , t h e lower per iodici ty pe rmi t t ed of higher magnet ic densi t ies in t ee th and core of a r m a t u r e , b u t silicon steels h a v e been developed wi th such high quali t ies in t h e m a t t e r of hysteresis losses t h a t t h e lower periodici t y no longer has a n y a d v a n t a g e in th is respect . All periodicities u p to 60 cycles are worked a t as high s a tu r a t i on as permeabi l i ty allows. Again, t h e smaller n u m b e r of poles in t h e 25-cycle machine requires a m u c h grea ter radial d e p t h of pole for hea t dissipation reasons , a n d grea t ly increased cross section of t h e copper on t h e pole. For these reasons, t h e to ta l q u a n t i t y of magne t i c mate r ia l in t h e poles and the to t a l a m o u n t of copper in t h e field-winding are greater t h a n in t h e corresponding 60-cycle genera tor .

    W i t h reference t o increase in mater ia l t h a t was in t roduced in order t o o b t a i n t h e h ighes t economic efficiency, i t m a y be said, t h a t a s far as t e m p e r a t u r e s were concerned, t h e a m o u n t of copper in b o t h a r m a t u r e and field could have been reduced a t least 20 per cent , and t h e a m o u n t of magne t i c mate r ia l as m u c h as 10 per cent . In order t o ob ta in ext remely high efficiency, \t was necessary t o reduce several or all of t h e var ious Kinds of losses, windage, hysteresis and eddy current , - R -and load losses. T h e mos t i m p o r t a n t factor in

    3 6 5

  • 3 6 6 FOSTER A N D GLASS: 65,000-KV-A. GENERATORS Journal . I. . E.

    t h e windage losses is per iphera l speed; hence, i t is generally bes t t o select smaller d iameter , a l though i t resul ts in increased magne t i c mate r ia l and copper . Lower hysteresis a n d eddy losses m a y be obta ined b y working a t lower densi t ies; consequent ly , g rea te r a m o u n t of mater ia l m u s t be used in t h e magne t i c p a r t s . Lower I 2 R losses can be ob ta ined b y increasing t h e q u a n t i t y of copper . Load losses can be k e p t lower b y conservat ive design in t h e m a t t e r of a r m a t u r e react ion, b u t t h e size of t h e mach ine is increased b y reason of t h e lower a r m a t u r e react ion.

    T h e electrical character is t ics of th i s genera tor a re in accord wi th w h a t is regarded a s bes t for power-producing purposes in large sys tems . T h e ampere t u r n s a t no load, 12,000 vol ts , a re a lmos t ident ical ly t h e same as required for r a t ed cur ren t on short-circui t .

    T h e calculated a r m a t u r e reac tance is 26 per cent . Unusua l features in t h e electrical design are t h e

    low po in t on sa tu ra t i on curve a t r a t ed vol tage, m a d e necessary b y t h e r equ i remen t of opera t ing cont inuously a t 13,200 vol ts , 68,250 kv-a . 80 per cent power factor, and t h e ve ry low-current densit ies a t which copper is working, approx imate ly 1300 a m -

    largest ever bui l t , would in itself be sufficient justificat ion for describing it , b u t in addi t ion , i t conta ins a few features t h a t a re ent i rely new, as far as t h e wri ters of th i s pape r know. M a n y large vert ical hydraul ic un i t s h a v e a l ready been bui l t , due to t he ever increasing dem a n d for power and to t h e greater simplicity and econo m y in power houses a n d auxil iary a p p a r a t u s t h u s ob ta ined . T h e pr incipal p a r t s of such large genera tors m a y be s t a t ed as s t a to r f rame; s t a to r core; s t a to r winding; shaft ; ro to r spider; poles; field coils; uppe r

    0 1000 2000 3000 . 4000 5000 6000 AMPERES ARMATURE

    FIG. 2 F I E L D CHARACTERISTIC CURVES A 100 per c e n t P o w e r F a c t o r 12 ,000 V o l t s 65 ,000 k v - a . BBi 80 " " " " 12 ,000 " 65 ,000 k v - a . C C i 80 " " " " * 13 ,200 " 6 8 , 2 5 0 k v - a .

    AMPERES FIELD

    FIG. 1 T H E 6 5 , 0 0 0 K V - A . GENERATOR OF THE NIAGARA FALLS POWER Co.

    Sa tura t ion C u r v e s AOpen Circu i t Full L o a d Current 100 per c e n t P o w e r F a c t o r C " " " 8 0 " D " " " zero " "

    peres per square inch in a r m a t u r e and 1100 in field, in order t o ob ta in t h e ve ry high efficiency.

    Fig . 1 conta ins Curves of no load, 100 per cent a n d 80 per cent power factor full-load sa tu ra t ion .

    Fig . 2 shows Curves of Field Charac ter i s t ics for th ree condit ions, viz., 100 per cent power factor, 65,000 kv-a. , 12,000 vo l t s ; 80 per cen t power factor, 65,000 kv-a. , 12,000 vol ts and 80 per cent power factor, 68,250 kv-a. , 13,200 vol t s .

    T h e fact t h a t th is genera tor is, for t h e t ime being, t h e

    bear ings ' spider; bear ings ; oiling sys tem; collector r ings . The re are numerous detai l p a r t s in connection wi th every one of these major p a r t s t h a t are of ext reme impor t ance a n d w o r t h y of descript ion. Before t ak ing u p t h e major p a r t s in order, we call a t t en t i on to Fig. 3, which shows t h e general a r r angemen t of t h e generator , t h e s t a to r supp