curtis turbine

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The Curtis Steam Turbine

Author(s): W. L. R. EmmetSource: Proceedings of the American Philosophical Society, Vol. 42, No. 172 (Jan. - Apr.,1903), pp. 68-84Published by: American Philosophical SocietyStable URL: http://www.jstor.org/stable/983643 .

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68 EMMET-THE CURTIS STEAM TURBINE. [April ,i. Yield ideals.2. Quality ideals.3. Seasonal ideals.4. Physical conformationdeals.5. Regional adaptationideals-as to climate, altitude,soil.6. Resistant deals-as to diseases and insects.The main improvementnd evolutionof agriculture re going tocome as theresultofgreater nd bettercrop yield and greaterandbetter nimal production. It is not to come primarily rom nven-tion, good roads, rural telephone, legislation, discussion ofeconomics. All these are merely ids. Increased crop and animalproductionare to come from two agencies: improvemnentn thecare that they receive; improvement n the plants and animalsthemselves. In otherwords,thenewagriculture s to be built uponthe combined resultsof bettercultivation nd betterbreeding. Sofar as thenew breeding is concerned, it is characterizedby perfectdefinitenessof purpose and effort, he stripping away of allarbitrarynd factitious tandards,the absence of speculativetheory

and the insistenceupon the great fact thatevery plant and animalhas individuality.CORNELL UNIVERSITY, ITHACA, N. Y.

THE CURTIS STEAM TURBINE.BY W. L. R. EMMET.(Read April 2, 1903.)

The developmentwhich this paper describes is based upon theoriginaltheories nd inventions f Mr. C. G. Curtis,ofNew York,whose ideas werefirstmade the subjectof patentapplication aboutI895. Since that time these inventions have been the subject ofexperimental nvestigation t Schenectady,underthe direction ofMr. Curtis and of theGeneral Electric Company's engineers; theobject of theseexperiments eing to establishdata and laws whichwould form basis for the correctdesign of commercialapparat"Us.The difficulties f such an investigation re very great. All newfactsmustbe establishedby the testsof differentmnachinesr partswhichare difficultnd expensiveto produce. About twoyearsago

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1903.] EMMET-THE CURTIS STEAM TURBINE. 69the results fthese xperimentsave us data which howedgreatcommercial ossibilities,nd sincethat imeworkhas goneonona large cale ntheproductionfcommercialmachines. The con-tracts or hesemachines owaggregate 30,000 H. P. in turbine-driven lectric eneratingnits, helargest ize so farbuilt being7500 H. P. Thusa great industryasbeen broughtntoexistencein a very hort ime, nd since theworkhas all been donein oneplaceandbya few ersons ery ittle nformationoncerningthasreached hepublic. This paper s thefirst rintedmatterwhichhasappeared n the ubject.

The reason orthis mmenise emand nd production, ithoutpublicitynd inso short time, s that the mprovementsffectedare radical neconorny,implicityndefficiencyf action.All improvementsn primemovers re of great mportanceotheengineeringorld. The steam urbinesdestined oeffecthefirst eally reatmprovementincethedaysof Watt, nd theformsof Curtis turbinehere describedmake the first reatstride nadvanceof other team ngines.Every fficientteam nginemnustrovidemeansbvwhich fairproportionftheexpansive orceofsteamcan be converted ntousefulwork. In theengines fJamesWatt nd hissuccessorshisresults accomplishednvarious egrees ythe pplication fpres-surefrom he steam to moving pistons. In steamturbinesheexpansive orcempartsmotion othe teamtself,ndthismotionis given up to a revolving art by mpacts f themoving teamupon t.The idea of the teamturbines quitesimple,nd is similarothat fthewater urbiner mpulsewheel. The practical ifficultywhich has heretoforereventedhe developmentf good steamturbinesies in theveryhighvelocitywhich teamcan impartoitselfnexpansion,nd thedifficultyn efficientlyransferringhismotion owheels tspeedspracticableor onstructionrpracticaluse. Steam xpandingrom50 poundsgaugepressure ersquareinch ntothe tmospheres capableof impartingo itself speed

of 2950feetper second, nd if it is expanded rom 50 poundsgauge pressurentoa 28-inch acuum t can attain velocity f40I0 feet ersecond. The spoutingvelocityfwaterdischargedfrom nozzlewithioo feethead is 8o feetper second. Thesefiguresllustratehevery adicaldifferencef conditionbetweenwater urbinesnd steamturbines. In both water nd steam ur-



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70 EMMET-THE CURTIS STEAM TURBINE. [April 2,bines thetheoreticalcondition of maximumeconomyexists whenthe et of fluidmoveswith a velocity equal to about twice thatofthevane against which it acts. In water-wheels his relation iseasily establishedunder all conditions,while with steam thetotalpowerproduces a velocityso high thatthe materials available forsimple wheelsand vanes are not capable of sustaining a properspeed relationto it underpracticable conditions.Before the appearanceof theCurtis urbine wopracticalmethodsof accomplishing fair economy had been devised, namely, theturbines f Carl De Laval, of Sweden, and of Hon. CharlesAlger-non Parsons,of England, both of which were broughtout morethanfifteen earsago.In the De Laval turbine he total powerof the steam s devotedto the productionof velocity n an expanding nozzle, whichpro-duces velocityveryefficiently. The jet so produced is deliveredagainsta set of vanes on a single wheel wlhich, y an ingeniousconstruction nd methodofsuspension, sadapted to operationat avery highperipheralvelocity. The veryhighrotative peed whichthisconstructionentails is made available fordynamo drivingbyveryperfectlymade spiral-cutgearswhicheffect ten-to-one peedreduction. The peripheralvelocity of the wheel in the largestDe Laval turbines s about I200 feetper second,while the velocitywhich energycan impartto steamis over 4000 feet per second.Thus thewheel fallsfar hortof thetheoretically conomical speed.In theParsons turbine he steam s carried in an axial directionthrough he pace provided, between succession ofinternalrevolv-ing cylinders nd external tationary ylinderswhichenclose them.Both the internal nd the externalcylindrical urfacesare coveredby manysuccessivecircles of vanes so arranged that thesteam hasto pass alternately hroughrows of moving and stationary anes.In passing throughthis turbinethe steam never acquires a speedwhich approaches the velocity which it attains in the De Lavalnozzle; but instead movesalong alternately, cquiring velocity bycxpansion,and partiallygiving it up by impactwith the movingvanes.Both of theseturbineshave attained some success,but neither,as thusfardeveloped, affords ufficientdvantage over the steamengine to cause any veryrapid or radical change in engineeringconditions.The important isadvantages of theDe Laval typeare, that t is



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1903.] EMMET-THE CURTIS STEAM TURBINE. 71limited by the imperfections f high-speedgearing, that its effi-ciency is not particularlyhigh,and that the design is not con-veniently pplicable to largesizes. The Parsonstype s principallylimited by the multiplicitynd weight of its parts,and the highcost ofconstruction.The Curtis turbineretains some of the features f its prede-cessors, but introducesnew ideas which make possiDle a muchlowerspeed, less weight,fewer nd simplerparts,highereconomy,less cost, and other mportant dvantages.The general arrangementof a turbine generating-unit f thistype is shown by the drawingswhich accompanythis paper. Itsfunctionsmaybe briefly escribedas follows, nd are illustrated ytheaccom-lpanyingut:

STEAM CHEST

NJOZZLEtMOVNGBLADESL((((((((((((((((E STAT/IONARY BLADESMOViNG BLADESSTATIONARYBLADESMOVING BL-ADE-S

L~~~~~oIAPHR APAGAM

MOVINVG"

BLA DES _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _MOWN G5LALADES DE ) ):K) )

Diagramof Nozzlesand Buckets n Curtis teamTurbine.



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72 EMIMET-THE CURTIS STEAM TURBINE. [April2,Velocity is imparted to the steam in an expanding nozzle sodesigned as to efficientlyonvertnearly all the expansive force,

between the pressure imits used, into velocity n thesteam itself.After eaving thenozzle, the steam passes successively hrough woor more lines of vanes on the moving element,which are placedalternatelywithreversedvanes on thestationary lement. In pass-ing successively hrough hesemoving and stationary lements,thevelocity acquired in the nozzle is fractionallyabstracted, andlargelygivenup to the moving element. Thus the steam is firstthrownagainst the first et of vanes of themoving element,andthenreboundsalternately rommoving to stationary anes until itis broughtnearly to rest. By this means a high steam velocity smade to efficientlympartmotionto a comparatively lowlymovingelement. The nozzle is generallymade up of manysections adja-cent to each other,so that the steampassesto thewheels n a broadbelt when all nozzle sectionsare in flow.This process of expansion in nozzle and subsequent abstractionof velocity by successive impacts with wheel vanes is generallyrepeated twoor more times,the devices foreach repetitionbeinggenerallydesignatedas a stage. There maybe variousnumbers fstages and variousnumbers f lines of movingvanes in each stage.The numberof stagesand the numberof lines of vanes in a stageare governed by the degree of expansion,the peripheralvelocityAhich is desirable or practicable, and by various conditions ofmechanicalexpediencv.Generally speaking, ower peripheral speeds entail more stages,more ines of vanesper stage, or both. Our general practice is toso divide up the steamexpansion,thatall stageshandle about equalpartsofthe totalpowerofthesteam.The losses and leakages of the earlier stages take the formofmoreheat or more steam for the later stages,and are thus n partregained. Much water of expansion,which might occasion lossby re-evaporation, s drained out of each stage into that whichsucceeds it.

The governing s effectedby successive closing of nozzles andconsequent narrowingof the active steam belt. The cut showspartof thenozzle open and part closed; the arrows howing spacefilledby live steam. In theprocessofgoverning, henozzles of thelaterstagesmayor maynotbe opened and closed so as to maintainan adjustment proportional to that of the firststage, which is



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1903.1 EMMET-THE CURTIS STEAM TURBINE. 73always the primary source of governing. Some improvement flight-load economy may be effectedby maintaining a relativeadjustmentof all nozzles; but in manycases the practical differ-ence in economy s not great,and automaticadjustmentof nozzleopening in later stages is dispensed with in the interest f sim-plicity. In some machines an approximate adjustment s main-tained by valves in laterstages, which open additional nozzles inresponse to increases of pressurebehind them. These are used asmuch for imiting he pressures n stage clhambers s formaintain-ing the light oad economy.

The principle of the Curtis steamturbine s susceptibleof appli-cation to a varietyof purposes Within the scope of this paper Iintend to give only a general idea concerning existingdesigns forits application to electric generators. Its development,even forthis purpose, s very recent, nd will doubtlessbe subjectto impor-tantfuturemprovements. In its present tate, however, t embod-ies many mportant dvantages,as has alreadybeen stated. Themost importantof these advantages is the high steam economywhich it affords niderverageconditionsof service. This economyis shown by the accompanying curves, which are derived fromactual testsof the first ommercialmachine of thistypewhich wasconmpleted. This machine drivesa dynamo of 6oo Kw. capacity.The curvesgive itsperformance t a speed of I500 R.P.M., whichis a safe and practical speed for commercialoperation, and whichcorrespondsto a peripheralvelocityof about 420 feetper second.The results,withsuperheat,given in these curves are not derivedactually from tests of this turbine, but are plotted from dataobtained on smaller turbines. They correspond to the resultsobtained on turbines f otlher ypes nd are undoubtedlyreliable.Curve i showsthe steamconsumption f thismachine in poundsper kilowatt-hour utput t various oads and under theconditionsstated,the lower curve giving the steam consumptionat variousloads with 150 degrees superheat.Curve 2 showstheresultswhichcould be obtained from histur-bine if it wereoperatedwith high pressureand a high degree ofsuperheat, hese conditions of operation being perfectly racticalwiththemachine,while with steamengines the use of such hightemperatures ould withordinary onstructions e prohibitive.The results hownby these curvesare betterthanany heretoforeproduced by steam turbines fany make or size, and are verymuch



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74 EMIMET---THE CURTIS STEAM TURBINE. pkpril2,betterthanthose obtainablefrom he typesof steamenginesgenerallypplied o theproductionfelectricity.It shouldbe noted hat hesecurves how a veryhigh fficiencyat light oads, as comparedwithresultsobtainablefrom teamengines,nd that heefficiencyoes not falloff t overload, s itmustnecessarilyo withall engineswhichoperate conomicallyundernormal ull-load onditions. This light-load nd overloadeconomys an importanteature f the Curtis urbine,ndarisesfrom hefact hat hefunctionsf itsworking artss virtuallyhesameunder ll conditionsf load.Curves3, 4 and 5 showthe effectpon steamconsumptionfchangesn the team ressure,hedegrees f superheatnd inthevacuum. It will be observedhat he uperheatndvacuum urvesare straightines o inclined s toindicate great dvantage y heuseof all degrees fsuperheatnd also an immense dvantage ntheuse ofveryhighvacuum. The most mportanteasonwhy heCurtis urbineo greatlyurpasseshe steamenginen economysthat t is adapted o use effectivelyhe highest ossible egreesofexpansion,while n thesteam ngine t is practicallympossibleoprovideforhigh degreesof expansion. As the exhaust ressureapproaches perfect acuum,he volumenaturallyncreases t arapidrate-thevolume f steamwitha 29"t vacuum eing doublethatwith 28" vacuum. To handlehighdegrees f expansion,twould, herefore,e necessaryo make cylindersf steam nginesvery arge, nd this ncreasefsizeandweight fparts ixes prac-tical imitwhich annotbe passedwithout xcessive ostandcom-plication. In theturbine,llehighest egreesof steamexpansionareeasilyprovided or, ndconsequently much arger roportionofthetotalworknsteam anbe utilized yturbineshanby teamengines.There reother onditionsntheCurtis urbine hichmakehighdegrees f vacuummore asily ttainable han hey reunder rdi-nary onditions. The machine s so constructedhat eakageofairintothevacuum hamber s easilyrendered mpossible. Theleakageof air into ondensing ngines s considerable,nd is gen-erallynot checkedowing o the smallvalue of improved acuumto an engine.With urbinesf thetypeheredescribed, o oil comes ntocon-tactwiththe steam,and consequentlyondensedwatercan betaken rom urfaceondensersndreturnedoboilers. Theuseof



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1903.] EMMET-THE CURTIS STEAM TURBINE. 76surface ondensersunder such conditions rendersunnecessary heintroduction f air either in feed or circulatingwater, and conse-quently makes possible a veryhighvacuumwith small air-pumpingapparatus.The results hown by these curves are obtained from machineof 6oo Kw. capacity, and are naturally nferior o resultswhich areexpected from hevery arge units which are now being built. Itis hoped thatverysoon after he reading of thispapera 5000 Kw.unit,whichis nowcomplete,will be put into operation n Chicago.This machine is expected to give considerably better steam econo-mies than are shownby theaccompanyingcurves, nd will be supe-rior particularly in the matter of light-load performance. Thevariationof efficiencyn this machine fromhalf load to fifty ercent. overload will not exceed threeper cent.The external appearance and dimensions of this5000 Kw. unitare shown by one of the drawings which accompany this paper,and another drawing shows this unit compared with an engine-drivengeneratingunit of similarcapacity. Each unit is shownascompletewithprimnemover and generator,one being themachineforChicago, above mentioned; theother,one of the units whichare operating in the Manhattan Railway Company's Power Sta-tion at New York. The comparison sufficientlyllustratestheimprovementwhich the turbine has introduced. The respectiveweightsof these completed units,exclusive of foundation, re inthe ratio of i: 8, and the saving in foundationsalone is a veryimportant item. Other drawings which accompany this papershowa 500 Kw. unitrecently nstalled at Newport, nd also a com-parisondrawn to the same scale between this 500 Kw. unit and acrosscompound engineunit of equal capacity designed to operateat ioo R.P.M. The contrasthere is evrenmorestriking.If the extremesimplicity f the Curtis turbine s considered incombinationwiththesefiguresnd comparisons, t is easy to appre-ciate thata very greatengineering dvance has been accomplished.It has been conservatively stimated that engine units, ike thosein theManhattanCompany's station,can be replaced by turbineslike that in Chicago, and that the cost of such replacement canbe paid forby saving in operating expensesin threeyears.Whenever an improvementhas been effected n prime movers,the influenceupon engineeringand business conditions has beenverymarked. When the release cut-off rinciple was introduced



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76 EMMET-THE CURTIS STEAM1TURBINE. [April ,by Corliss, a certain mprovementn engine ecolnomywas effected,and although this improvementwas accompanied by no diminu-tion in cost, the change resulted n a very great activity n enginebuilding, and the renewal of most of the large mill engines in thecountry. It is, therefore,afe to predict that the influence f thesteam turbinewill be of radical importance. The steamturbine s,on account of its high speed, particularly dapted to the drivingof electric generators, and its introduction will consequentlystimulate the use of electricityrather than other power trans-mitters.In the past themosteconomical use of steamhas been confinedto the most expensiveand elaborate plants,while in the futuretwill be withinthe reach ofall wherecondensingwater s available.

_ OComparativeizes f 000 Kw 75R P M Corhss Engine and 5000 Kw., 500 R.P.M. CurtisTurbine.

Comparative sizes of 5000 Kw., 75 R.P.M. Corliss Engine and 5000 Kw., 500 R.P.M, Curtis Turbine.

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1903.] EMMET-THE CURTIS STEAM TURBINE. 77

70 C Ct 1C C 1

~2 =-1: 1. s-~~~~~~~~~ ~ ~ ~ ~ ~ ~ Tii_ :

A _____f . 7>

Plan andElevation Of5000 Kw-,5oo R.P.M. CurtisTurbinewithGenerator.

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'78 EMMET-THE CURTIS STEAM TURBINE. [April ,

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a903.1 EMMET-TUE CURTIS STEAM TURBINE. 79

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80 EMMET-TTHE CURTIS STEAM TURBINE. FApril,

c a o3 ?C3 a .l ?

*k'00X'4 :CL :R:Smei7-

Plan and Elevationi of 5OO Kw., iSoo R.P.M. Curtis Turbine uAitli enerator.



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1903.] EMMET-THE CURTIS STEAM TURBINE. 81

Comparison f 500 Kw., Ioo R.P.M. Crosscompound ngineand 5OOKw., i8oo R.P.M.Curtis urbine.

PROC. AMER. PILILOS. SOC. XLII. 172. F. PRINTED MAY 27, 1903.



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82 EMMET-THE CURTIS STEAM TURBINE. [April ,

26

242.322

QJ,~~\

/00 200o 400_00 600 7000_ir1w.CURVE i.-Curve showingwater onsumption,n poundsperKw. hour, f6ooKw. Curtis SteamTurbine, peratingatI5oo R.P.M., with 40 lbs. gaugepressurend 28.51/ fvacuum_.iWithout uperheat.2 With 3500 F. superheat.



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1503.] EMMET-THE CURTIS STEAMI TURBINE. 83

22 _ _21

k20-19

/7

/00 200 300 400 500 600 700CURVE2.-Curve showingwater onsumption,npoundsperKw. hour,of 6ooKw. CurtisSteam Turbine,with differentoads; speed I500 R.P.M.;VaCUUm8.51; pressure 00 lbs. gauge,witlh5oO F. superheat.

621__-_- ]lllll1

/00 //0 120 /30 /40 /50 /60 /70 /60 /90 200/nitio/ Pressure (Gau3e)CURVE 3.--Curve showingwater onsumption,n poundsperKw. hour, f 6oo

Kw. CurtisSteqmTurbine, tfull oadwiihdifferentnitial ressures;speedI5oo R.P.M.; vacuum28.5"1.



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84 EMMET-THE CURTIS STEAM TURBINE. [April ,

20-__________1

t/7__________0 20 40 60 80 /00 /2o /40 /60&'perhet Degrees Fo-hr.CURVE4.--Curve showingwater onsumption,npoundsperKw. hour, f 6ooKw. Curtis Steam I'urbine,with differentegrees of superheatwhenoperating ith fullload at I500 R.P.M.; vacuum28.5/"; pressure 40 lbs.gauge.

27 -

25 -t24 _ __N__Q)23 ____\t22 _ _ _ - t21-20 -- N- - -

2/ 22 23 24 25 26 27 28 29Vaccuum Ins. MercuryCURVE 5.-Curve showingwater onsumption,n poundsperKw. hour, f 6ooKw. Curtis teamTurbine, t full oad withdifferentegrees of vacuum;speed I5oo R.P.M; steampressure40 lbs. gauge.

SCHENECTADY, N. V., APRIL 2, I903.

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