Steam turbine

The rotor of a modern steam turbine used in a power plant

A steam turbine is a device that extracts thermal energyfrom pressurized steam and uses it to do mechanical workon a rotating output shaft. Its modern manifestation wasinvented by Sir Charles Parsons in 1884.[1]

Because the turbine generates rotary motion, it is partic-ularly suited to be used to drive an electrical generator about 90% of all electricity generation in the UnitedStates (1996) is by use of steam turbines.[2] The steamturbine is a form of heat engine that derives much of itsimprovement in thermodynamic eciency from the useof multiple stages in the expansion of the steam, whichresults in a closer approach to the ideal reversible expan-sion process.

1 History

A 250 kW industrial steam turbine from 1910 (right) directlylinked to a generator (left).

The rst device that may be classied as a reaction steam

turbine was little more than a toy, the classic Aeolipile,described in the 1st century by Greek mathematicianHero ofAlexandria in Roman Egypt.[3][4][5] In 1551, Taqial-Din in Ottoman Egypt described a steam turbine withthe practical application of rotating a spit. Steam tur-bines were also described by the Italian Giovanni Branca(1629)[6] and JohnWilkins in England (1648).[7] The de-vices described by Taqi al-Din and Wilkins are todayknown as steam jacks.The modern steam turbine was invented in 1884 by SirCharles Parsons, whose rst model was connected to adynamo that generated 7.5 kW (10 hp) of electricity.[8]The invention of Parsons steam turbine made cheapand plentiful electricity possible and revolutionized ma-rine transport and naval warfare.[9] Parsons design wasa reaction type. His patent was licensed and the turbinescaled-up shortly after by an American, George Westing-house. The Parsons turbine also turned out to be easy toscale up. Parsons had the satisfaction of seeing his in-vention adopted for all major world power stations, andthe size of generators had increased from his rst 7.5kW set up to units of 50,000 kW capacity. Within Par-sons lifetime, the generating capacity of a unit was scaledup by about 10,000 times,[10] and the total output fromturbo-generators constructed by his rm C. A. Parsonsand Company and by their licensees, for land purposesalone, had exceeded thirty million horse-power.[8]

A number of other variations of turbines have been de-veloped that work eectively with steam. The de Lavalturbine (invented by Gustaf de Laval) accelerated thesteam to full speed before running it against a turbineblade. De Lavals impulse turbine is simpler, less expen-sive and does not need to be pressure-proof. It can op-erate with any pressure of steam, but is considerably lessecient. fr:Auguste Rateau developed a pressure com-pounded impulse turbine using the de Laval principle asearly as 1900, obtained a US patent in 1903, and appliedthe turbine to a French torpedo boat in 1904. He taught atthe cole des mines de Saint-tienne for a decade until1897, and later founded a successful company that wasincorporated into the Alstom rm after his death. Oneof the founders of the modern theory of steam and gasturbines was Aurel Stodola, a Slovak physicist and en-gineer and professor at the Swiss Polytechnical Institute(now ETH) in Zurich. His work Die Dampfturbinen undihre Aussichten als Wrmekraftmaschinen (English: TheSteam Turbine and its prospective use as a MechanicalEngine) was published in Berlin in 1903. A further bookDampf und Gas-Turbinen (English: Steam and Gas Tur-

1

2 2 TYPES

bines) was published in 1922.The Brown-Curtis turbine, an impulse type, which hadbeen originally developed and patented by the U.S. com-pany International Curtis Marine Turbine Company, wasdeveloped in the 1900s in conjunction with John Brown& Company. It was used in John Brown-engined mer-chant ships and warships, including liners and Royal Navywarships.

2 TypesSteam turbines aremade in a variety of sizes ranging fromsmall

2.3 Casing or shaft arrangements 3

turned to the boilers. On the left are several additionalreaction stages (on two large rotors) that rotate the tur-bine in reverse for astern operation, with steam admittedby a separate throttle. Since ships are rarely operated inreverse, eciency is not a priority in astern turbines, soonly a few stages are used to save cost.

2.2 Steam supply and exhaust conditions

A low-pressure steam turbine working below atmospheric pres-sure in a nuclear power plant

These types include condensing, non-condensing, reheat,extraction and induction.Condensing turbines are most commonly found in elec-trical power plants. These turbines exhaust steam from aboiler in a partially condensed state, typically of a qualitynear 90%, at a pressure well below atmospheric to acondenser.Non-condensing or back pressure turbines are mostwidely used for process steam applications. The exhaustpressure is controlled by a regulating valve to suit theneeds of the process steam pressure. These are com-monly found at reneries, district heating units, pulpand paper plants, and desalination facilities where largeamounts of low pressure process steam are needed.Reheat turbines are also used almost exclusively in elec-trical power plants. In a reheat turbine, steam ow ex-its from a high pressure section of the turbine and is re-turned to the boiler where additional superheat is added.The steam then goes back into an intermediate pressuresection of the turbine and continues its expansion. Us-ing reheat in a cycle increases the work output from theturbine and also the expansion reaches conclusion beforethe steam condenses, there by minimizing the erosion ofthe blades in last rows. In most of the cases, maximumnumber of reheats employed in a cycle is 2 as the cost ofsuper-heating the steam negates the increase in the workoutput from turbine.Extracting type turbines are common in all applications.In an extracting type turbine, steam is released from var-ious stages of the turbine, and used for industrial process

needs or sent to boiler feedwater heaters to improve over-all cycle eciency. Extraction ows may be controlledwith a valve, or left uncontrolled.Induction turbines introduce low pressure steam at an in-termediate stage to produce additional power.

2.3 Casing or shaft arrangements

These arrangements include single casing, tandem com-pound and cross compound turbines. Single casing unitsare the most basic style where a single casing and shaftare coupled to a generator. Tandem compound are usedwhere two or more casings are directly coupled togetherto drive a single generator. A cross compound turbinearrangement features two or more shafts not in line driv-ing two or more generators that often operate at dierentspeeds. A cross compound turbine is typically used formany large applications.

2.4 Two-ow rotors

A two-ow turbine rotor. The steam enters in the middle of theshaft, and exits at each end, balancing the axial force.

The moving steam imparts both a tangential and axialthrust on the turbine shaft, but the axial thrust in a simpleturbine is unopposed. To maintain the correct rotor posi-tion and balancing, this force must be counteracted by anopposing force. Thrust bearings can be used for the shaftbearings, the rotor can use dummy pistons, it can be dou-ble ow- the steam enters in the middle of the shaft andexits at both ends, or a combination of any of these. In adouble ow rotor, the blades in each half face oppositeways, so that the axial forces negate each other but thetangential forces act together. This design of rotor is alsocalled two-ow, double-axial-ow, or double-exhaust.This arrangement is common in low-pressure casings ofa compound turbine.[14]

4 3 PRINCIPLE OF OPERATION AND DESIGN

3 Principle of operation and designAn ideal steam turbine is considered to be an isentropicprocess, or constant entropy process, in which the entropyof the steam entering the turbine is equal to the entropyof the steam leaving the turbine. No steam turbine istruly isentropic, however, with typical isentropic ecien-cies ranging from 2090% based on the application ofthe turbine. The interior of a turbine comprises severalsets of blades or buckets. One set of stationary blades isconnected to the casing and one set of rotating blades isconnected to the shaft. The sets intermesh with certainminimum clearances, with the size and conguration ofsets varying to eciently exploit the expansion of steamat each stage.

3.1 Turbine eciency

To maximize turbine eciency the steam is expanded,doing work, in a number of stages. These stages are char-acterized by how the energy is extracted from them andare known as either impulse or reaction turbines. Moststeam turbines use a mixture of the reaction and impulsedesigns: each stage behaves as either one or the other, butthe overall turbine uses both. Typically, higher pressuresections are reaction type and lower pressure stages areimpulse type.

3.1.1 Impulse turbines

A selection of impulse turbine blades

An impulse turbine has xed nozzles that orient the steamow into high speed jets. These jets contain signi-cant kinetic energy, which is converted into shaft rota-tion by the bucket-like shaped rotor blades, as the steamjet changes direction. A pressure drop occurs across onlythe stationary blades, with a net increase in steam velocityacross the stage. As the steam ows through the nozzle itspressure falls from inlet pressure to the exit pressure (at-mospheric pressure, or more usually, the condenser vac-uum). Due to this high ratio of expansion of steam, thesteam leaves the nozzle with a very high velocity. Thesteam leaving the moving blades has a large portion ofthe maximum velocity of the steamwhen leaving the noz-

zle. The loss of energy due to this higher exit velocity iscommonly called the carry over velocity or leaving loss.The law of moment of momentum states that the sum ofthe moments of external forces acting on a uid which istemporarily occupying the control volume is equal to thenet time change of angular momentum ux through thecontrol volume.The swirling uid enters the control volume at radius r1with tangential velocity Vw1 and leaves at radius r2 withtangential velocity Vw2 .

Velocity triangle

A velocity triangle paves the way for a better understand-ing of the relationship between the various velocities. Inthe adjacent gure we have:

V1 and V2 are the absolute velocities at the inletand outlet respectively.Vf1 and Vf2 are the ow velocities at the inletand outlet respectively.Vw1+U and Vw2 are the swirl velocities at theinlet and outlet respectively.

3.1 Turbine eciency 5

Vr1 and Vr2 are the relative velocities at the in-let and outlet respectively.U1 and U2 are the velocities of the blade at theinlet and outlet respectively. is the guide vane angle and is the bladeangle.

Then by the law of moment of momentum, the torque onthe uid is given by:T = _m(r2Vw2 r1Vw1)For an impulse steam turbine: r2 = r1 = r . Therefore,the tangential force on the blades is Fu = _m(Vw1Vw2). The work done per unit time or power developed: W =T ! .When is the angular velocity of the turbine, then theblade speed is U = ! r . The power developed is thenW = _mU(Vw) .Blade eciencyBlade eciency ( b ) can be dened as the ratio of thework done on the blades to kinetic energy supplied to theuid, and is given byb =

Work DoneKinetic Energy Supplied =

2UVwV 21

Stage eciency

Convergent-divergent nozzle

Graph depicting eciency of Impulse turbine

A stage of an impulse turbine consists of a nozzle set and amoving wheel. The stage eciency denes a relationshipbetween enthalpy drop in the nozzle and work done in thestage.stage =

Work done on bladeEnergy supplied per stage =

UVwh

Where h = h2 h1 is the specic enthalpy drop ofsteam in the nozzle.By the rst law of thermodynamics: h1+ V

21

2 = h2+V 222

Assuming that V1 is appreciably less than V2 , we geth V

22

2 Furthermore, stage eciency is the product of bladeeciency and nozzle eciency, or stage = b NNozzle eciency is given by N = V

22

2(h1h2) , where theenthalpy (in J/Kg) of steam at the entrance of the nozzleis h1 and the enthalpy of steam at the exit of the nozzleis h2 . Vw = Vw1 (Vw2) Vw = Vw1 + Vw2Vw = Vr1 cos1 + Vr2 cos2Vw = Vr1 cos1(1+Vr2 cos 2Vr1 cos 1 )

The ratio of the cosines of the blade angles at the outletand inlet can be taken and denoted c = cos 2cos 1 . The ra-tio of steam velocities relative to the rotor speed at theoutlet to the inlet of the blade is dened by the frictioncoecient k = Vr2Vr1 .k < 1 and depicts the loss in the relative velocity due tofriction as the steam ows around the blades ( k = 1 forsmooth blades).b =

2UVwV 21

= 2U(cos1U/V1)(1+kc)V1The ratio of the blade speed to the absolute steam velocityat the inlet is termed the blade speed ratio = UV1b is maximum when dbd = 0 or, dd (2cos1 2(1 +kc)) = 0 . That implies = cos12 and therefore UV1 =cos12 . Now opt = UV1 =

cos12 (for a single stage

impulse turbine)Therefore the maximum value of stage eciency is ob-tained by putting the value of UV1 =

cos12 in the expres-

sion of b /We get: (b)max = 2( cos1 2)(1 + kc) =cos2 1(1+kc)

2 .For equiangular blades, 1 = 2 , therefore c = 1 , andwe get (b)max = cos

21(1+k)2 . If the friction due to the

blade surface is neglected then (b)max = cos2 1 .Conclusions on maximum eciency(b)max = cos2 11. For a given steam velocity work done per kg of steamwould be maximum when cos2 1 = 1 or 1 = 0 .2. As 1 increases, the work done on the blades reduces,but at the same time surface area of the blade reduces,therefore there are less frictional losses.

3.1.2 Reaction turbines

In the reaction turbine, the rotor blades themselves are ar-ranged to form convergent nozzles. This type of turbinemakes use of the reaction force produced as the steam ac-celerates through the nozzles formed by the rotor. Steamis directed onto the rotor by the xed vanes of the stator.

6 3 PRINCIPLE OF OPERATION AND DESIGN

It leaves the stator as a jet that lls the entire circumfer-ence of the rotor. The steam then changes direction andincreases its speed relative to the speed of the blades. Apressure drop occurs across both the stator and the rotor,with steam accelerating through the stator and decelerat-ing through the rotor, with no net change in steam velocityacross the stage but with a decrease in both pressure andtemperature, reecting the work performed in the drivingof the rotor.Blade eciencyEnergy input to the blades in a stage:E = h is equal to the kinetic energy supplied to thexed blades (f) + the kinetic energy supplied to the mov-ing blades (m).Or, E = enthalpy drop over the xed blades, hf + en-thalpy drop over the moving blades,hm .The eect of expansion of steam over the moving bladesis to increase the relative velocity at the exit. Thereforethe relative velocity at the exit Vr2 is always greater thanthe relative velocity at the inlet Vr1 .In terms of velocities, the enthalpy drop over the movingblades is given by:hm =

V 2r2V 2r12

(it contributes to a change in static pressure)The enthalpy drop in the xed blades, with the assump-tion that the velocity of steam entering the xed bladesis equal to the velocity of steam leaving the previouslymoving blades is given by:

Velocity diagram

hf = V21 V 202 where V0 is the inlet velocity of steam in

the nozzleV0 is very small and hence can be neglectedTherefore,hf = V

21

2

E = hf +hm

E =V 212 +

V 2r2V 2r12

A very widely used design has half degree of reactionor 50% reaction and this is known as Parsons turbine.

This consists of symmetrical rotor and stator blades. Forthis turbine the velocity triangle is similar and we have:1 = 2 , 1 = 2V1 = Vr2 , Vr1 = V2Assuming Parsons turbine and obtaining all the expres-sions we getE = V 21 V

2r1

2

From the inlet velocity triangle we have V 2r1 =V 21 + U

2 2UV1 cos1E = V 21 V

21

2 U2

2 +2UV1 cos1

2

E =V 21 U2+2UV1 cos1

2

Work done (for unit mass ow per second): W =U Vw = U (2 V1 cos1 U)Therefore the blade eciency is given byb =

2U(2V1 cos1U)V 21 U2+2V1U cos1

Condition of maximum blade eciency

Comparing Eciencies of Impulse and Reaction turbines

If = UV1 , then

(b)max =2(cos1)

V 21 U2+2UV1 cos1

For maximum eciency dbd = 0 , we get(1 2 + 2 cos1)(4 cos1 4) 2(2 cos1 )(2+ 2 cos1) = 0and this nally gives opt = UV1 = cos1Therefore (b)max is found by putting the value of =cos1 in the expression of blade eciency(b)reaction =

2 cos2 11+cos2 1

(b)impulse = cos2 1

3.2 Operation and maintenanceBecause of the high pressures used in the steam circuitsand the materials used, steam turbines and their casingshave high thermal inertia. When warming up a steam tur-bine for use, the main steam stop valves (after the boiler)have a bypass line to allow superheated steam to slowly

3.4 Thermodynamics of steam turbines 7

A modern steam turbine generator installation

bypass the valve and proceed to heat up the lines in thesystem along with the steam turbine. Also, a turning gearis engaged when there is no steam to slowly rotate theturbine to ensure even heating to prevent uneven expan-sion. After rst rotating the turbine by the turning gear,allowing time for the rotor to assume a straight plane (nobowing), then the turning gear is disengaged and steamis admitted to the turbine, rst to the astern blades thento the ahead blades slowly rotating the turbine at 1015RPM (0.170.25 Hz) to slowly warm the turbine. Thewarm up procedure for large steam turbines may exceedten hours.[15]

During normal operation, rotor imbalance can lead to vi-bration, which, because of the high rotation velocities,could lead to a blade breaking away from the rotor andthrough the casing. To reduce this risk, considerableeorts are spent to balance the turbine. Also, turbinesare run with high quality steam: either superheated (dry)steam, or saturated steam with a high dryness fraction.This prevents the rapid impingement and erosion of theblades which occurs when condensed water is blastedonto the blades (moisture carry over). Also, liquid wa-ter entering the blades may damage the thrust bearingsfor the turbine shaft. To prevent this, along with controlsand baes in the boilers to ensure high quality steam,condensate drains are installed in the steam piping lead-ing to the turbine.Maintenance requirements of modern steam turbines aresimple and incur low costs (typically around $0.005 perkWh);[15] their operational life often exceeds 50 years.[15]

3.3 Speed regulation

The control of a turbine with a governor is essential, asturbines need to be run up slowly to prevent damage andsome applications (such as the generation of alternatingcurrent electricity) require precise speed control.[16] Un-controlled acceleration of the turbine rotor can lead to anoverspeed trip, which causes the nozzle valves that con-trol the ow of steam to the turbine to close. If this failsthen the turbine may continue accelerating until it breaks

Diagram of a steam turbine generator system

apart, often catastrophically. Turbines are expensive tomake, requiring precision manufacture and special qual-ity materials.During normal operation in synchronization with theelectricity network, power plants are governed with a vepercent droop speed control. This means the full loadspeed is 100% and the no-load speed is 105%. This isrequired for the stable operation of the network with-out hunting and drop-outs of power plants. Normally thechanges in speed are minor. Adjustments in power outputare made by slowly raising the droop curve by increasingthe spring pressure on a centrifugal governor. Generallythis is a basic system requirement for all power plants be-cause the older and newer plants have to be compatible inresponse to the instantaneous changes in frequency with-out depending on outside communication.[17]

3.4 Thermodynamics of steam turbinesThe steam turbine operates on basic principles ofthermodynamics using the part 3-4 of the Rankine cycleshown in the adjoining diagram. Superheated vapor (ordry saturated vapor, depending on application) enters theturbine, after it having exited the boiler, at high temper-ature and high pressure. The high heat/pressure steam isconverted into kinetic energy using a nozzle (a xed noz-zle in an impulse type turbine or the xed blades in a reac-tion type turbine). Once the steam has exited the nozzle itis moving at high velocity and is sent to the blades of theturbine. A force is created on the blades due to the pres-sure of the vapor on the blades causing them to move. Agenerator or other such device can be placed on the shaft,and the energy that was in the vapor can now be storedand used. The gas exits the turbine as a saturated vapor(or liquid-vapor mix depending on application) at a lowertemperature and pressure than it entered with and is sentto the condenser to be cooled.[18] If we look at the rstlaw we can nd an equation comparing the rate at which

8 4 DIRECT DRIVE

T-s diagram of a superheated Rankine cycle

work is developed per unit mass. Assuming there is noheat transfer to the surrounding environment and that thechange in kinetic and potential energy is negligible whencompared to the change in specic enthalpy we come upwith the following equation

_W

_m= h3 h4

where

is the rate at which work is developed per unittime

is the rate of mass ow through the turbine

3.4.1 Isentropic eciency

To measure how well a turbine is performing we can lookat its isentropic eciency. This compares the actual per-formance of the turbine with the performance that wouldbe achieved by an ideal, isentropic, turbine.[19] When cal-culating this eciency, heat lost to the surroundings isassumed to be zero. The starting pressure and tempera-ture is the same for both the actual and the ideal turbines,but at turbine exit the energy content ('specic enthalpy')for the actual turbine is greater than that for the ideal tur-bine because of irreversibility in the actual turbine. Thespecic enthalpy is evaluated at the same pressure for theactual and ideal turbines in order to give a good compar-ison between the two.The isentropic eciency is found by dividing the actualwork by the ideal work.[19]

t =h3 h4h3 h4s

where

h3 is the specic enthalpy at state three

h4 is the specic enthalpy at state four for the actualturbine

h4s is the specic enthalpy at state four for the isen-tropic turbine

4 Direct drive

A direct-drive 5 MW steam turbine fueled with biomass

Electrical power stations use large steam turbines driv-ing electric generators to produce most (about 80%) ofthe worlds electricity. The advent of large steam tur-bines made central-station electricity generation practi-cal, since reciprocating steam engines of large rating be-came very bulky, and operated at slow speeds. Mostcentral stations are fossil fuel power plants and nuclearpower plants; some installations use geothermal steam, oruse concentrated solar power (CSP) to create the steam.Steam turbines can also be used directly to drive largecentrifugal pumps, such as feedwater pumps at a thermalpower plant.The turbines used for electric power generation are mostoften directly coupled to their generators. As the gen-erators must rotate at constant synchronous speeds ac-cording to the frequency of the electric power system, themost common speeds are 3,000 RPM for 50 Hz systems,and 3,600 RPM for 60 Hz systems. Since nuclear reac-tors have lower temperature limits than fossil-red plants,with lower steam quality, the turbine generator sets maybe arranged to operate at half these speeds, but with four-pole generators, to reduce erosion of turbine blades.[20]

5.1 Early development 9

5 Marine propulsionTSS and Turbine Steam Ship redirect here. For otheruses, see TSS (disambiguation).In steam-powered ships, compelling advantages of steam

The Turbinia, 1894, the rst steam turbine-powered ship

Parsons turbine from the 1928 Polish destroyer ORP Wicher.

turbines over reciprocating engines are smaller size, lowermaintenance, lighter weight, and lower vibration. Asteam turbine is only ecient when operating in the thou-sands of RPM, while the most eective propeller designsare for speeds less than 300 RPM; consequently, precise(thus expensive) reduction gears are usually required, al-though numerous early ships through World War I, suchas Turbinia, had direct drive from the steam turbines tothe propeller shafts. Another alternative is turbo-electrictransmission, in which an electrical generator run by thehigh-speed turbine is used to run one or more slow-speedelectric motors connected to the propeller shafts; preci-sion gear cutting may be a production bottleneck duringwartime. Turbo-electric drive was most used in large USwarships designed during World War I and in some fastliners, and was used in some troop transports and mass-production destroyer escorts in World War II. The pur-chase cost of turbines is oset by much lower fuel andmaintenance requirements and the small size of a tur-bine when compared to a reciprocating engine havingan equivalent power. However, from the 1950s dieselengines were capable of greater reliability and highereciencies: propulsion steam turbine cycle eciencieshave yet to break 50%, yet diesel engines today routinelyexceed 50%, especially in marine applications.[21][22][23]Diesel power plants also have lower operating costs since

fewer operators are required. Thus, conventional steampower is used in very few new ships. An exception isLNG carriers which often nd it more ecient to useboil-o gas with a steam turbine than to re-liquify it.Nuclear-powered ships and submarines use a nuclear re-actor to create steam for turbines. Nuclear power is oftenchosen where diesel power would be impractical (as insubmarine applications) or the logistics of refuelling posesignicant problems (for example, icebreakers). It hasbeen estimated that the reactor fuel for the Royal Navy'sVanguard class submarine is sucient to last 40 circum-navigations of the globe potentially sucient for thevessels entire service life. Nuclear propulsion has onlybeen applied to a very few commercial vessels due to theexpense of maintenance and the regulatory controls re-quired on nuclear systems and fuel cycles.

5.1 Early development

The development of steam turbine marine propulsionfrom 1894-1935 was dominated by the need to reconcilethe high ecient speed of the turbine with the low e-cient speed (less than 300 rpm) of the ships propeller atan overall cost competitive with reciprocating engines. In1894, ecient reduction gears were not available for thehigh powers required by ships, so direct drive was neces-sary. In the Turbinia, which has direct drive to each pro-peller shaft, the ecient speed of the turbine was reducedafter initial trials by directing the steam ow through allthree direct drive turbines (one on each shaft) in series,probably totaling around 200 turbine stages operating inseries. Also, there were three propellers on each shaft foroperation at high speeds.[24] The high shaft speeds of theera are represented by one of the rst US turbine-powereddestroyers, USS Smith (DD-17), launched in 1909, whichhad direct drive turbines and whose three shafts turned at724 rpm at 28.35 knots.[25] The use of turbines in severalcasings exhausting steam to each other in series becamestandard in most subsequent marine propulsion applica-tions, and is a form of cross-compounding. The rst tur-bine was called the high pressure (HP) turbine, the lastturbine was the low pressure (LP) turbine, and any turbinein between was an intermediate pressure (IP) turbine. Amuch later arrangement than Turbinia can be seen on theRMS Queen Mary in Long Beach, California, launchedin 1934, in which each shaft is powered by four turbinesin series connected to the ends of the two input shafts ofa single-reduction gearbox. They are the HP, 1st IP, 2ndIP, and LP turbines.

5.2 Cruising machinery and gearing

The quest for economy was even more important whencruising speeds were considered. Cruising speed isroughly 50% of a warships maximum speed and 20-25%of its maximum power level. This would be a speed used

10 5 MARINE PROPULSION

on long voyages when fuel economy is desired. Althoughthis brought the propeller speeds down to an ecientrange, turbine eciency was greatly reduced, and earlyturbine ships had poor cruising ranges. A solution thatproved useful through most of the steam turbine propul-sion era was the cruising turbine. This was an extra tur-bine to add even more stages, at rst attached directly toone or more shafts, exhausting to a stage partway alongthe HP turbine, and not used at high speeds. As reduc-tion gears became available around 1911, some ships, no-tably the USS Nevada (BB-36), had them on cruising tur-bines while retaining direct drive main turbines. Reduc-tion gears allowed turbines to operate in their ecientrange at a much higher speed than the shaft, but were ex-pensive to manufacture.Cruising turbines competed at rst with reciprocating en-gines for fuel economy. An example of the retentionof reciprocating engines on fast ships was the famousRMS Titanic of 1911, which along with her sisters RMSOlympic and HMHS Britannic had triple-expansion en-gines on the two outboard shafts, both exhausting to anLP turbine on the center shaft. After adopting turbineswith the Delaware-class battleships launched in 1909, theUnited States Navy reverted to reciprocating machineryon the New York-class battleships of 1912, then wentback to turbines on Nevada in 1914. The lingering fond-ness for reciprocating machinery was because the USNavy had no plans for capital ships exceeding 21 knotsuntil after World War I, so top speed was less impor-tant than economical cruising. The United States had ac-quired the Philippines and Hawaii as territories in 1898,and lacked the British Royal Navy's worldwide networkof coaling stations. Thus, the US Navy in 1900-1940 hadthe greatest need of any nation for fuel economy, espe-cially as the prospect of war with Japan arose followingWorld War I. This need was compounded by the US notlaunching any cruisers 1908-1920, so destroyers were re-quired to perform long-range missions usually assigned tocruisers. So, various cruising solutions were tted on USdestroyers launched 1908-1916. These included small re-ciprocating engines and geared or ungeared cruising tur-bines on one or two shafts. However, once fully gearedturbines proved economical in initial cost and fuel theywere rapidly adopted, with cruising turbines also includedon most ships. Beginning in 1915 all new Royal Navy de-stroyers had fully geared turbines, and the United Statesfollowed in 1917.In the Royal Navy, speed was a priority until the Battleof Jutland in mid-1916 showed that in the battlecruiserstoo much armour had been sacriced in its pursuit. TheBritish used exclusively turbine-powered warships from1906. Because they recognized that a signicant cruis-ing range would be desirable given their world-wide em-pire, some warships, notably the Queen Elizabeth-classbattleships, were tted with cruising turbines from 1912onwards following earlier experimental installations.In the US Navy, the Mahan-class destroyers, launched

1935-36, introduced double-reduction gearing. This fur-ther increased the turbine speed above the shaft speed,allowing smaller turbines than single-reduction gearing.Steam pressures and temperatures were also increas-ing progressively, from 300 psi/425 F (2.07 MPa/218C)(saturation temperature) on the World War I-eraWickes class to 615 psi/850 F (4.25 MPa/454 C)superheated steam on some World War II Fletcher-classdestroyers and later ships.[26][27] A standard congurationemerged of an axial-ow high pressure turbine (some-times with a cruising turbine attached) and a double-axial-ow low pressure turbine connected to a double-reduction gearbox. This arrangement continued through-out the steam era in the US Navy and was also used insome Royal Navy designs.[28][29] Machinery of this con-guration can be seen on many preserved World War II-era warships in several countries.[30] When US Navy war-ship construction resumed in the early 1950s, most sur-face combatants and aircraft carriers used 1,200 psi/950F (8.28 MPa/510 C) steam.[31] This continued until theend of the US Navy steam-powered warship era withthe Knox-class frigates of the early 1970s. Amphibiousand auxiliary ships continued to use 600 psi (4.14 MPa)steam post-World War II, with the USS Iwo Jima (LHD-7), launched in 2001, possibly being the last non-nuclearsteam-powered ship built for the US Navy. Except fornuclear-powered ships and submarines and LNG carri-ers,[32] steam turbines have been replaced by gas turbineson fast ships and by diesel engines on other ships.

5.3 Turbo-electric drive

The 50 Let Pobedy nuclear icebreaker with nuclear-turbo-electricpropulsion

Turbo-electric drive was introduced on the USS NewMexico (BB-40), launched in 1917. Over the next eightyears theUSNavy launched ve additional turbo-electric-powered battleships and two aircraft carriers (initially or-dered as Lexington-class battlecruisers). Tenmore turbo-electric capital ships were planned, but cancelled due tothe limits imposed by the Washington Naval Treaty. Al-though New Mexico was retted with geared turbines in a1931-33 ret, the remaining turbo-electric ships retainedthe system throughout their careers. This system used twolarge steam turbine generators to drive an electric motor

11

on each of four shafts. The system was less costly initiallythan reduction gears and made the ships more maneuver-able in port, with the shafts able to reverse rapidly and de-liver more reverse power than with most geared systems.Some ocean liners were also built with turbo-electricdrive, as were some troop transports andmass-productiondestroyer escorts inWorldWar II. However, when the USdesigned the treaty cruisers, beginning with the USSPensacola (CA-24) launched in 1927, geared turbineswere used for all fast steam-powered ships thereafter.

6 LocomotivesMain article: Steam turbine locomotive

A steam turbine locomotive engine is a steam locomotivedriven by a steam turbine.The main advantages of a steam turbine locomotive arebetter rotational balance and reduced hammer blow onthe track. However, a disadvantage is less exible out-put power so that turbine locomotives were best suitedfor long-haul operations at a constant output power.[33]

The rst steam turbine rail locomotive was built in 1908for the Ocine Meccaniche Miani Silvestri GrodonaComi, Milan, Italy. In 1924Krupp built the steam turbinelocomotive T18 001, operational in 1929, for DeutscheReichsbahn.

7 TestingBritish, German, other national and international testcodes are used to standardize the procedures and def-initions used to test steam turbines. Selection of thetest code to be used is an agreement between the pur-chaser and the manufacturer, and has some signicanceto the design of the turbine and associated systems. In theUnited States, ASME has produced several performancetest codes on steam turbines. These include ASME PTC6-2004, Steam Turbines, ASME PTC 6.2-2011, SteamTurbines in Combined Cycles, PTC 6S-1988, Proceduresfor Routine Performance Test of Steam Turbines. TheseASME performance test codes have gained internationalrecognition and acceptance for testing steam turbines.The single most important and dierentiating character-istic of ASME performance test codes, including PTC 6,is that the test uncertainty of the measurement indicatesthe quality of the test and is not to be used as a commer-cial tolerance.[34]

8 See also Balancing machine

Mercury vapour turbine Tesla turbine Turbine fr:Auguste Rateau, steam and combustion-engineturbine developer

9 References[1] Encyclopdia Britannica (1931-02-11). Sir Charles Al-

gernon Parsons (British engineer) - Britannica Online En-cyclopedia. Britannica.com. Retrieved 2010-09-12.

[2] Wiser, Wendell H. (2000). Energy resources: occurrence,production, conversion, use. Birkhuser. p. 190. ISBN978-0-387-98744-6.

[3] turbine. Encyclopdia Britannica Online

[4] A new look at Herons 'steam engine'" (1992-06-25).Archive for History of Exact Sciences 44 (2): 107-124.

[5] O'Connor, J. J.; E. F. Robertson (1999). Heron ofAlexan-dria. MacTutor

[6] "Power plant engineering". P. K. Nag (2002). TataMcGraw-Hill. p.432. ISBN 978-0-07-043599-5

[7] Taqi al-Din and the First Steam Turbine, 1551 A.D., webpage, accessed on line October 23, 2009; this web pagerefers to Ahmad Y Hassan (1976), Taqi al-Din and Ara-bic Mechanical Engineering, pp. 34-5, Institute for theHistory of Arabic Science, University of Aleppo.

[8]

[9]

[10] Parsons, Sir Charles A.. The Steam Turbine.

[11] Parsons, Sir Charles A., The Steam Turbine, p. 7-8

[12] Parsons, Sir Charles A., The Steam Turbine, p. 20-22

[13] Parsons, Sir Charles A., The Steam Turbine, p. 23-25

[14] Steam Turbines (Course No. M-3006)". PhD Engineer.Retrieved 2011-09-22.

[15] Energy and Environmental Analysis (2008). TechnologyCharacterization: Steam Turbines (2008)" (PDF). Reportprepared for U.S. Environmental Protection Agency. p. 13.Retrieved 25 February 2013.

[16] Whitaker, Jerry C. (2006). AC power systems handbook.Boca Raton, FL: Taylor and Francis. p. 35. ISBN 978-0-8493-4034-5.

[17] Speed Droop and Power Generation. Application Note01302. 2. Woodward. Speed

[18] Roymech, http://www.roymech.co.uk/Related/Thermos/Thermos_Steam_Turbine.html

[19] Fundamentals of Engineering Thermodynamics Moranand Shapiro, Published by Wiley

12 11 EXTERNAL LINKS

[20] Leyzerovich, Alexander (2005). Wet-steam Turbines forNuclear Power Plants. Tulsa OK: PennWell Books. p.111. ISBN 978-1-59370-032-4.

[21] MCC CFXUpdate23 LO A/W.qxd (PDF). Retrieved2010-09-12.

[22] New Benchmarks for Steam Turbine Eciency - PowerEngineering. Pepei.pennnet.com. Archived from theoriginal on 2010-11-18. Retrieved 2010-09-12.

[23] https://www.mhi.co.jp/technology/review/pdf/e451/e451021.pdf

[24] Parsons, Sir Charles A., The Steam Turbine, p. 26-31

[25] Friedman, Norman, USDestroyers, an Illustrated DesignHistory, Revised Edition, Naval Institute Press, Annapo-lis: 2004, p. 23-24.

[26] Destroyer History Foundation, 1,500 tonner web page

[27] Friedman, p. 472

[28] Bowie, David, Cruising Turbines of the Y-100 NavalPropulsion Machinery

[29] The Leander Project turbine page

[30] Historic Naval Ships Association website

[31] Friedman, p. 477

[32] Mitsubishi Heavy starts construction of rst Sayaendo se-ries LNG carrier. December 2012.

[33] Streeter, Tony: 'Testing the Limit' (Steam Railway Maga-zine: 2007, 336), pp. 85

[34] William P. Sanders (ed), Turbine Steam Path MechanicalDesign and Manufacture, Volume Iiia (PennWell Books,2004) ISBN 1-59370-009-1 page 292

10 Further reading Cotton, K.C. (1998). Evaluating and ImprovingSteam Turbine Performance.

Parsons, Charles A. (1911). The Steam Turbine.University Press, Cambridge.

Traupel, W. (1977). Thermische Turbomaschinen(in German).

Thurston, R. H. (1878). A History of the Growth ofthe Steam Engine. D. Appleton and Co.

11 External links Steam Turbines: A Book of Instruction for the Ad-justment and Operation of the Principal Types of thisClass of Prime Movers by Hubert E. Collins

Steam Turbine Construction at Mikes EngineeringWonders

Tutorial: Superheated Steam Flow Phenomenon in Steam Turbine Disk-StatorCavities Channeled by Balance Holes

Extreme Steam- Unusual Variations on The SteamLocomotive

Interactive Simulation of 350MW Steam Turbinewith Boiler developed by The University of Queens-land, in Brisbane Australia

Super-Steam...AnAmazing Story ofAchievementPopular Mechanics, August 1937

Modern Energetics - The Steam Turbine

13

12 Text and image sources, contributors, and licenses12.1 Text

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Contributors: Own work Original artist: Kiselev d File:AEG_marine_steam_turbine_(Rankin_Kennedy,_Modern_Engines,_Vol_VI).jpg Source: http://upload.wikimedia.org/

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12.3 Content license Creative Commons Attribution-Share Alike 3.0

HistoryTypesBlade and stage designSteam supply and exhaust conditionsCasing or shaft arrangementsTwo-flow rotors

Principle of operation and designTurbine efficiency Impulse turbinesReaction turbines

Operation and maintenanceSpeed regulationThermodynamics of steam turbinesIsentropic efficiency

Direct driveMarine propulsionEarly developmentCruising machinery and gearingTurbo-electric drive

LocomotivesTestingSee alsoReferencesFurther readingExternal linksText and image sources, contributors, and licensesTextImagesContent license