Steam Turbine

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Steam turbine
turbine was little more than a toy, the classic Aeolipile,
described in the 1st century by Greek mathematician
Hero of Alexandria in Roman Egypt.[3][4][5] In 1551, Taqi
al-Din in Ottoman Egypt described a steam turbine with
the practical application of rotating a spit. Steam turbines were also described by the Italian Giovanni Branca
(1629)[6] and John Wilkins in England (1648).[7] The devices described by Taqi al-Din and Wilkins are today
known as steam jacks.
The modern steam turbine was invented in 1884 by Sir
Charles Parsons, whose first model was connected to a
dynamo that generated 7.5 kW (10 hp) of electricity.[8]
The invention of Parsons’ steam turbine made cheap
and plentiful electricity possible and revolutionized marine transport and naval warfare.[9] Parsons’ design was
a reaction type. His patent was licensed and the turbine
scaled-up shortly after by an American, George Westinghouse. The Parsons turbine also turned out to be easy to
scale up. Parsons had the satisfaction of seeing his invention adopted for all major world power stations, and
the size of generators had increased from his first 7.5
kW set up to units of 50,000 kW capacity. Within Parson’s lifetime, the generating capacity of a unit was scaled
up by about 10,000 times,[10] and the total output from
turbo-generators constructed by his firm C. A. Parsons
and Company and by their licensees, for land purposes
alone, had exceeded thirty million horse-power.[8]

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

A steam turbine is a device that extracts thermal energy
from pressurized steam and uses it to do mechanical work
on a rotating output shaft. Its modern manifestation was
invented by Sir Charles Parsons in 1884.[1]
Because the turbine generates rotary motion, it is particularly suited to be used to drive an electrical generator
– about 90% of all electricity generation in the United
States (1996) is by use of steam turbines.[2] The steam
turbine is a form of heat engine that derives much of its
improvement in thermodynamic efficiency from the use
of multiple stages in the expansion of the steam, which
results in a closer approach to the ideal reversible expansion process.

1

A number of other variations of turbines have been developed that work effectively with steam. The de Laval
turbine (invented by Gustaf de Laval) accelerated the
steam to full speed before running it against a turbine
blade. De Laval’s impulse turbine is simpler, less expensive and does not need to be pressure-proof. It can operate with any pressure of steam, but is considerably less
efficient. fr:Auguste Rateau developed a pressure compounded impulse turbine using the de Laval principle as
early as 1900, obtained a US patent in 1903, and applied
the turbine to a French torpedo boat in 1904. He taught at
the École des mines de Saint-Étienne for a decade until
1897, and later founded a successful company that was
incorporated into the Alstom firm after his death. One
of the founders of the modern theory of steam and gas
turbines was Aurel Stodola, a Slovak physicist and engineer and professor at the Swiss Polytechnical Institute
(now ETH) in Zurich. His work Die Dampfturbinen und
ihre Aussichten als Wärmekraftmaschinen (English: The
Steam Turbine and its prospective use as a Mechanical
Engine) was published in Berlin in 1903. A further book
Dampf und Gas-Turbinen (English: Steam and Gas Tur-

History

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

The first device that may be classified as a reaction steam
1

2

2

bines) was published in 1922.

TYPES

Nozzles move due to both the impact of steam on them
and the reaction due to the high-velocity steam at the exit.
A turbine composed of moving nozzles alternating with
fixed nozzles is called a reaction turbine or Parsons turbine.

The Brown-Curtis turbine, an impulse type, which had
been originally developed and patented by the U.S. company International Curtis Marine Turbine Company, was
developed in the 1900s in conjunction with John Brown
& Company. It was used in John Brown-engined mer- Except for low-power applications, turbine blades are archant ships and warships, including liners and Royal Navy ranged in multiple stages in series, called compounding,
warships.
which greatly improves efficiency at low speeds.[11] A
reaction stage is a row of fixed nozzles followed by a
row of moving nozzles. Multiple reaction stages divide the pressure drop between the steam inlet and
2 Types
exhaust into numerous small drops, resulting in a
pressure-compounded turbine. Impulse stages may be
Steam turbines are made in a variety of sizes ranging from either pressure-compounded, velocity-compounded, or
small <0.75 kW (<1 hp) units (rare) used as mechani- pressure-velocity compounded. A pressure-compounded
cal drives for pumps, compressors and other shaft driven impulse stage is a row of fixed nozzles followed by a row
equipment, to 1 500 000 kW (1.5 GW; 2 000 000 hp) of moving blades, with multiple stages for compounding.
turbines used to generate electricity. There are several This is also known as a Rateau turbine, after its invenclassifications for modern steam turbines.
tor. A velocity-compounded impulse stage (invented by
Curtis and also called a “Curtis wheel”) is a row of fixed
nozzles followed by two or more rows of moving blades
2.1 Blade and stage design
alternating with rows of fixed blades. This divides the velocity drop across the stage into several smaller drops.[12]
A series of velocity-compounded impulse stages is called
Impulse Turbine
Reaction Turbine
a pressure-velocity compounded turbine.
Moving
buckets

Rotor

Fixed
nozzle

Rotating
nozzle

Moving
buckets

Rotating
nozzle

Fixed
nozzle

Rotor
Stator

Rotation
Pressure

Velocity

Pressure

Velocity

Schematic diagram outlining the difference between an impulse
and a 50% reaction turbine

Turbine blades are of two basic types, blades and nozzles.
Blades move entirely due to the impact of steam on them
and their profiles do not converge. This results in a steam
velocity drop and essentially no pressure drop as steam
moves through the blades. A turbine composed of blades
alternating with fixed nozzles is called an impulse turbine,
Curtis turbine, Rateau turbine, or Brown-Curtis turbine.
Nozzles appear similar to blades, but their profiles converge near the exit. This results in a steam pressure drop
and velocity increase as steam moves through the nozzles.

Diagram of an AEG marine steam turbine circa 1905

By 1905, when steam turbines were coming into use on
fast ships (such as HMS Dreadnought) and in land-based
power applications, it had been determined that it was desirable to use one or more Curtis wheels at the beginning
of a multi-stage turbine (where the steam pressure is highest), followed by reaction stages. This was more efficient
with high-pressure steam due to reduced leakage between
the turbine rotor and the casing.[13] This is illustrated in
the drawing of the German 1905 AEG marine steam turbine. The steam from the boilers enters from the right at
high pressure through a throttle, controlled manually by
an operator (in this case a sailor known as the throttleman). It passes through five Curtis wheels and numerous
reaction stages (the small blades at the edges of the two
large rotors in the middle) before exiting at low pressure,
almost certainly to a condenser. The condenser provides
a vacuum that maximizes the energy extracted from the
steam, and condenses the steam into feedwater to be re-

2.3

Casing or shaft arrangements

turned to the boilers. On the left are several additional
reaction stages (on two large rotors) that rotate the turbine in reverse for astern operation, with steam admitted
by a separate throttle. Since ships are rarely operated in
reverse, efficiency is not a priority in astern turbines, so
only a few stages are used to save cost.

2.2

Steam supply and exhaust conditions

3
needs or sent to boiler feedwater heaters to improve overall cycle efficiency. Extraction flows may be controlled
with a valve, or left uncontrolled.
Induction turbines introduce low pressure steam at an intermediate stage to produce additional power.

2.3 Casing or shaft arrangements
These arrangements include single casing, tandem compound and cross compound turbines. Single casing units
are the most basic style where a single casing and shaft
are coupled to a generator. Tandem compound are used
where two or more casings are directly coupled together
to drive a single generator. A cross compound turbine
arrangement features two or more shafts not in line driving two or more generators that often operate at different
speeds. A cross compound turbine is typically used for
many large applications.

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

2.4 Two-flow rotors

These types include condensing, non-condensing, reheat,
extraction and induction.
Condensing turbines are most commonly found in electrical power plants. These turbines exhaust steam from a
boiler in a partially condensed state, typically of a quality
near 90%, at a pressure well below atmospheric to a
condenser.
Non-condensing or back pressure turbines are most
widely used for process steam applications. The exhaust
pressure is controlled by a regulating valve to suit the
needs of the process steam pressure. These are commonly found at refineries, district heating units, pulp
and paper plants, and desalination facilities where large
amounts of low pressure process steam are needed.
A two-flow turbine rotor. The steam enters in the middle of the
Reheat turbines are also used almost exclusively in electrical power plants. In a reheat turbine, steam flow exits from a high pressure section of the turbine and is returned to the boiler where additional superheat is added.
The steam then goes back into an intermediate pressure
section of the turbine and continues its expansion. Using reheat in a cycle increases the work output from the
turbine and also the expansion reaches conclusion before
the steam condenses, there by minimizing the erosion of
the blades in last rows. In most of the cases, maximum
number of reheats employed in a cycle is 2 as the cost of
super-heating the steam negates the increase in the work
output from turbine.

shaft, and exits at each end, balancing the axial force.

The moving steam imparts both a tangential and axial
thrust on the turbine shaft, but the axial thrust in a simple
turbine is unopposed. To maintain the correct rotor position and balancing, this force must be counteracted by an
opposing force. Thrust bearings can be used for the shaft
bearings, the rotor can use dummy pistons, it can be double flow- the steam enters in the middle of the shaft and
exits at both ends, or a combination of any of these. In a
double flow rotor, the blades in each half face opposite
ways, so that the axial forces negate each other but the
tangential forces act together. This design of rotor is also
Extracting type turbines are common in all applications. called two-flow, double-axial-flow, or double-exhaust.
In an extracting type turbine, steam is released from var- This arrangement is common in low-pressure casings of
ious stages of the turbine, and used for industrial process a compound turbine.[14]

4

3

3

PRINCIPLE OF OPERATION AND DESIGN

Principle of operation and design

zle. The loss of energy due to this higher exit velocity is
commonly called the carry over velocity or leaving loss.

An ideal steam turbine is considered to be an isentropic
process, or constant entropy process, in which the entropy
of the steam entering the turbine is equal to the entropy
of the steam leaving the turbine. No steam turbine is
truly isentropic, however, with typical isentropic efficiencies ranging from 20–90% based on the application of
the turbine. The interior of a turbine comprises several
sets of blades or buckets. One set of stationary blades is
connected to the casing and one set of rotating blades is
connected to the shaft. The sets intermesh with certain
minimum clearances, with the size and configuration of
sets varying to efficiently exploit the expansion of steam
at each stage.

The law of moment of momentum states that the sum of
the moments of external forces acting on a fluid which is
temporarily occupying the control volume is equal to the
net time change of angular momentum flux through the
control volume.

3.1

The swirling fluid enters the control volume at radius r1
with tangential velocity Vw1 and leaves at radius r2 with
tangential velocity Vw2 .

Turbine efficiency

To maximize turbine efficiency the steam is expanded,
doing work, in a number of stages. These stages are characterized by how the energy is extracted from them and
are known as either impulse or reaction turbines. Most
steam turbines use a mixture of the reaction and impulse
designs: each stage behaves as either one or the other, but
the overall turbine uses both. Typically, higher pressure
sections are reaction type and lower pressure stages are
impulse type.
3.1.1

Impulse turbines

A selection of impulse turbine blades

An impulse turbine has fixed nozzles that orient the steam
flow into high speed jets. These jets contain significant kinetic energy, which is converted into shaft rotation by the bucket-like shaped rotor blades, as the steam
jet changes direction. A pressure drop occurs across only
the stationary blades, with a net increase in steam velocity
across the stage. As the steam flows through the nozzle its
pressure falls from inlet pressure to the exit pressure (atmospheric pressure, or more usually, the condenser vacuum). Due to this high ratio of expansion of steam, the
steam leaves the nozzle with a very high velocity. The
steam leaving the moving blades has a large portion of
the maximum velocity of the steam when leaving the noz-

Velocity triangle

A velocity triangle paves the way for a better understanding of the relationship between the various velocities. In
the adjacent figure we have:
V1 and V2 are the absolute velocities at the inlet
and outlet respectively.
Vf 1 and Vf 2 are the flow velocities at the inlet
and outlet respectively.
Vw1 + U and Vw2 are the swirl velocities at the
inlet and outlet respectively.

3.1

Turbine efficiency

5

Vr1 and Vr2 are the relative velocities at the inlet and outlet respectively.

Where ∆h = h2 − h1 is the specific enthalpy drop of
steam in the nozzle.

U1 and U2 are the velocities of the blade at the
inlet and outlet respectively.

By the first law of thermodynamics: h1 +

α is the guide vane angle and β is the blade
angle.

V12
2

= h2 +

V22
2

Assuming that V1 is appreciably less than V2 , we get ∆h
V2
≈ 22 Furthermore, stage efficiency is the product of blade
efficiency and nozzle efficiency, or ηstage = ηb ∗ ηN
2

2
Then by the law of moment of momentum, the torque on Nozzle efficiency is given by ηN = 2(hV−h
, where the
1
2)
the fluid is given by:
enthalpy (in J/Kg) of steam at the entrance of the nozzle
is h1 and the enthalpy of steam at the exit of the nozzle
T = m(r
˙ 2 Vw2 − r1 Vw1 )
is h2 . ∆Vw = Vw1 − (−Vw2 ) ∆Vw = Vw1 + Vw2
For an impulse steam turbine: r2 = r1 = r . Therefore, ∆V = V cos β + V cos β ∆V = V cos β (1+
w
r1
1
r2
2
w
r1
1
the tangential force on the blades is Fu = m(V
˙ w1 − Vw2 ) Vr2 cos β2 )
Vr1 cos β1
. The work done per unit time or power developed: W =
The ratio of the cosines of the blade angles at the outlet
T ∗ω.
β2
and inlet can be taken and denoted c = cos
cos β1 . The raWhen ω is the angular velocity of the turbine, then the tio of steam velocities relative to the rotor
speed at the
blade speed is U = ω ∗ r . The power developed is then outlet to the inlet of the blade is defined by the friction
W = mU
˙ (∆Vw ) .
coefficient k = VVr2
.
r1
Blade efficiency
k < 1 and depicts the loss in the relative velocity due to

Blade efficiency ( ηb ) can be defined as the ratio of the friction as the steam flows around the blades ( k = 1 for
work done on the blades to kinetic energy supplied to the smooth blades).
/V1 )(1+kc)
fluid, and is given by
w
ηb = 2UV∆V
= 2U (cos α1 −U
2
V1
1
2U Vw
W ork Done
ηb = Kinetic Energy Supplied = V 2
The ratio of the blade speed to the absolute steam velocity
1
at the inlet is termed the blade speed ratio ρ = VU1
Stage efficiency
d
2
b
ηb is maximum when dη
dρ = 0 or, dρ (2cos α1 − ρ (1 +
cos α1
kc)) = 0 . That implies ρ = 2 and therefore VU1 =
cos α1
. Now ρopt = VU1 = cos2α1 (for a single stage
2
impulse turbine)

Therefore the maximum value of stage efficiency is obtained by putting the value of VU1 = cos2α1 in the expression of ηb /
We get: (ηb )max = 2(ρ cos α1 − ρ2 )(1 + kc) =
cos2 α1 (1+kc)
.
2

Convergent-divergent nozzle

For equiangular blades, β1 = β2 , therefore c = 1 , and
2
we get (ηb )max = cos α12(1+k) . If the friction due to the
blade surface is neglected then (ηb )max = cos2 α1 .
Conclusions on maximum efficiency
(ηb )max = cos2 α1
1. For a given steam velocity work done per kg of steam
would be maximum when cos2 α1 = 1 or α1 = 0 .
2. As α1 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.
Graph depicting efficiency of Impulse turbine

A stage of an impulse turbine consists of a nozzle set and a
moving wheel. The stage efficiency defines a relationship
between enthalpy drop in the nozzle and work done in the
stage.
ηstage =

W ork done on blade
Energy supplied per stage

=

U ∆Vw
∆h

3.1.2 Reaction turbines
In the reaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of turbine
makes use of the reaction force produced as the steam accelerates through the nozzles formed by the rotor. Steam
is directed onto the rotor by the fixed vanes of the stator.

6

3

PRINCIPLE OF OPERATION AND DESIGN

It leaves the stator as a jet that fills the entire circumference of the rotor. The steam then changes direction and
increases its speed relative to the speed of the blades. A
pressure drop occurs across both the stator and the rotor,
with steam accelerating through the stator and decelerating through the rotor, with no net change in steam velocity
across the stage but with a decrease in both pressure and
temperature, reflecting the work performed in the driving
of the rotor.

This consists of symmetrical rotor and stator blades. For
this turbine the velocity triangle is similar and we have:

Blade efficiency

2
From the inlet velocity triangle we have Vr1
2
2
V1 + U − 2U V1 cos α1

Energy input to the blades in a stage:

α1 = β2 , β1 = α2
V1 = Vr2 , Vr1 = V2
Assuming Parson’s turbine and obtaining all the expressions we get
E = V12 −

2
Vr1
2

V2

=

2

2U V1 cos α1
U
2
1
2
E = ∆h is equal to the kinetic energy supplied to the E = V1 − 2 − 2 +
fixed blades (f) + the kinetic energy supplied to the movV12 −U 2 +2U V1 cos α1
E=
2
ing blades (m).
Work done (for unit mass flow per second): W =
Or, E = enthalpy drop over the fixed blades, ∆hf + enU ∗ ∆Vw = U ∗ (2 ∗ V1 cos α1 − U )
thalpy drop over the moving blades, ∆hm .
Therefore the blade efficiency is given by
The effect of expansion of steam over the moving blades
2U (2V1 cos α1 −U )
is to increase the relative velocity at the exit. Therefore ηb = V 2 −U 2 +2V
1 U cos α1
1
the relative velocity at the exit Vr2 is always greater than
Condition of maximum blade efficiency
the relative velocity at the inlet Vr1 .

In terms of velocities, the enthalpy drop over the moving
blades is given by:
∆hm =

2
2
Vr2
−Vr1
2

(it contributes to a change in static pressure)
The enthalpy drop in the fixed blades, with the assumption that the velocity of steam entering the fixed blades
is equal to the velocity of steam leaving the previously
moving blades is given by:

Comparing Efficiencies of Impulse and Reaction turbines

If ρ =

U
V1

, then

(ηb )max =

2ρ(cos α1 −ρ)
V12 −U 2 +2U V1 cos α1

For maximum efficiency

dηb


= 0 , we get

(1 − ρ2 + 2ρ cos α1 )(4 cos α1 − 4ρ) − 2ρ(2 cos α1 − ρ)(−2ρ + 2 cos α1 )
and this finally gives ρopt =

∆hf =
the nozzle

= cos α1

Therefore (ηb )max is found by putting the value of ρ =
cos α1 in the expression of blade efficiency

Velocity diagram
V12 −V02
2

U
V1

where V0 is the inlet velocity of steam in

(ηb )reaction =

2 cos2 α1
1+cos2 α1

(ηb )impulse = cos2 α1

V0 is very small and hence can be neglected
Therefore, ∆hf =

V12
2

E = ∆hf + ∆hm

3.2 Operation and maintenance

Because of the high pressures used in the steam circuits
and the materials used, steam turbines and their casings
E=
+
have high thermal inertia. When warming up a steam turA very widely used design has half degree of reaction bine for use, the main steam stop valves (after the boiler)
or 50% reaction and this is known as Parson’s turbine. have a bypass line to allow superheated steam to slowly
V12
2

2
2
Vr2
−Vr1
2

3.4

Thermodynamics of steam turbines

7

A modern steam turbine generator installation

bypass the valve and proceed to heat up the lines in the
system along with the steam turbine. Also, a turning gear
is engaged when there is no steam to slowly rotate the
turbine to ensure even heating to prevent uneven expansion. After first rotating the turbine by the turning gear,
allowing time for the rotor to assume a straight plane (no
bowing), then the turning gear is disengaged and steam
is admitted to the turbine, first to the astern blades then
to the ahead blades slowly rotating the turbine at 10–15
RPM (0.17–0.25 Hz) to slowly warm the turbine. The
warm up procedure for large steam turbines may exceed
ten hours.[15]
During normal operation, rotor imbalance can lead to vibration, which, because of the high rotation velocities,
could lead to a blade breaking away from the rotor and
through the casing. To reduce this risk, considerable
efforts are spent to balance the turbine. Also, turbines
are 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 the
blades which occurs when condensed water is blasted
onto the blades (moisture carry over). Also, liquid water entering the blades may damage the thrust bearings
for the turbine shaft. To prevent this, along with controls
and baffles in the boilers to ensure high quality steam,
condensate drains are installed in the steam piping leading to the turbine.
Maintenance requirements of modern steam turbines are
simple and incur low costs (typically around $0.005 per
kWh);[15] their operational life often exceeds 50 years.[15]

3.3

Speed regulation

The control of a turbine with a governor is essential, as
turbines need to be run up slowly to prevent damage and
some applications (such as the generation of alternating
current electricity) require precise speed control.[16] Uncontrolled acceleration of the turbine rotor can lead to an
overspeed trip, which causes the nozzle valves that control the flow of steam to the turbine to close. If this fails
then the turbine may continue accelerating until it breaks

Diagram of a steam turbine generator system

apart, often catastrophically. Turbines are expensive to
make, requiring precision manufacture and special quality materials.
During normal operation in synchronization with the
electricity network, power plants are governed with a five
percent droop speed control. This means the full load
speed is 100% and the no-load speed is 105%. This is
required for the stable operation of the network without hunting and drop-outs of power plants. Normally the
changes in speed are minor. Adjustments in power output
are made by slowly raising the droop curve by increasing
the spring pressure on a centrifugal governor. Generally
this is a basic system requirement for all power plants because the older and newer plants have to be compatible in
response to the instantaneous changes in frequency without depending on outside communication.[17]

3.4 Thermodynamics of steam turbines
The steam turbine operates on basic principles of
thermodynamics using the part 3-4 of the Rankine cycle
shown in the adjoining diagram. Superheated vapor (or
dry saturated vapor, depending on application) enters the
turbine, after it having exited the boiler, at high temperature and high pressure. The high heat/pressure steam is
converted into kinetic energy using a nozzle (a fixed nozzle in an impulse type turbine or the fixed blades in a reaction type turbine). Once the steam has exited the nozzle it
is moving at high velocity and is sent to the blades of the
turbine. A force is created on the blades due to the pressure of the vapor on the blades causing them to move. A
generator or other such device can be placed on the shaft,
and the energy that was in the vapor can now be stored
and used. The gas exits the turbine as a saturated vapor
(or liquid-vapor mix depending on application) at a lower
temperature and pressure than it entered with and is sent
to the condenser to be cooled.[18] If we look at the first
law we can find an equation comparing the rate at which

8

4 DIRECT DRIVE

ηt =

h3 − h4
h3 − h4s

where
• h3 is the specific enthalpy at state three
• h4 is the specific enthalpy at state four for the actual
turbine
• h4s is the specific enthalpy at state four for the isentropic turbine

4 Direct drive
T-s diagram of a superheated Rankine cycle

work is developed per unit mass. Assuming there is no
heat transfer to the surrounding environment and that the
change in kinetic and potential energy is negligible when
compared to the change in specific enthalpy we come up
with the following equation

˙
W
= h3 − h4
m
˙
where

A direct-drive 5 MW steam turbine fueled with biomass

• Ẇ is the rate at which work is developed per unit
Electrical power stations use large steam turbines drivtime
ing electric generators to produce most (about 80%) of
the world’s electricity. The advent of large steam tur• ṁ is the rate of mass flow through the turbine
bines made central-station electricity generation practical, since reciprocating steam engines of large rating be3.4.1 Isentropic efficiency
came very bulky, and operated at slow speeds. Most
central stations are fossil fuel power plants and nuclear
To measure how well a turbine is performing we can look power plants; some installations use geothermal steam, or
at its isentropic efficiency. This compares the actual per- use concentrated solar power (CSP) to create the steam.
formance of the turbine with the performance that would Steam turbines can also be used directly to drive large
be achieved by an ideal, isentropic, turbine.[19] When cal- centrifugal pumps, such as feedwater pumps at a thermal
culating this efficiency, heat lost to the surroundings is power plant.
assumed to be zero. The starting pressure and tempera- The turbines used for electric power generation are most
ture is the same for both the actual and the ideal turbines, often directly coupled to their generators. As the genbut at turbine exit the energy content ('specific enthalpy') erators must rotate at constant synchronous speeds acfor the actual turbine is greater than that for the ideal tur- cording to the frequency of the electric power system, the
bine because of irreversibility in the actual turbine. The most common speeds are 3,000 RPM for 50 Hz systems,
specific enthalpy is evaluated at the same pressure for the and 3,600 RPM for 60 Hz systems. Since nuclear reacactual and ideal turbines in order to give a good compar- tors have lower temperature limits than fossil-fired plants,
ison between the two.
with lower steam quality, the turbine generator sets may
The isentropic efficiency is found by dividing the actual be arranged to operate at half these speeds, but with fourpole generators, to reduce erosion of turbine blades.[20]
work by the ideal work.[19]

5.1

Early development

5

Marine propulsion

9

fewer operators are required. Thus, conventional steam
power is used in very few new ships. An exception is
“TSS” and “Turbine Steam Ship” redirect here. For other LNG carriers which often find it more efficient to use
boil-off gas with a steam turbine than to re-liquify it.
uses, see TSS (disambiguation).
In steam-powered ships, compelling advantages of steam Nuclear-powered ships and submarines use a nuclear reactor to create steam for turbines. Nuclear power is often
chosen where diesel power would be impractical (as in
submarine applications) or the logistics of refuelling pose
significant problems (for example, icebreakers). It has
been estimated that the reactor fuel for the Royal Navy's
Vanguard class submarine is sufficient to last 40 circumnavigations of the globe – potentially sufficient for the
vessel’s entire service life. Nuclear propulsion has only
been applied to a very few commercial vessels due to the
expense of maintenance and the regulatory controls required on nuclear systems and fuel cycles.

5.1 Early development
The Turbinia, 1894, the first steam turbine-powered ship

Parsons turbine from the 1928 Polish destroyer ORP Wicher.

turbines over reciprocating engines are smaller size, lower
maintenance, lighter weight, and lower vibration. A
steam turbine is only efficient when operating in the thousands of RPM, while the most effective propeller designs
are for speeds less than 300 RPM; consequently, precise
(thus expensive) reduction gears are usually required, although numerous early ships through World War I, such
as Turbinia, had direct drive from the steam turbines to
the propeller shafts. Another alternative is turbo-electric
transmission, in which an electrical generator run by the
high-speed turbine is used to run one or more slow-speed
electric motors connected to the propeller shafts; precision gear cutting may be a production bottleneck during
wartime. Turbo-electric drive was most used in large US
warships designed during World War I and in some fast
liners, and was used in some troop transports and massproduction destroyer escorts in World War II. The purchase cost of turbines is offset by much lower fuel and
maintenance requirements and the small size of a turbine when compared to a reciprocating engine having
an equivalent power. However, from the 1950s diesel
engines were capable of greater reliability and higher
efficiencies: propulsion steam turbine cycle efficiencies
have yet to break 50%, yet diesel engines today routinely
exceed 50%, especially in marine applications.[21][22][23]
Diesel power plants also have lower operating costs since

The development of steam turbine marine propulsion
from 1894-1935 was dominated by the need to reconcile
the high efficient speed of the turbine with the low efficient speed (less than 300 rpm) of the ship’s propeller at
an overall cost competitive with reciprocating engines. In
1894, efficient reduction gears were not available for the
high powers required by ships, so direct drive was necessary. In the Turbinia, which has direct drive to each propeller shaft, the efficient speed of the turbine was reduced
after initial trials by directing the steam flow through all
three direct drive turbines (one on each shaft) in series,
probably totaling around 200 turbine stages operating in
series. Also, there were three propellers on each shaft for
operation at high speeds.[24] The high shaft speeds of the
era are represented by one of the first US turbine-powered
destroyers, USS Smith (DD-17), launched in 1909, which
had direct drive turbines and whose three shafts turned at
724 rpm at 28.35 knots.[25] The use of turbines in several
casings exhausting steam to each other in series became
standard in most subsequent marine propulsion applications, and is a form of cross-compounding. The first turbine was called the high pressure (HP) turbine, the last
turbine was the low pressure (LP) turbine, and any turbine
in between was an intermediate pressure (IP) turbine. A
much later arrangement than Turbinia can be seen on the
RMS Queen Mary in Long Beach, California, launched
in 1934, in which each shaft is powered by four turbines
in series connected to the ends of the two input shafts of
a single-reduction gearbox. They are the HP, 1st IP, 2nd
IP, and LP turbines.

5.2 Cruising machinery and gearing
The quest for economy was even more important when
cruising speeds were considered. Cruising speed is
roughly 50% of a warship’s maximum speed and 20-25%
of its maximum power level. This would be a speed used

10
on long voyages when fuel economy is desired. Although
this brought the propeller speeds down to an efficient
range, turbine efficiency was greatly reduced, and early
turbine ships had poor cruising ranges. A solution that
proved useful through most of the steam turbine propulsion era was the cruising turbine. This was an extra turbine to add even more stages, at first attached directly to
one or more shafts, exhausting to a stage partway along
the HP turbine, and not used at high speeds. As reduction gears became available around 1911, some ships, notably the USS Nevada (BB-36), had them on cruising turbines while retaining direct drive main turbines. Reduction gears allowed turbines to operate in their efficient
range at a much higher speed than the shaft, but were expensive to manufacture.

5 MARINE PROPULSION
1935-36, introduced double-reduction gearing. This further increased the turbine speed above the shaft speed,
allowing smaller turbines than single-reduction gearing.
Steam pressures and temperatures were also increasing progressively, from 300 psi/425 F (2.07 MPa/218
C)(saturation temperature) on the World War I-era
Wickes class to 615 psi/850 F (4.25 MPa/454 C)
superheated steam on some World War II Fletcher-class
destroyers and later ships.[26][27] A standard configuration
emerged of an axial-flow high pressure turbine (sometimes with a cruising turbine attached) and a doubleaxial-flow low pressure turbine connected to a doublereduction gearbox. This arrangement continued throughout the steam era in the US Navy and was also used in
some Royal Navy designs.[28][29] Machinery of this configuration can be seen on many preserved World War IIera warships in several countries.[30] When US Navy warship construction resumed in the early 1950s, most surface combatants and aircraft carriers used 1,200 psi/950
F (8.28 MPa/510 C) steam.[31] This continued until the
end of the US Navy steam-powered warship era with
the Knox-class frigates of the early 1970s. Amphibious
and auxiliary ships continued to use 600 psi (4.14 MPa)
steam post-World War II, with the USS Iwo Jima (LHD7), launched in 2001, possibly being the last non-nuclear
steam-powered ship built for the US Navy. Except for
nuclear-powered ships and submarines and LNG carriers,[32] steam turbines have been replaced by gas turbines
on fast ships and by diesel engines on other ships.

Cruising turbines competed at first with reciprocating engines for fuel economy. An example of the retention
of reciprocating engines on fast ships was the famous
RMS Titanic of 1911, which along with her sisters RMS
Olympic and HMHS Britannic had triple-expansion engines on the two outboard shafts, both exhausting to an
LP turbine on the center shaft. After adopting turbines
with the Delaware-class battleships launched in 1909, the
United States Navy reverted to reciprocating machinery
on the New York-class battleships of 1912, then went
back to turbines on Nevada in 1914. The lingering fondness for reciprocating machinery was because the US
Navy had no plans for capital ships exceeding 21 knots
until after World War I, so top speed was less important than economical cruising. The United States had acquired the Philippines and Hawaii as territories in 1898,
5.3 Turbo-electric drive
and lacked the British Royal Navy's worldwide network
of coaling stations. Thus, the US Navy in 1900-1940 had
the greatest need of any nation for fuel economy, especially as the prospect of war with Japan arose following
World War I. This need was compounded by the US not
launching any cruisers 1908-1920, so destroyers were required to perform long-range missions usually assigned to
cruisers. So, various cruising solutions were fitted on US
destroyers launched 1908-1916. These included small reciprocating engines and geared or ungeared cruising turbines on one or two shafts. However, once fully geared
turbines proved economical in initial cost and fuel they
were rapidly adopted, with cruising turbines also included
on most ships. Beginning in 1915 all new Royal Navy de- The 50 Let Pobedy nuclear icebreaker with nuclear-turbo-electric
stroyers had fully geared turbines, and the United States propulsion
followed in 1917.
In the Royal Navy, speed was a priority until the Battle Turbo-electric drive was introduced on the USS New
of Jutland in mid-1916 showed that in the battlecruisers Mexico (BB-40), launched in 1917. Over the next eight
too much armour had been sacrificed in its pursuit. The years the US Navy launched five additional turbo-electricBritish used exclusively turbine-powered warships from powered battleships and two aircraft carriers (initially or1906. Because they recognized that a significant cruis- dered as Lexington-class battlecruisers). Ten more turboing range would be desirable given their world-wide em- electric capital ships were planned, but cancelled due to
pire, some warships, notably the Queen Elizabeth-class the limits imposed by the Washington Naval Treaty. Albattleships, were fitted with cruising turbines from 1912 though New Mexico was refitted with geared turbines in a
1931-33 refit, the remaining turbo-electric ships retained
onwards following earlier experimental installations.
the system throughout their careers. This system used two
In the US Navy, the Mahan-class destroyers, launched large steam turbine generators to drive an electric motor

11
on each of four shafts. The system was less costly initially
than reduction gears and made the ships more maneuverable in port, with the shafts able to reverse rapidly and deliver more reverse power than with most geared systems.
Some ocean liners were also built with turbo-electric
drive, as were some troop transports and mass-production
destroyer escorts in World War II. However, when the US
designed the “treaty cruisers”, beginning with the USS
Pensacola (CA-24) launched in 1927, geared turbines
were used for all fast steam-powered ships thereafter.

6

Locomotives

Main article: Steam turbine locomotive
A steam turbine locomotive engine is a steam locomotive
driven by a steam turbine.
The main advantages of a steam turbine locomotive are
better rotational balance and reduced hammer blow on
the track. However, a disadvantage is less flexible output power so that turbine locomotives were best suited
for long-haul operations at a constant output power.[33]
The first steam turbine rail locomotive was built in 1908
for the Officine Meccaniche Miani Silvestri Grodona
Comi, Milan, Italy. In 1924 Krupp built the steam turbine
locomotive T18 001, operational in 1929, for Deutsche
Reichsbahn.

7

Testing

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

9 References
[1] Encyclopædia Britannica (1931-02-11). “Sir Charles Algernon Parsons (British engineer) - Britannica Online Encyclopedia”. Britannica.com. Retrieved 2010-09-12.
[2] Wiser, Wendell H. (2000). Energy resources: occurrence,
production, conversion, use. Birkhäuser. p. 190. ISBN
978-0-387-98744-6.
[3] turbine. Encyclopædia Britannica Online
[4] A new look at Heron’s '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 of Alexandria. MacTutor
[6] "Power plant engineering". P. K. Nag (2002).
McGraw-Hill. p.432. ISBN 978-0-07-043599-5

Tata

[7] Taqi al-Din and the First Steam Turbine, 1551 A.D., web
page, accessed on line October 23, 2009; this web page
refers to Ahmad Y Hassan (1976), Taqi al-Din and Arabic Mechanical Engineering, pp. 34-5, Institute for the
History of Arabic Science, University of Aleppo.
[8]
[9]

British, German, other national and international test
codes are used to standardize the procedures and definitions used to test steam turbines. Selection of the
test code to be used is an agreement between the purchaser and the manufacturer, and has some significance
to the design of the turbine and associated systems. In the
United States, ASME has produced several performance
test codes on steam turbines. These include ASME PTC
6-2004, Steam Turbines, ASME PTC 6.2-2011, Steam
Turbines in Combined Cycles, PTC 6S-1988, Procedures
for Routine Performance Test of Steam Turbines. These
ASME performance test codes have gained international
recognition and acceptance for testing steam turbines.
The single most important and differentiating characteristic of ASME performance test codes, including PTC 6,
is that the test uncertainty of the measurement indicates
the quality of the test and is not to be used as a commercial tolerance.[34]

8

See also
• Balancing machine

[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). “Technology
Characterization: Steam Turbines (2008)" (PDF). Report
prepared 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 978-08493-4034-5.
[17] Speed Droop and Power Generation. Application Note
01302. 2. Woodward. Speed
[18] Roymech, http://www.roymech.co.uk/Related/Thermos/
Thermos_Steam_Turbine.html
[19] “Fundamentals of Engineering Thermodynamics” Moran
and Shapiro, Published by Wiley

12

11

[20] Leyzerovich, Alexander (2005). Wet-steam Turbines for
Nuclear Power Plants. Tulsa OK: PennWell Books. p.
111. ISBN 978-1-59370-032-4.
[21] “MCC CFXUpdate23 LO A/W.qxd” (PDF). Retrieved
2010-09-12.
[22] “New Benchmarks for Steam Turbine Efficiency - Power
Engineering”. Pepei.pennnet.com. Archived from the
original 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, “US Destroyers, an Illustrated Design
History, Revised Edition, Naval Institute Press, Annapolis: 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 Naval
Propulsion Machinery”
[29] The Leander Project turbine page
[30] Historic Naval Ships Association website
[31] Friedman, p. 477
[32] “Mitsubishi Heavy starts construction of first Sayaendo series LNG carrier”. December 2012.
[33] Streeter, Tony: 'Testing the Limit' (Steam Railway Magazine: 2007, 336), pp. 85
[34] William P. Sanders (ed), Turbine Steam Path Mechanical
Design and Manufacture, Volume Iiia (PennWell Books,
2004) ISBN 1-59370-009-1 page 292

10

Further reading

• Cotton, K.C. (1998). Evaluating and Improving
Steam 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 of
the Steam Engine. D. Appleton and Co.

11

External links

• Steam Turbines: A Book of Instruction for the Adjustment and Operation of the Principal Types of this
Class of Prime Movers by Hubert E. Collins

EXTERNAL LINKS

• Steam Turbine Construction at Mike’s Engineering
Wonders
• Tutorial: “Superheated Steam”
• Flow Phenomenon in Steam Turbine Disk-Stator
Cavities Channeled by Balance Holes
• Extreme Steam- Unusual Variations on The Steam
Locomotive
• Interactive Simulation of 350MW Steam Turbine
with Boiler developed by The University of Queensland, in Brisbane Australia
• “Super-Steam...An Amazing Story of Achievement”
Popular Mechanics, August 1937
• Modern Energetics - The Steam Turbine

13

12
12.1

Text and image sources, contributors, and licenses
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Tarquin, Ap, Rjstott, Ray Van De Walker, Heron, Mic, Rlandmann, Aarchiba, Markb, Doradus, Morven, Pollinator, Blainster, Halibutt,
Bkell, Fuelbottle, Seano1, Pengo, Jpo, Nunh-huh, Timpo, TDC, Leonard G., Khalid hassani, Gadfium, Geni, Piotrus, H Padleckas, Thincat, Bosmon, Dj245, Avihu, Lacrimosus, Discospinster, Rich Farmbrough, Vsmith, Rustl, Flatline, Alistair1978, SpookyMulder, Edgarde,
ESkog, Limbo socrates, Chairboy, Art LaPella, Robotje, Redlentil, Duk, Viriditas, Kjkolb, VBGFscJUn3, Hooperbloob, Jared81, Atlant,
Wtshymanski, Cburnett, Rtdrury, Mandarax, AllanHainey, DonSiano, Ian Dunster, Sango123, FlaBot, Old Moonraker, BjKa, Lignomontanus, Flying Jazz, Gwernol, Greenpowered, Spacepotato, Quentin X, Cyferx, Hellbus, IanManka, Gaius Cornelius, NawlinWiki, Wiki
alf, Adamrush, Dhollm, Jeffpower, Psy guy, Izuko, Djdaedalus, Sandstein, 2fort5r, Alureiter, Allens, Katieh5584, SmackBot, Emoscopes,
Hkhenson, Melchoir, Markus Schweiss, Jagged 85, RBX3, Chris the speller, CrookedAsterisk, Ksenon, Malarky, Jprg1966, Hichris, Hibernian, CSWarren, Hgrosser, Can't sleep, clown will eat me, Sephiroth BCR, GreatBigCircles, Georgeccampbell, SnappingTurtle, Mattamsn,
ShaunES, Bob Castle, Ohconfucius, Rory096, Tract789, LuYiSi, Peter Horn, StephenBuxton, Tawkerbot2, Insanephantom, Nczempin,
Sashimiwithwasabiandsoysauce, RottweilerCS, Optimist on the run, Omicronpersei8, Epbr123, Ultimus, Kablammo, John254, Doyley,
Z10x, Mentifisto, EdJogg, Rees11, WinBot, Makipedia, DarkAudit, JAnDbot, CosineKitty, ScandinavianRockguy, Mrbeer, Roleplayer,
Rexj, Abunyip, Beewine, Jahoe, Mclean007, Jim Douglas, Edward321, Gwern, Fredrosse, E2npau, CommonsDelinker, J.delanoy, Pharaoh
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Laptop geek, Ashlin augusty, Gmanoj16, Widr, Helpful Pixie Bot, Dlw20070716, R369, PR Alma, BG19bot, MusikAnimal, Ankit aba,
Kendall-K1, GKFX, Morning Sunshine, Michelev, Chie one, ChrisGualtieri, Iamanimesh, Mindyy1y, Saksham grover13, Sachin.singhal90,
Mogism, Bps633, Aftabbanoori, Smak1214, Pawan krishna, ShaftWork, RobDuch, GeorgAA7, Ondřej Perry, Shahin1009 and Anonymous: 373

12.2

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Contributors: Own work Original artist: Kiselev d
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License:
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Public domain Contributors: Scan from Kennedy, Rankin (1912 edition of 1905 book.) The Book of Modern Engines and Power Generators
(Vol. VI ed.), London: Caxton Original artist: Andy Dingley (scanner)
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14

12

TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

• File:Rankine_cycle_with_superheat.jpg Source:
http://upload.wikimedia.org/wikipedia/commons/0/0b/Rankine_cycle_with_
superheat.jpg License: CC-BY-SA-3.0 Contributors: Own work Original artist: Donebythesecondlaw at English Wikipedia
• File:TMW_773_-_Steam_turbine_generator_set.jpg Source: http://upload.wikimedia.org/wikipedia/commons/6/6c/TMW_773_-_
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• File:TurbineBlades.jpg Source: http://upload.wikimedia.org/wikipedia/commons/3/36/TurbineBlades.jpg License: CC-BY-SA-3.0
Contributors: Own work Original artist: Cblade
• File:Turbine_Philippsburg-1.jpg Source: http://upload.wikimedia.org/wikipedia/commons/c/c2/Turbine_Philippsburg-1.jpg License:
CC-BY-2.0 Contributors: Flickr photo page “Dampfturbine” Original artist: Christine und David Schmitt from Vienna, Austria, Austria
• File:Turbine_generator_systems1.png Source: http://upload.wikimedia.org/wikipedia/commons/6/6b/Turbine_generator_systems1.
png License: CC-BY-SA-3.0 Contributors: Own work Original artist: H Padleckas made this image in May-June 2007 by reworking a diagram called "Image:Dores-TG Cycle diag1.jpg” originally mostly hand-drawn and scanned into Engineering Wikia and English Wikipedia
by Dore chakravarty sometime about about November 2005. H Padleckas and Dore chakravarty have communicated about this reworking
of the original image through private e-mails. H Padleckas 00:54, 22 June 2007 (UTC)
• File:Turbines_impulse_v_reaction.svg Source: http://upload.wikimedia.org/wikipedia/commons/a/a6/Turbines_impulse_v_reaction.
svg License: CC-BY-SA-3.0 Contributors: This is a vector conversion of File:Turbines impulse v reaction.png Original artist: Originally
Emoscopes
• File:Turbinia_At_Speed.jpg Source: http://upload.wikimedia.org/wikipedia/commons/e/e9/Turbinia_At_Speed.jpg License: Public domain Contributors: 'Our Navy' Original artist: Alfred John West (1857-1937)
• File:Wirnik_turbiny_parowej_ORP_Wicher.jpg Source: http://upload.wikimedia.org/wikipedia/commons/e/e6/Wirnik_turbiny_
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