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A steam turbine is a
machine A machine is a man-made device that uses power to apply forces and control movement to perform an action. Machines can be driven by animals and people A people is a plurality of person A person (plural people or persons) is a being ...

machine
that extracts
thermal energy Thermal radiation in visible light can be seen on this hot metalwork. Thermal energy refers to several distinct physical concepts, such as the internal energy of a system; heat or sensible heat, which are defined as types of energy transfer (as is ...
from pressurized
steam Steam is water in the gas phase. This may occur due to evaporation, to due to boiling, where heat is applied until water reaches the enthalpy of vaporization. Steam that is saturated or Superheated steam, superheated is invisible; however, "stea ...

steam
and uses it to do
mechanical work In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), motion and behavior throug ...

mechanical work
on a rotating output shaft. Its modern manifestation was invented by
Charles Parsons
Charles Parsons
in 1884. Fabrication of a modern steam turbine involves advanced
metalwork Metalworking is the process of shaping and reshaping metals to create useful objects, parts, assemblies, and large scale structures. As a term it covers a wide and diverse range of processes, skills, and tools for producing objects on every scale: ...
to form high-grade steel alloys into precision parts using technologies that first became available in the 20th century; continued advances in durability and efficiency of steam turbines remains central to the
energy economics Energy economics is a broad scientific subject area which includes topics related to supply and use of energy in societies. Due to diversity of issues and methods applied and shared with a number of academic disciplines, energy economics doe ...
of the 21st century. The steam turbine is a form of
heat engine In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, radiation, and physical properties of matter. The behavior of these quantities is gove ...

heat engine
that derives much of its improvement in
thermodynamic efficiency In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, radiation, and physical properties of matter. The behavior of these quantities is governed ...
from the use of multiple stages in the expansion of the steam, which results in a closer approach to the ideal reversible expansion process. Because the
turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Lat ...

turbine
generates
rotary motion Rotation around a fixed axis is a special case of rotational motion. The fixed-Cartesian coordinate system, axis hypothesis excludes the possibility of an axis changing its orientation and cannot describe such phenomena as nutation, wobbling or ...
, it is particularly suited to be used to drive an
electrical generator In electricity generation, a generator is a device that converts motive power ( mechanical energy) into electrical power for use in an external circuit. Sources of mechanical energy include steam turbine A steam turbine is a device that extra ...
—about 85% of all electricity generation in the United States in the year 2014 was by use of steam turbines. A steam turbine connected to an electric generator is called a
turbo generator A turbo generator set or turbine generator set is the compound of a steam turbine A steam turbine is a device that extracts thermal energy from pressurized steam and uses it to do Work (physics), mechanical work on a rotating output shaft. I ...
. As of 2021, among the largest steam turbines in the world is the Arabelle steam turbines manufactured by GE based on an original design by
Alstom Alstom SA is a French multinational corporation, multinational rolling stock manufacturer operating worldwide in rail transport markets, active in the fields of passenger transportation, signalling, and locomotives, with products including the A ...
. An Arabelle turbine is 7 m in diameter, weighs 4000 tons and spins at 1500 rpm. In a typical nuclear installation, another 4000 tons of supporting steel structure is required, as well as 1000 tons of pumps, valves, and pipes. Technical concerns include rotor imbalance,
vibration Vibration is a mechanical phenomenon whereby oscillation Oscillation is the repetitive variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. The term '' vi ...

vibration
, bearing wear, and uneven expansion (various forms of
thermal shock Thermal shock is a type of rapidly transient mechanical load. By definition, it is a mechanical load caused by a rapid change of temperature of a certain point. It can be also extended to the case of a thermal gradient, which makes different par ...
). In large installations, even the sturdiest turbine is capable of shaking itself apart when operated out of trim.


History

The first device that may be classified as a reaction steam turbine was little more than a toy, the classic
Aeolipile An aeolipile, aeolipyle, or eolipile, also known as a Hero's engine, is a simple, bladeless radial steam turbine which spins when the central water container is heated. Torque In physics and mechanics Mechanics (Ancient Greek, Greek: ) ...
, described in the 1st century by
Hero of Alexandria up William Tell, a popular folk hero of Switzerland">folk_hero.html" ;"title="William Tell, a popular folk hero">William Tell, a popular folk hero of Switzerland. A hero (heroine in its feminine form) is a real person or a main fictional ch ...

Hero of Alexandria
in
Roman Egypt , conventional_long_name = Roman Egypt , common_name = Egypt , subdivision = Roman province, Province , nation = the Roman Empire , era = Late antiquity , capital = Alexandria , title_leader = Praefectus Augustalis , image_m ...

Roman Egypt
. In 1551, Taqi al-Din in
Ottoman Egypt The Eyalet of Egypt operated as an administrative division of the Ottoman Empire from 1517 to 1867. It originated as a result of the conquest of Mamluk Egypt by the Ottomans in 1517, following the Ottoman–Mamluk War (1516–1517) and the absorp ...

Ottoman Egypt
described a steam turbine with the practical application of rotating a spit. Steam turbines were also described by the Italian
Giovanni Branca Giovanni Branca (22 April 1571 – 24 January 1645) was an Italy, Italian engineer and architect, chiefly remembered today for what some commentators have taken to be an early steam turbine. Life Branca was born on 22 April 1571 in Sant'Angelo i ...
(1629) and
John Wilkins John Wilkins, (14 February 161419 November 1672) was an Anglican ministry, Anglican clergyman, natural philosophy, natural philosopher and author, and was one of the founders of the Royal Society. He was Bishop of Chester from 1668 until his d ...

John Wilkins
in England (1648). The devices described by Taqi al-Din and Wilkins are today known as
steam jack A roasting jack is a machine which rotates meat roasting on a spit (cooking aide), spit. It can also be called a spit jack, a spit engine or a turnspit, although this name can also refer to a human turning the spit, or a turnspit dog. Cooking mea ...
s. In 1672 an impulse turbine driven car was designed by
Ferdinand Verbiest Father Ferdinand Verbiest (9 October 1623 – 28 January 1688) was a Flemish people, Flemish Jesuit missionary in China during the Qing dynasty. He was born in Pittem near Tielt in the County of Flanders (now part of Belgium). He is known as Nan Hu ...
. A more modern version of this car was produced some time in the late 18th century by an unknown German mechanic. In 1775 at Soho
James Watt James Watt (; 30 January 1736 (19 January 1736 OS) – 25 August 1819) was a Scottish inventor, mechanical engineer, and chemist who improved on Thomas Newcomen's 1712 Newcomen steam engine with his Watt steam engine in 1776, which was ...

James Watt
designed a reaction turbine that was put to work there. In 1807 Polikarp Zalesov designed and constructed an impulse turbine, using it for the fire pump operation. In 1827 the Frenchmen Real and Pichon patented and constructed a compound impulse turbine. The modern steam turbine was invented in 1884 by , whose first model was connected to a
dynamo A dynamo is an electrical generator In electricity generation, a generator is a device that converts motive power ( mechanical energy) into electrical power for use in an external circuit. Sources of mechanical energy include steam turbine ...

dynamo
that generated of electricity. The invention of Parsons' steam turbine made cheap and plentiful electricity possible and revolutionized marine transport and naval warfare. Parsons' design was a
reaction Reaction may refer to a response (disambiguation), response to an action, event, or exposure. Examples: *Adverse drug reaction *Allergy, Allergic reaction *Chemical reaction *Chain reaction (disambiguation) *Commentary (disambiguation) *Emotional, r ...
type. His patent was licensed and the turbine scaled-up shortly after by an American,
George Westinghouse George Westinghouse Jr. (October 6, 1846 – March 12, 1914) was an American entrepreneur Entrepreneurship is the creation or extraction of value. With this definition, entrepreneurship is viewed as change, generally entailing risk beyond what ...

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 set up to units of capacity. Within Parsons' lifetime, the generating capacity of a unit was scaled up by about 10,000 times, 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. Other variations of turbines have been developed that work effectively with steam. The ''de Laval turbine'' (invented by
Gustaf de Laval Karl Gustaf Patrik de Laval (; 9 May 1845 – 2 February 1913) was a Swedish engineer and inventor who made important contributions to the design of steam turbines and dairy machinery. Life Gustaf de Laval was born at Orsa Municipality, Orsa in D ...
) accelerated the steam to full speed before running it against a turbine blade. De Laval's impulse turbine is simpler and less expensive and does not need to be pressure-proof. It can operate with any pressure of steam, but is considerably less efficient.
Auguste Rateau Auguste Rateau (13 October 1863 – 13 January 1930) was an engineer Engineers, as practitioners of engineering, are Professional, professionals who Invention, invent, design, analyze, build and test Machine, machines, complex systems, architect ...

Auguste Rateau
developed a pressure compounded impulse turbine using the de Laval principle as early as 1896, obtained a US patent in 1903, and applied the turbine to a French torpedo boat in 1904. He taught at the for a decade until 1897, and later founded a successful company that was incorporated into the
Alstom Alstom SA is a French multinational corporation, multinational rolling stock manufacturer operating worldwide in rail transport markets, active in the fields of passenger transportation, signalling, and locomotives, with products including the A ...
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 Eth (, uppercase Letter case (or just case) is the distinction between the letters that are in larger uppercase or capitals (or more formally ''majuscule'') and smaller lowercase (or more formally ''minuscule'') in the written represe ...

ETH
) in Zurich. His work (English: The Steam Turbine and its prospective use as a Heat Engine) was published in Berlin in 1903. A further book (English: Steam and Gas Turbines) was published in 1922. 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 John Brown and Company of Clydebank was a Scottish Naval architecture, marine engineering and shipbuilding firm. It built many notable and world-famous ships including , , , , , and the ''Queen Elizabeth 2''. At its height, from 1900 to the 19 ...
. It was used in John Brown-engined merchant ships and warships, including liners and Royal Navy warships.


Manufacturing

The present day manufacturing industry for steam turbines are made by manufacturers include *
Siemens Siemens AG ( ) is a German multinational conglomerate corporation headquartered in Munich and the largest industrial manufacturing company in Europe with branch offices abroad. The principal divisions of the corporation are ''Industry'', ' ...

Siemens
*
Mitsubishi The is a group of autonomous Japan , image_flag = Flag of Japan.svg , alt_flag = Centered deep red circle on a white rectangle , image_coat = Imperial Seal of Japan.svg , alt_coat ...

Mitsubishi
KwHI Toshiba IHI *
General Electric General Electric Company (GE) is an American Multinational corporation, multinational Conglomerate (company), conglomerate incorporated in New York State and headquartered in Boston. Until 2021, the company operated through GE Aviation, aviati ...
* Turboatom * Silmash and Ural TW *
BHEL Bharat Heavy Electricals Limited (BHEL) is an Indian Public sector undertakings in India, public sector engineering and manufacturing company based in New Delhi, India. Established in 1964, BHEL is India's largest power generation equipment manu ...
*
Alstom Alstom SA is a French multinational corporation, multinational rolling stock manufacturer operating worldwide in rail transport markets, active in the fields of passenger transportation, signalling, and locomotives, with products including the A ...
,
Doosan Škoda Power Doosan Škoda Power, a part of global company Doosan, is a manufacturer and supplier of equipment for power stations, machine rooms especially equipped for steam turbines. The portfolio includes steam turbines in the range of performances from 10 ...
,
Ansaldo Ansaldo Energia S.p.A. is an Italy, Italian power engineering company. It is based in Genoa, Italy. The absorbed parent company, Gio. Ansaldo & C., started in 1853. It was taken over by Leonardo S.p.A., Leonardo Spa. In 2011, Leonardo S.p.A. so ...
KTZ Energomash-Atomenergo
MAPNA MAPNA Group is a group of Iranian companies involved in development and execution of thermal and renewable power plants, oil & gas, railway transportation and other industrial projects as well as manufacturing main equipment including gas and steam ...
and
Toshiba is a Japanese multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational state, a sovereign sta ...
. and Chinese manufacturers like
Harbin Electric Harbin Electric Company Limited, formerly Harbin Power Equipment Company Limited, is a Chinese enterprise engaged in the research and development, manufacturing and construction of power plantPower Station or The Power Station may refer to: * Pow ...
,
Shanghai Electric Shanghai Electric (officially Shanghai Electric Group Company Limited) is a Chinese multinational power generation and electrical equipment manufacturing company headquartered in Shanghai. The company traces its roots to 1880. Shanghai Electr ...
, and
Dongfang Electric Dongfang Electric Corporation () is a Chinese state-owned manufacturer of power generators and the contracts of power stationPower Station or The Power Station may refer to: * Power station, a facility for the generation of electricity Music * ...
among others.


Types

Steam turbines are made in a variety of sizes ranging from small <0.75 kW (<1 hp) units (rare) used as mechanical drives for pumps, compressors and other shaft driven equipment, to turbines used to generate electricity. There are several classifications for modern steam turbines.


Blade and stage design

Turbine blades are of two basic types, blades and
nozzles A nozzle is a device designed to control the direction or characteristics of a fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. Fluids are a ...

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, , 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. 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 A turbine ( or ) (from the Greek , ''tyrbē'', or Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Lat ...

reaction turbine
or Parsons turbine. Except for low-power applications, turbine blades are arranged in multiple stages in series, called
compounding In the field of pharmacy, compounding (performed in compounding pharmacies) is preparation of a custom formulation of a medication to fit a unique need of a patient which cannot be met with commercially available products. This may be done for m ...
, which greatly improves
efficiency Efficiency is the (often measurable) ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without ...
at low speeds. 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 exhaust into numerous small drops, resulting in a pressure-compounded turbine. Impulse stages may be either pressure-compounded, velocity-compounded, or pressure-velocity compounded. A pressure-compounded impulse stage is a row of fixed nozzles followed by a row of moving blades, with multiple stages for compounding. This is also known as a Rateau turbine, after its inventor. 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 alternating with rows of fixed blades. This divides the velocity drop across the stage into several smaller drops. A series of velocity-compounded impulse stages is called a pressure-velocity compounded turbine. By 1905, when steam turbines were coming into use on fast ships (such as ) 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. This is illustrated in the drawing of the German 1905
AEG ''Allgemeine Elektricitäts-Gesellschaft AG'' (AEG; ) was a German producer of electrical equipment 250px, Electrical equipment part of the distribution system in a large building Electrical equipment includes any machine powered by electri ...

AEG
marine steam turbine. The steam from the
boiler Poland Poland ( pl, Polska ), officially the Republic of Poland ( pl, Rzeczpospolita Polska, links=no ), is a country located in Central Europe. It is divided into 16 Voivodeships of Poland, administrative provinces, covering an area of , ...
s enters from the right at high pressure through a
throttle A throttle is the mechanism by which fluid flow In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, i ...

throttle
, controlled manually by an operator (in this case a
sailor A sailor, seaman, mariner, or seafarer is a person who works aboard a watercraft as part of its crew, and may work in any one of a number of different fields that are related to the operation and maintenance of a ship. The profession of the sa ...

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__NOTOC__ Condenser may refer to: Heat transfer * Condenser (heat transfer), a device or unit used to condense vapor into liquid. Specific types include: ** Heat exchanger#HVAC air coils, HVAC air coils ** Condenser (laboratory), a range of laborat ...
. The condenser provides a vacuum that maximizes the energy extracted from the steam, and condenses the steam into
feedwater Boiler feedwater is an essential part of boiler operations. The feed water is put into the steam drum from a feed pump. In the steam drum the feed water is then turned into steam from the heat. After the steam is used it is then dumped to the ma ...
to be returned 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.


Blade design challenges

A major challenge facing turbine design was reducing the creep experienced by the blades. Because of the high temperatures and high stresses of operation, steam turbine materials become damaged through these mechanisms. As temperatures are increased in an effort to improve turbine efficiency, creep becomes significant. To limit creep, thermal coatings and
superalloy Nickel superalloy jet engine ( RB199) turbine blade A superalloy, or high-performance alloy, is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a ...
s with solid-solution strengthening and
grain boundary strengthening Grain-boundary strengthening (or Hall–Petch strengthening) is a method of strengthening materials by changing their average crystallite (grain) size. It is based on the observation that grain boundaries are insurmountable borders for dislocati ...
are used in blade designs. Protective coatings are used to reduce the thermal damage and to limit
oxidation (mild reducing agent) are added to powdered potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4 and composed of potassium ion, K+ and permanganate, . It is a purplish-black crystalline salt, ...

oxidation
. These coatings are often stabilized
zirconium dioxide Zirconium dioxide (), sometimes known as zirconia (not to be confused with zircon Zircon ( or ) is a mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is ...
-based ceramics. Using a thermal protective coating limits the temperature exposure of the nickel superalloy. This reduces the creep mechanisms experienced in the blade. Oxidation coatings limit efficiency losses caused by a buildup on the outside of the blades, which is especially important in the high-temperature environment. The nickel-based blades are alloyed with aluminum and titanium to improve strength and creep resistance. The
microstructure Microstructure is the very small scale structure of a material, defined as the structure of a prepared surface of material as revealed by an optical microscope above 25× magnification. The microstructure of a material (such as metals, polymer ...
of these alloys is composed of different regions of composition. A uniform dispersion of the gamma-prime phase – a combination of nickel, aluminum, and titanium – promotes the strength and creep resistance of the blade due to the microstructure.
Refractory A refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperature Temperature is a physical quantity that expresses hot and cold. ...
elements such as
rhenium Rhenium is a chemical element with the Symbol (chemistry), symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 element, group 7 of the periodic table. With an estimated average concentration of 1 pa ...

rhenium
and
ruthenium Ruthenium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same n ...

ruthenium
can be added to the alloy to improve creep strength. The addition of these elements reduces the diffusion of the gamma prime phase, thus preserving the
fatigue Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...
resistance, strength, and creep resistance.


Steam supply and exhaust conditions

Turbine types include condensing, non-condensing, reheat, extraction and induction.


Condensing turbines

Condensing turbines are most commonly found in electrical power plants. These turbines receive steam from a
boiler Poland Poland ( pl, Polska ), officially the Republic of Poland ( pl, Rzeczpospolita Polska, links=no ), is a country located in Central Europe. It is divided into 16 Voivodeships of Poland, administrative provinces, covering an area of , ...
and exhaust it to a
condenser__NOTOC__ Condenser may refer to: Heat transfer * Condenser (heat transfer), a device or unit used to condense vapor into liquid. Specific types include: ** Heat exchanger#HVAC air coils, HVAC air coils ** Condenser (laboratory), a range of laborat ...
. The exhausted steam is at a pressure well below atmospheric, and is in a partially condensed state, typically of a
quality Quality may refer to: Concepts *Quality (business), the ''non-inferiority'' or ''superiority'' of something *Quality (philosophy), an attribute or a property *Quality (physics), in response theory *Energy quality, used in various science disciplin ...
near 90%.


Back pressure turbines

Non-condensing or back pressure turbines are most widely used for process steam applications, in which the steam will be used for additional purposes after being exhausted from the turbine. 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 Desalination is a process that takes away mineral components from saline water Saline water (more commonly known as salt water) is water that contains a high concentration of solvation, dissolved salts (mainly sodium chloride). The salt conce ...
facilities where large amounts of low pressure process steam are needed.


Reheat turbines

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, thereby 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.


Extracting turbines

Extracting type turbines are common in all applications. In an extracting type turbine, steam is released from various stages of the turbine, and used for industrial process needs or sent to boiler
feedwater heaterImage:feedwater-heating.png, 375px, A Rankine cycle with two steam turbines and a single open feedwater heater. A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feedwater red ...
s to improve overall cycle efficiency. Extraction flows may be controlled with a valve, or left uncontrolled. Extracted steam results in a loss of power in the downstream stages of the turbine. Induction turbines introduce low pressure steam at an intermediate stage to produce additional power.


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 typical 1930s-1960s naval installation is illustrated below; this shows high- and low-pressure turbines driving a common reduction gear, with a geared cruising turbine on one high-pressure turbine.


Two-flow rotors

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 called two-flow, double-axial-flow, or double-exhaust. This arrangement is common in low-pressure casings of a compound turbine.


Principle of operation and design

An ideal steam turbine is considered to be an
isentropic process In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, radiation, and physical properties of matter. The behavior of these quantities is governed ...
, 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 to 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. Practical thermal efficiency of a steam turbine varies with turbine size, load condition, gap losses and friction losses. They reach top values up to about 50% in a turbine; smaller ones have a lower 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, lower pressure sections are reaction type and higher pressure stages are impulse type.


Impulse turbines

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 nozzle. The loss of energy due to this higher exit velocity is commonly called the carry over velocity or leaving loss. The law of states that the sum of the moments of external forces acting on a fluid which is temporarily occupying the
control volume In continuum mechanics and thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, radiation, and physical properties of matter. The behavior of the ...

control volume
is equal to the net time change of angular momentum flux through the control volume. The swirling fluid enters the control volume at radius r_1 with tangential velocity V_ and leaves at radius r_2 with tangential velocity V_. A
velocity triangleIn turbomachinery, a velocity triangle or a velocity diagram is a triangle representing the various components of velocities of the working fluid in a turbomachinery, turbomachine. Velocity triangles may be drawn for both the inlet and outlet section ...
paves the way for a better understanding of the relationship between the various velocities. In the adjacent figure we have: :V_1 and V_2 are the absolute velocities at the inlet and outlet respectively. :V_ and V_ are the flow velocities at the inlet and outlet respectively. :V_ and V_ are the swirl velocities at the inlet and outlet respectively, in the moving reference. :V_ and V_ are the relative velocities at the inlet and outlet respectively. :U_1 and U_2 are the velocities of the blade at the inlet and outlet respectively. :\alpha is the guide vane angle and \beta is the blade angle. Then by the law of moment of momentum, the torque on the fluid is given by: : T = \dot \left(r_2 V_ - r_1 V_\right) For an impulse steam turbine: r_2 = r_1 = r. Therefore, the tangential force on the blades is F_u = \dot\left(V_ - V_\right). The work done per unit time or power developed: W = T\omega. When ω is the angular velocity of the turbine, then the blade speed is U = \omega r. The power developed is then W = \dotU(\Delta V_w).


Blade efficiency

Blade efficiency () can be defined as the ratio of the work done on the blades to kinetic energy supplied to the fluid, and is given by : \eta_b = \frac = \frac


Stage efficiency

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. : = \frac = \frac Where \Delta h = h_2 - h_1 is the specific enthalpy drop of steam in the nozzle. By the
first law of thermodynamics The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic processes, distinguishing three kinds of transfer of energy, as heat, as thermodynamic work, and as energy associated with matter tran ...
: : h_1 + \frac^2 = h_2 + \frac^2 Assuming that V_1 is appreciably less than V_2, we get \approx \frac^2. Furthermore, stage efficiency is the product of blade efficiency and nozzle efficiency, or \eta_\text = \eta_b\eta_N. Nozzle efficiency is given by \eta_N = \frac, where the enthalpy (in J/Kg) of steam at the entrance of the nozzle is h_1 and the enthalpy of steam at the exit of the nozzle is h_2. : \begin \Delta V_w &= V_ - \left(-V_\right) \\ &= V_ + V_ \\ &= V_\cos\beta_1 + V_\cos\beta_2 \\ &= V_\cos\beta_1\left(1 + \frac\right) \end The ratio of the cosines of the blade angles at the outlet and inlet can be taken and denoted c = \frac. The ratio of steam velocities relative to the rotor speed at the outlet to the inlet of the blade is defined by the friction coefficient k = \frac. k < 1 and depicts the loss in the relative velocity due to friction as the steam flows around the blades (k = 1 for smooth blades). : \eta_b = \frac = \frac\left(\cos\alpha_1 - \frac\right)(1 + kc) The ratio of the blade speed to the absolute steam velocity at the inlet is termed the blade speed ratio \rho = \frac. \eta_b is maximum when \frac = 0 or, \frac\left(2(1 + kc)\right) = 0. That implies \rho = \frac\cos\alpha_1 and therefore \frac = \frac\cos\alpha_1. Now \rho_ = \frac = \frac\cos\alpha_1 (for a single stage impulse turbine). Therefore, the maximum value of stage efficiency is obtained by putting the value of \frac = \frac\cos\alpha_1 in the expression of \eta_b. We get: _\text = 2\left(\rho\cos\alpha_1 - \rho^2\right)(1 + kc) = \frac\cos^2\alpha_1 (1 + kc). For equiangular blades, \beta_1 = \beta_2, therefore c = 1, and we get _\text = \frac\cos^2\alpha_1(1 + k). If the friction due to the blade surface is neglected then _\text = \cos^2\alpha_1.


Conclusions on maximum efficiency

: _\text = \cos^2\alpha_1 # For a given steam velocity work done per kg of steam would be maximum when \cos^2\alpha_1 = 1 or \alpha_1 = 0 . # As \alpha_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.


Reaction turbines

In the ''reaction turbine'', the
rotor ROTOR was an elaborate air defence radar Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft An aircraft is a vehicle that is able to flight, fly ...
blades themselves are arranged to form convergent
nozzle A nozzle is a device designed to control the direction or characteristics of a fluid flow (especially to increase velocity) as it exits (or enters) an enclosed chamber or pipe. A nozzle is often a pipe or tube of varying cross sectional area, ...

nozzle
s. 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 The stator is the stationary part of a rotary system, found in electric generator In electricity generation, a generator is a device that converts motive power ( mechanical energy) into electrical power for use in an external circuit. So ...
. 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.


Blade efficiency

Energy input to the blades in a stage: E = \Delta h is equal to the kinetic energy supplied to the fixed blades (f) + the kinetic energy supplied to the moving blades (m). Or, E = enthalpy drop over the fixed blades, \Delta h_f + enthalpy drop over the moving blades, \Delta h_m. The effect of expansion of steam over the moving blades is to increase the relative velocity at the exit. Therefore, the relative velocity at the exit V_ is always greater than the relative velocity at the inlet V_. In terms of velocities, the enthalpy drop over the moving blades is given by: : \Delta h_m = \frac (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: : \Delta h_f = \frac where V0 is the inlet velocity of steam in the nozzle V_0 is very small and hence can be neglected. Therefore, \Delta h_f = \frac : \begin E &= \Delta h_f + \Delta h_m \\ &= \frac + \frac \end A very widely used design has half
degree of reaction In turbomachinery, Degree of reaction or reaction ratio (R) is defined as the ratio of the static pressure Pressure (symbol: ''p'' or ''P'') is the force In physics Physics (from grc, φυσική (ἐπιστήμη), physik ...
or 50% reaction and this is known as Parson's turbine. This consists of symmetrical rotor and stator blades. For this turbine the velocity triangle is similar and we have: : \alpha_1 = \beta_2, \beta_1 = \alpha_2 : V_1 = V_, V_ = V_2 Assuming ''Parson's turbine'' and obtaining all the expressions we get : E = V_1^2 - \frac From the inlet velocity triangle we have V_^2 = V_1^2 + U^2 - 2UV_1\cos\alpha_1 : \begin E &= V_1^2 - \frac - \frac + \frac \\ &= \frac \end Work done (for unit mass flow per second): W = U\Delta V_w = U\left(2V_1\cos\alpha_1 - U\right) Therefore, the blade efficiency is given by : \eta_b = \frac


Condition of maximum blade efficiency

If = \frac, then : _\text = \frac For maximum efficiency = 0, we get : \left(1 - \rho^2 + 2\rho\cos\alpha_1\right)\left(4\cos\alpha_1 - 4\rho\right) - 2\rho\left(2\cos\alpha_1 - \rho\right)\left(-2\rho + 2\cos\alpha_1\right) = 0 and this finally gives \rho_ = \frac = \cos\alpha_1 Therefore, _\text is found by putting the value of \rho = \cos\alpha_1 in the expression of blade efficiency : \begin _\text &= \frac \\ _\text &= \cos^2\alpha_1 \end


Operation and maintenance

Because of the high pressures used in the steam circuits and the materials used, steam turbines and their casings have high thermal inertia. When warming up a steam turbine for use, the main steam stop valves (after the boiler) have a bypass line to allow superheated steam to slowly 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. 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); their operational life often exceeds 50 years.


Speed regulation

The control of a turbine with a
governor A governor is, in most cases, a public official with the power to govern the executive branch The executive is the branch of government exercising authority in and holding Moral responsibility, responsibility for the governance of a State (p ...
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. Uncontrolled acceleration of the turbine rotor can lead to an overspeed trip, which causes the governor and throttle valves that control the flow of steam to the turbine to close. If these valves fail then the turbine may continue accelerating until it breaks 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 controlDroop speed control is a control mode used for AC electrical power generators, whereby the power output of a generator reduces as the line frequency increases. It is commonly used as the speed control mode of the governor A governor is, in most ca ...
. 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 Image:centrifugal governor.png, Drawing of a centrifugal "fly-ball" governor. The balls swing out as speed increases, which closes the valve, until a balance is achieved between demand and the proportional gain of the linkage and valve. A centrifug ...

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.


Thermodynamics of steam turbines

The steam turbine operates on basic principles of
thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by ...

thermodynamics
using the part 3-4 of the
Rankine cycle The Rankine cycle is an idealized thermodynamic cycle A thermodynamic cycle consists of a linked sequence of thermodynamic processes that involve transfer of heat and work into and out of the system, while varying pressure, temperature, and othe ...
shown in the adjoining diagram. Superheated steam (or dry saturated steam, depending on application) leaves the boiler at high temperature and high pressure. At entry to the turbine, the steam gains kinetic energy by passing through a nozzle (a fixed nozzle in an impulse type turbine or the fixed blades in a reaction type turbine). When the steam leaves the nozzle it is moving at high velocity towards the blades of the turbine rotor. 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 steam can now be stored and used. The steam leaves 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. The first law enables us to find a formula for the rate at which work is developed per unit mass. Assuming there is no heat transfer to the surrounding environment and that the changes in kinetic and potential energy are negligible compared to the change in specific
enthalpy Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant pr ...

enthalpy
we arrive at the following equation : \frac = h_3 - h_4 where * Ẇ is the rate at which work is developed per unit time * ṁ is the rate of mass flow through the turbine


Isentropic efficiency

To measure how well a turbine is performing we can look at its
isentropic In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, radiation, and physical properties of matter. The behavior of these quantities is governed ...

isentropic
efficiency. This compares the actual performance of the turbine with the performance that would be achieved by an ideal, isentropic, turbine. When calculating this efficiency, heat lost to the surroundings is assumed to be zero. Steam's starting pressure and temperature is the same for both the actual and the ideal turbines, but at turbine exit, steam's energy content ('specific enthalpy') for the actual turbine is greater than that for the ideal turbine because of irreversibility in the actual turbine. The specific enthalpy is evaluated at the same steam pressure for the actual and ideal turbines in order to give a good comparison between the two. The isentropic efficiency is found by dividing the actual work by the ideal work. : \eta_t = \frac where * ''h3'' is the specific enthalpy at state three * ''h4'' is the specific enthalpy at state 4 for the actual turbine * ''h4s'' is the specific enthalpy at state 4s for the isentropic turbine (but note that the adjacent diagram does not show state 4s: it is vertically below state 3)


Direct drive

Electrical power stations use large steam turbines driving
electric generator In electricity generation, a generator is a device that converts motive power ( mechanical energy) into electrical power for use in an external circuit. Sources of mechanical energy include steam turbine A steam turbine is a device that extra ...
s to produce most (about 80%) of the world's electricity. The advent of large steam turbines made central-station electricity generation practical, since reciprocating steam engines of large rating became very bulky, and operated at slow speeds. Most central stations are
fossil fuel power plant A fossil fuel power station is a thermal power station which burns a fossil fuel A fossil fuel is a fuel formed by natural processes, such as anaerobic decomposition of buried dead organism In biology, an organism (from Ancient ...
s and
nuclear power plant A nuclear power plant (sometimes abbreviated as NPP) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine A steam turbine i ...

nuclear power plant
s; some installations use geothermal steam, or use
concentrated solar power File:Ivanpah Solar Power Facility (2).jpg, The three towers of the Ivanpah Solar Power Facility Concentrated solar power (CSP, also known as concentrating solar power, concentrated solar thermal) systems generate solar power by using mirrors ...
(CSP) to create the steam. Steam turbines can also be used directly to drive large
centrifugal pump Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor. They are a sub-class of dynamic a ...

centrifugal pump
s, such as
feedwater pump A boiler feedwater pump is a specific type of pump used to pump feedwater into a boiler (steam generator), steam boiler. The water may be freshly supplied or returning Condensation, condensate produced as a result of the condensation of the steam p ...
s at a
thermal power plant A thermal power station is a power stationPower Station or The Power Station may refer to: * Power station, a facility for the generation of electricity Music * The Power Station (band), a 1980s supergroup ** ''The Power Station'' (album), ...
. The turbines used for electric power generation are most often directly coupled to their generators. As the generators must rotate at constant synchronous speeds according to the frequency of the electric power system, the most common speeds are 3,000 RPM for 50 Hz systems, and 3,600 RPM for 60 Hz systems. Since nuclear reactors have lower temperature limits than fossil-fired plants, with lower steam
quality Quality may refer to: Concepts *Quality (business), the ''non-inferiority'' or ''superiority'' of something *Quality (philosophy), an attribute or a property *Quality (physics), in response theory *Energy quality, used in various science disciplin ...
, the turbine generator sets may be arranged to operate at half these speeds, but with four-pole generators, to reduce erosion of turbine blades.


Marine propulsion

In
steamship A steamship, often referred to as a steamer, is a type of steam-powered vessel, typically ocean-faring and seaworthy, that is propelled by one or more steam engines that typically move (turn) propellers or Paddle steamer, paddlewheels. The first ...

steamship
s, advantages of steam turbines over reciprocating engines are smaller size, lower maintenance, lighter weight, and lower vibration. A steam turbine is efficient only 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 World War I or the First World War, often abbreviated as WWI or WW1, was a global war originating in Europe that lasted from 28 July 1914 to 11 November 1918. Contemporaneously known as the Great War or "The war to end war, the war ...

World War I
, such as ''
Turbinia ''Turbinia'' was the first steam turbine-powered steamship A steamship, often referred to as a steamer, is a type of steam-powered vessel, typically ocean-faring and seaworthy, that is propelled by one or more steam engines that typically mov ...
'', had direct drive from the steam turbines to the propeller shafts. Another alternative is
turbo-electric transmission A turbo-electric transmission uses electric generator In electricity generation, a generator is a device that converts motive power ( mechanical energy) into electrical power for use in an external circuit. Sources of mechanical energy inclu ...
, 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 mass-production
destroyer escorts Destroyer escort (DE) was the United States Navy ), (unofficial)."''Non sibi sed patriae''" ( en, "Not for self but for country") (unofficial). , colors = Blue and gold  , colors_label = Colors ...
in
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a World war, global war that lasted from 1939 to 1945. It involved World War II by country, the vast majority of the world's countries—including all the great ...
. The higher cost of turbines and the associated gears or generator/motor sets is offset by lower maintenance requirements and the smaller size of a turbine in comparison with a reciprocating engine of equal power, although the fuel costs are higher than those of a diesel engine because steam turbines have lower thermal efficiency. To reduce fuel costs the thermal efficiency of both types of engine have been improved over the years.


Early development

The development of steam turbine marine propulsion from 1894 to 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 , internal combustion, gasoline engine, gasoline piston engine. A reciprocating engine, also often known as a piston engine, is typically a heat engine (although there are also pneumatic motor, pneumatic and hydraulic motor, hydraulic reciprocatin ...
. In 1894, efficient reduction
gear Cast iron mortise wheel with wooden cogs (powered by an external water wheel) meshing with a cast iron gear wheel, connected to a pulley A pulley is a wheel on an axle or shaft (mechanical engineering), shaft that is designed to support ...

gear
s were not available for the high powers required by ships, so
direct drive A direct-drive mechanism is where the Transmission (mechanics), transmitting of torque from an electric motor to the output device (such as the driven wheels of a car) occurs without any Reduction gear, gearing reductions. Design The main benefit ...
was necessary. In ''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. The high shaft speeds of the era are represented by one of the first US turbine-powered
destroyer In naval A navy, naval force, or maritime force is the branch of a Nation's armed forces A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. It is typically ...
s, , launched in 1909, which had direct drive turbines and whose three shafts turned at 724 rpm at . 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 in
Long Beach, California Long Beach is a city in Los Angeles County, California. It is the list of United States cities by population, 42nd-most populous city in the United States, with a population of 466,742 as of 2020. A charter city, Long Beach is the List of cities ...
, 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.


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 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
battleship A battleship is a large armored warship A warship or combatant ship is a naval ship that is built and primarily intended for naval warfare. Usually they belong to the armed forces A military, also known collectively as armed force ...

battleship
, 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. 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 of 1911, which along with her sisters and had triple-expansion engines on the two outboard shafts, both exhausting to an LP turbine on the center shaft. After adopting turbines with the s launched in 1909, the
United States Navy ), (unofficial)."''Non sibi sed patriae''" ( en, "Not for self but for country") (unofficial). , colors = Blue and gold  , colors_label = Colors , march = "Anchors Aweigh" , mascot = , equipment = List of equipment of the United Sta ...
reverted to reciprocating machinery on the s 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 until after World War I, so top speed was less important than economical cruising. The United States had acquired the
Philippines The Philippines (; fil, Pilipinas or ''Filipinas'' ), officially the Republic of the Philippines ( fil, Republika ng Pilipinas), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republik ...

Philippines
and
Hawaii Hawaii ( ; haw, Hawaii or ) is a U.S. state, state in the Western United States, located in the Pacific Ocean about 2,000 miles from the U.S. mainland. It is the only state outside North America, the only state that is an archipelago, a ...

Hawaii
as territories in 1898, and lacked the British
Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare Naval warfare is human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and int ...
's worldwide network of
coaling station Fuelling stations, also known as coaling stations, are repositories of fuel (initially coal and later oil) that have been located to service commercial and naval vessels. Today, the term "coaling station" can also refer to coal storage and feeding ...
s. 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 destroyers had fully geared turbines, and the United States followed in 1917. In the
Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare Naval warfare is human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and int ...
, speed was a priority until the Battle of Jutland in mid-1916 showed that in the battlecruisers too much armour had been sacrificed in its pursuit. The British used exclusively turbine-powered warships from 1906. Because they recognized that a long cruising range would be desirable given their worldwide empire, some warships, notably the s, were fitted with cruising turbines from 1912 onwards following earlier experimental installations. In the US Navy, the s, launched 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 / [saturated steam] on the World War I-era to / [superheated steam] on some World War II s and later ships. A standard configuration emerged of an axial-flow high-pressure turbine (sometimes with a cruising turbine attached) and a double-axial-flow low-pressure turbine connected to a double-reduction gearbox. This arrangement continued throughout the steam era in the US Navy and was also used in some Royal Navy designs. Machinery of this configuration can be seen on many preserved World War II-era warships in several countries. When US Navy warship construction resumed in the early 1950s, most surface combatants and aircraft carriers used / steam. This continued until the end of the US Navy steam-powered warship era with the s of the early 1970s. Amphibious and auxiliary ships continued to use steam post-World War II, with , launched in 2001, possibly the last non-nuclear steam-powered ship built for the US Navy.


Turbo-electric drive

Turbo-electric transmission, Turbo-electric drive was introduced on the battleship , launched in 1917. Over the next eight years the US Navy launched five additional turbo-electric-powered battleships and two aircraft carriers (initially ordered as s). Ten more turbo-electric capital ships were planned, but cancelled due to the limits imposed by the Washington Naval Treaty. Although ''New Mexico'' was refitted with geared turbines in a 1931–1933 refit, the remaining turbo-electric ships retained the system throughout their careers. This system used two large steam turbine generators to drive an electric motor 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 Destroyer escort (DE) was the United States Navy ), (unofficial)."''Non sibi sed patriae''" ( en, "Not for self but for country") (unofficial). , colors = Blue and gold  , colors_label = Colors ...
in
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a World war, global war that lasted from 1939 to 1945. It involved World War II by country, the vast majority of the world's countries—including all the great ...
. However, when the US designed the "treaty cruisers", beginning with launched in 1927, geared turbines were used to conserve weight, and remained in use for all fast steam-powered ships thereafter.


Current usage

Since the 1980s, steam turbines have been replaced by gas turbines on fast ships and by diesel engines on other ships; exceptions are nuclear marine propulsion, nuclear-powered ships and submarines and LNG carriers. Some auxiliary ships continue to use steam propulsion. In the U.S. Navy, the conventionally powered steam turbine is still in use on all but one of the Wasp-class amphibious assault ship, Wasp-class amphibious assault ships. The
Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare Naval warfare is human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and int ...
decommissioned its last conventional steam-powered surface warship class, the , in 2002, with the Italian Navy following in 2006 by decommissioning its last conventional steam-powered surface warships, the s. In 2013, the French Navy ended its steam era with the decommissioning of its last . Amongst the other blue-water navies, the Russian Navy currently operates steam-powered s and s. The Indian Navy currently operates INS ''Vikramaditya'', a modified ; it also operates three s commissioned in the early 2000s and one scheduled for decommissioning. The Chinese Navy currently operates steam-powered s, s along with s and the lone Type 051B destroyer. Most other naval forces have either retired or re-engined their steam-powered warships. As of 2020, the Mexican Navy operates four steam-powered former U.S. s. The Egyptian Navy and the Republic of China Navy respectively operate two and six former U.S. s. The Ecuadorian Navy currently operates two steam-powered s (modified s). Today, propulsion steam turbine cycle efficiencies have yet to break 50%, yet diesel engines routinely exceed 50%, especially in marine applications. Diesel power plants also have lower operating costs since fewer operators are required. Thus, conventional steam power is used in very few new ships. An exception is LNG carriers which often find it more economical to use LNG carrier#Reliquefaction and boil-off, boil-off gas with a steam turbine than to re-liquify it. Nuclear marine propulsion, 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 The Royal Navy (RN) is the United Kingdom's naval warfare Naval warfare is human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and int ...
's s 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 Nuclear marine propulsion#Civilian nuclear ships, commercial vessels due to the expense of maintenance and the regulatory controls required on nuclear systems and fuel cycles.


Locomotives

A steam turbine locomotive engine is a steam locomotive driven by a steam turbine. 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. 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.


Testing

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 cycle, 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.


See also

* Balancing machine * Mercury vapour turbine * Steam engine * Tesla turbine


References


Notes


Sources

* * * * * * * * * * * * * * * * * * * * * *


Further reading

* * * * *


External links

* ''gutenberg:27687, 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
Steam Turbine Construction at Mike's Engineering Wonders

Tutorial: "Superheated Steam"

Flow Phenomenon in Steam Turbine Disk-Stator Cavities Channeled by Balance Holes

Guide to the Test of a 100 K.W. De Laval Steam Turbine with an Introduction on the Principles of Design circa 1920



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

{{DEFAULTSORT:Steam Turbine 1884 introductions Arab inventions Egyptian inventions English inventions History of the steam engine, Turbine Steam engines, Turbine Steam turbines, 19th-century inventions