A steam turbine is a rotary machine that extracts energy from pressurized steam and delivers mechanical power through a rotating shaft. Steam passes through stationary passages and moving blades, expanding toward a lower pressure while driving the rotor. The shaft can operate an electric generator, pump, compressor, or propulsion system. Unlike a reciprocating steam engine, a turbine produces continuous rotation without a piston-and-crank mechanism. Steam turbines are used in power stations, industrial facilities, and marine installations. (betterbuildingssolutioncenter.energy.gov)
Historical development
Practical modern steam turbines emerged in the late nineteenth century. Gustaf de Laval patented a turbine for steam and other motive power in 1883 and subsequently developed arrangements that converted steam energy into a high-velocity jet before it reached the turbine wheel. This approach became associated with impulse turbines. In 1884, Charles Parsons developed a multistage turbine connected to an electrical generator; an original example survives in the Science Museum Group collection. (en.wikisource.org)
Parsons divided steam expansion among successive stages rather than imposing the entire pressure drop on one wheel. This made efficient power extraction possible without requiring excessively high blade speeds. His work helped establish turbine-driven electricity generation and marine propulsion. The experimental vessel Turbinia demonstrated turbine propulsion at the 1897 naval review celebrating Queen Victoria’s Diamond Jubilee, contributing to its adoption in naval and commercial steamships. (asme.org)
Operating principles
A turbine’s operation combines thermodynamics with the mechanics of fluid flow. Stationary nozzles or blade passages accelerate steam by allowing it to expand. Moving blades redirect the flow, changing its momentum and exerting a tangential force on the rotor. This produces torque; shaft power is the product of torque and angular velocity. Some installations use a reduction gear to match turbine speed to the requirements of the driven machine. (energy.gov)
Two principal stage designs are distinguished:
- Impulse stages: Ideally, the pressure drop occurs in the stationary nozzles, while pressure remains approximately constant across the moving blades. The rotor extracts power by changing the direction and velocity of the steam jets.
- Reaction stages: Steam expands in both stationary and moving blade passages. The moving passages also act as nozzles, and their pressure drop contributes to the force driving the rotor.
These categories describe how expansion is distributed, rather than separate sources of energy. Both designs convert energy in steam into shaft work. (energy.gov)
Construction and arrangements
A basic turbine contains stationary blades, moving blades attached to a rotor, and a pressure-retaining casing. Larger machines distribute expansion across numerous stages. Designers select blade geometry and stage arrangements for the required steam conditions, power output, and operating range. The resulting machine is therefore closely matched to its intended application rather than being interchangeable with any steam supply. (energy.gov)
Turbines are also classified by their exhaust arrangements. A condensing turbine exhausts into a condenser at a pressure below atmospheric pressure, increasing the available expansion and electrical output. A backpressure turbine discharges steam at a pressure suitable for another use, such as industrial heating. An extraction turbine removes part of the steam at an intermediate pressure; remaining steam can continue through subsequent stages. These configurations accommodate different balances between power production and useful heat delivery. (energy.gov)
Role in steam power cycles
In a conventional Rankine cycle, a pump raises the pressure of liquid water, a heat source produces steam, the turbine extracts work, and a condenser returns the exhaust to liquid. The turbine is only one component of this system: it does not itself supply the heat needed to generate steam. In nuclear power stations, energy released in the reactor ultimately produces the steam that turns the turbine and generator. (arxiv.org)
Practical cycles may include reheating between turbine sections and regenerative feedwater heating. Reheating limits excessive moisture during later expansion, while regeneration uses steam extracted from intermediate stages to warm feedwater before it enters the boiler. Moisture matters because high-speed water droplets can erode blades and reduce turbine performance. These modifications concern the behavior of the complete power cycle, not simply the efficiency of an isolated turbine. (epa.gov)
Applications and operating constraints
Steam can be generated using fossil fuels, biomass, or recovered industrial heat. In combined-cycle power plants, heat in gas turbine exhaust produces steam for an additional turbine. Smaller steam turbines also drive industrial pumps and compressors directly, avoiding an intermediate electrical conversion. (betterbuildingssolutioncenter.energy.gov)
In combined heat and power systems, backpressure or extraction steam supplies industrial processes or district heating while the turbine produces electricity. A turbine can also replace part of the function of a pressure-reducing valve, recovering mechanical power from a pressure reduction that would otherwise produce no shaft work. Overall CHP efficiency counts both useful heat and electricity and must not be confused with electricity-only efficiency. (betterbuildingssolutioncenter.energy.gov)
Operating conditions impose material and performance limits. Components must withstand high rotational speeds, temperature gradients, and exposure to steam. Superheated steam helps reduce moisture-related blade erosion, while hotter operating conditions require suitable alloy steels or nickel-based alloys. Maintenance includes inspection, repair, component replacement, and condition monitoring; digital monitoring can support maintenance based on observed equipment condition rather than elapsed operating time alone. (eere-exchange.energy.gov)