Steam turbine

A steam turbine is a special kind of machine that uses hot, pressured steam to create movement. This movement can do useful work, like turning the blades of a fan or making electricity.

The modern steam turbine was invented by Sir Charles Parsons in 1884. It changed how ships could travel and how we move around the world.

Steam turbines are very important because they help turn heat energy into electricity. When the steam spins inside the turbine, it creates a whirling motion that powers generators. These generators are used in power plants that burn fossil fuels, use nuclear fuels, or even use energy from the Earth or sun.

Making a steam turbine needs careful work with strong metals and precise engineering. The biggest steam turbine ever made can produce more than one thousand megawatts of power. Two of these huge machines will be used at the Hinkley Point C Nuclear Power Station in England.

History

Long ago, people made simple machines that used steam to spin. One early example was a small toy called the Aeolipile, made by Hero of Alexandria in Roman Egypt. Later, Charles Parsons invented the steam turbine in 1884. His first machine could make electricity, and it changed everything — making power easier to get and helping ships travel faster.

Parsons' design was used in big power stations around the world. Other inventors also made new kinds of steam turbines. These machines helped bring electricity to many places and changed how ships and power plants worked.

Manufacturing

Many companies make steam turbines today. Some of these companies include Ansaldo, Arabelle Solutions, Curtiss-Wright, Baker Hughes, and Doosan Škoda Power. Others are Dongfang Electric, EBARA-Elliot Energy, GE Vernova, Harbin Electric, and Larsen & Toubro. The list also includes Leningradsky Metallichesky Zavod, MAN Energy Solutions, MAPNA, Mitsubishi Heavy Industries, and Shanghai Electric. Additionally, there is Siemens Energy, Triveni Engineering & Industries, Ural TW, and EMS Power Machines.

Types

Steam turbines come in many sizes. They have blades and nozzles. Blades move when steam hits them, and nozzles change the steam’s pressure and speed.

There are two main types: impulse turbines and reaction turbines. Impulse turbines move by steam hitting the blades. Reaction turbines move by both steam hitting the blades and the steam’s pressure.

Most turbines have many stages to work better. The steam pressure drops a little at each stage, helping the turbine work at low speeds.

By 1905, steam turbines were used on fast ships and in power plants. High-pressure steam would enter through a throttle and pass through several stages before leaving at low pressure. Some turbines could also run in reverse for ships, though this was not as efficient.

Turbine types include condensing, non-condensing, reheat, extracting, and induction turbines.

Condensing turbines are used in power plants. They take steam from a boiler and let it out at very low pressure into a condenser.

Non-condensing turbines are used when the steam is needed for other purposes after leaving the turbine. The pressure is adjusted to match what is needed.

Reheat turbines are also used in power plants. Steam leaves a high-pressure part, goes back to the boiler to be heated more, then returns to the turbine to keep working.

Extracting turbines let steam out at different points to be used for other processes. This can lower the turbine’s power a little.

Induction turbines add low-pressure steam in the middle to make more power.

In some turbines, the steam pushes the shaft in two directions. Special designs like double-flow rotors are used to balance this, where steam enters in the middle and exits at both ends.

Principle of operation and design

A steam turbine is a machine that uses hot steam to spin a shaft and do work. It was invented by Sir Charles Parsons in 1884 and changed how ships could move.

Inside a steam turbine are sets of blades. Some blades are fixed and attached to the outer part, while others can spin and are attached to the shaft. The blades are arranged so that steam flows through them in a way that makes the shaft spin.

Impulse turbines

An impulse turbine uses special nozzles to turn steam into fast-moving jets. These jets hit the spinning blades, making them turn. The steam pressure drops only in the fixed blades, and its speed increases a lot. This high-speed steam then hits the moving blades, giving them energy to spin.

When the steam leaves the moving blades, it still has some speed, which means some energy is lost. This loss is called "carry over velocity" or "leaving loss."

The way the fluid moves follows certain rules that help us understand how the turbine works. These rules relate the speed and direction of the steam at different points in the turbine.

A "velocity triangle" helps explain how different speeds of the steam and blades relate to each other. These speeds include:

• The overall speed of the steam entering and leaving the turbine.
• The flow speed of the steam.
• The swirl speed of the steam.
• The speed of the blades.
• The angles of the blades.

Using these relationships, we can find out how much turning force the turbine creates and how much power it can generate.

Blade efficiency

Blade efficiency measures how well the blades turn the steam’s energy into spinning motion. It is calculated by comparing the work done on the blades to the energy supplied by the steam.

Stage efficiency

A stage of an impulse turbine includes a set of nozzles and a moving wheel of blades. Stage efficiency looks at how well the energy from the steam is turned into work by the blades. It relates the drop in steam energy in the nozzles to the work done by the blades.

By the rules of heat and energy, we know that the drop in steam energy in the nozzles is almost equal to the extra speed the steam gains. Stage efficiency is also the product of blade efficiency and nozzle efficiency.

Nozzle efficiency compares the actual speed the steam reaches to the ideal speed it should reach based on the drop in steam energy.

The design of some turbines, known as Parson’s turbine, uses symmetrical blades for both the fixed and moving parts.

Condition of maximum blade efficiency

To find the condition for the highest blade efficiency, we use a special way of comparing speeds. This shows that the best efficiency happens when the ratio of blade speed to steam speed equals the angle of the blades.

Operation and maintenance

Steam turbines need to be warmed up slowly to avoid damage. When starting, steam is allowed to flow slowly through the turbine to heat it up evenly. This warm-up can take many hours for large turbines.

During normal use, it’s important to keep the turbine balanced to prevent vibrations that could break blades. The steam used must be dry to stop damage to the blades and bearings. Regular maintenance keeps the turbine running well for many years.

Speed regulation

Turbines need to run at the right speed, especially when making electricity. Controls called governors adjust the steam flow to keep the speed steady. If the turbine speeds up too much, the governor shuts off steam to prevent damage.

Thermodynamics of steam turbines

Steam turbines work using basic heat and energy rules. Hot, high-pressure steam from a boiler enters the turbine and turns into fast-moving jets that spin the blades. This spinning can power a generator to make electricity. The steam leaves the turbine at a lower temperature and pressure and is cooled in a condenser.

We can measure how well a turbine works by looking at its isentropic efficiency. This compares the real performance of the turbine to an ideal one, assuming no heat loss. The efficiency is found by comparing the actual work done to the ideal work possible.

Direct drive

Power plants use big steam turbines to turn electric generators. These turbines help make most of the world's electricity. They made it easier to make electricity in big stations because old steam engines were too big and slow. Most of these plants burn fossil fuels or use nuclear power, but some use geothermal energy or concentrated solar power to make steam. Steam turbines can also power large pumps at power plants.

The turbines used for making electricity are usually connected right to the generators. Generators need to turn at steady speeds to match the power system's frequency. They often turn at 3,000 RPM for 50 Hz systems and 3,600 RPM for 60 Hz systems. Nuclear reactors, which have lower temperature limits, sometimes use turbine sets that turn at half these speeds with special generators to protect the turbine blades.

Marine propulsion

See also: Marine steam engine

In steamships, steam turbines have some advantages over older engines. They are smaller, lighter, and need less upkeep. But steam turbines work best at very high speeds, while ship propellers work best at slower speeds. Because of this, special gears are usually needed to connect the turbine to the propeller. Some early ships, like Turbinia, connected the turbine directly to the propeller without gears. Another way is turbo-electric transmission, where the turbine powers a generator that then powers an electric motor connected to the propeller. This was used in some big warships and fast ships during World War I and II.

Steam turbines cost more and need more complex gears or generators, but they save on upkeep and are smaller than older engines. Even though they use more fuel than diesel engines, they have become more efficient over time.

Locomotives

A steam turbine locomotive is a special type of steam locomotive that uses a steam turbine to move. The first one was made in 1908 in Milan, Italy. Later, in 1924, a company called Krupp built another one for Deutsche Reichsbahn, and it started working in 1929.

These locomotives moved more smoothly and hit the tracks less hard. But they were not good at changing speeds quickly, so they worked best for long trips where the power stayed the same.

Testing

Different countries and groups have rules for testing steam turbines. These rules help everyone do the tests the same way and see how well the turbine works.

In the United States, a group called ASME made test rules for steam turbines. These rules are used around the world to make sure the tests are fair and accurate. One special thing about these rules is that they show how exact the test results are.