Steam turbine

A steam turbine is a special kind of machine that uses hot, pressured steam to create movement. This movement can be used to do useful work, like turning the blades of a fan or spinning a generator to make electricity. The modern steam turbine was invented by Sir Charles Parsons in 1884, and 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 can power generators. These generators are used in power plants that burn fossil fuels, use nuclear fuels, or even use energy from the Earth or sun. In the United States alone, almost half of the electricity we use comes from steam turbines.

Making a steam turbine needs very 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, showing just how important these machines are for providing clean and reliable energy.

History

Long ago, people created simple machines that used steam to spin around. One early example was a tiny toy called the Aeolipile, made by Hero of Alexandria in Roman Egypt. Over time, others also made small steam machines. But the steam turbine as we know it today was invented in 1884 by Charles Parsons. 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 created new kinds of steam turbines, each with their own ideas and improvements. These machines helped bring electricity to many places and changed how ships and power plants worked.

Manufacturing

Today, many companies make steam turbines. 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 because steam hits them, while nozzles change the steam’s pressure and speed.

There are two main types: impulse turbines and reaction turbines. Impulse turbines use steam hitting blades to move, while reaction turbines use both steam hitting and the steam’s pressure to move.

Most turbines have many stages to improve efficiency. This means the steam pressure drops a little at each stage, making the turbine work better 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 where 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. To balance this, special designs like double-flow rotors are used, where steam enters in the middle and exits at both ends, balancing the forces.

Principle of operation and design

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

Inside a steam turbine are sets of blades. Some blades are fixed and attached to the outer casing, 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. For this design, certain relationships between blade angles and steam speeds simplify the calculations.

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

Electrical power stations use large steam turbines to drive electric generators, producing most of the world's electricity. These turbines made it practical to generate electricity in central stations because older steam engines were too big and slow. Most of these stations use fossil fuels or nuclear power, but some use geothermal energy or concentrated solar power to create steam. Steam turbines can also directly power big pumps at thermal power plants.

The turbines used for making electricity are usually connected directly to the generators. Because generators need to turn at steady speeds to match the power system's frequency, they commonly 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 several advantages over older engines. They are smaller, lighter, need less maintenance, and vibrate less. However, 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 option is turbo-electric transmission, where the turbine powers a generator that then powers an electric motor connected to the propeller. This was common in some large warships and fast liners during World War I and II.

Steam turbines cost more and need more complex gears or generators, but they save on maintenance and are smaller than older engines. Even though they use more fuel than diesel engines, their efficiency has improved over time.

Locomotives

A steam turbine locomotive is a special type of steam locomotive that uses a steam turbine to move. The very 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 had some good points, like smoother movement and less hard hitting on the tracks. But they were not as good for changing speeds quickly, so they worked best for long trips where the power stayed the same.

Testing

Different countries and groups have special rules for testing steam turbines to make sure everyone does the tests the same way. These rules help decide how well the turbine works.

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