The steam turbine on a page about engines? Maybe you wondered about it. It is hardly used in means of transport, but the steam turbine has many things in common with the combustion engine. The steam turbine changes chemically stored energy into mechanical energy, too. It's called a heat-force engine. The steam turbine works similarly to the water turbine, which is known probably by everyone. Not water, but steam is used as working medium.
Turbine types
When people began to use water power to win mechanical work, they looked first for the best forms of impellers. Three types were established thereby and variations of them are used today in various applications, among other in steam turbines in power stations, as marine propellers, as compressors in gas turbines etc. These three types are introduced here:
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Besides the types described above, there are still other types of water turbines, e.g. the Bànki turbine, which are not closer described here.
From the water- to the steam turbine
The won realizations with water power let the researchers expect similar results with steam, too. Numerous engineers took part in the development of the steam turbine in the second half of the 19. Century. To mention are the Englishman Charles Parsons, the Swede Carl Gustav Laval and the American Charles Curtis, who made crucial contributions for the development of the steam turbine.
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| Diagram: 2-step steam turbine after Parsons (1883). This turbine possesses two impellers and an idler in the center. enlarge (154 K, 510 * 570), Image (18 K, 255 * 285), Mini steam turbine (For your website) (11 K, 100 * 112) |
Mode of operation of the steam turbine
Since it is a steam jet and no more a water jet who meets the turbine now, the laws of thermodynamics are to be observed now. The modern steam turbine is an action turbine (no reaction turbine), i.e. the steam jet meets from a being certain nozzle the freely turning impeller. There's a high pressure in front of the turbine, while behind it a low pressure is maintained, so there's a pressure gradient: Steam shoots through the turbine to the rear end. It delivers kinetic energy to the impeller and cools down thereby: The pressure sinks.
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Multi-level steam turbines
In modern steam turbines not only one impeller is propelled, but several being in a series. Between them idlers are situated, which don't turn. The gas changes its direction passing an idler, in order to perform optimally work again in the next impeller. Turbines with several impellers are called multi-level. The principle was developed 1883 by Parsons. As you know, with the cooling gas expands. Therefore it is to be paid attention when building steam turbines to a further problem: With the number of passed impellers also the volume increases, which leads to a larger diameter of the impellers. Because of that, multi-level turbines are always conical.
Coupling of several turbines
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| Grafic: Coupled steam turbine. source: Helmut Hütten, "Motoren", Motorbuchverlag Stuttgart, S.379 |
In power stations today, different types of turbines are used in a series, e.g. one high pressure -, two medium- and four low pressure turbines. This coupling leads to an excellent efficiency (over 40%), which is even better than the efficiency of large diesel engines. This characteristic and the relatively favorable production make the steam turbine competitionless in power stations. Coupled with a generator and fired by an atomic reactor, they produce enormously much electric current. The strongest steam turbines achieve today performances of more than 1000 megawatts.
