Uncle Bobs Tips: Generator Guide

Steam Turbines

Large steam turbines driving turbo-generators are used by electrical power stations to produce most of the world's electricity.

A steam turbine is a form of heat engine that extracts the energy of pressurized super-heated steam as mechanical movement. Since the turbine generates rotary motion, it is particularly suited to drive an electrical generator. The modern steam turbine was invented in 1884 by an Irishman, Charles A. Parsons, whose design was connected to a dynamo that generated 7.5 kW of electricity. His model was improved upon shortly after by an American, George Westinghouse, whose model was followed by the de Laval turbine (invented by Gustaf de Leval), which accelerated the steam to full speed before running it against a turbine blade. This was good, since the turbine is simpler, less expensive and does not need to be pressure-proof. This means that it can operate with any pressure of steam.

Here are the basic principles of how a steam turbine works: Nozzles in a steam turbine apply pressurized supersonic steam to a set of curved blades mounted on a rotor. Each blade whips the steam back in the opposite direction, simultaneously allowing the steam to expand a little. A stationary blade then redirects the steam towards the next set of blades toward the exhaust end with the gap between acting like a nozzle. The process repeats in successive stages until the steam is exhausted at nearly atmospheric pressure. Turbines always consist of a number of stages, with each stage being carefully optimised for the pressure and volume of steam that it contacts. Because high pressure steam travels so fast, the turbine must rotate very quickly. In order to protect it against vibrations and the extremely strong centrifugal forces experienced by the blade, the rotor and its blades must be extremely well balanced, and it must be made out of the strongest available materials.

To ensure even heating and to prevent uneven expansion, when warming up a steam turbine for use, the main stop valves before 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. In addition, when there is no steam, a turning gear is engaged to the turbine to slowly rotate the turbine. The turning gear is disengaged when first rotating the turbine by steam. When a steam turbine such as a turbo-generator is operating, any water entering the blades can cause destruction of the thrust a turbine with a governor is essential.

Today, problems with turbines are rare and maintenance requirements relatively small. Although turbines are expensive to make, requiring precision manufacture and special quality materials, this purchase cost is offset by much lower fuel and maintenance requirements and the small size of a turbine when compared to a reciprocating engine having an equivalent power.

Large steam turbines driving turbo-generators are used by electrical power stations to produce most of the world's electricity. These centralised stations are of two types: fossil fuel power plants and nuclear power plants. Steam turbines are also used in ships, where their small size is an advantage. Steam turbine locomotives were also tested, but with limited success.

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