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Posted by: poornakumar b on 2010-02-15, 07:50:20
You are entering into the design procedure of a 'turbine' that is the subject matter of a typical course in electrical engineering. Again, design of 'Thermal' plant is different from 'hydel (hydro-electric)' design. In 'thermal' (Thermodynamics) case it depends on the steam pressure and temperature (normally) - in how many stages (a stage has one wheel like turbine rotor) till the last when the pressure comes down to atmospheric pressure (nearly a hundred thousand Pascals or 14 pounds per square inch). Mostly the exhaust steam from condenser stage is collected in an economiser where it gives up heat to 'water' that gets pre-heated before converting into steam thus recycling the waste heat. 'Parsons' designed and operated the first steam turbine and the basic design is still good where 80% electricity is produced by steam turbines that includes nuclear power generation. Hydro-electric generation has different turbines for different 'heads' (a head is the height through which water falls unobstructed onto the turbine), most of them mounted horizontally (axis vertical). For a thousand feet head 'Pelton wheel' is the choice, for medium heads of five to eight hundred feet 'Francis' turbine is used. 'Kaplan' turbine design is preferred for small heads of upto ten feet. I saw a Francis turbine rotating at 18 3/ 4 rpm (75 revolutions in 4 minutes). The mechanical power (rotary power) is in the shaft (now) on which the rotor of the electric generator is mounted. Shaft is only delivering the power to electrical generator called 'Alternator'. Questions like magnetic strength of the magnets and the length of the coil are in the design of the machinery. It varies from plant to plant and on power generation specification. |
