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98-Mar-B5 December 2016 Page 5 of 20 QUESTION 3 HYDRO TURBINE DESIGN Refer to the Examination Paper Attachments Page 13 Hydro Turbine Parameters. ar In the preliminary stages in the design of a hydro power plant some basic dimensions need to be established. The conditions suggest a turbine of the Francis type as shown in the figure above. Each turbine has to have a power output under the available head as indicated below: Electrical power output Available net head 200 MW 110 m A typical Francis turbine has the following characteristics: Efficiency Specific speed Runner blade inlet angle Flow velocity ratio Blade velocity ratio See chart on Page 13 Ns = 0.9 a = 22° (relative to tangent to runner) Vatroute/Vjet = 0.77 Volade/jot = 0.6583 Note that Vjet is the free jet velocity when subject to the given head. (a) Determine, from the diagram of efficiencies for hydro turbines, the expected efficiency and hence the hydraulic power input to achieve the specified electrical output (1) (b) (c) Calculate the rotational speed of the turbine and hence the runner diameter (4) Draw a velocity (vector) diagram of the flow conditions at the runner inlet and determine the radial inlet velocity. A scale of 10 mm = 2.5 m is suggested. (3) Calculate the water flow rate and hence the height of the runner inlet (vertical height of flow area). (e) [ 10 marks)
98-Mar-B5 December 2016 Page 13 of 20 EXAMINATION PAPER ATACHMENTS QUESTION 3 HYDRO TURBINE PARAMETERS Turbine Efficiencies 1.0 Francis Kaplan Pelton Efficiency, lo 0.8 0.04 1 2.0 0.1 4.0 10 0.2 0.4 1.0 Specific speed, so (rad) Typical design point efficiencies for Pelton, Francis and Kaplan turbines Velocity Diagram Stationary pivoted guide vanes 1.41 Hai Relative oath 24. V1 02 Rotating runner vane Absolute path 2 Velocity vectors for radial inward flow hydraulic turbine (Francis type) Microsoft Word File