The specific speed of a turbine is the speed of an imaginary turbine, identical with the given turbine, which

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  1. delivers unit discharge under unit speed
  2. delivers unit discharge under unit head
  3. develops unit power under unit speed
  4. develops unit power under unit head

Answer (Detailed Solution Below)

Option 4 : develops unit power under unit head
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Explanation:

The specific speed of a turbine is defined as, the speed of a geometrically similar Turbine that would develop unit power when working under a unit head (1m head). Is prescribed by the relation  \({N_s} = \frac{{N\sqrt P }}{{{H^{\frac{5}{4}}}}}\)

  • Low specific speed turbine: The specific speed is less than 50. (varying from 10 to 35 for single jet and up to 50 for a double jet) Example: Pelton wheel turbine
  • Medium-specific turbine: The specific speed varies from 50 to 250. Example: Francis turbine
  • High specific turbine: the specific speed is more than 250. Example: Kaplan or propeller turbine
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