Specific speed of a turbine is defined as the speed of the turbine which:

Explanation:

Specific speed: 

• It is defined as the speed of a similar turbine working under a head of 1 m to produce a power output of 1 kW. The specific speed is useful to compare the performance of the various type of turbines. The specific speed differs for the different type of turbines and is the same for the model and actual turbine.

​\({N_s} = \frac{{N\sqrt P }}{{{H^{\frac{5}{4}}}}}\)

Following are the range of specific speed of different turbines

• The specific speed of Pelton wheel turbine (single jet) is in the range of 10-35
• The specific speed of Pelton wheel turbine (multiple jets) is in the range of 35-60
• The specific speed of the Francis turbine is in the range of 60-300.
• The specific speed of the Kaplan/propeller turbine is greater than 300.

Important Points  The classification of the turbine based on the basis of the operating head

The specific speed of a turbine is in the range of