What is a Turbine?

What is a Turbine? There are a lot of definition of turbine. We sort of turbine definitions from different sources.

Turbine : A turbine has blades at one end and electromagnets at the other which create electricity as the blades move. Turbines are using in creating electricity from wind, water and steam power. Biomass

Turbine : The part of a generating unit which is spun by the force of water or steam to drive an electric generator. A turbine usually consists of a series of curved vanes or blades on a central spindle. Chelanpud

Turbine : Rotary engine in which the kinetic energy of a moving fluid is converted into mechanical energy by causing a bladed rotor to rotate. Princeton


  • Water under pressure contains energy.
  • Turbines convert the energy in water into rotating mechanical energy.
  • Impulse turbines convert the kinetic energy of a jet of water to mechanical energy.
  • Reaction turbines convert potential energy in pressurized water to mechanical energy.

Impulse Turbines

An impulse turbine the potential energy, or the head of water, is first converted into kinetic energy by discharging water through a carefully shaped nozzle. The jet, discharged into air, is directed onto curved buckets fixed on the periphery of the runner to extract the water energy and convert it to useful work.ic of an reaction turbine

  • Tolerate sand.
  • Easy to fabricate.
  • Efficient at wide a range of head and flow.
  • A nozzle converts pressurised water into a high-speed jet of water.
Schematic of an impulse turbine

Pelton Turbine


–Low Flow

–Medium to High Head


–Medium Flow

-Medium to High Head


–High Flow

–Low to Medium Head

Pelton Turbine

The Pelton wheel is among the most efficient types of water turbines. It was invented by Lester Allan Pelton (1829–1908) in the 1870s, and is an impulse machine, meaning that it uses the principle of Newton’s second law to extract energy from a jet of fluid.

  • At least one jet of water strike the buckets at atmospheric pressure.
  • Maximum jet diameter about 1/3 bucket width.
  • More jets increase flow and are used at low head.

Turgo Turbines

The Turgo turbine is an impulse water turbine designed for medium head applications. Operational Turgo Turbines achieve efficiencies of about 87%. In factory and lab tests Turgo Turbines perform with efficiencies of up to 90%.

  • Similar to Pelton runner, but a more complex blade design.
  • Greater flow possible

Crossflow Turbines

Banki or Mitchell turbine.A cross-flow turbine, Banki-Michell turbine, or Ossberger turbine is a water turbine developed by the Australian Anthony Michell, the Hungarian Donát Bánki and the German Fritz Ossberger.

  • Shaft oriented horizontally.
  • Rectangular nozzle forms the jet.
  • Water strikes the blades twice.
  • A control vane changes jet size

Reaction Turbines

In a reaction turbine, forces driving the rotor are achieved by the reaction of an accelerating water flow in the runner while the pressure drops. The reaction principle can be observed in a rotary lawn sprinkler where the emerging jet drives the rotor in the opposite direction. Due to the great variety of possible runner designs, reaction turbines can be used over a much larger range of heads.

  • Expensive blade manufacture.
  • High flow rates.
  • More site specific than impulse.
  • Uses pressure drop across turbine.
  • Cavitationmust be avoided.
  • High turbine speed at low head.
Differences between impulse and reaction turbine

Reaction Turbines

  • Francis

–Medium Head

  • Propeller and Kaplan

–Low Head

  • Pump as Turbine

–Medium Head

Francis Turbine

Francis turbines are probably used most extensively because of their wider range of suitable heads, characteristically from three to 600 metres. At the high-head range, the flow rate and the output must be large; otherwise the runner becomes too small for reasonable fabrication. At the low-head end, propeller turbines are usually more efficient unless the power output is also small.

  • Guide vanes may be adjusted by governor.
  • Efficiency decreases as flow decreases.
  • Water flow is radial from exterior to interior.
  • Flow changes gradually from radial to axial.

Propeller Turbine

Fixed propeller-type turbines are generally used for large units at low heads, resulting in large diameters and slow rotational speeds.

  • Similar to ships propeller.
  • Has guide vanes similar to Francis Turbine.
  • A Kaplan Turbine has variable pitch blades.
  • Part flow efficiency is poor

Pump as Turbine

  • Centrifugal pumps may be used as turbines.
  • Low cost due to mass production.
  • No direct correlation between pump characteristics and turbine characteristics.
  • Flow is fixed for a given head.
  • Some manufacturers have tested their pumps as turbines.
  • Good for grid-tie with induction motors.


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•Microhydroby Scott Davis
•MicrohydroDesign Manualby Adam Harvey
•Waterturbine.comfor picohydrounits
•BC Hydro Handbook
•Idaho National Labs

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