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Types of Hydraulic Turbines

Tania Alam

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Turbines are machines which convert fluid energy to mechanical energy. When the fluid used is water, they are called hydraulic turbines. 
Hydraulic turbines may be classified on the basis of four characteristics :
 
 
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  • On the basis of the type of energy at the turbine inlet
Impulse turbine
  • total head of the incoming fluid is converted in to a large velocity head at the exit of the supply nozzle ( entire available energy of the water is converted in to kinetic energy.)
  • water entering the runner of a reaction turbine has only kinetic energy
  • the rotation of runner or rotor (rotating part of the turbine) is due to impulse action
  • Flow regulation is possible without loss
  • Unit is installed above the tailrace
  • Casing has no hydraulic function to perform, because the jet is unconfined and is at atmospheric pressure. Thus, casing serves only to prevent splashing of water.
  • It is not essential that the wheel should run full and air has free access to the buckets.

eg - Pelton wheel turbine ( efficient with a large head and lower flow rate.)

 
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Reaction or Pressure turbine
  • the penstock pipe feeds water to a row of fixed blades through casing that convert a part of the pressure energy into kinetic energy before water enters the runner
  • water entering the runner of a reaction turbine has both pressure energy and kinetic energy
  • the rotation of runner or rotor (rotating part of the turbine) is partly due to impulse action and partly due to change in pressure over the runner blades
  • Water leaving the turbine is still left with some energy (pressure energy and kinetic energy) 
  • It is not possible to regulate the flow without loss
  • Unit is entirely submerged in water below the tailrace
  • Casing is absolutely necessary, because the pressure at inlet to the turbine is much higher than the pressure at outlet. Unit has to be sealed from atmospheric pressure.
  • Water completely fills the vane passage.

 eg - Francis and Kaplan turbines ( efficient with medium to low heads and high flow rates )

 
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  • On the basis of the direction of flow through the runner
Tangential flow turbine
 

Direction of flow is along the tangent of the runner

 eg - Pelton wheel turbine.

 
pelton turbine.gif
 
Radial flow turbine
 

Direction of flow is in radial direction

  • radially inwards or centripetal type, eg- old Francis turbine
  • radially outwards or centrifugal type, eg -Fourneyron turbine
Stay_guide_vanes.png       Reaction.gif
 
Axial flow turbine
 
  • Direction of flow is parallel to that of the axis of rotation of the runner
  • the shaft of the turbine is vertical, lower end of the shaft is made larger which is known as hub (acts as runner)

 

eg - Propeller turbine ( vanes are fixed to the hub and they are not adjustable )

       Kaplan turbine (vanes on hub are adjustable )

 

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Mixed flow turbine
 
  • Water flows through the runner in the radial direction but leaves in a direction parallel to the axis of rotation of the runner

 eg- Modern Francis turbine.

 
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  • On the basis of the head at the turbine inlet

High head turbine

  • net head varies from 150m to 2000m or even more
  • small quantity of water required

eg -: Pelton wheel turbine.

 

Medium head turbine

  • net head varies from 30m to 150m
  • moderate quantity of water required

eg -: Francis turbine.

Low head turbine

  • net head less than 30m
  • large quantity of water required

eg -: Kaplan turbine.

 
  • On the basis of the  specific speed of the turbine

Before getting into this type, one should know what the specific speed of a turbine is. It defined as, the speed of a geometrically similar turbine that would develop unit power when working under a unit head (1m head).


 

Low specific speed turbine

  • specific speed is less than 50. (varying from 10 to 35 for single jet and up to 50 for double jet ) 

eg -: Pelton wheel turbine.


 

Medium specific speed turbine

  • specific speed varies from 50 to 250

eg -: Francis turbine


 

High specific speed turbine

  • specific speed more than 250

eg -: Kaplan turbine

   
 
References :

1. Course contents on NPTEL website

2. A textbook of Fluid Mechanics and HydraulicMachines - R.K. Bansal

3. Fluid Mechanics: Including Hydraulic Machines - A.K. Jain

7 hours, 59 minutes ago


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Hello,

interesting article.

I think you mixed the examples for high and mixed head turbines. Acc. to my knowledge (I'm not an expert in hydroenergy) Pelton turbines are use for high heads. I have seen such turbines in northern Italy or on the island of Madeira, where they get high heads due to the mountains.

I'm invested in a power plant with Francis turbines (unfortunately only a small one), where the height seems to be about 10m, perhaps 15m between max. height and outlet at the end of the suction tube.

Regards,

Alban

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21 hours ago, Tania Alam said:

Dear @Alban Kronenberger,

Thank you so much for pointing out the mistake. I actually interchanged the examples of High head and medium head turbines, while formatting. And it's good to see people, actually reading your post so carefully and providing you feedback.

Regards,

Tania

do correct it for others

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On 12/7/2016 at 1:50 AM, Mostafa El-moughazy said:

What is the meaning of the head turbine

In simple words, head is a representation of the energy contained in a fluid, it may be potential or kinetic. If you want a detailed explanation you can read the answers on Quora to the question "What is head in pumps? What is the physical meaning of head in pressure head, velocity head, kinetic head, etc.?" Although the answers are written for pumps, the explanations are quite well-written and valid for turbines as well.

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