Classification Of Hydraulic Turbine

⚡️Impulse turbine

Energy available at inlet kinetic energy 

1)Pelton wheel Turbine 

●High head tangential flow turbine

●Note-  Casing is only to prevent splashing of water does not form in Hydraulic function in pelton Wheel Turbine

●Nozzle at end of penstock convert pressure energy into kinetic energy

●Bucket shape double hemispherical Cup or Bowl

●Hydraulic efficiency of pelton wheel will be maximum when the velocity of wheel is the half the velocity of the jet of water at inlet u=V1/2

●Angle of deflection of the jet through bucket 165°

●Jet ratio(m)= Pitch diameter of pelton wheel(D) /diameter of jet(d)

●Number of bucket (Z) = 15+0.5m

●Speed ratio (fi) =velocity of pelton wheel (u)/ velocity of Jet from nozzle(√2gh)
= 0.43 to 0.47

⚡️Reaction turbine

Energy at inlet kinetic energy + pressure energy

●To maximize the efficiency of reaction turbine angle of absolute velocity at outlet is 90°
i.e. Vw2=0

1) Francis turbine
●Old Francis =  Inward radial flow reaction turbine ( water flows from outward to inward )
● Modern Francis = Mixed flow reaction turbine (i.e. inward radial + Axial)

2) Kaplan & propeller
Axial flow reaction turbine

●Kaplan = Vanes are Adjustable
●Propeller = Vanes are fixed to the hub and they are not adjustable

Note - Servometer used to adjustment of runner blades

⭐️Draft tube 

 Tube or pipe of gradually increasing area is used for discharging water from the exit of turbine to the tail race
Always submerged in water below Tail race level

●Converts kinetic energy into the pressure energy
●To increase  the net head on the turbine
●It permits negative head

Turbine             Sp. Speed       Head         
--------------------------------------------------------                                                                     
Pelton
1)Single Jet         10-35            >250m
2)Double Jet       35-60

FRANCIS             60-300          30-250m

KAPLAN &.        300- 1000      <30m
 Propeller
---------------------------------------------------------

⚡️Specific speed of turbine 

Speed at which turbine runs when it is working under a unit head and develops unit horsepower
 (N√p)/(H^5/4)

◆Characteristic curves of hydraulic turbine
1)Main characteristic curve constant head
2)Operating characteristic curves constant speed
3) Muchel curve or Isoefficiency curve constant efficiency

Governing of turbine operation by which speed of turbine kept constant at all condition of working

⭐️Cavitation of turbine 

When pressure falls below below Vapour pressure

●Only reaction turbine and centrifugal pumps subjected to cavitation

●In reaction turbine cavitation may occur at outlet of the runner or at the inlet of the draft tube

●In centrifugal pumps cavitation occurs at the inlet of impeller of pump Or at the suction side of the pump

Note= When Thoma cavitation factor greater than critical cavitation factor cavitation will not occur


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