1. G.H. Patel College of Engineering and Technology
: Fluid Power Engineering
ALA
TOPIC : PELTON WHEEL TURBINE
5th semester, AY:
: Milan Baria
: Shepal Bhansali
: Sanket Bhatt
: Karan Chunavala
: Ravi Dhandhania

2. Introduction
It is a free jet impulse turbine names after the American Engineer Lester Pelton( ) who contributed much to its development.
It is impulse, tangential flow, high head and low specific speed turbine.
The energy available at inlet of the turbine is only kinetic energy. So , it is called impulse turbine.

3. Running Video

4. Figure

5. Main Parts Of Pelton Wheel
Nozzle : It is a conical guide mechanism
Guides the water to flow at a desired direction
Regulate the flow of water
A conical spear operates inside nozzle in axial direction, used to control the quantity of water flowing through nozzle.
When the spear is pushed forward into the nozzle it reduces the area of jet, so quantity of water flowing through jet is reduced.

6. Continued.. 2) Runner and buckets:
A runner is a circular disc fixed to a horizontal shaft.
On periphery of runner, buckets are fixed uniformly.
Shape of bucket: Double hemispherical cup or bowl
Each bucket is divided into two symmetrical parts by dividing wall known as splitter.
The purpose of splitter is to split the water jet in two equal parts without shock.
When the bucket is exactly hemispherical cup, jet gets deflected through an angle 180· , force exerted on runner will be maximum.

7. Continued.. The surface of bucket is made very smooth.
Bucket is mode of bronze, stainless steel or cast iron.

9. Continued.. 3) Casing: The main function of casing is :
To prevent splashing of water
To guide the water to flow to tail race and provides safety against accidents.
In Pelton wheel , static pressure of water is atmosphere throughout turbine and hence it has no hydraulic function to perform.

10. Continued..
4) Break nozzle: It is used when it is required to stop turbine suddenly.
During shut-down, water flow through nozzle is stopped, but turbine rotates at higher speed because of inertia
So, breaking jet directed through break nozzle opposite to direction of rotation of runner.
This produces breaking torque on the bucket and stops runner immediately.

11. Continued..
5) Penstock: It is a large size pipe which conveys water from the high level reservoir to the inlet of the turbine
It is made of steel, concrete or wood depending upon head and quantity of water required.
6) Tail race: It is a passage for discharging water leaving the turbine into river.

12. Velocity Triangles

13. Continue… Velocity of runner, u1= u2= u= πDN/60
where, N= speed of wheel in RPM
D= diameter of wheel
α=0, θ=0, So, Vw1=V1 & Vr1=V1-u
u and V1 in same direction
For smooth surface of buckets, Vr1=Vr2
For non-smooth surface of buckets, energy losses due to impact at splitter . So, Vr2= KVr1
where K= blade friction co-efficient

14. Continued..
From impulse moment theorem, force exerted by jet of water on bucket in direction of motion of blade,
Fx= ρAV1 [Vw1±Vw2]
where, A= cross section area of jet = πd2/4
d= diameter of jet , ρ= density of water
Here, − sign is used when β>90° ,
+ sign is used when β<90°
Work done by jet on runner per second,
W= Fx × u = ρAV1 [Vw1±Vw2] × u

15. Continued.. Work done per second per unit weight of water striking,
WD/sec/unit weight = ρAV1 [Vw1±Vw2] ×u
ρAV1 × g
Kinetic energy of jet per second,
K.E.= mV12 = ρAV1×V12= ρAV13
Hydraulic efficiency,
ηh = WD per sec / K.E. of jet per sec
= ρAV1 [Vw1±Vw2] × u / ρAV13/2
∴ ηh= 2 [Vw1±Vw2] × u
V12

16. Continued.. But Vw1= V1 & Vr1= V1 −u = Vr2
From outlet velocity triangle,
Vw2= Vr2cosϕ−u2= Vr1cosϕ−u = (V1−u) cosϕ−u
ηh = 2[ V1+ (V1−u) cosϕ −u ] × u
V12
= 2[ (V1−u) + (V1−u) cosϕ ] × u
= 2 (V1−u) [ 1+ cosϕ ] × u

17. Continued.. The hydraulic efficiency will be maximum when , du
d[ ηh ] = 0 du
∴ d [ 2 (V1−u) ( 1+ cosϕ )× u ] = 0
du V12
∴ 2( 1+ cosϕ ) d [ V1u−u2] = 0
V du
∴ V1− 2u = 0
∴ u = V1 2

18. Continued..
Hence , hydraulic efficiency of Pelton wheel is maximum when the velocity of the wheel is half of the velocity of jet at inlet.
So, Maximum hydraulic efficiency,
(ηh)max =[2 (V1−u)[ 1+ cosϕ ]×u/ V12 ] u=V1/2
V12
= 2 ( V1− V1/2) ( 1+ cosϕ) ×(V1/2)
∴ (ηh)max = (1 + cos ϕ ) 2

19. Design aspect Velocity of jet : V1 = Cv (2gH)1/2
where , Cv = co-efficient of velocity = 0.98 to 0.99
H = net head on turbine
Velocity of wheel: u = Ku (2gH)1/2
where , Ku = speed ratio = 0.43 to 0.48
Angle of deflection of the jet (ϕ) : It may be taken as 165° or ϕ= 180−β if no angle of deflection is given.
Mean diameter of Pelton wheel :
D = 60u πN

20. Continued..
Jet ratio (m) : It is ratio of mean diameter of Pelton wheel (D) to diameter of jet (d).
Mostly it lies between 11 to 16.
m = D d
Number of buckets (z) : The no. of buckets for a Pelton wheel should be such that water jet is completely utilized by the buckets.
z = D 2d

21. Continued..
Number of jet (n) : In pelton wheel normally one nozzle is used.
However, more than one nozzle may be employed when more power is to be produced with same wheel, but maximum no. of nozzle is restricted to 6.
n = total flow rate of water
flow rate of water through a single jet
∴ n = Q q
where, q = π d2 V1 4

22. Continued.. Dimension of bucket : Length = 2d to 3d Width = 3d to 4d
Depth = 0.8 d to 1.2 d
where, d = diameter of jet

23. Specific speed of Pelton wheel
Specific speed may be defined as the speed of a geometrically similar turbine that would produce unit power under unit head at maximum efficiency.
Mathematically,
Ns = N√P
H5/4
where, N = normal speed of turbine in rpm
P = turbine power output in kW
H = net head of turbine in m

24. Continued.. Now, N = u×60 but u = Ku (2gH)1/2 πD ∴ N = 84.59 Ku H1/2 D
Now, Q = A × V1 = π d2 × Cv (2gH)1/2 4
= d2 × Cv × H1/2
Also, P = ηo × ρgQH
1000

25. Continued.. P = 34.128 d2 × H 3/2 × Cv × ηo
Putting value of Q in above equ., we get,
P = d2 × H 3/2 × Cv × ηo
Putting values of N and P in equ. of specific speed,
Ns = 494 × Ku × d × ( Cv × ηo)1/2 D
Put Ku = , Cv = , ηo = 0.85 , we get ,
Ns = 202 d = 202
D m
where, m = jet ratio = D/d

26. Continued..
Therefore specific speed of Pelton wheel is inversely proportional to the jet ratio for single jet.
For multi jet Pelton wheel ,
Ns = 202 √n m
where, n = no. of jets

27. Facts Of Pelton Wheel
Water strikes the runner tangential to the path of rotation of runner.
It is preferred at very high head and low discharge applications.
Specific speed of Pelton wheel : 9 to 40
Head available : above 250 m
Governing is done by needle valve fitted into the nozzle .

28. Characteristic Curves

31. Governing of Pelton wheel
Governing in Pelton wheel is done by means of air pressure governor with double regulation as spear and deflector control, which consists of
Centrifugal governor
Oil pump
Relay or control valve
Servomotor with spear rod and spear
Deflector mechanism

35. Video of Governing
Governing of Pelton Turbine.mp4