detailed theory and formulas for pelton wheel turbine.

1. IMPULSE TURBINE
 SUBMITTED TO- SUBMITTED BY-Mr.
ABHISHEK CHAUHAN KANWALDEEP SINGH
SG12927
MECHANICAL 5THSEM

2. IIMMPPUULLSSEE TTUURRBBIINNEE
Impulse turbine is the one in which the available
hydraulic energy is first converted into kinetic energy by
means of efficient nozzle.
High velocity jet issuing from the nozzle then strikes a
series of buckets fixed around the rim of wheel(runner).
The buckets change the direction of jet without changing
its pressure.
The resulting change in momentum sets bucket and
wheel into rotary motion and thus mechanical energy is
made available at the turbine shaft.

3. PPEELLTTOONN WWHHEEEELL TTUURRBBIINNEE
A pelton wheel is a free jet impulse turbine named
after the American engineer Lester Pelton (1829-
1908) .It is simple and the only hydraulic turbine
,which operates efficiently and is invariably used for
heads in excess of 450m . Smooth running and good
performance are the other common features of this
unit.

4. DDEESSCCRRIIPPTTIIOONN OOFF PPEELLTTOONN IIMMPPUULLSSEE
TTUURRBBIINNEE
 PENSTOCK- It is a large size conduit
which conveys water from high level
reservoir to the turbine . The penstock
may be of wood ,concrete ,or steel.
 SPEAR AND NOZZLE-Nozzle is used to
convert hydraulic energy into kinetic
energy .Spear is so arranged that it
can move forward or backward there
by decreasing or increasing the annular
area of nozzle passage.

5. CASING-Casing is provided to prevent strong splash
of water ,which scatter in all directions and to guide
the water to the tail race.
This casing also acts as a safeguard against accidents.
RUNNER WITH BUCKET- The turbine rotor,
called the runner , is a circular disk carrying a number
of cup shaped buckets which are arranged
equidistantly around the periphery of the disk .
For low heads the buckets are made of cast iron ,but for
higher heads they are made of bronze ,cast steel,or
stainless steel.

6. BREAKING JET-when the nozzle is completely
closed ,the amount of water striking the runner
reduces to zero. But the runner due to inertia goes on
revolving for long time . To stop the runner in short
time , a small nozzle is provided which directs the jet
of water on the back of vanes . This jet of water is
called breaking jet.

7. GGOOVVEERRNNIINNGG MMEECCHHAANNIISSMM
Speed of the turbine runner is required to be
maintained constant so that the electric generator
coupled directly to the turbine shaft runs at constant
speed under varying load conditions.

8. DDeessiiggnn ooff PPeellttoonn ttuurrbbiinneess

9. NNUUMMBBEERR OOFF JJEETTSS
Generally a pelton wheel has one
nozzle or one jet . However a number
of nozzles may be employed when
more power is to be produced with
the same wheel .The nozzles are
spaced evenly around the same runner.
Theoretically 6 nozzles can be used
with one pelton wheel.
Practical considerations ,however ,limit the use of not
more than 2 jets per runner for a vertical runner, and
not more than 4 per runner when it is in horizontal
position.

10. NNUUMMBBEERR OOFF BBUUCCKKEETTSS
 The number of buckets should be few as possible so that
there is little loss due to friction.
 The jet of water must be fully utilized so that no water from
the jet goes waste i.e no water escapes without striking the
buckets .
 Z=15+D/2d
DEPTH AND WIDTH OF BUCKETS
Width of bucket =5d
Depth of bucket =1.2d

11. JJEETT RRAATTIIOO
m represents the ratio of the pitch circle
diameter to the jet diameter. (m=D/d)
For maximum hydraulic efficiency ,the jet ratio
lies between 11 and 15 and normally a jet
ratio of 12 is adopted.
A bulky installation results when a larger value
of jet ratio is adopted.
Its value is nearly equal to 12.

12. VVEELLOOCCIITTYY TTRRIIAANNGGLLEESS
The inner velocity triangle is drawn at the
splitter and outlet velocity triangle is drawn at
the outer edge of the bucket

13. H=net head acting on the pelton wheel
=Hg -Hf , where Hg=gross head and hf=4fLV2/D*2g
Where D*=dia of penstock, N =speed of the wheel in
rpm
D=dia of wheel, d=dia of the jet
THEN V1=velocity of jet at inlet=sq. root2gH
u=u1=u2=3.14DN/60
the velocity triangle at inlet will be a straight line where
Vr1=V1-U1=V1-u
Vw1=V1

14. PPOOWWEERR
WATER POWER-The
power supplied by the water jet is called as
water power, WP.
Power supplied by jet=wQH=pgQH
where Q is the discharge supplied by water jet in
cubic meter per sec,and H is the net or effective
head in .
 BUCKET POWER-The
power developed at the turbine buckets is
called as bucket power,BP.
The power delivered by the bucket wheel is
=m(Vu1+Vu2)u

15. EEFFFFIICCIIEENNCCYY
OVERALL EFFICIENCY
=power available at the turbine shaft/power
available from the water jet
n0= shaft power/water power=P/wQH
 HYDRAULIC EFFICIENCY
=work done per sec/k.e per second
nh=((Vu1+Vu2)u)/gH

16. VOLUMETRIC EFFICIENCY
=Volume of water actually striking the buckets/total
water supplied by the jet
=nv =Qa/Q=Q-q/Q
 MECHANICAL EFFICIENCY
=shaft power/water power=P/wQaH