THE PELTON WHEEL
NYAGROWA MIMISA DICKENS
To study the variance of the power output and overall efficiency
against discharge with the head retained as a constant at normal
JOMO KENYATTA UNIVERSITY OF AGRICULTURE AND TECHNOLOGY
PERFORMANCE TEST OF A PELTON WHEEL TURBINE
To study the variance of the power output and overall efficiency against discharge with
the head retained as a constant at normal speed.
The findings of an experiment carried out to study the properties and performance of a
pelton wheel are herein discussed with much emphasis placed on the output
measured. The resulting output was discussed against the theoretical output to
determine presence and causes of a deviation. The results were presented in graphical
method and the properties of the graph used to discuss the properties of the turbine
Flow was varied and head measured against each variance to indicate the power in the
system. Other parameters necessary for the study were also measured and recorded
for the study. The pelton wheel under study was of a smal ler scale though it acted as a
representative of a similar system in large scale.
The results were also used for the checking of scaling laws used for rturbines.
A pelton wheel turbine is a tangential flow impulse hydraulic machine that is actively
used for the production of power from kinetic energy of flowing water. It is the only
form of impulse turbine in common industrial use. It is a robust and simple machine
that is ideal for the production of power from low volume water flows at a high head
with reasonable efficiency.
The pelton wheel used in this experiment, although a model, reproduces all the
characteristics of full size machines and allows an experimental program to determine
the performance of a turbine and also to verify the theory of design.
Impulse turbines operate through a mechanism that first converts head through a
nozzle into high velocity, which strikes the buckets at single position as they pass
by.jet flows past the buckets is quite essential at constant pressure thus runner
passages are never fully filled. These turbines are suited for relatively low power and
high head derivations. The pelton wheel turbine is comprised of three basic
components that include the stationary inlet nozzle, the runner and the casing. The
multiple buckets form the runner. They are mounted on a rotating wheel. They are
shaped in a manner that divides the flow in half and turn in a velocity vector that is
The nozzle is positioned in a similar plane as the wheel and is arrange d so that the jet
of water impinges tangentially on to the buckets. The nozzle is controlled by movement
of the spear regulator along the axis of the nozzle which alters the annular space
between the spear and the housing. A static pressure tapping is provided to enable the
measurement of the water pressure in the inlet.
Fig. The configuration of the nozzle and buckets in a Pelton wheel turbine
The nozzle is controlled by movement of the spear regulator along the axis of the
nozzle which alters the annular space between the spear and the housing, the spear
being shaped so as to induce the fluid to coalesce into a circular jet of varying
diameter according to the position of the spear.
A friction dynamometer consists of a 60mm diameter brake wheel fitted with a fabric
brake band which is tensioned by a weight hanger and masses with the fixed end
being secures via a spring balance to the support frame. A tachometer may be used to
measure the speed of the turbine.
Fig. General arrangement of the pelton wheel turbine
FIG. Arrangement of Apparatus used in the Pelton Wheel Turbine Test
For the purpose of the study, the following system of apparatus were used
List of apparatus as labeled
in the diagram above
N :Nozzle G :Hook Gauge
NV :Needle valve
PB :Plony brake T :Main tank
W :Waterway TW :Triangular weir
A thermometer was also used for the determination of the water temperature.
The tachometer was used optically in the determination of the speed of the turbine so
as to retain the speed at 900rpm.
The sluice valve, V-2, was opened to supply water to the turbine, and the needle
valve of the nozzle, N, was opened manually by the handle, MV, to allow the water
flow. As the turbine rotated cooling water was supplied into the plony brake.
Importance was taken such that the temperature did not exceed 60º C for the most
Initially the needle valve was fully opened, and the sluice was adjusted to bring the
pressure head on the turbine to 27m.
The pressure head was maintained at 27m throughout the experiment period,
and was monitored by the pressure gauge-PG -2. To maintain the turbine speed at
900rpm, the adjusting screw of the plony brake, Z, was tightened and when the arm of
the plony brake got. At that speed, the spring balance, X, reading (Kg) was recorded as
the load on the plony brake.
The experiment was performed several times (15 times) by shutting the needle valve in
bits. It was noted that for each revolution the needle advanced 1.25mm.
As a precautionary measure the needle valve, NV, was not shut completely
before shutting off the sluice valve, V-2, because the pump water pressure might
break some of the vinyl tubes between the sluice valve and the needle valve.
Theoretical Knowledge pertaining to the experiment
The efficiency of the turbine is defined as the ratio between the power developed by the
turbine to the available water power. Figure below shows the layout of a hydro-electric
power plant in which the turbine is pelton wheel. Water from the reservoir flows
through the penstock at the outlet of which is fitted a nozzle. The nozzle increases the
kinetic energy of the water jets. These water jets strike the bucket of the runner
making it rotate.
The two main parts of the pelton turbine are:
i. the nozzle and the flow regulating arrangement
ii. the runner with the buckets
Fig. Indication of actual state of operation of a pelton wheel turbine
The amount of water striking the buckets is controlled by providing a spear in the
nozzle as shown in Figure below. The spear is a conical needle which is operated either
by a band wheel or automatically in an axial direction depending on the size of the
unit. When the spear is pushed forward into the nozzle, the amount of water striking
the runner is reduced, where as if the spear is pushed back the amount of water is
Fig. Velocity Analysis
Figure below shows the pelton turbine. It consists of a circular disc (the runner) on the
periphery of which a number of buckets evenly spaced are fixed. The shape of the
buckets is a double hemispherical cup or bowl. Each bucket is divided into two
symmetrical parts by a dividing wall which is known as a splitter. The jet of water
strikes the splitter which then divides
the jet into two equal parts and the jet comes out at the outer edge of the bucket. The
buckets are shaped in such a way the jet gets deflected through 160° or 170°.
Definition of terms
1. Total Head: The difference between the head race level and the tail race level
when no water is flowing is known as Total Head (Hg).
2. Net Head: It is also called the effective head and is the available head at the
inlet of the turbine. When water is flowing from head race to turbine, there is
head loss due to friction between the water and the penstocks. There could also
be minor head losses such as loss due to bends, pipe fittings and entrance loss
of penstock etc. If hf is the total head loss, then net head on the turbine is given
by H = Hg − hf Pelton turbine is best suited to operating under very high heads
compared with other types of turbines.
3. Overall Efficiency: The overall efficiency of a pelton turbine is the ratio of the
useful power output to the power input. Mathematically,
Overall efficiency(ηov) =
Power available to the shaft
Power suppied at the inlet
Power supplied at the inlet of the turbine or the water horse power is given by the
Whe re ρ = density of wate r (kg/m3),
g = acceleration due to gravity (9.81m2/sec),
Q = discharge,
H = net head (m).
The power losses that occur within a turbine are attributed to volumetric, mechanical
and hydraulic losses. Volumetric losses ## some of the volume of the water is
discharged to the # without striking the runner buckets. Thus the ratio of the volume
of the water # striking the runner to the volume of the water supplied to the turbine is
defined as the volumetric efficiency.
Volumetric efficiency(ηv) =
volume of water striking the bucket
volume of water supplied to the turbine
The shaft horse power (SHP) output is less than power input due to power consumed
in overcoming mechanical friction at bearings and stuffing boxes. The ratio of the
power available at the shaft of the turbine to the power developed by the runner is
calle d the me chanical e fficiency (ηm) of the turbine.
Power at the shaft of the turbine
Power developed by the runner
The water head actually utilized by a turbine is less than that available because of
frictional losses as water flows across the buckets. The water power at the inlet of the
turbine due to hydraulic losses as the vanes are not smooth and water jet is not
completely turned back. The ratio of the power developed by the runner to the
available powe r at the inlet is known as the hydraulic e fficiency (η h) of the pelton
Power developed by the runner
Power available at the inlet
Normal overall efficiency (ηov) = ηv ∙ ηm ∙ ηh
Performance characteristic curve of pelton turbines
These are curves with the help of which the exact performance behavior of the
turbines under different working conditions can be ascertained. The curves are plotted
from the results of the tests performed on turbines under different working conditions.
The quantities that can be varied during a test on a turbine are: speed, head,
discharge, power, overall efficiency and gate opening.
If the speed and water head of a pelton turbine are maintained at constant values,
then the curves obtained by plotting the discharge (Q) against both the power outputs
and the overall efficiencies are called the operating characteristic curves of the pelton
Preparation of the Experiment
The asbestos of the plony brake (PB) (details as shown in Figure 4) should be oiled
before the experiment is started. This ensures easier reading of the load on the spring
The sluice valves, V-1, 2, 3 are put in closed positions. Before the pump is started
ensure that it is filled up with water i.e. primary and once started it should not be
allowed to run for long before opening any of the valves V-1, 2, 3. This is to prevent it
from getting overheated.
Figure: Details of the plony brake
A triangular weir is used to determine the discharge through the circuit. The water
head through the weir is measured with a hook gauge; first the zero water head is
measured. This is done as follows:
Kee ping the water flowing over the weir, observe reflection of the end of the weir ‘V’ on
the water from the upper stream side. Open the cork valve (V-8) positioned under the
waterway, to lower the surface water level and then read the water head with the hook
gauge when the end of the weir ‘V’ coincide s with end of the shade ‘V’ re flecte d on the
surface of the water. This reading is recorded as the zero water head. Then close cork
valve (V-8) to prepare for the other readings.
The other water heads are read when the point of the hook gauge coincides with the
reflection itself in the water through a glass window. In every case allow the water to
settle before recording the reading i.e. waits for about 5 minutes after the flow
adjustment before you take the next reading.
1. It was ensured that the centrifugal pump that supplies water in this system
is primed first before the mortar is started.
2. The gate openings were set carefully and throughout each gate opening, the
spear wheel and the delivery valve were not changed.
Properties of turbine
Revolution speed (N) 900 rpm
Pressure head on turbine 27 m
Length of the handle of the plony brake 0.130 m
Properties of V-notch
Half angle of V-notch (θ) 45°
Coefficient of discharge (CdV) 0.576
Coefficient (KV) 1.360
Crest level (hook gauge) 0.21805 m
V-notch Properties of water Theoretic
1 0.17020 0.04785 0.681 18.0 998.595 2.401 14 2.287 95.248
2 0.16280 0.05525 0.976 19.5 998.305 3.439 20 3.267 95.007
3 0.15645 0.06160 1.281 19.5 998.305 4.514 27 4.411 97.717
4 0.15255 0.06550 1.493 20.0 998.203 5.262 32 5.228 99.345
5 0.14865 0.06940 1.726 20.0 998.203 6.081 36 5.881 96.717
6 0.14700 0.07105 1.830 20.0 998.203 6.449 38 6.208 96.266
7 0.14525 0.07280 1.945 20.0 998.203 6.853 40 6.535 95.353
8 0.14400 0.07405 2.029 20.0 998.203 7.151 40 6.535 91.379
9 0.14265 0.07540 2.123 20.0 998.203 7.481 41 6.698 89.528
10 0.14180 0.07625 2.183 20.0 998.203 7.694 41 6.698 87.053
a) The theoretical power input (Pth) of the turbine given by the expression:
75 × 60
Whe re ρ = density of water (de pends on the water temperature and atmospheric
Q = discharge,
H = net water head on the turbine (given H=27m).
998.595 ∗ 9.81 ∗ 27 ∗ 0.681
75 × 60
b) The actual power output (Pa) of the turbine is obtained from the expression:
75 × 60
Where x = length of the handle of the plony brake (given as 0.130m),
N = revolution per minute of the turbine (supposed to be 900rpm),
w = load exerted by the plony brake (kg) read on the spring balance.
2π ∗ 0.13 ∗ 900 ∗ 14
75 × 60
Pa =2.287 HP
c) The ove rall e fficiency of the pe lton turbine (η ov) is given by the formula:
Calculate the overall efficiencies of the pelton turbine at each discharge
Power Out (HP) efficiency (%)
y = -1E+09x3 + 5E+06x2 - 2357.9x + 1.9629
0.0012 0.0014 0.0016 0.0018 0.002 0.0022
From the above calculations the values of actual power output are slightly lower
than the values of theoretical power output of the turbine and thus from this a
relationship between the discharge, actual output and efficiency can be shown using a
graph as indicated below.
y = -2E+07x2 + 39797x + 73.253
From this relationship, it is possible to prove that the higher the power output of a
turbine, the higher the efficiency. These are functions of the discharge.
It is also correct to indicaate that efficiency of the system increases with increase in
the specific speed of the pelton wheel. This has been derived from the relationship of
the values collected, tabulated and graphed as herein.
Power out (HP)
This experiment was carried out with an acceptable level of accuracy. It was
generally a success as the results obtained were useful for the analysis of the
properties of the machine.
From the experimental results, it became possible for the real picture of the
operational basis of the machine to be displayed in such a way that the characteristics
of the turbine were visible in the graphical analysis used.
The experiment was not fully accurate due to several errors that resulted from
several misdoings. The greatest being that it became really difficult to acquire readings
from the spring balance since the setup was vibrating as result of the operation of the
machine. As such, this explains the slight deviation of the results obtained in the
experiment that were later reflected in the graphs drawn to represent the work.
Other errors may have resulted from unseen leakages in the system and
observational and computational errors. The experiment was, however, carried out
with a great level of keenness to reduce the occurrence of such errors.
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