project final
TRANSCRIPT
Malampuzha Hydel Plant Project Report’ 08- 09
Dept. of Mechanical Engg Page 1 Govt. Engg. College, Thrissur
1. I�TRODUCTIO�
Hydro power is the largest renewable energy resource being used
for the generation of electricity. In India, hydro power projects with a
station capacity of up to 25 megawatt (MW) each fall under the category
of small hydro power (SHP). India has an estimated SHP potential of
about 15 000 MW, of which about 11% has been tapped so far.
Here we take up an analysis of the technical inefficiency, time and
cost overruns in the Malampuzha mini Hydel power project. This is of
very significance in the present context of arguments by the government
in favour of private sector participation in power generating capacity
addition, under the pretext of a resources crunch. The government is said
to be under a tight constraint of severe funds scarcity and hence incapable
of undertaking new projects for power development. However, we will
find that this argument is flimsy to the extent that the government is
actually over-spending on each of the projects undertaken.
Each project involves immense cost overrun, and the machines
implemented are of inferior quality. Had the government been able to
implement each project efficiently within the normally expected
constraints of time and cost, then it could have saved huge resources and
hence undertaken a large number of additional projects. The problem is in
the inefficiency of management, to forecast the needs and to find the best
for the state, coupled with the political economy of corruption. This
paper, has the limited objective of bringing into light this aspect.
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2. HISTORICAL PERSPECTIVE
Evolution of Modern Turbine from the Water Wheel
The water turbine has a rich and varied history and has been
developed as a result of natural evolutionary process from the
waterwheel. The water turbine was originally used for direct drive of
machinery; its use for the generation of electricity is comparatively
recent. Much of its development occurred in France. England had cheap
and plentiful sources of coal which sparked the industrial revolution in
the eighteenth century, but Nineteenth century France had only water as
its most abundant energy resource. To this day houille blanche ‘ white
coal’ is the term for water power.
Bernard Forest de Belidor, a Hydraulic and Military Engineer
authored (1737-1753) the monumental 4 Volume architecture
Hydraulique, a descriptive compilation of Hydraulic Engineering
information of every sort.
The water Wheel described by Belidor departed from convention
by having a vertical axis of rotation and being enclosed in along
cylindrical chamber in approximately one meter in diameter. Large
quantities of water, supplied from a tapered sluice at a tangent to the
chamber, entered with considerable rotational velocity. This pre-swirl
combined with the weight of water above the wheel was the driving
force. The original tub wheel had an efficiency of only 15%-20%.
Water Turbine development proceeded on several fronts from
1750- 1850. The classical Horizontal-axis waterwheel was improved by
such Engineers as John Smeaton (1724-1792) of England, who used the
first avowed model experiments in this endeavor and also played an
important role in windmill development, and Jean Victor Poncelet (1788-
Malampuzha Hydel Plant Project Report’ 08- 09
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1867) of France. These improvements resulted in waterwheels having
efficiencies in the range of 60% -70 %.
At the same time reaction turbines were being considered by
several workers. The great Swiss Mathematician Leonhard Eular (1707 –
1783) investigated the theory of operation of these devices. A practical
application of the concept was introduced in France in 1807 by Mannoury
de Ectot (1777 – 1822). His machines were, in effect, radial outward-flow
machines. The theoretical analysis of Claude Buridin ( 1790 – 1893), a
French professor of mining engineering who introduced the word
‘turbine’ in engineering terminology, contributed much to our
understanding of shock-free entry and exit with minimum velocity as the
basic requirements for high efficiency
A student of Buridin, Benoit Fourneyon (1802 – 67), put his
teacher’s theory to practical use, which led to the development of high
speed outward flow turbines with efficiencies of the order of 80 percent.
Fourneyron developed some 100 turbines in france and elsewhere in
Europe. Fourneyron turbines, successful as they were, lacked flexibility
and were only efficient over a narrow range of operating conditions. The
modern Francis turbine is the result of this line of development. At the
same time, European engineers addressed the idea of axial flow
machines, today which are represented by propeller turbines of both fixed
pitch and the Kaplan type.
Just as the vertical axis hub wheels of Belidor evolved into
modern reaction turbines of the Francis and Kaplan type, development of
the classical horizontal axis waterwheel reached its peak with the
introduction of impulse turbine. The seeds of development were sown in
1826 when Poncelet described the criteria for an efficient waterwheel.
These ideas were cultivated in the late nineteenth century by a group of
California engineers that included Lester A. Pelton (1829-1908).
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His name was given to the pelton wheel, which consists of a jet or
jets of water impinging on an array of specially shaped buckets closely
spaced around the periphery of a wheel. Thus, the relatively high speed
reaction turbines trace their roots to the vertical axis tub wheels of
Belidor, where as the pelton wheel can be considered as a direct
development of the more familiar horizontal axis waterwheel.
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3. MALAMPUZHA HYDEL PROJECT
– A� OVERVIEW
Malampuzha, one of the first projects planned in the State to
generate electricity from water let out from an irrigation dam. The
contract for the design, supply and installation works were awarded to a
private firm which allegedly had no previous experience in such projects.
A mini Hydel project of 2.5 MW with an annual generation of 5.6
MU, this scheme envisages construction of a power station on the
downstream side of the existing irrigation dam (owned by the State
PWD) to utilize the irrigation release. Started in 1987 and expected to be
online by 1989, this mini project is now expected to be commissioned ‘in
the near future’. After 12 years with a time overrun of about 10 years as
in 1999-2000, the capital cost was revised from the original Rs. 295 lakhs
to Rs. 679 lakhs – an increase of about 130 per cent. Now it has reached
an alarming value of 697 lakhs- a total increase of 136 percent!
The civil work was done by the KSEB. Though the company
started the erection work in 1992, it took as many as four years to attempt
at a trial run. However, during the trial run, some defects were noticed in
the butterfly valve. In 1997, another trial run was tried, but again during
the run, a valve disc got broken. In 2004 it was brought into operation but
after working for 200 days it malfunctioned. The shaft of the turbine was
broken, and from that day to present it remains non-functional.
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Dept. of Mechanical Engg Page 6 Govt. Engg. College, Thrissur
4. BASIC DEFI�ITIO�S
4.1 DEFI�ITIO� OF HEAD
4.1.1 Effective Head (�et Head)
The effective head is the net head available to the turbine unit for
power production. This head is the static gross head, the difference
between the level of water in the Forebay/impoundment and the tail water
level at the outlet, less the hydraulic losses of the water passage as shown
in Fig. 1.1. The effective head is used for all power calculations. The
hydraulic losses can vary from essentially zero to amounts so significant
that the energy potential of the site is seriously restricted.
In general a hydraulic loss of one velocity head (V2/2g) or greater
would not be uncommon. The hydraulic losses through the turbine and
draft tube are accounted for in the turbine efficiency.
4.1.2 Gross Head (Hg)
It is the difference in elevation between the water levels of the
forebay and the tailrace.
4.1.3 Maximum Head (Hmax)
It is the gross head resulting from the difference in elevation
between the maximum forebay level without surcharge and the tailrace
level without spillway discharge, and with one unit operating at speed no-
load (turbine discharge of approximately 5% of rated flow). Under this
condition, hydraulic losses are negligible and nay be disregarded.
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4.1.4 Minimum Head (Hmin)
It is the net head resulting from the difference in elevation between
the minimum forebay level and the tailrace level minus losses with all
turbines operating at full gate.
4.1.5 Design Head (Hd)
It is the net head at which peak efficiency is desired. This head
should preferably approximate the weighted average head, but must be so
selected that the maximum and minimum heads are not beyond the
permissible operating range of the turbine. This is the head which
determines the basic dimensions of the turbine and therefore of the power
plant.
4.1.6 Rated head (Hr)
It is the net head at which the full-gate output of the turbine
produce the generator rated output in kilowatts. The turbine nameplate
rating usually is given at this head. Selection of this head requires
foresight and deliberation.
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Dept. of Mechanical Engg Page 9 Govt. Engg. College, Thrissur
4.2 CLASSIFICATIO� A�D TYPES OF TURBI�ES
Turbines can be either reaction or impulse types. The turbines type
indicates the manner in which the water causes the turbine runner to
rotate. Reaction turbine operates with their runners fully flooded and
develops torque because of the reaction of water pressure against runner
blades. Impulse turbines operate with their runner in air and convert the
water’s pressure energy into kinetic energy of a jet that impinges onto the
runner buckets to develop torque.
Reaction turbines are classified as Francis (mixed flow) or axial
flow. Axial flow turbines are available with both fixed blades (Propeller)
and variable pitch blades (Kaplan). Both axial flow (Propeller & Kaplan)
and Francis turbines may be mounted either horizontally or vertically.
Additionally, Propeller turbines may be slant mounted. Out of this we are
interested in Axial flow (Kaplan& Tubular) turbines only.
4.2.1 AXIAL FLOW TURBI�ES
Axial flow turbines are those in which flow through the runner is
aligned with the axis of rotation. Axial flow hydraulic turbines have been
used for net heads up to 40 meters with power output up to 25 MW.
However, they are generally used in head applications below 35 meters
Tubular turbine (S-type). S-turbines are used below 30 meters head and 8
MW capacity. Specific mechanical designs, civil construction, and
economic factors must be given full consideration when selecting among
these three axial flow turbine arrangements.
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Propeller Turbines -
A propeller turbine is one having a runner with four, five or six
blades in which the water passes through the runner in an axial direction
with respect to the shaft. The pitch of the blades will be fixed. Principal
components consist of a water supply case, wicket gates, a runner and a
draft tube.
The efficiency curve of a typical fixed blade Propeller turbine
forms a sharp peak, more abrupt than a Francis turbine curve. Propeller
turbines may be operated at power outputs with flow from 40-105% of
the rated flow. Discharge rates above 105% may be obtained; however,
the higher rates are generally above the turbine and generator
manufacturers’ guarantees.
Kaplan Turbines (Vertical)
A Kaplan Turbine is one having a varying blade pitch. For these
units the peak efficiency occurs at different outputs depending on the
blade setting. An envelope of the efficiency curves cover the range of
blade pitch settings forms the variable pitch efficiency curve. This
efficiency curve is broad and flat. . The conventional propeller or Kaplan
(variable pitch blade) turbines are mounted with a vertical shaft.
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Fig. 2: Kaplan turbine (vertical)
The vertical units are equipped with a wicket gate assembly to
permit placing the unit on line at synchronous speed, to regulate speed
and load, and to shutdown the unit. The wicket gate mechanism units are
actuated by hydraulic servomotors. Small units may be actuated by
electric motor gate operators. Variable pitch units are equipped with a
cam mechanism to coordinate the pitch of the blade with gate position
and head. Digital control envisages Control of wicket gates and blade
angle by independent servomotors coordinated by digital control.
Fixed blade units are less costly than variable pitch blade turbines;
however, the power operating ranges are more limited. Four blade
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designs may be used up to 12 meters of head, five blade designs to 20
meters and six blade designs to 35 meters. In general, peak efficiencies
are approximately the same as for Francis turbines.
Many units are in satisfactorily operation from 60 to 140% of
design head. Efficiency loss at higher heads drops 2 to 5% points below
peak efficiency at the design head and as much as 15% points at lower
heads. Variable pitch propeller turbines without wicket gates are called
Semi Kaplan turbine.
Kaplan Features
• Simple designs for ease of erection and simple foundation details
• Low cost solutions for exploiting low head potential
• Water lubricated shaft bearing system
• Entire range of Kaplan runners available in three, four, five & six
blades
• Simplified interface with powerhouse structure to reduce overall
civil costs
Tubular turbines
Tubular or tube turbines are horizontal or slant mounted units with
propeller runners. The generators are located outside of the water
passageway. Tube turbines are available equipped with fixed or variable
pitch runners and with or without wicket gate assemblies. Performance
characteristics of a tube turbine are similar to the performance
characteristics discussed for propeller turbines. The efficiency of a tube
turbine will be one to two % higher than for a vertical propeller turbine of
the same size since the water passageway has less change in direction.
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Fig 3: Tubular turbines (Horizontal Kaplan)
The performance range of the tube turbine with variable pitch blade
and without wicket gates is greater than for a fixed blade propeller turbine
but less than for a Kaplan turbine. The water flow through the turbine is
controlled by changing the pitch of the runner blades.
When it is not required to regulate turbine discharge and power
output, a fixed blade runner (propeller) may be used. This results in a
lower cost of both the turbine and governor system.. Several items of
auxiliary equipments are often necessary for the operation of tube
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turbines. All tube turbines without wicket gates should be equipped with
a shut off valve automatically operated to provide shut-off and start-up
functions.
Tube turbines can be connected either directly to the generator or
through a speed increaser. The speed increaser would allow the use of a
higher speed generator, typically 750 or 1000 r/min, instead of a
generator operating at turbine speed. The choice to utilize a speed
increaser is an economic decision. Speed increasers lower the overall
plant efficiency by about 1% for a single gear increaser and about 2% for
double gear increaser. (The manufacturer can supply exact data regarding
the efficiency of speed increasers). This loss of efficiency and the cost of
the speed increaser must be compared to the reduction in cost for the
smaller generator. It is recommended that speed increaser option should
not be used for unit sizes above 5 MW capacity.
The required civil features are different for horizontal units than for
vertical units. Horizontally mounted tube turbines require more floor area
than vertically mounted units. The area required may be lessened by slant
mounting, however, additional turbine costs are incurred as a large axial
thrust bearing is required. Excavation and powerhouse height for a
horizontal unit is less than that required for a vertical unit.
Standard Tube turbines of Bharat Heavy Electrical based on
runner diameter is shown in Figure 2.
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Fig. 4: Tubular Turbine
�omenclature
1. Runner
2. Main inlet valve
3. valve servomotor
4. stay valve
5. Runner chamber
6. Turbine bearings
7. Shaft seal
8. Draft tube
9. gear box
10. Generator
11. Generator bearing
12. Runner bearing
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4.3 SPECIFIC SPEED (�s)
The term specific speed used in classifying types of turbines and
characteristics of turbines within types is generally the basis of selection
procedure. This term is specified as the speed in revolutions per minute at
which the given turbine would rotate, if reduced homologically in size, so
that it would develop one metric horse power at full gate opening under
one meter head. Low specific speeds are associated with high heads and
high specific speeds are associated with low heads. Moreover, there is a
wide range of specific speeds which may be suitable for a given head.
Selection of a high specific speed for a given head will result in a
smaller turbine and generator, with savings in capital cost. However, the
reaction turbine will have to be placed lower, for which the cost may
offset the savings. The values of electrical energy, plant factor, interest
rate, and period of analysis enter into the selection of an economic
specific speed.
Commonly used mathematically expression in India for specific speed
is power based (English System) is as follows:
�s = � √Pr ÷ (Hr) 5/4
Where N = revolutions per Minute
Pr = power in metric horse power at full gate opening – (1 kW =
0.86 metric hp)
Hr =rated head in m.
The specific speed value defines the approximate head range
application for each turbine type and size. Low head units tend to have a
high specific speed, and high-head units to have a low specific speed.
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Flow based metric system for specific speed (Nq) used in Europe is given
by equitation below.
�q = �Q0.5÷H0.75
Where Nq = Specific Speed
N = Speed in rpm
Q = Flow in cubic meters/second
H = Net Head in meters
Specific speed (metric HP units) range of different types of turbines is as
follows:
Table 1: The range of specific speed for various turbines.
TURBI�ES SPECIFIC SPEED
Fixed blade propeller turbines 300 – 1000
Adjustable blade Kaplan turbines 300 – 1000
Francis turbines 65 - 445
Pelton Turbine 16-20 per jet*
Cross flow turbine 12-80 per jet*
* For multiple jets the power is proportionally increased
The basic graph between Specific speed Vs Head is given below
(Fig. 5)
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4.4 EFFICIE�CIES OF A TURBI�E (η)
The different types of efficiencies are
1. Hydraulic efficiency
2. Mechanical efficiency
3. Volumetric efficiency
4. Overall efficiency
4.4.1 Hydraulic efficiency ηh:
It is defined as the ratio of power given by water to the runner of a
turbine to the power supplied by the water at the inlet of the turbine. Thus
mathematically
ηh = Power delivered to the runner = R.P Power supplied at inlet W.P
Where R.P = runner power
W.P = water power
4.4.2 Mechanical efficiency – ηm
The power delivered by water is transmitted to the shaft of the
turbine. But due to the mechanical losses cent percent power won’t be
delivered at the shaft. The ratio of power available at the shaft to that
delivered to the runner is defined as the mechanical efficiency of the
turbine. Mathematically,
ηm = Power at the shaft of the turbine = S.P
Power delivered by turbine R.P
Where S.P= Shaft power
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4.4.3 Volumetric efficiency – ηv
The volume of water striking the runner of a turbine is slightly less
than the volume of the water supplied to the turbine. Some volume of the
water is discharged to the tail race without striking the runner of the
turbine. Thus the ratio of the volume of the water actually striking the
runner to the volume of water supplied to the turbine is defined as the
volumetric efficiency.
Ηv = Volume of water actually striking the runner Volume of water supplied to the turbine
4.4.4 Overall efficiency – ηo
It is defined as the ratio of power available at the shaft of the
turbine to the power supplied by the water at the inlet of the turbine. It is
written as:
ηo = Volume available at the shaft of the turbine = S.P Power supplied at the inlet of the turbine W.P
S.P × R.P = ηh× ηm R.P × W.P
ηo= ηh× ηm
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4.5 U�IT QUA�TITIES
In order to predict the behavior of a turbine working under varying
conditions of head, speed, output, and gate opening, the results are
obtained in terms of quantities which may be obtained when the head on
the turbine is reduced to unity. The conditions of the turbine under unit
head are such that the efficiency of the turbine remains unaffected. The
followings are the three important unit quantities which must be studied
under unit head:
i) unit speed
ii) unit power
iii) unit discharge
4.5.1 Unit Speed
The unit speed is defined as the speed of the turbine working under
a unit head (i.e. under a head of 1m). It is denoted by Nu
�u = � √H
Where N = Speed of a turbine under a head H
4.5.2 Unit Discharge
It is defined as the discharge of the turbine, which is working under
unit head (i.e. under a head of 1m). It is denoted by Qu. the expression for
unit discharge is given as
Qu = Q
√H
Where Q = Discharge through the turbine under a
head H
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4.5.3 Unit Power
It is defined as the discharge of the turbine, which is working under
unit head (i.e. under a head of 1m). It is denoted by Pu. the expression for
unit discharge is given as
Pu = P H3/2
Where P = Power developed by a turbine under a head H
Use of unit quantities (�u, Qu, Pu)
If a turbine is working under different head the behavior of the
turbine can be easily known from the values of the unit quantities.
Let H1, H2 ,H3, H4, H5…be the different heads under which turbine
works
Then, �u = �1 = �2
√H √H
Qu = Q1 = Q2
√H √H
Pu = P1 = P2 H3/2 H3/2
Thus if the rated speed, rated discharge, rated head, rated power are
known then we can find out the unit quantities and there by find the
speed, discharge and power for different heads.
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4.6 CAVITATIO� I� TURBI�ES
When the pressure in any part of the flow passage reaches
the vapour pressure of the flowing liquid, it starts vaporizing and small
bubbles of vapour form in large numbers. These bubbles (or vapour-filled
pockets or cavities) are carried along by the flow, and on reaching the
high pressure zones these bubbles suddenly collapse as the vapour
condenses to liquid again. Due to sudden collapsing of bubbles or cavities
the surrounding liquid rushes into fill them. The liquid moving from all
directions collides at the center of the cavity, thus giving rise to very high
local pressure, which may be as high as 686.7MN ̸ m2. Any solid surface
in the vicinity is also subjected to these intense pressures. The alternate
formation and collapse of vapour bubbles may cause severe damage to
the surface which ultimately fails by fatigue and the surface becomes
badly scored and pitted. This phenomenon is known as cavitation which
is found to occur in turbines as well as in various hydraulic structures
such as penstocks, gates, valves, spillways etc.
In reaction turbines the cavitation may occur at the runner
exit or the inlet to the draft tube where the pressure is considerably
reduced. Due to cavitation the metal of the runner vanes and the draft
tube is gradually eaten away in these zones, which results in lowering
the efficiency of the turbine. As such the turbine components should be
so designed that as far as possible cavitation is eliminated. In order to
determine whether cavitation will occur in any portion of the turbine,
D.Thoma of Germany has developed a dimensionless parameter called
Thoma’s cavitation factor σ which is expressed as
σ = ( Ha- Hv – Hs ) ̸ H 4.6.1
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Where H is atmospheric pressure head; H is vapour pressure head; H is
suction pressure head (or height of runner outlet above tail race); and H is
working head of the turbine. Complete similarity in respect of can be
ensured if the value of σ is same in both the model and prototype.
Moreover it has reduced up to a certain value up to which its efficiency
n0 remains constant. A further decrease in the value of σ results in a
sharp fall in ηo. The value of σ at this turning point is called the critical
cavitation factor σc. The value for σc for different turbines may be
determined with the help of following empirical relationships:
For Francis Turbines
σc = 0.625 { Ns /380.78}2
For Propeller turbines
σ c = 0.28+{ (1/7.5) { Ns /380.78}3 } 4.6.2
For Kaplan turbines, values of σc obtained in the above equation
should be increased by 10%.
In the above expression Ns is in (r.p.m, kW, m) units. However if
Ns is in (r.p.m, h.p, m) units, the expression for σc would be as follows:
For Francis turbines
σc = 0.625 { Ns /444}2
For Propeller turbines
σ c = 0.28+{ (1/7.5) { Ns /444}3 }
Again for Kaplan turbines, value for σc obtained by the above
equation should be increased by 10%
4.6.1 Suction Specific Speed.
In addition to Thoma’s criterion the consideration of suction
specific speed provides another very useful criterion for establishing
similarity in respect of cavitation in the turbines. The suction specific
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speed S may be defined as the speed of a geometrically similar turbine
such that when it is developing a power equal to 1 kilowatt (or in metric
units equal to 1 metric horse power ) the total suction head Hsv is equal to
1m (in absolute units). According to this definition the expression for
suction specific speed may be obtained by replacing H, given in the
equation for the specific speed, by total suction head Hsv. Thus
S = (N√P) ⁄ Hsv5/4 4.6.3
By having the same value of suction specific speed for the model
and the prototype turbines the similarity in respect of cavitation can be
established
The total suction head Hsv can be expressed as
Hsv = Ha− Hv –Hs 4.6.4
And hence from the equation 4.6.1
Hsv = σH 4.6.5
By substituting the value of Hsv in the equation 4.6.3, we get
S = (N√P) ⁄ (σ H)5/4 Or
σ = (Ns ⁄ S)4/5 4.6.6
Equation 4.6.6 represents the relation between the two parameters σ and
S, both of which are useful for establishing a similarity in respect of
cavitation in the model and prototype turbines. However, the concept of
suction specific speed is more commonly used in case of pumps.
Cavitation protection is an important criterion in Kaplan turbine
blade design. In Kaplan turbines cavitation occurs at a number of
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different locations, notably at the blade leading edge, on the blade suction
side, in both tip and hub gaps and on the discharge ring. Cavitation can
result in frosting or pitting in the above-mentioned locations. Its severity
depends on design and operating regime of the machine. Cavitation itself
is primarily a local effect.
The discharge ring cavitation often occurs in a number of discrete
circumferential patches corresponding to the number of guide vanes. At
first sight this is surprising, because we assume that the low pressure
zones caused by the rotating blades are responsible for the cavitation.
Therefore any effect would be expected to occur at the entire
circumference of the discharge ring. Since that is not the case, we can
conclude that unsteady flow behavior driven by the rotor-stator
interaction of the guide vanes and blades have to be responsible for the
effect. Due to the various physical effects involved, unsteady two-phase
flow with highly locally refined meshes is required for the numerical
simulation of the Kaplan turbine cavitation phenomena
4.7 HYDRO-TURBI�E GOVER�I�G SYSTEM
Governor control system for Hydro Turbines is basically a feed
back control system which senses the speed and power of the generating
unit or the water level of the forebay of the hydroelectric installation etc.
and takes control action for operating the discharge/load controlling
devices in accordance with the deviation of actual set point from the
reference point. Governor control systems of all units suitable for isolated
operation are a feed back control system that controls the speed and
power output of the hydroelectric turbine. Water level controllers can be
used for grid connected units. Governing system comprises of following
sections.
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a) Control section
b) Mechanical hydraulic Actuation section
The control section may be mechanical; analogue electronic or
digital. Actuator can be hydraulic controlled, mechanical (motor) or load
actuator. Load actuator are used in micro Hydel range; mechanical (motor
operated) may be used say up to 1000 kW unit size. Hydro actuators are
mostly used.
Figure 6: PLC circuit system
Type of Governor Control Section
• Mechanical Controller • Electro-Hydraulic Governor – Analogue Electronics • Electro Hydraulic Governor – Digital Governors
Electro Hydraulic Governor – Digital Governors
In digital governor, digital controller is used in turbine governing
system. This is also PID controller. Digital control hardware running an
application programme accomplishes the required control function with
this system. Digital controllers used for turbine governing system are
very flexible and can be used for functions not directly related to the
turbine governing control function. Present day trend is to use digital
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governing control system in hydroelectric units. The major advantages of
microprocessor based system over the earlier analogue governors (based
on solid state electronic circuitry) are higher reliability, self diagnostic
feature, modular design, flexibility of changing control functions via
software, stability of set parameters, reduced wiring and easy remote
control through optical fibre cables. Microprocessor based governor
control system are capable of carrying out the following control functions
in addition to speed control during idle run , operating in isolated grid;
interconnected operation and islanding operation.
• Control the power output depending on variation in grid frequency
i.e load frequency control
• Joint power control of a number of generating units in a power station
• Power control as per water levels in Fore-bay and/or Tail-race
• Automatic Starting / Stopping by single command
• Fast response to transient conditions
• Control from remote place Supervisory Control And Data Acquisition
(SCADA)
Personnel Computers (PC) /Programmable Logic Controller
(PLC) based Digital Governors
Modern control schemes also utilise personal computers (PCs) in
conjunction with PLC control systems. The PCs are utilized with man-
machine interface (MMI) software for control display graphics, historical
data and trend displays, computerized maintenance management systems
(CMMS), and remote communication and control. In addition, the PLC
programming software is usually resident on the PC, eliminating the need
for a separate programming terminal implement or changes the PLC
software coding. A PC also can be used for graphical displays of plant
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data, greatly enhancing operational control. Standard Microsoft-based
graphical display software packages are available for installation on a
standard PC. The software package can be utilized on the PC to create
specific powerhouse graphical displays based upon real-time PLC inputs.
These displays typically include control displays with select-before-
execute logical, informational displays for plant RTD temperatures, or
historical trending plots of headwater, tail water, and flow data. Modems
with both dial-out and dial-in capabilities can be located in the PC, the
PLC, or both to provide off-site access to plant information. These
modems may also be utilised to control the plant operation from a remote
location.
Programmable Logic Controller (PLC) type plant controllers with a
manually operated back up system combined with PC based SCADA
system are used as Governors and for Plant control and data acquisition.
This makes the system costly but reliability is stated to be good and can
be used for small hydro generation control. It is considered that dedicated
digital control systems which is digital P.C. based can perform all
functions of governing, unit control and protection as well as for data
storage and can be more economical, dependable and are being
manufactured in U.S.A., Europe, India and other countries. These
dedicated systems with back up manual control facility of speed control
in emergency by dedicated semi automatic digital controllers can be an
option and is also recommended for UNDP-GEF projects in India.
Monitoring and control and data acquisition system (SCADA system) can
be a part of the P.C. based digital governor and generation control
equipment. Provision of data storage of one month with 16 MB of Ram
memory and a 540 to 850 MB Hard Drive as part of the PC based
governing and control system should be provided. This data could be
retrieved on a floppy drive after one month for examination. As the
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communication links develop the data can also be transmitted via a
Modem to a remote point for examination and supervisory control.
Auxiliary control normally forms a part of digital governor. It is further
recommended that water jet diverters of emergency closure of inlet valves
be provided to avoid over speeding to runaway in case of governor failure
emergency.
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5. TECH�ICAL DESCRIPTIO�
5.1 GE�ERAL DETAILS
The turbine is horizontal shaft semi- Kaplan (tubular, S-shaped) of
standardized design with movable runner blades and fixed guide vanes.
The system has one elbow of cylindrical and straight axially symmetric
draft tube.
The turbine shell is a tubular type with 6 fixed guide vanes. For
mechanical stability of the Turbine, 2 sets of rods, welded to embedded
sole plates and a concrete block around the turbine casing is provided.
The runner of the Kaplan Turbine include a Hub made of cast steel 13/4
Chromium nickel S.S blade with 2 bush bearings
The shaft line is supported by a concrete pedestal and reinforced by
a third set of rods, located under the thrust bearing. It constituted by a
hollow shaft on the runner side bolted to the solid shaft on the Generator
side. The shaft line is oil immersed and never in contact with water.
The turbine has a simplified oil system with pump supplying oil to
the blade control mechanism under high pressure. The oil flows in the
bearing, then in the Turbine casing and finally in the tube which act as a
cooler. The oil is then directed to the thrust- block and to the upstream
bearing before returning to the oil tank.
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Figure 8: Turbine’s major components
5.2 TURBI�E’S MAJOR COMPO�E�TS
5.2.1 Distributor
The distributor is embedded in concrete and welded at the upstream
side, to the elbow type inlet duct. A casing containing mechanical items is
held by six guide vanes. It also consist of a controllable blade runner, a
servomotor oil distributing system, a casing and a thrust block connected
by a tube inside which the shaft lines rotates. It also consists of a sliding
throat ring which is capable of retracting into the draft tube.
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5.2.2 Shaft Line
The shaft line constituted by a hollow shaft on the runner side
bolted to the solid shaft on the generator side. The shaft on the runner
side forms the servo motor cylinder. The shaft line is supported by
spherical roller bearing. The thrust towards the downstream side due to
the pressure on the runner is taken by thrust bearing thrust block support
and clamping nut. The shaft line is oil immersed and never in contact
with water.
5.2.3 Runner
The runner includes a hub made of alloy steel.13/4 Chromium
Nickel S .S Blades with two bush bearings. Blade water tightness is
ensured by the lever connected to the blade by oil seal. The blades are
driven by the lever connected to the blade by cotter-pin. The motion is
ensured by a conventional Kaplan link and the stem system which
includes 4 connecting stem, 4 clevises and a bronze head (Bracket). The
power transmission to the shaft line is carried out by 4 keys. The runner is
arrested by a hydraulic / lock nut
The system operates as follows: the pressurization of the space
between the hub and the sealing ring nut put the shaft on the runner side
in tension. Then it is sufficient to tighten sealing ring lock nut manually
and to allow the pressure to drop to attain the required clamping
5.2.4 Shaft Seal
The seal is of mechanical type. It includes 2 mechanical seal rings
adhering to the seal support. This bronze part can slide depending on the
mechanical seal wear and tear. The casing sealing is ensured by oil seal
(Solosele G seal). The seal support and the mechanical seal ring are
forced against the friction plate by a spring ring and by the water
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pressure. The mechanical seal leakage of water is recovered by a channel
passing through the arm and draining out through a 50 mm diameter pipe.
Even when the mechanical seal is worn out the seal support is supported
by butt-strap, thereby avoiding any contact between any fixed parts and
rotating parts
5.2.5 Blade Control System
The blades are controlled by the cross head motion. The cross head
is connected to the blade control system which acts as a piston head in the
shaft, on the runner side. The rotation forces due to the links and stem are
taken up by two guides on the runner cap. The oil pressure is applied to
either side of the piston through holes drilled in the shaft. The shaft
rotating pipes are connected to the distributor fixed pipes through a
system of three floating bush which are mounted on the shaft with a very
close clearance and intended to minimize oil leakage outside the blade
control system.
5.2.6 Oil Station and Oil Systems
The turbine includes two different oil systems whose supply is
ensured by hydraulic power pack and lubrication oil supply unit. When
blade operating order is given the solenoid valve is energized in one of
the directions and the oil flows to the servomotor through one of both
pipes. The servomotor oil return is directed into the solenoid valve
towards the system.
The lubricating oil supply unit ensure the 3 bar pressure that no
over pressure will never occur in the turbine. In this way, the lubricating
is never interrupted. The oil flows in the bearing, then in the Turbine
casing and finally in the tube acting as a cooler. The oil is then directed to
the thrust block and to the upstream bearing before returning to the oil
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tank. A pressure gauge on the thrust block permits to visualize the
internal pressure of the lubricating system in the turbine.
5.2.7 Draft Tube
The draft tube is a pipe of gradually increasing area which connects
the outlet of the runner to the tail race. It is used for discharging water
from the exit of the turbine to the tail race. The draft tubes also have the
following purposes:
• It permits a negative head to be established at the outlet of
the runner and thereby increase the net head on the turbine.
• It converts large proportion of kinetic energy rejected to the
tail race into useful pressure energy.
The draft tube used here is a horizontal conical draft tube with an
inlet diameter of 2000mm and outlet diameter of 37600mm.this helps in
creating a suction pressure which helps in the successful discharge of the
fluid.
5.2.8 Penstock
The penstock is used to bring water from the reservoir to the
turbine. It gets connected to the distributor of the turbine system. A
cylindrical hollow tube of 2000mm diameter is used here. It also consists
of bellows at the elbows. These elbows are dynamically inefficient.
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5.2.9 ELECTRICAL EQUIPME�TS
Typically these includes:-
• Generator & its Auxiliaries
• Switchgear Panels
• Cables
• Generator Transformer
• Switchyard Layout & Structures
• Instrument Transformer
• Circuit Breaker
• Disconnecting Switch
• Lightning Arrester
• Control & Protection Panels of Generator & Transformer
• Automation of Turbine, Control & Protection
• Supervisory Control And Data Acquisition (SCADA)
• Illumination of Power house & Switchyard
• Ventilation system
• Fire Fighting Equipment
5.3 TECH�ICAL DETAILS
Turbine:
1. Type : Upstream elbow Semi Kaplan
Make : BEACON NEYPRIC
2. Rated Head : 14.4 m
3. Rated Discharge : 23.14 m3/s
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4. Rated output : 2950 kW
5. Rated Speed : 375 rpm
6. Runaway Speed : 1050 rpm
7. Runner
a) Diameter : 1900 mm
b) Number of blades : 4 No.s
c) Hub Diameter : 810 mm
d) Material
(i) Runner : 13 /4 Chromium Nickel S S
(ii) Hub : Cast Steel
8. Turbine Bearing : Thrust bearing 620*340*170
Spherical Roller 440*260*144
9. Coupling type : Resilient
(i) H-660-Low speed
(ii) H-660-High speed
Make : WELLMAN
10. Inlet Valve
a) Type : Butterfly
b) Operation : Hydraulic
c) Diameter : 1850 mm
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Make : FOURESS
11. Maximum head : 24.8 m
12. Minimum head : 8.3 m
Generator:
1. Make : JYOTHI
2. Capacity : 2.5MW
3. Gen. Voltage : 11000 V
4. Type of excitation : Static
5. Generation : 5.6M. Units/ year (Anticipated)
Dam:
1. Full reservoir level : 115.09 m
2. Min. draw down level : 99.5 m
3. Gross storage : 236.7 Mm3
4. Live storage : 226.5 Mm3
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6. HYDEL PLA�T –PRESE�T SITUATIO�
The Malampuzha mini Hydel project is a non-working dead
investment. The project, since its completion, has worked only for 200
days.
The problem of the Hydel plant starts from its selection of the
turbine. The selection of the turbine must have been done on the basis of
specific head and the required power and available head.
�s = � √Pr ÷ (Hr) 5/4 6.1
Where N=speed of rotation (rpm)
Pr = Rated power
Hr = Rated head
From the technical description given we obtain the values
N =375rpm
Pr =2950kW
Hr =14.4m
Therefore Ns= 375 ×√2950 ÷ 14.4 = 726.08
�s =726.08
For this specific speed, the most suited turbine was a vertical
Kaplan turbine with Syphon intake. But unfortunately they have placed
a horizontal semi Kaplan turbine.
A horizontal semi Kaplan turbine has a flow in axial direction. It
has fixed guide vanes and movable runner vanes. These kinds of turbines
need a specific speed of 1000-1250. Although it can work on the given
specific speed the efficiency of the system will be under objection
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Table 2: comparison of two types of Turbine
S �o. Parameter TUBULAR (SEMI KAPLA�)
VERTICAL WITH SIPHO� I�TAKE
1 Inlet Valve Required Not Required
2 Draft tube gate Required Not Required
3 Drainage pump Required Not Required as setting is above maximum tail race level
4 Dewatering pump Required Not Required as setting is above tail race
5 Cost of civil work High Low
6 Efficiency 1% higher
Table 2: Comparison between Tubular and Vertical Kaplan with siphon
intake
6.1 Calculation based on the log book values
Table 3: log book calculation
Head
(m)
Discharge
(cussecs)
Discharge
(m3/sec)
Power
(kw)
Efficiency
(%)
21.36 550 15.576 2300 70.47
25.3 520 14.726 2300 62.93
23.7 540 15.293 2300 64.69
22.4 500 14.16 2300 73.92
21.4 550 15.576 2300 70.34
20.4 550 15.576 2300 73.79
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Sample Calculation (Set. �o: 4)
Water Level = 112m
Net Head (H) = Water level - Runner level - Tail race level
= 112 - 88 - 1.6
=22.4m
Discharge (Q) = 500 cussecs
= 500 * 0.02832
= 14.16 m3/sec
Output Power = 2300 kw
Efficiency = S. P/ρgQH
Where ρ = density of water = 1000kg/m3
g = acceleration due to gravity = 9.81 m/s2
Efficiency = 2300*1000/1000*9.81*14.16*22.4
=0.7392
= 73.92 %
According to Beacon Neyrpic, the manufactures of the turbine,
Rated Head = 14.14 m
Rated Power = 2950 kw
Rated Discharge = 23.3 m3/sec
So efficiency for this system is
Efficiency = 2950*1000/1000*9.81*14.14*23.3
=0.9127
= 91.27 %
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The efficiency of the turbine in general working condition is
obtained to be less than the efficiency stated by the manufacturer. These
may be due to the problems with the following components of the system
1. Penstock
2. Draft Tube
3. Inlet Shutter
4. Flow Meter
1. Penstock
The penstock that they use there right now is a double elbowed one for
which the efficiency is too low. Also there is only one butterfly valve to
stop the flow of water towards the Turbine. This may cause problem
during maintenance work. Also if the butterfly valve fails, we cannot
control the flow of water to the Turbine The butterfly valve is
hydraulically controlled.
2. Draft tube
The draft tube mounted here is a conical draft tube. All low-head, high
discharge turbines has to be given amply dimensioned draft tubes. This
draft tube must be suitably designed. The height of the draft tube was too
great and hence the water pressure around the runner became so low. This
creates cavitation problems, and it is necessary to mount the runner below
tail-race level. The negative head created by the draft tube is too low. The
draft tube is not designed to fulfill the maximum head of the Turbine
3. Inlet shutter
As mentioned, the flow of inlet water is completely controlled by
the butterfly valve. A failure to this valve will result in complete failure
of the project. In order to nullify this, we can create an inlet gate or a
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shutter which can control the flow at the beginning itself. This helps in
the maintenance work of the dam.
4. Flow meter
The flow meter is a pre- requisite for the proper functioning of the
turbine. As we know the efficient working of the turbine is mainly
controlled by the head available and the discharge. This discharge or the
flow rate is calculated using the flow meter. A flow meter calculates the
rate of flow of liquid through the penstock and this value is fed into the
PLC circuit which controls the blade angle. Depending upon the
discharge or flow rate the PLC circuit changes the blade angle so as to
obtain the required rpm.
But this flow meter was missing in the project site. That means
there was no control of the flow of liquid through the turbine.
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7. TECH�ICAL FEASIBLITY OF THE
PROJECT
Since the basic structure of the plant is already built, a wide range
change of the structure is not possible, i.e. we can’t now change the
horizontal Kaplan into a vertical Kaplan with siphon intake. So the
technical feasibility study of the plant will be restricted to the present
situation existing over there.
One of the major limitations we came up during our project is:
i) Non- operational system
ii) Flow meter
iii) Net head calculation
iv) Mechanical and electrical losses
v) Fixed guide vanes
vi) Blade angle
7.1 �on- operational system
Since the complete system is non-operational we couldn’t take the
readings from the system. Some readings such as the flow rate, runner
speed, blade angle etc could only be found out during its operation. So
such values should be assumed. This can be done in two ways; either we
can rely upon the technical details provided by the manufacturer or find
out the values which we obtained during its operation (The log book
values). We opted for the log book values.
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7.3 Flow meter
As discussed earlier, the flow meter was missing in the project site.
This was one of the major limitations for our project. The values we
obtained from the log book were calculated using Canal Discharge
method. As we know, the major parameters for a Kaplan turbine are
discharge, head and speed. The relation between these three are
controlled or regulated by a flow meter. Three flow meters must be
placed- near the inlet, near the distributor and near the draft tube. These
three flow meters will give us the actual flow rate and also the pressure
drop (energy drop) occurring along the system. It also helps us to find out
the velocity of flow of water through the system.
7.4 �et head calculation
The net head is calculated as the difference of dam water level
and the tail race level, which is a false reading. The net head is the
difference between gross head and frictional head loss. This frictional
head loss is not calculated in the reading. So the head reading has to be
revised.
7.5 Blade angle
The blade angle of the turbine has to be provided by the
manufacturers. These blade angles must be fed into the PLC circuit and
the circuit controls the movement of the blade according to the varying
discharge. But here, no details about the blade angles have been provided
by the manufacturer. Due to these technical limitations the operators are
changing the blade angles by trial and error method.
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7.6 Fixed guide vanes
The Kaplan turbine used here is a horizontal semi Kaplan turbine.
It has fixed guide vanes .These fixed guide vanes are set at a particular
angle by the manufacturer which cannot be changed. The exit angle of the
guide vanes may not be the same as that of the inlet angle of the runner.
This obstructs the shock-free flow of the water into the runner. This
produces turbulence by which the hydraulic efficiency of the turbine is
reduced.
It has been found out that the rated power is obtained at a discharge
of 17 m3/sec (rated discharge) and 19.5m head (rated head). This was
found out during its 200 days of operation. This increase in head is
mainly due to the change in the net head range which varies from 15m-
25m head.
So all the calculation for the efficiency improvement will be based
on these values
Rated Power= 2950kW
Rated head=19.5m
Rated discharge=17 m3/sec
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8. EFFICIE�CY IMPROVEME�T
η= shaft power / water power =S.P/ ρ g QH
The efficiency of the turbine can be increased by
i) Increasing discharge
ii) Increasing head
iii) Increasing shaft power
But as you can see the efficiency is inversely proportional to the
head and discharge. This may make us to feel that the above statement is
false. But what happens is that when head is increased the discharge
through the pipe will be increased. Now this head and discharge are
directly proportional to the power.
In the case of Kaplan turbine the efficiency of the turbine is
assumed to be constant and the value of shaft power is found out. Hence
the concept of increasing efficiency generally implies to the improvement
of shaft power for a given head. For this first we will find out the shaft
power developed at different heads (for a given efficiency) Let the rated
efficiency be 90%
Shaft power and discharge calculation using Qu and Pu
Qu= Q1/√H1= Q2√H2 = …….
Pu= P1/H13/2= P2/H2
3/2 = …….
Here rated power is 2950 kW = P (Since rated power will be equal to
rated output at maximum efficiency)
Rated discharge is 600cusecs = 600*.02831=16.99= 17m3/sec = Q
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Rated head= 19.5m = H
Efficiency for the given parameters
η= S.P/W.P
η= 2950/9.81*17*19.5 = 90 %
Qu = Q/√H = 17/√19.5 = 3.80 Qu= 3.80
Pu = P/√H3 = 2950/√18.62 = 34.26 Pu= 34.26
Table 5: Calculation of Plant Factor
HEAD
(m)
DISCHARGE
(m3/sec)
POWER
(kW)
PLANT
FACTOR (%)
15 14.91 1990.32 67.46
16 15.40 2192.64 74.33
17 15.87 2401.30 81.40
18 16.33 2616.35 88.68
19 16.78 2837.38 96.18
20 17.22 3064.30 100.00
21 17.64 3296.97 100.00
22 18.06 3535.26 100.00
23 18.46 3779.02 100.00
24 18.86 4028.13 100.00
25 19.25 4282.50 100.00
The plant factor is assumed to be 100% for power values higher
than the rated power.
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But discharge cannot be varied in this manner as it produces highly
varying torque on the shaft. Hence the discharge is kept constant for
certain specific heads and not varied for a particular range of head. Now
the discharge is reduced by closing the inlet of the penstock. This will
reduce the power as the power is proportional to discharge also.
Generally a Hydel plant is defined by its plant factor. Plant factor is
defined as the ratio of power generated to the rated power.
i.e. Plant factor = Power generated Rated power
.
i) Calculation of velocity of flow through the turbine
The velocity of the flow can be found out from the formula
Q = π/4(Do2-Dh
2) ×V1
Where Q = discharge through the runner
Do = Runner outer diameter
Dh = diameter of hub
V1 = velocity of flow at inlet.
For this calculation let’s take the rated discharge.
So Q = 17 m3/sec
Do= 1900mm = 1.9 m
Dh = 810mm = 0.81 m
Therefore V1= 7.32 m/sec
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ii) Calculation of frictional head loss
The frictional head loss can be calculated by
∆ Hf = V12/2g
Where g = 9.81m/sec2
∆ Hf = 2.74m
iii) Calculation of net head
The net head is the head available to the turbine unit for power
production. This head is the static gross head, the difference between the
level of water in the Forebay/impoundment and the tail water level at the
outlet, less the hydraulic losses of the water passage.
i.e. ∆ H = ∆ Hg - ∆ Hf
Where ∆ H = net head
∆ Hg = gross head = water level – tailrace level
∆ Hf = frictional head
Therefore ∆ H = (water level- 89.6- 2.74)
= (water level – 92.34)
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9. IMPROVISATIO� �EEDED
The efficiency of a low head Kaplan turbine (as in our case)
generally depends upon the draft tube loss and the runner loss. The runner
loss is mainly due to the improper blade angles. The draft tube losses are
generally based on the cavitation problems.
9.1 I�STALL A FLOW METER
Controlling the flow rate of liquid is a key control mechanism for
any Kaplan plant. There are many different types of devices available to
measure flow.
Flow meters are classified on the basis of the parameter which is
used for flow measurement. They are mainly classified into three. They
are:
1. Head Type:
I. Orifice Plates
II. Rotameters
III. Venturi Tubes
2. Velocity Type
I. Magnetic
II. Vortex
III. Differential Pressure Meter
3. Displacement
I. Turbine Meter
Out of these we suggest the installation of turbine flow meter or
differential pressure meter
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Differential-Pressure Meters
Design overview:
While many different types of differential-pressure flow meters are
available, this discussion will focus on one type. The technology
discussed here involves the measurement of a pressure differential across
a stack of laminar flow plates. During operation, a pressure drop is
created as fluid enters through the meter's inlet. The fluid is forced to
form thin laminar streams, which flow in parallel paths between the
internal plates separated by spacers.
The pressure differential created by the fluid drag is measured by a
differential-pressure sensor connected to the top of the cavity plate. The
differential pressure from one end of the laminar flow plates to the other
end is linear and proportional to the flow rate of the liquid.
What makes this technology unique is the linear relationship
between differential pressure, viscosity and flow, which is given by the
following equation
Q = K [P1-P2)/µµµµ]
where (units vary per approach):
Q = Volumetric flowrate
P1 = Static pressure at the inlet
P2 = Static pressure at the outlet
µµµµ = Viscosity of the fluid
K = Constant factor determined by the geometry of the restriction
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Dept. of Mechanical Engg Page 53 Govt. Engg. College, Thrissur
Variances in temperature and pressure, which often cause errors in
variable-area flow meters, can be easily handled by adding a pressure
sensor (separate from the differential-pressure sensor in the basic design)
and a temperature sensor to the design, and correct the flow readings to
standard pressure and temperature (77°F and 1 atm). Typical accuracy for
the design is ±2-3% fullscale.
Advantages:
As with mass flow meters, the differential-pressure meter has no
moving parts to wear out.
For control applications, these meters are available with a built-in
proportioning valve for onboard or remote control of the flow rate. With a
wide variety of flow ranges and models for both gases and liquids, the
differential-pressure meter is one of the most versatile designs currently
on the market.
Turbine Meters
Design Overview:
Many designs exist for turbine flow meters, but most are a
variation on the same theme. As fluid flows through the meter, a turbine
rotates at a speed that is proportional to the flow rate. Signal generators,
usually located within the rotor itself, provide magnetic pulses that are
electronically sensed through a pickup coil and calibrated to read flow
units. In some designs, an integral display may show both the flow rate
and the total flow since power-up.
Because of the rotating blades in a turbine meter, the output signal
will be a sine wave voltage (V) of the form:
Malampuzha Hydel Plant Project Report’ 08- 09
Dept. of Mechanical Engg Page 54 Govt. Engg. College, Thrissur
V= K ωωωω sin (� ωωωω t)
where:
K = The amplitude of one sine wave
ωωωω = The rotational velocity of the blades
� = The number of blades that pass the pickup in one full rotation
t = Time
Because the output signal is proportional to the rotational velocity
of the turbines—which, in turn, is proportional to the liquid flow—the
signal is easily scaled and calibrated to read flow rate and flow
totalization. Turbine flow sensors generally have accuracies in the range
of ±0.25-1% full-scale.
Advantages:
The main advantages of the turbine meter are its high accuracy
(±0.25% accuracy or better is not unusual) and repeatability, fast response
rate (down to a few milliseconds), high pressure and temperature
capabilities (i.e., up to 5,000 psi and 800°F with high-temperature pick
coils), and compact rugged construction. Some manufacturer's have taken
turbine meter design to the next level by incorporating advanced
electronics that perform temperature compensation, signal conditioning
and linearization, all within a few milliseconds.
Disadvantage:
The disadvantage of the turbine meter is that is relatively expensive
and has rotating parts in the liquid stream. And, most turbine meters need
a straight section of pipe upstream from the flow meter in order to reduce
Malampuzha Hydel Plant Project Report’ 08- 09
Dept. of Mechanical Engg Page 55 Govt. Engg. College, Thrissur
turbulent flow. This may make installation a challenge in small areas.
However, some newer turbine meters reduce or eliminate the amount of
straight pipe required upstream, by incorporating flow straighteners into
the body of the unit.
Another disadvantage in some designs is a loss of linearity at the
low-flow end. Low-velocity performance and calibration can be affected
by the natural change in bearing friction over time. However, today's self-
lubricated retainers, low-drag fluid bearings, and jeweled-pivot bearings
all help to reduce the friction points, thereby allowing for greater
accuracy and repeatability in lower-flow applications.
9.2 EXCAVATE THE SITE DEPTH TO 85 M
By excavating the total depth of the project site into 85 m, the
minimum head from which the power can be generated will be
lowered to 8.3 m; i.e. we can generate power even at a water level of
97m. This helps the plant to generate power even at the worst
condition of draught.
9.3 I�TRODUCE MOVABLE GUIDE VA�ES RATHER THA�
FIXED O�ES
As mentioned earlier, the fixed guide vanes will not give a
shock free entrance of water stream into the runner at every angle.
This results in poor efficiency or decreased runner power. This is a
great loss. So the fixed guide vane has to be changed into a movable
guide vane.
Malampuzha Hydel Plant Project Report’ 08- 09
Dept. of Mechanical Engg Page 56 Govt. Engg. College, Thrissur
To control these movable vanes, we have to include a PLC
circuit which controls the blade angle of the guide vanes. This PLC
circuit must be developed designed and should be installed by the
manufacturers itself.
The PLC circuit of the runner vane and the guide vane can be
incorporated. Since, for the shock-free entrance of the water stream,
the outlet angle of the guide vane and the inlet angle of the runner
vane must be equal. So by using a suitable PLC circuit we can control
both the runner and the guide vane angles together and there by
produce higher efficiency rates.
9.4 USE OF A� S-SHAPED DRAFT TUBE
The conical draft tube placed over there is a horizontal conical
draft tube whose efficiency is under suspicion. The efficiency of this type
of draft tube is dependent on the angle of the diverging walls. Small
divergence angles require long diffusers. Here a small diffuser has been
used. This can be made into fully functional by shanging the divergence
angle to about 15 degrees rather than the typical optimum value of about
7 degrees.
The horizontal conical tube is neither having the required divergent
angle nor the required length. So this conical draft tube can be changed
into a S-shaped draft tube. The feature in favour for the S-shaped draft
tube is the flexibility of placing the runner above the tail race level. This
helps in the maintenance work and also in increasing the net head without
causing cavitational problems.
Malampuzha Hydel Plant Project Report’ 08- 09
Dept. of Mechanical Engg Page 57 Govt. Engg. College, Thrissur
10. CO�CLUSIO�
The Malampuzha dam at present is a dead investment. Among the
many flaws that make it, we decided to focus on the major three:
1. The turbine efficiency at the time of working was only around 70%
as opposed to the rated efficiency of 90%
2. The basic construction caused cavitation problems in the draft tube
3. Since there was no flow meter to measure the flow rate, the blade
angles were adjusted on the basis a trial and error method.
Providing answers to these problems would be a start towards
renovation of the Hydel project.
With a view towards increasing efficiency, we redesigned the
construction so that the output efficiency becomes 90%
Suggestions put forth include:
1. Increasing head by lowering draft tube
2. Replacing semi-Kaplan with a full Kaplan turbine
3. Installation of flow meter at the start of penstock, inlet of runner
and inlet of draft tube
4. A PLC circuit is set-up to take the readings from the flow meter
and make corresponding changes to the blade angles.
Malampuzha Hydel Plant Project Report’ 08- 09
Dept. of Mechanical Engg Page 58 Govt. Engg. College, Thrissur
BIBILIOGRAPHY
1. Beacon Neyrpic turbine operation and maintenance manual
2. Dr.R. K. Bansal, Fluid Mechanics and Hydraulic Machines
3. Dr. P. N. Modi & Dr. S. M. Seth, Hydraulics and Fluid Machines
including Hydraulic Machines
4. S. Ramamrutham & R. Narayan, Hydraulics Fluid Mechanics &
Fluid Machines
5. Roger E. A. Arndt, Ceaser Farell & Joseph M. Wetzel, Small And
Mini Hydropower Systems by
6. Indian Institute of Technology, Roorkee , Guide For Selection of
Turbine and Governing System For Small Hydro Power
7. www.wikipedia.com