Short Notes: Francis and Kaplan Turbines | Short Notes for Mechanical Engineering PDF Download

 Page 1


Francis and Kaplan Turbines
 
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Francis and Kaplan Turbines
 
1. Penstock:- It is a long pipe at the outlet of which a nozzle is fitted. The water 
from reservoir flows through the penstock. The nozzle increases the kinetic 
energy of water flowing through the penstock.
2. Casing:- In case of reaction turbine, casing and runner are always full of 
water. The water from the penstocks enters the casing which is of spiral 
shape in which area of cross-section of the casing goes on decreasing 
gradually. The casing completely surrounds the runner of the turbine. The 
casing is made of spiral shape, so that the water may enter the runner at 
constant velocity throughout the circumference of the runner. The casing is 
made of concrete or cast steel.
3. Guide Mechanism:- It consists of a stationary circular wheel all-round the 
runner of the turbine. The stationary guide vanes are fixed on the guide 
mechanism. The guide vanes allow the water to strike the vanes fixed on the 
runner without shake at inlet. Also by a suitable arrangement, the width 
between two adjacent vanes of a guide's mechanism can be altered so that 
the amount of water striking the runner can vary.
4. Runner:- It is a circular wheel on which a series of radial curved vanes are 
fixed. The surface of the vanes is made very smooth. The radial curved vanes 
are so shaped that the water enters and leaves the runner without shock. The 
runners are made of cast steel, cast iron or stainless steel. They are keyed to 
the shaft.
5. Draft tube:- The pressure at the exit of the runner of a reaction turbine is 
generally less than atmosphere pressure. The water at exit cannot be directly 
discharged to the tail race. A tube or pipe of gradually increasing area is used 
for discharging water from the exit of the turbine to the tail race. This tube of 
increasing area is called draft tube. The draft tube, in addition to serve a 
passage for water discharge, has the following two purposes also.
° The turbine may be placed above the tail race and hence turbine may be 
inspected properly.
° The kinetic energy rejected at the outlet of the turbine is converted into 
useful pressure energy.
Kaplan Turbine:- Kaplan Reaction turbines are axial flow turbines in which the flow 
is parallel to the axis of the shaft. They are low head, high discharge turbine.
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Francis and Kaplan Turbines
 
1. Penstock:- It is a long pipe at the outlet of which a nozzle is fitted. The water 
from reservoir flows through the penstock. The nozzle increases the kinetic 
energy of water flowing through the penstock.
2. Casing:- In case of reaction turbine, casing and runner are always full of 
water. The water from the penstocks enters the casing which is of spiral 
shape in which area of cross-section of the casing goes on decreasing 
gradually. The casing completely surrounds the runner of the turbine. The 
casing is made of spiral shape, so that the water may enter the runner at 
constant velocity throughout the circumference of the runner. The casing is 
made of concrete or cast steel.
3. Guide Mechanism:- It consists of a stationary circular wheel all-round the 
runner of the turbine. The stationary guide vanes are fixed on the guide 
mechanism. The guide vanes allow the water to strike the vanes fixed on the 
runner without shake at inlet. Also by a suitable arrangement, the width 
between two adjacent vanes of a guide's mechanism can be altered so that 
the amount of water striking the runner can vary.
4. Runner:- It is a circular wheel on which a series of radial curved vanes are 
fixed. The surface of the vanes is made very smooth. The radial curved vanes 
are so shaped that the water enters and leaves the runner without shock. The 
runners are made of cast steel, cast iron or stainless steel. They are keyed to 
the shaft.
5. Draft tube:- The pressure at the exit of the runner of a reaction turbine is 
generally less than atmosphere pressure. The water at exit cannot be directly 
discharged to the tail race. A tube or pipe of gradually increasing area is used 
for discharging water from the exit of the turbine to the tail race. This tube of 
increasing area is called draft tube. The draft tube, in addition to serve a 
passage for water discharge, has the following two purposes also.
° The turbine may be placed above the tail race and hence turbine may be 
inspected properly.
° The kinetic energy rejected at the outlet of the turbine is converted into 
useful pressure energy.
Kaplan Turbine:- Kaplan Reaction turbines are axial flow turbines in which the flow 
is parallel to the axis of the shaft. They are low head, high discharge turbine.
Kaplan is also known as propeller turbine. Kaplan turbine is a propeller type water [ i 
turbine along with the adjustable blades. Mainly it is designed for low head water 
applications.
In this water turn at right angles between the guide vanes, runner & then flow 
parallel to the shaft. It is inward flow reaction turbine. The flow was along the 
radius from periphery to the centre of the runner. (From outer dia to the inner dia of 
runner).
It is capable of giving high efficiency at overloads (up to 15-20%), at normal loads 
(up to 94%). The runner of this turbine is in the form of boss or hub which extends 
in a bigger dia. Casing with proper adjustment of blades during running. The blade 
angles should be properly adjusted so that water enters & flow through the runner 
blades without shock.
1. Penstock:- It is the water way used to carry the water from the reservoir to the 
turbine. At the inlet of the penstock trash cracks are used to prevent the 
debris from going into the turbine.
2. Spiral or Scroll casing:- In case of reaction turbine casing and runner are 
always full of water. The water from the penstock enters the casing which is 
of spiral shape in which area of cross-section of the casing goes on 
decreasing gradually. The casing completely surrounds the runner of the 
turbine. The casing is made of spiral shape, so that the water may enter the 
runner at constant velocity throughout the circumference of the runner.
3. Guide Mechanism:- It consists of a stationary circular wheel all-round the 
runner of the turbine. The stationary guide vanes are fixed on the guide 
mechanism. The guide vanes allow the water to strike the vanes fixed on the 
runner without shock at inlet. Also by a suitable arrangement, the width 
between two adjacent vanes of a guide mechanism can be altered so that the 
amount of water striking the runner can be varied. A space, called
whirl Chamber, is provided between the guide vanes and the runner. In this 
chamber, the flow turns by 90° & move as a free vortex i.e without the aid of 
any external torque. The radial component changes into axial component due 
to the guidance from the fixed housing.
4. Runner:- It is a circular wheel, also called 'hub' or 'bass' on which a series of 
radial curved vanes are fixed. The surface of the vanes is made very smooth. 
The radial curved vanes are so shaped that water enters and leaves the runner 
without shock. The runners are made of cast steel, cast iron or stainless steel. 
In Kaplan turbine, the shaft is the extended part of runner with smaller 
diameter.
5. Draft tube:- The pressure at the exit of an axial turbine is generally less than 
atmospheric pressure. The water at exit cannot be directly discharged to the 
tail race. A tube or pipe of a gradually increasing area is used for discharging 
water from the exit of the turbine to the tail race. This tube of increasing area 
is called draft tube.
Working of the Kaplan turbine:
Due to the low water heads it allows the water flow at larger in the Kaplan turbine. 
With help of the guide vane the water enters. So the guide vanes are aligned to give 
the flow a suitable degree of swirl. The swirl is determined according to the rotor of 
the turbine. The water flow from the guide vanes are passes through the curved 
structure which forces the radial flow to direction of axial. The swirl is imparted by 
the inlet guide vanes and they are not in the form of free vortex. With a component
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Francis and Kaplan Turbines
 
1. Penstock:- It is a long pipe at the outlet of which a nozzle is fitted. The water 
from reservoir flows through the penstock. The nozzle increases the kinetic 
energy of water flowing through the penstock.
2. Casing:- In case of reaction turbine, casing and runner are always full of 
water. The water from the penstocks enters the casing which is of spiral 
shape in which area of cross-section of the casing goes on decreasing 
gradually. The casing completely surrounds the runner of the turbine. The 
casing is made of spiral shape, so that the water may enter the runner at 
constant velocity throughout the circumference of the runner. The casing is 
made of concrete or cast steel.
3. Guide Mechanism:- It consists of a stationary circular wheel all-round the 
runner of the turbine. The stationary guide vanes are fixed on the guide 
mechanism. The guide vanes allow the water to strike the vanes fixed on the 
runner without shake at inlet. Also by a suitable arrangement, the width 
between two adjacent vanes of a guide's mechanism can be altered so that 
the amount of water striking the runner can vary.
4. Runner:- It is a circular wheel on which a series of radial curved vanes are 
fixed. The surface of the vanes is made very smooth. The radial curved vanes 
are so shaped that the water enters and leaves the runner without shock. The 
runners are made of cast steel, cast iron or stainless steel. They are keyed to 
the shaft.
5. Draft tube:- The pressure at the exit of the runner of a reaction turbine is 
generally less than atmosphere pressure. The water at exit cannot be directly 
discharged to the tail race. A tube or pipe of gradually increasing area is used 
for discharging water from the exit of the turbine to the tail race. This tube of 
increasing area is called draft tube. The draft tube, in addition to serve a 
passage for water discharge, has the following two purposes also.
° The turbine may be placed above the tail race and hence turbine may be 
inspected properly.
° The kinetic energy rejected at the outlet of the turbine is converted into 
useful pressure energy.
Kaplan Turbine:- Kaplan Reaction turbines are axial flow turbines in which the flow 
is parallel to the axis of the shaft. They are low head, high discharge turbine.
Kaplan is also known as propeller turbine. Kaplan turbine is a propeller type water [ i 
turbine along with the adjustable blades. Mainly it is designed for low head water 
applications.
In this water turn at right angles between the guide vanes, runner & then flow 
parallel to the shaft. It is inward flow reaction turbine. The flow was along the 
radius from periphery to the centre of the runner. (From outer dia to the inner dia of 
runner).
It is capable of giving high efficiency at overloads (up to 15-20%), at normal loads 
(up to 94%). The runner of this turbine is in the form of boss or hub which extends 
in a bigger dia. Casing with proper adjustment of blades during running. The blade 
angles should be properly adjusted so that water enters & flow through the runner 
blades without shock.
1. Penstock:- It is the water way used to carry the water from the reservoir to the 
turbine. At the inlet of the penstock trash cracks are used to prevent the 
debris from going into the turbine.
2. Spiral or Scroll casing:- In case of reaction turbine casing and runner are 
always full of water. The water from the penstock enters the casing which is 
of spiral shape in which area of cross-section of the casing goes on 
decreasing gradually. The casing completely surrounds the runner of the 
turbine. The casing is made of spiral shape, so that the water may enter the 
runner at constant velocity throughout the circumference of the runner.
3. Guide Mechanism:- It consists of a stationary circular wheel all-round the 
runner of the turbine. The stationary guide vanes are fixed on the guide 
mechanism. The guide vanes allow the water to strike the vanes fixed on the 
runner without shock at inlet. Also by a suitable arrangement, the width 
between two adjacent vanes of a guide mechanism can be altered so that the 
amount of water striking the runner can be varied. A space, called
whirl Chamber, is provided between the guide vanes and the runner. In this 
chamber, the flow turns by 90° & move as a free vortex i.e without the aid of 
any external torque. The radial component changes into axial component due 
to the guidance from the fixed housing.
4. Runner:- It is a circular wheel, also called 'hub' or 'bass' on which a series of 
radial curved vanes are fixed. The surface of the vanes is made very smooth. 
The radial curved vanes are so shaped that water enters and leaves the runner 
without shock. The runners are made of cast steel, cast iron or stainless steel. 
In Kaplan turbine, the shaft is the extended part of runner with smaller 
diameter.
5. Draft tube:- The pressure at the exit of an axial turbine is generally less than 
atmospheric pressure. The water at exit cannot be directly discharged to the 
tail race. A tube or pipe of a gradually increasing area is used for discharging 
water from the exit of the turbine to the tail race. This tube of increasing area 
is called draft tube.
Working of the Kaplan turbine:
Due to the low water heads it allows the water flow at larger in the Kaplan turbine. 
With help of the guide vane the water enters. So the guide vanes are aligned to give 
the flow a suitable degree of swirl. The swirl is determined according to the rotor of 
the turbine. The water flow from the guide vanes are passes through the curved 
structure which forces the radial flow to direction of axial. The swirl is imparted by 
the inlet guide vanes and they are not in the form of free vortex. With a component
of the swirl in the form of axial flow are applies forces on the blades of the rotor. 
Due to the force it loses both angular and linear momentum.
Advantages of Kaplan turbine:
• Runner vanes are adjusted in the Kaplan
• Very low heads are required
• Very small no of blades are used nearly 3 to 8 blades
• Less resistance has to be overcome.
Disadvantages:
• Position of the shaft is only in vertical direction
• Speed of the turbine is 250 to 850
• High speed generator is required
• Large Flow rate must be required.
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