Kaplan Turbine is an axial reaction flow turbine and has adjustable blades. When the water flows parallel to the axis of the rotation of the shaft, the turbine is known as the axial flow turbine.
And if the head of the inlet of the turbine is the sum of pressure energy and kinetic energy during the flow of water through a runner a part of pressure energy is converted into kinetic energy, the turbine is known as reaction turbine.
For the axial flow reaction turbine, the shaft of the turbine is vertical. The lower end of the shaft is made larger which is known as a hub or boss. The vanes are fixed on the hub and hence hub acts as a runner for the axial flow reaction turbine.
It was developed in 1913 by the Austrian professor Viktor Kaplan. The Kaplan turbine was an evolution of the Francis turbine. Its invention allowed efficient power production in the low head application that was not possible with the Francis turbine.
Kaplan turbine is now widely used throughout the world for high-flow, low head power production. The Kaplan turbine is an axial flow reaction turbine because the water is moving in the axial direction.
Main Parts of Kaplan Turbine:
A Kaplan Turbine is consisted of:
Guide vane mechanism,
Hub with vanes or runner of the turbine, and
The scroll casing is a spiral type of casing that decreases the cross-section area. First, the water from the penstocks enters the scroll casing and then moves to the guide vanes.
From the guide vanes, the water turns through 90° and flows axially through the runner.
The scroll casing protects the runner, runner blades, guide vanes and other internal parts of the turbine from external damage to the turbine.
Guide Vanes Mechanism:
This is the only controlling part of the whole turbine. which opens and closes depending upon the demand of power requirement.
When the more power output requirements, it opens wider to allow more water to hit the blades of the rotor.
And when low power output requires, it closes to cease the flow of water.
When the guide vanes are absent then the turbine cannot work efficiently and so that the efficiency of the turbine decreases.
Hub with vanes or Runner of the turbine:
The term "Runner" in the Kaplan turbine plays an important role. The runner is the rotating part of the turbine in which helps in the production of electricity. The shaft is connected to the shaft of the generator.
The runner of this turbine has a large boss on which its blades are attached and the blades of the runner are adjustable to an optimum angle of attack for maximum power output. The blades of the Kaplan turbine have twist along its length.
Twist along its length in the Kaplan turbine is provided because to have always the optimum angle of strike for all cross-section of blades and hence to achieve greater efficiency of the turbine.
At the exit of the runner of Reaction Turbine, the pressure available here is generally less than the atmospheric pressure. The water at the exit cannot be directly discharged to the tailrace.
A tube or pipe is gradually increasing area and this is used for discharging water from the exit of the turbine to the tailrace.
So, the increasing area of the tube or pipe is called a Draft tube. One end of the draft tube is connected to the runner outlet and the other end is submerged below the level of water in the tail-race.
The main important point is that the Draft tube is used only in the Reaction turbine.
There are 4 types of draft tube:
Simple Elbow Draft Tube
Elbow with the varying cross-section
Moody Spreading Draft Tube.
Conical Diffuser or Divergent Draft Tube
Working Principle of the Kaplan Turbine:
Kaplan turbine is an axial flow reaction turbine. So the working fluid changes the pressure as it moves across the turbine and gives energy.
Power recapitulates from both the Hydrostatic head and kinetic energy of the following water.
From the penstock, the water is coming to enter into the casing. Here flow pressure is not lost because the shape of casing is designed in such a way that it does not lose the flow.
From the casing, the water is entering into the guide vane. Here rotor is attached so the water comes with much pressure and hence it rotates the runner.
From the runner, the water enters into draft tube here pressure and kinetic energy decreases. The remaining kinetic energy gets converted into pressure energy and hence increases the pressure of water.
Further rotation of the turbine is used to rotate the shaft of a generator and further used for the generation or production of electricity.
Let's check out this video from Learn Engineering!
Advantages of the Kaplan Turbine:
The advantages of the Kaplan Turbine are listed below:
This turbine work more efficiently at low water head and high flow rates as compared with other turbines.
This is smaller in size.
The efficiency of the Kaplan turbine is very high as compares with other types of hydraulic turbines.
The Kaplan turbine is easy to construct and
The space requirement is less.
Disadvantages of Kaplan Turbine:
Although there are some disadvantages of the Kaplan Turbine and those are:
The position of the shaft is only in the vertical direction.
A large flow rate must be required.
The main disadvantages are the cavitation process. which occurs due to pressure drops in the draft tube.
The use of the draft tube and proper material generally stainless steel for the runner blades may reduce the cavitation problem to a greater extent.
Applications of Kaplan Turbine:
Here are some applications of Kaplan Turbine:
Kaplan turbines are widely used throughout the world for electric power production. They cover the lowest head hydro sites and are especially suited for high flow conditions.
Inexpensive microturbines are manufactured for individual power production with as little as two feet of head.
Large Kaplan turbines are individually designed for each site to operate at the highest possible efficiency, typically over 90%.
They are very expensive to design, manufacture and install but operate for decades.
In today's lesson, we learned what are the parts of a Kaplan Turbine, how its work and advantages, disadvantages, and application of the Kaplan Turbine.
I hope I am able to clear your all doubts, still, if you have any further query feel free to ask me in the comment section or you can use our community portal too.
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