Introduction
In today’s blog, we will discuss What is the Kaplan turbine, Kaplan turbine head range, Kaplan Turbine components, Kaplan turbine runner, How Kaplan turbine works.
What is the Kaplan turbine
In 1913, Austrian professor Viktor Kaplan first designed the turbine that combines automatically adjusted propeller blades with automatically adjusted wicket gates. To achieve the highest efficiency. After him, the turbine developed on axial flow reaction principle is named as Kaplan Turbine.
Water pressure combined with the velocity means this flow has kinetic energy as well as pressure.
The axial flow is clearly mentioned in the name; the water flows along the shaft axis. That means the water stream coming from penstock is parallel to the axis of rotation of the turbine.
Kaplan turbine is a propeller turbine having adjustable blades assembly generally used for low head and high flow plants. And it is evolved from the Francis turbine.
Kaplan turbine head range
Don’t look above your eyebrows; Head is the height of standing water. There is no fixed rule, but below 30 meters, the water flow is considered low head flow.
Kaplan Turbine components
Moving further, every turbine has the components on which its function depends; you might have thought if the function of every turbine is the same, then why do we have to learn about its components and construction again and again because every turbine has a different pattern of operation and according to its flow, head, the action of water on moving blades it varies.
Following are the components of the Kaplan turbine
- penstock
- Scroll casing
- Guide vanes mechanism
- Draft tube
- Runner blades
- Runner
Penstock
Penstock is a pipe or a long channel that connects the reservoir to the turbine building. However, it also carries water. In the case of the Francis, turbine penstock is connected to the spiral casing.
Scroll casing
As the name indicated, it is a roll (ex. roll of paper)
Scroll casing is basically of spiral shade specimen whose cross-sectional area decreases from start to end.
Water from the dam flows through the penstock to scroll casing and guide vanes to the turbine.
The primary function of scroll casing is to protect and shield the interior parts such as runner, runner blades, and guide vanes from external damage.
Flowing water turns through guide vanes by 90 degrees and flows axially over the runner.
Guide vane mechanism
It is used as a guiding mechanism.
The Guide vanes are fixed vanes whose primary function is to guide the flow direction towards the turbine.
Guide vanes change the angle between blades so that angle at which water strikes blades can be controlled. However, this regulates the flow of water entering the twisted blades of the turbine to maintain turbine performance.
This mechanism opens and closes based on the power demand at the output end of the generator.
If the required power output is more than guide vanes open to circulate more water flow. And if the necessary output is less, the guide vane closes its blade to reduce the circulation of water to the turbine.
Hence with the help of a guide vane mechanism, the efficiency of the turbine is increased.
Draft tube
The draft tube is an outlet of the Kaplan turbine to the tailrace.
An outlet of the reaction turbine is such that available pressure is generally smaller than atmospheric pressure.
After rotating the turbine, the remaining water discharges from the draft tube; due to the draft tube arrangement, the turbine can be placed in a high area so that maintenance and handling can become more accessible.
Construction of the draft tube is such that the cross-sectional area is less at the start, but it starts increasing as we go down toward the tailrace. That means a cross-sectional area of the draft tube increase gradually.
As we know that water requires to flow turbine is of high velocity, and after discharging the water axially, this creases low vapor pressure due to which cavitational problem occurs; this problem is solved with the help of the draft tube
The draft tube has the diffuser’s shape. We all know that the diffuser decreases the velocity and increases water pressure. Therefore with increased pressure, cavitations reduce.
Due to the expanding area of the tube, it is named a draft tube. Runner outlet is attached to one end of the draft tube, and the opposite end is submerged beneath the level of water in the tailrace.
Runner blades
Runner blades are mounted on a circular disc known as a runner.
These runner blades are adjustable to an optimum angle of attack for maximum output.
The structure of blades for the Kaplan turbine is twisted along the length to obtain maximum efficiency.
Kaplan turbine runner
Runner, it is not a person who runs neither door runner. In the case of a hydroelectric power plant, the runner is of circular shape. The number of blades is mounted with equal spacing.
A runner is the essential part of the turbine, which provides motion when struck by water. It is a part of the turbine where the water energy is transferred into the rotational force that is mechanical energy that drives the generators.
How Kaplan turbine works
The water from the storage reservoir is carried through the penstock to the scroll casing. The decreasing area of the scroll casing maintains the flow pressure of water. This high pressured water is then guided by the guide vane mechanism toward the runner blades.
The vanes are so adjustable that it changes itself according to the requirement of flow rate. The direction of the water is axial to that of the runner blade since it takes 90-degree turns.
Runner starts rotating as the water guided by guide vanes strikes on the runner blades due to the reaction force of water. To get the optimum angle of attack for all cross-sections of blades, the runner blades have twisted along their length.
After rotating the runner blades, water discharges from the draft tube, where its pressure and kinetic energy decrease. The kinetic energy is then converted into pressure energy, and this pressure is reduced while discharging through the draft tube.
This turbine rotation converts the kinetic energy of water into mechanical energy, which is then fed to a generator, where this energy is converted into electrical output.
In our upcoming blog, we will discuss the working of hydroelectric power plants.
