Kaplan turbine is a famous type of reaction turbine. It is essentially a propeller with adjustable blades in a tube. A Kaplan turbine is an axial turbine, which means that the flow direction does not change as it passes through the rotor.
The inlet guide can be opened and closed to regulate the flow through the turbine. When they are completely off, they completely stop the flow of water and stop the turbine. Depending on the location of the inlet drive vanes, they introduce a different number of “swirls” into the water flow and ensure that the water strikes the rotor at the most suitable angle for maximum performance. The pitch of the rotor blades is also adjustable, from a flat profile for very low flow to an inclined profile for high flow.
Working principle of Kaplan Turbine
The head at the turbine inlet is the sum of the pressure and the kinetic force. As the water passes through the channel, part of the pressure energy is converted into the driving force of the turbine. The Kaplan turbine shaft is a vertical axial flow reaction, and the lower end of the shaft becomes larger, which is called the hub or head. The hub is attached by blades and behaves like a runner, but the water enters the runner in the axial direction and also exits in the axial direction.
The pressure on the exit blade is more minor than the pressure on the inlet blade. The effect of the reaction causes the energy transfer, that is, by the variation of the relative speed of the blade.
Now let’s study how it works:
First of all, water enters the turbine chamber. The turbine shaft attaches the impeller blades or turbine blades. The flow of water directs the blades. Controlling the flow of water is done by driving vanes. The water hits the runner’s blade if it is open.
If the turbine shaft rotates the impeller, the impeller blades also start rotating. The generator is connected to the turbine shaft to generate electricity. The water used for the rotation of the blades enters the suction pipe. Water flows from the draft tube into the overflow and into the river.
Kaplan Turbine Parts
Kaplan Turbine consists of the following main parts:
⦁ Turbine Shaft
⦁ Guide Vane
⦁ Runner Vanes
⦁ Scroll Casing
This is an important component used to spin the electric motor to generate electricity. The turbine shaft attaches to the impeller blades. The Kaplan turbine shaft rotates when impeller blades rotate, which helps produce electricity.
Because the turbine shaft spins at a high speed of 1800-3600 rpm, it must be heat resistant. The material by which the turbine shaft is manufactured is structural steel.
The guide vane acts as a control gate, which means it adjusts water flow as needed. The water flow is maximum when the guide vane is fully open; then, the turbine blades are exerted by maximum pressure, so more energy can be generated.
When the driving vanes are half-open, the water flow is relatively low. Therefore, less water acts on the turbine blades and less pressure force, resulting in less energy generation.
The runner vane is an integral part of the turbine. Blades attach the runner.
The shaft is connected to the generator with the runner starts. As it rotates, so does the shaft.
Scroll casing is a particular type of casing that can minimize the cross-section. The spiral casing of the Kaplan turbine helps protect the impeller, impeller blades, etc.
The water enters the conduit through a pressure hose and then flows into the driving vane. Now the water flows from here to the runner.
The draft tube is similar to the pipe but has a more extended cross-section. The fluid pressure is increased by the draft tube. Water cannot be sucked directly into the tube. Its function is to drain the water into the suction pipe.
In simple words, the tail is used to release the water used to rotate the impeller blades or turbine blades.
Advantages of the Kaplan turbine
The Kaplan turbine has the below-given advantages:
⦁ Kaplan turbines are used for low loads.
⦁ The turbine size is small.
⦁ Therefore, due to the limited size, the space required is also very small.
⦁ For high discharge, applications can be used.
⦁ Very high specific speeds can be achieved.
⦁ Less loss of component loading efficiency.
⦁ These turbines have higher efficiency than Francis turbines.
Disadvantages of the Kaplan Turbines
The following disadvantages of Kaplan turbines are:
⦁ They need high maintenance costs.
⦁ Knitting is done when the pressure in the exhaust pipe decreases. To eliminate this problem, stainless steel as a pipe material can be used.
⦁ Water leaks in the generator room can cause congestion problems.
Applications of Kaplan Turbines
The following applications for Kaplan turbines are:
⦁ The main application of Kaplan turbines is the generation of hydroelectric power.
⦁ Kaplan turbines are smaller and easier to build.