Short Answer:
Hydraulic turbines are machines that convert the energy of flowing water into mechanical energy. They are used mainly in hydroelectric power plants to generate electricity. The classification of hydraulic turbines depends on the head of water, direction of flow, and working principle.
The main types of hydraulic turbines are impulse turbines and reaction turbines. Impulse turbines include the Pelton wheel, which works under high heads, while reaction turbines include the Francis turbine and Kaplan turbine, which are used for medium and low heads respectively. The selection of turbine type depends on the site conditions and available water head.
Detailed Explanation :
Types of Hydraulic Turbines
Hydraulic turbines are rotating devices that convert the potential and kinetic energy of water into mechanical energy, which is later transformed into electrical energy by a generator. The classification of hydraulic turbines is based on several factors such as head, discharge, flow direction, and working principle. Understanding the types of hydraulic turbines is essential for selecting the most efficient turbine for a particular hydropower project.
- Classification Based on Type of Energy Conversion
There are mainly two types of hydraulic turbines depending on how water energy is converted inside the turbine:
- Impulse Turbine:
In an impulse turbine, all the potential energy of water is converted into kinetic energy before striking the turbine blades. The water jet from a nozzle strikes the buckets or blades, and the impulse force of the water rotates the turbine runner. The water pressure remains constant throughout the runner, and only velocity changes. These turbines are suitable for high head and low discharge conditions.- Example: Pelton Wheel Turbine.
- Head Range: 150 m to 1800 m.
- Working Principle: Converts kinetic energy of a high-speed water jet into mechanical energy.
- Applications: High-head hydropower stations in mountainous regions.
- Reaction Turbine:
In a reaction turbine, water energy is partly converted into kinetic energy and partly into pressure energy within the runner. The water flows over the blades, causing a reaction force that makes the runner rotate. The pressure of the water continuously decreases as it passes through the turbine. These turbines are suitable for medium and low head conditions with large discharge.- Examples: Francis Turbine and Kaplan Turbine.
- Head Range: 2 m to 500 m depending on the type.
- Working Principle: Works on both impulse and reaction forces of water.
- Applications: Medium and low-head hydropower plants.
- Classification Based on Direction of Flow
Hydraulic turbines can also be classified based on the direction of water flow through the runner blades:
- Tangential Flow Turbine:
The water jet strikes the runner tangentially. It is mainly used in impulse turbines like the Pelton wheel. - Radial Flow Turbine:
Water flows radially inward or outward with respect to the runner’s axis. The Francis turbine is a radial-flow type. - Axial Flow Turbine:
In these turbines, water flows parallel to the axis of the runner shaft. The Kaplan turbine is an example of an axial-flow turbine. - Mixed Flow Turbine:
Water enters the runner radially and leaves axially. The Francis turbine also falls in this category as it allows both radial entry and axial exit.
- Classification Based on Head of Water
The head (height of water level above the turbine) determines which turbine is most suitable for the site.
- High-Head Turbines:
- Head above 250 meters.
- Used for high-pressure and low discharge.
- Example: Pelton Wheel.
- Medium-Head Turbines:
- Head between 30 to 250 meters.
- Used where moderate discharge is available.
- Example: Francis Turbine.
- Low-Head Turbines:
- Head below 30 meters.
- Used where a large volume of water is available at low height.
- Example: Kaplan Turbine and Propeller Turbine.
- Main Types of Hydraulic Turbines
(a) Pelton Wheel Turbine:
It is an impulse turbine that uses one or more jets of water striking the buckets fitted around the runner. The kinetic energy of water is completely converted to mechanical energy. It is best suited for high-head and low-discharge applications.
(b) Francis Turbine:
This is a mixed-flow reaction turbine. Water enters the runner radially and leaves axially. It operates efficiently under medium head and discharge conditions. It is the most widely used turbine in hydroelectric power stations.
(c) Kaplan Turbine:
The Kaplan turbine is an axial-flow reaction turbine with adjustable blades. It works efficiently under low-head and high-discharge conditions. The adjustable runner blades help maintain efficiency under varying loads.
- Comparison Between Impulse and Reaction Turbines
- Energy Conversion:
Impulse turbines convert all pressure energy into kinetic energy before striking the blades, while reaction turbines use both pressure and velocity changes for energy conversion. - Flow Direction:
Impulse turbines have tangential flow, whereas reaction turbines have radial or axial flow. - Casing Requirement:
Impulse turbines require simple casing mainly for water direction, but reaction turbines need airtight casing to maintain pressure differences. - Head Range:
Impulse turbines operate under high head, while reaction turbines are used for medium to low head conditions.
- Selection of Turbine Type
The selection of a suitable turbine depends upon:
- The available head and discharge.
- The required speed of operation.
- The power to be developed.
- The type of site and installation layout.
For example, in mountainous areas with high head, Pelton wheels are preferred, while in plains with medium head, Francis turbines are used. For very low head and large flow, Kaplan turbines are ideal.
Conclusion
Hydraulic turbines are essential components in hydroelectric power generation. Their selection and design depend on the head, discharge, and energy conversion method. The main types are impulse turbines (like Pelton wheel) and reaction turbines (like Francis and Kaplan turbines). Each type is suitable for different working conditions, ensuring efficient use of water energy for mechanical and electrical power generation.