Short Answer:

Turbines are mechanical devices that convert fluid energy into mechanical energy by rotating a shaft. Depending on the working principle and direction of fluid flow, turbines are divided into different types. The two main types are impulse turbines and reaction turbines. Impulse turbines use the kinetic energy of water, while reaction turbines use both pressure and kinetic energy.

Each type of turbine is designed according to the available water head and flow rate. For example, the Pelton wheel is used for high-head, low-flow applications, while Francis and Kaplan turbines are used for medium and low-head, high-flow conditions.

Detailed Explanation:

Types of Turbines

Turbines are one of the most important prime movers used in hydroelectric power plants to convert hydraulic energy into mechanical energy. The mechanical energy is then used to rotate an electric generator, producing electricity. The classification of turbines is mainly based on the energy conversion method, direction of water flow, and head of water available at the site.

Broadly, turbines are classified into two main types:

1. Impulse Turbines
2. Reaction Turbines

Let’s understand each type in detail.

1. Impulse Turbine

An impulse turbine works entirely on the kinetic energy of water. In this type, high-velocity water jets are directed through nozzles onto the blades (or buckets) of the turbine runner. The water jet strikes the blades tangentially, and due to the change in momentum, the runner rotates, producing mechanical energy.

Working Principle:
The entire energy of water is converted into kinetic energy before it hits the turbine blades. The pressure of water remains constant while passing through the runner because all pressure energy is already converted into velocity energy by the nozzle.

Main Features of Impulse Turbine:

• Operates under high head and low discharge conditions.
• Works under atmospheric pressure inside the casing.
• The flow of water is tangential to the runner.
• Efficiency is high when the water jet strikes the blades correctly.

Examples of Impulse Turbines:

• Pelton Wheel Turbine: Used for high-head applications (above 250 meters).
• Turgo Impulse Turbine: Suitable for medium head and small hydro plants.
• Banki or Cross-Flow Turbine: Used for low-cost and small power plants.

Impulse turbines are simple in construction, easy to maintain, and suitable for locations with high heads and low flow rates, such as mountainous regions.

2. Reaction Turbine

A reaction turbine works on the combined action of pressure energy and kinetic energy of water. In this type, water flows continuously over the blades of the runner, and both pressure and velocity change during flow. The pressure difference between the inlet and outlet of the turbine blades causes the runner to rotate.

Working Principle:
In reaction turbines, only a part of the total head is converted into velocity energy before entering the runner, while the remaining part is converted inside the runner. The casing and draft tube help maintain pressure and ensure efficient energy conversion.

Main Features of Reaction Turbine:

• Operates under low or medium head and high discharge conditions.
• The entire flow passage is filled with water (completely submerged).
• The flow of water is radial, axial, or mixed, depending on turbine design.
• High efficiency and smooth operation.

Examples of Reaction Turbines:

• Francis Turbine: A mixed-flow turbine used for medium head (20–200 m).
• Kaplan Turbine: A propeller-type turbine suitable for low head and high flow rate.
• Propeller Turbine: Works efficiently in low-head, large-volume flow applications.

Reaction turbines are preferred in low-head regions where a large volume of water is available. Their design allows efficient conversion of both pressure and velocity energy into mechanical rotation.

Other Classifications of Turbines

Apart from the main classification, turbines can also be grouped based on other parameters:

1. Based on Flow Direction:
   • Tangential Flow: Pelton turbine.
   • Radial Flow: Francis turbine.
   • Axial Flow: Kaplan turbine.
   • Mixed Flow: Combination of radial and axial directions.
2. Based on Head of Water:
   • High Head Turbines: Pelton wheel.
   • Medium Head Turbines: Francis turbine.
   • Low Head Turbines: Kaplan and Propeller turbines.
3. Based on Specific Speed:
   • Low Specific Speed: Pelton wheel.
   • Medium Specific Speed: Francis turbine.
   • High Specific Speed: Kaplan turbine.

These classifications help in selecting the right turbine type for a particular site based on water availability, head, and energy requirement.

Conclusion:

In conclusion, turbines are classified mainly into impulse and reaction types, depending on how they utilize water energy. Impulse turbines depend on kinetic energy, while reaction turbines use both kinetic and pressure energy. The choice of turbine depends on factors like water head, discharge, and site conditions. Each turbine type has its own working characteristics and efficiency range. Understanding the types of turbines helps engineers select the most efficient system for hydroelectric power generation and water energy utilization.