Short Answer:
The types of hydraulic turbines are mainly classified based on the head of water, the direction of flow, and how water energy is converted into mechanical energy. The two main types are Impulse turbines and Reaction turbines.
In impulse turbines, water strikes the turbine blades with high velocity through nozzles, while in reaction turbines, water flows over the blades completely filling the passage. Common examples include the Pelton wheel (impulse turbine), and the Francis and Kaplan turbines (reaction turbines). Each type is chosen depending on water head, flow rate, and site conditions.
Detailed Explanation :
Types of Hydraulic Turbines
A hydraulic turbine is a machine that converts the energy of flowing or falling water into mechanical energy, which is then converted into electrical energy by a generator. The selection of a turbine for a hydroelectric power plant depends on the head (height of water fall), flow rate, and power requirement.
Hydraulic turbines are broadly classified into two main types: Impulse turbines and Reaction turbines. Each type has different working principles and is suitable for different site conditions.
- Impulse Turbine
An impulse turbine works on the principle of converting the kinetic energy of a high-velocity water jet into mechanical energy. In this turbine, water flows through nozzles and strikes the turbine blades (or buckets), causing the wheel to rotate. The pressure of water remains constant throughout, as all energy is converted into kinetic energy before striking the blades.
Main Features of Impulse Turbine:
- Water jet strikes the blades at atmospheric pressure.
- The runner (rotating wheel) operates in air.
- Suitable for high head and low discharge (low flow rate) conditions.
- The energy transfer takes place due to impulse force.
Example: Pelton wheel turbine.
Working Principle of Impulse Turbine:
- Water from the reservoir flows through the penstock and reaches the nozzle.
- The nozzle converts the pressure energy of water into a high-speed jet.
- The jet of water strikes the buckets on the runner, transferring kinetic energy to the wheel.
- The direction of the jet changes, and the change in momentum causes the runner to rotate.
- The mechanical energy produced is used to drive a generator.
Example – Pelton Wheel Turbine:
- Used for high head (above 300 m) and low discharge conditions.
- The wheel has cup-shaped buckets arranged around its circumference.
- The jet of water strikes the center of each bucket, splits into two, and exits at the sides.
- The efficiency of a Pelton wheel can reach up to 85–90%.
Advantages of Impulse Turbine:
- Simple in design and construction.
- Easy to maintain.
- Suitable for high head sites.
- High efficiency under steady flow.
Disadvantages:
- Not suitable for low head conditions.
- Large in size for high flow rates.
- Reaction Turbine
A reaction turbine works on the principle of converting both the pressure energy and kinetic energy of water into mechanical energy. In this turbine, water flows completely through the blades, and the pressure of water changes during the flow.
Main Features of Reaction Turbine:
- Operates under water, completely filled with water.
- Suitable for medium and low head with high discharge conditions.
- Energy is transferred due to the reaction of flowing water on the blades.
- The casing and draft tube are required to collect and guide the water.
Examples:
- Francis Turbine (mixed flow type)
- Kaplan Turbine (axial flow type)
- a) Francis Turbine
The Francis turbine is the most commonly used reaction turbine. It is a mixed flow turbine, meaning water enters radially and exits axially.
Construction and Working:
- Water from the penstock enters the spiral casing around the runner.
- The guide vanes direct water onto the runner blades at the proper angle.
- As water flows through the runner blades, both pressure and velocity decrease, causing the runner to rotate.
- The water then exits through the draft tube, which helps recover kinetic energy.
Operating Conditions:
- Head: 30–600 meters.
- Efficiency: Around 90%.
- Used in medium head and large-scale hydroelectric plants.
Advantages:
- High efficiency and compact design.
- Can handle large variations in load.
- Suitable for medium head applications.
- b) Kaplan Turbine
The Kaplan turbine is an axial flow reaction turbine invented by Viktor Kaplan. Water flows parallel to the axis of the runner shaft. It is suitable for low head and high discharge conditions.
Construction and Working:
- Water enters through a scroll casing and passes through adjustable guide vanes.
- It then flows over the adjustable runner blades of the Kaplan turbine.
- The angle of the runner blades and guide vanes can be adjusted according to the water flow, maintaining high efficiency at variable loads.
- Water finally exits through the draft tube into the tailrace.
Operating Conditions:
- Head: 2–40 meters.
- Efficiency: 85–90%.
- Used in low head, high discharge rivers.
Advantages:
- Adjustable blades give high efficiency even with fluctuating water flow.
- Compact design and easy to install.
Disadvantages:
- Complex construction and high maintenance cost.
Comparison Between Impulse and Reaction Turbines
| Feature | Impulse Turbine | Reaction Turbine |
| Energy conversion | Kinetic energy only | Kinetic + Pressure energy |
| Pressure change | Constant | Decreases across the runner |
| Head range | High head | Medium to low head |
| Flow of water | Air (open) | Fully filled with water |
| Examples | Pelton wheel | Francis, Kaplan turbines |
(Note: Only for clarity – no tables in final format if not allowed.)
Other Classifications of Hydraulic Turbines
- According to Head:
- High head: Pelton wheel
- Medium head: Francis turbine
- Low head: Kaplan turbine
- According to Direction of Flow:
- Tangential flow: Pelton wheel
- Radial flow: Old Francis turbine
- Axial flow: Kaplan turbine
- Mixed flow: Modern Francis turbine
- According to Discharge:
- Constant discharge type
- Variable discharge type
Conclusion :
The types of hydraulic turbines are mainly divided into impulse and reaction types, depending on how they convert water energy into mechanical energy. The Pelton wheel is used for high head and low discharge, while Francis and Kaplan turbines are used for medium and low head respectively.
Each turbine type is designed to suit specific site conditions, ensuring efficient utilization of water energy for electricity generation. The proper selection of a turbine helps achieve high efficiency, long life, and reliable operation of a hydroelectric power plant.