What is Impulse Turbine? Working and Construction
Introduction
An impulse turbine is a hydro turbine that operates on impulse force. It is designed to work in high-head, low-flow conditions. A nozzle first converts the water’s potential energy into kinetic energy. The high-velocity water jet then strikes the turbine blades, transferring its kinetic energy to the rotor and causing it to spin. This rotational motion drives a generator, producing electricity.
The impulse turbine is one of the most straightforward and efficient types of turbines, making it a popular choice for hydropower plants in mountainous regions or areas with significant elevation differences. Unlike reaction turbines, which rely on pressure and kinetic energy, impulse turbines utilize only the kinetic energy of the water jet, making them highly effective in specific applications.
What is an Impulse Turbine?
An impulse turbine is a hydro turbine that converts water’s kinetic energy into mechanical energy to generate electricity. It operates on the principle of impulse force, where a high-velocity jet of water strikes the turbine blades, causing them to rotate. This turbine is primarily used in high-head, low-flow water applications. The key feature of an impulse turbine is that it converts the entire hydraulic energy of water into kinetic energy before it strikes the turbine blades, unlike reaction turbines, which utilize both pressure and kinetic energy.
Construction of an Impulse Turbine
The impulse turbine consists of several critical components that efficiently convert water energy into mechanical energy. These components include:
- Penstock: A penstock is a large pipe or channel that carries water from a reservoir or dam to the turbine. It is designed to withstand high pressure and ensures a steady water flow to the turbine.
- Nozzle: The nozzle is a key component that converts water’s pressure energy into kinetic energy. It directs a high-velocity jet of water onto the turbine blades.
- Runner/Impeller: The runner consists of a circular disk mounted on a rotating shaft (rotor). Cup-shaped or spoon-shaped blades (buckets) surround its circumference at even intervals.
- Bucket: Engineers design buckets to capture the water jet’s kinetic energy efficiently. Manufacturers typically use durable materials like cast iron or stainless steel to withstand high-impact forces. The bucket’s shape deflects the water jet at an optimal angle (usually around 170 degrees) to maximize energy transfer while avoiding interference with the next bucket.
- Casing: The casing is a protective cover of cast iron or steel. It prevents water splashing and directs water flow away from the turbine after it strikes the buckets. It also shields the internal components from environmental damage.
- Braking Jet: When the water supply is turned off, the braking jet stops the turbine blades from rotating. It directs a jet of water against the back of the buckets to slow down and eventually stop the turbine.
- Spear: The spear is a conical-shaped component connected to the nozzle. It regulates water flow into the nozzle, allowing for precise control of the water jet’s velocity and direction.
Working Principle of an Impulse Turbine
The impulse turbine operates based on Newton’s second law of motion. The working process follows these steps:
- Water Supply: A high-elevation reservoir stores water and directs it to the turbine through a penstock.
Energy Conversion in Nozzle: The nozzle accelerates the water by converting its pressure into kinetic energy, creating a high-velocity water jet.
- Striking the Blades: The high-velocity water jet hits the buckets mounted on the runner, transferring kinetic energy to the blades.
- Rotation of the Runner: The force of the water jet causes the runner to rotate, converting the water’s kinetic energy into mechanical energy.
- Electricity Generation: The rotating shaft drives a connected generator, turning the generator coil to produce electricity.
- Water Discharge: After striking the buckets, the water exits the turbine and flows away through the casing.
Types of Impulse Turbines
Impulse turbines are classified into three main types based on their design and application:
1). Pelton Turbine
The Pelton turbine is the most commonly used impulse turbine. It features double-cupped buckets with a splitter in the middle, which divides the water jet into two streams for improved efficiency.
Key Features:
- High efficiency (up to 95%).
- Suitable for high-head, low-flow applications.
- Water discharge capacity ranges from 5 to 1000 liters per second.
- It requires complex and costly penstock systems due to high head requirements.
2). Turgo Turbine
The Turgo turbine is designed for medium-head applications. It uses single-cupped buckets, and the water jet strikes the blades at a 20-degree angle.
Key Features:
- It handles higher flow rates than Pelton turbines.
- Operates at high rotational speeds.
- Simple to assemble and maintain.
3). Cross-Flow Turbine
The cross-flow turbine, or the Banki-Michel turbine, is used in small hydropower plants. It allows water to flow across the blades radially, making it suitable for low-head applications.
Key Features:
- Simple design and low maintenance.
- Suitable for flow rates ranging from 20 to 2000 liters per second.
- Used in hydropower plants with power ratings from 5 kW to 3 MW.
Applications of Impulse Turbines
Impulse turbines serve various applications, especially in hydropower generation. Key uses include:
- Hydropower Plants: High-head hydropower plants generate electricity using impulse turbines. These turbines perform well in locations with significant elevation differences and low water flow rates.
- Micro-Hydropower Systems: Small-scale hydropower systems employ impulse turbines to supply electricity to remote areas.
- Industrial Applications: Industries rely on impulse turbines for mechanical energy in processes such as pumping and grinding.
- Renewable Energy Projects are crucial in renewable energy projects, contributing to sustainable power generation.
Advantages of Impulse Turbines
- High efficiency in high-head, low-flow conditions.
- Simple design and effortless maintenance.
- Suitable for remote and off-grid locations.
- Durable and capable of withstanding high-impact forces.
Conclusion
Impulse turbines are vital to hydropower systems, particularly in high-head applications. They convert the kinetic energy of a water jet into mechanical energy, which generates electricity. Engineers widely use impulse turbines in hydropower plants, micro-hydropower systems, and industrial applications thanks to their robust design, high efficiency, and versatility. Understanding their construction, working principles, and types helps select the right turbine for specific energy needs.
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