What Is The Structure Of A Hydroelectric Power Plant?

Hydroelectric power is a renewable energy source that generates electricity from flowing water. The term hydroelectric comes from the Greek words “hydro” meaning water and “elektron” meaning amber, which was used in ancient times to generate static electricity.

Humans have been using the power of water for thousands of years, but it wasn’t until the late 19th century that hydroelectric power began being used to generate electricity on a large scale. In 1878, the world’s first hydroelectric power plant opened on the Fox River in Appleton, Wisconsin, United States.

Today, hydroelectric power provides around 16% of the world’s electricity from facilities located in over 160 countries. It is one of the leading renewable electricity sources due to its low operating costs and ability to quickly adjust power output. Hydroelectric power is considered an environmentally clean energy source as it emits much less pollution than fossil fuel-based generation.

Some key benefits of hydroelectric power plants include:

Renewable – Hydroelectricity is produced from flowing water, which is continuously replenished through the water cycle.

Clean energy – It does not burn fuel, so it does not emit greenhouse gases or cause air pollution.
Reliable – Rainfall and river water flow can generally be predicted allowing for consistent electricity production.
Long lifespan – Hydroelectric facilities typically have life spans of 50-100 years.

Energy storage – Water can be stored in reservoirs and released when electricity demand is high.

Table of Contents

Dam

The dam is an important component of a hydroelectric power plant. Its purpose is to create a reservoir and control the flow of water. The water stored in the reservoir will be used to generate electricity as it flows through the power plant.

There are different types of dams used in hydroelectric plants such as gravity dams, arch dams, buttress dams, and earth dams. Gravity dams are made of concrete or masonry and rely on their weight and shape for stability. Arch dams have a curved design that transfers water pressure into the abutments. Buttress dams have supports or buttresses connected to the main dam. Earth dams are made of compacted earth material such as soil, rock-fill, silt and clay. The dam stores water in the reservoir upstream and regulates the flow downstream (1).

Major parts of a dam include the upstream face, downstream face, crest, abutments and spillways. The upstream face holds back the reservoir water while the downstream face supports the structure. The crest is the top of the dam and overflow is released through spillways (2).

(1) https://www.iberdrola.com/about-us/what-we-do/hydroelectric-power/types-dams
(2) https://www.energy.gov/eere/water/types-hydropower-plants

Reservoir

The purpose of the reservoir in a hydroelectric power plant is to store water that will be used to generate electricity. The size of the reservoir varies greatly depending on the capacity of the power plant. Many reservoirs are able to hold several months’ worth of flow from the river. This allows electricity to be generated even when river flows are low. The reservoir creates an artificial lake behind the dam that can cover many square miles of land (“Hydroelectric reservoir”, n.d.).

The water in the reservoir contains potential energy that gets converted into kinetic energy as it moves through the dam. Having a large reservoir capacity allows the plant operators to generate power on demand when electricity is needed (“Types of Hydropower Plants”, n.d.). Overall, the reservoir serves as a giant battery, storing energy in the form of water when electricity demand is low and releasing it when demand is high.

Intake

The intake structure is the interface between the reservoir and the water conveyance system (penstock or tunnel). Its purpose is to control the amount of water flowing into the penstock and turbine. The intake contains gates, valves, trash racks, and screens to regulate water flow and filter out debris that could damage equipment downstream.

Trash racks are installed at the entrance to the intake to stop large debris from entering. They consist of a series of metal bars spaced close enough to allow water through while trapping floating logs, branches and other trash.

The intake gates/valves are used to control the flow of water into the penstock. They can be completely closed for inspection and maintenance. Partially closing the gates is a means of reducing water flow and power output when electricity demand is low.

Fine screens may also be used to filter out small debris that could still damage equipment. Automatic rakes clean the screens periodically.

The intake structure is an important control point for regulating the amount of water that drives the turbines to match power production with demand. Proper design considers hydraulic head pressure, equipment reliability, and maintenance access.

Sources:

https://www.sciencedirect.com/topics/engineering/intake-structure

https://www.kgalglobal.com/intakes

Penstock

The penstock is a pipeline that serves as the conveyance structure to deliver water from the intake to the turbine. It is a large pipe, usually made of steel or concrete, that can range in diameter from 10 feet for a small facility to 30 feet for a large hydroelectric dam. The size and length of the penstock depends on factors like the layout of the site, quantity of water flow, and the amount of hydraulic head (vertical drop) available.

The main purpose of the penstock is to channel water with minimal losses from the reservoir to the turbine. It is designed to be large enough to convey the necessary volume of water. The smooth interior surface and downward slope allow water to flow rapidly under the force of gravity. The penstock pipe must withstand high water pressures, especially at lower elevations near the turbine.

Since the moving water transmits energy to the turbine, the penstock plays a key role in maximizing efficiency. Strategically placing the turbine near the bottom of the penstock minimizes friction losses. The ideal angle, diameter, and length promote water velocity while limiting pressure issues from the weight of the downward flowing water.

Turbine

The turbine is a critical component of a hydroelectric power plant as it converts the energy of the moving water into mechanical energy. There are several types of turbines used in hydro plants, with the choice dependent on the height of the water drop and the desired output. The most common turbines used are [Pelton](https://www.slideshare.net/IsuruDhananjaya2/training-report-50429800), Francis, and Kaplan turbines.

Pelton turbines are suited for locations with a large head of water, where the water drop from the reservoir to the turbine is substantial. The high-velocity water emerging from the penstock impacts spoon-shaped buckets on the turbine, converting the kinetic energy into rotation. Francis turbines can operate over a range of heads and are the most widely used turbine type. They contain fixed vanes that direct water flow onto the turbine runner. Kaplan turbines have adjustable vanes and blades, making them well-suited for locations with low head heights.

By harnessing the natural power of moving water, the turbine is a vital component in generating clean electricity from hydroelectric projects.

Generator

The generator is the component that converts the mechanical energy from the turbine into electrical energy. The generator typically consists of coils of wire that rotate inside a magnetic field. When the coils move through the magnetic field, it induces a current in the coils due to electromagnetic induction. This conversion of mechanical energy into electrical energy is known as the dynamo effect. The electricity generated can then be transmitted to homes and businesses.

The generator is coupled directly to the turbine shaft. When the turbine spins due to the force of the water, it causes the coils in the generator to spin as well. There are different types of generators used in hydroelectric plants, such as synchronous generators and induction generators. The components that make up a generator include: rotor coils to produce current (these are usually on the rotating side), stator coils to generate magnetic field (usually on the stationary side), a shaft that couples the generator to the turbine, a power converter to convert the electricity to a stable frequency, and bearings and cooling systems.

Transformer

The transformer is a critical component of the hydroelectric plant. It steps up the voltage of the electricity generated by the turbines and generator for efficient transmission over long distances (source). Transformers operate based on the principles of electromagnetic induction. When the alternating current from the generator passes through the transformer’s primary winding, it creates a changing magnetic field. This changing magnetic flux induces a voltage in the transformer’s secondary winding due to electromagnetic induction. By carefully selecting the number of turns in the primary and secondary windings, the transformer can increase (‘step up’) or decrease (‘step down’) the voltage as needed.

For hydroelectric plants, step-up transformers are used to increase the voltage (often from around 12,000 volts to as high as 500,000 volts) for transmission over transmission lines with reduced power losses. The increased voltage allows the power to be transmitted over long distances to reach customers efficiently. Without the step-up transformer stage, much of the power would be lost as heat in the transmission lines. Overall, the transformer plays a vital role in hydroelectric plants by enabling the generated electricity to be transmitted to distant areas where the power is utilized.

Transmission

After the electricity is generated at the hydroelectric dam, it needs to be transmitted to the electrical grid so that it can be distributed for use. This is done via transmission lines that carry high-voltage electricity from the generator to substations near population centers (Energy.gov, 2022).

The transmission lines that carry electricity from a hydroelectric dam can stretch hundreds of miles to reach substations and customers. High-voltage transmission lines are necessary because they can carry electricity efficiently over long distances with less energy lost during transmission (Penlight, 2020). At the substation, transformers then step down the electricity to lower voltages that are safer for typical distribution and household use.

Environmental Impact

Hydroelectric dams and reservoirs can have significant environmental impacts, especially on wildlife habitats and populations. Flooding land to create a reservoir drastically alters ecosystems, converting forests, wetlands, and other habitat into artificial lakes. This destroys existing habitats and forces wildlife to relocate or adapt to a new environment. Reservoirs also fragment habitats and create barriers for fish and other wildlife migration patterns.(Journal Renewable Energy)

Dam operations often lead to unnatural fluctuations in downstream water flows and temperatures that further disrupt wildlife. Fish and other aquatic life can be killed or have their migration patterns hindered by dams blocking access to spawning grounds. Terrestrial species like river otters and reptiles are also impacted by changing water levels downstream.(Discover the power of hydroelectric plants)

To help mitigate environmental damage, techniques like fish ladders, minimum flow releases, and reservoir habitat enhancements can be implemented. Careful dam siting and operation are also important to reduce impacts. However, fundamentally altering river ecosystems is an inevitable consequence of large hydroelectric projects.