What Is In A Hydropower Plant?

Hydropower is a form of renewable energy that harnesses the power of flowing water to generate electricity. It relies on the water cycle, where solar energy heats water on the surface of rivers, lakes, and oceans, which evaporates and forms clouds. The water eventually condenses and falls back to earth as precipitation. The gravitational force of falling or flowing water can be used to spin turbines and generators that produce electricity (https://www.eia.gov/energyexplained/hydropower/).

Hydropower has a long history in the United States, starting with mechanical hydropower that used falling water to turn a wheel or turbine to perform work. The first U.S. hydroelectric power plant opened on the Fox River near Appleton, Wisconsin in 1882. Today, hydropower is the nation’s leading renewable energy source and provides over 6% of total U.S. electricity generation and 44% of renewable electricity generation as of 2019 (https://www.eia.gov/energyexplained/hydropower/where-hydropower-is-generated.php). Hydropower offers the benefits of clean, renewable electricity without direct greenhouse gas emissions.

Table of Contents

Dam

The dam is a crucial component of hydropower plants. The dam serves several important purposes:

Impoundment – The dam blocks the river flow and creates a large reservoir or lake behind it to store water.

Intake – The dam helps control the flow of water going into the intake structure. The intake allows only the amount of water needed for power generation to enter.

Diversion – The dam diverts river water into pipes and tunnels that lead to the turbines in the powerhouse.

There are several types of dams used in hydropower projects:

Embankment dams – Made of earth, rockfill or tailings, which slopes on the downstream side and supports the water pressure directly.

Gravity dams – Made of concrete or stone masonry and uses its weight and internal strength to withstand water pressure.

Arch dams – Curved dams that transfers water pressure into the canyon walls through arch action.

Buttress dams – Has a watertight upstream side supported by a series of buttresses on the downstream side.

Reservoir

The reservoir is an essential component of a hydropower plant. It is an artificial lake that is created by damming a river. The main purpose of the reservoir is to store water that will be used to generate electricity.

Reservoirs can vary greatly in size. Some of the largest reservoirs in the world are man-made lakes formed by hydroelectric dams. For example, Lake Kariba in Africa is one of the world’s largest reservoirs with a surface area of over 5,000 square kilometers. The size of the reservoir depends on factors like the geography of the location, how much water needs to be stored, and the energy generating capacity.

While reservoirs provide water storage for renewable hydropower, they can also have negative environmental impacts. Flooding land to create a reservoir results in the loss of forests and wildlife habitats. Reservoirs may also change local climate conditions and affect water quality. Methane emissions can be produced by the decomposition of flooded biomass. Careful planning is required to minimize the environmental footprint of hydroelectric reservoirs.

Intake

The intake is the entrance to the hydropower plant that controls water flow from the reservoir into the rest of the system. Its purpose is to regulate and direct water towards the penstocks while filtering out debris and silt that could damage equipment downstream.

Intakes are equipped with gates, screens, and trash racks to serve their function. Intake gates like radial, roller, and slide gates control water flow and can completely stop water from entering the system for maintenance (source). Screens filter and remove debris from the water, while trash racks prevent larger objects like logs and branches from entering. The intake is also where headrace tunnels begin that divert water towards the turbines (source).

The intake design depends on the dam type and head available. Important factors include regulating capacity, screens to filter debris, and gates for flow control. Overall, the intake controls and directs water into the hydropower plant under a range of flow conditions.

Penstock

The penstock is a closed conduit that delivers water from the intake to the turbines inside the powerhouse. Its purpose is to carry large volumes of water efficiently with minimal losses. Penstocks are commonly constructed from steel, concrete or wood.The world’s largest penstocks were recently installed at the Dubai Deep Tunnel Stormwater System. They are designed to withstand immense internal pressure from the water.

The penstock diameter balances efficient flow and material cost. The flow velocity must be fast enough to avoid sediment settling in the conduit. At the same time, overly fast flows cause unwanted pipe friction losses. Gentle slopes and smooth turning radii are used to minimize turbulence. Air venting and anchorage at bends prevent damage from hydraulic hammer and water pressure.

Turbine

The turbine is the heart of the hydropower plant. Its purpose is to convert the energy of flowing water into mechanical energy using large blades. This mechanical energy powers the generator, which converts it into electrical energy.

There are two main types of hydro turbines used in power plants:

Impulse turbines – Utilize the velocity of water to move the runner and discharges to atmospheric pressure. Common impulse turbines include Pelton wheels and Turgo impulse turbines (https://www.energy.gov/eere/water/types-hydropower-turbines).
Reaction turbines – Operate with pressure and moving water. Common reaction turbines include Kaplan, Francis and Diagonal Flow turbines

The main parts of a turbine include the runner, shaft, blades, wicket gates/nozzles, and casing. The runner has curved blades attached and rotates when water strikes them. The wicket gates or nozzles direct the flow of water onto the blades. The power generated gets transferred through the shaft and casing directs water away from the turbine.

Generator

The generator is a critical component of a hydroelectric plant. Its purpose is to convert the mechanical energy of the spinning turbine into electrical energy. The generator works based on electromagnetic induction. As the turbine causes the rotor to spin inside the generator, it rotates a magnetic field past stationary wire coils, inducing a current in the coils and generating electricity. The electricity is then stepped up to a higher voltage by transformers before being transmitted to the electric grid.

There are several types of generators used in hydroelectric plants:
Synchronous generators are the most common type. The rotor spins at the same speed as the turbine. They can generate reactive power to help support grid voltage and frequency.
Induction generators are asynchronous and turn slightly slower than synchronous speed. They are simple and robust but cannot supply reactive power.
Permanent magnet generators use permanent magnets instead of electromagnets on the rotor. This removes the need to supply excitation current.

The size of the generator depends on the flow rate and hydraulic head of the site. Larger generators are generally more efficient at converting mechanical power to electrical power. Proper generator selection is critical for maximizing the power output and revenue from a hydro plant.

Transformer

The transformer is a critical component in a hydroelectric power plant. Its purpose is to increase the voltage of the electricity generated by the turbines before it enters the transmission lines (How Electrical Transformer Cores Assist in Hydroelectric …). Transformers allow the transmission of electricity over long distances with minimal power loss, enabling it to be distributed to homes and businesses (Energy – Student Resources: Hydroelectric Power).

Transformers operate through the principles of electromagnetic induction. The transformer contains primary and secondary coil windings around an iron core. Alternating current in the primary winding creates a changing magnetic field in the core, inducing a voltage in the secondary winding. The ratio of turns between the windings sets the voltage transformation ratio. For example, a step-up transformer increases the voltage and decreases the current.

Hydroelectric plants use step-up transformers to increase the generator output voltage (2-22 kV) up to transmission voltage levels of 115 kV or higher (Transformer for Hydroelectric Power Stations). Common types are two-winding transformers, auto-transformers, and converter transformers. Large hydro stations may also use generator step-up transformers located in the powerhouse next to each generator.

Powerhouse

The powerhouse is the structure that houses the turbines and generators in a hydropower plant. Its purpose is to convert the energy of falling water into electrical energy. The powerhouse is located at the base of the dam or near the outlet of the penstock. It contains several key components:

Turbines – The fast-moving water from the penstock spins the turbines. There are different types of turbines used in hydropower plants, such as Francis, Kaplan, and Pelton turbines.

Generators – The turbine shaft is connected to a generator which converts the mechanical energy into electrical energy. Large electromagnets in the generator rotate past copper wire coils to produce electricity.
Transformers – Transformers are used to increase the voltage for transmission along the power lines.
Control equipment – The flow of water into the turbines and output of electricity is controlled and monitored by computerized control systems.

The powerhouse may also contain additional equipment like cooling systems, lubrication systems, and maintenance facilities. The electricity generated exits the powerhouse and is fed into transmission lines that carry the power to substations and distribution networks.

Transmission

The purpose of the transmission system is to move the electricity from the generator to substations before distributing it to consumers. The transmission lines connect the power plant to the grid for wider distribution. Most transmission lines carry electricity at high voltages between 46,000 to 765,000 volts. This is done to minimize power losses along the lines. According to the U.S. Energy Information Administration, annual electricity transmission and distribution losses average about 5% in the United States. These high voltage lines are maintained by the utility and run from the power plant to substations near population centers.

Transmission towers and cables carry electricity over long distances to the distribution grid. The towers are made from steel lattices or tubular steel and are designed to withstand extreme weather conditions. Aluminum conductor steel reinforced (ACSR) cables are commonly used which have a steel core for strength and aluminum conductors. Low loss conductors can also be used which incorporate composite cores to reduce power loss. Long underground and underwater cables are used in some cases to transmit electricity across water bodies or through mountain regions. Advanced monitoring, control and communication systems are also used to manage the transmission grid and reroute power as needed.

Sources:
https://www.eia.gov/tools/faqs/faq.php?id=105&t=3
https://insideenergy.org/2015/11/06/lost-in-transmission-how-much-electricity-disappears-between-a-power-plant-and-your-plug/