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Saturday, 26 April 2008


Hydropower Basics
Flowing water creates energy that can be captured and turned into electricity.
This is called hydropower.
Hydropower is currently the largest source of renewable power, generating nearly 10% of the electricity used in the United States.
The most common type of hydropower plant uses a dam on a river to store water in a reservoir.
Water released from the reservoir flows through a turbine, spinning it, which, in turn, activates a generator to produce electricity.
But hydropower doesn't necessarily require a large dam.
Some hydropower plants just use a small canal to channel the river water through a turbine.

Another type of hydropower plant—called a pumped storage plant—can even store power.
The power is sent from a power grid into the electric generators.
The generators then spin the turbines backward, which causes the turbines to pump water from a river or lower reservoir to an upper reservoir, where the power is stored.
To use the power, the water is released from the upper reservoir back down into the river or lower reservoir.
This spins the turbines forward, activating the generators to produce electricity.

Types of Hydropower
Impoundment
An impoundment facility, typically a large hydropower system, uses a dam to store river water in a reservoir.
The water may be released either to meet changing electricity needs or to maintain a constant reservoir level.

Diversion
A diversion, sometimes called run-of-river, facility channels a portion of a river through a canal or penstock.
It may not require the use of a dam.

Pumped Storage
When the demand for electricity is low, a pumped storage facility stores energy by pumping water from a lower reservoir to an upper reservoir.
During periods of high electrical demand, the water is released back to the lower reservoir to generate electricity.

Sizes of Hydropower Plants
Facilities range in size from large power plants that supply many consumers with electricity to small and micro plants that individuals operate for their own energy needs or to sell power to utilities.

Large Hydropower
Although definitions vary, DOE defines large hydropower as facilities that have a capacity of more than 30 megawatts.

Small Hydropower
Although definitions vary, DOE defines small hydropower as facilities that have a capacity of 0.1 to 30 megawatts.

Micro Hydropower
A micro hydropower plant has a capacity of up to 100 kilowatts (0.1 megawatts).

Turbine Technologies
There are many types of turbines used for hydropower, and they are chosen based on their particular application and the height of standing water—referred to as "head"—available to drive them.
The turning part of the turbine is called the runner.
The most common turbines are as follows:
Pelton Turbine
A Pelton turbine has one or more jets of water impinging on the buckets of a runner that looks like a water wheel.
The Pelton turbines are used for high-head sites (50 feet to 6,000 feet) and can be as large as 200 megawatts.
Francis Turbine
A Francis turbine has a runner with fixed vanes, usually nine or more.
water enters the turbine in a radial direction with respect to the shaft, and is discharged in an axial direction.
Francis turbines will operate from 10 feet to 2,000 feet of head and can be as large as 800 megawatts.
Propeller Turbine
A propeller has a runner with three to six fixed blades, like a boat propeller.
The water passes through the runner and drives the blades.
Propeller turbines can operate from 10 feet to 300 feet of head and can be as large as 100 megawatts.
Kaplan Turbine
A Kaplan turbine is a type of propeller turbine in which the pitch of the blades can be changed to improve performance.
Kaplan turbines can be as large as 400 megawatts.

How Hydropower Works
Most hydropower projects use a dam and a reservoir to retain water from a river.
When the stored water is released, it passes through and rotates turbines, which spin generators to produce electricity.
Water stored in a reservoir can be accessed quickly for use during times when the demand for electricity is high.
Dammed hydropower projects can also be built as power storage facilities.
During periods of peak electricity demand, these facilities operate much like a traditional hydropower plant — water released from the upper reservoir passes through turbines, which spins generators to produce electricity.
However, during periods of low electricity use, electricity from the grid is used to spin the turbines backward, which causes the turbines to pump water from a river or lower reservoir to an upper reservoir, where the water can be stored until the demand for electricity is high again.
A third type of hydropower project, called "run of the river", does not require large impoundment dams (although it may require a small, less obtrusive dam).
Instead, a portion of a river's water is diverted into a canal or pipe to spin turbines.

How Hydropower is Used
Hydropower is currently the largest and least expensive source of renewable electricity produced in the United States.
Large and small-scale hydropower projects are most commonly used by clean power generators to produce electricity.
Our Buying Clean Electricity section provides information on buying electricity generated from hydro and other renewable resources in your state.
Many large-scale dam projects have been criticized for altering wildlife habitats, impeding fish migration, and affecting water quality and flow patterns.
As a result of increased environmental regulation, the National Hydropower Association forecasts a decline in large-scale hydropower use through 2020.
Research and development efforts have succeeded in reducing many of these environmental impacts through the use of fish ladders (to aid fish migration), fish screens, new turbine designs, and reservoir aeration.
Although funding has been limited, current research focuses on the development of a "next generation turbine, which is expected to further increase fish survival rates and improve environmental conditions.
A very small hydropower (called microhydro) project can also be installed to meet the electricity needs of a single home or small business, and is especially useful for those in remote areas.

Reference Web site :http://people.howstuffworks.com/http://www.eere.energy.gov/RE/hydropower.html

;2:57:00 am


Thursday, 24 April 2008


Hydropower Plants
Worldwide, hydropower plants produce about 24 percent of the world's electricity and supply more than 1 billion people with power.
The world's hydropower plants output a combined total of 675,000 megawatts, the energy equivalent of 3.6 billion barrels of oil, according to the National Renewable Energy Laboratory.
There are more than 2,000 hydropower plants operating in the United States, making hydropower the country's largest renewable energy source.



Hydropower plants harness water's energy and use simple mechanics to convert that energy into electricity.
Hydropower plants are actually based on a rather simple concept -- water flowing through a dam turns a turbine, which turns a generator.

Here are the basic components of a conventional hydropower plant:



1. Dam - Most hydropower plants rely on a dam that holds back water, creating a large reservoir. Often, this reservoir is used as a recreational lake, such as Lake Roosevelt at the Grand Coulee Dam in Washington State.

2. Intake - Gates on the dam open and gravity pulls the water through the penstock, a pipeline that leads to the turbine. Water builds up pressure as it flows through this pipe.

3. Turbine - The water strikes and turns the large blades of a turbine, which is attached to a generator above it by way of a shaft. The most common type of turbine for hydropower plants is the Francis Turbine, which looks like a big disc with curved blades. A turbine can weigh as much as 172 tons and turn at a rate of 90 revolutions per minute (rpm), according to the Foundation for Water & Energy Education (FWEE).

4. Generators - As the turbine blades turn, so do a series of magnets inside the generator. Giant magnets rotate past copper coils, producing alternating current (AC) by moving electrons. (You'll learn more about how the generator works later.)

5. Transformer - The transformer inside the powerhouse takes the AC and converts it to higher-voltage current.

6. Power lines - Out of every power plant come four wires: the three phases of power being produced simultaneously plus a neutral or ground common to all three. (Read How Power Distribution Grids Work to learn more about power line transmission.)

7. Outflow - Used water is carried through pipelines, called tailraces, and re-enters the river downstream.



Pumped Storage
The majority of hydropower plants work in the manner described above.
However, there's another type of hydropower plant, called the pumped-storage plant.
In a conventional hydropower plant, the water from the reservoir flows through the plant, exits and is carried down stream.
A pumped-storage plant has two reservoirs:

1. Upper reservoir - Like a conventional hydropower plant, a dam creates a reservoir. The water in this reservoir flows through the hydropower plant to create electricity.

2. Lower reservoir - Water exiting the hydropower plant flows into a lower reservoir rather than re-entering the river and flowing downstream.

Using a reversible turbine, the plant can pump water back to the upper reservoir. This is done in off-peak hours.
Essentially, the second reservoir refills the upper reservoir.
By pumping water back to the upper reservoir, the plant has more water to generate electricity during periods of peak consumption.

Inside the Generator
The heart of the hydroelectric power plant is the generator. Most hydropower plants have several of these generators.



The generator, as you might have guessed, generates the electricity.
The basic process of generating electricity in this manner is to rotate a series of magnets inside coils of wire.
This process moves electrons, which produces electrical current.




The Hoover Dam has a total of 17 generators, each of which can generate up to 133 megawatts. The total capacity of the Hoover Dam hydropower plant is 2,074 megawatts.
Each generator is made of certain basic parts:
1. Shaft
2. Excitor
3. Rotor
4. Stator
As the turbine turns, the excitor sends an electrical current to the rotor.
The rotor is a series of large electromagnets that spins inside a tightly-wound coil of copper wire, called the stator.
The magnetic field between the coil and the magnets creates an electric current.

In the Hoover Dam, a current of 16,500 volts moves from the generator to the transformer, where the current ramps up to 230,000 volts before being transmitted.

;2:39:00 am


Sunday, 13 April 2008


hello people!:D
instead of using that incomprehendable wetpaint, lets just use blogger!
since everybody knows how to use it anw(:
i'm going to do up the blogskin and profile and everything now, so yea,
please constantly blog and tag and everything!

xoxo, qiaohui.
[edited]
the tagboard's darn sucky, but whatever, we've got our WEBSITE!:D

;7:34:00 am


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