Connecticut Water Trails Association
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Connecticut Water Trails Association |
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Connecticut Water Trails Program History Of Connecticut's Water Trails History of Hydroelectric Power
Rocky River Power Station - Candlewood Lake
The Power Of Water
When watching a river roll by, it's hard to imagine the force it's carrying. If you have ever been white-water rafting, then you've felt a small part of the river's power. White-water rapids are created as a river, carrying a large amount of water downhill, bottlenecks through a narrow passageway. As the river is forced through this opening, its flow quickens. Floods are another example of how much force a tremendous volume of water can have.
Water is a very important energy resource. The
concept of hydro electric energy is not new. Running water has been used
as a source of energy for many thousands of years. In times gone by
water energy was used to grind corn for agriculture and private use.
Simple Beginnings
Use of hydropower peaked in the mid-20th century,
but the idea of using water for power generation goes back thousands of
years. A hydropower plant is basically an oversized water wheel.
More than 2,000 years ago, the Greeks are said to have used a
water wheel for grinding wheat into flour. These ancient water wheels
are like the turbines of today, spinning as a stream of water hits the
blades. The gears of the wheel ground the wheat into flour.
Hydropower
Hydropower comes from the force of moving water and
is a clean, renewable and environmentally friendly source of energy.
There is no fuel to burn so there are no emissions released into the
air. The use of hydropower is also economical and helps conserve our
fossil fuels.
Hydropower plants capture the energy of falling
water to generate electricity. A turbine converts the kinetic energy of
falling water into mechanical energy; then a generator converts the
mechanical energy from the turbine into electrical energy.
Hydroplants range in size from "micro-hydros" that
power only a few homes to giant dams like the Hoover Dam that provide
electricity for millions of people.
Parts Of A Hydroelectric Plant
Most conventional hydroelectric plants include four
major components:
Dam
- This is usually located in a valley near a natural lake. This raises the
water level of the river to create falling water. Also controls the flow
of water. The reservoir that is formed is, in effect, stored energy. The
dam is thicker at the bottom than at the top. This is because as the water
gets deeper its pressure increases. Hydro electric power stations can also
be erected next to a fast-flowing river. In this case the water flow
cannot be controlled or stored.
The decision to build a hydroelectric dam depends on three conditions being fulfilled:
Good Topographical Situation: the ideal is a river canyon or in general a narrowing of the river. If a maximum amount of water is to be stored, the volume of the basin above the dam must also be calculated. A wide flat valley is perfect!
The Right Geological Formations:
the rocks on which the dam is supported must be stable and
waterproof, both for reasons of efficiency and safety.
The Right Hydrological Conditions: precipitation over the water catchment area that feeds the supply basin of the dam must be sufficient to fill the dam and to compensate for evaporation losses from the retaining lake. Finally any inhabitants of the storage basin that is going to be submerged must be moved and compensated for the disruption.
There Are Two Main Types Of Dam:
Gravity Dams : which are totally supported on the bedrock base. This base must be especially resistant, since it will support the whole weight of the retained water. Gravity dams are in concrete or in earth or rock fill.
Dams do not
only retain water: they also hold back sediments eroded by the river
that feeds the retaining basin. They therefore have a tendency to fill up
with mud over time. For example:
since its commencement four years ago, the dam at Sanmenxia on the Houang
Ho river in China has lost 41% of its storage capacity because of mud
sedimentation.
It is therefore necessary to cater for the pumping
of these sediments, or their regular emptying by means of a conduit
placed at the bottom of the dam. These emptying operations are delicate.
Beware of an influx of muddy water downstream from the dam; neither the
inhabitants nor the fish like that!
The design of a hydroelectric dam must take account
of the risk factors and reduce them to a minimum:
The resistance to periods when the river is in
spate must be studied: in 1889, the dam at Johnston in the United
States gave way under the impact of flood waters, claiming 2000
victims. Today all dams are equipped with means of dealing with
spate conditions.
The resistance of the dam to earthquakes must be
studied and assessed. It is also necessary to take account of the
stability of the land surrounding the retaining basin: in 1963 a
gigantic landslide fell into the retaining lake of the dam at Vaiont
in Italy. The dam resisted, but an enormous wave of water flowed
over the top of the dam, claiming 3000 victims in the valley below.
Permanent inspection of the dam itself for: infiltration of water into the body of the dam or under the dam (the “fox effect”), deformations
A study of the ecological impact, particularly around and downstream of major dams. Example: the construction of the colossal Assouan dam on the Nile in Egypt (160 billion m3 of retained water capacity) has had a number of effects, amongst others a significant reduction in the silt content of the water downstream from the dam. Result: the Nile delta which previously reached the sea, has started to retreat (at a rate of several tens of meters a year in certain places). The peasant farmers on the delta have to use more fertilizer to maintain their agricultural yields, because of the deficit in the amount of alluvial material brought down by the annual flood conditions, compared to the situation before construction of the dam.
Ecological Impact
- The ecological impact of medium-sized dams is also
significant. For
example: the stagnant water in the retaining lake behind
a dam has a tendency to be under-oxygenated: the fish that
live in the impoverished water that comes out of the
turbines do not appreciate the situation. On the other hand,
when water from the top of the dam is suddenly released it
is heavily enriched in oxygen and contains tiny air bubbles.
The fish don’t like that either … It is not easy to keep the
little creatures satisfied!
Human Impact Study.
The creation of the retaining lake for very large dams in
particular, leads to the displacement of numerous people and
can drown significant areas of cultivated land. For example:
filling the retaining lake for the largest hydroelectric dam
in the world, that of the Three Canyons on the Yang Tse
Kiang in China, started in 2003 and will be completed in
2009 (the dam is 185m high, 2km long, represents 22 billion
of investment, the plant has twenty-six 700-MW turbines
producing 18 200 MW of power, the equivalent of ten nuclear
generating plants!). Between 1.2 and 1.9 million people will
be displaced, all of whom must be found new homes and given
new land to cultivate!
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.
Turbine - Water
is channeled into the dam via tunnels. The force of falling water
pushing against the turbine's blades causes the turbine to spin. A water
turbine is much like a windmill, except the energy is provided by
falling water instead of wind. The turbine converts the kinetic energy
of falling water into mechanical energy.
Generator – 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.
Connected to the turbine by shafts and possibly
gears so when the turbine spins, so do a series of magnets inside the
generator. Giant magnets rotate past copper coils, causing the generator
to spin also. Converts the mechanical energy from the turbine into
electric energy. Producing alternating current (AC) by moving electrons.
Generators in hydropower plants work just like the generators in other
types of power plants.
Transformer - The
transformer inside the powerhouse takes the AC and converts it to
higher-voltage current.
Transmission Lines
- Conduct electricity from the hydropower plant to homes and business.
Outflow - Used
water is carried through pipelines, called tailraces, and re-enters the
river downstream.
The water in the reservoir is considered stored
energy. When the gates open, the water flowing through the penstock
becomes kinetic energy because it's in motion. The amount of electricity
that is generated is determined by several factors. Two of those factors
are the volume of water flow and the amount of hydraulic head. The head
refers to the distance between the water surface and the turbines. As
the head and flow increase, so does the electricity generated. The head
is usually dependent upon the amount of water in the reservoir.
How Much Electricity Can A Hydroelectric Plant
Make?
The amount of electricity a hydropower plant
produces depends on two factors:
How Far the Water Falls.
The farther the water falls, the more power it has. Generally, the
distance that the water falls depends on the size of the dam. The higher
the dam, the farther the water falls and the more power it has.
Scientists would say that the power of falling water is "directly
proportional" to the distance it falls. In other words, water falling
twice as far has twice as much energy.
Amount of Water Falling.
More water falling through the turbine will produce more power. The
amount of water available depends on the amount of water flowing down
the river. Bigger rivers have more flowing water and can produce more
energy. Power is also "directly proportional" to river flow. A river
with twice the amount of flowing water as another river can produce
twice as much energy.
Generating electricity through hydroelectric plants is done as follows:
Stage One: The force of moving water is very powerful,
and a hydroelectric plant uses that force to generate
electricity. Hydroelectric plants are built near moving water
such as a river and also man-made facilities, such as dams, that
create moving water. The dams are built on reservoirs or lakes
and have gates that can open or close to control the water
flowing over the dam.
Advantages And Disadvantages
There are several advantages and disadvantages to
hydro electric energy production.
Advantages
One big advantage is that energy is free once the
dam is built. Another plus is that there is no waste or pollution
created by hydro electric power stations. This form of energy is also
much more reliable than wind, solar or wave power. Water can be stored
and used during times of peak usage and power is constant.
Disadvantages
The disadvantages of generating hydro electric
energy are the costs involved in building large dams and its negative
environmental impacts. When a dam is built large areas upstream are
flooded and this can destroy bird and animal habitats. It is also not
always easy to find the correct site for the dam. It may not fit in with
the needs of residents and wildlife.
Hydro electric energy can also affect the quality of water in the area. Quality and quantity of water resources can be impacted and this can affect the plant and fish life in the lake and river. While hydro electric energy may not be the perfect solution to our energy problems at present, there is hope that technological advances can minimize ecological impacts and see this type of energy being utilized more in the future.
Connecticut Light & Power : CL&P History About NU - Northeast Utilities
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