ELECTRICITY
The Nature of Electricity
Electricity is a little different from the other sources
of energy that we talk about. Unlike coal, petroleum, or
solar energy, electricity is a secondary--not
primary--source of energy. That means we must use other
(primary) sources of energy to make electricity. It also
means we can't classify electricity as a renewable or
nonrenewable form of energy. The energy source we use to
make electricity may be renewable or nonrenewable, but
electricity is neither.
Making Electricity
Almost all electricity made in the United States is
generated by large, central power plants. These plants
typically use coal, nuclear fission, natural gas, or
other energy sources to produce heat energy which
superheats water into steam. The very high pressure of
the steam (75-100 times normal atmospheric pressure)
turns the blades of a turbine. (At a hydroelectric plant,
the force of falling water turns the blades.) The blades
are connected to a generator which houses a large magnet
surrounded by a coiled copper wire. The blades spin the
magnet rapidly, rotating the magnet inside the coil and
producing an electric current. The steam, which is still
very hot but back to normal pressure, now goes to a
condenser where it is cooled into water by passing it
through pipes circulating over a large body of water or
cooling tower. The water then returns to the boiler to be
used again. Power plants can capture some of the heat
from the cooling stream. In old plants, the heat was
simply wasted.
Moving Electricity from power Plants to Homes
We are using more and more electricity every year. One
reason electricity is used so much, it's easy to move
from one place to another. Electricity can be produced at
a power plant and moved long distances before it is used.
Let's follow the path of electricity from power plant to
a light bulb in your home.
First, the electricity is generated at the power plant.
Next, it goes by wire to a transformer that "steps
up" the voltage. A transformer step up the voltage
of electricity from the 2,300 to 22,000 volts produced by
a generator to as much as 765,000 volts (345,000 volts is
typical). Power companies step up the voltage because
less electricity is lost along the lines when the voltage
is high.
The electricity is then sent on a nationwide network of
transmission lines made of aluminum. Transmission lines
are the huge tower lines you may see when you're on a
highway. The lines are interconnected, so should one line
fail, another will take over the load.
Step-down transformers located at substations along the
lines reduce the voltage to 12,000 volts. Substations are
small buildings or fenced-in yards containing switches,
transformers, and other electrical equipment.
Electricity is then carried over distribution lines which
bring electricity to your home. Distribution lines may
either by overhead or underground. Overhead distribution
line are the electric lines that you see along streets.
Before electricity enters your house, the voltage is
reduced again at another transformer, usually a large
gray can mounted on an electric pole. This transformer
reduces the electricity to the 120 volts that are needed
to run the light bulb in your home.
Electricity enter your house through a three-wire cable.
The "live wires" are then brought from the
circuit breaker or fuse box to power outlets and wall
switches in your home. An electric meter measures how
much electricity you use so the utility company can bill
you.
The time it takes for electricity to travel through these
steps--from the power plant to the light bulb in your
home--is a tiny fraction of one second!
Power to the People
Everyone knows how important electricity is to our lives.
All it takes is a power failure to remind us how much we
depend on it. Life would be very different without
electricity--no more instant light from flicking a
switch; no more television; no more refrigerators; or
stereos; or video games; or hundreds of other
conveniences we take for granted. You could almost say
the American economy runs on electricity.
It's the business of electric utility companies to make
sure electricity is there when we need it. How do they do
it? First, some terms; reliability; capacity; base load;
power pools; and peak demand.
RELIABILITY is the capability of a utility
company to provide electricity to its customers 100
percent of the time. A reliable electric service is
without blackouts or brownouts.
To ensure uninterrupted electric service, laws require
most utility companies to have 15-20 percent more
capacity than they need to meet peak demands. This means
a utility company whose peak load is 12,000MW, would need
to have about 14,000 MW of installed electrical capacity.
This helps ensure there will be enough electricity to go
around even if equipment were to break down on a hot
summer afternoon.
CAPACITY is the total quantity of electricity a
utility company has online and ready to deliver when
people need it. A large utility company may operate
several plants to generate electricity for it customers.
A utility company has seven 1,000-MW (megawatt) plants,
eight 500-MW plants, and 30 100-MW plants has a total
capacity of 14,000-MW.
BASE-LOAD POWER is the electricity generated by
utility companies around-the-clock, using the most
inexpensive energy sources--usually coal, nuclear, and
hydropower. Base-load power station s usually run at full
or near capacity,
When many people want electricity at the same time, there
is a PEAK DEMAND. Power companies must be ready for peak
demands so there is enough power for everyone. During the
day's peak, between 12:00 noon and 6:00 p.m., additional
generating equipment has to be used to meet increased
demand. This equipment is more expensive to operate.
These peak load generators run on natural gas, diesel or
hydro and can be running in seconds. The more this
equipment is used, the higher our utility bills. By
managing the use of electricity during the peak hours, we
can help keep costs down.
The use of POWER POOLS is another way electric
companies make their systems more reliable. Power pools
link utilities together so they can share power as it is
needed.
A power failure in one system can be covered by a
neighboring power company until the problem is corrected.
There are nine regional power pool networks in North
America. The key is to share power rather than lost it.
The reliability of U.S. electric service is excellent,
usually better than 99 percent. In some countries,
electric power may go out several times in a day.
Power outages in the United States are usually caused by
such random occurrences as lightning, a tree limb falling
no electric wires, or a car hitting a utility poll.
|
Here is Bonneville Dam in
Oregon. A Dam is one of the ways that energy can be
produced using a renewable source. See across for more
information on making eletricity.
Energy runs through high power lines, transformers and
then into your home. With out this process energy would
never get to you from the power plant and you would never
be able to watch television like this child.
Some times local energy companies use graphs that look
like this to convey to their customers the load that they
have to handle during a particularly heavy load.
Sometimes energy companies have to borrow from others to
keep from browning out. (see definition of brownout
across) |
