Transcript 21.3 Electrical Energy Generation and Transmission

21.3 Electrical Energy Generation and Transmission
Photographs of large
cities, such as
Seattle, Washington,
are visible reminders
of how much people
electrical
rely on __________
energy.
21.3 Electrical Energy Generation and Transmission
Generating Electric Current
How is voltage induced in a conductor?
Name two types of generators
How can a transformer change voltage
and current?
What are some sources of electrical
energy in the United States?
21.3 Electrical Energy Generation and Transmission
Generating Electric Current
A magnetic field can be used to produce an
___________
current.
electric
Electromagnetic _____________is
induction
• ________________
the
process of generating a current by moving an
electrical conductor relative to a magnetic field.
21.3 Electrical Energy Generation and Transmission
Generating Electric Current
According to Faraday’s law, a voltage is induced
magnetic
in a conductor by a changing ____________
field.
•Changing the magnetic field through a coil of wire
voltage
induces a ____________
in the coil.
•A current results if the coil is part of a complete
circuit
_____________.
21.3 Electrical Energy Generation and Transmission
Generating Electric Current
According to Faraday’s law, the moving magnetic
current
field induces a __________
in the coil.
Movement of magnet
When
magnet is not
moving
_________,
there is no
current
detected.
Coil
When magnet is
moving, the
current changes
direction
____________
when the
magnet
changes
direction.
Galvanometer shows that
the current is flowing.
21.3 Electrical Energy Generation and Transmission
Generators
Most of the electrical energy used in homes
and businesses is produced at large power
plants using generators.
• A generator is a device that converts
mechanical
electrical
____________
energy into ___________energy
by rotating a coil of wire in a magnetic field.
• Electric current is generated by the relative
magnetic
motion of a conducting coil in a ____________
field.
21.3 Electrical Energy Generation and Transmission
Generators
The two types of generators are:
AC generators
1. ______________________
DC generators
2. ______________________
21.3 Electrical Energy Generation and Transmission
Generators
AC Generators
alternating
An AC generator produces ___________
current
____________,
in which charges flow first in one
direction and then in the other direction.
The generator looks very similar to an electric
mechanical
motor but converts _______________
energy into
electrical
_______________
electrical energy instead.
21.3 Electrical Energy Generation and Transmission
Generators
In a simple AC
generator, an
_________force
external
rotates the loop of
wire in the
magnetic field. This
induces a
current
_________in
the
wire.
Wire loop
Slip rings
Direction in
which the loop
is turned
21.3 Electrical Energy Generation and Transmission
Generators
A wire coil in the generator is attached to
metal bands called_________
_________.
slip
rings
• The slip rings are in contact with metal
brushes that are in turn attached to a circuit.
_________
• As the loop of wire is rotated, the magnetic field
current in the wire, which
induces a _________
reverses
___________direction
every
Wire loop
half rotation.
Slip rings
21.3 Electrical Energy Generation and Transmission
Generators
Small generators provide power in areas that are
not served by power companies or provide
power
electrical energy during a __________
outage
__________.
21.3 Electrical Energy Generation and Transmission
Generators
DC Generators
direct
A DC generator produces a _________
current.
• Its design is very much like the design of an AC
commutator
generator except that a _____________
replaces the
slip rings.
• As opposite sides of the commutator touch the brush,
the current that leaves the generator flows in only
one
_______
direction.
21.3 Electrical Energy Generation and Transmission
Transformers
transformer
A ____________
is a device that increases or
decreases the voltage and current of two linked AC
circuits.
21.3 Electrical Energy Generation and Transmission
Transformers
Electrical energy from power plants is
transmitted through power lines at
voltages
___________
too high to be used safely in
homes.
changed
The voltage must be __________,
or
transformed. A series of transformers
changes high-voltage current in power lines
240-volt
into ____________
current.
21.3 Electrical Energy Generation and Transmission
Transformers
Why Transformers Are Needed
DC generators
• Early power plants used _______________
because the power plants were close to the
customers.
• Over long distances, the resistance of
transmission wires causes large losses of
power, which can be reduced by using lower
current and higher _________.
voltage
________
• Only AC voltage and current can be
transformed
____________.
21.3 Electrical Energy Generation and Transmission
Transformers: Changing Voltage and Current
A transformer has two sets of coils wrapped around a ringiron
shaped ________
core.
primary
• When there is an alternating current in the __________
coil, the current creates a changing magnetic field in the
iron core.
secondary
• Because the iron core is also inside the ___________
coil, the changing field induces an alternating current in
the secondary coil.
Step-down Transformer
Soft iron core
Low voltage
High voltage
400 turns
100 turns
Step-up Transformer
Low voltage
High voltage
100 turns
400 turns
AC Source
AC Source
Primary coil
Secondary coil
21.3 Electrical Energy Generation and Transmission
Transformers
turns
The number of _________
in the primary and
secondary coils determines the voltage and
current.
divide
• To calculate the voltage, __________
the
number of turns in the secondary coil by the
number of turns in the primary coil.
output
• The result is the ratio of the __________
voltage to the input voltage.
21.3 Electrical Energy Generation and Transmission
Transformers
Transformers are very efficient because very
little energy is lost as __________.
heat
• There is also an ___________
relationship
inverse
between current and voltage.
• If voltage ___________
increases in the secondary coil,
the current must _____________
decrease in the same
ratio.
21.3 Electrical Energy Generation and Transmission
Transformers
Types of Transformers
step-down
A ____________
transformer decreases voltage
and increases current.
• Occurs just before the electrical energy reaches
homes
people’s ___________.
21.3 Electrical Energy Generation and Transmission
Math Calculation
0.25
30 volts
21.3 Electrical Energy Generation and Transmission
Transformers
step-up
A ____________
transformer increases
voltage and decreases current.
• Occurs when electrical energy _________
leaves
the power plant
• Makes it an easier and more efficient way
to bring electrical energy to houses from
transmission
long-distance ____________.
21.3 Electrical Energy Generation and Transmission
Math Calculation
4
80 volts
21.3 Electrical Energy Generation and Transmission
Electrical Energy for Your Home
Most of the electrical energy generated in the
coal
United States is produced using _________
as
an energy source. Some other sources are
water
nuclear energy,
________
(hydroelectric), ________
natural gas, and ___________.
petroleum
wind, _________
21.3 Electrical Energy Generation and Transmission
Electrical Energy for Your Home
turbine
A ____________
is a device with fanlike
blades that turn when pushed, for example,
by water or steam.
• A turbine converts energy from various
sources (i.e. coal, nuclear energy, etc) into
electrical
_____________
energy.
21.3 Electrical Energy Generation and Transmission
Electrical Energy for Your Home
To produce electrical energy,
the turbine may turn the coils
of a _____________,
or it
generator
may spin _____________
magnets
around the coils of wire.
21.3 Electrical Energy Generation and Transmission
Electrical Energy for Your Home
A power plant transmits electrical energy at
hundreds of thousands of ________.
volts
• After the current passes travels through highvoltage transmission lines, the voltage is
stepped down at a substation, to a few
thousand
_____________
volts.
• The electrical energy is then distributed and
220 and ______
240
stepped down to between _______
volts.
240-volt
• Appliances like an electric stove use _________
circuits. Most other appliances in the home use
120 volts
___________.
21.3 Electrical Energy Generation and Transmission
Assessment Questions
1. In a DC generator, the commutator
a.
b.
c.
d.
generates an electric current.
replaces the slip rings.
reduces the voltage.
reverses the direction of the direct current.
21.3 Electrical Energy Generation and Transmission
Assessment Questions
2. A transformer has 400 turns on the primary coil
and 1600 turns on the secondary coil. What is the
output voltage if the input is 1,000 volts?
a.
b.
c.
d.
250 V
500 V
2,000 V
4,000 V
21.3 Electrical Energy Generation and Transmission
Assessment Questions
3. Which property would you want to increase in
transmitting electrical energy as efficiently as
possible over long distances?
a.
b.
c.
d.
current
voltage
resistance
insulation
21.3 Electrical Energy Generation and Transmission
Assessment Questions
4. In electromagnetic induction, an electric current is
induced by the motion of an electrical conductor
relative to a magnetic field.
True
False