Transcript Electrical Energy Generation and Transmission

Electrical Energy Generation
and Transmission
Physical Science
Chapter 21 Section 3
Science Journal Entry 46
• Explain the difference between
Earth’s geographic north pole
and Earth’s magnetic north pole.
Be sure to mention magnetic
declination.
Science Journal Entry #47
• Explain how the strength of an
electromagnet may be increased.
Science Journal Entry 48
• Describe the path that electricity
takes from the power plant to
your home.
Science Journal Entry #49
• Explain the difference
between a step-up and a stepdown transformer.
Generating Electric Current
• Electromagnetic Induction is the process of generating
a current by moving an electrical conductor relative to
a magnetic field.
• The English scientist Michael Faraday (1791-1867)
discovered electromagnetic induction in 1831.
• According to Faraday’s law, if a coil is a part of a
complete circuit, changing the magnetic field through
the coil of wire will induce a voltage in the coil
producing a current.
• If you place a magnet in a coil, no current is produced
if it does not move but if either the coil or the magnet
is moving an alternating current will be produced.
Question Set One
• 1. What is the process of generating a current by
moving an electrical conductor relative to a
magnetic field?
• 2. Who discovered electromagnetic induction in
1831?
• 3. If a coil is a part of a complete circuit, changing
the magnetic field through the coil will induce a
_____ in the coil producing a ____.
• 4. T or F If you place a magnet in a coil, no current
is produced if it moves.
• 5. What is required to produce an alternating
current by electromagnetic induction?
Generators
• The electric energy used in homes and businesses
is produced in large power plants by generators. A
generator is a device that converts mechanical
energy into electrical energy by rotating a coil of
wire in a magnetic field. The two types of
generators are AC and DC generators. Most power
plants today use AC generators. A wire coil in the
generator is attached to metal bands called slip
rings. The 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 induces a current
in the wire. It is called AC for alternating current
since the electric current alternates its direction.
DC Generators
• In a DC (direct current) generator, the
commutator replaces the slip rings. Although
an alternating current is induced in the wire,
direct current is produced. One side of the
commutator contacts a brush and when the
current is induced in the other direction the
other side of the commutator touches the
other brush. This moves it in a circular
direction producing direct rather than
alternating current.
Question Set Two
• 6. What is a device that converts mechanical energy
into electrical energy by rotating a coil of wire in a
magnetic field?
• 7. What are the two types of generators?
• 8. Which is used by most power plants today?
• 9. What are the metal bands that the wire coil in a
generator is attached to called?
• 10. The rings are in contact with ___ ____that are in
turn attached to a ______.
• 11. Why are AC generators called AC?
• 12. What takes the place of the slip rings in a DC
generator and what type of current is produced?
• 13. T or F The commutator comes in contact with the
metal brushes on both sides of it but not
simultaneously.
Transformers
• Since electricity is transmitted through power lines
at very high voltages, the voltage has to be
transformed into 240-volt current that enters your
home. A transformer is a device that increases or
decreases the voltage and current of two linked AC
circuits. AC (alternating current) induces a
constantly changing magnetic field. The changing
magnetic field induces an alternating current in a
nearby coil with a different number of turns.
• DC current can not transmit power far enough
without overheating the wires. Only AC current is
able to transmit a lower current at a higher
voltage.
Types of Transformers
• There are two types of transformers: the stepdown transformer and the step up transformer. A
step-down transformer decreases voltage and
increases current. A step-up transformer increases
voltage and decreases current.
• Each transformer has two sets of coils wrapped
around a ring-shaped iron core. In the primary coil,
the current creates a changing magnetic field in
the iron core. Since this iron core is also inside the
secondary coil, the changing field induces an
alternating current in the secondary coil.
Question Set Three
• 14. What is a device that increases or decreases the
voltage and current of two linked AC circuits?
• 15. T or F AC (alternating current) induces a
constantly changing magnetic field.
• 16. Why is AC current better than DC current at
transmitting power at greater distances?
• 17. AC current is able to transmit a _____ current at a
higher _______.
• 18. What are the two types of transformers and how
are they different?
• 19. In what coil does the current generate a magnetic
field and in which coil is the alternating current
induced?
Changing Voltage and Current
• The number of turns in the primary and secondary
coils determines the voltage and current.
• To calculate the voltage, divide the number of
turns in the secondary coil by the number of turns
in the primary coil. This gives you the ratio of the
output voltage to the input voltage.
• Electric power (in watts) is equal to the current
(amps) x the voltage.
• P(watts) = I (amps) x V(volts)
• Since the power must be the same in the primary
coil and secondary coil, if voltage increases in the
secondary coil, the current must decrease in the
same ratio.
Question Set Four
• 20. What determines the voltage and current in
the transfer?
• 21. How is the voltage calculated and what ratio
does that give?
• 22. What does the formula P=IxV stand for and
what units are used?
• 23. T or F Power has to be the same in the primary
coil as in the secondary coil.
• 24. If voltage increases, the current has to ______.
• 25. If current increases, the voltage has to ______.
Electrical Energy Sources and Turbines
• Most of the electrical energy generated in the
United States is produced by coal as an energy
source. Other sources for electrical energy are
water (hydroelectric), nuclear energy, wind,
natural gas and petroleum.
• A turbine can convert energy from these sources
into electrical energy. A turbine is a device with
fanlike blades that turn when pushed by water or
steam. Water is heated to provide the steam
needed to turn turbines. It may be heated by the
burning of fossil fuels or nuclear reactions. Water
pouring over a dam can also turn a turbine.
From the Power Plant to Your Home
• The turbine may turn the coils of a generator or it
may spin magnets around the coils of wire to
produce electrical energy.
• The energy from the power plant is stepped up to
hundreds of thousands of volts. After the voltage
travels along the high voltage lines, it is stepped
down by transformers at a substation to a few
thousand volts. The electrical energy is distributed
to neighborhoods after it is stepped down to
between 220 and 240 volts. Though most
appliances use 120 volts, an electric stove uses 240
volt circuits.
Question Set Five
• 26. What is most of the electrical energy in the US
produced by?
• 27. What are five other sources for electrical energy?
• 28. What is a device with fanlike blades that turn
when pushed by water or steam?
• 29. In what two ways does a turbine produce
electrical energy?
• 30. The energy from the power plant is ____ ___ to
hundreds of thousands of volts.
• 31. How many times will the voltage be stepped down
and to what voltage?
• 32. What is the difference between the amount of
voltage that most appliances have to the electric
stove?