Transcript Document 390

Chapter 11
Magnetism
Electrical Generation
Electrical Transmission
Environmental Impacts of High Voltage Lines
Standard Power Generation
Cogeneration and Combined Cycle Plants
Energy in the News
Magnets
Lodestone or magnetite- first recognized by the Greeks in
500 BC. Used to make a compass needle.
Like charges repel. Unlike charges repel. Magnetite= Fe3O4
Earths’ Magnetic Field Lines
Magnetic Particles Lined Up in Field
Dark:
Elongated
Magnetic
Particles
Pyrotite?
Light:
Radiolarian
Skeletons
What
direction
Are the
Field lines?
Electrical Currents Make
Magnetic Fields
Wire carrying current affects a compass needle:
Original experiment by Oersted that discovered magnetic fields produced
by electrical currents.
Coils of Wire (Solenoids)
Parallel Currents Attract
Parallel Currents in Loops Attract
Parts of an Electric Motor
http://www.howstuffworks.com/motor2.htm
Simple Electric
Motor
Outside:
Field magnet
(permanent
Magnet)
Inside:
Rotating
Electromagnet
Reverses its field
every half rotation
Detail of Electromagnet in Motor
Electromagnet is connected to
A battery or other power source
Armature (green) allows the current
Direction to switch every 180
Degree rotation, thus switching
The North and south poles of
The Electromagnet
Two Types of Current
Direct Current (DC): constant intensity and sign
Alternating Current(AC): varying intensity and sign
Some devices generate direct current, some
Generate alternating current.
A Moving Magnet Produces Current
in the Wire
Electrical Generator
What type of current is made by this generator?
What could turn the generator?
Electrical Generator: Second
View
Wire is turned
In the magnetic
Field
Result: Current
In the wire.
Alternating Current from Generator
Cross Section of Gas Turbine
Gas turns blades on left: Right side connected to generator
High Voltage Transmission Lines
Typical Voltage:
345,000 Volts
Why are the voltages
So high?
Transformer: Changes Voltage
and Current (not Power)
Two coils with alterating
Current. First coil induces
A current in the second coil.
Difference in voltage
Proportional to difference in
Number of windings of
Wire.
Vin * Iin = Vout * I out
Transformer on Power Pole
Why is the voltage stepped
Down at the last minute, just
Before power is sent into
The house?
Overall Electrical Distribution
Typical Magnetic and Electrical Fields
High voltage transmission lines: exposure MIGHT correlate
With leukemia and brain cancer. Studies very contradictory.
Costs of Electricity
Costs of Transmitting Energy
Transmission lines: most expensive way to move energy
Moving energy in gas pipelines, by barge or by rail is much
Cheaper. ( cost is about half). Why?
Turbines (Jet Engines)
How a Turbine Engine Works
http://www.howstuffworks.com/turbine.htm/
Air Enters
On Right..
Shaft is
Turned to
Generate
Electricity
On Left.
Detail of Turbine Combustion Area
Cogeneration Power Plant=
Both Heat and Power Output
Separate Power
and Heat
Generation
vs
Cogeneration
Efficiency of Cogeneration
Coal Gasification with CoGeneration