Transcript Power Grid in High School Physics

Power Grid in High School
Physics (and Vice Versa!)
Matthew W. Milligan
Farragut High School
CURENT – Research Experience for Teachers (RET)
July 17, 2012
Knoxville, Tennessee
Power Grid & High School Physics
I.
II.
Frequency Disturbance
- FNET data & animation
- wave phenomena
Modeling the Grid in the Classroom
- series and parallel circuits
- significance of I2R
- conservation of energy
- generators basics
A hand-crank DC
generator is used as
a power source for a
classroom electrical
“grid” that models
properties of the
actual AC power
grid.
Students get a true
hands-on experience!
Data acquisition
system measures
voltages and
currents
Switches are used to simulate
generator and load changes
A “lamp cord”
serves as the
“transmission line”
Students can judge the
power produced by
tactile feedback of their
own exertion and the
power consumed by
visual feedback of
brightness of the lamps.
Experiment 1:
Explore the effects of
changes in generation
and changes in load.
Power Transmission– Effect of Load Change
A
G
G
Generators
V
Transmission
Line
Variable
Load
Effect of Load Change on Generation
The result is an increase in
voltage output of generator
At t = 5 s, the switch is
opened, decreasing the load
Effect of Load Change on Generation
Student compensates to bring
the voltage back down.
The result is an increase in
voltage output of generator
Lower current means less power
needs to be generated, so less
effort is needed to turn the crank
Effect of Load Change on Generation
The result is initially a
decrease in generator
voltage, but again student
compensates (eventually)
The switch is then closed,
increasing the load
Questions for Students
• If the load changes, why must student(s) exert
a different amount of force to crank the
generator(s)?
• How is there an increase in electric power
delivered across the transmission line even
though the voltage is not increased?
• What happens in an actual power plant if there
is a sudden and significant change in the load?
• What differences would occur if generators are
present at both ends of the transmission line?
Experiment 2:
Explore the effects of
different transmission
line voltages.
Power Transmission Model – “Low Voltage”
A
G
G
Generators
Vin
Vout
Transmission
Line
Load
Power Transmission Model – “High Voltage”
A
G
Vin
Vout
G
Generators
Transmission
Line
Load
Questions for Students
• Although there is clearly better efficiency
delivering electric power at high voltage, what
are disadvantages of the series connections?
• How are the actual generators of the nation’s
power grid interconnected?
• How is high voltage transmission achieved?
• If energy is conserved, what becomes of the
wasted electrical power (accounting for
difference between input and output)?
Experiment 3:
Explore the use of
energy storage in a
power grid.
Power Grid Model – With Energy Storage (Capacitor)
A
Io
Is
A
G
Vin
Vout
Capacitor
Initially energy is put into
the capacitor (while the load
is “low” – switch is off).
The result is a release of
energy from the capacitor
At t = 31 s, the
switch is closed,
increasing the load
AC Power?
• It may be very difficult to synchronize multiple
generators – but might be fun to try!
• Commercially made hand-crank generators AC
generators are hard to find (nonexistent?).
• Bicycle “dynamos” may be adaptable for the
classroom…
Bicycle “dynamo”
AC generator
Improvised handle
and flywheel
Experiment 4:
Vary the load on
an AC generator
The light can be seen to
flicker as the wheel turns…
AC Power Demonstration
A
V
Bicycle
Dynamo
Variable
Load
Load is varied by switch as
dynamo flywheel spins freely…
Resistance Increases
Resistance Decreases
This represents electrical
energy “extracted” from the
free spinning dynamo
EMF determined by
AC Power – Ideas to Explore
• Experiment with variations in flywheel/handle
design.
• Try turning the dynamo by using a falling
mass hanging from string wrapped around
wheel and axle. This would provide constant
torque and it would be easy to determine the
energy or power input.