Download Grid Model Activity

Grid Model Activity
John Welch, Cabrillo College
Concepts and skills taught:
The power grid does not currently include any storage.
Power generation must constantly be adjusted to the current demand, or load.
We can’t generate enough power to supply all possible loads simultaneously, but instead we strive to
meet ‘peak demand.’
When generation falls short of demand, the voltage drops and we get ‘brown outs.’
Power companies continually adjust the ‘mix’ of power sources, depending on time of day, year, and
based on cost.
Power is lost when transmitted long distances.
Power plants and loads are all connected basically in parallel.
Centralized vs. distributed power.
The idea of a simplified model as a learning tool.
What is the ‘smart grid?’
Materials:
Hand cranked DC generators, such as ‘Genecon’.
6V Flashlight bulbs
Spring ‘junction boxes’.
‘zip cord’
Voltage display – via Vernier or Pasco interfaces, or some other meter.
Activity:
Instructor sets up the model grid like this:
There should be enough bulbs so that all the generators working together don’t have enough power to
fully light all the bulbs.
Have some power stations far away on very long wires (nuclear power is good for this).
Have at least two banks of bulbs at different locations to represent different towns or neighborhoods.
Students are assigned different roles: nuclear power plants, solar power plants, wind power, coal power,
and consumers.
Depending on class size and materials available, each type of power can have several hand crank
generators in parallel, so that that the different types of power can be ‘ramped up’ or down.
(Power plants not currently in use should disconnect so that they don’t become loads as motors.)
Activities:
System voltage and ‘brown outs’:
Start with a medium sized load (2-3 bulbs in parallel) and one ‘power plant’ and discover with the class
how much voltage is needed to keep them fairly bright. Decide on what the nominal voltage for this
model should be.
Now screw in more bulbs and notice with the class that the voltage goes down and the lights go dim. Ask
the student with the generator if it gets harder to turn the crank.
Ask students if they have heard the term ‘brownout’.
Parallel configuration:
Show students that any of the lights can be powered by any of the generators – because everything is
connected in parallel.
Transmission Losses:
Try one power source at a time, lighting a few bulbs at the front of the room. The generator that is
farthest away should have trouble keeping the voltage high enough. Ask – why? (you can put a resistor
in their line if you need in order to ‘fake’ the power loss situation.)
Sizing of generation facilities:
Screw in all the bulbs and see if all generators working together can power them. (Should not be
possible) Ask – is this a realistic model?
Response to changing demand:
Have multiple sources of power going (i.e. coal team, wind team, etc.), keeping the system at its rated
voltage. Then have ‘consumers’ change the number of bulbs that are screwed in, and make generators
have to respond to try to keep the voltage constant. Discuss – how might real power companies do this?
Mix of power sources:
Make up different scenarios and ask students what would be the best mix of power sources.
For example: “Now it’s evening in January on the east coast.” – “Now it’s noon in Florida in July,” “Now
it’s midnight in California in March.” and have them discuss which power sources to use first.