Power Grids: What they mean to you?
Subject Area(s)
Physics
Associated Unit
Power
Lesson Title
Reliability Check of Power Grid
Grade Level
(11-12)
Lesson #
2 of 3
Time Required
1 class
Summary
Students are to understand the importance of the power grid by
completing a reliability check of several factors in a free simulation
program.
Engineering Connection
Power grids and blackouts
Engineering Category
Electrical Engineering
Keywords
Power, energy, utilities
Pre-Requisite Knowledge
Students must understand the basic power grid operation.
https://reports.energy.gov/BlackoutFinal-Web.pdf ; Figure 2.1.
Educational Standards
Texas Essential Knowledge and Skills / Physics
3 - (C) evaluate the impact of research on scientific thought, society, and the
environment;
(D) describe the connection between physics and future careers; and
(E) research and describe the history of physics and contributions of
scientists.
6 - (B) research and describe the historical development of the concepts of
gravitational, electrical, and magnetic force;
(F) identify examples of electrical and magnetic forces in everyday life.
Learning Objectives

To understand the role that utility companies and electrical engineers
perform in making sure that power is reliable.

To perform and understand the process of reliability checks on a
power grid.
Introduction / Motivation
Videos on power failures:
http://www.nttworldwide.com/xfmrfail1.htm
www.metacafe.com/watch/39058/transformer_fire_video
http://www.liveleak.com/view?i=d03_1189103877
Lesson Background & Concepts for Teachers
http://205.243.100.155/frames/longarc.htm#500_kV_Switch
Electrical Engineers use a simulation software Power World,
powerworld.com, that simulates power grids. The software is a tool to
better understand and manipulate existing power grids as well as create
new ones. The simulation software allows the user to change many
variables in order to perform reliability checks. Here is B5Reserve from
the simulation files inside the program Power World, version 14. The B5
refers to the number of buses or junctions.
SUNDANCE
BRIGHTON
600 MW
7 Mvar
E
0 MW
0 Mvar
A
203%
slack
A
MVA
RR: NO
0 MW
Amps
RR: YES
0 MW
A
D
Amps
223 MW
0 Mvar
A
A
Amps
A
A
Amps
69 MW
2 Mvar
RR: YES
0 MW
ALTA
0 MW
2 Mvar
RR: YES
0 MW
PARK CITY
Amps
223 MW
0 Mvar
B
223 MW
0 Mvar
ZONE I
0 MW
3 Mvar
C
RR: YES
0 MW
SOLITUDE
The generators are shown in blue, showing a total of five generators. The
one in the top left is configured to be the slack bus. This means that it is
the regulator of the power system. For all of Texas, there may be only 1-2
designated slack buses, with others able to be turned on manually as a
slack bus. Each power configuration must have at least one slack bus.
These generators have an Automatic Generator Control (AGC) that works
only on AC transmission lines. The AGC tests and regulates the
frequency, which is not generated in a DC transmission line. The system
above is overloaded in the transmission lines at the top, shown in red.
Some of the ways to fix the overload would be:
You can disconnect the transmission lines by clicking on the red squares
on either end, making it open.
You can increase the power delivery of the generator.
You can decrease the load.
Some of the terms from the software:
Term
Variable
Real Power
P
Q
Reactive Power
Apparent Power
S
Units
Watt
var
VA
The terms are related by the equation S = √(P2+Q2)
The example above shows one zone and the other as an external zone.
Texas has a total of 8 zones. The rule of most power transmission
designs is N -1, which is that the power must still be able to flow if one
bus fails. In New York, the system is so complex, the capability is N -6.
This would allow up to six buses to fail or go off line and the power would
still flow.
Vocabulary / Definitions
Word
Definition
Bus
An electrical conductor that serves as a common connection for two or more
electrical circuits.
Load
The amount of electric power delivered or required at any specific point or points
on a system. The requirement originates at the energy-consuming equipment of
the consumers.
Current
A flow of electrons in an electrical conductor. The strength or rate of movement
of the electricity is measured in amperes.
Reactive
The portion of apparent power that does no work and is referred to as kilovars;
power
this type of power must be supplied to most types of magnetic equipment, such
as motors, and is supplied by generator or by electrostatic equipment.
Real Power
The work-producing part of apparent power that measures the rate of supply of
energy and is denoted as kilowatts (kW).
Lesson:
Students will complete the Power Grid Simulation.
Power Grid Simulation Student Worksheet
Purpose:
Today you will be playing the role of an Electrical Engineer by completing a reliability
check of a power system in order to understand the importance of the power grid. This
will check the reliability by the assumption of N-1. The rule of most power transmission
systems is N -1, which is that the power must still be able to flow if one part is taken off
line. The generator, transmission line, or load may be taken off line for maintenance or
due to failure or natural disaster. With any of these cases, an electrical engineer would
want the power to still be delivered to the customer.
Procedure / Results:
Step 2
1. Log on to Power World software at powerworld.com – it should show as Simulator
14.
2. Click on the round blue world at the top left corner (see diagram below) and then
open case.
3. Open case B7Flat example.
4. Using the Tool Bar – Click on “Tools”. Click on the green “Play” button to start
simulation. If the button is not green, make sure that the far left it is in “Run Mode”.
Step 4
5. Using the tool bar, go to “Draw”, then “Zoom” on the far left if you need to move
around or change your view. (You can also use a mouse to make an easy zoom).
6. Fill in the table to denote the information you observe prior to making any changes.
Table 1: Initial Properties / Observations
Case Hourly Cost
Top Area Cost
Left Area Cost
Right Area Cost
Created by: D. Reynolds / July 2009
RET Project at UTA / NSF Grant EEC-0808687
Step 5
Real Life Application
What does the spinning
circle represent?
What do the green arrows
represent?
What do the red dots
represent?
What do the blue and
white circles represent?
What do the black arrows
represent?
7. For Bus 1 (junction), click on the up arrow one time. What do you notice? Why?
Step 7
Step 9
8. What happens if you keep adding to the value of MW (MegaWatts)?
9. Click on the red box just connected to the generator. Explain what happens? What
happens to the hourly cost factors?
10. What happens to the blue and white meters? At what percentage do they change?
How would an electrical engineer respond to this information?
Created by: D. Reynolds / July 2009
RET Project at UTA / NSF Grant EEC-0808687
11. Now repeat the same thing, starting with generator 2, then generator 4, and so on.
Click only where there are connections to the generators. Note what happens as you
click on each red box.
12. Go back and click on the same boxes, now green. Add or subtract to MW values of
the black arrows and explain what happens. What in real life would this represent?
Step 12
13. The transmission lines all have two red boxes, one on each end. Pick any
transmission line, and click on one of the red boxes. What happens? Are any
customers affected; how do you know?
14. Now click on one a second transmission line, taking this line down as well. What
happens? Are any customers affected; how do you know?
Conclusion:
You have now completed a reliability check of your power system. What factors did you test
within your system? Do these factors satisfy the N-1 rule? Why is this information useful to an
electrical engineer? What would happen if these types of reliability checks were not performed?
Do reliability checks always prevent power blackouts? Give an example.
Created by: D. Reynolds / July 2009
RET Project at UTA / NSF Grant EEC-0808687
Lesson Closure
Discussion with class on the role of an electrical engineer. Students will
discuss power grid failures with an electrical engineer guest speaker.
Assessment
Teacher will grade the laboratory report.
Lesson Extension
Complete part III Power Grids What They Mean To You by building a
wind generator.
Multimedia Support Free download version for student use, version 14 – Go to
www.powerworld.com under the download section.
Other
Ethics will be discussed in how electrical engineers make decisions to
prevent blackouts.
Creator
Danielle Reynolds / Duncanville High School
Sponsor
University of Texas at Arlington / Electrical Engineering
National Science Foundation under Grant No. EEC-0808687