1. An Overview of the U.S. Electric Power Grid
Generation Choices, Reliability, Challenges
Tom Ferguson, P.E.
Adjunct Instructor
Dept. of Electrical Engineering
University of Minnesota, Duluth
Presentation to EE 1001
September 15, 2016

2. Where Electricity Comes From
For many, this is all they need to know
Need more power? Add more outlets
But there is a lot more that happens behind the outlet

3. What Do We Know About This?
We plug LOADS into it
It has THREE prongs in standard layout
The VOLTAGE is ~115 VAC
The WAVEFORM is sinusoidal
Only 60 Hz (cycles per second) is present
ELECTRONS come from somewhere
It’s almost always “ON”
BUT!
Limited to 15 AMPS
Europe uses different plug
Voltage varies + 5%
Waveform is usually not “clean”
Harmonics may be present
Electrons come from THOUSANDS of generators
It’s 99.99% reliable (off for 53 minutes/yr)
For many, this is all they need to know
Need more power? Add more outlets
But there is a lot more that happens behind the outlet

4. Nuggets of Knowledge Nugget #1
Electricity in the U.S. is an ELECTROMAGNETIC WAVE
with a
FREQUENCY OF 60 CYCLES PER SECOND, or
60 hertz (abbreviated 60 Hz)

5. Nuggets of Knowledge Nugget #2
A wave’s FREQUENCY and VELOCITY
determine its
WAVELENGTH, λ (lambda)
(the distance between wave crests)
For electricity:
λ = 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 = 𝑣 𝑓 = 300,000,000 𝑚/𝑠 60 𝐻𝑧 = 5000 km!
(3000 miles)

6. Basic Electric Power System

7. Nuggets of Knowledge Nugget # 3
A simple TRANSFORMER has TWO WINDINGS wrapped around an IRON CORE
VOLTAGES are TRANSFORMED according to the TURNS RATIO:
𝑉1 𝑉2 = 𝑛1 𝑛2
Where “n” is the number of turns

8. High Voltage Transmission
Long distance carrier of electricity
Connects generators with loads
High voltage reduces current flow (P=V x I)
Reduced current reduces losses (Ploss=I2R)
Transmits energy at essentially speed of light

9. The Grid Powers Society
Human behavior repeats itself daily
Morning routine: lights, hot water, electronics
Stores open: lights, heating/cooling
Industry starts: pumps, motors, arc furnaces
The grid must respond to these loads
generators must be ready and reliable
generators must be controllable to match load
The grid is very dynamic

10. A Typical Day on the California Grid
1 Megawatt
can power
about 500
homes
Ramps up
by 4500 MW
in 80 minutes
2 p.m.
4 a.m.

11. Nuggets of Knowledge Nugget #4
POWER is the product of VOLTAGE and CURRENT or
Power (W, watts) = Voltage (V, volts) X Current (I, Amperes)
P = V * I
One MEGAWATT can supply about 500 homes

12. Generating Choices What types of generation are used?
Varies across U.S. according to
availability of fossil fuels
availability of renewable energy sources
water availability
environmental limitations
state policies on renewables and nonrenewable generation

13. Power Generation Technologies
Electric power has broad portolio
That’s good, it’s secure, reliable

14. 2014 Renewables 13% Includes Hydro Nuclear 20% Biomass Wind
Solid Waste
Geothermal
Solar PV
Solar Thermal
Nuclear 20%
Natural Gas 27%
Coal 39%
Source: U.S. Energy Information Administration,
Electric Power Monthly (June 2015). Percentages based on Table 1.1 for 2014 Calender Year.
Updated 9/2015. Percentages on an ENERGY basis, not capacity.

15. Challenges with Wind No mechanical energy storage (no inertia)
1 MW of nuclear = 8 to 12 MW of wind
Not dispatchable
Negative correlation
with loads
When loads are greatest
during the mid-day,
wind generation is lowest.
Conversely, wind is highest
when least needed (night).

16. Nuggets of Knowledge Nugget #5
Three Synchronized Regions in U.S.
Eastern U.S. (east of Rockies)
Western U.S.
Texas
Nugget #5:
All generators in
each region are
synchronized

17. Putting It All Together
“The Grid” = Generators (about 18,000) + HV Transmission Network

18. Why Do the Lights Go Out? Power plant outages
Transmission line failures
Solar storms
Lightning and high winds
Animals (squirrels, rodents, snakes)
Car and train accidents
The high-voltage transmission system is already very “smart”
The low-voltage distribution system has
MANY OPPORTUNITIES FOR IMPROVEMENT
The “smart grid” technologies are best suited to the low-voltage system

19. Good Luck!