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 20, 2012

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 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 ALL 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. 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
transmission/distribution lines must be intact
It had better work well, as loads increase quickly

5. A Typical Day on the California Grid
1 Megawatt
can power
about 1000
homes
Ramps up
by 4500 MW
in 80 minutes
2 p.m.
4 a.m.

6. 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

7. Generating Choices Generators usually fall into one of 3 regions:
Base Load
Must run essentially 24/7 annually
Expensive to build, but provides lowest cost over time
Intermediate Load
Must run perhaps 50% of time
Less costly to build, but more costly to run
Peak Load
Runs only to meet peak demands
Least expensive to build, most costly to run
We can visualize these regions on a Load Duration Curve

8. Intermediate Load Generation
Peak
Load
Gen
Intermediate Load Generation
Base Load Generation

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

10. Includes
Hydro
Biomass
Wind
Solid Waste
Geothermal
Solar PV
Solar Thermal
Percentages on an ENERGY basis, not capacity.

11. Where Do These Technologies Fit on our Load Duration Curve?
Peak
Load
Gen
Gas,
Hydro
Intermediate Load Generation
Hydro, Natural Gas, Solid Waste
Base Load Generation
Nuclear, Coal, Geothermal, Wind*, Solar*
*Wind and solar output must be taken when available, sometimes affecting baseload gen

12. Challenges with Wind Adds no inertia to grid (no energy storage)
Poor low-voltage behavior
Limited contribution to peak load capability
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).

13. Tying Generators Together with Loads
High Voltage Transmission Lines
Connect generators with loads
Transmit energy at near speed of light
High voltage reduces current flow (P=V x I)
Reduced current reduces losses (Ploss=I2R)

14. Tying Generators Together with Loads
Three Synchronized Regions in U.S.
Eastern U.S. (east of Rockies)
Western U.S.
Texas
All generators in
each region are
synchronized

15. Putting It All Together
“The Grid” = Generators (about 18,000) + HV Transmission Network
In 2008, 356 new, large-scale generators were added to the US grid

16. Grid Reliability Standards exist to ensure reliability
Extensive filings and audits
Severe financial penalties
Wide-area (multi-state) reliability affected by:
Major outages of generators or transmission lines
Growth of non-dispatchable wind and solar
Inability to run existing or build new baseload gen
Climate change: warmer water and less of it
Local reliability affected by:
Lightning and high winds
Animals (squirrels, rodents, snakes)
Right-of-way incursions (traffic accidents, train derailments)

17. Good Luck!