Transcript EE1001_Fall_2012__for_Posting[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
Where Electricity Comes From
What Do We Know About This?
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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!
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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)
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
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.
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
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
Peak
Load
Gen
Intermediate Load Generation
Base Load Generation
Power Generation Technologies
Includes
• Hydro
• Biomass
• Wind
• Solid Waste
• Geothermal
• Solar PV
• Solar Thermal
Percentages on an ENERGY basis, not capacity.
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
Challenges with Wind
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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).
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)
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
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
Grid Reliability
• Standards exist to ensure reliability
– Extensive filings and audits
– Severe financial penalties
• Wide-area (multi-state) reliability affected by:
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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)
Good Luck!