College of Engineering
Wind-Related
Transmission/Distribution
Technologies & Needs
James McCalley (jdm@iastate.edu)
REU Short Course on
Wind Energy Science, Engineering and Policy
June 17, 2011
Discovery with Purpose
www.engineering.iastate.edu
Windfarm Electrical System:
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Three transmission/distribution related issues:
Windfar
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Windfar
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Windfar
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Windfar
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LEVEL 2
LEVEL 3
MULTI-FARM
COLLECTION
NETWORK
LEVEL 2
MULTI-FARM
COLLECTION
NETWORK
BACKBONE
TRANSMISSION
LEVEL 1
LEVEL 1
Windfar
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Windfar
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Windfar
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Windfar
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Level 1, Multi-turbine collection network: Interconnect turbines to transmission sub.
Level 2, Multi-farm collection network: Interconnect windfarms to backbone trans.
Level 3, Backbone transmission: Transport energy from resources to load centers.
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Multi-turbine collector network
• Common voltage levels are 13.8, 25, 34.5 kV
• Three-phase, always underground, cable
POI or
connection
to the grid
Collector System
Station
Interconnection
Transmission Line
Individual WTGs
Feeders and Laterals (overhead
and/or underground)
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Multi-turbine collector network
Multi-turbine collector network
In the midwest, cutting drain tiles is a common problem that
windfarm developers must contend with.
Level 2: Multifarm collection networks
Wind farms site where the wind resources are good, close
to existing transmission that has residual capacity. If
capacity is insufficient, one of the below happens:
• Wind farm is not built;
• Special protection schemes are used;
• Incremental transmission upgrades are made;
• Extensive transmission upgrades are implemented.
OK when considering 3.7 GW wind out of 10GW total.
Not OK when considering 20 GW wind out of 30GW total.
There has not been much intentionality at level 2…. yet.
But we need to consider Level 2 Designs, before wind grows
much more.
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Level 2: Multifarm collection networks - Examples
• Depends on backbone transmission (may very well change….)
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The backbone transmission issue: Where are the people?
…But where are the resources?
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Long-term National Planning &
Resource Integration
SOLAR
CLEAN-FOSSIL GEOTHERMAL
Where, when, & how
to interconnect?
BIOMASS
NUCLEAR
Wind
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Questions on backbone transmission
• Is transmission expensive?
• Who pays for transmission? Who permits it?
• Are there choices for transmission technologies?
• Have we ever had a national transmission plan?
• Why do many people feel “NIMBY” for transmission?
• Why not just put it underground?
• Transmission raises cost of energy at sending end
and reduces it at receiving end  why does sending
end generally like it & receiving end often does not?
• If a national transmission superhighway lowers
average cost of energy for the nation, why not build it?
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Transmission Technologies
HVAC:
69kV, 115kV, 138kV, 161kV and 230kV
EHVAC:
345kV, 500kV, 765kV
Long distance must be overhead due to high line charging.
HVDC:
500kV, 600kV, 800kV, Today, all high-capacity HVDC is thyristor-based
Overhead DC lines less expensive than AC lines but higher termination
investment cost. 400 miles is approximate breakover distance.
Intermediate terminals (on-off ramps) are expensive. Use of IGBT-based
voltage-source converters (lite) alleviates this but only at lower capacities.
Long-distance HVDC underground bulk transmission is possible.
Underground Superconducting Pipe
Regional Transmission: HSIL, GIL, HVDC-lite
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Transmission Technologies
Fig. 4: Cost comparisons between HVDC and EHVAC for 6000 MW of capacity
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Superconducting pipe
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Tres Amigas
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American Superconductor
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AEP Conceptual 765--kV overlay for wind integration
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20%
Strong
West
20%
Strong
Offshore
20%
Distributed
30%
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20
20%
Strong
20%
20%
Strong Distributed Offshore
Most
Economical West
+ RPS
30%
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Criteria for a national overlay design
• Facilitate low-carbon resource development
• Move generation to load centers
• Low total costs (investment + production)
• Reduce overall national energy costs
• Avoid “pockets” of high energy costs
• Minimal environmental impact
• Resilient to large-scale disruptions
• Flexible for adaptation to future infrastructure
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Green Power Express
Cost: $10 billion
Voltage: 765 kV
Mileage: 3000 miles
Who: ITC
Proposed date: 2020
Capacity: 12000 MW
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SPP EHV Overlay - Ultimate
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ERCOT - CREZ
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PacifiCorp Gateway Project
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NREL’s Eastern Wind Integration and Transmission
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Background
A Brief Introduction of Our Proposed Study Process:
1. Determine 40 years’ generation and load portfolio using NETPLAN.
Transmission capacities = inf.
2. Identify source/sink nodes under certain criteria
3. Obtain an initial transmission candidate topology (graph theory)

Get a min cost spanning tree connect all nodes;

Apply “reliability” constraints like N-1 security and rule of 3
4. Optimization. Determine capacities. Discard those arcs with no
investment. Can coordinate with the first step
5. Transmission technology selection.
6. Production cost simulation
7. Power flow, stability studies, etc.
Identifying Futures
Key drivers
Examples
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References
J. McCalley, W. Jewell, T. Mount and D. Osborn, “Technologies, Tools, and Procedures
for Energy Systems Planning at the National Level,” to appear in Power and Energy
Magazine.
Slides from Midwest ISO Engineering Presentations in EE 552 (2008 and 2010).
McCalley lecture notes from EE 552.
N. Reddy, “Superconductor Electricity Pipelines: A compelling solution to today’s longhaul transmission challenges,” Right of Way, May/June, 2010, pp. 26-33, available at
www.irwaonline.org/EWEB/upload/may_web_SuperConductor.pdf.
R. Dunlop, R. Gutman, and P. Marchenko, “Analytical Development of Loadability
Characteristics for EHV and UHV Transmission Lines,” IEEE Transactions on Power
Apparatus and Systems, Vol. PAS-98, No. 2, March/April 1979.
R. Gutman, E. Wilcox, 21st Century Transmission Planning: The Intersection of
Engineering, Economics, and Environment,” CIGRE, 2009, Calgary.
J. Fleeman, R. Gutman, M. Heyeck, M. Bahrman, and B. Normark, “EHV AC and HVDC
Transmission Working Together to Integrate Renewable Power,” CIGRE Paper 978-285873-080-3, 2009.
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