College of Engineering

Discovery with Purpose www.engineering.iastate.edu

June 17, 2011

Wind-Related Transmission/Distribution

Technologies & NeedsJames McCalley (jdm@iastate.edu)

REU Short Course on Wind Energy Science, Engineering and Policy

Windfarm Electrical System:

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Three transmission/distribution related issues:

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Windfarm

Windfarm

Windfarm

Windfarm

Windfarm

Windfarm

Windfarm

Windfarm

MULTI-FARM COLLECTION

NETWORK

MULTI-FARM COLLECTION

NETWORK

LEVEL 1 LEVEL 2 LEVEL 3 LEVEL 2 LEVEL 1

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.

Multi-turbine collector network• Common voltage levels are 13.8, 25, 34.5 kV• Three-phase, always underground, cable

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POI or connection to the grid Collector System

Station

Feeders and Laterals (overhead and/or underground)

Individual WTGs

Interconnection Transmission Line

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.

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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.

Level 2: Multifarm collection networks - Examples

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• Depends on backbone transmission (may very well change….)

The backbone transmission issue: Where are the people?

…But where are the resources?

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NUCLEAR

Long-term National Planning & Resource Integration

GEOTHERMALSOLAR

WindBIOMASS

CLEAN-FOSSIL

Where, when, & how to interconnect?

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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 TechnologiesHVAC: 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%StrongWest

20%Distributed

20%StrongOffshore

30%

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30%20%StrongWest

20%Distributed

20%StrongOffshoreMost

Economical+ RPS

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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

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Cost: $10 billionVoltage: 765 kVMileage: 3000 milesWho: ITCProposed date: 2020Capacity: 12000 MW

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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BackgroundA 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 criteria3. 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 simulation7. Power flow, stability studies, etc.

Identifying Futures

Key drivers Examples

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ReferencesJ. 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 long-haul 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 978-2-85873-080-3, 2009.

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