WECC Board of Directors Meeting

1
Wind Generation Interconnection and Integration
Status and Challenges

• WECC Board of Directors Meeting
• November 30, 2005Tucson, Arizona

Robert M. ZavadilVice-President Principal
Consultant144-E Market Place BoulevardKnoxville,
Tennessee 37922Tel [phone] ext.
149bobz_at_enernex.comwww.enernex.com
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Wind Plant Interconnection History

• Early (1980s into 1990s)
• Wind generation viewed as curiosity
• Special care taken to design and protect grid
  interface
• Preferred action for turbines during grid
  disturbance was to disconnect
• California thing
• Mid 1990s
• Development of large wind generation facilities
  outside of California
• Increasing plant sizes crossed threshold for
  interconnection evaluations
• Control area penetration still negligible, so
  studies were many times more of a formality
• 2000 to present
• Continued growth of wind generation led to
  questions that could no longer be prudently
  neglected
• West Texas voltage and transmission capacity
  questions
• Growing awareness of wind plant sensitivity to
  grid disturbances, and possible consequences
  (with further growth)
• Recognition of the unique characteristics of
  wind, and the potential for increased operating
  costs as penetration grows (integration
  questions)
• Continued favorable environment for further
  development of wind generation

3
Interconnection vs. Integration

• Convenient categories for all issues and
  challenges related to wind generation
• Interconnection
• Questions are primarily technical, centered on
  transmission network
• Thermal, voltage, transfer limits
• System stability and security
• Focus in on events, contingencies, abnormal
  conditions
• Integration
• Larger emphasis on economics
• Involves interaction of all generators with all
  loads
• Transmission capacity also plays a role
• Focus on normal operating conditions

4
Relationship to System Reliability

• Reliability is the driver for power system
  engineering and operations practice
• The transmission network is a major factor in
  power system reliability
• Interconnection
• New network elements must not jeopardize the
  operation of any other network equipment
• The ability of the system to withstand a major
  disruption must not be diminished by the
  connection of a new element
• Integration
• Wind generation will likely result in
  re-deployments of other network elements
• All practices and mechanisms for maintaining
  system reliability must not be infringed

5
Status Wind Generation Interconnection in
North America

• Activities underway simultaneously at many levels
• Achieving convergence is a necessity
• Most individual interconnection procedures must
  comply with FERC 2003a
• Will also adhere to NERC view, as yet not fully
  determined
• Technical capabilities are increasing
• Growing database of wind turbine models for
  analysis platforms
• Increasing industry experience with power system
  studies involving wind generation facilities
• Consensus on technical performance requirements
• Much progress has been made over past five years,
  but next few years should be interesting
  nonetheless

6
The Present - Interconnection

• A number of efforts to sort out Interconnection
  issues for wind generation are underway in the
  North America
• FERC Order 2003a
• AWEA best practices
• NERC wind generation task force
• WECC reliability standards for wind generation,
  model development
• Alberta Electric System Operator (AESO)
  interconnection guidelines
• Western Area Power Administration transmission
  issues related to wind development in the Dakotas
• New York ISO Impact of Wind Generation on
  Reliability of NYSBPS
• Growing awareness of wind generation within the
  IEEE Power Engineering Society (IEEE PES)
• Wind Generation TF
• Seminars and special sessions
• Interest from other technical committees
  formative stages
• UWIG

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Wind Generation Technology

• Wind turbine electrical technology
• Conventional induction machines
• Induction machines w/ static power converter
  control
• A few utilize more exotic technology (e.g.,
  direct drive)
• Important considerations for integration studies
• Steady-state characteristics P, Q, PF
• Dynamic response to grid disturbances
• Intermittency variation of P Q with time
• Output quality
• Wind plant Technology
• Behavior of aggregate plant can depend greatly on
  this element
• Advanced capabilities with advanced SCADA
• Distributed static VAr generation
• Ramp rate control

8
Interconnection Challenges

• Remote facilities
• Typically interconnection to weak transmission
  network
• Transmission capacity questions
• Reactive power dispatch
• Dynamic character of wind generation
• Reactive power planning for network must be
  coordinated with wind plants
• Interconnection requirements are evolving
• Were typically very simple
• Evolving to voltage control, dynamic reactive
  power management

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Windplant Modeling Challenges

• How to model large number of relatively small
  generators?
• Unfamiliar generator technologies (relative to
  conventional synchronous machines and generating
  plants)
• Sometimes extensive medium voltage system plant
  Q is very dependent on MV system (I2X)
• Auxiliary equipment and systems
• Switched capacitors on collector system
• Switched capacitors at interconnect substation
• Plant-level systems
• GE DVAR
• Variable and uncertain fuel supply

10
Emergence of Grid Codes

• Burst onto the scene about four years ago
• Driven in U.S. by two major technical issues
  (primarily)
• Turbine sensitivity to grid voltage disturbances
  (low-voltage ride-through)
• Reactive power management / voltage control
• Led to major challenges for industry
• Turbine design
• Plant design
• Recognition of the wind industry uniqueness
• Short project lead times
• Modeling complexity

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FERC Order 2003a, 661

• Wind generation recognized as requiring some
  special considerations in Order 2003a
• Input from collection of stakeholders organized
  by AWEA
• Concerns captured as Appendix G to order
• Appendix G
• Developed by AWEA-led stakeholder group
• Low-voltage ride-through (right)
• Basic reactive power requirements
• Need for SCADA
• Issued by FERC as Order 661
• NERC objects to parts of 661, files request for
  rehearing
• FERC directs AWEA and NERC to resolve

Wind plant LVRT specification from Appendix G of
FERC Order 2003a
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NERC/AWEA Resolution on LVRT

• All wind generating plants subject to FERC Order
  No. 661 and not covered by the transition period
  must meet the following requirements
• Wind generating plants are required to remain
  in-service during three phase faults with normal
  clearing (which is a time period of approximately
  4 9 cycles) and single line to ground faults
  with delayed clearing, and subsequent post-fault
  voltage recovery to pre-fault voltage unless
  clearing the fault effectively disconnects the
  generator form the system.
• The clearing time requirement for a three-phase
  fault will be specific to the wind generating
  plant substation location, as determined by and
  documented by the transmission provider.
• The maximum clearing time the wind generating
  plant shall be required to withstand for a
  three-phase fault shall be 9 cycles
• after which, if the fault remains the wind
  generating plant may disconnect from the
  transmission system.
• The wind generating plant shall remain
  interconnected during such a fault on the
  transmission system for a voltage level as low a
  zero volts, as measured at the high voltage side
  of the wind GSU.

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New LVRT Requirement per FERC (cont)

• This requirement does not apply to faults that
  would occur between the wind generator terminals
  and the high side of the GSU.
• Wind generating plants may trip after the fault
  period if this action is intended as part of a
  special protection scheme.
• Wind generating plants may meet the LVRT
  requirements of this standard by (utilizing) the
  performance of the generators or by installing
  additional equipment (e.g., Static VAr
  Compensators, etc.) within the wind generating
  plant or by a combination of generator
  performance and additional equipment.
• Existing individual generating units that are, or
  have been, interconnected to the network at the
  same location at the effected date of the
  Appendix G LVRT Standard are exempt from meeting
  the Appendix G LVRT Standard for the remaining
  life of the existing generation equipment.
  Existing individual generator units that are
  replaced are required to meet the Appendix G LVRT
  Standard.

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Wind Generation Technology Trends

• Wind Turbines
• Continuing movement to variable speed
• Emergence of full-converter topologies
• Enhanced grid compatibility (driven by grid
  codes)
• Continued emphasis on production, availability
  (low wind speed)
• Wind Plants
• Increasing emphasis on interconnection behavior
  of entire plant, not just turbine
• Higher performance driven by grid codes (e.g.
  LVRT, voltage control requirements
• Other
• Research and development on advanced features
  (e.g. intertial and governor response)

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NERC Wind Generation Task Force

• In wake of Order 2003a, established task force to
  assess power system planning and reliability
  issues related to wind generation
• Task Force convened January, 2005 with cross
  section of stakeholder technical representatives
• Transmission owners/operators
• Regional Transmission Organizations
• Generating companies
• Wind Industry (AWEA UWIG)
• Objectives
• Identify any and all issues related to wind
  generation that have implications for power
  system reliability
• Determine if issue can be addressed through
  standards
• Develop SARs (standards authorization requests)
  for areas where new standards may be necessary
• TF assignment complicated by ongoing,
  comprehensive revision of NERC standards
• Task Force Period of Performance CY2005

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WECC Wind Turbine Modeling Initiative - Drivers

• Wind generation is no longer invisible
• WECC has 3.7 GW of wind generation capacity
  installed
• Some areas are experiencing high saturation
  levels
• Significant expansion expected in the near future
• Adequate simulation models are indispensable
• Identify and address impact of new generator
  additions
• Perform planning studies to maintain system
  reliability at the local and regional level
• The Status Quo is not acceptable to WECC
• One-of-a-kind and proprietary models are
  incompatible with the current system modeling
  practice in WECC
• Difficult and confusing for users
• Cannot be maintained in base cases once plant is
  built

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Proposed standard models

• Based on characteristics of grid interface
• Type A conventional induction generator
• Type B wound rotor induction generator with
  variable rotor resistance
• Type C doubly-fed induction generator
• Type D full converter interface

Type A
Type B
Type C
Type D
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Technical challenges

• Wind generator modeling versus wind plant
  modeling
• Wind plant equivalencing is required to reduce
  data and computational burden
• WGMG will first concentrate on development of
  generic WTG dynamic models
• Grid versus wind disturbances
• Performance in response to grid disturbances can
  be modeled reasonably well using generic models
• Performance in response to wind disturbances
  could introduce complications but note that
  this is less importance in the planning
  environment

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Technical challenges

• Single and multiple generator equivalencing

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Wind Generation Interconnection -Other Ongoing
Activities

• UWIG
• IEEE PES
• Power System Dynamics Committee Wind Gen. TF
• Other technical committees in process of
  engaging
• Wind Power Coordinating Committee established
  under Technical Council (June 2005)
• International
• Significant research ongoing
• Coordination with US efforts
• UWIG
• WECC

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Wind Integration Why the Concern?

• Wind generation is an attractive source of
  electric energy
• The electric power business is based on capacity
• System planning
• Reliability considerations
• Wind energy doesnt fit this model well
• Variability
• Uncertainty
• What are the financial consequences of these
  attributes?

22
What is Integration Cost?

• Does buying wind energy increase costs to serve
  the remaining load?
• Depends on the definition of buying
• Consensus that the qualitative answer is Yes
• Real question is How much?
• General Definition
• Increased cost of serving load not served by wind
• Can be evaluated by comparing wind to equivalent
  energy source that imposes no incremental burden
  on operations
• Elements
• Conventional ancillary service regulation,
  reserves etc.
• Increased costs due to variability of wind
  generation
• Increased costs due to increased uncertainty in
  unit commitment and scheduling
• Possibly some costs due to the actual value of
  energy delivered vs. the reference

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Dealing with Variability and Uncertainty

• We are accustomed to working with some degree of
  variability and uncertainty
• Variability
• Load varies by seconds, minutes, hours, by day
  type, and with weather
• Supply resources may not be available or limited
  in capacity due to partial outages
• Prices for power purchases or sales exhibit are
  not constant
• Uncertainty
• Operational plans are made on basis of best
  available forecasts of needs some error is
  inherent
• Supply side resource available with some
  probability (usually high)

Key Questions

• How does wind generation affect this existing
  variability and uncertainty?
• What are the costs associated with the changes?
• Can we maintain the integrity of the system under
  these new conditions?

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Wind Generation Modeling Challenges

• Most of the wind generation yet to be built
• Expected geographic spread is substantial
• Neglecting transmission issues, control area
  impacts are based on the behavior of the
  aggregate wind generation, not individual plants
• Supply resources are managed as a group to meet
  load, maintain reliability and minimize cost
• No one-to-X backups

A realistic representation of the wind generation
is critical to the study results
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Approach Re-creating the Weather

• Historical years (2000, 2002, 2003)
• Increased temporal and spatial resolution (5 km2,
  10 min.)
• Use historical data to initialize and guide
  numerical weather model
• Save important weather variables at points of
  interest

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Baseline Data for Study

• Multiple years of 10-minute resolution data for
• System load (scaled to study year)
• Aggregate wind generation
• Load data wind generation data from corresponding
  years
• Allows a wide-rage of what if questions to be
  addressed through simulations and calculations

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Low Correlation Period
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High Correlation Period
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Distribution of Hourly Changes(normalized)
Aggregate Production
Individual Plants
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General Findings from Studies to Date

• Good wind generation data is critical for
  assessing power system impacts
• Chronological, historical
• Relatively high resolution
• Long-term
• Represents geographic diversity
• Correlated with actual load
• Statistical and mathematical processing can help
  identify operating challenges

Ramp up requirement increased by wind
Ramp down requirement increased by wind
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Variability and Uncertainty Examples
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Insights and Perspectives

• Geographic dispersion of wind plants
• Substantially reduces effects of shorter-term
  wind plant output fluctuations
• Major impacts seen at hourly level and with
  short-term planning (unit commitment and
  scheduling)
• Wind generation forecasting can help to reduce
  these impacts
• Markets
• Access to liquid day-ahead and real-time markets
  can reduce integration costs
• Provide additional low- to modest- priced
  resources for balancing and dealing with
  uncertainty of wind generation

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Insights and Perspectives

• Wind Generation Modeling
• Meteorological simulations can provide
  high-quality data for assessing impacts
• Labor and computationally intensive, but superior
  to alternative methods
• Analytical Methods
• Statistical and mathematical techniques can
  provide useful results more exhaustive
  validation would be helpful
• Chronological simulations of power system
  operation are most straightforward (approach and
  results understandable by widest range of
  stakeholders) can be labor intensive and
  relatively costly, however

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Status - Integration

• Assessment of Integration questions also
  continues in the form of specific, focused
  studies, e.g.
• Xcel Energy Minnesota (integration cost study)
• Xcel Energy - Colorado (integration cost study)
• State of Minnesota (Dept. of Commerce)/Xcel RDF
• Sacramento Municipal Utility District
  (prospective integration study)
• CAISO/CEC (integration study related to RPS)
• BPA (shaping and firming services for wind
  generation)
• Manitoba Hydro (integration study)
• AESO (wind generation market impact assessment)
• Analysis techniques are becoming more
  sophisticated and better accepted
• High-fidelity chronological models of regional
  wind scenarios
• Detailed consideration of specific operational
  practices or market rules
• Application of power industry tools for analysis

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Summary of Wind Integration Studies
Source UWIG
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Ongoing Wind Integration Studies in WECC

• EnerNex Studies
• Sacramento Municipal Utility District
• Public Service New Mexico
• Idaho Power
• Avista Corporation
• Public Service Colorado
• Others
• California Intermittency Project (GE, for the CEC
  and CPUC)
• Pacificorp (internal)
• Puget Sound PL (internal)
• Alberta Electric System Operator

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Public Service New Mexico on the tails of
the curve

• Operating challenges with wind generation
• Existing 200 MW plant has measurable effect on
  control performance
• More wind planned for control area
• PNM control area
• Small relative to existing wind
• General shortage of regulating resources
• Cannot purchase regulation service
• Large, concentrated wind plant has significant
  impacts on CPS2

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Wind Generation and ACE
Source A. Ellis Public Service New Mexico
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High Resolution Simulations The Next Step
Areva TD eterra-simulatordispatcher training
environment
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Question How are Wind Generation Forecasts used
in Power System Operations and Planning ?

• Honest Answers
• Poorly, at the moment, and
• Were really not sure
• Forecasting experience in US
• Required by some more recent PPAs
• Little attention paid to requirements for use
• Motivation and incentives lacking
• Therefore, view is that wind generation forecasts
  are of little value

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Value Propositions for Forecasting

• Economic
• Characteristics of wind generation - variability
  and uncertainty are managed with minimum
  financial impact to remainder of supply portfolio
• Positive attributes e.g. correlation with load
  or hydro inflows are leveraged
• Security Reliability
• Performance of energy transportation and delivery
  infrastructure is not compromised
• Quality of electric service to customers is
  maintained

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Nonetheless,

• Wind generation forecasting seen as key to
  continued wind industry growth
• Value of wind generation forecast being
  demonstrated in some integration studies
• e.g. NYSERDA study by GE
• 100 million annual forecast value
• Work beginning on next phase
• Testing of hypotheses
• Concepts to implementation
• Measuring performance and value, then fine tuning
• Significant Activities in U.S.
• XCEL Energy/MN RDF
• Evolution of CA PIRP forecasting program
• Various integration studies focused on use of
  short-term wind generation forecasts in RT
  operations

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Status Wind Integration Costs from North
American Studies

• A number of studies conducted over past five
  years
• More in progress
• Findings
• Total integration costs for modest penetrations
  of wind generation (to 15 or 20) range from a
  couple to 5/MWH of delivered wind energy
• Costs due to planning uncertainty and hourly
  variability seem to be most significant
• Regulation costs are small
• Much work remains
• Forecasting impact/value
• Sensitivity of integration costs to resource
  portfolio, operating practices
• Market impacts
• Enhanced algorithms for planning with higher
  uncertainty
• Use of short-term forecast information in RT
  operations

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Opportunities for Collaboration

• Wind issues are entering the power engineering
  mainstream
• Much to do
• Talent and resource applied to problems is
  increasing steadily
• IEEE PES is stepping up to the plate
• Wind Plant Dynamics Working Group (2004)
• Wind Power Coordinating Committee (2005)
• Utility Wind Integration Group (UWIG)
• Is currently the most active and relevant forum
  for exchange of wind energy-related power system
  information
• Has taken on a more active role with formation of
  working groups (2004)
• Groups work to identify and address most urgent
  questions regarding interconnection and
  integration of wind turbines and wind plants

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UWIG Focus Areas and Topics

• Operating Impacts Users Group
• Methods for assessing operating impacts
• Wind energy forecasting
• High wind penetrations in a carbon-constrained
  world
• Wind generation capacity valuation methods
• Best practices for wind plant integration
• Modeling and Interconnection Users Group
• Wind turbine and plant models for dynamic
  simulations
• Generic models for interconnection screening
  studies and base case models (WECC)
• Short-circuit behavior of wind plants

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IEEE Power Energy , November 2005