Power System Issues for Bulk Wind Generation: Status and Needs

Robert ZavadilVice President & Principal Consultant

EnerNex Corporation448 N. Cedar Bluff Road

Suite 349Knoxville, TN 37923Tel: (865) 671-6650bobz@enernex.comwww.enernex.com

Stanford GCEP Energy WorkshopApril 26, 2004

Frances C. Arrillaga Alumni Center, Stanford University

Development of Large Scale Wind Generation in the U.S.

Confined to California until mid 1990’sLarge plants now operating in many control areas

Great Plains (MN, IA)TexasPacific Northwest

Changing “utility” perspectivesInstalled capacity forecast to grow significantlyInfluence on behavior of grid can no longer be ignoredSystem-level impacts will likely need to be addressed as wind capacity increases

Power industry evolution creates turbulent backdropCompetitive marketsNew organizations and alliancesNew business practices“New” emphasis on reliability

Fundamental Power System Engineering Challenges

Wind generation technology is novel relative to conventional generating equipment and systemsWind generation is an energy resource in a capacityworldExperience with wind generation is nonexistent compared with conventional resources

Engineering Practice for Large Power Systems

Based on computer tools and computational techniques for “predicting” performance and behavior – no “plug and play”Methods require appropriate characterization of each system element – generators, loads, transmission, etc.Experience also critical to understanding what system states are of most interest (what to study)

Major Categories of Power System Studies

InterconnectionPlanningForensicSpecial

Present FocusInterconnection Evaluations

Mandated for connection of any new element to gridMust evaluate:

- Voltage control / reactive power management- Thermal considerations / equipment ratings- Short-circuit behavior- Large-signal dynamic behavior- Reliability / security

Integration StudiesIncreasing concern as wind generation capacity in a given control area growsFocuses on the normal operation of the system

- Voltage regulation and frequency control- Short-term system planning and scheduling- Transmission utilization and congestion issues- Influence on overall production cost- Ancillary services - Market influences and impacts

Modeling Challenges for Wind Generation

Uneasy “fit” with conventional toolsinduction machines rather than synchronous generators “novel” control technology – e.g. flux-vector control of induction machinesUnfamiliar mechanical system & prime moverMany small generators vs. few large generatorsExpansive plant electrical system

Unique operational characteristicsNot dispatchableMore difficult to identify appropriate “states” to be analyzed

Interconnection Challenges for Wind Generation

Remote facilitiesTypically interconnection to weak transmission networkDesigns can be challenging

Reactive power managementCritical for controlling voltageDynamic character of wind generation Reactive power planning for network must be coordinated with wind plants

Interconnection requirements are evolvingWere typically very simpleEvolving to voltage control, dynamic reactive power management

Wind Plant Interconnect BusVoltageas function of P and Q for Weak Network

1.10 pu

1.05 pu

1.00 pu

Evolving Interconnection Requirements are driving Wind Technology Development

More robust turbine designsLow-voltage ride-throughMore desirable dynamic response characteristics

Better wind plant designsPlant-level planning of reactive compensationInterconnection bus behavior within specsImproved medium-voltage collector system design

Ongoing needsValidated modelsNew modelsExperience

ERCOT Dynamic Model Development

Urgent need in wind and power industries for modelsERCOT took industry lead in addressing issueLaunched 12-month effort to develop and validate dynamic windplantmodels for PSS/E platformProject began late July, 2002Monitoring effort included to provide field data for validating modelsPSS/E user models delivered September, 2003

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Interconnection SummaryEarly plants experienced start-up problems due to inadequate facility and interconnect designLessons learned are being incorporated into new plant designsSignificant challenges and needs remain:

Better characterization of wind turbine and plant performancePlant and turbine modeling for power system studies not well developedModels and assumptions for wind generation require validationPower system engineering practice for wind plant design is stillrelatively immature

AssessmentPlaying “catch upMaking progress

Energy vs. Capacity

Engineering evaluations biased toward capacityDesign for peak conditionsVoltage can be related directly to power, not energyTransmission capacity

System operators deal with “MW for the hour” not MWHSystem security and reliability linked more closely to capacityShort-term operations planning and scheduling, market mechanisms utilize predictions and forecasts

Wind generation is the ultimate “as-available” generating resource

Forecast power production vs. time can only be done approximatelySubstantial amounts of as-available or non-dispatchable resources are a poor fit with tools and analytical methods for power system operation

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Output Variations of 250 MW WindplantLoad-Following (minute-by-minute) time frame

10 MW

Wind Generation Integration

Definition: Quantifying the affects of the unique characteristics of wind generation on the rest of the system, marketsIssue is increasing in importance

Level of concern proportional to installed wind capacity/control area capacityEvolving power markets add more complexity

Multiple studies conducted, underway“screening” assessments related to RPS-driven wind generation procurementsSome analytical studiesMarket-based assessments

Status: Large-Scale Grid-Connected Wind Generation

Efforts focused on fitting wind generation into existing practice and methodologies

Real-time operationsShort-term planning, scheduling, and optimizationLonger-term capacity valuation

Industry transition and conventional practice dictate current perspectives on wind energy

Reliability and security assessmentEvolution of market-mechanisms

Long-term BarriersTransmission – moving large amounts of energy long distancesOperations – creating structures and mechanisms that accommodate energy sources

Grid Integration Opportunities

TransmissionMaximizing utilization of existing gridAdvanced technologies - FACTS, HVDC, higher-phase order (e.g. six-phase)

OperationsUtilizing advanced technologies like forecastingSophisticated systems for real-time operationsNew methodologies for short-term planning and scheduling

Storage