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Power Delivery Systems TutorialUniversity of California, BerkeleySeptember 15, 2006Dr. Alexandra von MeierSonoma State UniversityThis Workshop is sponsored by the PIERProgram of the California Energy Commissionin conjunction with the California Institute ofEnergy Efficiency, University of California,Office of the PresidentCEC Contract Number 500-01-043Questions about power systems ingeneralPower distribution systemsHuman factors and other complexitiesassociated with technologicalinnovation, especially human factorsQuestions about power systemsHow to visualize the grid?Why are grids large and interconnected?Why transmit power at high voltages?Why use alternating current?Why use three phases?What is reactive power?How to predict power flow?How to balance supply and demand?How to assess performance?Questions about power systemsHow to visualize the grid?Why are grids large and interconnected?Why transmit power at high voltages?Why use alternating current?Why use three phases?What is reactive power?How to predict power flow?How to balance supply and demand?How to assess performance?Rendition of a power system from PG&E’s websitewww.pge.comMy PG&EserviceentranceTransmission lines (230 kV)Busbars, transformers and circuit breakers at CotatisubstationLakeville Transmission SubstationCalifornia’s electrictransmission systemby utilitywww.energy.ca.govPath 15 (500 kV line): California’s BackboneCalifornia within the synchronous a.c. grid of theWestern Systems Coordinating Council (WSCC)www.energy.ca.govCA Electricity Consumption: 288 billion kWh in 2005Source: California Energy Commissionwww.energy.ca.govRough Overview of California Energy UseElectricityNatural GasTransportationQuestions about power systemsHow to visualize the grid?Why are grids large and interconnected?Why transmit power at high voltages?Why use alternating current?Why use three phases?What is reactive power?How to predict power flow?How to balance supply and demand?How to assess performance?Why are grids large andinterconnected?• Economies of scale• Load factor• Pooled resourcesLoad factor = average demand peak demandCoincident demand = combined demand that actuallyoccurs at a given timeNon-coincident demand = total connected demand thatdoesn’t usually occur all at onceQuestions about power systemsHow to visualize the grid?Why are grids large and interconnected?Why transmit power at high voltages?Why use alternating current?Why use three phases?What is reactive power?How to predict power flow?How to balance supply and demand?How to assess performance?(Casual) Definition of TermsThree voltage levels:Subtransmission (60-115kV)Primary distribution (12-21kV)Secondary distribution(120/240V)Questions about power systemsHow to visualize the grid?Why are grids large and interconnected?Why transmit power at high voltages?Why use alternating current?Why use three phases?What is reactive power?How to predict power flow?How to balance supply and demand?How to assess performance?Basic TransformerThe turns ratio determines the voltage: V2 / V1 = n2 / n1To satisfy energy conservation, current varies inversely with voltage:P1 = P2 and P = IV, thus I1V1 = I2V2 (neglecting losses)The most basic generatorQuestions about power systemsHow to visualize the grid?Why are grids large and interconnected?Why transmit power at high voltages?Why use alternating current?Why use three phases?What is reactive power?How to predict power flow?How to balance supply and demand?How to assess performance?Three-phase, synchronous generatorQuestions about power systemsHow to visualize the grid?Why are grids large and interconnected?Why transmit power at high voltages?Why use alternating current?Why use three phases?What is reactive power?How to predict power flow?How to balance supply and demand?How to assess performance?Reactive PowerThe “bad cholesterol”of power linesQuestions about power systemsHow to visualize the grid?Why are grids large and interconnected?Why transmit power at high voltages?Why use alternating current?Why use three phases?What is reactive power?How to predict power flow?How to balance supply and demand?How to assess performance?Power flow analysis for a 5-bus systemQuestions about power systemsHow to visualize the grid?Why are grids large and interconnected?Why transmit power at high voltages?Why use alternating current?Why use three phases?What is reactive power?How to predict power flow?How to balance supply and demand?How to assess performance?Power generated = Power demanded“The Law of Energy Conservation is strictlyenforced.”Real power imbalance:Loss of frequency controlReactive power imbalance:Loss of voltage controlHow to balance supply & demand?Successive approximations on differenttime scales: 1. Scheduling2. Generator control3. StabilityGenerator control: operating “on the governor”Generator Voltage AngleQuestions about power systemsHow to visualize the grid?Why are grids large and interconnected?Why transmit power at high voltages?Why use alternating current?Why use three phases?What is reactive power?How to predict power flow?How to balance supply and demand?How to assess performance?Power System PerformanceMeasuresPower quality: voltagea.c. frequencywaveformReliability: outage frequency & durationprobabilistic measuresSecurity: contingency analysisThe a.c. sine wave and power quality:voltage magnitude, frequency, and waveformwww.niagaramohawk.comMeasures of reliability:Outage frequencyOutage durationLoss-of-load probability (LOLP)Loss-of-load expectation (LOLE)Expected unserved energy (EUE)Security:The width of the operatingenvelopeContingency Analysis and theN-1 CriterionA “contingency”Securityand theN-1 CriterionWhat is reliability worth?Key concepts:Obligation to serveOne-day-in-ten-years criterion“Gold-plating”Value of Service (VOS)Human FactorsDistribution Engineers and Operators:Different responsibilities,different culturesDifferent ResponsibilitiesSample engineering tasks:Planning, equipment selection & sizing, innovation.Engineers’ responsibility:Make system perform optimally under designconditions.Sample operation tasks:Switching, maintenance, service restoration.Operators’ responsibility:Make system perform safely and minimize harmunder any conceivable condition; avert calamity.Different Cultures:Cognitive representations of distributionsystemsEngineering representation: Operator representation:Abstract PhysicalAnalytical HolisticFormal
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