Overview of Modern Interconnected Power System

Overview of Power SystemsOverview of Power Systems

What is Power System

Transmission Mesh (or Loop) (Why?) Reliability: main concern A contingency has system-wide effects Distribution Radial (Why?) Economics! A fault has local disruption Protection issues3Historical Background1882: Power station at Pearl Station New York by Edison supplying power to 59 consumers, 110 V DC, Cable 1.5 km, lamp load. 1884: Motors were developed1886: Limitations of DC become apparent, higher losses and voltage drops. William Stanley developed first commercial ac system1889: AC transmission line 4kV, single phase, in north America between Willamette falls to Portland by Westinghouse. 1893: First three phase line in Southern California, 12 km, 2.3 kV.

Historical Background1922-1990: 165 kV -> 1200 kV1920: Europe standardized 60 Hz and suspended insulators for HV.1954: HVDC transmission system by Swedish Power Board.1972: Back-to-back connected HVDC station providing asynchronous tie between power systems Quebec and New Brunswick. Interconnected Power SystemWe are witnessing enormous development in terms of voltage rating, power ratings, components, architecture, planning, etc. Modern power system are vast electrical networks inter-connecting hundreds of rudimentary systems spread over a country giving rise to national grid. Advantages of interconnections:Reduced reserve capacityReduced capital costEffective and economic use of available generationImproved reliability, operational efficiency and energy securityDisadvantagesFault propagationHigher circuit breaker ratingsProper management of dispatch of powerMajor ConcernsPower Quality: Maintain the supply at desired frequency and voltage level

Reliability: Minimization loss of load probability

Security: Robustness of system to remain in normal state even if some contingencies take place.

Stability: Ability to maintain synchronism under disturbances and maintain steady state post-disturbance operation

Economy: Minimize capital and operational (running and maintenance) costs

ConstraintsEquipment constraints: Equipments must operate within specified limitRelated to voltage (Dielectric constraints)Related to current (Thermal constraints)

System ConstraintsConstraints due to stabilityConstraints due to reliabilityConstraints due to securityContingenciesContingenciesPower outagesNetwork outagesPower systems experience a wide variety of disturbances. It is impractical and uneconomical to design the systems to be stable for every possible contingency.

Design contingenciesA permanent three phase or phase to ground fault on any generator or transmission line with reclosing facility.Loss of any element without fault.Phase to ground fault on circuit breaker and cleared in normal timeExtreme contingenciesLoss of entire generation of generating stationLoss of all lines emanating from generating stationSudden dropping of major load or major load center

System ConstraintsLoad Constraints or Equality Constraints (L or E)Real and reactive power balance

Operating Constraints or Inequality Constraints (O or I)Operating voltage limits, line loading limits, etc.

Operating States and Control StrategiesNormalE, IAlertE, IEmergencyE, IIn extremisE, IRestorativeE, IPreventive controlsRestorative controlsRestorative controlsEmergency controlsResynchronizeGeneration shifting or increased reserveFault clearing, excitation cotrol, phase-shifting transformer, generation tripping or run-back, load curtailmentLoad shedding, controlled system separtionGeneration rescheduling, element switchingControl of Power System

Ref: P. Kundur, Power System Stability and Control. New York: McGraw-Hill, 1994.Static Var comp, Syn condensor, switched capacitor, reactors, tap changing transformers, phase shifting transformers, HVDC

12Smart GridUsing information to substantially improve performance (by monitoring as well as control) and lower cost of electric service

Real-time pricingDemand responseDistributed generationAutomated meteringIntermittent generationEnergy storageFault and failure anticipationSensorsDynamic switchingInformation flows

Drivers of Smart GridPerformance

ReliabilityEfficiencyQualityCost

MaintenanceReplacementEnergyClimate Change

RenewablesDistributed GenerationElectric Vehicles

SensorsPower ElectronicsTechnology

CommunicationSmart metersAdvanced computingBusiness analytics