Illustrated Glossary - Substations | Occupational ... - OSHA

Substation Functions · Change voltage from one level to another · Regulate voltage to compensate for system voltage changes · Switch transmission and distribution ... Skiptomaincontent eTools ElectricPowerGeneration,Transmission,andDistribution:IllustratedGlossary-Substations ElectricPowerGeneration,Transmission,andDistributioneTool ElectricPowerGenerationMenu Home Scope SafetyandHealthTopicsPage GlossaryofTerms IllustratedGlossary(02/2004) Credits Generationvs.Transmission/Distribution Transmissionvs.Distribution Substations MedicalServicesandFirstAid 4-minuteRescueRequirements FirstAidRequirements PoleTopandManholeRequirements HazardAssessmentandJobBriefing JobBriefingsandBestPractices Energizedvs.DeenergizedWork MinimumApproachDistances(MAD) DisablingofReclosersandRemotelyOperatedDevices LiveLine/BareHandWork HazardousEnergyControl Lockout/Tagout:Generation DeenergizingLinesandEquipmentforEmployeeProtection EquipotentialZone ProtectiveGrounding(Bonding) PortableGroundingEquipment GroundingforEmployeeProtection OverheadLineWork UseofAerialLifts Line-ClearanceTreeTrimming IllustratedGlossary»Substations Asubstationisahigh-voltageelectricsystemfacility.Itisusedtoswitchgenerators,equipment,andcircuitsorlinesinandoutofasystem.ItalsoisusedtochangeACvoltagesfromoneleveltoanother,and/orchangealternatingcurrenttodirectcurrentordirectcurrenttoalternatingcurrent.Somesubstationsaresmallwithlittlemorethanatransformerandassociatedswitches.Othersareverylargewithseveraltransformersanddozensofswitchesandotherequipment.Therearethreeaspectstosubstations: Figure1.Typicalsubstation SubstationTypes:Although,therearegenerallyfourtypesofsubstationstherearesubstationsthatareacombinationoftwoormoretypes. Step-upTransmissionSubstation Step-downTransmissionSubstation DistributionSubstation UndergroundDistributionSubstation SubstationFunctions SubstationEquipment Step-upTransmissionSubstation Astep-uptransmissionsubstationreceiveselectricpowerfromanearbygeneratingfacilityandusesalargepowertransformertoincreasethevoltagefortransmissiontodistantlocations.Atransmissionbusisusedtodistributeelectricpowertooneormoretransmissionlines.Therecanalsobeatapontheincomingpowerfeedfromthegenerationplanttoprovideelectricpowertooperateequipmentinthegenerationplant. Asubstationcanhavecircuitbreakersthatareusedtoswitchgenerationandtransmissioncircuitsinandoutofserviceasneededorforemergenciesrequiringshut-downofpowertoacircuitorredirectionofpower. Thespecificvoltagesleavingastep-uptransmissionsubstationaredeterminedbythecustomerneedsoftheutilitysupplyingpowerandtotherequirementsofanyconnectionstoregionalgrids.Typicalvoltagesare: Highvoltage(HV)ac: 69kV,115kV,138kV,161kV,230kV Extra-highvoltage(EHV)ac: 345kV,500kV,765kV Ultra-highvoltage(UHV)ac: 1100kV,1500kV Direct-currenthighvoltage(dcHV): ±250kV,±400kV,±500kV Directcurrentvoltageiseitherpositiveornegativepolarity.ADClinehastwoconductors,soonewouldbepositiveandtheothernegative. Step-downTransmissionSubstation Step-downtransmissionsubstationsarelocatedatswitchingpointsinanelectricalgrid.Theyconnectdifferentpartsofagridandareasourceforsubtransmissionlinesordistributionlines.Thestep-downsubstationcanchangethetransmissionvoltagetoasubtransmissionvoltage,usually69kV.Thesubtransmissionvoltagelinescanthenserveasasourcetodistributionsubstations.Sometimes,poweristappedfromthesubtransmissionlineforuseinanindustrialfacilityalongtheway.Oterwise,thepowergoestoadistributionsubstation. DistributionSubstation Distributionsubstationsarelocatedneartotheend-users.Distributionsubstationtransformerschangethetransmissionorsubtransmissionvoltagetolowerlevelsforusebyend-users.Typicaldistributionvoltagesvaryfrom34,500Y/19,920voltsto4,160Y/2400volts. 34,500Y/19,920voltsisinterpretedasathree-phasecircuitwithagroundedneutralsource.Thiswouldhavethreehigh-voltageconductorsorwiresandonegroundedneutralconductor,atotaloffourwires.Thevoltagebetweenthethreephaseconductorsorwireswouldbe34,500voltsandthevoltagebetweenonephaseconductorandtheneutralgroundwouldbe19,920volts. Fromherethepowerisdistributedtoindustrial,commercial,andresidentialcustomers. UndergroundDistributionSubstation Undergrounddistributionsubstationsarealsolocatedneartotheend-users.Distributionsubstationtransformerschangethesubtransmissionvoltagetolowerlevelsforusebyend-users.Typicaldistributionvoltagesvaryfrom34,500Y/19,920voltsto4,160Y/2400volts. Anundergroundsystemmayconsistoftheseparts: Conduits DuctRuns Manholes High-VoltageUndergroundCables TransformerVault Riser Transformers Fromherethepowerisdistributedtoindustrial,commercial,andresidentialcustomers. SubstationFunctions Substationsaredesignedtoaccomplishthefollowingfunctions,althoughnotallsubstationshaveallthesefunctions: Changevoltagefromoneleveltoanother Regulatevoltagetocompensateforsystemvoltagechanges Switchtransmissionanddistributioncircuitsintoandoutofthegridsystem Measureelectricpowerqualitiesflowinginthecircuits Connectcommunicationsignalstothecircuits Eliminatelightningandotherelectricalsurgesfromthesystem Connectelectricgenerationplantstothesystem Makeinterconnectionsbetweentheelectricsystemsofmorethanoneutility Controlreactivekilovolt-amperessuppliedtoandtheflowofreactivekilovolt-amperesinthecircuits Additionalinformation: TheLineman'sandCableman'sHandbook,Shoemaker,T.M.,Mack,J.E.,TenthEdition2002,McGraw-Hill. SubstationEquipment Themajorcomponentsofatypicalsubstationare: AirCircuitBreaker Batteries BusSupportInsulators CapacitorBank CircuitSwitchers ConcreteFoundation Conduits ControlHouse ControlPanels ControlWires ConverterStations CouplingCapacitors CurrentTransformers DisconnectSwitches DistributionBus DuctRuns FrequencyChangers GroundingResistors GroundingTransformers High-VoltageUndergroundCables High-VoltageFuses LightningArresters Manholes Metal-cladSwitchgear Meters Microwave OilCircuitBreakers PotentialTransformers Potheads Power-lineCarrier PowerTransformers Rectifiers Relays SF6CircuitBreakers ShuntReactors SteelSuperstructures SupervisoryControl SuspensionInsulators SynchronousCondensers TransmissionBus VacuumCircuitBreakers Additionalinformation: TheLineman'sandCableman'sHandbook,Shoemaker,T.M.,Mack,J.E.,TenthEdition2002,McGraw-Hill.