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    22 TWOTWOPOWER SYSTEMPOWER SYSTEM

    LAYOUT ANDLAYOUT ANDRELAYING PRINCIPLESRELAYING PRINCIPLES

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    Power system layout,

    Review of short circuit calculation

    Electrical engineering basic concepts

    Three phase review and per unit. Voltage levels,

    ne ne an ree ne agram, Generation system layout,

    Transmission Layout,

    Distribution layout,

    Substation

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    Simplified generation system

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    Generation illustration (a) single phase

    and (b) three phase

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    Typical

    generating

    plant one line

    diagram

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    Electrical Power System LayoutElectrical Power System Layout

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    Operating Voltage Levels

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    Operating Voltage LevelsOperating Voltage Levels

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    ThreeThree--Line and OneLine and One--LineLine

    DiagramsDiagrams

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    OneOne--line diagramline diagram

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    Interc.system

    Advantages

    Reliability

    Economic

    Disadvantages

    Complex

    Power loss

    Voltage drop

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    diagram symbols

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    Impedance diagram for a power system

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    Bulk powertransmission system

    transmit power

    -

    Change of power

    Between utilities.

    single line outageDoes not affect.

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    345 KV transmission

    line to transmit bulk

    power from remote

    generating plants to

    the system loadcenters.

    Note, there are2conductor/phase

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    Subtransmission system. Note there is a set

    of air break switches to isolate the line sec.

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    ApplicationApplication 22..22

    Disconnect the system forfaults;

    F2

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    Over all view of transmission

    substation

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    Air break switch installation

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    Transfer bus

    scheme

    CB conn. TL to

    main bus

    disc. Sw. conn. TL

    to transfer bus

    Tr CB conn.

    Buses 1,2

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    Application 2.3It is required to remove one of

    the CBs

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    Radial distribution layout

    Most economic

    One CB for TL

    Lowest Flexibility.

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    Distribution

    substation one

    line diagram

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    Overhead secondary dist. system

    Radial manner

    is used at each

    user cables or

    overhead mayused

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    S k

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    Spot network system

    Similar to

    net.system but

    supply isolatedload centers in a

    particular location-floors of high rise

    building.

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    44thth Lec.Lec.CHCH 22

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    ChCh 22

    PRINCIPLESPRINCIPLES

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    RELAY OPERATINGRELAY OPERATING

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    INTRODUCTIONINTRODUCTION InIn general,general, aa relayrelay cancan bebe designeddesigned toto

    respondrespond toto anyany observableobservable parameterparameter ororeffecteffect.. TheThe fundamentalfundamental problemproblem inin powerpowersystemsystem protectionprotection isis toto definedefine thethe quantitiesquantities

    abnormalabnormal conditionsconditions..ThisThis problemproblem ofof beingbeingableable toto distinguishdistinguish betweenbetween normalnormal andandabnormalabnormal conditionsconditions isis compoundedcompounded byby

    thethe factfact thatthat 'normal''normal' inin thethe presentpresent sensesensemeansmeans thatthat thethe disturbancedisturbance isis outsideoutside thethezonezone ofof protectionprotection..

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    Problem of relay selectivity forProblem of relay selectivity for

    faults at zone boundaryfaults at zone boundary

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    DETECTION OF FAULTSDETECTION OF FAULTS

    InIn general,general, asas faultsfaults (short(short--circuits)circuits)occur,occur, currentscurrents increaseincrease inin magnitude,magnitude,

    andand voltagesvoltages gogo downdown.. BesidesBesides thesethesemagnitudemagnitude changeschanges ofof thethe acac quantities,quantities,otherother chan eschan es mama occuroccur inin oneone oror moremore

    ofof thethe followingfollowing parametersparameters:: phasephase anglesangles ofof currentcurrent andand voltagevoltage

    phasors,phasors, harmonicharmonic componentscomponents,, activeactive

    andand reactivereactive powerpower,, frequencyfrequency ofof thethepowerpower system,system, etcetc..

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    Level DetectionLevel DetectionThisThis isis thethe simplestsimplest ofof allall relayrelay

    operatingoperating principlesprinciples.. AsAs reviewedreviewed ininSuctionSuction 22..11,, faultfault currentcurrent

    greatergreater thanthan thethe normalnormal loadloadcurrentscurrents thatthat existexist inin aa powerpower

    systemsystem.. ConsiderConsider thethe motormotorconnectionconnection toto aa 44 kVkV powerpower systemsystemshownshown inin FigureFigure 22..22..

    O t t ti fO t t ti f

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    Overcurrent protection of aOvercurrent protection of a

    motormotor

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    ExampleExample TheThe fullfull loadload currentcurrent forfor thethe motormotor isis245245

    amperesamperes.. AllowingAllowing forfor anan emergencyemergencyoverloadoverload capabilitycapability ofof 2525%%,, aa currentcurrent ofof11..2525**245245==346346 amperesamperes oror lowerlower shouldshouldcorrespondcorrespond toto normalnormal operationoperation.. AnyAny

    aboveabove346346 amperesamperesbyby aa safetysafety marginmargin ininthethe presentpresent example)example) maymay bebe takentaken totomoanmoan thatthat aa fault,fault, oror somesome otherother abnormalabnormal

    condition,condition, existsexists insideinside thethe zonezone ofofprotectionprotection ofof thethe motormotor..

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    Pickup Setting of the RelayPickup Setting of the Relay TheThe levellevel aboveabove whichwhich thethe relayrelay operatesoperates isis

    knownknown asas thethepickuppickup settingsetting ofof thethe relayrelay.. ForForallall currentscurrents aboveabove thethe pickup,pickup, thethe relayrelay

    operates,operates, andand forfor currentscurrents smallersmaller thanthan thethe

    pickuppickup valuevalue,,thethe relayrelay takestakes nono actionaction.. ItIt isisofof coursecourse possiblepossible toto arrangearrange thethe relayrelay toto

    operateoperate forfor valuesvalues smallersmaller thanthan thethe pickuppickup

    valuevalue,, andand taketake nono actionaction forfor valuesvalues aboveabove

    thethe pickuppickup.. AnAn underunder voltagevoltage relayrelay isis ananexampleexample ofof suchsuch aa relayrelay..

    Characteristic of a level detectorCharacteristic of a level detector

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    Characteristic of a level detectorCharacteristic of a level detector

    relayrelay

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    Magnitude comparison relayingMagnitude comparison relaying

    for two parallel transmission linesfor two parallel transmission lines

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    Magnitude comparisonMagnitude comparisonOneOne couldcould useuse aa magnitudemagnitude

    comparisoncomparison relayrelay whichwhich comparescomparesthethe magnitudesmagnitudes ofof thethe twotwo lineline

    currentscurrents anan .. ssgreatergreater thanthan || IBIB || ++ ,, andand lineline BB isisnotnot open,open, thethe relayrelay wouldwould declaredeclare aa

    faultfault onon lineline AA andand triptrip it,it, wherewhere isisaa suitablesuitable tolerancetolerance..

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    Differential ComparisonDifferential ComparisonDifferentialDifferential comparisoncomparison isis oneone ofof

    thethe mostmost sensitivesensitive andand effectiveeffectivemethodsmethods ofof providingproviding protectionprotection..

    differentialdifferential comparisoncomparison isis quitequitesimple,simple, andand cancan bebe bestbest understoodunderstood

    byby referringreferring toto thethe generatorgeneratorwindingwinding shownshown inin FigureFigure 22..55..

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    Phase Angle ComparisonPhase Angle Comparison

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    Pilot RelayingPilot Relaying CertainCertain relayingrelaying principlesprinciples areare basedbased

    uponupon informationinformation obtainedobtained byby thethe relayrelayfromfrom aa remoteremote locationlocation.. TheThe informationinformationisis usuallusuall --althou halthou h notnot alwa salwa s -- inin thethe

    formform ofof contactcontact statusstatus (open(open oror closed)closed)..TheThe informationinformation isis sentsent overover aacommunicationcommunication channelchannel usingusing powerpower

    lineline carrier,carrier, microwave,microwave, oror telephonetelephonecircuitscircuits..

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    Harmonic ContentHarmonic Content

    TheseThese abnormalabnormal conditionsconditions cancan bebe

    detecteddetected byby sensingsensing thethe harmonicharmoniccontentcontent throughthrough filtersfilters inin

    -- ,,

    oror byby calculationcalculation inin digitaldigital relaysrelays.. OnceOnceitit isis determineddetermined thatthat anan abnormalabnormalconditioncondition exists,exists, aa decisiondecision cancan bebemademade whetherwhether somesome controlcontrol actionaction isisrequiredrequired..

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    Frequency SensingFrequency Sensing

    NormalNormal powerpower systemsystem operationoperation isis atat 5050 oror 6060Hz,Hz, dependingdepending uponupon thethe countrycountry.. AnyAnydeviationdeviation fromfrom thesethese valuesvalues indicatesindicates thatthat aaproblemproblem existsexists oror isis imminentimminent.. FrequencyFrequency

    ,,

    countingcounting ofof zerozero crossingscrossings ofof waveformswaveforms inin aaunitunit ofof time,time, oror byby specialspecial samplingsampling andanddigitaldigital computercomputer techniquestechniques.. FrequencyFrequencysensingsensing relaysrelays maymay bebe usedused toto taketakecorrectivecorrective actionsactions whichwhich willwill bringbring thethesystemsystem frequencyfrequency backback toto normalnormal..

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    RelaysRelays

    SomeSome relaysrelays areare alsoalso designeddesigned toto respondrespond totomechanicalmechanical devicesdevices suchsuch asas fluidfluid levelleveldetectors,detectors, pressurepressure oror temperaturetemperature sensors,sensors,etcetc.. RelaysRelays maymay bebe constructedconstructed fromfrom

    solenoids,solenoids, hingedhinged armatures,armatures, inductioninductiondiscs,discs, solidsolid statestate elementselements suchsuch asas diodes,diodes,SCRs,SCRs, transistorstransistors oror magneticmagnetic oror operationaloperationalamplifiers,amplifiers, oror digitaldigital computerscomputers usingusinganaloganalog--toto--digitaldigital convertersconverters andandmicroprocessorsmicroprocessors

    THERMAL RELAYSTHERMAL RELAYS

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    THERMAL RELAYSTHERMAL RELAYS

    Electromagnetic relay, HingedElectromagnetic relay, Hinged

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    armature relaysarmature relays

    SOLIDSOLID--STATE RELAYSSTATE RELAYS

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    SOLIDSOLID--STATE RELAYSSTATE RELAYS

    SolidSolid--state Instantaneous Overstate Instantaneous Over--

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    SolidSolid state Instantaneous Overstate Instantaneous Over

    current Relaycurrent Relay

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    WaveformWaveform

    of theof thesolidsolid--statestate

    ns an anens an aneousous

    overcurreovercurrent relaynt relay

    COMPUTER RELAYSCOMPUTER RELAYS

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    COMPUTER RELAYSCOMPUTER RELAYS