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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