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TKE474High Voltage Engineering~High Voltage Engineering~
HighVoltageGenerationg g
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Hi hV l G iHighVoltageGeneration
1. Testingtheinsulationofpowerapparatus2. Simulationofovervoltages thatoccurinpowerg p
systems
powerfrequencyACDCSwitchingandlightningimpulsevoltages.
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I. GenerationofHighACVoltage
AselectricpowertransmissionwithhighACAselectricpowertransmissionwithhighACvoltagespredominatesintransmissionanddistributionsystems,themostcommonformofy ,testingHVapparatusisrelatedtohighACvoltages.
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Si l St T f SingleStageTransformer
SingleunittestingtransformersdonotdifferSingle unittestingtransformersdonotdifferfromsinglephasepowertransformer.However,particularattentionisgiventoheavyp g yinsulationofthehighvoltagewinding
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Theironcore,aswellasoneterminalofthelowl dhi h l i di i ll voltageandhighvoltagewindings,isusually
maintainedatearthpotential.Theotherterminalofthehighvoltagewindingwouldbeinsulatedofthehighvoltagewindingwouldbeinsulatedtothefulloutputvoltage.
Considerableeconomyisachieved,however,ifthecenterpointratherthanoneterminalofthehighvoltagewindingisearthed.
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CascadedTransformers
TwoStageTransformer
Th S T f ThreeStageTransformer
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Firsttransformerisatgroundpotential,Thesecondandthirdtransformersarekeptg p , poninsulators
Thehighvoltagewinding ofthefirstunitisconnectedtothetankofthesecondunit
Thelowvoltagewinding ofthesecondunitis Thelowvoltagewinding ofthesecondunitissuppliedfromtheexcitationwinding ofthefirsttransformer,whichisinserieswiththehighvoltagewinding ofthefirsttransformer 300kV
output
atitshighvoltageend.
Theratingoftheexcitationwinding isalmostidenticaltothatoftheprimarywinding. 200kV
VU
o
n
199kV
240V
240V
100kV
LVprimarywinding U
U1
I
n
s
u
l
a
t
i
240V
99kV
240Vinpu
LVprimarywindingHVsecondarywindingExcitationwinding
U22U2 3U2
U1
U1
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240Vpt
U1
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2.GenerationofHighDCVoltage
DCvoltagesaremainlyusedforpurescientificDCvoltagesaremainlyusedforpurescientificresearchworkandfortestingequipmentrelatedtoHVDCtransmissionsystems
R ifi AC DC Rectifier convertsACtoDC
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Halfwaverectifier asinglediodeisusedtopasseitherthepositiveornegativehalfcycleofACwhileblockingtheother.
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Fullwaverectifier convertsbothpolaritiesofinputwaveformintoDCp
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VOLTAGEDOUBLERVOLTAGEDOUBLER
twohalfwaverectifiercircuitsareconnectedinopposition,thusproducinganunsmoothedunidirectionalvoltage.Theoutputvoltagehasa
k l f V
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peakvalueof3Vs
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VOLTAGEMULTIPLIER
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ImpulseVoltageSourcesImpulseVoltageSourcesR1Rv
C2C1 R2U0 u2 SurgecapacitorC1ischargedandtheswitchisclosedandtheswitchisclosed
Triggered(ignitable)spheregapgapNonTriggered(nonignitable)spheregapignitable)spheregap
13/12/201113/12/2011 https://noppa.tkk.fi/noppa/kurssi/s18.3150
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RR R1
C2C1 R2U0
Rv
u2 ThechargeinC1 isdistributedg 1quicklybetweenloadcapacitanceC2 untilthevoltage
b hb loverbothbecomeequal Duringthisdistributionphase
i f di someenergyistransformedintoheat mainlybydampingresistanceR (determinesresistanceR1(determinesimpulsevoltagefrontT1)
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RR R1
C2C1 R2U0
Rv
u2 OnceC2 ischarged,voltagehasreacheditsmaximumvaluereacheditsmaximumvalue(impulsevoltagepeakUp)
Next,thedischargephasestarts.Remainingenergyistransformedi t h t i l i di h intoheatmainlyindischargeresistanceR2(determinesimpulsevoltagetailT2).
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Singlestageimpulsegeneratorreaches~100kVg g p g Forhighervoltagesbasiccircuitsareconstructedontopofeachothertocreaten stagegeneratorsg g
MarxGenerator ErwinMarx(1923)
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Capacitorsarechargedinparallel todesiredvoltageandfirstsparkgapistriggered Therapidchangeinpotentialcausesthesubsequentgapstoignitecausing
R'D
R''D
thesubsequentgapstoignitecausingthestagesto beconnectedinseries Cumulativevoltageischarging
R'E
C'
G
(applied)voltagetimesnumberofstages
R'C
R'D
R'E
CS
CBG
( )tuO
R'C
R'D
R'
C'S
GR
E
C'S
R'C
UC
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3StageImpulseVoltageGenerator
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R' D
R'' D
R' D
R'' D
R' D
D
R' E
C' S
G
R' D
R' E
C' S
G
R'
R'C
D
R' E
C' S
CBG
( )tuO
R' D
R' CR' E
C' S
CBG( )tu
O
R' C
R D
R' E
C' SR' CU C
GGR' C
D
R' E
C' SR' CU C
G
SCC
Charging Discharging
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Charging
Discharging
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U1.00.9
0.5
0.3
0
T1 T2
t
DampingresistanceR1 andloadcapacitanceC2determinefronttimeT andtimetopeakTdeterminefronttimeT1 andtimetopeakTpDischargeresistanceR2 andsurgecapacitanceC determinetimetohalfvalueTcapacitanceC1 determinetimetohalfvalueT2(tailtime)
R limitscurrenttoprotectsource
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R c limitscurrenttoprotectsource
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ImpulseCurrentSources
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IfthecapacitorCischargedtoal V ddi h d h h voltageVanddischargedwhenthe
gapGistriggered.thecurrenti canbeshowntovarywithtimebeshowntovarywithtimeaccordingtotherelation:
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