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.

Fullwaverectifier convertsbothpolaritiesofinputwaveformintoDCp

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VOLTAGEDOUBLERVOLTAGEDOUBLER

twohalfwaverectifiercircuitsareconnectedinopposition,thusproducinganunsmoothedunidirectionalvoltage.Theoutputvoltagehasa

k l f V

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peakvalueof3Vs

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

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

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

ImpulseCurrentSources

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IfthecapacitorCischargedtoal V ddi h d h h voltageVanddischargedwhenthe

gapGistriggered.thecurrenti canbeshowntovarywithtimebeshowntovarywithtimeaccordingtotherelation:

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