MOV的使用指导.docx

MOV的使用指导.docx

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MOV的使用指导

MOVbasedprotectioncircuitdesignguideline

TableofContents

Introduction3

1.Singlephase120VACprotectioncircuitdesign3

1.1Designparametersforsinglephase120VACprotectioncircuit3

1.2.MOVselectioncriteria4

1.3CalculatingpeakMOVcurrentduring6kV,3000Abi-wavesurgeevents5

1.4SimulatingpeakMOVcurrentduring6kV,3000Abi-wavesurgeevents7

1.5Determiningthenumberofequivalent6kV,3000Abi-wavesurgeevents8

1.6MOVselectionrefinementbaseduponagreedandestablishedpassandfailcriteria9

1.7Fuseselectionrequirements12

1.8GasDischargeTube（GDT）selectionrequirements14

1.9SparkGapselectionrequirements16

2.Twophase240VACprotectioncircuitdesign17

2.1.Designparametersfortwophase,240VACL1-L2protectioncircuit17

2.2MOVselectioncriteria18

2.3CalculatingpeakMOVcurrentduring6kV,3000Abi-wavesurgeevents19

2.4SimulatingpeakMOVcurrentduring6kV,3000Abi-wavesurgeevents19

2.5Determiningthenumberofequivalent6kV,3000Abi-wavesurgeevents19

2.6MOVselectionrefinementbaseduponagreedandestablishedpassandfailcriteria20

2.7Fuseselectionrequirements21

2.8GasDischargeTube（GDT）selectionrequirements21

1.9SparkGapselectionrequirements21

Introduction

ThisdocumentdescribesaselectionprocedureforanMOVthatistoprovideaprotectionforspecificcontroldeviceduringsurgeeventsonthepowerline.ThegoalistoselectMOVdevicescapableofwithstanding（orfailingsafely）thesurgetestsasoutlinedinETP910testprocedure,whilesimultaneouslyprovidingspecifieddegreeofprotectiontocontrolcomponentsplaceddownstreamfromsaidMOVs.

1.Singlephase120VACprotectioncircuitdesign

1.1Designparametersforsinglephase120VACprotectioncircuit

Linevoltage:

120VAC+-10%

Surgegenerator:

Ringwave3kV,250A,12ohmsinternalimpedance

Ringwave6kV,500A,12ohmsinternalimpedance

Bi-wave3kV,1500A,2ohmsinternalimpedance

Bi-wave6kV,3000A,2ohmsinternalimpedance

Surgeapplicationmodes:

Line1toNeutral（L1-N）

Line1toEarthGround（L1--G）

NeutraltoEarthGround（N--G）

Line1andNeutraltoEarthGround（L1&N-G）

Timedelay/modestested:

Ten（10）secondsdelaybetweenringwavesurgeevents.

One

（1）minutedelaybetweenbi-wavesurgeevents.

TheEUTtestedonaverageinthree（3）modes.

Noofsurgesperconnection:

L1-N180ringwavesurges（3kV,250A）

180ringwavesurges（6kV,500A）

18bi-wavesurges（3kV,1500A）

18bi-wavesurge（6kV,3000A）

L1—G180ringwavesurges（3kV,250A）

180ringwavesurges（6kV,500A）

18bi-wavesurges（3kV,1500A）

18bi-wavesurge（6kV,3000A）

N—G180ringwavesurges（3kV,250A）

180ringwavesurges（6kV,500A）

18bi-wavesurges（3kV,1500A）

18bi-wavesurge（6kV,3000A）

L1&N-G180ringwavesurges（3kV,250A）

180ringwavesurges（6kV,500A）

18bi-wavesurges（3kV,1500A）

18bi-wavesurges（6kV,3000A）

Levelofprotection:

1kV（peak）differentialmode

Itisassumedthatunprotectedcontrolelectronicscanwithstandvoltagetransientsasdescribedabove.

Circuitdiagram:

Figure1–SchematicdiagramofMOVbasedprotectioncircuitforsinglephase120VACapplications

NoofsurgesperMOV:

L1-NMOV360ringwavesurges（3kV,250A）

360ringwavesurges（6kV,500A）

36bi-wavesurges（3kV,1500A）

36bi-wavesurge（6kV,3000A）

N-GNDMOV540ringwavesurges（3kV,250A）

540ringwavesurges（6kV,500A）

54bi-wavesurges（3kV,1500A）

54bi-wavesurge（6kV,3000A）

1.2.MOVselectioncriteria

Numberofsurgeevents-ItisclearfromtestdescriptionabovethatselectedMOVswillbeexposedtoalargenumberofsurgeeventswithhighpeakcurrentvalues.AfirstselectioncriterionistopickanMOVfamilythatisspecificallydesignedforrepetitivesurgeapplicationswithhighpeakcurrents.ForexamplewecannarrowourselectiondowntoC-IIIseriesMOVsmadebyLittelfuse,sincetheyarespecificallydesignedforrepetitivesurgeapplications.

MOVoperatingvoltage（VAC）-ForU.S.powergrid,thelinevoltageisspecifiedat120VAC+10%,-15%.Wearemostlyconcernedwithpositivevoltagetolerance;negativevoltagetolerancehasnoimpactonMOVvoltageratingselection.ThehighestRMSvoltageexpectedonUSpowergridis132VAC（RMS）.Toprovideadequatemargin,wemayselect150VAC（RMS）ratedMOVs.WecanfurthernarrowourcomponentselectiondowntoV150sub-serieswithinC-IIIseriesofMOVsmadebyLittelfuse.

MOVwithstandingenergy（J）-ItisapparentfromtestdescriptionabovethatselectedMOVswillbeexposedtoalargenumberofsurgeeventswithhighpeakcurrentvalues.Theserepetitive,high-energysurgeeventsdemandhighwithstandingenergyofselectedMOVs.Toensureadequateprotectionforelectroniccomponentsthroughoutcompletedurationofthesurgetest,weinitiallymayselectthehighestwithstandingenergyMOVswithinchosensub-family（justasastartingpoint）.MorespecificallywemayselectV150LA20CPpartnumberwithinV150sub-seriesofC-IIIseriesofMOVsmadebyLittelfuse.RefertotheexcerptfromtheMOVspecificationshownbelow.

Table1–V150LA20CPMOVspecification（courtesyofLittelfuse）

Observethatselectedpartcanwithstandupto215J.AsourdesigngetsrefinedwemayopttoselectV150LA10CPwithwithstandingenergyof100JorV150LA5CPwithwithstandingenergyof50J.RefertotheexcerptfromtheMOVspecificationsshownbelow.

Table2–V150LA5CPandV150LA10CPMOVspecifications（courtesyofLittelfuse）

Thefinalcomponentselectionwillbebasedonthefollowingparameters:

1.PeakMOVcurrentduring6kV,3000Abi-wavesurgeevents.

2.Thenumberofequivalent6kV,3000Abi-wavesurgeeventsMOVmustwithstandbeforeitfails.

3.RepetitivesurgecapabilityforspecificMOVfamily.

4.Passandfailcriteriaforspecificsurgetest,orwhatareacceptancecriteriaforeachtypeofsurgetest.Forexample-itmaybeacceptableforMOVtofailsafeduring6kV,3000Abi-wavesurgetest,butitmustpassallothersurgetests.

1.3CalculatingpeakMOVcurrentduring6kV,3000Abi-wavesurgeevents

Thepeakcurrentgeneratedbysurgegeneratorundershortcircuitconditionsisgivenbelow.Observethatinternalresistanceofsurgegeneratoris2ohms.

（1）

ThecurrentthroughtheMOVwillbethehighestiftheMOV“clamps”thevoltageatthelowestlevel.Thisistheworstcase.DuetothepresenceofMOVinthecircuitthesurgegeneratorcurrentwillbereducedtoavaluesmallerthantheshortcircuitpeakcurrentdefinedabove.ThepeaksurgegeneratorcurrentiscalculatedbyselectinganoperatingpointonMOVV/IcurveasshowninFigure2:

（2）

CalculatingpeakMOVcurrentisaniterativeprocess.ThegoalistofindcorrectoperatingpointontheMOVV/Icurve.Thisissomewhatanimpreciseprocessgiventhatthescalesarelogarithmic,soadditionalcautionanddiligencemustbeexercised.Thestepsareasfollows:

1.DesignerselectsanoperatingpointonapplicableMOVcurve.

2.Horizontallineisdrawnpassingthroughtheoperatingpointandintersectingvertical（voltage）axisofthegraph.

3.ThepointwheredrawnlineintersectsvoltageaxisdefinestheMOVclampingvoltage.

4.MOVclampingvoltageissubstitutedintoequation

（2）andpeakMOVcurrentiscalculated.

5.Verticallineisdrawnpassingthroughselectedoperatingpointandintersectinghorizontal（current）axisofthegraph.

6.IfoperatingpointcurrentontheV/Igraphandcalculatedvalueofcurrentmatch,theprocessiscomplete.Otherwiseanewoperatingpointisselectedandsteps1–6arerepeated.

Inthisspecificexampleabove,operatingpointforV150LA20C（P）ischosenbyfollowingthird（3rd）curvefromthebottomandobservingwherethecurveintersectsapproximately3000Acurrentmarking.TheMOVclampingvoltageatthatcurrentisapproximately500V.Thediscrepancyofpredictedandcalculatedpeakcurrentvalueisacceptablegivenlogarithmicscale.RefertoFigure2shownbelow.

Figure2-V/IcharacteristiccurvesforC-IIIseries,20mmdiameterMOVparts（courtesyofLittelfuse）

1.4SimulatingpeakMOVcurrentduring6kV,3000Abi-wavesurgeevents

AlternatemethodtodeterminepeakMOVcurrentinvolvescreatinganequivalentcircuitmodelinPSPICEbasedcircuitsimulationsoftware,importingdesiredMOVPSPICEmodel（s）,andperformingPSPICEsimulation.TheMOVPSPICEmodelsareavailableatrespectivemanufacturer’swebsite.TheresultsofcircuitsimulationareshowninFigures3-5.

ToMOV

6000VDC

Figure3–Schematicdiagramofsurgegeneratorequivalentcircuit

Figure4–Shortcircuitresponseofsurgegeneratormodel.Observepeaksurgevoltageofapproximately6000V（greentrace）andpeaksurgecurrentof3000A（redtrace）

2.74kA

516V

Figure5–SimulatedMOVpeakcurrentandMOVclampingvoltage

Observethatcalculatedandsimulatedpeakcurrentsandclampingvoltagesareveryclosetoeachotherwhichprovidesadditionalconfidenceinvalidityofourassumptions,calculationsandsimulations.Morespecifically:

CalculatedMOV“clamping”voltage=500VCalculatedpeakMOVcurrent=2.75kA

SimulatedMOV“clamping”voltage=516VSimulatedpeakMOVcurrent=2.74kA

1.5Determiningthenumberofequivalent6kV,3000Abi-wavesurgeevents

VastmajorityofMOVmanufacturersderatetheircomponentsbasedupon6kV,3000Abi-wavesurgeevents.Inadditionto6kV,3000Abi-wavesurgetest,GEalsoadministers3kV,1500Abi-wavesurgetest,3kV,250Aringwavesurgetest,and6kV,500Aringwavesurgetest.Thereisaneedtodeviseamethodtoconvertalltestedsurgeeventsintoequ