Three Phase Power MeasurementsWord下载.docx
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Three Phase Power MeasurementsWord下载.docx
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3.0DEFINITIONS
3.1NotApplicable
4.0REQUIREMENTS
4.1ThefollowingisalinktotheTroubleShootingGuidedocument.
DiagnosticsandTroubleShootingGuide
5.0RELATEDDOCUMENTS
5.1L09-0198–Unitary–RecommendedUseFor“AutomaticLoadSwitchBoxes
5.2ThreePhasePowerMeasurements:
6.0REVISIONHISTORY
6.1RevisionA–3/8/04
DiagnosticsandTroubleShootingGuide
TABLEOFCONTENTS:
I.INTRODUCTION
A.Purpose&
Scope
B.Objectives
II.COMMONPRACTICES
A.ThreePhaseDesignations
B.ColorCodes
C:
CurrentTransformersSecondaryLeads
III.WATTMETERWIRINGDIAGRAMS
A.TwoCoilWattmeterMethod
B.WT130ConnectionDiagram
C.2505ConnectionDiagram
IV.CURRENTTRANSFORMERS
A.WestonType2andType5
B.ITITopTapandPass-ThroughCT
C.YEW_2241CT
V.“BAD”METERREADINGS
A.CurrentPhasesMixed-up.
B.VoltagePhasesMixed-up.
C.DiagramofVoltageandCurrentVectors
D.TroubleShootingTIPS
VI.TROUBLESHOOTING:
What’stheProblem?
A.IsItaPhasingPROBLEM?
B.ZeroornearzeroReadings.
C.“Bad/Goofy”Readings.
D.NegativePowerReadings.
VII.APPENDIX
A.VoltagePhaseShifts:
B.CurrentPhaseShifts
C.WattmeterPowerReading
D.Line-VoltageandLine-CurrentVectors
E.PowerMeterVoltageandCurrentVectors
ByFredAhlstrom
Date:
Feb27,2004
Scope:
This“TroubleShootingGuide”isintendedtoassistthereaderintheunderstandingofthreephasepowermeasurementsandbeaguidetohelpdeterminepossiblecausesoferroneouspowermeterreadings.
Thisdocumentdealswiththree-phasepowermeasurementsusingthethree-wire,two-metermethod.ThemethodgenerallyusedbytheLaCrosselaboratory.
WorkprocedureL09-0198--Unitary-RecommendedUsefor“AutomaticLoadSwitchBoxes”coverstheload-switch-boxwiringandtheinstallationofcurrenttransformers.This“TroubleShootingGuide”includesmuchofthesameinformation.
Thoughsometechnicaldefinitionsandinformationonvectoranalysisispresented,thisdocumentisnotatechnicalpaper.
Ifyouarelookingfortechnicalinformation,theoreticalderivations,mathematical“proofs”,etc.,thenrefertoanygoodtextoncircuitanalysis.
Chapter12-6;
POWERMEASURMENTINTHREE-PHASESYSTEMS;
B.Objective:
Theobjectiveofthisdocumentistoassistyouinunderstanding,diagnosingandtroubleshooting“bad”wattmeterreadings.Also,someofourcommonpracticesandmethodsaredocumented.
Thebestwayto“troubleshoot”isto“DoitRighttheFirstTime”.
“Phasing”problemsareoftenthecauseof“Bad”powermeterreadings.Thisdocumentcanbeusedasareferenceguideforthecorrectinstallationofcurrenttransformers,andasaguidetoverifycorrectpowermeterwiring.
A.Threephasedesignations
Typically,thethreeleads,inthree-phase,three-wirepowersystemsarereferredtoasLine-A,Line-B,Line-Corleg-A,leg-B,leg-C,orphase-A,phase-B,phase-C.
Lineorlegispreferred,becausephase-voltageandphase-currentarenotthesameasline-currentandline-voltage.
Othercommondesignationsofthethreelinesare:
abc
L1L2L3
T1T2T3
RST
Useconventional:
LefttoRight;
ToptoBottom;
orClockwise.
LefttoRight.ToptoBottom.Clockwise.
ABCAAB
BC
C
B.ColorCodes:
Thereisnotauniversalcolorcode.
Commoncolorcodes;
B.O.Y.orR.W.B.ornone.
A=B.(brown)R.(red)
B=O.(orange)W.(white)
C=Y.(yellow)B.(black)
BOYisusuallycoloredtapeonlargersizewires.
RWBisthecolorofwireinsulationonsmallerwires.
C:
CurrentTransformersSecondaryLeads:
TheCurrentTransformer(CT)Secondaryleadsshouldbelabeled:
“A±
”&
“A”and“C±
“C”
Theletter“X”or“x”isoftenusedfor“±
”symbol.
Ax=A±
ColorscommonlyusedareRed,White,andBlack.
GoodpracticeistousepairsofRed/WhiteandBlack/White.Thewhiteleadisinstalledonthe“non-±
”terminal,thegroundedterminal.
Preferred,Red/WhiteonCT-AandBlack/WhiteonCT-C.
B.WT130ConnectionDiagram
C.2505WattmeterConnectionDiagram
A.WiringDiagramforWestonType2andType5CurrentTransformers
WESTONTYPE2WESTONTYPE5
PrimaryTaps:
Thenumberedterminalsandthe“±
“terminal(top)aretheprimarytaps.Inthe“passthrough”arrangement,thenameplate-sideoftheCT(seephoto)istheLINE-side.
(Noticethe±
signonthenameplate)
SecondaryTaps:
Theothertwoterminalpostsarethesecondarytaps.Anunmarkedoneanda“±
”one.
CurrentTransformersmusthavethesecondarytaps“shunted”.Ifnot,theywill“burnup”
Thereisasecondaryshunt(slidejumperswitch)betweenthesecondaryterminalposts.Inuse,thisswitchmustbeOPEN.Theloadswitchboxorthewattmeter’scurrentcoilsprovidestheshunt.
B.ITITopTapandPass-ThroughCT
ITItopTapCTITIPass-Through
The“H1”and“H2”terminalsaretheprimarytaps.
Inthe“passthrough”arrangement,the“nameplate”-sideoftheCT(seephoto)istheLINE-side.(Noticethe“H1”moldedintheCTcase,left-sidecenterofhole.)
The“X1”and“X2”terminalsarethesecondarytaps.The“X1”isthe“±
”.
CurrentTransformersmusthavethesecondarytaps“shunted”.Ifnot,theywill“burnup”
Theloadswitchboxorthewattmeter’scurrentcoilsprovidestheshunt.
C.YEW2241CT
YEW2241:
topviewYEW2241:
“L”(line)sideofhole.Notice:
“L”abovehole.
Thenumberedterminalsandthe“L”(±
)terminalaretheprimarytaps.Inthe“passthrough”arrangement,the“L”-sideoftheCT(seephoto)istheLINE-side.(Thereisa“L”abovethehole.)
Thetwoterminalslabeled“5A”&
“±
”arethesecondarytaps.
CurrentTransformersmusthavetheirsecondaryleads“shunted”.Ifnot,theywill“burnup”
TheswitchontopoftheCTisasecondaryshunt(jumper).Inuse,thisswitchwillbe“OPEN”.Theloadswitchboxorthewattmeter’scurrentcoilsprovidestheshunt.
V.“BAD”METERREADINGS
A.ReadingswithCurrentPhasesMixed-up.
B.ReadingswithVoltagePhasesMixed-up.
D.Troubleshootingtips
Manyproblemshavesimplesolutions.Don'
timmediatelyassumethatyourproblemissomecombinationofesotericcomplexconvolutedfailures.Itmaybeassimpleasshuntswitchesorablownfuse(s).
Because,therearemanywaysthatthingscanbewrong,thebestwayto“de-bug”or“troubleshoot”isto“doitrightthefirsttime”.And,thebestwayto“troubleshoot”maybetoinspect/traceeachCTandVoltagelead.
A.IsitaPhasingPROBLEM?
“Bad”wattmeterreadingscanbecausedbyproblemsotherthan“phasemix-ups”.
1.Somepossiblecauses:
Fuses:
Mainpower;
Unitundertest,internal;
Wattmeter,internal;
Voltageleadlines.
Other?
Looseconnections:
Voltageleads;
CTleads,primaryorsecondary;
Unitundertest.
Wattmeter:
Incorrectconfiguration;
scalingshouldbeoff.
Ranges;
notover-ranged.
Voltageelementdead;
Currentelementdead;
Other?
Currenttransformers:
ShuntedatCT;
oratloadswitchbox.
Range(ratio)sameforeach,andcorrect.
CT’saredead.
LoadSwitchBox:
Contactorsfailtoenergize;
Contactorsfailedclosed;
Poweroff.(120V)
2.VoltageRea
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