YOKOGAWA WT310EH - Page 89

6-7
IM WT310E-01EN
Harmonic Measurement (Option)
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App
Index
Note
• IfthefundamentalfrequencyofthePLLsourcecannotbemeasuredduetofluctuationsordistortion,
correct measurement results cannot be obtained. We suggest that you set the PLL source to the voltage,
which has relatively smaller distortion than the current.
• Ifthefundamentalfrequencyis200Hzorlessandhighfrequencycomponentsarepresent,wesuggest
thatyouturnonthefrequencyfilter(500Hzcutofffrequency).
• IftheamplitudeofthePLLsourceinputsignalissmallcomparedtotheratedrange,PLLsynchronization
mayfail.ChangethemeasurementrangesothattheamplitudelevelofthePLLsourceis50%orhigher
thantheratedrange(100%orhigherifthecrestfactorissetto6or6A).
Measured Harmonic Order
Youcansettheupperlimitofmeasuredharmonicorderintherangeof2to50.However,therange
varies depending on the fundamental (1st harmonic) frequency. This is because the upper limit of
harmonicsthatarecomputedvariesdependingonthefundamentalfrequency.Thedefaultvalueis50.
Example
• Upto50whenthefundamentalfrequencyis50Hz
• Upto4whenthefundamentalfrequencyis1.2kHz
Note
• Whenaharmonicorderexceedingtheupperlimitisspecified,displayBshowshyphens(-----).
• Fordetailsontheupperlimitofmeasuredharmonicorder,seesection7.3intheGettingStartedGuide,
IM WT310E-02EN.
THD equation
Select the THD equation from below. The default value is iEC.
Thefollowingexplanationisforwhentheupperlimitofmeasuredharmonicorderis50.Iftheupper
limitislessthan50,computationisperformedtotheupperlimit.
• iEC:Computestheratioofthermsvalueofthe2ndto50thharmoniccomponenttothatofthe
fundamental (1st order).
• CSA:Computestheratioofthermsvalueofthe2ndto50thharmoniccomponenttothatoftherms
valueofthe1stto50thcomponent.
Equation
iEC
/C1
n
k=2
(Ck)
2
×100
CSA
/
n
k=2
(Ck)
2
n
k=1
(Ck)
2
×100
• C
1
: Fundamental (1st harmonic) component
• C
k
: Fundamental or harmonic component
• k: Measuredharmonicorder
• n:Upperlimitofmeasuredharmonicorder.Thisvaluevariesdependingonthefundamental
frequency of the PLL source.
6.3 Setting the PLL Source, Measured Harmonic Order, and THD Equation