YOKOGAWA WT310EH - Page 130

App-24
IM WT310E-01EN
Error in Three-Phase Power
The error when measuring power of a three-phase, three-wire system using elements 1 and 3 of the
WT332E/WT333E is explained with the next example.
• Voltagemeasurementrange:150V,measuredvoltage:100VforU1,U3,andUΣ
• Currentmeasurementrange:1A,measuredcurrent:0.8AforI1,I3,andIΣ
• Measuredpower:P1=69.28W,P3=69.28W,PΣ=138.56W
• 60Hzsinewaveforbothvoltageandcurrent
• Phasedifferencebetweenthevoltageandcurrentsignals=0°
• Phaseanglebetweenphases=60°
Three-Phase Measurement Range
Forthethree-phasemeasurementrange,refertothetableofΣfunctionequationsonpageApp-2.
This table shows the expressions that the WT332E/WT333E uses to internally calculate the measured
values. This table also applies to how to think about the measurement range. In this example, we will
apply the three-phase, three-wire (3P3W) column.
Voltage and Current
Three-phasevoltage(UΣ)measurementrange=(U1measurementrange+U3measurementrange)/2
=(150+150)/2=150
Three-phasecurrent(IΣ)measurementrange=(I1measurementrange+I3measurementrange)/2=(1
+1)/2=1
Thereadingerrorandrangeerrorincludedinthemeasuredthree-phasevoltage(UΣ;100.00V)areas
follows:
• Readingerror:100.00[V]×0.1%=0.1[V]
• Rangeerror:150[V]×0.05%=0.075[V]
Theerrorincludedin100.00[V]isthesumofthereadingandrangeerrors,whichis±0.175[V].This
correspondsto0.175%ofthedisplayedvalue.BecausethemeasuredvaluesofU1andU3arethe
same,UΣalsohasthesameerror.Thesamecalculationmethodappliesforthecurrents.
Power
ReferringtothetableofΣfunctionequationsonpageApp-2,thepowerrangeisasfollows:
Three-phasepower(PΣ)measurementrange
=P1measurementrange+P3measurementrange
=(U1measurementrange×I1measurementrange)+(U3measurementrange×I3measurement
range)
=(150×1)+(150×1)
=300
Thereadingerrorandrangeerrorincludedinthemeasuredthree-phasepower(PΣ;138.56W)areas
follows:
• Readingerror:138.56[W]×0.1%=0.13856[W]
• Rangeerror:300[W]×0.05%=0.15[W]
Theerrorincludedin138.56[W]isthesumofthereadingandrangeerrors,whichis±0.28856[W].
Thiscorrespondstoapproximately0.208%ofthedisplayedvalue.
Appendix 5 Measurement Accuracy and Measurement Error