Why are the Measured Values Negative When Measuring a Balanced Three-Phase Load?
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In the three-phase three-wire, or 3V3A wiring scheme, the phase angle of voltage and current input to each input differs from that of the actual load because it is the line to line voltage that is measured.
In three-phase signals where the phase angle of voltage and current is 0°, if you wire the WT1600 for 3V3A:
- For input element 1, the phase difference of voltage and current is +30°
- For input element 2, the phase difference of voltage and current is -30°
- For input element 3, the phase difference of voltage and current is +90°(Notated with a + if the current lags the voltage, and a - if the current leads)
In an actual three-phase load, if the phase difference of phase voltage and phase current is α°, the phase difference of each input element of the power meter is:
- For input element 1, the phase difference of voltage and current is α° +30°
- For input element 2, the phase difference of voltage and current is α° -30°
- For input element 3, the phase difference of voltage and current is α° +90°
As for the total value of α (the phase difference of phase voltage and phase current in the acutal load) on a given element, the value α° +30°, or α° -30°, or α° +90° can be larger than 90°
In that case, the measured power value for that input element may be - (negative). However, this is due to the fact that the measureing method is "apparent" or "for purposes of line to line voltage measurement," and does not reflect the true value of the load, which can never by negative.
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