Why are the Measured Values Negative When Measuring a Balanced Three-Phase Load?

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.

Please download and refer to the attached document for more information.

Related Products & Solutions

Precision Power Analyzer WT3000

With 0.02% accuracy and 1MHz bandwidth, the WT3000 delivers where the highest precision measurements are required. It is the industry standard for R&D work on inverters, motor drives, lighting systems and electronic ballasts, UPS systems, aircraft power, transformer testing, and other power conversion devices.

WT1800 High Performance Power Analyzer

The WT1800 High Performance Power Analyzer from Yokogawa Test&Measurement offers maximum flexibility with up to six wattmeter elements, high bandwidths, simultaneous high speed digitizing, and wide voltage and current ranges. Although this model is still available, the newer WT1800E offers higher accuracy.

WT2010/WT2030 Digital Power Meters

The WT2000 digital powermeter series has been designed with emphasis on basic performance (bandwidth, accuracy, response speed, and noise immunity) from the viewpoint of measurement of electrical quantities. The broad range of functions of these power analyzers enable them to be used in various fields of applications.

WT500 - Mid Range

  • Power and Harmonic (THD) Measurements with Independent Range Controls
  • Efficiency measurements of AC/DC or DC/AC Inverters & Motors

 

Power Analyzers and Power Meters

Measure characteristics of devices that generate, transform or consume electricity. Also called power meters or wattmeters, these devices measure parameters such as true power (watts), power factor, harmonics, and efficiency.

Precision Making

Top