Why do I need a vector diagram?

Modern reference standards and calibration devices have usually a graphical function to show the relationship between the voltages and the currents. Most equipment manufacturers call this function vector diagram or vectorial diagram.
In fact it is a phasor diagram. It represents a the phase relations of a sinusoidal rotating system at a certain time.
The system rotation (everything inside the circle) is anti-clockwise. The graph is shown either with

  • current phase L1 in zero degrees position
  • voltage phase L1 in 90° position

Actually the vector diagrams in test equipments are showing only the angles and not the amplitude of the phases. The reason behind is that you won’t see very small current vectors with the given resolution. Anyway, we can nicely read all amplitude values from the instrument. Common practice is to show the voltages with higher amplitude than the currents (voltages are on the outer circle).

Main use for vector diagrams is to check the proper connection of the instrument before you make error measurements.
If you see e.g. that the current of a phase is in opposite to the voltage, it is likely possible that the current clamp is connected in the wrong direction.

The simulation below is kept very simple. You can set the phase angles between I and U, the phase sequence and the reference for the system. The power values are calculated based on your settings.

phase L1 phase L2 phase L3
reference sequence

With a right-click on desktop PCs you can save your drawing(s).

Why do I need a vector diagram?
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Published by

Lao Ren

more than 30 years experience in energy metering Product Director Shenzhen CLOU Electronics

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