Why do I need a Vector Diagram?

Modern reference standards and calibration devices usually have 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 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.
Click the “DRAW” button to begin the animation.

L1 L2 L3
Angle I-U
reference sequence

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

Editor's note: This article was originally published in July 2019 and has been updated for comprehensiveness.

One Reply to “Why do I need a Vector Diagram?”
  1. Thanks, you are right with this typical problems. How we can make this problems most of users can detect, meaning both, Utility and users.

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