Current transformer

To connect current transformers to the measuring devices or controllers, please consider the following factors:

  • Dimensioning
  • Power
  • Current direction


The right dimensioning is important for the current transformers' primary current. If the current transformer is too small, meaning the primary current is too high, this will result in saturation. If it is too large, the primary current will not be sufficient to induce an adequate secondary current.


A current transformer's power in VA depends on its design. For operation of the internal measuring transformer, you have to ensure at least about 0.3 VA of power at the measurement system (multimess, multicomp). Please also note the great influence the transformer line has on the power:

Consumption of transformer lines

Cross section mm² Cu /5A  /1A  Explanation: 
1 1 0,04  A transformer supplying a measuring device at a distance of 10 meters with a 2.5mm² Cu cable requires a power of at least 4.1 VA (=10*0,41) for the line alone.
The measuring device itself requires power as well.
1,5  0,685  0,0274 
2,5  0,41  0,0164 
0,254  0,0102 
0,169  0,068 
10  0,0975  0,0039 
16  0,062  0,0025 


Current direction

Connect the transformer lines K and L to the measuring devices in distribution measurements so that a positive current is displayed. In individual cases, for example large regenerative drives, current may flow in braking operation as well. In this case, if everything is connected correctly, the current is displayed as a negative value.

For input measurements, make the connection in such a way that consumption is displayed as a positive current/power value.

For measurements in distributed power generation systems, make the connection in a way ensuring that the current is displayed as a positive value in operation (=supply) as well.

Connection of switchgear couplings is at the user's discretion. However, you have to choose the drawing object in visual energy 4 taking the correct current direction into account. For this reason, the switchgear containing the measuring device is usually defined as the output, the remote station as the input and the measuring device is connected accordingly.


Incorrect connection of a compensation controller results in erroneous control behavior and incorrect connection of measuring devices results in incorrect balance sheets in visual energy 4!

Aron - circuit

You can find the connection diagrams of the multimess devices here.

Two compensation systems on a coupled busbar

The illustration below shows a transformer circuit with two compensation systems in one network that are coupled together on a busbar with a section switch: