To identify the correct installation orientation for a current transformer, determine the direction of energy flow in the cable you are measuring. P1 indicates the side where the current source is located, while P2 indicates the load side.
Connections of the primary winding are designated "K" and "L" or "P1" and "P2", while connections of the secondary winding are designated "k" and "l" or "S1" and "S2". The polarity must be established so the "flow direction of energy" runs from K to L.
Accidentally swapping the S1/S2 terminals can produce erroneous measurements and cause incorrect control behavior in Emax and PFC systems.
Fig.: Installation orientation of current transformers
Fig.: Direction of energy flow
The power consumption (in watts) caused by line losses can be calculated as follows:
Note that with every temperature change of 10°C, the power consumed by the cables increases by 4%.
You can calculate consumption using this equation:
Pv = UMG 1 + UMG 2 +....+ PLine + PTerminals ....?
When carrying out measurement via two current transformers, the overall transformer ratio of the current transformers must be programmed into the measuring device.
Example: Both current transformers have a ratio of 1,000/5 A. The total measurement is carried out using a summation transformer 5+5 / 5 A.
The UMG setup should be:
Primary current: 1,000 A + 1,000 A = 2,000 A
Secondary current: 5 A
According to VDE 0414, current and voltage transformers should be secondary grounded from a series voltage of 3.6 kV. For low voltage, grounding can be omitted if the current transformers do not have large metal contact surfaces. However, it's common practice to ground low voltage transformers too, typically on S1. Grounding can also take place on the S1(k) or S2(k) terminal. Important: Always ground on the same side!
If you are retrofitting a measuring device and only have a protective core available, we recommend using a winding current transformer 5/5 for decoupling the protection core. This ensures accurate measurements while preserving the safety functionality of the protection transformer.