Operating Principle; Rated Current Dimensions - Circutor AFQm IP54 Serie Manual De Instrucciones

4.2.- OPERATING PRINCIPLE

Active filters are based on the following principle:
In other words, they detect the difference between the desired sine wave (I
signal deformed by the harmonics (I
shows the wave shapes of the currents injected by the active filters.
Figure 22
These show the required wave (I

4.3.- RATED CURRENT DIMENSIONS

The purchased active filter must be sized for the harmonic currents it has to filter. The rated current of
the AFQm IP54 must be at least 20% higher than the maximum level of harmonics to be filtered. This
factor may be higher depending on the installation features.
The active filters can suffer from overloading when trying to cancel the harmonic currents in high-im-
pedance, short-circuit mains. The clearest symptom for detecting such cases is that they originally
start from a THD(V) (under voltage) of over 3%. It has been seen that the higher the initial THD(V), the
greater the chance of filter overload.
The reason for this behaviour is that the load does not behave as a current source, but rather the larger
the harmonic current absorbed by the filter the more harmonics are produced by the load, which can
produce up to more than double what was initially measured.
116
I = I
FILTER MaINS
Equation 5: Operating principle.
). And they inject the difference between both waves (I
LOAD
), the existing deformed wave (I
M
aINS
Figure 22: Current in the load, in the filter and in the mains.
- I
LOaD
M
aINS
) and the filter current (I
LOAD
AFQm IP54
) of the current and the
).
FILTER
).
FILTER
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