42
AFQm
Instruction Manual
harmonics measured in the load by a safety factor (FS
h
). In other words:
I
FiLTER
(AFQm) = [FS
h
* I
LOaD
* THD(I)]
Where:
I
FILTER
(AFQm): rated current of the active filter.
FS
h
: safety factor > 1.2.
I
LOAD
: maximum current of the load.
THD(I): harmonic distortion of the load current.
Equation 6:Rated current of the AFQm.
To calculate this safety factor you must first know the parameter called short-circuit ratio R
SC
, at the
connection point of the PCL transducers (not on the installation input). The short-circuit ratio is de-
fined as the ratio between the short-circuit current of a mains (I
SC
) and the rated current of the set of
non-linear transducers (I
CNL
) producing the harmonics to be filtered.
(Equation 7)
% =
1
∗100
% =
1
∗100
=
�
1
2
+
2
2
+
3
2
+
5
2
+ ⋯
=
�
1
2
+
2
2
+
3
2
+
5
2
+ ⋯
(
)
% =
�
2
2
+
3
2
+
5
2
+ ⋯
1
(
)
% =
�
2
2
+
3
2
+
5
2
+ ⋯
1
=
−
(
)
=
[
ℎ
∗
∗()
]
=
Equation 7:Calculating the short-circuit ratio R
SC
.
In a real installation, the short-circuit current (I
SC
) in the PCL can be assessed by having the voltage at
the said point for two different load currents.
For example, full load, I
A
and 10% load, I
B
. If V
OC
is the rated voltage at no-load, the I
SC
, can be calculated
using the formula shown in Figure 35:
Figure 35:Graph for calculating I
SC
.
The safety factor (FS
h
) can be obtained from the graph in Figure 36:
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