CIRCUTOR AFQ Series - Manual (Page 19)

AFQ-4W
Instruction Manual 19
Storage time Process
< 1 year No special treatment required.
1-2 years
Connect the AFQ-4W to the mains at least one
hour before starting up the unit.
> 2 years
Connect the AFQ-4W to the mains at least one
hour before starting up the unit. Restrict the
maximum load current to 5 mA.
Table 2: Start-up process depending on storage time.
3.4.- SIZING THE NOMINAL CURRENT OF THE AFQ-4W
The purchased active filter must be sized for the harmonic currents it has to filter.
The nominal current of the AFQ-4W 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-impedance, 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.
To avoid this phenomenon, it is best to oversize the active filter by multiplying the
initial current of harmonics measured in the load by a safety factor (SF
h
). In
other words:
I
filter
(AFQ) = [SF
h
· I
load
· THD(I) ]
Where:
I
filter
(AFQ): nominal current of the active filter
SF
h
: safety factor > 1.2.
I
load
: load maximum current
THD(I): load current harmonic distortion
Equation 1: AFQ-4W nominal current
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 defined as the ratio between the short-
circuit current of a mains (I
SC
) and the nominal current of the set of non-linear
transducers (I
NLC
) producing the harmonics to be filtered. ( Equation 2 )