ABB PQFS Installation, Operation And Maintenance Instructions page 157

Under exceptional conditions it is possible that the active filter is showing a 100%
load indication whereas its nominal RMS current rating is not yet attained. This is
because the filter has reached an operating limit other than the RMS current limit.
Possible other limits are:
•
Temperature limit due to a too high ambient temperature or a failing cooling
system.
•
Peak current limit due to an a-typical peak current requirement of the load.
•
Peak voltage limit due to an a-typical DC-link voltage requirement of the load
or due to a high network voltage.
Under all these conditions, the filter will run in limited mode and may not attain
100% of its nominal current rating.
−
Harmonics put in 'standby' by the filter system:
When selecting a harmonic that has not been selected before, the filter will
identify the network characteristics for this harmonic. After this process, the
filter will launch the filtering process for the component considered. If during the
network identification process for a given harmonic a special (problematic)
condition is encountered, the system puts the component in 'standby'. In that
case the harmonic selected is not filtered for the time being. Special network
conditions include extremely high impedance of the supply network or extremely
low impedance towards the load. When consulting the harmonic selection table
of the PQF-Manager, harmonics put in 'standby' can be recognized by the label 'S'
that is displayed in the harmonic selection column (which reads otherwise either
'Y' or 'N'). The following possibilities exist to bring a harmonic out of standby:
•
The user restarts a network identification process by changing the 'S'
indication into a 'Y' indication in the harmonic selection table.
•
The filter automatically restarts an identification process on all harmonics
that were put in standby previously when a successful identification of
another harmonic is made. As a result, the harmonic considered will be
automatically filtered when the network conditions allow for this.
−
If plain capacitors (i.e. capacitor banks not incorporating detuning reactors) are
present in the network it is recommended to switch them off or change them into
detuned banks. Sometimes, the commissioning engineer is faced with an
installation where both an active filter and plain capacitors are present however.
While this is an ill-advised and a technically unsound situation, ABB has
acknowledged that in this case also the active filter should aim to give an optimal
performance. For this reason the control software of the filter incorporates a
Stability Detection Program (SDP) that aims to increase the filter performance in
this type of applications.
In installations where plain capacitors are present and cannot be switched off or
changed to detuned capacitor banks, adhere to the recommendations below for
optimal results.
Manual Power Quality Filter PQFS  Commissioning instructions 157