ABB PQFM, Instruction Manual

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68 Electrical design and installation  Manual Power Quality Filter PQFM
6.10.8 CT connections for the case that detuned capacitor banks are installed
adjacent but downstream to the active filter CTs
In some installations appropriately detuned capacitor banks are installed adjacent to the
active filter units, but they are connected downstream of the filter CTs. If this is the case
and if background distortion is present on the supply network then it is recommended
to connect the detuned capacitor banks physically upstream of the CT connections (Cf.
Figure 48 ). When this is not possible a CT arrangement can be made such that the
current flowing into the detuned capacitor bank is subtracted from the total current
measured by the filtering CTs. This is illustrated in
Figure 49 .
Feeding
transformer Filter CTs
Detuned
capacitor
bank
PQFx
+ -
Figure 50: Alternative connection approach for installations where detuned capacitor banks are
installed adjacent to the active filter but downstream to the active filter CTs
By using the approach shown in Figure 50 it is ensured that the filter performance
remains optimal without the loss of filter resources when background distortion is
present on the supply network.
6.10.9 CT connections for the case that passive filters and active filters are
installed in the same network
In installations where both passive filters and active filters are present, the CT
connection scheme of
Figure 51 must be used. If in practice the installation scheme of
Figure 52 exists, it must be modified as per the guidelines of Figure 53 .
Feeding
transformer Filter CTs
Linear and
non-linear
loads
PQFx
Passive filter
Figure 51: Recommended connection diagram for PQFM and passive filters