Manual Power Quality Filter PQFS Electrical design and installation 47
6.8.2 Connection of the PQFS in 4-wire mode
Use the 4-wire connecting mode for installations where there is a need for neutral
current filtering and/or line to neutral balancing. In this mode, the active filter can
compensate 15 individual harmonic components.
In order to connect the PQFS in 4-wire mode, follow the guidelines of Section 6.8.1 with
the exception that:
4. Make also a hole for the neutral cable in the protective cover noting the larger section
required for the neutral.
6. Connect the three power cables and the neutral cable. Whereas the three power cables
can be connected as describes in item 6 of Section 6.8.1, the neutral cable has to be
connected to the neutral connection point (Cf. Figure 29).
Figure 29: Connection of the neutral cable when using the PQFS in 4-wire mode
The cable lugs for the neutral cables should comply with:
− Maximum lug width: in accordance with terminal width
− Minimum lug eye diameter: M8
Appropriate torque must be applied to ensure that cables are properly fixed.
Other points in the connection procedure are as per previous Section.
Remarks:
In case of regenerative loads (e.g. loads that may inject active energy to the
network, usually called 4Q-loads), it is very important to connect the PQF
outside the protection of this load. Indeed, consider Figure 30 where a common
protection is installed for both the regenerative load and for the PQF. When the
load re-injects energy to the network and the mains protection trips, the whole
energy may be pushed into the PQF, which may damage it severely. Figure 31
shows the admitted protection scheme for regenerative loads. In this case, if
the breaker of the load trips, the PQF is isolated from the energy fed back by the
drive.
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