Fuji Electric FRENIC-VG Series, User Manual

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6.6 High-Speed Serial Communication-Capable Terminal Block
6-151
Chap. 6
CO
NTR
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TIONS
6.6.12 Wiring inductance (direct parallel connection)
When a motor is driven by the direct parallel connection system, the control by the direct parallel
connection cannot be performed normally in some cases by the influence of a surge voltage caused by the
switching of the inverters.
Therefore, it is recommended to insert OFLs that suppress the occurrence of the surge voltage.
If a space for storing OFL filters cannot be secured in a cabinet, however, the motor operation by the
direct parallel connection system becomes possible when suppressing the surge voltage to a level that
causes no trouble to the direct parallel control by
the wiring inductance between inverters and the
motor (regulated by electric wire length).
This section explains the wiring inductance (wiring length) in the direct parallel connection system.
Wiring restrictions of direct parallel operation
L1=L2 and according to "section 6.6.12.1" and "section 6.6.12.2."
Figure 6.6.13 Explanation Figure of Restriction Items of Direct Parallel Connection
Two inverters in the direct parallel connection are shown, but the same applies to the case of
three inverters.
When cabtire cables or shielded wires are used from the relay terminal block BOX (branch point
for the direct parallel connection), wiring length longer by three times or more than the lengths
described in the "section 6.6.12.1" and "section 6.6.12.2" is required.
Make sure to connect the inverters with the electric wires of the same length. (Relationship of
L1=L2 in the figure above)
Either primary or secondary side of contactor is
allowed for use when using OFL filter.
However, the wiring length between OFL filters
should be made 2 to 20 m.
(The total length for 3 units in the case of direct
parallel connection of 3 units.)
Figure 6.6.14
Restrictions for use of OFL filter
DC powe
r supply
Stack VG
Contactor
Motor
Relay terminal block box
(branching from motor terminals
is acceptable.)
Stack VG
Contactor
L1
L2
OFL filter
OFL can be substituted
instead of wiring inductance.