Control Techniques Commander SE Guide D'utilisation page 31

The maximum cable lengths were measured using cable with capacitance of 130pF/m.
This capacitance was measured by taking one phase as one node and the screen
(shield) and earth (ground) (if any) as the other node and measuring the capacitance
between the two points.
High Capacitance Cables
Most cables have an insulating jacket between the cores and the armour or shield;
these cables have a low capacitance and are recommended. Cables that do not have
an insulating jacket tend to have high capacitance.
If a high capacitance cable is used, the maximum cable lengths in Table 4.3 should be
halved.
For further information please refer to the Commander SE Advanced User Guide.
Multiple Motors
For advice on multiple motor applications where a number of small motors are
connected to the output of one drive, please refer to the Commander SE Advanced
User Guide.
4.4.3 Use of line reactors
Line reactors can be used to reduce supply harmonics and also should be used if any of
the following conditions apply:
• Supply capacity exceeds 200kVA
• Fault current exceeds 5kA
• Power-factor correction equipment is connected close to the drives
• Large DC drives having no or ineffective line reactors connected to the supply
• Direct on-line started motor(s) are connected to the supply and, when any of these
motors are started, a dip is produced in excess of 20% of the actual supply voltage
During any of the above conditions, excessive peak current may flow in the input bridge.
This may cause nuisance drive tripping or, in extreme cases, failure of the input bridge.
A line reactor should then be connected in each phase of the supply to the input bridge.
Line reactor(s) add the required impedance to the AC supply in order to reduce current
transients to a level that can be tolerated by the input bridge. An impedance value of 2%
is usually recommended.
Three individual reactors, or a single three-phase reactor should be used. Each network
of drives must have its own reactor(s).
RFI filters (for EMC purposes) do not give adequate protection against these
conditions.
CAUTION
Commander SE User Guide
Issue Number 9 www.controltechniques.com
31