Danfoss AAF00x Operating Instructions Manual page 30

How to Install
Table 4.5 shows the minimum CT burden for different wire
gauge at wire length of 50m and standard wire resistance
value:
Wire Gauge Resistance
[mm2 / AWG] [Ohm/Km] [meters / feet]
1.5 / #16 13.3
2.5 / #14 8.2
4 / #12 5.1
6 / #10 3.4
10 / #8 2
Table 4.5 Minimum CT Burden
For a fixed CT burden the maximum allowed wire length
can be calculated as:
[M] = ([VA]-1.25) / (25*[Ohm/M])
Below the maximum wire length of CT with 2.5mm
and resistor value equal 8.2 Ohm/km:
Wire Gauge Resistance
[mm2 / AWG] [Ohm/Km]
2.5 / #14 8.2
2.5 / #14 8.2
2.5 / #14 8.2
2.5 / #14 8.2
2.5 / #14 8.2
Example
Calculation example for correct current transformer for an
application with:
RMS= 653Amp, Distance between filter and CT's of 30m.
RMS=653*1.1= 719A, CT RMS = 750Amp. Burden :
2
30m@2.5mm wire => 25*0.0082*30+1.25=7.4 => 7.5 [VA].
Current transformer installation
The unit only supports three CT installations. External CTs
should be installed on all three phases to detect the
harmonic content of the grid. The flow direction of the
sensor is in most cases indicated by an arrow. The arrow
should point in the direction of the current flow and so
towards the load. In case the flow direction is incorrectly
programmed the polarity can be changed via filter
300-25 CT Polarity. 300-25 CT Polarity can program the
polarity of all three phases individually.
VLT Active Filter AAF 00x
Wire length Minimum CT
burden [VA]
50 / 164 >16.6
50 / 164 >10.2
50 / 164 > 6.3
50 / 164 > 4.2
50 / 164 > 2.5
2 wires
Minimum CT Wire length
burden [VA] [meter / feet]
5 <18m / 60
7.5 <30m / 100
10 <42m / 140
15 <67m / 220
30 <140m / 460
MG.90.V2.02 - VLT® is a registered Danfoss trademark
L1
K L
L2
K L
L3
K L
1
91 92 93
L1 L2
1 or 5 Amp CT Set-up
To allow for possible reuse of already present CT
transformers, the VLT Active Filter allows use of either 1
Amp or 5 Amp CTs. The filter is as standard set-up for 5
Amp CT feedback. If the CTs are 1 Amp, redirect the CT
terminal plug from slot MK101, pos. 1, to MK108, pos. 2,
on the AFC card, see Illustration 4.29.
4
3
1
2
Illustration 4.29 AFC Board
Individual or group compensation
The compensation of the filter depends on the signal that
is returned from the current transformers. The point of
installation for these sensors is so determine the loads that
are corrected.
K L
K L
K L
2
95
L3
5
6
29
4 4