Nm/in-lbs
13
0B
B7
41
.1
0
Illustration 4.28 Tightening Bolts with Torque Wrench
NOTE
Always use a torque wrench to tighten the bolts.
4.5.6 Shielded Cables
It is important that shielded cables are connected in a
proper way to ensure high EMC immunity and low
emissions.
Connection can be made using either cable glands or
clamps:
•
EMC cable glands: Generally available cable
glands can be used to ensure an optimum EMC
connection.
•
EMC cable clamp: Clamps allowing easy
connection are supplied with the unit.
4.5.7 Current Transformer (CT)
The filter operates in close loop operation by receiving
current signals for external current transformers. The
received signal is processed and the filter reacts according
to programmed actions.
CAUTION
Incorrect current transformer connection, installation or
configuration will lead to unintended and uncontrollable
behaviour of the filter.
NOTE
The current transformers are not part of the filter package
and must be purchased separately.
Current transformer specification
The Active Filter supports most current transformers. The
current transformers have to have the following specifi-
cations:
Technical specification of Active filter passive current
transformers:
RMS
maximum measured RMS current
Accuracy
0.5% or better (Class 0.5)
Secondary rated
current
1A or 5A (5A is recommended)
Set-up via hardware
Rated frequency
50/60 Hz
Rated power/burden
See
(AAF’s burden equal 2m
Ω
)
Rated power/
burden [VA]
5
7.5
10
15
30
Impedance of
current CT [
Ω
]
≤ 0.15
≤ 0.25
≤ 0.35
≤ 0.55
≤ 1.15
Table 4.4 Rated Power/Burden
NOTE
All other technical data like dynamic rated current,
maximal permitted operating voltage, thermal
dimensioning of continuous current, thermal dimensioning
of short-time current, over current limit, isolation class,
working temperature range etc. are specific values of the
system and have to be defined during the project planning
phase of the equipment.
RMS Specification
The minimum RMS has to be determined by the total
current that passes through the current transformer. It is
important that the current sensor is not too small leading
to saturation of the sensor. Add 10% margin and pick the
next following bigger standard RMS rate. It is advised to
use current transformers which has a RMS rating close to
the maximum current that flows through it to allow the
highest possible accuracy of the measurement and so an
ideal compensation.
CT Burden
In order to ensure that the current transformer performs
according to specifications, the rated burden should not
be above the true current requirement by the Active Filter.
The burden of the CT is depending on the wire type and
the cable length between the CT and the filter CT
connection terminal. The filter itself contributes with 2m
Ω
.
NOTE
The accuracy of the CT is depending on wire type and
length of the cable between filter and current transformer.
The required (minimum) CT burden can be calculated as:
[VA] = 25*[Ohm/M] *[M]+1.25
[Ohm/M] being the cable resistance in Ohm/meter, [M]
being the cable length in meters
How to Install
VLT Active Filter AAF 00x
28
MG.90.V2.02 - VLT® is a registered Danfoss trademark
4
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