4.5.2 Earthing
The following basic issues need to be considered when
installing an active filter, so as to obtain electromagnetic
compatibility (EMC).
•
Safety earthing: Please note that the active filter
has leakage current and must be earthed
appropriately for safety reasons. Apply local
safety regulations.
•
High-frequency earthing: Keep the earth wire
connections as short as possible.
Connect the different earth systems at the lowest possible
conductor impedance. The lowest possible conductor
impedance is obtained by keeping the conductor as short
as possible and by using the greatest possible surface area.
The metal cabinets of the different devices are mounted
on the cabinet rear plate using the lowest possible HF
impedance. This avoids having different HF voltages for
the individual devices and avoids the risk of radio
interference currents running in connection cables that
may be used between the devices. The radio interference
will have been reduced. In order to obtain a low HF
impedance, use the fastening bolts of the devices as HF
connection to the rear plate. It is necessary to remove
insulating paint or similar from the fastening points.
EARTH
TERMINALS
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Illustration 4.27 Example of Earth Terminal Position
4.5.3 Extra Protection (RCD)
ELCB, RCD, GFCI relays or multiple protective earthings are
often used as extra protection, or needed to provide
compliance with local safety regulations. In case of an
earth fault, a DC component may develop in the fault
current. If ELCB relays are used, local regulations must be
observed. To reassure effective protection and unintended
tripping of protective relays, all relays must be suitable for
protection of 3-phase equipment with active current infeed
and for a brief discharge during power-up. It is
recommended to use a type with adjustable trip amplitude
and time characteristics. Select a current sensor with
sensitivity of more then 200mA and not less than 0.1-
second operation time.
4.5.4 RFI Switch
Mains supply isolated from earth
If the Active filter is supplied from an isolated mains
source (IT mains, floating delta and grounded delta) or
TT/TN-S mains with grounded leg, the RFI switch is
recommended to be turned off (OFF) 1) via
14-50 RFI Filter
on the unit. For further reference, see IEC 364-3. In OFF,
the internal RFI capacities between the chassis and the
intermediate circuit are cut off to avoid damage to the
intermediate circuit and to reduce the earth capacity
currents (according to IEC 61800-3). Please also refer to the
application note VLT on IT mains, MN.90.CX.02. It is
important to use isolation monitors that are capable for
use together with power electronics (IEC 61557-8).
4.5.5 Torque
When tightening all electrical connections it is very
important to tighten with the correct torque. Too low or
too high torque results in a bad electrical connection. Use
a torque wrench to ensure correct torque. Below is the
tightening torque required for the mains terminal:
Frame size
Torque
Bolt size
D
19Nm
M10
E
19Nm
M10
How to Install
VLT Active Filter AAF 00x
MG.90.V2.02 - VLT® is a registered Danfoss trademark
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