4.1.2 Earthing
The following basic issues need to be considered when instal-
ling a frequency converter, so as to obtain electromagnetic
compatibility (EMC).
•
Safety earthing: Please note that the frequency converter has
a high 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 re-
duced.
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.
4.1.3 Extra Protection (RCD)
ELCB relays, multiple protective earthing or earthing can be used as ex-
tra protection, provided that local safety regulations are complied with.
In the case of an earth fault, a DC component may develop in the fault
current.
If ELCB relays are used, local regulations must be observed. Relays
must be suitable for protection of 3-phase equipment with a bridge rec-
tifier and for a brief discharge on power-up.
See also the section
Special Conditions
in the Design Guide.
4.1.4 RFI Switch
Mains supply isolated from earth
If the frequency converter 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 par. 14-50
RFI Filter
on the drive and par. 14-50
RFI Filter
on the
filter. For further reference, see IEC 364-3. In case optimum EMC per-
formance is needed, parallel motors are connected or the motor cable
length is above 25 m, it is recommended to set par. 14-50
RFI Filter
to
[ON].
1)
Not available for 525-600/690V frequency converters in frame sizes
D, E and F.
In OFF, the internal RFI capacities (filter capacitors) between the chas-
sis and the intermediate circuit are cut off to avoid damage to the inter-
mediate 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 to-
gether with power electronics (IEC 61557-8).
VLT HVAC Drive High Power Operating In-
structions
4 Electrical Installation
MG.11.F3.02 - VLT
®
is a registered Danfoss trademark
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