3.6.2 Grounding
The following basic issues need to be considered when installing an adjustable frequency drive, so as to obtain electromagnetic com-
patibility (EMC).
• Safety grounding: Please note that the adjustable frequency drive has a high leakage current and must be grounded appropriately for safety
reasons. Always follow local safety regulations.
• High-frequency grounding: Keep the ground wire connections as short as possible.
Connect the different ground 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 prevents having different
HF voltages for the individual devices and prevents the risk of radio interference currents running in connection cables that may be used between the
devices, as radio interference is reduced.
In order to obtain a low HF impedance, use the fastening bolts of the devices as HF connections to the rear plate. It is necessary to remove insulating
paint and the like from the fastening points.
3.6.3 Extra Protection (RCD)
ELCB relays, multiple protective grounding or grounding can be used as extra protection, provided that local safety regulations are complied with.
In the case of a ground 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 rectifier and for
a brief discharge on power-up.
See also the section
Special Conditions
in the Design Guide.
3.6.4 RFI Switch
Line power supply isolated from ground
If the adjustable frequency drive is supplied from an isolated line power source ( IT line power, floating delta and grounded delta) or TT/TN-S line power
with grounded leg, the RFI switch is recommended to be turned off (OFF)
1)
via par. 14-50
RFI Filter
. For further reference, see IEC 364-3. In case
optimum EMC performance is needed, parallel motors are connected or the motor cable length is above 82 ft [25 m], it is recommended to set
par. 14-50
RFI Filter
to [ON].
1)
Not available for 525–600/690 V adjustable frequency drives.
In OFF, the internal RFI capacities (filter capacitors) between the chassis and the intermediate circuit are cut off to avoid damage to the intermediate
circuit and to reduce the ground capacity currents (according to IEC 61800-3).
Please also refer to the application note
VLT on IT line power, MN.90.CX.02.
It is important to use isolation monitors that are capable of being used with
power electronics (IEC 61557-8).
VLT AQUA High Power Instruction Manual 3 How to Install
MG.20.P3.22 - VLT
®
is a registered Danfoss trademark
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