Danfoss vlt fc 300 Instruction Manual page 40

®
VLT Automation Drive FC 300 12-Pulse
How to Install
Instruction Manual High Power
3.3.3 Grounding
The following basic issues need to be considered when
installing an adjustable frequency drive, so as to obtain
electromagnetic compatibility (EMC).
•
Safety grounding: 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.
3.3.4 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 Special Conditions in the Design Guide,
MG33BXYY.
3.3.5 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 14-50 RFI 1 on the adjustable frequency drive and
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14-50 RFI 1 on the 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 80 ft [25 m], it is recommended to set 14-50 RFI 1 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, MN90CX02. It is important to use isolation monitors
that are capable for use together with power electronics
(IEC 61557-8).
3.3.6 Torque
When tightening all electrical connections it is important
to tighten with the correct torque. Too low or too high
torque results in a poor electrical connection. Use a torque
wrench to ensure correct torque.
Nm/in-lbs
Figure 3.32 Always use a torque wrench to tighten the bolts.
3-31
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