53
MG.30.A7.02 - VLT
®
is a registered Danfoss trademark
EMC installation
In support of our claim that the VLT
®
frequency converter complies with the
protection requirements for emission and
immunity under EMC directive 89/336/
EEC, a Technical Construction File (TCF)
has been prepared for each model. Such
a file defines the EMC requirements and
the measurements made in accordance
with harmonised EMC standards in a
Power Drive System (PDS) that consists of
a VLT
®
frequency converter, a control
cable and the controls (control box), motor
cable and motor plus any options added.
The Technical Construction File is pre-
pared on this basis in cooperation with an
authorised EMC laboratory (Competent
Body).
In most cases the VLT frequency con-
verter is used by professionals of the trade
as a complex component forming part of a
larger appliance, system or installation. It
must be noted that the responsibility for
the final EMC properties of the appliance,
system or installation rests with the fitter.
As an aid to the fitter, Danfoss has pre-
pared EMC installation guidelines for the
Power Drive System. The standards and
testing levels stated for the Power Drive
System are complied with, provided that
the EMC-correct installation guidelines are
applied.
The following basic issues need to be
considered when installing a frequency
converter, so as to obtain electromagnetic
compatibility (EMC).
Safety earthing:
Please note: 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 great-
est possible surface area. A flat conductor,
for example, has a lower HF impedance
than a round conductor for the same
conductor square value.
If more than one appliance is installed in
cabinets, the cabinet rear plate, which
must be made of metal, should be used as
a common earth reference plate. The
metal cabinets of the different appliances
are mounted on the cabinet rear plate
using the lowest possible HF impedance.
This avoids having different HF voltages
for the individual appliances and avoids
the risk of radio interference currents
running in connection cables that may be
used between the appliances.
In order to obtain a low HF impedance,
use the fastening bolts of the appliances
as HF connection to the rear plate. It is
necessary to remove insulating paint or
similar from the fastening points.
The control cable and the filtered mains
cable should be installed separately from
the motor and brake cables to prevent
interference coupling. Normally, a distance
of 20 cm will be sufficient, but it is recom-
mended to keep the greatest possible
distance wherever possible, especially
where cables are installed in parallel over a
substantial distance. (Seperation should
increase in proportion).
With respect to sensitive signal cables,
such as telephone cables and data cables,
the greatest possible distance is recom-
mended with a minimum of 1 m per 5 m of
power cable (mains, motor and brake
cable). It must be pointed out that the
necessary distance depends on the sensi-
tivity of the installation and the signal
cables, and that therefore no precise
values can be stated.
If cable clamps are used, sensitive signal
cables are not to be placed in the same
cable clamps as the motor cable or brake
cable.
If signal cables are to cross power cables,
this should be done at an angle of 90
degrees.
Remember that all noisy in- or outgoing
cables to/from a cabinet should be
screened or filtered.
Cables
Earthing
Compliance with EMC
directive 89/336/EEC
Screened cables
The screen must be a low HF-impedance
screem. This is ensured by using a braided
screen of cobber, aluminium or iron.
Screen armour intended for mechanical
protection, for example, is not suitable for
an EMC-correct installation.
