Danfoss VLT 3006 Product Manual page 55

Radio interference
in general
54
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
EMC installation
Electrical interference from the cable
network, cable-borne interference, 150
kHz-30 MHz, and airborne interference
from the drive system, 30 MHz-1 GHz, is
for frequencies under approx. 50 MHz
produced in particular by the inverter, the
motor cable and the motor system.
As the sketch below shows, capacitive
currents in the motor cable together with
high du/dt from the motor voltage will
produce interference.
Use of screened motor cable increases
the leakage current I, (see fig. below). This
is because screened cables have higher
capacitance to earth than unscreened
cables. If the leakage current is not fil-
tered, it will cause greater interference on
the mains in the radio leakage range under
approx. 5 MHz. Since the leakage current
I is carried back to units through the
1
screen (I ), in principle this will give only a
4
small electromagnetic field from the
screened motor cable, according to the
figure below.
In cases where the screen must be placed
on a mounting panel for the VLT
quency converter, the mounting panel
must be of metal because the screen
currents must be led back to the unit. It is
also important to ensure good electrical
contact from the mounting screws through
the mounting curve to the VLT
converter.
With regard to installation, it is generally
less complicated to use unscreened
cables than screened cables. To observe
the EN55011-1A requirements to radiated
interference (30MHz-1GHz) a motor filter
®
MG.30.A7.02 - VLT is a registered Danfoss trademark
The screen reduces the radiated inter-
ference, but increases the low frequency
interference on the mains. With a mains
filter, the interference level on the mains
will be reduced to around the same level
for both screened and unscreened cables.
The motor cable screen must be con-
nected to the VLT
the motor enclosure. The best way to do
this is to use screen clamps to avoid unr
ravelled screen ends. These increase the
screen impedance at higher frequencies,
which reduces the screen effect and
increases the interference current (I
When screened cable is used for
PROFIBUS, control cable, signal interface
and brake, the screen must be mounted on
the enclosure at both ends. In certain
situations, however, it will be necessary to
break the screen to avoid current loops.
must be installed when using unscreened
® fre- cables.
In order the reduce the interference level
from the system overall (unit + installation)
as far as possible, it is important to make
motor and brake cables as short as
possible.
®
frequency
Cables with a sensitive signal level may
not be led together with motor and brake
cables.
Radio interference higher than 50 MHz
(airborne) will be particularly affected by
the control electronics.
® 's enclosure as well as
).
4