Rfi Switch; Mains Supply Interference/Harmonics - Danfoss VLT AutomationDrive FC 300 Design Manual

Electrical Installation
50/60 Hz Ground Loops
With very long control cables, ground loops may occur.
Eliminate ground loops by connecting one end of the
screen-to-ground with a 100nF capacitor (keeping leads
short).
PLC
PE
100nF
Illustration 7.60 Eliminating Ground Loops by Connecting
Earth/Ground to 100nF Capacitor
Avoid EMC Noise on Serial Communication
This terminal is connected to earth via an internal RC link.
Use twisted-pair cables to reduce interference between
conductors. The recommended method is shown in
Illustration 7.62.
FC
69
68
61
PE
PE
2
Illustration 7.61 Using Twisted Pair Cables to Reduce
Interference
1 2
Min. 16 mm
2 Equalizing cable
Table 7.73 Legend to Illustration 7.61
Alternatively, the connection to terminal 61 can be
omitted:
FC
69
68
PE
PE
2
Illustration 7.62 Reducing Interference by Omitting Terminal
61
1 2
Min. 16 mm
2 Equalizing cable
Table 7.74 Legend to Illustration 7.62
®
VLT AutomationDrive FC 300 Design Guide 90-1200 kW
FC
PE
<10 mm
FC
69
68
61
PE
<10 mm
PE
1
FC
68
69
PE
<10 mm
PE
1
MG34S202 - Rev. 2013-08-19

7.8.4 RFI Switch

Mains Supply Isolated from Earth
If the frequency converter is supplied from an isolated
mains source (IT mains, floating delta, or grounded delta)
or TT/TN-S mains with grounded leg, the RFI switch is
recommended to be turned off (OFF)
on the frequency converter and 14-50 RFI Filter on the
filter. For more detail, see IEC 364-3. In OFF, the filter
capacitors between the chassis and the intermediate circuit
are cut off to avoid damage to the intermediate circuit and
to reduce the earth capacity currents (according to IEC
61800-3).
If optimum EMC performance is needed or parallel motors
are connected or the motor cable length is above 25 m,
Danfoss recommends setting the 14-50 RFI Filter to [ON].
Refer also to the Application Note, VLT on IT Mains, MN50P.
It is important to use isolation monitors that are capable
for use together with power electronics (IEC 61557-8).

7.9 Mains Supply Interference/Harmonics

A frequency converter takes up a non-sinusoidal current
from mains, which increases the input current I
sinusoidal current is transformed by means of a Fourier
analysis and split into sine-wave currents with different
frequencies. See Table 7.75.
Harmonic currents
Hz 50 Hz
Table 7.75 Non-Sinusoidal Current Split into Sine-Wave Currents
with Different Frequencies
The harmonics do not affect the power consumption
directly, but increase the heat losses in the transformer
and cables. Therefore, in plants with a high percentage of
rectifier load, it is necessary to maintain harmonic currents
at a low level to avoid overload of the transformer and
high temperature in the cables.
NOTICE
Some of the harmonic currents might disturb communi-
cation equipment connected to the same transformer or
cause resonance in connection with power-factor
correction batteries.
Harmonic current
I
RMS
I
1
I
5
I
7
I
11-49
Table 7.76 Harmonic Currents Compared to the RMS Input Current
1) via 14-50 RFI Filter
. A non-
RMS
I I I
1 5 7
250 Hz 350 Hz
Input current
1.0
0.9
0.4
0.2
<0.1
215
7 7