Danfoss VLT AQUA Drive Design Manual page 111

VLT ® AQUA Drive Design Guide
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b.
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5.9.1. AC Line Supply Interference/Harmonics
An adjustable frequency drive takes up a non-
sinusoidal current from the line power, which
increases the input current I
oidal current is transformed by means of a
Fourier analysis and split up into sine-wave
currents with different frequencies, i.e., dif-
ferent harmonic currents I
basic frequency:
Correct grounding
Control cables and cables for serial
communication must be fitted with
cable clamps at both ends to ensure
the best possible electrical contact.1
Wrong grounding
Do not use twisted cable ends (pig-
tails). They increase the shield impe-
dance at high frequencies.1
Protection with respect
ground potential between the
PLC and VLT
If the ground potential between the
adjustable frequency drive and the
PLC (etc.) is different, electric noise
may occur that will disturb the entire
system. Solve this problem by fitting
an equalizing cable next to the con-
trol cable. Minimum cable cross-sec-
tion: 0.025 in 2 [16 mm 2 ].1
For 50/60 Hz ground loops
If very long control cables are used,
50/60 Hz ground loops may occur.
Solve this problem by connecting
one end of the shield to ground via a
100nF capacitor (keeping
short).1
Cables for serial communica-
tion
Eliminate low-frequency noise cur-
rents between two adjustable fre-
quency drives by connecting one end
of the shield to terminal 61. This ter-
minal is grounded via an internal RC
link. Use twisted-pair cables to re-
duce the differential mode interfer-
ence between the conductors.1
. A non-sinus-
RMS
with 50 Hz as the
N
MG.20.N2.22 - VLT ® is a registered Danfoss trademark.
to
leads
Harmonic currents
Hz
5. How to Install
I I I
1 5 7
50 Hz 250 Hz 350 Hz
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