9.5.2 Grounding of Shielded Control Cables
Correct shielding
The preferred method usually is to secure control and
serial communication cables with shielding clamps
provided at both ends to ensure best possible high
frequency cable contact. If the ground potential between
the frequency converter and the PLC is different, electric
noise can occur that disturbs the entire system. Solve this
problem by fitting an equalizing cable next to the control
cable. Minimum cable cross-section: 16 mm
2
(4 AWG).
1
2
PE
FC
PE
PLC
130BB922.12
PE
PE
<10 mm
1 Minimum 16 mm
2
(4 AWG)
2 Equalizing cable
Illustration 9.9 Correct Shielding
50/60 Hz ground loops
With long control cables, ground loops can occur. To
eliminate ground loops, connect 1 end of the shield-to-
ground with a 100 nF capacitor (keeping leads short).
100nF
FC
PE
PE
PLC
<10 mm
130BB609.12
Illustration 9.10 Avoiding Ground Loops
Avoid EMC noise on serial communication
This terminal is connected to ground via an internal RC
link. To reduce interference between conductors, use
twisted-pair cables.
PE
FC
PE
FC
130BB923.12
PE
PE
69
68
61
69
68
61
1
2
<10 mm
1 Minimum 16 mm
2
(4 AWG)
2 Equalizing cable
Illustration 9.11 Recommended Method for Avoiding EMC
Noise
Alternatively, the connection to terminal 61 can be
omitted:
PE
FC
PE
FC
130BB924.12
PE
PE
69
69
68
68
1
2
<10 mm
1 Minimum 16 mm
2
(4 AWG)
2 Equalizing cable
Illustration 9.12 Shielding without Using Terminal 61
9.6 General Aspects of Harmonics
Non-linear loads such as found with 6-pulse frequency
converters do not draw current uniformly from the power
line. This non-sinusoidal current has components which are
multiples of the basic current frequency. These
components are referred to as harmonics. It is important to
control the total harmonic distortion on the mains supply.
Although the harmonic currents do not directly affect
electrical energy consumption, they generate heat in
wiring and transformers that can affect other devices on
the same power line.
9.7 Harmonics Analysis
Since harmonics increase heat losses, it is important to
design systems with harmonics in mind to prevent
overloading the transformer, inductors, and wiring.
When necessary, perform an analysis of the system
harmonics to determine equipment effects.
A non-sinusoidal current is transformed with a Fourier
series analysis into sine-wave currents at different
frequencies, that is, different harmonic currents I
N
with 50
Hz or 60 Hz as the basic frequency.
Abbreviation
Description
f
1
Basic frequency (50 Hz or 60 Hz)
I
1
Current at the basic frequency
U
1
Voltage at the basic frequency
I
n
Current at the n
th
harmonic frequency
U
n
Voltage at the n
th
harmonic frequency
n
Harmonic order
Table 9.6 Harmonics-related Abbreviations
Basic
current (I
1
)
Harmonic current (I
n
)
Current
I
1
I
5
I
7
I
11
Frequency
[Hz]
50
250
350
550
Table 9.7 Basic Currents and Harmonic Currents
EMC and Harmonics
VLT
®
Parallel Drive Modules
100
Danfoss A/S © 6/2016 All rights reserved.
MG37N102
9
9
Summary of Contents for VLT 380-500 V
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