General Aspects Of Harmonics; Harmonics Analysis - Danfoss VLT 380-500 V Design Manual

EMC and Harmonics
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
1 Minimum 16 mm
Illustration 9.9 Correct Shielding
9 9
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).
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.
1 Minimum 16 mm
Illustration 9.11 Recommended Method for Avoiding EMC
Noise
Alternatively, the connection to terminal 61 can be
omitted:
100
VLT
2
PLC FC
PE PE <10 mm
PE PE
1
2
2 2 Equalizing cable
(4 AWG)
PLC FC
PE
PE
100nF <10 mm
FC FC
69 69
68 68
61
61
PE PE <10 mm
PE PE
1
2
2 2 Equalizing cable
(4 AWG)
Danfoss A/S © 6/2016 All rights reserved.
®
Parallel Drive Modules
1 Minimum 16 mm
(4 AWG).
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
Hz or 60 Hz as the basic frequency.
Abbreviation
f
1
I
1
U
1
I
n
U
n
n
Table 9.6 Harmonics-related Abbreviations
Current
Frequency
[Hz]
Table 9.7 Basic Currents and Harmonic Currents
FC FC
69 68
68 69
PE PE
<10 mm
PE PE
1
2
2 Equalizing cable
2 (4 AWG)
Description
Basic frequency (50 Hz or 60 Hz)
Current at the basic frequency
Voltage at the basic frequency
Current at the n th harmonic frequency
th
Voltage at the n harmonic frequency
Harmonic order
Basic Harmonic current (I
current (I )
1
I I I
1 5 7
50 250 350
with 50
N
)
n
I
11
550
MG37N102