Mains Supply Interference/Harmonics; The Effect Of Harmonics In A Power Distribution System - Danfoss VLT AutomationDrive FC 300 Design Manual

Introduction
Basic standard
Acceptance criterion
Voltage range: 200-240 V, 380-500 V, 525-600 V, 525-690 V
Line
Motor
Brake
Load sharing
Control wires
Standard bus
Relay wires
Application and Fieldbus
options
LCP cable
External 24 V DC
Enclosure
Table 3.14 EMC Immunity Form
1) Injection on cable shield
AD: Air Discharge
CD: Contact Discharge

3.6 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 up into sine-wave currents with different
frequencies, i.e. different harmonic currents I
as the basic frequency.
Harmonic currents
Hz 50 Hz
Table 3.15 Transformed Non-sinusoidal Current
The harmonics do not affect the power consumption
directly but increase the heat losses in the installation
(transformer, cables). Consequently, in plants with a high
percentage of rectifier load, maintain harmonic currents at
a low level to avoid overload of the transformer and high
temperature in the cables.
Illustration 3.24 Intermediate Circuit Coils
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®
VLT AutomationDrive FC 300 Design Guide, 0.25-75 kW
Burst Surge
IEC 61000-4-4 IEC 61000-4-5
B B
2 kV/2 Ω DM
4 kV CM
4 kV/12 Ω CM
4 kV CM
4 kV/2 Ω
4 kV CM
4 kV/2 Ω 1)
4 kV CM
4 kV/2 Ω
2 kV CM 1)
2 kV/2 Ω
2 kV CM 1)
2 kV/2 Ω
2 kV CM
2 kV/2 Ω
2 kV CM
2 kV/2 Ω
2 kV CM 2 kV/2 Ω
0.5 kV/2 Ω DM
2 V CM
1 kV/12 Ω CM
— —
. A non-
RMS
with 50 Hz
N
I I I
1 5 7
250 Hz 350 Hz
®
MG33BE02 - VLT is a registered Danfoss trademark
ESD Radiated electromagnetic
IEC
61000-4-2 IEC 61000-4-3
B
—
1) —
—
1) —
—
—
1) —
1) —
1)
—
—
8 kV AD
6 kV CD
CM: Common mode
DM: Differential mode
NOTE
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.
I
RMS
I
1
I
5
I
7
I
11-49
Table 3.16 Harmonic currents compared to the RMS input current
To ensure low harmonic currents, the frequency converter
is equipped with intermediate circuit coils as standard. DC-
coils reduce the total harmonic distortion (THD) to 40%.
3.6.1 The Effect of Harmonics in a Power
Distribution System
In Illustration 3.25 a transformer is connected on the
primary side to a point of common coupling PCC1, on the
medium voltage supply. The transformer has an
impedance Z and feeds a number of loads. The point of
xfr
RF common
field mode voltage
IEC 61000-4-6
A A
— 10 V
RMS
— 10 V
RMS
— 10 V
RMS
— 10 V
RMS
— 10 V
RMS
10 V
—
RMS
— 10 V
RMS
— 10 V
RMS
10 V
—
RMS
— 10 V
RMS
10V/m —
Input current
1.0
0.9
0.4
0.2
< 0.1
3 3
41