Danfoss VLT HVAC Basic Drive FC 100 Series Design Manual page 34

Introduction to VLT HVAC Ba...
2.7.4 General Aspects of Harmonics
Emission
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 50Hz
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.
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.
To ensure low harmonic currents, the frequency converter
is equipped with intermediate circuit coils as standard. This
normally reduces the input current I
The voltage distortion on the mains supply voltage
depends on the size of the harmonic currents multiplied
by the mains impedance for the frequency in question.
The total voltage distortion THD is calculated on the basis
of the individual voltage harmonics using this formula:
2 2 2
THD % = U + U + ... + U
5 7 N
(U % of U)
N
VLT HVAC Basic Drive Design Guide
. A non-
RMS
with 50Hz
N
I I I
1 5 7
250Hz 350Hz
by 40%.
RMS
®
MG.18.C2.02 - VLT is a registered Danfoss trademark
2.7.5 Harmonics Emission Requirements
Equipment connected to the public supply network
Options: Definition:
1 IEC/EN 61000-3-2 Class A for 3-phase balanced
equipment (for professional equipment only up to
1kW total power).
2 IEC/EN 61000-3-12 Equipment 16A-75A and profes-
sional equipment as from 1kW up to 16A phase
current.
2.7.6 Harmonics Test Results (Emission)
Power sizes up to PK75 in T2 and T4 complies with IEC/EN
61000-3-2 Class A. Power sizes from P1K1 and up to P18K
in T2 and up to P90K in T4 complies with IEC/EN
61000-3-12, Table 4.
Individual Harmonic Current I
I
5
Actual 0.25-11kW,
32.6
200V (typical)
≥120
Limit for R 40
sce
Harmonic current distortion factor (%)
THD
Actual 0.25-11kW,
39
200V (typical)
≥120
Limit for R 48
sce
Individual Harmonic Current I
I
5
Actual 0.37-22kW,
36.7
380-480V (typical)
≥120
Limit for R 40
sce
Harmonic current distortion factor (%)
THD
Actual 0.37-22kW,
44.4
380-480V (typical)
≥120
Limit for R 48
sce
Individual Harmonic Current I
I
5
Actual 30-90kW,
36.7
380-480V (typical)
≥120
Limit for R 40
sce
Harmonic current distortion factor (%)
THD
Actual 30-90kW,
40.6
380-480V (typical)
≥120
Limit for R 48
sce
Provided that the short-circuit power of the supply S
greater than or equal to:
/I (%)
n 1
I I I
7 11 13
16.6 8.0 6.0
25 15 10
PWHD
41.4
46
/I (%)
n 1
I I I
7 11 13
20.8 7.6 6.4
25 15 10
PWHD
40.8
46
/I (%)
n 1
I I I
7 11 13
13.8 6.9 4.2
25 15 10
PWHD
28.8
46
is
sc
33
2 2