Danfoss FC 102 Design Manual page 46

Introduction to VLT® HVAC D...
2.9.3 General Aspects of Harmonics
Emission
2 2
A frequency converter takes up a non-sinusoidal current
from mains, which increases the input current I
sinusoidal current is transformed with a Fourier analysis
and split into sine-wave currents with different frequencies,
that is, different harmonic currents I
frequency:
Hz
Table 2.20 Harmonic Currents
The harmonics do not affect the power consumption
directly, but increase the heat losses in the installation
(transformer, cables). So, 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 2.33 Harmonic Currents
NOTICE
Some of the harmonic currents might disturb communi-
cation equipment connected to the same transformer or
cause resonance 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 based on the
individual voltage harmonics using this formula:
2 2
THD % = U + U + ... +
5 7
(U % of U)
N
44
Design Guide
with 50 Hz basic
n
I I
1 5
50 250
by 40%.
RMS
2
U
N
Danfoss A/S © Rev. 06/2014 All rights reserved.
2.9.4 Harmonics Emission Requirements
Equipment connected to the public supply network
Options
. A non-
RMS
1
2
I
7
350
Table 2.21 Connected Equipment
2.9.5 Harmonics Test Results (Emission)
Power sizes up to PK75 in T2 and T4 comply with IEC/EN
61000-3-2 Class A. Power sizes from P1K1 and up to P18K
in T2 and up to P90K in T4 comply with IEC/EN
61000-3-12, Table 4. Power sizes P110 - P450 in T4 also
comply with IEC/EN 61000-3-12 even though not required
because currents are above 75 A.
Actual
(typical)
Limit for
R ≥120
sce
Actual
(typical)
Limit for
R ≥120
sce
Table 2.22 Harmonics Test Results (Emission)
If the short-circuit power of the supply S
or equal to:
SSC 3 × RSCE × Umains × Iequ = 3 × 120 × 400 × Iequ
=
at the interface point between the user's supply and the
public system (R
It is the responsibility of the installer or user of the
equipment to ensure that the equipment is connected
only to a supply with a short-circuit power S
or equal to what is specified above. If necessary, consult
the distribution network operator.
Other power sizes can be connected to the public supply
network by consultation with the distribution network
operator.
Compliance with various system level guidelines:
The harmonic current data in Table 2.22 are given in
accordance with IEC/EN61000-3-12 with reference to the
Definition
IEC/EN 61000-3-2 Class A for 3-phase balanced
equipment (for professional equipment only up to 1
kW total power).
IEC/EN 61000-3-12 Equipment 16 A-75 A and profes-
sional equipment as from 1 kW up to 16 A phase
current.
Individual harmonic current I
I I I
5 7 11
40 20 10
40 25 15
Harmonic current distortion factor (%)
THD
46
48
sc
).
sce
/I (%)
n 1
I
13
8
10
PWHD
45
46
is greater than
greater than
sc
MG11BC02