Danfoss VLT FC 102 Series Design Manual page 51

Introduction to VLT® HVAC D...
4) T7, 50–125 hp [37–90 kW] complies with class A group 1 with 82 ft [25 m] motor cable. Some restrictions for the installation apply (contact
Danfoss for details).
HX, H1, H2, H3, H4 or H5 is defined in the type code pos. 16-17 for EMC filters
HX - No EMC filters built in the adjustable frequency drive (600 V units only)
H1 - Integrated EMC filter. Fulfill EN 55011 Class A1/B and EN/IEC 61800-3 Category 1/2
H2 - No additional EMC filter. Fulfill EN 55011 Class A2 and EN/IEC 61800-3 Category 3
H3 - Integrated EMC filter. Fulfill EN 55011 class A1/B and EN/IEC 61800-3 Category 1/2
H4 - Integrated EMC filter. Fulfill EN 55011 class A1 and EN/IEC 61800-3 Category 2
H5 – Marine versions. Fulfill same emissions levels as H2 versions
2.9.3 General Aspects of Harmonics Emission
An adjustable frequency drive takes up a non-sinusoidal current from the line power, which increases the input current I
A non-sinusoidal current is transformed with a Fourier analysis and split into sine-wave currents with different frequencies,
that is, different harmonic currents I
Hz
Table 2.20 Harmonic Currents
The harmonics do not affect the power consumption directly, but they do 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.
Figure 2.33 Harmonic Currents
NOTICE!
Some of the harmonic currents might disturb communication equipment connected to the same transformer or cause
resonance with power-factor correction batteries.
To ensure low harmonic currents, the adjustable frequency drive is equipped with intermediate circuit coils as standard. This
normally reduces the input current I
The voltage distortion on the line power supply voltage depends on the size of the harmonic currents multiplied by the line
power impedance for the frequency in question. The total voltage distortion THD is calculated based on the individual
voltage harmonics using this formula:
2 2 2
THD % = U U U
+ + ... +
5 7 N
(U % of U)
N
MG11BC22
Design Guide
with 50 Hz basic frequency:
n
I
1
50
by 40%.
RMS
Danfoss A/S © Rev. 06/2014 All rights reserved.
I I
5 7
250 350
2 2
.
RMS
49