Harmonics - Danfoss VLT AQUA Drive FC 202 Design Manual

System Integration
3 3
3. Lower the IGBT switching frequency.
4. Modify the inverter waveform, 60° AVM vs.
SFAVM.
5. Install a shaft grounding system or use an
isolating coupling.
6. Apply conductive lubrication.
7. Use minimum speed settings if possible.
8. Try to ensure the line voltage is balanced to
ground. This can be difficult for IT, TT, TN-CS or
Grounded leg systems.
9. Use a dU/dt or sine-wave filter.

3.2.7 Harmonics

Electrical devices with diode rectifiers, such as fluorescent
lights, computers, copiers, fax machines, various laboratory
equipment and telecommunications systems, can add
harmonic distortion to a line power supply. Adjustable
frequency drives use a diode bridge input, which can also
contribute to harmonic distortion.
The adjustable frequency drive does not draw current
uniformly from the power line. This non-sinusoidal current
has components that are multiples of the fundamental
current frequency. These components are referred to as
harmonics. It is important to control the total harmonic
distortion on the line power supply. Although the
harmonic currents do not directly affect electrical energy
consumption, they generate heat in wiring and
transformers and can affect other devices on the same
power line.
3.2.7.1 Harmonic Analysis
Various characteristics of a building's electrical system
determine the exact harmonic contribution of the drive to
the THD of a facility and its ability to meet IEEE standards.
Generalizations about the harmonic contribution of
adjustable frequency drives on a specific facility is difficult.
When necessary, perform an analysis of the system
harmonics to determine equipment effects.
An adjustable frequency drive takes up a non-sinusoidal
current from the line power, which increases the input
50
2e Make sure that the impedance from
adjustable frequency drive to building
ground is lower that the grounding
impedance of the machine. This can be
difficult for pumps.
2f Make a direct ground connection
between the motor and load motor.
Danfoss A/S © 09/2014 All rights reserved.
®
VLT AQUA Drive FC 202
current I
means of a Fourier series analysis and split up into sine-
wave currents with different frequencies, i.e., different
harmonic currents I
fundamental frequency.
The harmonics do not affect the power consumption
directly, but increase the heat losses in the installation
(transformer, inductors, cables). Consequently, in power
plants with a high percentage of rectifier load, harmonic
currents should be kept at a low level to avoid overload of
the transformer, inductors, and cables.
Abbreviation
f
1
I
1
U
1
I
n
U
n
n
Table 3.9 Harmonics-related Abbreviations
Current
Frequency
[Hz]
Table 3.10 Transformed Non-sinusoidal Current
Current
Input current
Table 3.11 Harmonic Currents Compared to the RMS Input
Current
Figure 3.3 Intermediate Circuit Coils
NOTICE!
Some of the harmonic currents can disturb communi-
cation equipment connected to the same transformer or
cause resonance in connection with power-factor
correction capacitors.
To ensure low harmonic currents, the adjustable frequency
drive is equipped with passive filters. DC coils reduce the
total harmonic distortion (THD) to 40%.
. A non-sinusoidal current is transformed by
RMS
with 50 Hz or 60 Hz as the
N
Description
fundamental frequency
fundamental current
fundamental voltage
harmonic currents
harmonic voltage
harmonic order
Fundamental Harmonic current (I
current (I )
1
I I
1 5
50 250
Harmonic current
I I I
RMS 1
1.0 0.9 0.4
)
n
I I
7 11
350 550
I I
5 7 11-49
0.2 < 0.1
MG20N622