Engineering Guide CDA3000
6-3
6 Selection of supplementary components
DE
EN
1
2
3
4
5
6
7
A
System load
The total voltage distortion THD is calculated from the individual harmon-
ics according to the following formula:
U
n
as % of U
fundamental
Mains voltage asymmetry
According to IEC1000-2-4 the mains voltage asymmetry may be only 2%.
In summary: The example shows that the benefit of a line choke
with 4 % short-circuit voltage is wide-ranging, and so it
should not be omitted from any machine or system.
Without line choke With line choke Change
4 kW inverter, line
impedance 0.6 mH
4 kW inverter, line
impedance
0.6 mH
Without line
choke to with
line choke
Voltage distortion (THD) 99 % 33 % -67 %
Mains current amplitude 18.9 A 9.7 A -48 %
Mains current effective 8.5 A 6,23 A -27 %
Commutation notches
referred to the mains
voltage
28 V 8 V -70%
Life of the DC-link
capacitors
Nominal life
2 to 3 times
nominal life
+200 to 300 %
Table 6.2 Change in system load resulting from insertion of a line choke
with 4 % short-circuit voltage based on the example of a 4 kW
inverter CDA34.010
Without line choke With line choke
4 kW inverter, line
impedance 0.6 mH
4 kW inverter, line
impedance 0.6 mH
Mains voltage asymmetry 0 % +3 % -3 % 0 % +3 % -3 %
Mains current amplitude 18.9 A 25.4 A 25.1 A 9.7 A 10.7 A 11 A
Mains current effective 8.5 A 10.5 A 10,2 A 6,2 A 6.7 A 6.8 A
Table 6.3 Effect of the line choke with asymmetrical mains voltage
based on the example of a 4 kW inverter CDA34.010
TDH U
5
2
U
7
2
+ …U
41
2
=
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