12-pulse parallel connection
3.2 Configuration
12-pulse applications
Compact User Manual, 09/2015, A5E34871844H
19
Dimensioning of the smoothing reactors
The correct dimensioning of smoothing reactors is very important and should be made only
by persons with sufficient knowledge of 12-pulse applications.
If the inductance of the smoothing reactors is too low, instead of 60° long current blocks,
this may result in 30° long current blocks of twice the size in both partial converters. In this
case, even if the semiconductor fuses are correctly dimensioned, the thyristors may not be
protected and will quickly be destroyed.
A smoothing reactor is used for each of the two partial converters. The reactor is a 2-value
reactor. This means that the inductance of the reactor is defined for two current values.
The reactor is thermally dimensioned according to the rms value of the DC reactor current.
The following formulas are used for rough estimates of the reactor values.
Calculating the required inductance:
= Inductance of the reactor at 0.2 × I
= inductance of the reactor at 0.33 x I
dmax
Inductance for 50 Hz line frequency:
Inductance for 60 Hz line frequency:
= Half rated DC current of the DC motor
= Half maximum current of the DC motor
= rated voltage of the line supply, U
If the condition is not fulfilled, L
D2
must be increased accordingly.
The condition is satisfied when I
dmax
< 2 × I
dn
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