Siemens SINAMICS G130 Engineering Manual page 115

12-pulse parallel connection of S120 Smart Line Modules
With 12-pulse parallel connections, up to four Smart Line Modules are supplied by a three-winding transformer on the
line side. In this case, an even number of modules, i.e. two or four, must be divided between the two secondary
windings. It is absolutely essential that the Smart Line Modules of both secondary windings are controlled by
means of two Control Units because of the phase displacement of 30º. The use of two Control Units is
necessary because, in contrast to the Basic Line Modules, the gating impulses for the IGBTs in Smart Line
Modules are synchronized by the Control Unit. Thus all Smart Line Modules controlled by one Control Unit
must be connected to the same transformer winding with equal phase position.
u = 4%
k
DRIVE-CLiQ
SLM 1
connection
Control
Unit 1
12-pulse parallel connection of S120 Smart Line Modules
As Smart Line Modules have no electronic current sharing control, three-winding transformer, power cabling and line
reactors must meet the following requirements in order to provide a balanced current:
•
Three-winding transformer must be symmetrical, recommended vector groups Dy5d0 or Dy11d0.
•
Relative short-circuit voltage of three-winding transformer u
•
Difference between relative short-circuit voltages of secondary windings Δu
•
Difference between no-load voltages of secondary windings ΔV ≤ 0.5 %.
•
Use of symmetrical power cabling between the transformer and the Smart Line Modules (cables of
identical type with the same cross-section and length)
•
Use of line reactors with a relative short-circuit voltage of u
A double-tier transformer is generally the only means of meeting the requirements of a three-winding transformer for
this application. Alternative solutions for obtaining a phase displacement of 30 °, such as two separate transformers
with different vector groups, cannot be used due to the inadmissibly high tolerances involved.
The current reduction from the rated value for individual Smart Line Modules in a parallel connection is 7.5 %. This is
also valid for the simplest form of a 12-pulse parallel configuration, if only one Smart Line Module is connected to
each secondary transformer winding, because also in this configuration the transformer's tolerance can lead to an
uneven current distribution.
Due to the phase displacement of 30º between both secondary winding systems and the control of both systems by
separate Control Units, it is generally not possible to ensure, that both systems contribute equally to the pre-charging
of the connected DC link. In order to prevent the overloading of individual systems during precharging, the 12-pulse
parallel connection of Smart Line Modules must be dimensioned in such a way that each system is individually able
to pre-charge the DC link.
Fundamental Principles and System Description
Three-winding
transformer
u = 4%
k
SLM 3
DC Link +
Engineering Information
Phase displacement
30° electr.
u = 4% u = 4%
k
k
SLM 2
-
≥ 4 %.
k
= 4 %.
k
SINAMICS Engineering Manual - May 2008
DRIVE-CLiQ
SLM 4
connection
Control
Unit 2
≤ 5 %.
k
115/396
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