Fundamental Principles and System Description
Engineering Information
SINAMICS Engineering Manual – November 2015
Ó Siemens AG
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1.15.5 Parallel connection of S120 Active Line Modules
A parallel connection of Active Line Modules can be supplied either by a two-winding transformer or by a three-
winding transformer of which the secondary windings deliver voltages with optional phase displacement (e.g. 30°
electr.).
When the parallel connection is supplied by a three-winding transformer, it is absolutely essential to install two
Control Units and operate them according to the master-slave principle, see also subsection "Redundant line supply
concepts with SINAMICS Active Infeed" in section "Redundant line supply concepts". Owing to the very low harmonic
effects on the supply system associated with the Active Infeed, no benefits with respect to reduced harmonic effects
are gained by the use of a three-winding transformer with a phase displacement of 30° electr. (by contrast with the
line-commutated Basic Infeeds and Smart Infeeds). This also means however that the harmonic effects on the
system do not increase (in contrast to line-commutated Basic Infeeds and Smart Infeeds) when the transformer is
loaded asymmetrically (failure of one of the two Active Infeeds and operation on only one secondary winding of the
three-winding transformer).
Parallel connection of S120 Active Line Modules supplied by a two-winding transformer
When a parallel connection is supplied by a single two-winding transformer, up to four Active Line Modules are
synchronously controlled by one common Control Unit. Synchronous control by the common Control Unit requires
that all the Active Line Modules in the parallel connection must be connected to the same line supply with identical
phasing and this is achieved automatically if the parallel connection is supplied by a single two-winding transformer.
Parallel connection of S120 Active Line Modules supplied by a two-winding transformer
The following measures help to ensure balanced currents in parallel connections of Active Line Modules:
· Use of an electronic current sharing control (ΔI control)
· Reactors in the Clean Power Filters of the Active Interface Modules
· Use of symmetrical power cabling between the transformer and the parallel-connected Active Interface
Modules / Active Line Modules (cables of identical type with the same cross-section and length)
The current reduction from the rated value for individual Active Interface Modules / Active Line Modules in a parallel
connection is 5 %.
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