Fundamental Principles and System Description
Engineering Information
SINAMICS Engineering Manual – November 2015
Ó Siemens AG
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· Symmetrical power cabling at the plant side between the transformer and the parallel-connected Infeeds
and between the parallel-connected Motor Modules and the motor (use of cables of the same type with
identical cross-section and length)
· Use of an electronic current sharing control (ΔI control)
In practice, however, it is not generally possible to achieve an absolutely symmetrical current distribution, even when
several of the above measures are combined. As a result, a slight current reduction of a few per cent below the rated
current must be taken into account when parallel connections of power units are configured.
The current reduction from the rated value of the individual modules is as follows:
· 7.5 % for parallel connections of S120 Basic Line Modules and S120 Smart Line Modules because the
modules are not equipped with an electronic current sharing control
· 5.0 % for parallel connections of S120 Active Line Modules and S120 Motor Modules because the
modules are equipped with an electronic current sharing control
1.15.3 Parallel connection of S120 Basic Line Modules
Parallel connections of Basic Line Modules can be implemented as either a 6-pulse circuit if the parallel-connected
modules are connected to a two-winding transformer, or as a 12-pulse circuit if the parallel-connected modules are
connected to a three-winding transformer with secondary windings that supply voltages with a phase shift of 30 °.
6-pulse parallel connection of S120 Basic Line Modules
With the 6-pulse parallel connection, up to four Basic Line Modules are supplied by a common two-winding
transformer on the line side and controlled by a common Control Unit.
6-pulse parallel connection of S120 Basic Line Modules
As Basic Line Modules have no electronic current sharing control, the current must be balanced by the following
measures:
· Use of line reactors with a relative short-circuit voltage of v
k
= 2 %
· Use of symmetrical power cabling between the transformer and the parallel-connected BLMs (cables of
identical type with the same cross-section and length)
The current reduction from the rated value for individual Basic Line Modules in a parallel connection is 7.5 %.
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