Parallel Connection Of S120 Motor Modules - Siemens SINAMICS G130 Engineering Manual

Since the three-winding transformer has a star winding and a delta winding and the delta winding has no neutral point
that could be grounded in any meaningful way, parallel connections of S120 Active Line Modules are usually
connected to two non-grounded secondary windings and thus to an IT supply system. For this reason, it is necessary
to provide an insulation monitor.
Owing to the phase displacement between the two subsystems when these are controlled by separate Control Units,
it cannot be absolutely guaranteed that both subsystems participate equally in the pre-charging of the connected DC
link. In order to ensure that individual subsystems are not overloaded during precharging, the parallel connection of
Active Line Modules supplied by a three-winding transformer should be dimensioned where possible such that each
subsystem is able to precharge the entire DC link on its own.
1.15.6

Parallel connection of S120 Motor Modules

In vector control mode (drive object of vector type), up to four Motor Modules operating in parallel can supply a single
motor The motor can have either electrically isolated winding systems or a common winding system. The kind of
.
winding system combined with the number of Motor Modules determine the decoupling measures which need to be
implemented at the outputs of the parallel-connected Motor Modules.
The two possible variants, i.e.
·
motor with electrically isolated winding systems,
·
motor with a common winding system,
are discussed in more detail below.
Motors with electrically isolated winding systems
Motors in the power range from about 1 MW to 4 MW, which is the usual range for converter parallel connections,
generally feature several parallel windings. If these parallel windings are not interconnected inside the motor, but
connected separately to its terminal box(es), then the motor winding systems are separately accessible. In this
instance, it is often possible to dimension the parallel connection of S120 Motor Modules in such a way that each
winding system of the motor is supplied by exactly one of the Motor Modules in the parallel connection. The diagram
below shows this type of arrangement.
Motor with electrically isolated winding systems supplied by a parallel connection of S120 Motor Modules
Due to the electrical isolation of the winding systems, this arrangement offers the advantage that no decoupling
measures need to be implemented at the converter output in order to limit any potential circulating currents between
the parallel-connected Motor Modules (no minimum cable lengths and no motor reactors or filters).
Both types of modulation systems, i.e. space vector modulation and pulse-edge modulation, can be used. When the
parallel connection is supplied by Basic Infeeds or Smart Infeeds, the maximum obtainable output voltage is almost
equal to the line supply voltage on the input side of the Infeed (97 %). When the parallel connection is supplied by
Active Infeeds a higher output voltage than the line supply voltage on the input side of the Infeed can be obtained due
to the increased DC link voltage.
The current reduction for parallel connections is 5 % referred to the rated currents of the individual Motor Modules.
Fundamental Principles and System Description
SINAMICS Engineering Manual – November 2015
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