Siemens SINAMICS G130 Engineering Manual page 117

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
taken separately to its terminal box(es), then the motor winding systems are separately accessible. In such cases, it
is often possible to dimension the parallel connection of S120 Motor Modules in such a way that each motor winding
system is effectively supplied by a separate Motor Module of 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 following advantages:
•
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)
•
Both types of modulation system, i.e. space vector modulation and pulse-edge modulation can be used,
i.e. when the parallel connection is supplied by Basic Infeeds or Smart Infeeds, the maximum
obtainable output voltage is almost equal to the input voltage from the Infeeds at the three-phase side
(97 %). When the parallel connection is supplied by Active Infeeds, a higher output voltage than the
input voltage at the three-phase side can be obtained due to the increased DC link voltage.
The current reduction from the rated value for the individual Motor Modules in a parallel connection is 5 %.
Note:
The number of separate winding systems that can be implemented in the motor depends on the number of motor
poles. This means that it is not always possible to achieve an optimum assignment between parallel-connected Motor
Modules and winding systems. For instance, a parallel connection of two Motor Modules might be the best solution in
terms of cost and volume for a motor which can, however, be designed with only three separate winding systems. In
this case, it would be necessary to select three lower-power-output Motor Modules for the parallel connection, or the
motor would need to be connected up as a motor with a common winding system. If the latter option were chosen,
decoupling measures would need to be implemented and it would not be possible to use pulse-edge modulation.
To make best use of the advantages described above, new installations should always be assessed for the possibility
of using a motor with separate winding systems and a coordinated parallel connection of Motor Modules. If this
variant is feasible, it should be used whenever possible.
Fundamental Principles and System Description
Engineering Information
SINAMICS Engineering Manual - May 2008
© Siemens AG
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