Admissible And Inadmissible Winding Systems For Parallel Connections Of Sinamics Converters - Siemens SINAMICS G130 Engineering Manual

Fundamental Principles and System Description
Engineering Information
Motors with a common winding system
It is not possible to use motors with electrically isolated winding systems for many applications, e.g. it might not be
possible to implement the required number of winding systems due to the pole number or because the motor is not
supplied by Siemens or because a motor with a common winding system is already available for the application. In
such cases, the outputs of the parallel-connected Motor Modules are interconnected via the motor cables in the
motor terminal box. The diagram below shows this type of arrangement.
Motor with common winding system supplied by a parallel connection of S120 Motor Modules
Due to the electrical coupling of the winding systems, the following disadvantages are associated with this
arrangement:
•
Decoupling measures have to be implemented at the converter output in order to limit any potential
circulating currents between the parallel-connected Motor Modules. Decoupling can be implemented
through the use of cables of minimum lengths between the Motor Modules and the motor or
alternatively through the installation of motor reactors at the output of each Motor Module. (For details
of minimum cable lengths, please refer to the section "Parallel connection of Motor Modules" of the
chapter "Modular Cabinet Unit System SINAMICS S120 Cabinet Modules".
•
Space vector modulation is the only permissible modulation system. Pulse-edge modulation cannot be
utilized. The electrical coupling between the winding systems means that the transition between space
vector and pulse-edge modulation modes cannot be controlled and shutdown on over-current on
changeover from one mode to the other would be unavoidable. Since pulse-edge modulation mode is
not available, the maximum output voltage is limited to about 92 % of the three-phase input voltage
when the parallel connection is supplied by Basic Infeeds or Smart Infeeds. When the parallel
connection is supplied by Active Infeeds, a higher output voltage than the input voltage can be obtained
due to the increased DC link voltage, even when the unit cannot operate in pulse-edge modulation
mode.
The current reduction from the rated value for the individual Motor Modules in a parallel connection is 5 %.

Admissible and inadmissible winding systems for parallel connections of SINAMICS converters

The previous sections have discussed the subject of motors with electrically isolated winding systems and motors
with a common winding system, but without exactly defining the properties that are required of "electrically isolated
winding systems" or "common winding systems" to make them suitable for operation with parallel connections of
SINAMICS converters.
The possible variants of winding systems for converter parallel connections are discussed in more detail below and
the systems are categorized as either admissible or inadmissible for parallel connections of SINAMICS converters.
SINAMICS Engineering Manual – May 2008
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