Siemens SINAMICS G130 Engineering Manual page 202

Fundamental Principles and System Description
Engineering Information
Note:
The number of separate winding systems that can be implemented in the motor depends on the number of motor
poles. The values in brackets are theoretically possible, but they are generally impossible to implement in practice
owing to lack of space.
Number of motor poles
2
4
6
8
Possible number of separate winding systems as a function of the number of poles
It is therefore sometimes impossible to achieve an optimum assignment between the number of Motor Modules and
the practicable number of winding systems. For instance, a parallel connection of three Motor Modules with 1200 kW
rated output in each case might be the best solution in terms of cost and volume, but the motor itself can be designed
with only two or four separate winding systems. In this case, the alternative solution of four Motor Modules, each with
900 kW rated output, must be implemented, or the motor must be connected as described in section "Admissible and
inadmissible winding systems for parallel connections of converters". Please note that the latter option necessitates
the implementation of decoupling measures (minimum cable lengths or motor reactors and/or filters).
To make best use of the advantage described above, new installations should always be assessed for the possibility
of using a motor with separate winding systems and assigning the same number of Motor Modules capable of parallel
connection. If this variant is feasible, it should be preferred over all other options.
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 disadvantage of this arrangement is that decoupling
measures need to be implemented at the converter output in order to limit any potential circulating currents between
the parallel-connected Motor Modules. Decoupling can be achieved either through the use of cables of minimum
lengths between the Motor Modules and the motor or through the provision of motor reactors or filters at the output of
each Motor Module. The required minimum cable lengths are specified in the unit-specific chapters "General
Information about Built-in and Cabinet Units SINAMICS S120" and "General Information about Modular Cabinet Units
SINAMICS S120 Cabinet Modules".
SINAMICS Engineering Manual – November 2015
202/528
Ó Siemens AG
Possible number of separate winding systems
2
2, 4
2, 3, (6)
2, 4, (8)