Siemens SINAMICS G130 Engineering Manual page 61

Fundamental Principles and System Description
Engineering Information
In the case of Basic Line Modules for the SINAMICS S120 modular system equipped with diodes, precharging is
carried out via resistors, which create losses. Due to the power loss that occurs in the resistors during precharging,
the permissible DC link capacitance of the connected inverters (S120 Motor Modules) is limited to a lower value than
with Basic Line Modules equipped with thyristors.
The maximum permissible DC link capacitance for the different S120 Basic Line Modules can be found in the section
"Checking the maximum DC link capacitance" of the chapter "SINAMICS S120, General Information about Built-in
and Cabinet Units".
To achieve an increased output power rating, it is possible to connect up to four S120 Basic Line Modules in parallel
(including 6-pulse and 12-pulse configurations). Further details can be found in the section "Parallel connections of
converters".
Due to the operating principle of the 6-pulse three-phase bridge circuit, the Basic Infeed causes relatively high
harmonic effects on the supply system. The line current contains a high harmonic content with harmonic numbers
h = n 6 ± 1, where n assumes integers 1, 2, 3, etc. The Total Harmonic Distortion factor of current THD(I) is
*
typically in the range from about 30 % to 45 %. For further information about harmonic characteristics, please refer to
the section "Harmonic effects on the supply system". Line Harmonics Filters LHF can be installed on the line side of
G130 chassis units and G150 cabinet units in order to reduce the effects of harmonics on the supply. These reduce
the total harmonic distortion factor THD(I) to below 7.5%. A similar reduction can also be achieved with 12-pulse
circuits, i.e. by supplying two Basic Line Modules from a three-winding transformer with a 30 ° phase displacement
between its voltages.
The criteria for defining of the required transformer power rating, taking into account the harmonic load as well as the
characteristics of three-winding transformers in 12-pulse operation, are described in the section "Transfomers".
SINAMICS Engineering Manual - May 2008
61/396
© Siemens AG