Siemens SINAMICS S120 Commissioning Manual page 120

Commissioning
2.10 Commissioning of power units connected in parallel
Parallel connection with one or two Control Units
If an infeed is deactivated, the pre-charging must be able to charge the rest of the infeeds in
the DC link. E.g. The pre-charging time is doubled when only one infeed is available instead
of previously two infeeds in parallel. If possible, the infeeds should be dimensioned such that
one infeed, or with redundant interconnection (2 Control Units), one subsystem is able to
pre-charge the whole DC link.
The connected capacitance should not be too large. However, pre-charging double an
infeed's rated capacitance (one of two infeeds previously out of operation) will work with no
problems.
Pre-charging contactor monitoring
To monitor pre-charging contactors (for infeed failure), auxiliary terminal blocks must be
retrospectively connected to the pre-charging contactors.
The following diagram shows the basic concept of interconnection:
Figure 2-28 Pre-charging monitoring
The contactor states are monitored using the logic blocks "free blocks" in the SINAMICS
drive. If one of the contactors does not pick up, an external fault message is generated.
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Commissioning Manual, (IH1), 01/2011, 6SL3097-4AF00-0BP1
Commissioning Manual