Commissioning The Function - Siemens SINAMICS S120 Function Manual

Function modules
9.9 Master/slave function for Active Infeed
Electrical isolation of infeed units
To successfully implement the structure, a means of electrically isolating the infeed units from
the line supply is required in addition to the SINAMICS components. This is to prevent
circulating currents from developing if the pulse patterns of the Active Line Modules are not
synchronized.
Two solutions are possible for the electrical isolation:
● Using an isolating transformer for each slave infeed train. The primary side of the
transformer is to be connected to the grounded or ungrounded line transformer. The
secondary side must never be grounded.
● Using a three-winding transformer for the master and slave infeed units. In this case, only
the neutral point of one winding may be grounded to prevent further electrical coupling via
ground.
For both solutions, a separate transformer must be used for the infeed units for each
Active Line Module (slaves 1 to 3).
Use of a DC switch
When an infeed unit develops a fault, it is disconnected on the line side by the line contactor,
on the DC-link side using a DC breaker. Infeed units must not be switched in to a charged DC
link. The DC link must be discharged before another infeed train can be switched in.
An infeed unit may only be connected to a charged DC link if a DC breaker with pre-charging
branch is installed.
9.9.2

Commissioning the function

Overview
The individual steps for commissioning the "Master/Slave" function are described in the
following.
Commissioning the line and DC link identification
Before the "Master/Slave" function is enabled in the Startdrive engineering tool, the line and
DC-link identification (see Chapter Line supply and DC link identification (Page 35)) must be put
into operation during commissioning for each infeed train.
The corresponding instructions for the commissioning of infeed units in the SINAMICS S120
with Startdrive Commissioning Manual apply.
Once each individual infeed unit has been identified, the correct inductance for current control
and the DC link capacitance for voltage control are set.
If a DC breaker for isolating the infeed unit from the DC link is installed, DC link identification
must be performed again for all active infeed units after one infeed unit has been disconnected,
as it is necessary to acquire the DC link capacitance again. If the DC link capacitance is not
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Function Manual, 06/2019, 6SL3097-5AB00-0BP2
Drive functions