Siemens SINAMICS G130 Engineering Manual page 115

Variant 2 with Active Infeed (master-slave configuration); boundary conditions to be observed:
·
Both of the two Active Infeeds (master and slave) must be electrically isolated on the line side to prevent
circulating currents that may otherwise occur between the systems as a result of autonomous,
unsynchronized operation with two independent Control Units. This electrical isolation, which is absolutely
essential, is ensured by means of the three-winding transformer.
Depending on the type of supply system required (grounded TN supply system or non-grounded IT supply
system), the star point of the star winding supplying the master Infeed can be grounded (TN supply system)
or remain open (IT supply system). With respect to voltage loads on the DC link and on the motor windings
to ground, however, operation with a non-grounded IT supply system is preferable. The winding for the slave
Infeed must remain non-grounded in all cases.
·
If it is acceptable to operate the DC link at half power if an Active Infeed fails, each Active Infeed can be
dimensioned for half the infeed current, taking into account a current derating of 5% with respect to the rated
current. If the full infeed power is required if an Active Infeed fails, each of the two Active Infeeds and the
associated transformer windings must be dimensioned for the full power required for the DC link.
·
Each Active Line Module in conjunction with its Active Interface Module must be able to precharge the
complete common DC link capacitance.
Variant 3 with Active Infeed (master-slave configuration); boundary conditions to be observed:
·
The Active Infeeds (master and slave(s)) must be electrically isolated on the line side to prevent circulating
currents that may otherwise occur between the systems as a result of autonomous, unsynchronized
operation with independent Control Units.
Depending on whether the Active Infeeds are supplied from a common low-voltage supply system or from
different medium-voltage supply systems, a distinction is made between two configurations:
a) Supply from a common low-voltage supply system:
- The master Infeed is connected directly to the low-voltage supply system, whereby the supply system
can be operated as either a grounded (TN) or non-grounded (IT) supply system. With respect to
voltage loads on the DC link and on the motor windings to ground, however, operation with a non-
grounded IT supply system is preferable.
- The slave Infeed(s) must be supplied by its / their own isolation transformer, whereby all secondary
windings must be non-grounded.
Fundamental Principles and System Description
SINAMICS Engineering Manual – November 2015
Engineering Information
115/528
Ó Siemens AG