Siemens SINAMICS S120 Function Manual page 324

Function modules
7.11 Parallel connection of power units
with exactly the same line voltage, the current distribution is largely symmetrical in normal
operation, even with uncontrolled infeeds. The infeeds can thus be dimensioned such that,
taking into account a minor current derating factor, each can carry 50 % of the total current.
However, if one infeed fails, only half the output remains available. If the full output needs to
be available when one infeed fails, then each infeed must be dimensioned to carry the full
current.
12-pulse infeed
With the 12-pulse infeed circuit variant, the two redundant infeeds of identical type are also
connected to the supply system, but via a three-winding transformer. Depending on the
transformer design, the line-side voltages of the two infeeds will include minor tolerances of
between about 0.5 % to 1 %. These can cause slightly asymmetrical current distribution in
normal operation when uncontrolled infeeds are used and current derating factors must be
applied accordingly. If the full output needs to be available when one infeed fails, then each
infeed must be dimensioned to carry the full current.
6-pulse, 12-pulse infeed
When separate Control Units are used, pre-charging may not be synchronized accurately
enough, i.e. one converter system must be able to pre-charge the total capacitance of the
drive line-up. Pre-charging power for the DC link in parallel operation must be dimensioned
so that the capacitance of the DC link can be fully charged by a single converter system.
Otherwise a separate pre-charging device must be provided.
Basic Line Modules (BLM)
Features
● The DC link voltage is greater than the rms value of the line rated voltage by a factor of
● They are used in cases where regenerative feedback capability is not required.
● If regenerative conditions occur in the drive line-up, Braking Modules must be used
Basic Line Modules are available for the following voltages and power ratings:
Line voltage / unit rating
380 ... 480 V 3 AC / 200 ... 710 kW
500 ... 690 V 3 AC / 250 ... 1100 kW
The following rules must be observed when connecting Basic Line Modules in parallel:
● Up to 4 identical Basic Line Modules can be connected in parallel.
● A shared Control Unit must be used to implement the parallel connection.
● Special Line Connection Modules are available for the parallel connection.
● With multiple infeeds, power must be supplied to the systems from a common infeed
● A current reduction (derating) of 7.5 % must be taken into consideration, regardless of the
As Basic Line Modules have no current compensation control, the three-winding transformer,
power cabling and line reactors must meet the following requirements in order to provide a
balanced current:
324
1.35.
because they convert the excess energy
into heat using braking resistors.
point (i.e. the modules cannot be operated on different supplies).
number of modules connected in parallel.
Function Manual, (FH1), 10/2008, 6SL3097-2AB00-0BP5
Drive functions