Siemens SINAMICS S120 Combi User Manual page 51

An isolating/autotransformer (matching transformer) must be dimensioned for the total of all
loads connected to it. The apparent powers required must be determined and added as
indicated in the table titled "Transformer configuration instructions". If the transformer is too
small (S
in other loads at this connecting point.
If other loads are connected to the secondary side of the matching transformer, the boundary
conditions indicated under a) and b) must be followed when selecting the matching
transformer.
S
n1
u = short-circuit voltage of the matching transformer in %
k
(must be between 1% and 3% for the S120 Combi)
S
K
A sufficiently high system fault level (short-circuit power) is required to ensure that when a
fault does occur, the fuses rupture in the specified time. An insufficient system fault level
(short-circuit power) increases the time to trip beyond permissible levels (e.g. a fire is
possible).
Supplementary conditions
a) Rated power
The rated power of the matching transformer S
the rated power P
S
n1
Example:
The minimum rated power of a matching transformer for a 16 kW S120 Combi Power
Module is 21 kVA.
b) Short-circuit power
In order to avoid faults and disturbances at the other loads that are connected to the
secondary side of the matching transformer, the total short-circuit power of the plant
connection and that of the matching transformer at the connection point must reach the
following values:
S
K line
Special case:
During operation with only one supply at a transformer, the values may be reduced by the
factor 0.73.
S
K line
For example S
From S
SINAMICS S120 Combi
Manual, Edition 07/2012, 6SL3097-4AV00-0BP3
or S ), this can lead to increased line voltage dips and faults in the line supply and
n k
, S = calculated rated power of the transformer resulting from a) and b)
n2
= short-circuit power.
WARNING
of the S120 Combi Power Module.
n
≥ 1.27 • P
n
≥ 70 • P
n
≥ 0.73 • 70 • P
n
for 16 kW S120 Combi Power Module: S
K line
the required rated power of the matching transformer can be calculated.
K transformer
Line-side power components
2.8 Line connection versions
must always be a factor of 1.27 higher than
n1
= 0.82 MVA = 820 kVA
K line
49