Siemens SINAMICS S120 Combi Manual page 52

Line-side power components
3.8 Line connection versions
An isolating transformer / 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 underdimensioned (S
faults in the line supply and 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 complied with when selecting the matching
transformer.
S , S
n1
u = short-circuit voltage of the matching transformer in %
k
(must be between 1% ... 3% for the S120 Combi)
S = short-circuit power.
K
Electric shock due to the connection of an unsuitable power supply
If the short-circuit power is not sufficiently high enough to trip the fuse in the event of a fault,
there is a risk of electric shock or fire.
• Use a power supply which generates a sufficient system fault level.
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:
When operating with only one supply at a transformer, the values may be reduced by the
factor 0.73.
S
K line
52
= calculated rated power of the transformer resulting from a) and b)
n2
WARNING
of the S120 Combi Power Module.
n
≥ 1.27 • P
n
≥ 70 • P
n
≥ 0.73 • 70 • P
n
or S ), this can lead to increased line voltage dips and
n k
must always be a factor of 1.27 higher than
n1
SINAMICS S120 Combi
Manual, 11/2017, 6SL3097-4AV00-0BP7