Siemens SINAMICS S120 - Page 121

Line Connection Booksize
2.13 Line connection variants
Booksize power units
Manual, (GH2), 06/2008, 6SL3097-2AC00-0BP6
121
A matching transformer must be dimensioned for the total of all loads connected to it. The
apparent power required for the Line Modules must be determined and added as indicated
in table "Transformer configuration instructions". If the transformer S
n
or S
k
is too small, this
can lead to increased line voltage dips and faults in the system 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 followed when selecting the
matching transformer.
S
n1
, S
n2
= calculated rated power of the transformer resulting from a) and b)
u
k
= short-circuit voltage of the matching transformer in %
(must be between 1% and 3% for Active Line Modules and Smart Line Modules)
S
K
= short-circuit power.
WARNING
A sufficiently high system fault level (short-circuit power) is required to ensure that when a
ground 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).
Boundary condition a) Rated power
The rated power (S
n1
) of the matching transformer must always be 1.27 x P
n
Line Module.
S
n1
≥ 1.27 • P
n
Example:
The minimum rated power of a matching transformer for 16 kW Line Modules is 21 kVA.
Boundary condition 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 sum of the system fault level (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
≥ 70 • P
n
(for Active Line Module and Smart Line Module)
S
K line
≥ 30 • P
n
(for Basic Line Module)
Special case:
During operation with only one supply at a transformer, the values may be reduced by the
factor 0.73.
S
K line
≥ 0.73 • 70 • P
n
(for Active Line Module and Smart Line Module)
S
K line
≥ 0.73 • 30 • P
n
(for Basic Line Module)
For example S
K line
for 16 kW Active Line Module: S
K line
= 0.82 MVA = 820 kVA