Siemens NXAIR Operating Instructions Manual page 147

•
The selected HV HRC fuse-link limits the sustained symmetrical short-circuit current I
through current I
D
for HV HRC fuse-links with different rated currents). The maximum permissible let-through current is
I = 46 kA.
D
Requirements
The coordination of the components of the motor circuit requires the following:
•
The let-through current I
•
In case of low-voltage supply via a control transformer, short-circuit currents ranging above the limit
breaking capacity must be interrupted within 80 ms. This requirement does not apply if
•
the mechanical latch is provided.
or
•
the opening times have been extended so much that – in the a.m. current range – the contactor
can only open when the fuse-link has interrupted the current.
•
Due to the arising motor starting current, the instant when the motor starts represents the maximum
stress for the HV HRC fuse-link. This stress must neither operate nor pre-damage the fuse-link.
•
Other factors of influence on the stress of the HV HRC fuse-links are the starting time and the
starting frequency of the motors.
110-0134.9 / 14
Operating the contactor panel with panel width 435 mm
, shown in the diagram for the current-limiting characteristics (I
must not exceed 46 kA at 7.2 kV/12 kV.
D
NXAIR / ≤ 40 kA
to the let-
K
as a function of I
D K
147