IV404E Rev.000 SIEL S.p.A.
Issue date: 2017-06-05 Pag. 19 di 90 + FR
With
battery power supply (
first fault) in the event of a shortcircuit on one of the outputs (second fault)
it must be possible for the fuse to be open before the inverter shuts down.
If the shortcircuit is of the three-phase type, the inverter can supply a current for 1 second that is 1.8 times
the value of the rated current of the UPS output (with a single phase shortcircuit the current is around 3
times the value).
In the worst-case scenario, that is a three-phase shortcircuit then a smaller current, the condition occurs if:
[kVA]
300
400
500
600
Rated output current:
[A]
433
578
722
867
Shortcircuit current (three-phase) 1.8 times the rated output current for 1
second
Maximum fuse at the UPS output for selectivity:
Fuse size for type gG fuse [A]
125
125
160
200
Fuse size for type aM fuse
[A]
80
100
125
160
At least five feeders are necessary in order to use the UPS at rated load with fuses of type gG.
To sum up, when there is a shortcircuit on the output, there are two alternatives if only the line affected by
the shortcircuit is to be isolated; let us consider the example of the 300kVA:
selectivity with both mains power supply and battery power supply;
the load has to be shared between at least five feeders, each sized at 20% of the rated power.
selectivity, with mains power supply only:
since it is considered unlikely that after a first fault a second fault will occur in the limited time
of operation from the battery
, it is sufficient to share the output between two lines, each sized
for 50% of the rated power.
