Pag. 14 / 57 0MNMPMK10NPENUB 00
3.1.2 Selectivity
The system where the UPS is inserted must be set up in such a way that in the event of a shortcircuit on one of the
lines downstream of the UPS, the fuse on the output opens while the upstream fuse normally works. This is known
as selectivity, and ensures that the
remaining feeders maintain the
power supply.
In order to select the correct
protection devices to be inserted
downstream of the UPS, the
following two operating modes have
to be taken into consideration:
mains power supply and battery
power supply.
With mains power supply the output fuse must be selective with the input fuse; the condition is verified for the
following values:
At least two feeders are necessary in order to use the UPS at rated load with fuses of type gG.
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.
At least 2÷3 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 40kVA:
selectivity with both mains power supply and battery power supply;
the load has to be shared between at least three feeders, each sized at 33% 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.
H
+/-
LOAD
UPS
SWBY
SWIN
SWOUT
+/-
BATTERY CABINET
kVA 10 15 20 30 40 60 80 100
rated output current: [A] 43 65 87 130 174 260 348 435
type gG fuse used at the bypass input
(as shown in the table of connections) [A]
50 80 100 160 200 315 400 500
maximum fuse at the UPS output for selectivity:
fuse size for type gG fuse [A] 32 50 63 100 125 200 250 315
fuse size for type aM fuse [A] 16 25 36 63 80 125 160 200
kVA 10 15 20 30 40 60 80
rated output current: [A] 43 65 87 130 174 260 348 435
shortcircuit current 3 times the rated output current for 1 second
maximum fuse at the UPS output for selectivity:
fuse size for type gG fuse [A] 25 32 40 63 80 100 160 160
fuse size for type aM fuse [A] 12 20 20 40 50 63 125 125
To Next Page
Loading...
