Riello UPS MASTER HE, User Manual

Page: 13 / 57

0MNMHEM30RUENUB 00 pag. 13 / 57
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 MASTER HE ,
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:
[kVA] 300 400 500 600 800
Rated output current: [A] 433 578 722 867 1155
Type gG fuse used at the UPS input
(as shown in the
table of connections ) [A]
500 630 800 1000 1250
Maximum fuse at the UPS output for selectivity:
Fuse size for type gG fuse [A]
315 400 500 630 800
Fuse size for type aM fuse [A] 200 250 315 400 500
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.
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] 300 400 500 600 800
Rated output current: [A] 433 578 722 867 1155
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]
125 125 160 200 250
Fuse size for type aM fuse [A] 80 100 125 160 200
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.
H
+/-
L
O
A
D
UPS
SWBY
SWIN
SWOUT
+/-
BATTERY CABINET