ABB SPAJ 131 C User Manual And Technical Description page 11

Example 1.
Protection of
industrial low-
voltage switchgear
1 2 3 4 5 6 7 8 9
U3
SPAJ 131 C
Fig. 5. Overcurrent relay SPAJ 131 C used to protect an outgoing feeder in industrial switchgear.
The switch settings are shown in the table on the next page.
The low-set stage of the overcurrent module
SPCJ 3C3 operates as overcurrent and short
circuit protection for the low-voltage switchgear
and as back-up protection for the outgoing
feeder of the distribution switchgear. The low-
set stage is set to extends to the next protection
stage. The setting of the low-set stage should be
selected so as to ensure that the protection
operates selectively together with the fuses on
the outgoing feeders. The high-set stage is set to
operate at close-by short circuits.
L1 L2 L3
+
~
( )
Uaux
- ~
( )
BS IRF
10 11 61 62 70 71 72
~
E
U3
+ -
SGR/1
IRF
t >,k
3I>
SGB
4
5
t >>
3I>>
U1
Ι
+
0
START1 SIGNAL1 TRIP2
77 78 80 81 68 69
D C
1 1
SGR
3 2 4 7 5
SS1
TS1
SS2
TS2
I/O
Separate protection for the low-voltage switch-
gear is important if there are several distribution
transformer along the same feeder. In particular
faults in low-voltage switchgear fed by the smaller
transformers of a system are not always capable
of starting the overcurrent relay of the distribu-
tion switchgear feeder.
Current asymmetry, if it appears, does not have
to be allowed for in the current settings, because
due to the peak-to-peak measurement method
employed by the overcurrent relay such asym-
metry does not affect the operation of the relay.
0
-
Ι
-
+
Rx Tx
TRIP1
+
SERIAL
PORT
65 66
B A
1 1
8
6
U2
11