6.1.6.3 Possible ASCT connections for REB670
M12137-3 v4
It is possible to connect the ASCTs for summated bus dif
ferential protection with
REB670:
• at the end of the main CT circuit (for example, beyond the other protective relays,
as shown in Figure
85
• in series with other secondary equipment when some other relay must be located at
the end of the main CT circuit , as shown in Figure 86
End connection is the preferred arrangement as it gives greater sensitivity for
summation type bus differential protection (as shown in T
able
24 for more
information).
However, it should be noted that these two connection types must not be mixed. This
means that within one busbar installation all auxiliary summation CT
s have to be either
end-connected or series-connected.
Typical end-connection with ASCT is shown in Figure
85.
en06000128_ansi.vsd
A
B
C
N
IA
IB
IC
IN
Other
relays
Auxiliary Summation CT
type SLCE 8;
1/1A or 5/1A or 2/1A
N4
S1
S2
Main CT
2000/1A or 2000/5A
or 2000/2A
AI0
3
X401
5
6
REB 670 with 1A CTs
P1
N1
P2
P3
N2
P4
P5
N3
P6
I
SUMM
ANSI06000128 V1 EN-US
Figure 85: End-connection with ASCT connected to CT3 input
It is important to notice that even in the case of 5A or 2A main CTs, secondary current
of the summation CTs shall be connected to the IED with 1A CT inputs (as shown in
Figure 85). The reason for this is that the rated secondary current of ASCT is always
1A irrespective of the rated secondary current of the main CT.
Refer to section "SLCE 8/ASCT characteristics for end-connection" for detailed ASCT
current calculations for end-connection.
Typical series-connection with ASCT is shown in Figure 86.
Section 6 1MRK 505 370-UUS A
Differential protection
168 Busbar protection REB670 2.2 ANSI
Application manual
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