ABB Relion 670 Series Applications Manual page 146

Section 6
Differential protection
Main CT
2000/1A or 2000/5A
or 2000/2A
ANSI06000128 V1 EN-US
Figure 85:
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
calculations for end-connection.
Typical series-connection with ASCT is shown in Figure 86.
Main CT
2000/1A
or 2000/5A
or 2000/2A
Other
relays
Other
relays
ANSI06000129 V1 EN-US
Figure 86:
140
IA
A
IB
B
Other
relays
IC
C
IN
N
End-connection with ASCT connected to CT3 input
"SLCE 8/ASCT characteristics for end-connection"
A B C N
IA IB IC
IN
Series-connection with ASCT connected to CT3 input
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Auxiliary Summation CT
type SLCE 8;
1/1A or 5/1A or 2/1A
I
P1
SUMM
N1
S1
P2
P3
N4
N2
P4
P5
N3
S2
P6
Auxiliary Summation CT
type SLCE 8; 1/1 or 5/1A or 2/1A
IA
I
P1 SUMM
N1
S1
P2
P3
N4
N2
IC
P4
P5
S
N3
IN
2
P6
1MRK 505 370-UUS Rev. K
REB 670 with 1A CTs
en06000128_ansi.vsd
for detailed ASCT current
REB 670 with 1A CTs
en06000129_ansi.vsd
Busbar protection REB670
Application manual