ABB RELION 670 Series Applications Manual page 144

Section 6
Differential protection
Main CT
2000/1A or 2000/5A
or 2000/2A
ANSI06000128 V1 EN-US
Figure 75: 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 75). 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 76.
Main CT
2000/1A
or 2000/5A
or 2000/2A
Other
relays
Other
relays
ANSI06000129 V1 EN-US
Figure 76: Series-connection with ASCT connected to CT3 input
138
IA
A
IB
B
Other
relays
IC
C
IN
N
"SLCE 8/ASCT characteristics for end-connection"
A B C N
IA IB IC
IN
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 505 337-UUS A
REB 670 with 1A CTs
en06000128_ansi.vsd
for detailed ASCT current
REB 670 with 1A CTs
en06000129_ansi.vsd
Application manual