Possible Asct Connections For Reb670 - ABB REB670 Applications Manual

Section 6
Differential protection
6.1.5.3
154

Possible ASCT connections for REB670

It is possible to connect the ASCTs for summated bus differential protection with
REB670:
• at the end of the main CT circuit (for example, beyond the other protective relays, as
shown in figure 75
• 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
End connection is the preferred arrangement as it gives greater sensitivity for summation
type bus differential protection (as shown in table
However, it should be noted that these two connection types must not be mixed. This
means that within one busbar installation all auxiliary summation CTs have to be either
end-connected or series-connected.
Typical end-connection with ASCT is shown in figure 75.
Main CT
2000/1A or 2000/5A
or 2000/2A
A
B
Other
relays
C
N
ANSI06000128 V1 EN
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 "SLCE 8/ASCT characteristics for end-connection"
current calculations for end-connection.
Typical series-connection with ASCT is shown in figure 76.
24
Auxiliary Summation CT
type SLCE 8;
1/1A or 5/1A or 2/1A
IA
P1
N1
IB
S1
P2
P3
N2 N4
IC
P4
P5
N3
IN
S2
P6
1MRK 505 337-UUS -
76
for more information).
I
SUMM
REB 670 with 1A CTs
en06000128_ansi.vsd
for detailed ASCT
Application manual