ABB Relion 670 Series Applications Manual page 145
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- Technical manual (1432 pages) ,
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1MRK 505 370-UUS Rev. K
•
main CT rated primary current is not important for ASCT selection
•
possible main CT ratio differences will be compensated by a parameter setting in the IED
•
rated secondary current of ASCT is 1A for all types. That means that secondary ASCT winding
should be always connected to the IED with 1A CT inputs, irrespective of the rated secondary
current of the main CT
All of these features simplify the ordering of the ASCTs. Practically, in order to purchase ASCTs, the only
required information is the main CT rated secondary current that is, (1A, 2A or 5A).
Table
23
Table 23:
Type of fault
ASCT SLCE 8;
1/1A
ASCT SLCE 8;
5/1A
ASCT SLCE 8;
2/1A
where:
•
N1, N2, N3 & N4 are ASCT windings turn numbers (see Figure 84)
•
Vkp is knee point voltage, at 1.6T, of the secondary winding with N4 turns
•
Burden is the total 3Ph load of ASCT imposed to the main CT
6.1.6.3
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
•
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 85.
Busbar protection REB670
Application manual
summarizes the ASCT data:
Auxiliary summation CT data
N1
N2
52
52
12
12
26
26
Due to ASCT design, the ASCTs for summated bus differential protection, must always
be mounted as close as possible to the IED (that is, in the same protection cubicle).
85
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N3
N4
104
90
24
104
52
90
86
24
for more information).
Differential protection
Vkp [V]
Burden [VA]
33
1.0
38
1.0
33
1.0
Section 6
M12137-3 v4
139
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