• Only one measuring circuit is utilized for all fault types (that is, no redundancy for
multi-phase faults)
• Primary fault sensitivity varies depending on the type of fault and involved
phase(s), see T
able
24
• The load currents in the healthy phases might produce the stabilizing current when
an internal single phase to ground fault occurs. However
, there is no problem for
solidly gounded systems with high ground-fault currents
• No indication of faulty phase(s) in case of an internal fault
• Not possible to fully utilize Open CT detection feature
6.1.6.2 Auxiliary summation CTs
M12136-4 v4
Auxiliary Summation Current Transformer (that is, ASCT in further text) of the type
SLCE 8 is used with the summation principle of the IED. The principle drawing of one
such ASCT is shown in Figure
84.
Auxiliary Summation CT
type SLCE 8; X/1A
N4
S1
S2
en03000118_ansi.vsd
P1
N1
P2
P3
N2
P4
P5
N3
P6
ANSI03000118 V1 EN-US
Figure 84: Principle ASCT drawing
The ASCT has three primary windings and one secondary winding. In further text, turn
numbers of these windings will be marked with N1, N2, N3 & N4, respectively (see
Figure
84 for more information).
There are three types of ASCT for REB670:
Section 6 1MRK 505 370-UUS A
Differential protection
166 Busbar protection REB670 2.2 ANSI
Application manual
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