Auxiliary Summation Cts - ABB REB670 Applications Manual

Section 6
Differential protection
6.1.6.2
166
• 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 Table 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

Auxiliary summation CTs

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
P1
N1
S1
P2
P3
N4
N2
P4
P5
N3
S2
P6
en03000118_ansi.vsd
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:
1MRK 505 370-UUS A
M12136-4 v4
Busbar protection REB670 2.2 ANSI
Application manual