ABB REB670 - Page 170

principal differences between full, phase-segregated bus differential protection scheme
and summation type bus differential protection scheme are shown in Figure 82.
Auxiliary Summation CT *)
type SLCE 8; 1/1A, 2/1A or 5/1A
+
Three one-phase
REB670
Single one-phase
REB670
Up to 18 pcs
auxiliary CTs
*) One SLCE 8 per main CT
REB670
with 1A
CT inputs
REB670
REB670
REB670
@
IEC06000126_2_en.vsd
IEC06000126 V2 EN-US
Figure 82: Difference between phase segregated & summation type differential
protection
In the full phase-segregated design, three one-phase REB670 IEDs (that is, one per
phase) are used. However for the summation type only single one-phase REB670 IED
plus one auxiliary summation CT per each main CT is required. These auxiliary
summation CTs convert each main CT three-phase currents to a single-phase output
current, which are all measured by one REB670 IED. The differential calculation is
then made on a single-phase basis. By doing so, this more cost effective bus
differential protection can be applied. Due to this characteristic, this summation type of
bus differential protection can be applied for all types of stations arrangements up to
two differential zones as shown in Section Two-zone busbar arrangments, for three
one-phase IEDs.
As an example, the necessary equipment for the summation type, busbar differential
protection for a single busbar station with up to 24 bays, is shown in Figure 83.
Section 6 1MRK 505 370-UUS A
Differential protection
164 Busbar protection REB670 2.2 ANSI
Application manual