ABB REB670 Applications Manual page 156

Section 6
Differential protection
150
Three one-phase
REB670
REB670
REB670
REB670
IEC06000126 V2 EN
Figure 72: 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 as shown section
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 73.
Single one-phase
REB670
REB670
@
+
with 1A
CT inputs
"Different busbar
1MRK 505 337-UUS -
Auxiliary Summation CT *)
type SLCE 8; 1/1A, 2/1A or 5/1A
Up to 18 pcs
auxiliary CTs
*) One SLCE 8 per main CT
IEC06000126_2_en.vsd
arrangements", for
Application manual