ABB REB670 Series Applications Manual page 140

Section 6
Differential protection
IEC16000151 V1 EN-US
Figure 80: ACT configuration example for three bus-sectionalizing disconnectors
6.1.6 Summation principle
Summation principle is mainly intended for two-zone busbar protection applications.
6.1.6.1 Introduction
A simplified bus differential protection for phase and earth faults can be obtained by using a
single one-phase IED with external auxiliary summation current transformers for all busbar
arrangements with up to two differential zones. By using this approach, more cost effective
bus differential protection can be obtained. Such a solution makes it feasible to apply bus
differential protection even to medium voltage substations. The principal differences between
full, phase-segregated bus differential protection scheme and summation type bus differential
protection scheme are shown in Figure 81.
REB670
IEC06000126 V2 EN-US
Figure 81: Difference between phase segregated & summation type differential
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
134
Three one-phase
REB670
REB670
REB670
protection
Single one-phase
REB670
REB670
@
+
with 1A
CT inputs
GUID-B09585B4-A1B8-4E29-A469-25997493E434 v1
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
Busbar protection REB670
1MRK 505 370-UEN D
IEC16000151-1.en.vsdx
M12135-3 v4
Application manual