ABB Relion 670 Series Applications Manual page 142

Section 6
Differential protection
IEC16000151 V2 EN-US
Figure 81:
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 ground 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 82.
Three one-phase
REB670
IEC06000126 V2 EN-US
Figure 82:
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
136
ACT configuration example for three bus-sectionalizing disconnectors
REB670
REB670
@
REB670
Difference between phase segregated & summation type differential protection
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Single one-phase
REB670 type SLCE 8; 1/1A, 2/1A or 5/1A
REB670
Up to 18 pcs
+
with 1A
auxiliary CTs
CT inputs
1MRK 505 370-UUS Rev. K
IEC16000151-2-en-us.vsdx
GUID-B09585B4-A1B8-4E29-A469-25997493E434 v1
Auxiliary Summation CT *)
*) One SLCE 8 per main CT
IEC06000126_2_en.vsd
Busbar protection REB670
M12135-3 v4
Application manual