ABB REB670 Series Applications Manual page 141

1MRK 505 370-UEN D
arrangements up to two differential zones as shown in Section
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 82.
Main CTs
IEC06000127 V2 EN-US
Figure 82: Principle CT connections for the complete station
This summation type bus differential protection still has the same main CT requirements as
outlined in section
• main CT ratio differences can be tolerated up to 10:1 (for example, 3000/5A CT can be
balanced against CT"s as low as 300/5)
• different main CT ratios are compensated numerically by a parameter setting
• main CT shall not saturate quicker than 2 ms ( refer to section
secondary e.m.f. requirements"
point voltage)
However, due to the summation principle this type of busbar protection scheme has the
following limitations:
Busbar protection REB670
Application manual
LA LB
IA1 IB1
L1 L2 L3 N
IA2 IB2
CT1
"Rated equivalent secondary e.m.f.
LX
IX1
L1 L2 L3 N L1
IX2
CT2 . . .
IED
with 1A
CT inputs
requirements". Some of these are:
for detailed CT requirements regarding main CT knee-
Differential protection
Two-zone busbar
A-bus
L2 L3 N
Summation CTs
CT24
IEC06000127_2_en.vsd
"Rated equivalent
Section 6
arrangments,
135