ABB REB670 Series, Applications Manual

Page: 141 / 476

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 82 .
IED
with 1A
CT inputs
IB2 IX2 IA2
L1 L2 L3 N
IA1 IB1 IX1
LA LB LX
A-bus
Summation CTs
Main CTs
CT1 CT2 . . . CT24
IEC06000127_2_en.vsd
L1 L2 L3 N L1 L2 L3 N
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 "Rated equivalent secondary e.m.f. requirements" . Some of these are:
• 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 "Rated equivalent
secondary e.m.f. requirements" for detailed CT requirements regarding main CT knee-
point voltage)
However, due to the summation principle this type of busbar protection scheme has the
following limitations:
1MRK 505 370-UEN D Section 6
Differential protection
Busbar protection REB670 135
Application manual