ABB Relion 670 Series Applications Manual page 143

1MRK 505 370-UUS Rev. K
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 up to two differential zones as shown in Section
Two-zone busbar
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 83.
Main CTs
ANSI06000127 V2 EN-US
Figure 83:
This summation type bus differential protection still has the same main CT requirements as outlined in
section "Rated equivalent secondary e.m.f.
• 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
requirements"
However, due to the summation principle this type of busbar protection scheme has the following
limitations:
Busbar protection REB670
Application manual
arrangments, for three one-phase IEDs.
LA LB
IA1 IB1
52 52
A B C N A
IA2 IB2
CT1
Principle CT connections for the complete station
for detailed CT requirements regarding main CT knee-point voltage)
© 2017 - 2021 Hitachi Power Grids. All rights reserved
LX
IX1
52
B C N A B
IX2
CT2 . . . CT24
IED
with 1A
CT inputs
requirements". Some of these are:
A-bus
C N
Summation CTs
ANSI06000127_2_en.vsd
"Rated equivalent secondary e.m.f.
Section 6
Differential protection
137