ABB REB670 Applications Manual page 157

1MRK 505 337-UUS -
Application manual
LA
IA1
Main CTs
52
A B C
IA2
CT1
ANSI06000127 V2 EN
Figure 73: Principle CT connections for the complete station
This summation type bus differential protection still has the same main CT requirements
as outlined in section "". 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
requirements regarding main CT knee-point voltage)
However, due to the summation principle this type of busbar protection scheme has the
following limitations:
LB LX
IB1 IX1
52 52
A B C N
N
IB2 IX2
CT2 . . .
IED
with 1A
CT inputs
Section 6
Differential protection
A-bus
A B C N
Summation CTs
CT24
ANSI06000127_2_en.vsd
"" for detailed CT
151