ABB REB670 Applications Manual page 124

Section 6
Differential protection
118
Busbar
BI1
Protection
152
Feeder
BI1
Protection
A
ANSI06000138 V1 EN
Figure 48: Typical CT locations in a feeder bay
where:
A = two CTs are available one on each side of the feeder circuit breaker
B = one CT is available on the line side of the feeder circuit breaker
C = one CT is available on the bus side of the feeder circuit breaker
1 = End fault region
In figure 48, /A where two CTs are available in a feeder bay the end fault protection is not
an issue. The busbar and feeder protection zones overlap across feeder circuit breaker and
all faults between these two CTs will be instantly detected and tripped by both protection
schemes. As a consequence of such fault both busbar and feeder will be disconnected from
the power system.
In figure 48/B where one CT is available on the line side of the feeder circuit breaker the
primary fault between CT and CB will cause certain problems. Typically such fault will
be detected and tripped by busbar protection. However to completely clear such fault the
remote feeder end CB must be tripped as well. It shall be noted that for the feeder
protection such fault will be either a reverse fault (that is, distance protection used for
feeder protection) or external fault (that is, line/transformer differential protection used
for feeder protection).
In figure 48/C where one CT is available on the bus side of the feeder circuit breaker the
primary fault between CT and CB will cause problem as well. Typically such fault will be
detected and tripped by feeder protection. However, to completely clear such fault the
associated busbar section must be tripped as well. It shall be noted that the busbar
differential protection will classify such fault as external and without any additional
measures the busbar protection will remain stable.
For better understanding end fault protection applications within busbar protection, the
figure 49 is used.
Busbar
Protection
152
BI1
1
Feeder
B
Protection
1MRK 505 337-UUS -
Busbar
Protection
BI1
152
Feeder 1
Protection
C
en06000138_ansi.vsd
Application manual