en06000138.vsd
BI1
QA1
BI1
Busbar
Protection
Feeder
Protection
BI1
QA1
Busbar
Protection
Feeder
Protection
QA1
BI1
Busbar
Protection
Feeder
Protection
A B
1
C
1
IEC06000138 V1 EN-US
Figure 50: 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 50/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
50/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
50/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
51 is provided.
Section 6 1MRK 505 370-UEN D
Differential protection
106 Busbar protection REB670
Application manual
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