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Section 6
Differential protection
When the bus coupler/section breaker is open, to disconnect this current from both zones,
additional configuration logic is required by using the binary input, for example
two-zone differential protections . Figure
following two binary inputs are at least necessary in order to guaranty proper operation of
such logic:
•
Normally closed contact of the bus section or bus coupler circuit breaker
•
Signal from the bus section or bus coupler circuit breaker closing circuit that somebody
wants to close the breaker.
This solution does not depend on contact timing between the main contacts and auxiliary
contact of the circuit breaker. It directly follows the philosophy used for RADSS/REB 103
schemes used for similar applications before. Principle connection between the bus-coupler
CB normally closed auxiliary contact ("b" contact), REB670 and internal configuration logic, as
shown in Figure 47.
QB1
QB2
QA1
BI1
2400/1
Bus-Coupler
Bay
IEC06000155 V1 EN-US
Figure 47: Bus coupler bay with one CT and "b" aux. contact only from CB
This scheme will disconnect the section/coupler CTs after a pre-set time length (≥80 ms
recommended) defined by the parameter setting
block from the moment of opening of the section/coupler CB (that is, from the moment when
auxiliary "b" contact operates). Nevertheless this time delay is absolutely necessary in order to
prevent racing between the opening of the main breaker contact and disconnection of the CT
from the differential zones. This scheme will as well disconnect the CT in case of the operation
of any of the two internal differential zones used in the scheme. This will secure the delayed
(≥150 ms, depending one the values of the setting
internal fault within the blind zone even in case of section/coupler circuit breaker failure
during such fault. This facility will improve the performance of the busbar protection scheme
when one CT is located on only one side of the bus-section / bus-coupler circuit breaker.
With GIS or live tank circuit breakers, owing to high cost of HV CT installations, sometimes no
current transformers are available in bus-section or bus-coupler bay. This is the third solution
shown in Figure
104
Zone A
Zone B
REB 670
b
BIM
CB Closing
Signal
External or Internal
Bus-Coupler BFP
Backup Trip Command
Bus-Coupler Backup
OC Trip
TRM
CT Input
A/D
Other
Equipment
48
47
provides an example of such logic. Moreover, the
t=1s
t
³1
&
Bxxx
BLKTR
TRIP
CTRLZA
CONNZA
CTRLZB
CONNZB
ZEROCUR
TRZONE
TRBAY
I3PB1
Parameter ZoneSel must
be set to "FixedToZA&-ZB"
tZeroCurrent=150ms
BBP & BFP trip command to Bus-Coupler breaker
en06000155.vsd
tZeroCurrent in the relevant bay function
tZeroCurrent ) clearing and tripping of the
1MRK 505 370-UEN D
ZEROCUR in
BOM
Busbar protection REB670
Application manual
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