ABB RELION 670 Series Applications Manual page 111

1MRK 505 337-UUS A
189
289
BI1
Bus-Coupler
Bay
ANSI06000155 V1 EN-US
Figure 45: Bus coupler bay with one CT and b aux. contact only from CB
This scheme will disconnect the section/coupler CTs after about 80 ms (pre-set time under
parameter setting
of the section/coupler CB ( that is, from the moment when auxiliary b contact makes).
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 (about 150 ms) clearing and
tripping of the 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
Application manual
Zone A
Zone B
REB 670
b
152
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
tZeroCurrent in the relevant bay function block) from the moment of opening
46
t=1s
t
OR
AND
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_ansi.vsd
Differential protection
BOM
Section 6
105