Westinghouse KC-4, Installation, Operation & Maintenance Instructions Manual

Page: 73 / 178

T Y P E
K C-4
R E LAY
L. 41 -776.1 J
BKR.2 FAILURE DETECTION
DEVICE TYPE
TRB-2
KC-4
52
62
TD-5
62X AU
62Z
868 WL
86BF
878
94T
86BF2
_r- - TRI P
LaKR.-1
_r-TRIP
L aKR.-3
_r--BLOCK RECL
LaKR.-1
r BLOCK RECL
LeKR.-2
r��i"'
LBKR.-3
_r--UNE A
L...t�f�S
W
lLINE
B
DESCRIPTION
ZENER TRIPPING UNIT
OVE"RCURRENT DETECTOR
POWER CIRCUIT BREAKER
BREAKER FAILURE TIMER W/TX
B.
F.
INITIATE AUX.-PRI
B F INITIATE AUX.-BACKUP
B.F. IN!TIATE AUX.-BUS
BUS DIFF. LOCKOUT AUX.
8 F. LOCKOUT AUX
BUS DIFF. RELAY
TRIPPING AUX.
_.
:HIGH- T H R E S H O L D TYPE(4MS PICKUP)
86BF2
NO.
REQ'O
OWG
3 /BAY
..
l
187A696
I I B KR. 188A640
3/BAY
1/BKR.
3515AI7
1/LINE 3500A85
1/LINE 3500AB5
liB US 3500A85
II
BUS
1/BKR
1/LINE
3500A88
.... =WITH SUPERVISING LIGHT, USE EITHER 868 CONTACT OR TRB-2
BLOCKING ZENER BUT NOT BOTH,
f
:OPTIONAL FOR SEAL-IN OF
62X
AND 62Y CONTACTS.
l428Cl8
Sub 5
Fig. 4. External Connections for the KC-4 Relay - Breaker Failure Protection of a Breaker-and-a-Half Bus Arrangement - One Timer
per Breaker.
plished by line relays, so these actions are re­
dundant. H owever, the blocking of reclosing for
breaker 2, and reclose blocking at the remote
terminal via the transfer-trip signal, are now
provided. Also, 86B-L now strips bus L to isolate
the failed breaker l .
N ow, refer to the breaker 2 failure detection
circuit. BFI is provided by 62X and Y contacts for
lines A and B, since a fault on either initiates
tripping of breaker 2. I f breaker 2 fails and the
timer 62 delay expires, lockout switch 86BF is
energized. Contacts of 86BF trip breakers 1 and 3,
block reclosing on all 3 breakers, and transfer-trip
lines A and B. Some of these actions are redund­
ant-for example, a line A fault does not require
re-tripping of breaker l . But none of these re­
dundant actions are detrimental. Remember that
transfer-tripping of the remote end of the faulted
line isn't really redundant since it performs the
important additional function of blocking re­
closing at the remote terminal.
The TX relay is shown providing optional seal-
in of B F I contacts as described for the single-bus
single-breaker case above.
As mentioned before, on breaker failure
protection, a separate timer for each breaker has
an advantage over a common timer per bus, and
also most of the breaker-and-a-half bus arrange­
ments are applied to the rather high voltage
system . Therefore, it
is
recommended that a
separate timer be applied for each breaker for
the breaker-and-a-half bus arrangement.
R I N G B U S ARRAN GEM ENT
Figure 5 shows the line and breaker-failure
protection circuits for a ring bus . The symmetry
of the bus permits a simple circuit for the latter
function. U sing breaker 2 as an example, B F I is
provided by 62X and 62Y contacts from lines A
and B, since a fault on either line initiates breaker
2 tripping. If the time delay expires, the lockout
switch 86BF trips adjacent breakers 1 and 3 ;
blocks reclosing o f breakers 1 , 2, and 3 ; and
transfer-trips both line A and line B. As in the
breaker-and-a-half scheme, redundant actions are
7
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