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

Page: 92 / 178

T Y P E K C-4
MEAKER LINE
BUS
aRUKU
ITATION
BUS
PHASE: ROTATION A
I
l -UY
ItA-A --
Dtf'F. LOCkOUT AUX.
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P
HO
I
._
.. Q�TH'IItiN0LD TY,.fl..t..;,.CKUPJ:
f·�o:',t��:.�.u.a.cPmnCTt.
f:•:wrr�OA
C:OflfT,t.eJ_IIULTIII'UCATfQJI Of.l(c- .. ,ow:-.:ultUIIT
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-,-
- - - - - ,-- - _,
1427C95
SUB . 1 1
Fig.
3.
External Connections for the KC-4 Relay - Breaker Failure Protection o f a Single Bus/Single Breaker Arrangement
with One Timer per Breaker.
set to accommodate the slowest breaker. Sep­
arate timers provide faster backup clearing
for fast breakers .
(3)
With separate timers, the bus can be recon­
figured without rewiring the breaker failure
circuits.
(4) If 8 FI seal-in is needed it is easy to obtain
with separate timers. With a single timer,
auxiliary relays and blocking diodes must be
added whose cost mitigates the timer savings.
BREAKER-AN D-A-HALF ARRANGEMENT
Figure 4 show breaker-failure protection cir­
cuits for a breaker-and-a-half bus arrangement,
with one timer for each breaker.
The basic functioning of the scheme of figure 4
I S
the same as for · the single bus-single breaker
case.
First, consider the breaker 1 failure detection
6
circuit as an example for a breaker adj acent to a
bus. 8r'eaker-failure timing is initiated not only
for faults on line A, but on bus L as well. Auxiliary
relay 62Z-L in
the Bus-L
clearing circuit provides
8 F I to breaker-failure schemes for breakers 1 , 4 ,
and others o n bus L whenever a bus fault occurs
and bus differential relay 878-L operates.
For a bus fault on L and a failure of breaker 1 ,
the timer 62 will energize lockout switch 868F
directly which will in turn cause tripping and re­
close blocking of breaker 2 and transfer tripping
of breakers at the remote end of line A. The timer
62 also energizes lockout switch 868-L through a
TR8-2 blocking diode; this is not detrimental but
is redundant since 868- L was already tripped by
the bus relay
8 7 8- L .
Now consider a fault on line A and a failure
of breaker
I .
8FI is provided by 62X and Y. The
timer 62 wil l energize 86Z and 868-L th rough
TR 8-2 as just described. In this case, breaker 2
and remote-breaker tripping were already accom-
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