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

Page: 72 / 178

T Y P E
K C-4
BREAKER L I N E BUS BREAKER
STATION BUS PHASE ROTATION A , B , C
r - - - - - ,
PRIMARY
§ I
I
RELAYS
I
I
I
' - - - -
-
-'
50 50
r - - - - - ,
I
PHASE
A
OEV. NO. TYPE FUNCTION
TR8 2 ZENER TRIPPING UNIT
50 KC-4 OVER CURRENT DETECTOR
50 X
OVERCURRENT AUX.(OPTIN-IALI
52
POWER CIRCUIT BREAKER
BREAKER FAILURE TIMER
62X BKR. fAIL. I N I TIATING AUX.
BKR FAIL. I N I T IAT I N G AUX
868 LOCKOUTAUX
878 BUS OIFF. R E LAY
9< T
T R I P P I N G AUX.
DWG. NO
187A696
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3500A85
3515A17
3500A85
3500A85
3500A68
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BLOCKING ZENER BUT NOT BOTH.
t
:OPTIONAL FOR SEAL-IN Of 62X MO 62Y CONTACTS.
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BACKUP
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PROT
8 6 8 F ( O N F P E R B K N i
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T R A N S F E R
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TRIP
C
B R E A K E R FAILURE
T I M E R C K T
C
PRIMARY
T R I P CKT
C
BACKUP
T R I P CKT
OTHER
BREAKER
CIRCUITS
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142 7C9 5
Sub 9
Fig.
3.
External Connections for the KC-4 Relay - Breaker Failure Protection of a Single Bus/Single Breaker A rrangemen t
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) I f B F I 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 .
B R EAKER-AND-A- H AL F 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. Breaker-failure timing is initiated not only
for faults on line A, but on bus L as well. A uxiliary
relay
62Z-L
in the
Bus-L
clearing circuit provides
B F I to breaker-failure schemes for breakers l , 4,
and others on 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 86BF
directly which will in turn cause tripping and re ..
close blocking of b reaker 2 and transfer tripping
of breakers at the remote end of line A. The timer
62 also energizes lockout switch 868-L through
a
T RB-2 blocking diode; this is not detrimental but
is redundant since 868-L was already tripped by
the bus relay 878- L .
Now consider a fault o n line A and a failure:
of breaker 1 . BFI is provided by 62X and Y . The
timer 62 will energize 86Z and 868-L through
T R B-2 as j ust described. In this case, breaker
2
and remote-breaker tripping were already accom-
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