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

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T Y P E K C-4
closed. The contact of timer 62 closes , energiz­
ing the bus lock-out relay 86B through 62X or 62Y
and KC-4 contacts . Relay 86B then trips all the
breakers on the bus.
The TRB- 1 rectifier in the primary - protection
circuits of Fig . 4 blocks the flow of red-light super­
vision current through the 62X coil.
An MG-6 relay performs the 62X function in Fig .
4 . Actually an S G will suffice unless a directional­
comparison blocking system provides the primary
protection. With this system two MG-6 contacts seal
around the RRG and RRP contacts. (Refer to drawing
540D54 2 for the details of this arrangement. )
B rea k e r - a n d - a -H a l f A r r a n g e m e n t
Typical trip and control circuits for breaker­
failure back-up protection for the breaker-and-a-half
bus arrangement are shown in Fig . 5 . The trip cir­
cuits are shown for breaker 1 and breaker 2 and the
line-A protection. Similar circuits would exist for
breaker 3 and line B . Protection against a breaker-1
or breaker-2 failure for line-A faults is included .
Assuming a failure of breaker 2 for a fault on
line B , the bre aker-failure timer 62 associated with
breaker 1 is energized by 62X or 62Y from line B .
Since the KC-4 current detector 50-2 which i s sup­
plied by breaker-2 current does not drop out , 62 of
breaker 1 operates to trip breaker 1 . When 62-ICS is
operated
by
break er- ! trip current ,
86LN is e nergized .
One 86LN contact stops the transmission of a block­
ing signal on line A , allowing the remote pilot relays
to trip the remote line-A breaker , if they detect the
fault . Thus , t he fault on line B is now cleared . An­
other 86LN contact blocks high-speed reclosing of
breaker 1 . Other 86LN contacts energize the breaker-
1 and breaker-2 trip-coil circuits to provide for a trip­
free operation should either breaker be prematurely
closed in.
An essential function , the selection of the faulty
breaker , is performed by the KC-4 . Relays 62X and
62Y indicate that the fault has not been cleared , but
they are unable to define for a line-A fault whether
breaker 1 or breaker 2 is still feeding current to the
fault . The 50-1 or 50-2 KC-4 performs this job.
6
Now , if breaker 1 fails for a fault on line A , b us
L is cleared. This is accomplished by the bus L
breaker-failure timer which is energized by the line-A
relay 62X or 62Y cont act. When 62 operat e s , 86B is
energized to dump b us L . For this sequence , t he cur­
rent detector 50- 1 selects the faulty breaker .
Note that the bus L timer eire uit in Fig . 5 is the
same as that used with the single bus/ single breaker
arrangement in Fig . 4. An identical timer circuit (not
shown) is associat ed with bus R in Fig. 5 . There are
also timers for each bay ( e . g . , associated
with
breakers 1 and 3 ) . These trip the appropriat e outside
breaker for a middle breaker failur e . These timer cir­
cuit s are associated with the breaker to be tripped .
This same approach i s used for ring buses , a s will
now be explained .
R i n g B u s A rra n g e m e n t
The circuits for the ring b u s are shown in Fig . 6
with trip and control circuits outlined for breaker 2 ,
together with line-B primary and back-up protection
circuit s . As with the breaker-and-a-half Scheme , the
primary protection uses tripping rectifier s , and the
backup uses an auxiliary relay to trip two breakers.
As before , the 62X and 62Y relays are operated by
the primary and back-up relays , respectively .
Assume a failure of breaker 2 for a fault on line
B. Line-B relay 62X or 62Y is operated and e nergizes
breaker-2 time r . Since current detector 50 for breaker
2 remains energized by the breaker-2 current , 62
operates to energize relay 86LN . Relay 86LN trips
breakers 1 and 3 , blocks reclosing on breakers 1 , 2 ,
and 3 , and stops carrier o n lines A and B . The trip­
ping of breaker 3 and the stopping of carrier of line
B is unnecessary , since it is assumed that the pro­
tective relays have already accomplished these
results. Although unnecessary, these functions do no
harm and simplify the circuitry by permitting the
86LN relay to trip breakers and stop c arrier symmetri­
cally , without regard to whether the fault is on line
A or line B .
The purpose of stopping carrier o n line A i s t o
remove carrier blocking t o permit remote carrier relay
relay tripping. Otherwise , line A continues to feed
the fault through breaker 2 until a back-up relay
operates or until the fault b urns clear .
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