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front of the switch, which allows the operation indi
cator target to drop. The target is reset from the out
side of the case by a push rod located at the bottom
of the cover.
The front spring, in addition to holding the tar
get , provides restraint for the armature and thus con
trols the pickup v alue of the sw itch.
O P E R A T I O N
G e n e r a l
When any one o f the overcurre nt unit s 0 1 . r 3 or
I0) operates, it energizes the X unit. When used for
bre aker-failure relaying , one or more of the X-unit
contacts supervise the breaker-failure timing circuits
to prevent other breakers from being unneces sarily
tripped. When the proper bre aker successfully inter
rupts the fault current the KC-3 relay quickly �isables
the breaker-failure timing circuit. In addition , where
the line relays trip two bre akers such as on a ring
bus, the KC-3 selects which of the two breakers has
failed. When the phas e overcurrent unit s r 1 and I3
are set above lo ad-current level, the KC-3 also func
tions as a fault detector to prevent undesired tripping
by test personnel . The following paragraphs describe
KC- 3 op eration in more detail for different system
bus connections.
S i n g l e B u s / S i n g l e B r e a k e r Ar r a ng e m e n t
Unless something fail s , current flow i n the
bre aker s hould cease shortly after the trip circuit is
ene rgized. The time int erval between these two
occurrences
will be the breaker-interrupting time. If
this interruption does
not occ ur ,
breaker-failure re
laying will initi ate the tripping of other breakers.
Fig. 5 shows how this is accomplished . Unless
something fails either the prinary or back-up relays
initiate tripping of the faulted line breaker. Note that
the primary and b ack-up relays connect to separate
sets of current transforme rs and d-e supplies. This
way a failure in one or the other circuits will not
dis able all of the protection.
When the prim ary protection operates it energi<�es
6 2X; the back-up protection energizes 6 2Y. Cont acts
of these two auxiliaries start the breaker-failure
timer 6 2 , through the K C- 3 contact 50X. If the line
breaker fails to clear the fault, contact 50X remains
closed. The SG contact of timer 6 2 closes, energiz
ing the bu s lock-out relay 86B through 6 2X or 6 2Y
and 50X contacts. Relay 86B then trips all the
breakers on the bus.
6
The TRB- 1 rectifier in the primary - protection
circuits of Fig. 5 blocks the flow of red-light super
vision current through the 6 2X coil. If the KC-3 phase
overcurrent units, are s et above load current , a 50X
contact may be inserted in series with the 62X coil
to block the red-light currents. Then, the TRB- 1 is
not needed.
An MG-6 relay performs the 6 2X function in Fig.
5. Actually an SG will suffice unless a directional
comparison blocking sy stem provides the primary
protection. With this system two MG-6 contacts seal
around the RRG and RRP contacts. (Refer to drawing
5400542 for the details of this arrangeme nt. )
B r e a k e r- a n d - a - H a l f A r r a n g e m en t
Typical trip and control circuits for breaker
failure back-up protection for the breaker-and-a-half
bus arrangement are shown in Fig. 6. The trip cir
cuits are shown for breaker 1 and breaker 2 and the
line-A protecticn. 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 bre aker 2 for a fault on
line B, the breaker-failure timer 62 as sociated with
bre aker 1 is energized by 62X or 62Y from line B
. •
Since the KC-3 current detector 50-2 which is sup
plied by breaker-2 current does not drop out , 62 of
breaker 1 operates to trip breaker 1. rWhen 62-ICS is
operated by breaker- 1 trip current . 86LN is energized .
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 t hey det ect the
fault . Thus, the fault on line B is now cleared. An
other 86LN contact blocks high-speed reclosing of
bre aker 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-3. Relay s 6 2X and
62Y indi cate 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 qment to the
fault. The 50- 1 or 50-2 KC- 3 performs this job.
Now, if break er 1 fails for a fault on line A , bus
L is cleared . This is accomplished by the bus L
breaker-failure timer which is energized by the line-A
relay 62X or 6 2Y contact. When 62 operat e s , 86B i s
energized t o dump bus L . For this sequenc e , the cur
rent detector 50- 1 selects the faulty breaker.
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Содержание KC-4
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