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

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T Y P E
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
540054 2 for the details of this arrangeme nt. )
Breaker-and-a-Half Arrangement
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
circuits for line A and bus L are shown . Similar cir­
cuits would exist for breaker
3 .
line B and bus R.
cuits would exist for breaker
3.
line B and bus R.
Protection against break er 2 failure for line A faults
and breaker 1 failure for line A or bus L faults is
discussed below. All other breaker failure fault com­
binations are equivalent to one of these three
combinations . For example, protection against a
breaker
3
failure for bus R faults is similar to the
protection against a breaker 1 failure for bus L faults.
Assuming a failure of breaker 2 for a fault
on line A, the breaker-failure timer 6 2 associated
with breaker 2 is energized by 62X or 62Y from
line A. Since the KC-4 current detector 50-2 which
is supplied by breaker 2 current does not
drop out, 62 of breaker 2 operates 86LN of
br eaker 2. One 86LN contact trip s break e r
3 .
Another 86LN contact stops the transmission of a
blocking signal on line B. allowing the remote pilot
relays to trip the remote line B breaker. if they de­
tect the fault. Thus, the fault on line A is now
cleared. Another 86LN contact blocks high-sp eed re­
closing of breaker
3.
Note that the timer is associa­
ted with the middle breaker. which is the breaker
that has failed. The timer causes tripping of both
outside breakers , which is the same approach used
for ring bus protection, to be described later.
An essential function, the selection of the faulty
breaker, is performed by the KC-4 . Relays 6 2X and
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.
If breaker 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
6
detector 50-1 selects the faulty breaker. Note that
the line A part of the bus L timer circuit in Fig. 5
is the same as that used with the single bus/ single
breaker arrangement in Fig . 4
If breaker 1 fails for a fault on bus L it is de­
sirable to trip breaker 2 and stop the transmission
of blocking carrier on line A. This is accomplished
.by the 86Z device which is energized through 62ZL.
50-1 and 6 2L contacts and a six ohm resistor. as
shown in Fig. 5. One 86Z contact trips breaker 2.
Other 86Z contacts stop blocking carrier on line A
and block reclosing of breaker 2. The six ohm re­
sistor and the 86Z coil are both low impedance
compared to the 62L circuit re sistance. Therefor e,
the 86Z coil will not affect the 6 2L timing, and the
62L timing circuit current will not be enough to pick­
up the 86Z device. The six ohm circuit maintains
approximately half-voltage on the 62L device after
the timing is completed. The purpose of this seem­
ingly involved circuitry is to permit a single current
detector. device 50-1, to supervise 62L timing ,
86BL tripping and 86Z tripping.
Ri n g B us A rra n g e m e n t
The circuits for the ring bus are shown i n Fig. 6
with trip and control circuits outlined for breaker 2.
together with line-B primary and back-up protection
circuits. As with the breaker-and-a-half scheme. the
primary protection uses tripping rectifiers, and the
backup us es an auxiliary relay to trip two breakers.
As before, the 6 2X 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 energizes
breaker-2 timer . 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 on 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 carrier symmetri­
cally, without regard to whether the fault is on line
A or line B.
The purpose of stopping carrier on line A is to
remove carrier blocking to permit remote carrier relay
relay tripping. Otherwise , line A continue s to feed
the fault through breaker 2 until a back-up relay
operates or until the fault burns clear.
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