Westinghouse KC-4, Инструкция по установке, эксплуатации и обслуживанию

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T Y P E
86BF coil, backwards through the closed 62A con­
tact, through the KC-4 terminals 1 and 2, and
finally into terminal 9 of the T D-S. This sneak
current may prevent the TD-S from dropping out,
a normally-closed 86BF contact cuts off the T D-S.
In the primary breaker-tripping circuit, the
T R B-2 blocking diode prevents red supervising­
light current from flowing in the 62X coil.
In both the primary and the backup tripping
circuits, the 62X and 62Y coils are connected to
follow the protective relay contacts and should
never be connected in series with S2a contacts.
Otherwise, BFI is lost when the breaker functions
mechanically, opening S2a, but fails to interrupt
current flow. The resistor in parallel with the 94T
auxiliary dissipates 62S Watts in a 1 2S Vdc control
scheme. It draws sufficient current to hold an ICS
in the line backup tripping circuits picked up, and
may burn if the S2a contact doesn't open. A 86BF
contact deenergizes the backup circuit to prevent
this.
For a bus fault, the 87B relay contact energizes
the 86B lockout auxiliary to strip the bus and
block reclosing. The blocking valves T RB-2
prevent the 87B from energizing the 86BF aux­
iliaries. H owever, in case of breaker failure during
a bus fault, the BF:I auxiliary 62Z relay is picked
up by 87B. The closure of contact 62Z provides
a signal in the breaker failure scheme to energize
the T D-S timer, then picks up the corresponding
86BF auxiliary. 86BF contact initiates the transfer
trip for isolating the faulted bus.
Figure 2 also shows how B FI seal-in can be
provided when one timer is used per bus. The T D-S
relay containing the TX relay cannot be used here.
A separate 62S auxiliary relay is provided for each
breaker, each with a T RB-2 blocking diode to
isolate the circuits on multiple breakers from
one another.
Figure 3 shows a breaker-failure scheme for
the same bus arrangement. The key differences
are that (a) now a separate T D-S timer is dedicated
to each breaker; and (b) in this scheme B F I seal-in
is provided by the TX auxiliary in TD-S.
The telephone relay coil TX in parallel with
the T D-S timer 62 is optionally used to seal-in 62X
and 62Y contacts. When the KC-4 contacts and
62X or Y contacts are both closed, both the timer
circuit and TX are energized; TX seals around
62X and Y so that only the opening of the KC-4
contacts can stop the timer. This may be needed
when 62X and Y are energized by potential­
polarized distance relays. If a close-in fault occurs
so that the polarizing potential collapses com­
pletely, the distance relay will reset after stored
energy in the polarizing circuit damps out
(usually l S to 30 ms ). This will cause dropout
of 62X or Y , even if the breaker has failed and
the fault remains. The TX contact will keep the
timer energized for this critical situation, allowing
the breaker failure scheme to function and strip
the bus.
I n figure 3 , the ICS in the TD-S now provides
the seal-in and target functions, since a separate
T D-S is dedicated to each breaker.
With the KC-4 connected adj acent to the de
positive supply as shown in figure 3, a SOX auxil­
iary relay can be connected between terminal 2 of
the KC-4 and de negative. SOX then follows the
KC-4 and provides contact multiplication. This
allows the KC-4 to perform other non-breaker­
failure functions. For example, a SOX contact can
be used to supervise a distance relay trip circuit
to prevent false-tripping on loss of ac potential
supply.
Although using a separate timer for each
breaker is more costly than the scheme of figure
2, there are several performance advantages:
( I )
For a fault which begins on one line and sub­
sequently spreads to another (such as can occur
on a double-circuit tower), the common timer
in figure 2 will energized by the initial fault.
H owever, even if the breaker clears the first
line affected, the 62X and Y contacts and KC-4
relay of the second faulted line will keep the
timer energized. The time delay may expire
and the bus may be stripped before the second
breaker clears the fault, even though no
breaker failed.
(2) I f the breakers on the bus have different
interrupting times, a common timer m ust be
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