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

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Note that the bu:;; L timer circuit in Fig. 6 is the
same as t hat used with the single bu:;;/single breaker
arrangement in Fig. 5 . tAn identical timer circuit (not
shown) is associated with bu:;; R in Fig. 6. rrhere are
also timers for each bay ( e . g . , associated with
breakers 1 and 3). rrhese trip the appropriate outside
breaker for a middle breaker failure. These timer cir­
cuits are associated with the breaker to be tripped.
This sam e approach is used for ring buse s , as will
now be explained.
R i n g B u s Arrang e m e n t
The circuits for t h s ring bus are shown i n Fig. 7
with trip and control circuits outlined for breaker 2,
together with line-B primary and back-up protection
circuits. As with the break er-and-a-half scheme, the
primary protection uses tripping rectifiers, and the
backup uses an auxiliary relay to trip two breakers.
As b efore , the 62X and 6 2l; relays are operated by
the primary and back-up relay s , respectively.
Assume a failure of breaker 1 for a fault on line
D. Line-D relay 6 2X or 6 2Y is op erated and energizes
breaker- 2 timer. Since KC- 3 50- 1 remains energized
by the breaker- 1 current , 6 2 operates to trip breaker
2. The
res
unit of relay 62 also operates to energize
relay 86LN during breaker-2 .tripping. Relay 86LN
blocks b reaker- 2 reclosing and sets up the break er- 2
trip circuit to provide a trip-free operation if this
breaker is closed in prematurely.
Now assume that breaker 3 fails for a fault on
line C. Again, breaker 2 should be tripped. Breaker-2
timer is energized through 50- 3 and line-C 62X or 62Y
contact. Relay 62X or 62Y indicates a line-C fault,
and 50-3X selects breaker 3 as faulty. Relay 62
times out to trip breaker 2 and also to energize 86LN.
Relay 86LN cannot determine which carrier
blocking signal should be interrupted, since a breaker-
2 trip occurs when either breaker 1 or 3 fails. There­
fore, relay 5 is used in conj unction with relay 86LN
to stop carrier on line A or line B whe n breaker 2
trips . Relay 5 is energized by the primary relays. If
breaker 1 fails for a fault on line D , relay 5 of line D
is energized, setting up the Line-A carrier stop cir­
cuit so that when relay 86LN is operated in the
breaker- 2 t'rip circuit , carrier blocking will be removed
from line A to permit remote carrier relay tripping .
Otherwise, line A continues to feed the fault through
breaker 2 until a back-up relay operates or until the
fault burns clear.
8
C H A R A C T E R ! S T I C S
The Phase Overcurrent Units are available in
the following current ranges:
R an g e T ap s
0 . 5 - 2 Amp s .
0 . 5 0 . 75 1.0 1. 25 1 . 5 2
1 - 4 1 . 0 1. 5
2.0 2. 5 3 . 0 4 . 0
2 - 8 2 3 4 5 6 8
The tap value is the m1mmum current required
to just close the overcurrent relay contacts. For
pickup setting s in between taps refer to the section
under adjustments. The pickup and dropout time
curves for the phase overcurrent units and telephone
relay is shown in Fig. 8. The Ground
Unit is available in the 0. 5 - 2 or 1 to 4 ampere
range. The pickup setting is continuously adj ustable
over the range. The pickup and dropout time of the
ground overcurrent unit and telephone relay is shown
in Fig. 9.
T r i p C i r c u i t
The m ain contacts will safely close 30 amperes
at 250 volts d-e and the seal-in contacts of the indi­
cating contactor switch will safely carry this current
long enough to trip a circuit breaker.
The indicating contactor switch has two taps
that provide a pickup setting of 0. 2 or 2 amperes. To
change taps requires connecting of lead located in
front of the tap block to the desired setting by means
of a screw connection.
T r i p C i r c u i t C o n s t a n t s
Indicating Contactor Switch -
0 . 3 amp . tap 6. 5 ohms d-e re sistance
2.0 amp. tap 0 . 15 ohms d-e resistance
A u x i l i ar y R e l a y
( X)
With rated voltage applied, the contact closing
time upon energization and the contact opening time
upon de-energization is approximately 5 milliseconds.
The rectifiers S#508C320H 14 3·20 P silicon recti­
fiers have a peak inverse voltage rating of 700 volts
d-e.
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