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

Page: 4 / 178

T Y PE K C-4 RELAY
T ra nsf orm e r
The transformer i s a saturating type consisting
of a tapped primary winding and a secondary winding"
A varistor is connected across the secondary wind­
ing to reduce the voltage peaks applied to the in­
duction cylinder unit and phase shifting capacitor"
I nd i cat i ng C on t a c to r S w i t c h U n i t ( I C S")
The indicating contactor switch is a small d-e
operated clapper type device" A magnetic armature,
to which leaf-spring mounted contacts are attached,
is attracted to the magnetic core upon energization
of the switch" When the switch closes, the moving
contacts bridge two stationary contacts, completing
the trip circuiL Al so during this operation two fin­
g(;'!rs on the armature deflect a spring located on the
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 valve of the switch"
OPER ATION
I ns t a n t a n e o us Ov e r c u r r e n t U n i t
Operation o f the instantaneous overcurrent unit
occurs when the primary current of the transformer
exceeds a value as marked on the tap plate" Upon
application of current to the transformer, a voltage
is induced in the secondary winding" This voltage
is impres sed upon the parallel connected pairs of
cylinder unit coils" The capacitor connected in
series with one pair of coils shifts the current flowing
in these coils in reference to the current flowing in
the other pair of coils"
As a result, the air gap
fluxes of the cylinder unit are out of phase and a
contact closing torque is produced"
The primary of the transformer is tapped and
brought out to a tap connector block for ease in
changing the pickup current of the relay" The use of
a tapped transformer provide s approximately the same
energy level at a given multiple of pickup current for
any tap setting, resulting in one time curve through­
out the range of the relay"
G e n e r a l Operati o n Of S c h em e
When the proper breaker successfully inter­
rupts the fault current the KC-4 relay quickly disabl es
the breaker-failure timing circuit In addition , where
the line relays trip two breakers such as on a ring
4
IMSTAIITAIIEOUS
OVEitCURitENT
(Ur'fflt C'l:l.UIIIT)
tiiOICATIIfG
CONTACTOR
S�ITCH
IIISTAIITAJIEOUS
DYER CURRENT
(MIDDLE CYL.UMIT)
•IIST.UTAifEOUS
OYER CURRENT
(LOWER CYL UNIT)
CHASSIS OPERATED
SHotTIIIG SWITCH
REDHAMDLE
TEST SWITCH
CUIIEMT TEST
""
TEIIMIIN.i
188A64o'
Fig. 3. Internal Schematic ofthe KC-4 Relay in the FT-4 1
Case.
bus , the KC-4 s el ects which of the two breakers has
failed" When the phase overcurrent units and 13
are set above load-current level, the KC-4
func­
tions as a fault detector to prevent undesired tripping
by test personneL The following paragraphs describe
KC-4 operation in more detail for different system
bus connections"
S i ng l e B us/ S i ng l e B re ak e r A rr a ng em e n t
Unless something fails, current flow i n the
breaker should cease shortly after the trip circuit is
energized"
The time interval between these two
occurrences will be the breaker-interrupting time. If
this interruption does not occur, breaker-failure re­
laying will initiate the tripping of other breakers"
Fig" 4 shows how this is accomplished" Unless
something fails either the primary of back-up relays
initiate tripping of the faulted line breaker" Note that
the primary and back-up relays connect to s eparate
sets of current transformers and d-e supplies. This
way a failure in one or the other circuits will not
disable all of the protection"
When the primary protection operates, it energizes
62X; the back-up protection energizes 62Y. Contacts
of these two auxiliaries start the breaker -failure
timer 62, through the KC-4 contacts . If the line
breaker fails to clear the fault , KC-4 contacts remains
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
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