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

Page: 54 / 178

TY PE KC-2 H I G H SPEED OVERC U R RENT
A transformer and varistor assembly is used in
conj unction with the overcurrent unit. The
transformer is of the saturating type which limits
the energy to the overcurrent unit and reduces the
burden on the operating CT .
The primary of the transformer is tapped and
brought out a tap connector block for ease in
changing the pick-up current of the relay. The use
of a tapped transformer provides approximately
the same energy level at a given multiple of pick­
up current for any tap setting, resulting in one
time curve throughout the range of the relay.
Across the secondary is connected a non-linear
resistor known as a varistor. The effect of the
varistor is to reduce the voltage peaks applied to
the overcurrent unit and phase shifting capacitor.
I N D I CAT I N G CONTACTOR SWITCH U N I T
( I C S)
The indicating contactor switch is a small de
operated clapper type device. A magnetic ar­
mature, 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 con­
tacts, completing the trip circuit. Also during this
operation two fingers on the armature deflect a
spring located on the front of the switch, which
allows the operation indicator target to drop. The
target is reset from the outside of the case
by
a
push rod located at the bottom of the cover.
The front spring, in addition to holding the
target, provides restraint for the armature and
thus controls the pickup value of the switch .
2
C HARACTERISTICS
The relay is available in the follolwing current
ranges:
Range
Taps
0.5 - 2 amps 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
4 - 1 6 4 6 8 9 1 2 1 6
10 - 40 10 1 5 20 24 30 40
The tap value is the minimum current required
to just close the overcurrent relay contacts . For
pick-up settings in between taps refer to the sec­
tion under adjustments.
C ONTACTS
The moving contact assembly in the over ..
current unit has been factory adjusted for low con ..
tact bounce performance and should not be dis ..
turbed .
TRIP C I R C U IT
The main contacts will safely close 30 amperes
at 250 volts de and the seal-in contacts of the in­
dicating contactor switch will safely carry this
current long enough to trip a circuit breaker.
T R I P C I RC U I T C O N STANT
Indicating contactor Switch (ICS)
1 ampere rating: 0 . 1 ohms de resistance
0.2/2.0 ampere rating: 0.2 tap
-
6.5 ohms
2 tap
-
0. 1 5 ohms
S ETTI NGS
OVERC U RRENT U N IT ( I )
The only setting required i s the pickup current
setting which is made by means of the connector
screw located on the tap plate. By placing the con­
nector screw
in the desired tap, the relay will just
close its contacts at the tap value current.
CAUTION:
Since the tap block connector screw
carried operating current, be sure
that the screw is turned tight.
In order to avoid opening the current
transformer circuits when changing taps under
load, connect the spare tap screw in the desired
tap position before removing the other tap screw
from the original tap position.
I N DICATI NG C O N TACTOR SWITCH ( I C S )
N o setting i s required for relays with a 1 .0
ampere unit. For relays with a 0.2j2.0 ampere un­
it, connect the lead located in front of the tap
block to the desired setting by means of the con­
necting screw. When the relay energizes a 1 25- or
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