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

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INST A L L ATION
Westinghouse
J.L. 41-766.1B
•
O PER ATION
•
MAINTENANCE
INSTRUCTIONS
TYPES SC. SCI, SV AND SV-1 RELAYS
CAUTION Before putting protective relays into
service, remove all blocking which may have been
inserted for the purpose of securing the p arts during
shipment, make sure that all moving p arts operate
freely, inspect the contacts to see that they are clean
and close properly, and operate the relay to check
the settings and electrical connections.
A P P L I C A T I O N
The types SC and SC-1 current relays and the
types SV and SV- 1 voltage relays are applicable where
an instantaneous plunger relay of high accuracy is
required. These relays are suitable for protective ser­
vice , and for auxiliary service where some of their
special features are desired. They are adjustable over
a wide range of voltage or current, are provided with
mechanical operation indicators, and have a c alibra­
ted scale which indicates the pick-up setting. Both
contacts can readily be changed from "make" to
"break " . The volt-ampere burden is low.
The typ e SC and SV relays have a high ratio of
drop-out to pick-up (90 to 98%) and are particularly
suitable for fault detector relays. The type SC-1 and
SV-1 relays have a lower ratio of drop-out to pick-up.
This low er ratio may be desirable in some applications,
and it makes possible a plunger pull characteristic
which permits the operation of a latching device. The
latch is combined with the mechanical operation indi­
cator, and prevents further motion of the moving con­
tacts after the relay has operated.
C O N S T R U C T I O N
The types SC , SC- 1 and SV and SV-1 relays oper­
ate on the solenoid principle. A U- shaped iron frame,
mounted on the moulded base, supports the coil and
serves as the external magnetic path for the coil. The
coil surrounds a core and flux shunt. The upper end
of the core is threaded and projects through the upper
side of the frame , to which it is fastened by a nut. A
tube threaded on the outside at its lower end is as­
sembled in the core , and the threaded end extends be­
low the core. A graphite bushing, which is the lower
SU PERSEDES I .L. 41-766.1A
* Denotes changed from superseded issue.
bearing for the plunger shaft, is assembled in the
lower end of this threaded tube. It is held in place
by two split spring sleeves, one above and one below
the bearing. The split sleeves must be compressed
to insert them in the tube and they will remain at any
position in which they are placed. The bearing for
the upper end of the plunger shaft is a graphite bush­
ing which is pressed in the upper end of the core. This
bearing is visible when the plunger is in the ener­
gized position. The plunger itself does not touch the
w alls of the tube in which it moves.
A flux shunt which surrounds the core is screwed
on the tube , and its lower end proj ects below the re­
lay frame. The position of this shunt determines the
pick-up setting of the relay. The lower end of the
shunt is beveled and knurled, so that it can be grasp ed
by the fingers and turned to change the setting. A
calibrated scale plate is mounted adj acent to the
shunt. A groove just above the knurl in the lower end
of the shunt serves as an index m ark, and the relay
pick-up setting is indicated by the calibration scale
marking which i s adjacent to the groove.
The construction of the plunger, core and flux
shunt (which differ in details in the various types of
these relays) causes the plunger to float in its ener­
gized position, without being held against a stop ,
even when energized much above the pick-up value.
Consequently, there is negligible noise and the con­
tacts are free from chatter, even on heavy overloads
and in 25 cycle applications.
The core, shunt and plunger construction also
provides the high ratio of drop-out to pickup in the
SC and SV relays. This ratio is above 90% for any
pick-up setting. In the latch type relays it is necessary
for the plunger to rise with sufficient force to oper­
ate the latch positively and to deflect the stationary
contacts sufficiently to prevent their opening, when
the relay is de- energized, due to play in the latch.
It is necessary to have a lower ratio of drop-out to
pick-up in, order to obtain this characteristic, and
this lower ratio m ay be desirable in some applica­
tions where the latch is not required. The plunger
EFFECTI VE AP RI L 1965
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