Westinghouse KRD-4, Installation, Operation, & Maintenance Instruction

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Westinghouse
I . L 4 1 - 1 37H
INSTALLATION
•
OPERATION
•
MAINTENANCE
INS T RUC T IONS
DIRECTIO NAL OVERCU R R E NT G RO U N D R ELAY
TYPES K RP K RC A N D K R D
C A U T I O N
B efore putting relays into service , re­
move all blocking which may have been inserted for
the purpose of s ecuring the parts during shipment,
make sure that all moving parts operate freely, in­
spect the contacts to see that they are clean and
clos e properly , and operate the relay to check the
settings and electrical connections.
A P P L I C A T I O N
Thes e relays are high speed ground directional
overcurrent relays which are used for the protection
of transmission lines and feeder circuits .
They are also u s e d , without modification to pro­
vide directional ground fault protection in the
KD
carrier relaying scheme. Operation of the relays in
connection with the c arrier scheme is fully described
in I .L.
4 1- 9 1 1 .
T h e type
KRP
relay i s u s e d where residual volt­
age is available for polarizin g the directional unit.
The type
KRC
is used where this residual voltage
is not available and residual current must be used.
The type
KRD
relay is a dual polarized relay which
can be polarized from a potential sourc e , from a local
ground source or from both simultaneously.
C O N S T R U C T I O N A N D O P E R A T I O N
D i rec t i o n a l U n i t ( D )
The directional unit i s a product induction cylinder
type unit operating on the interaction betwee n the
polarizing circuit flux and the operatin g circuit flux.
Mechanically, the directional unit is composed of
four basic components: A die-cast aluminum frame ,
an electromagnet, a moving element assembly , and
a molded bridge.
The frame serves as the mountin g structure for
the magnetic core . The magnetic core w hich houses
the lower pin bearing is secured to the frame by a
locking nut . The bearing can be replaced, if neces­
sary , without having to remove the magnetic core
from the frame .
SUPERSEDES I . L. 4 1 - 1 37G
* Denotes change from su perseded i s sue.
Th e e lectromagnet h a s two s eries-connected
polarizing coils mounted diametrically opposite one
another; two s eries-connected operating coils mounted
diam etrically opposite one another; two magnetic
adjustin g plugs; upper and lower adjustin g plug
clips , and two locating pins. The locatin g pins are
used to accurately position the lower pin bearing,
which is threaded into the bridge. The e le ctromagnet
is s ecured
to the frame by four mounting screw s .
T h e moving element assembly consists of a spiral
spring, contact carrying member, and an aluminum
cylinder assembled to a molded hub which holds the
shaft. The shaft has removable top and bottom j ewel
bearings.
The shaft rides between the bottom pin
bearing and the upper pin bearing with the cylinder
rotating in an air gap formed by the electromagnet
and the magnetic core.
The bridge is secured to the electromagnet and
frame by two mounting screws. In addition to holding
the upper pin bearing, the tridge i s u s ed for mounting
the adjustable stationary contact housing. The sta­
tionary contact housing i s h eld in position by a
spring type clamp. The spring adjuster is located on
the underside of the bridge and is attached to the
moving contact arm by a spiral spring. The spring
adjuster is also held in place by a spring type clamp .
With the contacts closed, the electrical conn ec­
tion is made through the stationary c ontact housing
clamp , to the movi n g contact, through the spiral
spring out to the spring adjuster clamp.
O v ercurrent U n i t ( I )
The overcurrent unit is s imilar i n construction to
the directional unit. The time phase relationship o f
the two air gap fluxes necessary for t h e development
of torque is achieved by m eans o f a capacitor con­
nected in series with one pair of pole windings .
The normally-clos ed contact of the directional
unit is connected acros s one pair of pole windings
of the overcurrent unit as shown in the internal sche­
matics.
This arrangement short-circuits the opera­
ting current around the pole windings; preventing the
overcurrent unit from developing torque . If the direc-
E FFECT I V E J U N E 1 968
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