Westinghouse KRD-4 Installation, Operation, & Maintenance Instruction

(
CAUTION:
Before putting relays into servi c e , re­
move all blocking which may have been inserted for
the purpose of securing the parts during shipment,
make sure that all moving parts operate freely, in­
spect the contacts to see that they are clean and
clo se properly , and operate the relay to check the
settings and electrical conne ctio ns.
A P P L I C A T I O N
KRD- 4
The relay is a high speed directional over­
current relay which is used for the protection of trans­
mission lines and feeder transmission lines and feeder
circuits. These relays are dual polariz e d relays which
can be polarized from a potential source , from a local
ground source, or from both simultaneously.
They are also used, without modificatio n s to pro­
vide directional ground fault protection in the
carrier relaying scheme. Op eration of the relays in
connection with the carrier schem e is fully described
I . L . 4 1-9 1 1.
in
C O N S T R U C T I O N
KRD- 4
The typ e
relay consists of a dual polarized directional unit,
an instantaneous overcurrent unit, and an indicating
contactor switch. The principal parts of the relay and
their location are shown in Fig.
A. D I R ECTIONAL UNI T ( D)
The directional unit of the
inductio n cylinder unit, phase shifting network , and
a de-coupling network .
l, I nduction Cyl i nder U n i t
The cylinder unit is a product type in which tor­
que is produced by the phase relationship of an oper­
ating flux and a polarizing flux on an aluminum cylin­
der supporting a moving contact arm . A contact op en­
ing torque or a co ntact clo sing torque is produced
depending upon the phase relationship between the
two flu x e s .
S U P E R S E D E S I . L . 41 - l 37 . 3 C
*Den otes chan ge from s u p erseded i s s u e .
INSTALLATION
INSTRUCTIONS
TYPE KRD-4 DIRECTIONAL OVERCURRENT
GROUND RELAY
directional overcurrent ground
3.
1
to
KRD- 4
consists of an
OPERATION
•
The cylinder unit consists of three basic ass em­
blies: an electroma gnet assembly, a moving elem ent
assembl y , and a stationary closing assembly.
The electromagnet assembly consists of an elec­
tromagnet , an adjustable magnetic core, two magnetic
adjusting plugs, lower bearing pin , and a die-casted
aluminum frame . The moving element ass embly con­
sists of a spiral spring, contact carrying membe r , and
an aluminum cylinder which i s a s s embled to a mol d ed
hub which holds the s haft. The shaft ha s removable
top and bottom j ewel bearings. The stationary con­
tact assembly consists of a molded bridge , upper
bearing pin, stationary contact housing and spring
adjuster i s located on the underside of the bridge
and is held in place by a spring type clamp. It is
attached to the moving contact arm by a spual spring.
The electromagnet has four poles, two o perating
KD-4
poles and two polarizing poles. Each pair of pol es
are diametrically opposite each other and are excited
by series connected coils. (Two sets of seri e s con­
nected coils are used to excite the polarizing poles,
one set for current polarizing and the other set for
voltage polarizing). The electromagnet is permanently
mounted to the frame in such a manner that an air
gap exists between the pole fac e s of the electromagnet
and the magnetic core. The aluminum cylinder of the
element assembly rotates in
m oving
the upper and lower pin bearing.
With the contacts closed, the el ectrical connec­
tion is made through the stationary contact housing
c lamp, then the moving contact, through the spiral
spring out to the spring adjusted clamp.
2.
P h a se Sh i fting Network
The p ha s e shifting network consists of a resistor,
capacitor and reactor in the polarizing circuit of the
directional unit, and a saturable shunt in the oper­
ating circuit.
3. De-Coupl i n g Network
The de-coupling .network consists of an air gap
Westinghouse
LL. 41 - 1 37.3D
MAINTENANCE
•
this air
EF F E C T I V E J U N E 1 971
gap on