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

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(
Westinghouse
LL. 41 -1 37.3D
INSTALLATION
•
OPERATION
•
MAINTENANCE
INSTRUCTIONS
TYPE KRD-4 DIRECTIONAL OVERCURRENT
GROUND RELAY
CAUTION:
Before putting relays into service, 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
The
KRD- 4
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 polarized relays which
can be polarized from a potential source , from a local
ground source, or from both simultaneously.
They are also used, without modifications to pro­
vide directional ground fault protection in the
KD-4
carrier relaying scheme. Op eration of the relays in
connection with the carrier scheme is fully described
in
I . L . 4 1-9 1 1.
C O N S T R U C T I O N
The typ e
KRD- 4
directional overcurrent ground
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.
1
to
3.
A. DI RECTIONAL UNI T (D)
The directional unit of the
KRD- 4
consists of an
inductio n cylinder unit, phase shifting network , and
a de-coupling network .
l, I nduction Cyl i nder Unit
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 fluxes.
SUPERSEDES I . L. 41 - l 37.3C
*Den otes chan ge from superseded issue .
The cylinder unit consists of three basic ass em­
blies: an electroma gnet assembly, a moving elem ent
assembly, 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 member, and
an aluminum cylinder which is assembled to a molded
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 is 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 operating
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 series 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 faces of the electromagnet
and the magnetic core. The aluminum cylinder of the
m oving
element assembly rotates in
this air
gap on
the upper and lower pin bearing.
With the contacts closed, the el ectrical connec­
tion is made through the stationary contact housing
clamp, then the moving contact, through the spiral
spring out to the spring adjusted clamp.
2.
Phase Shi fting Network
The phase 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 ing Network
The de-coupling .network consists of an air gap
EF FECTIVE J U N E 1 971
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