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

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D I R ECT IONAL OV ERCURR ENT GROUND R E LAYS I . L . 4 1 - 1 37 K
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I N S T A NTA N E OU S O V E R CURRENT U N I T
T YPICAL
C L O S I NG TI M E
(
FOR T W O E L E M E N T D U A L
)
POL A R I Z E D
RELAY
6 7 8 9 10
20
40 50
MU LT I P LES
OF
P I C K U P
)33109
* Fig.
6.
Typical Operating Times for the in stantaneous Type KRC and KRD overcurrent unit ( When Current Po larized) Relays.
3.
The sensitivity adjustment is made by vary­
ing the tension of the spiral spring attached
to
the
movin g element assembly . The spring is adj usted
by placing a screwdriver or similar tool into one of
the notches located on th e periphery of the spring
adjuster and totating it.
T
he spring adjuster i s
located on the underside o f the bridge and is held i:n
place by a spring type c lamp that does not have to
be loosened prior to making the necessary adjust­
ments.
Before applying current , block open the normally­
closed contact of the directional unit. Insert the tap
screw in the minimum value tap s etting and adjust
the spring such that the contacts will close as in­
dicated by a neon lamp in the contact circuit when
energized with the required current. The pick up of
the overcurrent unit with the tap screw in any other
tap should
be
within ±5% of tap value .
If adj ustme nt of pick-up current in between tap
settings is desired insert the tap screw in the next
lowest tap setting and adjust the s pring as described.
It should
be
noted that this adjustment results in a
slightly different time characteristic curve and burden.
D i rect i o n a l U n i t ( D )
I n the type KRP and KRC relays the directional
unit is the lower unit. In the type KRD the d irec­
tional units are the lower and middle units .
1. The upper bearing screw shoul d be screwed
down until there is approximately . 0 25 cl earance
between it and the top of the shaft bearing. The upper
pin bearing should then be securely l o cked in posi­
tion with th e lock nut.
2. Contact gap adj ustment for the directional
unit is made with the mov in g contact in the reset
position , i . e . , against the right side of the bridge.
Advance the right hand stationary contact until the
contacts j ust close. Then advance the stationary
contact an additional one-half turn.
Now move in the left-hand stationary contact
until it just touches the moving contact . Then back
1 1
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