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

Page: 71 / 114

TYPE K RV R ELAY
.IDICATIII
COIITACTII
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Wtlll HUTifE IIITAITUEM
NUIITT U
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lltfCTIIIII.
•n
COITACT1 CLOSE.
SATUIATIII
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CIAISIS OPWTO
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anca
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TDIIUI.
Fig. 3. Internal Schematic of the Type K R V Relay in the
Type FT3 1 Case.
I n sta n t an eo u s O v ercu rrent U n i t T ra n s fo rm er
This transformer is of the saturating type for
limiting the energy to the instantaneous overcurrent
unit at higher values of fault current and to reduce
C.T. burden. The primary winding is tapped and these
taps are brought out to a tap block fo r eas e in chang­
ing the pick-up of the instantaneous ove rcurrent unit.
The use of a tapped transformer provides approximate­
ly the same en ergy level at a given multiple of pick­
up current for any tap setting, resulting in one time
curve throughout the rang e of the relay.
Across the secondary is connected a non-lin ear
resistor known as a varistor. The effect of the varis­
tor is to reduce the voltage peak s applied to the
overcurrent unit and phase shifting capacitor.
A u x i l i a ry S w i tc h ( C S - 1 )
The auxiliary switch i s a small solenoid type
d . c. switch. A cylindrical plunger, with a silver disc
mounted on its lower end, moves in the core of the
solenoid. As the plunger travels upward, the disc
bridges the silver stationary contacts. A tapped re­
sistor is used to enable one to use the contactor
switch on a
24, 4 8 , 1 2 5
or
250
volt d.c. system con­
nected per Fig.
6.
The op eration of the CS-1 switch
is controlled by the directional contact (D) and the I
contact. It' s function is to insure coordination be­
tween the directional contact (D) and the I contact
to prevent tripping on reversed faults ( where th e
directional contact was closed on load).
I n d i ca t i n g Conta c to r S w i tc h ( I C S )
The d-e indicating contactor switch is a small
clapper type device. A magnetic armature, to which
leaf-spring mounted contacts are attached, is at­
tracted to the magnetic core upon en ergization of the
switch . When the switch closes, the moving con­
tacts bridge two stationary contacts, completing the
trip circuit. Also during this operation two fingers on
the armature deflect a spring located on the front of
the switch, which allows the op eration indicator
target to drop.
The front spring, in addition to holding the tar­
get, provides restraint for the armature and thu s con­
trols the pick-up value of th e switch.
C H A R A C T E R I S T I C S
The relays are available in the following current
rang es:
Instantaneous Overcurrent Unit (I)
Range
Taps
0 . 5-2 Amps
0 . 5 0 . 7 5 1 . 0 1 . 2 5 1 . 5 2
1-4 1 . 0 1 . 5 2 . 0
2 . 5
3 . 0
4 . 0
2-8 2
3
4
5 6 8
4- 1 6 4 6 8
9 1 2 16
1 0-40 10 1 5 20
24 30 40
*
20- 8 0 2 0 30
40 48 60 80
The tap value is the minimum current required
to ju st close the relay contacts.
The time vs. current characteristics for the in­
stantan eou s overcurrent unit is shown in Fig. 4 .
The time
v
s
.
current
characteri sti cs
for
the
di­
rectio nal unit is shown in Fig. 5 .
T ri p C i rc u i t
Th e relay contacts will safely close
3 0
amp eres
at
250
volts d . c. and the seal-in contacts of the in­
dicating contactor switch will safely carry this cur­
rent long enough to trip a circuit breaker.
T r i p C i rc u i t Co n s t a n t s
The indicating contactor switch has a pickup o f
approximately
1
ampere. I t s d-e resistance i s
0 . 1
ohms.
A u xi l i a ry S w i t c h ( C S- 1 )
The auxiliary switch has a d-e resistance of
3
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