Westinghouse KRD-4, Инструкция по установке, эксплуатации и обслуживанию

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TYP E KRD-4 DI R ECTIONAL O V E RCUR RENT
GROUND RELAY
transform er, c apacitor , reactor, and re sistor. Elec­
trically thi s n etwork is equivalent to the polarizin g
circuit of t h e induction cylinder unit and is utilized
to minimize the couplin g betw een the current and
pot ential polarized sources.
B. I NSTAN TAN EOUS OVERCURRENT UN I T (I)
The i nstantaneous overcurrent unit consists of an
induction cylinder unit, capacitor, vari stor , and a
transformer. The components are connected such that
a contact cl osing torque is produced when the current
exceeds a spe cified value.
1.
Cyl inder Unit
The cylinder unit i s similar in construction to the
cylinder unit of the directional unit except that all
coils are similar . The phase rel ationship of the two
air gap fluxes necessary for the development of tor­
que is achieved by means of a capacitor co nnected
in series with one pair of pole windings.
2.
Tran sformer
Th e transformer is a saturating typ e con sisting
of a tapped primary winding and a secondary wind­
ing. A varistor i s connect ed acros s the secondary
winding to reduce the voltage p e ak s applied to the
cylinder unit and phase shifting capacitor.
C. I NDI CATI NG CONTACTOR SWI TCH ( I CS)
The indi cating contactor switch is a small d-e
operated clapper type device. A magnetic armature
to whic h leaf- spring mounted contacts are attached,
i s attracted to the m agnetic core upon en ergization
of the switch. When the switch clo s e s , the moving
contacts bridge two stationary contacts, completing
the trip circuit. Also during this op eration two fingers
o n the armature defl ect a spring located on the front
of the switch, which allows the operation indicator
target to drop. The target is reset from outside of the
case by a push rod located at the bottom of the cover.
The front spring, in addition to holding the tar­
get, provides r e st raint for the armature and thus con­
trols the pickup value of th e switch.
O P E R A T I O N
The typ e K RD-4 relay is connected to the pro­
tected transmis sion line as shown in Fig. 4. In such
a conn ectio n , the relay o perates to di sconnect th e
line for ground faults of a definite magnitude that are
flowing in a spe cified direction.
4
The directional unit of the relay compar e s the
phas e angle between the fault current and the polari­
zing quantiti e s of the system and either p roduce s a
contact closing torque for faults in the trip direction
or produces a contact opening torque for faults in the
non-trip directio n . Relay op eration occurs when both
the direction al unit and the instantaneous o vercurrent
unit close their contacts. Henc e , the fault current
must be greater than the tap s etting of the o vercurrent
unit.
For faults in the non-trip direction , a contact
opening torque is produc ed by the directional unit
such that the normally clo sed contact of t hi s unit
shorts out a pair of windings on the o vercurrent unit.
This prevents th e overcurrent unit from developing
torque to close its contacts. For faults in the trip
directio n , the directional unit will pick up and re­
move this short circuit , allowing the overcurrent con­
tact to commence clo sing almost simultaneously
with the directional contact for high speed operation.
C H A R A C T E R I S T I C S
The rel ays are availabl e in the fo llowing current
ranges:
R ange
0 . 5- 2 Amp s . 0.5 _D . 7 5
1-4
1 . 0
1 . 5
4- 16 4 . 0
6 . 0
10-40 10 1 5
Taps
1 . 0
1 . 25
1 . 5 2
2 . 0
2 . 5 3 . 0
4 . 0
8 . 0 9 . 0 1 2 1 6
20 2 5 3 0 40
The tap value i s the minimum current r equired to
just close the overcurrent relay contacts. For pickup
s ettings in b etween tap s refer to the s e ction under
SETTINGS.
The KRD-4 relay i s de signed for dual polarizing
and can b e polarized from a potential source, a local
ground source or from both simultan eously. When the re­
l ay is potential polarized, the m aximum torque of the
relay occurs when the op erating current lags the
polarizing voltage by approximat ely 65 degrees. When
the relay is current pol arized, the maximum torque of
the relay occurs when the operating current i s in
phase with the polarizing current.
TIME CURVES
The time curv e s for the KRD-4 relay are shown
in Fig. 5 and 6. Fig. 5 includ e s three curv e s which
are :
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