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Directional overcur-
rent relay module
SPCS 4D11 and
SPCS 4D12
Directional or non-
directional earth-fault
relay module
SPCS 2D26
ABB Automation
The overcurrent relay modules SPCJ 4D11 and
SPCS 4D12 include three overcurrent stages.
By using all three stages and giving each overcur-
rent stage its own operate value and operate time
good selectivity with short operate times can be
obtained.
The operation of the short-circuit protection in
this example is based on blockings between the
protection levels. This means that when start-
ing, the I>> stage of the overcurrent relay mod-
ule of the feeder provides a blocking signal to the
I>> stage of the overcurrent relay module of the
infeeder. When no blocking signal is received,
the infeeder overcurrent relay module perceives
the fault as being within its own protection zone
and trips the circuit breaker. Thus it is possible
to use a minimum operate time of 120 ms at
busbar system faults.
The low-set stage I> is used as a directional stage
operating in "forward" direction. Definite time
operation has been used in this example, but
inverse time characteristic can also be selected
for this stage. The current setting of the stage I>
must extend to the setting of the following
protection stage.
The high-set stage I>> is also used as a direc-
tional stage that operates in the same direction
as the low-set stage. The current setting of this
stage has been selected so that the stage operates
at short circuits occurring close to the substa-
tion. Further, the start of the stage I>> is used to
block the infeeder protection if the fault is
located on the outgoing feeder.
In the resonant earthed network illustrated in
this example the relay module SPCS 2D26 is
used for the directional earth-fault protection of
the feeders.
Directional earth fault relays should also be used
at frequent network changes or when high sen-
sitivity is to be achieved. A directional earth-
fault relay allows earth faults with fault resistances
of several thousand ohms to be detected in
overhead lines. Changes in the extension of the
network due to varying the network configura-
tion do not cause inselectivity, because the di-
rection of the earth fault current of a faulty
feeder is opposite to that of a healthy feeder.
The non-directional high-set stage I>>> is not
used in this example. When long operate times
are used for the directional stages, the second
high-set stage should however be used as back-
up protection. The stages I> and I>> can deter-
mine the direction of the current for about 2.5
s after a total collapse of the voltage. If a trip
signal is not delivered within 2.5 s after a voltage
collapse, the trip must be performed non-
directionally by the second high-set stage I>>>.
The directional element of each phase current,
determines the direction of the current by meas-
uring the phase difference between the current
and the opposite phase-to-phase voltage. Since,
in this case, the relay is used to protect a feeder
with the zero-sequence source behind the relay-
ing point, the base angle -30° should be, as
shown in Fig. 9 below, selected.
I
L1
-80°
Forward
direction
U
1
ϕ
No
operation
U
3
Fig. 9. Directional element of phase L
The basic angle of the relay module SPCS 2D26
can be set at 0°, -30°, -60° or -90°. When the
network to be protected is resonant earthed or
earthed via a resistor as in this example , the basic
angle should be set at 0°. When an isolated
neutral system is protected the basic angle is set
at -90°. In addition it is possible to use an
external control signal BS1 or BS2 for selecting
the basic angle (0°/-90°) to be automatically
determined by the earthing situation of the
network. When the control voltage is connected,
the basic angle ϕ
= -90°.
b
The start value of the low-set stage of the earth-
fault relay module should be set low enough to
fulfil the sensitivity requirements of the safety
regulations. The requirements regarding oper-
ate times are mainly fulfilled by the operation of
the high-set stage I
>.
02
ϕ
b
ϕ
b =-30°
U
23
U
2
+80°
1
19
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