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Parallel feeders
Directional overcur-
rent relay modules
SPCS 4D11 and
SPCS 4D12
Directional or non-
directional earth-fault
relay module
SPCS 2D26
14
The block diagram on page 13 shows the relay
SPAA 348 C sited at the infeeder of a substation.
This connection can be be used for protecting
parallel feeders as shown in the Fig 6. When
parallel feeders are used, it is necessary to apply
directional relays at the receiving end, while
non-directional relays are sufficient at the feed-
ing end. Selectivity is then achieved by setting
the directional relays and their directional ele-
ments to look into the protected line, and giving
them time and current settings lower than those
of the non-directional relays in the feeding end.
Since the relay SPAS 348 C includes three
overcurrent stages and a versatile earth-fault
module, one relay can be used for the overcur-
rent and earth-fault protection of the busbar
system and for the protection of the parallel
feeders.
A possible DC component does not have to be
considered in the current setting, because due to
the peak-to-peak measurement method used,
The directional low-set stages I> are set to look
into the protected line. This means that the low
set-stages I> are set to operate in reverse direc-
tion by means of SGF switches. When definite
time function is used, the operate times of the
directional low-set stages I> should be at least
150 ms shorter than those of the non-direc-
tional stages of the relays in the feeding end . The
current settings of the directional stages looking
in reverse direction is normally 50% of the
normal full load of the protected circuit.
In the network illustrated in this example the
relay module SPCS 2D26 is used for the earth-
fault protection of the busbar system and as
backup earth-fault protection of the outgoing
feeders.
An earth-fault somewhere in a galvanically con-
nected power system causes residual voltage.
The residual overvoltage protection of the mod-
ule SPCS 2D26 measures the residual voltage
from the open delta winding of the voltage
transformers.
The low-set stage U
> of the module indicates
0b
beginning earth-faults. Normally the residual
voltage in a healthy isolated network is very
small, even less than 1% of the maximum re-
sidual voltage value. Thus the low-set residual
voltage stage can be given a low setting value.
The start signal of the low-set stage U
used for enabling the non-directional earth-
fault current measuring relays of the feeders. To
asymmetry does not affect the sensitivity of the
start operations.
Fig. 6. Directional relays protecting parallell
feeders
The directional high-set stages I>> are used for
the short-circuit protection of the busbar system
and, if required, the non-directional high-set
stage can be used as backup protection for the
outgoing feeders and the busbar system.
Definite time operation has been used in Exam-
ple 1, but inverse time characteristic can be
selected for the stage I> as well.
prevent unnecessary operation of the earth-fault
relays during a short circuit or when a motor is
started, the tripping of the non-directional earth-
fault relays of the outgoing feeders are normally
blocked. If the outgoing feeders are provided
with directional earth-fault relays, no enable
signal is required.
The trip signal of the U
signal for high resistivity earth faults (earth
faults not detected by any other protection
unit).
The residual voltage stages U
used to protect the busbar system and serve as
non-selective back-up protection for the feeder
earth-fault protection. The stage U
used to open the bus section breaker or to
disconnect the feeder(s) most prone to faults.
Should a fault still persist after tripping of this
> can be
stage, the second stage U
0b
circuit breaker finally.
SPAS
SPAS
348 C
348 C
> stage is used as alarm
0b
> and U
01
02
> can be
01
> opens the infeeder
02
ABB Automation
> are
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