ABB SPAC 531 C User Manual And Technical Description page 105

Description of
operation
The overcurrent relay module SPCJ 3C3 can be
used in single-phase, two-phase or three-phase
protection relays and it contains two overcur-
rent stages, i.e. a low-set overcurrent stage I>
and a high-set overcurrent stage I>>.
The low-set or high-set overcurrent stage starts
if the current on one of the protected phases
exceeds the set start value of the concerned stage.
On starting, the concerned stage provides a
starting signal SS1 or SS2 and simultaneously
the operation indicator of the stage is lit with
yellow light. If the overcurrent situation lasts
long enough to exceed the set operation delay,
the stage that started provides a tripping signal,
TS1 or TS2. At the same time the operation
indicator of the concerned stage is lit with red
light. The red operation indicator remains lit
although the protection stage resets. The yellow
start indications and the red operation indica-
tions can be given self-reset or latching mode of
operation. When the latching mode is selected
the indicators are restet with the RESET push-
button on the module's front panel or by the
command V101 or V102 over the serial inter-
face.
The operation of the low-set overcurrent stage
I> can be blocked by routing a blocking signal
BTS1 to the stage. Similarly, the operation of
the high-set overcurrent stage I>> can be blocked
by a blocking signal BTS2. The blockings are
selected by means of switchgroup SGB on the
PC board of the relay module.
If the protection relay incorporates an auto-
reclose relay module, switchgroup SGB is addi-
tionally used for the purpose of selecting the
start signals for the auto-reclose module. The
instructions for selector switchgroup SGB are
given in the general description of the pro-
tection relay unit, in association with the dia-
gram illustrating the signals between the relay
modules.
The operation of the low-set overcurrent stage
I> can be based on definite time or inverse
definite minimum time (IDMT) characteristic.
The required operation characteristic is selected
with switch SG1/3. At definite time character-
istic the operation time t> can be selected within
one of the three available setting ranges of the
stage. The operation time setting range is se-
lected with switches SG1/1 and SG1/2. When
inverse time characteristic (IDMT) is used four
time/current curve groups with different slopes
of inversity are available. The required charac-
teristic is selected with switches SG1/1 and
SG1/2.
The operation time t>> of the high-set overcur-
rent stage is set separately. The setting range,
one of three available, is selected by means of
switches SG1/7 and SG1/8.
Normally both overcurrent stages are self-reset.
With the selector switch SG1/4 both stages can
be given a so called latching function, which
means that the tripping output is kept energized
after an operation though the fault has disap-
peared, until separately reset. The outputs are
reset by pressing the push-buttons STEP and
RESET simultaneously or by the commands
V101 or V102 over the serial interface. See also
table (switchgroup SG3) on page 9 in chapter
"Selector switches".
The set start value of the high-set overcurrent
stage I>> may be automatically doubled when the
protected object is energized, i.e. during a current
inrush situation. Thus the set start value of the
high-set overcurrent stage can be lower than the
connection inrush current. The automatic dou-
bling feature is selected with switch SG1/5. A
starting situation is defined as a situation where
the phase currents increase from a value below
0.12 x I> to a value exceeding 3.0 x I> in less than
60 ms. The starting situation ceases when the
phase currents fall below 2.0 x I>.
The setting range of the high-set overcurrent
stage is selected with switch SG1/6. Two alter-
natives setting ranges are available, 2.5...20 x I
and 0.5...4.0 x I . When the lower range is
n
chosen the relay module will contain two almost
identical operation stages. In this case the over-
current module SPCJ 3C3 may be used e.g. as a
two-stage load shedding module. The operation
of the high-set overcurrent stage may be blocked
by choosing the setting value ∞, infinite.
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