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Description of
function
Phase overcurrent
unit
The phase overcurrent unit of the relay module
SPCJ 4D29 is designed for single-phase, two-
phase or three-phase overcurrent protection. It
includes two overcurrent stages, i.e. a low-set
overcurrent stage I> and a high-set overcurrent
stage I>>.
The low-set or high-set phase overcurrent stage
starts if the current on one or several of the
phases exceeds the set start current value of the
stage concerned. When the stage starts it gen-
erates a start signal SS1 or TS1 and simultane-
ously the digital display on the front panel
indicates starting. If the overcurrent situation
lasts long enough to exceed the set operate
time, the stage operates and generates a trip
signal TS2. At the same time the operation
indicator is lit with red light. The red operation
indicator remains lit although the stage resets.
The indicator is reset by pushing the RESET
push-button. By proper configuration of the
output relay switchgroups an additional auxil-
iary trip signal TS1 can be obtained.
The operation of the low-set phase overcurrent
stage I> or the high-set phase overcurrent stage
I>> can be blocked by routing a blocking signal
BS to the unit. The blocking configuration is
set with switchgroup SGB.
The operation of the low-set phase overcurrent
stage can be based on definite time or inverse
time characteristic. The operation characteris-
tic is selected with the SGF1/1...3 switches.
At definite time operation characteristic the
operate time t> is set in seconds within the
range, 0.05...300 s. When the inverse time
operation characteristic (IDMT) is selected,
four internationally standardized and two com-
plementary time/current curves are available.
The selector switches SGF1/1...3 are also used
for selecting the desired operation characteris-
tic.
Note!
The maximum continuous current carrying
capacity of the energizing inputs is 4 x I
which must be observed when relay settings are
calculated.
Note!
At inverse time characteristic the effective set-
ting range of the low-set overcurrent stage is
0.5...2.5 x I
, although start current settings
n
within the range 2.5...5.0 x I
relay. At inverse time characteristic any start
current setting above 2.5 x I
stage will be regarded as being equal to 2.5 x I
Note!
The operation of the low-set stage based on
inverse time characteristic will be blocked by
starting of the high-set stage. Then the operate
time of the overcurrent unit is determined by
the set operate time of the high-set stage at heavy
fault currents.
The setting range of the operate time t>> of the
high-set phase overcurrent stage is 0.04...300 s.
The operate signal of the two overcurrent stages
is provided with a latching feature (switch
SGB/6) which means that the operate signal
TS2 is kept high after an operation, although
the overcurrent stage resets. The latched TS2
signal is reset by pushing the RESET and PRO-
GRAM push-buttons simultaneously or via the
serial port using the command V101, see also
chapter "Selector switches".
The set start current value I>> of the high-set
phase overcurrent stage can be doubled auto-
matically on connection of the protected object
to the network, i.e. at starting. In this way the
start current of the high-set phase overcurrent
stage can be given a lower value than the level of
the connection inrush current. The automatic
doubling function is selected with switch SGF1/5.
The starting, which activates the doubling func-
tion, is defined as a situation where the phase
currents rise from a value below 0.12 x I> to a
value exceeding 1.5 x I> in less than 60 ms. The
function stops when the currents fall below 1.25
x I>.
The setting range of the start current of the high-
set phase overcurrent stage is 0.5...40 x I
When the high-set stage is given a start current
setting in the lower end of the setting range, the
relay module will contain two almost identical
overcurrent stages. This enables the overcurrent
unit of the SPCJ 4D29 module to be used, for
example, in two-stage load shedding applica-
tions.
,
The high-set phase overcurrent stage can be set
n
out of operation with switch SGF2/5. When the
high-set stage is set out of operation the display
shows "- - -", indicating that the start current
setting is infinite.
can be set on the
n
of the low-set
n
.
n
.
n
3
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