Description Of Function - ABB SPAC 536 C User Manual

Description of
function
Overcurrent unit
The overcurrent unit of the combined overcur-
rent and earth-fault module SPCJ 4D24 is de-
signed for single-phase, two-phase or three-
phase operation. It contains two overcurrent
stages, i.e. a low-set overcurrent stage I> and a
high-set overcurrent stage I>>.
The low-set or high-set current stage starts if
the current on one of the phases exceeds the
setting value of the stage concerned. When start-
ing, the concerned stage provides a starting sig-
nal SS1 or TS1 and simultaneously the digital
display on the front panel indicates starting. If
the overcurrent situation lasts long enough to
exceed the set operating time, the stage that
started calls for a C.B. tripping by providing a
tripping signal TS2. At the same time the op-
eration indicator goes on with red light. The
red operation indicator remains on although the
stage resets. The indicator is reset with the RE-
SET push-button. By proper configuration of
the output relay switchgroups an additional
auxiliary trip signal TS1 can be generated.
The maximum continuous current carrying ca-
pacity of the energizing inputs is 4 x I
must be observed when relay settings are calcu-
lated.
The operation of the low-set overcurrent stage
I> or the high-set overcurrent stage I>> can be
blocked by bringing a blocking signal BS to the
unit. The blocking configuration is set by means
of switchgroup SGB.
The operation of the low-set overcurrent stage
can be based on a definite time or an inverse
time characteristic. The mode of operation is
programmed with SGF1/1...3. At definite time
mode of operation the operating time t> is di-
rectly set in seconds within the setting range,
0.05...300 s. When using inverse time mode of
operation (I.D.M.T.) four internationally stand-
ardized and two special type time/current char-
acteristics are available. The programming
switches SGF1/1...3 are also used for selecting
the desired operation characteristic.
The operating time t>> of the high-set overcur-
rent stage is set separately within the range
0.04...300 s.
The operation of the two overcurrent stages is
provided with a latching facility (switch SGB/6)
keeping the tripping output energized, although
the signal which caused the operation disap-
pears. The stages are reset by simultaneous press-
ing of the push-buttons RESET and PRO-
GRAM, see section "Programming switches".
The setting value I>>/I
current stage may be subject to automatic dou-
bling when connecting the protected object to
the network, i.e. in a starting situation. Thus
the setting value of the high-set overcurrent stage
may be lower than the connection inrush cur-
rent. The automatic doubling function is se-
lected with switch SGF1/5. The starting situa-
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
starting situation comes to an end when the
currents fall below 1.25 x I>.
The setting range of the high-set overcurrent
stage is 0.5...40 x I
in the lower end of the range, the module will
, which contain two almost identical operation stages.
n
In this case the overcurrent unit of the SPCJ
4D24 module may be used for e.g. two-stage
load shedding purposes.
The operation of the high-set overcurrent stage
may be set out of operation by means of switch
SGF2/5. When the high-set unit is set out of
operation the display shows a "- - -" readout,
indicating that the operating value is infinite.
Note!
At inverse time characteristic the effective set-
ting range of the low-set overcurrent stage is
0.5...2.5 x I
within the range 2.5...5.0 x I
relay. At inverse time characteristic any start
current setting above 2.5 x I
will be regarded as being equal to 2.5 x I
Note!
The operation of the low-set stage based on in-
verse time characteristic will be blocked by start-
ing 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.
of the high-set over-
n
. When selecting a setting
n
, although start current settings
n
can be set on the
n
of the low-set stage
n
.
n
3