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2
D e s c r i p t i o n o f f u n c t i o n
Overcurrent unit
The overcurrent unit of the combined overcurrent and earth-fault module SPCJ 4D24 is designed 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 starting, the concerned stage provides a starting signal 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 operation indicator goes on with red light. The red operation indicator
remains on although the stage resets. The indicator is reset with the RESET push-button. By proper
configuration of the output relay switchgroups an additional auxiliary trip signal TS1 can be generated.
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 directly set in seconds within the setting range, 0.05...300 s. When using inverse time
mode of operation (I.D.M.T.) four internationally standardized and two special type time/current characteri-
stics are available. The programming switches SGF1 / 1...3 are also used for selecting the desired operation
characteristic.
Note! If the setting is higher than 2.5 x I
, the maximum continuous carry (3 x I
) and the levelling out of
n
n
the IDMT-curves at high current levels must be noted.
Note! The high-current end of any inverse time characteristic is determined by the high-set stage which, when
started, inhibits the low-set stage operation. The trip time is thus equal to the set t>> for any current higher
than I>>. In order to get a trip signal, the stage I>> must also of course be linked to a trip output relay.
The operating time t>> of the high-set overcurrent 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 disappears. The stages are reset
by simultaneous pressing of the push-buttons RESET and PROGRAM, see section "Programming switches".
The setting value I>>/I
of the high-set overcurrent stage may be subject to automatic doubling when
n
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 current. The automatic doubling function is
selected with switch SGF1/5. The starting situation 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
. When selecting a setting in the lower end
n
of the range, the module will contain two almost identical operation stages. 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.
PAINOS
PAINOS
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