32
TB MRI(K)3-C 03.02 E
5.5
Protection Parameters
5.5.1 Pickup current for phase
overcurrent element
The setting value for this parameter that appears on the
display is related to the nominal current (I
N
) of the relay.
This means: pickup current (Is) = displayed value x
nominal current (I
N
) e.g. displayed value = 1.25 then, Is
= 1.25 x I
N
.
5.5.2 Trip Characteristics for the Phase
Overcurrent Element (I>)
There are the following standard trip time characteristics
available:
DEFT
-
Definite Time (definite time
overcurrent protection)
NINV -
Normal inverse
VINV
-
Very inverse
EINV
-
Extremely inverse
RINV
-
RI-Inverse
LINV
-
Long term Inverse
5.5.3 Tripping Time or Time Factor for the
Phase Overcurrent Element
Normally, after change of the trip characteristics, the
tripping time or the time factor also has to be changed
accordingly. In order to avoid an unsuitable combina-
tion between trip characteristics and tripping time or
time factor, the following measures are initiated by the
MRI(K)3-C
::::
The LED for adjustment of the tripping time or time factor
starts to flash after the trip characteristics have changed.
By this warning signal the operator is reminded to adjust
the tripping time or time factor to the changed opera-
tional mode or trip time characteristics. This warning
signal keeps flashing until the tripping time or time factor
are re-adjusted. If re-adjustment has not been done
within 5 minutes (the time to enable parameter setting),
then the processor sets the tripping time or time factor to
the highest sensible value (smallest possible tripping time
).
When adjusting to the “Definite Time” trip characteristic,
the definite tripping time displayed is shown as seconds
(e.g. 0.35 = 0.35s). By pressing push-buttons <+><->
this time can be changed step by step in the range
0.04s – 260s
When adjusting to the “Inverse Time” trip characteristics,
the time factor (tI>) is displayed. This factor can be
changed also by push buttons <+><-> step by step in
the range 0.05 – 20.0.
If the tripping time or time factor are set to infinite long
(on the display “EXIT” is shown) then trip of the relay
overcurrent element is blocked. The WARNING/
ALARM function is still active. During this time LEDs I>
and t> are red.
5.5.4 Fast/Time tripping by switch ON of
the CB for the overcurrent lement
After switch ON the CB a pick up of the I> element
happens directly within 200ms, it is possible to switch
OFF without time delay when this parameter is already
set.
Figure 5.2
5.5.5 Reset Mode for the Trip Characteris-
tics in the Phase Current Path
In order to ensure that the trip function is reliable even
with repeated error pulses, each of them shorter than the
set tripping time, the RESET mode for the trip characteris-
tics can be changed over. With a setting of “60s“ the
elapsed tripping time is frozen and is only reset after
60s faultless operation. Should another fault occur
within these 60s, the tripping time counter remains in
operation. With the setting “_ 0s“ the counter is imme-
diately reset when the fault current is interrupted and it
is restarted when the fault current has returned again.
