SEG Electronics GmbH
Manual MRG3
46
DOK-TD-MRG3, Rev. D
5.4.6 Settable threshold
Correct frequency measuring or vector surge measuring cannot be obtained if the system voltage
is very low, for instance during generator start up or voltage failure. False tripping of the MRG3 in
such cases is prevented by an adjustable voltage threshold U
B
. If the system voltage is below this
threshold, these functions of the relay are blocked.
During adjustment of U
B
the LEDs f and
/df light up.
5.5
Protection parameter “Over current”
5.5.1 Pickup value for phase over current element
When setting the pick-up value for this parameter, the setting value that appears on the display is
related to the generator rated current in %. This setting is accompanied by LEDs I + 1 + >.
5.5.2 Time current characteristics for phase over current element
By setting this parameter, one of the following 6 messages appears on the display:
DEFT -
Definite Time
NINV -
Normal Inverse (type A)
VINV
-
Very Inverse (type B)
EINV
-
Extremely Inverse (type C)
RINV -
RI-Inverse
LINV
-
Long Time Inverse
Any of these six characteristics can be changed by using <+> <->-push buttons and stored by
means of the push button <ENTER>-.
5.5.3 Trip delay or time factor for phase over current element
After change of the tripping characteristic the LEDs l + 1 + > + t> for tripping time and time factor
setting (t.) will flash up. This warning signal is an indication for the user to align the tripping time
and/or the time factor to the modified operating mode and/or tripping time characteristic.
The warning signal continues flashing until the tripping time and/or time factor have been newly pa-
rameter-used.
If - within a period of 5 minutes (time for release of parameters) - new parameters were not entered
by the user, the processor will automatically set tripping time and/or time factor to the most respon-
sive adjustment value (lowest possible tripping time).When the time delay or the time multiplier is
set out of range (Text "EXIT" appears on the display), the low set element of the over current relay
is blocked. The "WARN"- alarm relay, however, remains activated.
After modification of the tripping characteristic, as a general rule, tripping time and time factor re-
spectively, should be modified as well. To avoid improper combinations between tripping character-
istic and tripping time respectively time factor, the proceeding is as follows:
Upon adjustment to th
e “Definite Time” tripping characteristic, the independent tripping time indi-
cated in seconds (e.g. 0.35 = 0.35 seconds) will appear on the display. This tripping time can be
gradually changed by means of the push buttons<+> <->. Upon setting of the definite time tripping
characteristics, the time factor (tl>) appears on the display and LEDs l + 1 + > + t> light up. It can
also be modified successively via push buttons <+> <->.