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TD_MRI1_06.05_GB
If line impedance and internal resistance of the gen-
erator is only ohmic:
If line impedance and internal resistance of the gen-
erator is only inductive:
The maximum sensitivity angle corresponds to the R/L
component.
Figure 4.3:
TRIP/NO-TRIP region for directional element in
MRI1.
In this case the advance direction is
defined as TRIP region and the reverse direction
as NO-TRIP region.
By means of accurate hardware design and by using
an efficient directional algorithm a high sensitivity for
the voltage sensing circuit and a high accuracy for
phase angle measurement are achieved so that a cor-
rect directional decision can be made even by close
three-phase faults.
As an addition, to avoid maloperations due to distur-
bances, at least 2 periods (40 ms at 50 Hz) are
evaluated.
For the
MRI1
-overcurrent relays with directional feature
different time delays or time multipliers can be set for
forward and backward faults (ref. to chapter 5.2.3
and 5.2.6).
If the trip delay for backward faults is set longer than
the one for forward faults, the protective relay works
as a "backup"-relay for the other lines on the same
busbar. This means that the relay can clear a fault in
the backward direction with a longer time delay in
case of refusal of the relay or the circuit breaker on the
faulted line.
If the trip delay for backward faults is set out of range
(on the display "EXIT"), the relay will not trip in case of
backward faults.
The assignment of the output relays can be used to se-
lect in which direction the failure is to be indicated (re-
fer also to Chapter 5.2.15). It is possible to indicate
the activation and/or the tripping for each tripping di-
rection via the output relays.