Fault resistance reach
M13142-176 v7
The fault resistance reaches in forward direction
RFFwPP, must cover RFPP
Zm
with at least
25% margin.
RFPP
Zm
is the setting of fault resistance for phase-to-phase fault for the longest
overreaching zone to be covered by FDPSPDIS, see Figure
. The minimum recommended
reach can be calculated according to equation
.
1.25
zm
RFFwPP
RFPP
³
×
EQUATION1318 V3 EN-US
(Equation 119)
where:
RFPP
Zm
is the setting of the longest reach of the overreaching zones that must be covered by FDPSPDIS .
Equation
modified is applicable also for the
RFRvPP as follows:
min
1.25
zmRv
RFRvPP
RFPP
³
×
EQUATION2264 V1 EN-US
(Equation 120)
Equation
is also valid for three-phase fault. The proposed margin of 25% will cater for the
risk of cut off of the zone measuring characteristic that might occur at three-phase fault when
FDPSPDIS characteristic angle is changed from 60 degrees to 90 degrees (rotated 30° anti-
clock wise).
Section 7
1MRK 505 343-UEN B
Impedance protection
194
Application manual
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