ABB RELION 670 Series Applications Manual page 200

Section 7
Impedance protection
Fault resistance reach
The fault resistance reaches in forward direction
25% margin.
overreaching zone to be covered by FDPSPDIS, see Figure 105. The minimum recommended
reach can be calculated according to equation 113.
RFFwPP
EQUATION1318 V3 EN-US
where:
RFPP
Zm
Equation
RFRvPP
EQUATION2264 V1 EN-US
Equation
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).
194
RFPP is the setting of fault resistance for phase-to-phase fault for the longest
Zm
³ ×
1.25 RFPP
zm
is the setting of the longest reach of the overreaching zones that must be covered by FDPSPDIS .
113 modified is applicable also for the
³ ×
1.25 RFPP
min zmRv
113 is also valid for three-phase fault. The proposed margin of 25% will cater for the
RFFwPP , must cover RFPP
RFRvPP as follows:
1MRK 504 152-UEN B
M13142-176 v7
with at least
Zm
(Equation 113)
(Equation 114)
Application manual