The resistive reach in reverse direction must be set longer than the longest reverse
zones. In blocking schemes it must be set longer than the overreaching zone at remote
end that is used in the communication scheme. In equation 174 the index ZmRv
references the specific zone to be coordinated to.
ZmRv
RFltREvPG 1.2 RFPG³ ×
EQUATION1726 V1 EN (Equation 174)
Phase-to-phase fault in forward direction
Reactive reach
The reach in reactive direction is determined by phase-to-ground reach setting X1. No
extra setting is required.
Resistive reach
In the same way as for phase-to-ground fault, the reach is automatically calculated
based on setting X1. The reach will be X1/tan(60°) =X1/√(3).
Fault resistance reach
The fault resistance reaches in forward direction RFItFwdPP, 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 (21), see figure
110.
The minimum recommended reach can be calculated according to equation 175.
EQUATION1318-ANSI V1 EN (Equation 175)
where:
RFPP
Zm
is the setting of the longest reach of the overreaching zones that must be covered by
FDPSPDIS (21).
Equation 175 modified is applicable also for the RFltRevPP as follows:
min
Re 1.25
zmRv
RFlt vPP RFPP³ ×
EQUATION2264-ANSI V1 EN
Equation 175 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 (21) characteristic angle is changed from 60 degrees to 90
degrees (rotated 30° anti-clock wise).
Section 3 1MRK504116-UUS C
IED application
256
Application manual
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