ABB RET670 Applications Manual page 358

Section 3
IED application
352
where:
RFPP
is the setting of the longest reach of the overreaching zones that must be covered by
Zm
FRPSPDIS (21).
Equation 288 and 289 are 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 FRPSPDIS (21)characteristic angle is changed from 60
degrees to 90 degrees or from 70 degrees to 100 degrees (rotated 30° anti-clock wise).
1MRK504116-UUS C
Application manual