ABB RET670 Applications Manual page 354

Section 3
IED application
348
For normal overhead lines, the angle for the loop impedance φ for phase-to-ground
fault defined according to equation 170.
+
X1 XN
j =
arctan L
+
R1 RN
L
EQUATION2115 V1 EN
But in some applications, for instance cable lines, the angle of the loop might be less
than the set angle. In these applications, the settings of fault resistance coverage in
forward and reverse direction, RFltFwdPG and RFltRevPG for phase-to-ground faults
and RFltRevPP and RFltRevPP for phase-to-phase faults have to be increased to avoid
that the phase selection characteristic must cut off some part of the zone characteristic.
The necessary increased setting of the fault resistance coverage can be derived from
trigonometric evaluation of the basic characteristic for respectively fault type.
The following setting guideline considers normal overhead lines applications and
provides two different setting alternatives:
A)
B)
The following figures illustrate alternative B).
Phase-to-ground fault in forward direction
With reference to figure 156, the following equations for the setting calculations can be
obtained.
Index PHS in images and equations reference settings for Phase
selection with load encroachment function (FRPSPDIS, 21) and index
Zm reference settings for Distance protection function (ZMRPDIS).
A recommended characteristic angle of 60 degrees
for the phase selection
A characteristic angle of 90 and 70 degrees for
phase-to-ground and phase-to-phase respectively,
like implemented in the REL500 series
1MRK504116-UUS C
(Equation 282)
Application manual