ABB RELION RET670, Applications Manual

Page: 358 / 1016

For normal overhead lines, the angle for the loop impedance φ for phase-to-ground
fault defined according to equation
240 .
L
L
X1
arctan
R1
+
j =
+
XN
RN
EQUATION2115 V1 EN-US
(Equation 240)
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) A recommended characteristic angle of 60 degrees
for the phase selection
B) A characteristic angle of 90 and 70 degrees for
phase-to-ground and phase-to-phase respectively,
like implemented in the REL500 series
The following figures illustrate alternative B).
8.10.3.1 Phase-to-ground fault in forward direction
GUID-47B1D249-60C8-4F71-A4FF-D57594219952 v1
With reference to figure 167 , 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).
Section 8
1MRK 504 163-UUS A
Impedance protection
352 Transformer protection RET670 2.2 ANSI
Application manual