ABB Relion 670 Series Technical Reference Manual page 259

1MRK505222-UUS C
Technical reference manual
I jX
A
ArgNegRes
ANSI06000466 V1 EN
Figure 124: Simplified characteristic for offset mho in forward direction for A-to-
ground fault
Offset mho, reverse direction
In the same way as for offset in forward direction, the selection of offset mho in
reverse direction will introduce an extra criterion for operation compare to the normal
offset mho. The extra is that the angle between the fault voltage and the fault current
shall lie between the blinders in second and fourth quadrant. The operation area in
second quadrant is limited by the blinder defined as 180° -ArgDir and in fourth
quadrant ArgNegRes+180°, see figure 125.
The conditions for operation of offset mho in reverse direction for A-to-ground fault is
90≤β≤270 and 180°-Argdir≤φ≤ArgNegRes+180°.
The β is derived according to equation
between the voltage and current.
V
A
f
IA·R
I
A
ArgDir
en 06000466 _ansi.vsd
41 for the offset mho circle and φ is the angle
Section 6
Impedance protection
253