ABB Relion 650 Series Technical Manual page 122

Section 5
Impedance protection
ANSI06000466 V1 EN-US
Figure 64: 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 65.
The conditions for operation of offset mho in reverse direction for A-to-ground fault is 90≤β≤270
and 180°-
The β is derived according to equation for the offset mho circle and φ is the angle between the
voltage and current.
116
I jX
A
ArgNegRes
I
A
Argdir ≤φ≤ ArgNegRes +180°.
© Copyright 2011 ABB Power Grids. All rights reserved
V
A
f
IA·R
ArgDir
en 06000466 _ansi.vsd
1MRK 506 326-UUS B
SEMOD154224-341 v4
Line distance protection REL650
Technical manual