ABB Relion 650 Series Technical Manual page 120

Section 5
Impedance protection
ANSI09000120 V1 EN-US
Figure 62: Simplified offset mho characteristic and vector diagram for phase A-to-ground
Operation occurs if 90≤β≤270.
Offset mho
The characteristic for offset mho at ground fault is a circle containing the two vectors from the
Z and ZRev where Z and Zrev are the setting reach for the positive sequence impedance in
origin
forward, reverse direction respectively. The vector
LineAng and the angle for ZRev is LineAng +180°.
The condition for operation at phase-to-ground fault is that the angle β between the two
compensated voltages Vcomp1 and Vcomp2 is greater or equal to 90° see figure 63. The angle will
be 90° for fault location on the boundary of the circle.
The angle β for A-to-ground fault can be defined as

β =
arg


EQUATION1802-ANSI-650 V1 EN-US
Table continues on next page
114
I X
A·
I ·Z
A
fault

− ⋅
V I Z
A A

( )
− − ⋅

V I Z Re v
A A
© Copyright 2011 ABB Power Grids. All rights reserved
I ·ZN
A
V
comp
ß
I • Z
A loop
Vpol
f
I ( Ref)
A
ANSI09000120-1-en.vsd
Z in the impedance plane has the settable angle
1MRK 506 326-UUS B
I ·R
A
Line distance protection REL650
Technical manual
SEMOD154224-309 v4
(Equation 20)