ABB Relion 670 Series Technical Reference Manual page 257

1MRK505222-UUS C
Technical reference manual
I X
A·
I ·ZPE
A
ANSI06000472 V1 EN
Figure 122: Simplified offset mho characteristic and vector diagram for phase A-to-
ground fault
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 origin ZPE and ZRevPE where ZPE and ZrevPE are the setting reach for the
positive sequence impedance in forward respective reverse direction. The vector ZPE
in the impedance plane has the settable angle AngZPE and the angle for ZRevPP is
AngZPE+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 123.
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
Table continues on next page
IA·ZN
V
comp
ß
I • Z
A loop
Vpol
f
I
A
IA (Ref)
en06000472_ansi.vsd
Section 6
Impedance protection
·R
251