ABB Relion 670 series, Technical Manual

Page: 234 / 1432

comp
V
ß
I
A·
X
I
A
·R
I
A
·ZPE
IA·ZN
loop A
Z • I
f
Vpol
IA (Ref)
en06000472_ansi.vsd
ANSI06000472 V1 EN-US
Figure 103: Simplified offset mho characteristic and vector diagram for phase A-to-ground
fault
Operation occurs if 90≤β≤270.
Offset mho
SEMOD154224-309 v5
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 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 104 . 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
Section 7 1MRK 502 066-UUS B
Impedance protection
228
Technical manual