ABB REL650 series, Technical Manual

Page: 123 / 856

comp
V
ß
I
A·
X
I
A
·R
I
A
·Z
I
A
·ZN
loop A
Z • I
f
Vpol
I
A
( Ref)
ANSI09000120-1-en.vsd
ANSI09000120 V1 EN
Figure 45: 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
Z and ZRev where Z and Zrev are the setting reach for the positive sequence
impedance in forward, reverse direction respectively. The vector Z in the impedance plane
has the settable angle 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
46 . 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
V I Z
V I Z v
A A
A A
Re
EQUATION1802-ANSI-650 V1 EN
(Equation 22)
Table continues on next page
1MRK 506 335-UUS A
Section 6
Impedance protection
117
Technical manual