ß
IAB·X
IAB·R
-
en07000109_ansi.vsd
ANSI07000109 V1 EN-US
Figure 99: Simplified mho characteristic and vector diagram for phase A-to-B fault
Offset Mho
SEMOD154224-242 v4
The characteristic for offset mho is a circle where two points on the circle are the setting
parameters
ZPP
and
ZRevPP
. The vector ZPP in the impedance plane has the settable angle
AngZPP
and the angle for
ZRevPP
is
AngZPP+180°
.
The condition for operation at phase-to-phase fault is that the angle β between the two
compensated voltages Vcomp1 and Vcomp2 is greater than or equal to 90° (figure
100). The angle
will be 90° for fault location on the boundary of the circle.
The angle β for A-to-B fault can be defined according to equation 56.
AB
AB
-I ZPP
arg
-(-I ZRevPP)
V
V
×
×
b =
æ ö
ç ÷
è ø
EQUATION1792-ANSI V1 EN-US (Equation 56)
where
EQUATION1801 V1 EN-US
is the V
AB
voltage
ZRevPP is the positive sequence impedance setting for phase-to-phase fault in reverse direction
1MRK 502 066-UUS B Section 7
Impedance protection
223
Technical manual
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