ABB Relion 670 series, Technical Manual

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ß
I
AB
·
X
I
AB
·R
-
en07000109_ansi.vsd
comp AB
V
=V
AB
I ZPP
×
pol
V
AB
V
AB
I ZPP
×
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 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
V
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