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2
1
L
L
U
1 2
1
L L
set
I
Z
set
L
L
L
L
comp
Z
I
U
U
1
2
1
2
1
pol
U
jX
I
L
L
2
1
R
I
L
L
2
1
IEC15000060-1-en.vsdx
IEC15000060 V1 EN-US
Figure 49:
Simplified mho characteristic and vector diagram for phase L1-to-
L2 fault
Offset Mho
GUID-3E13E6D5-0832-4386-9677-9A40BFF42F8F v2
The characteristic for offset mho is a circle with origin as the center and magnitude
of
Z
set
1
as the radius, where
Z
set
1
is settable through the resistance and reactance
settings.
The condition for operation at phase-to-phase fault is that the angle β between the
two compensated voltages is greater than or equal to 90° (figure
). The angle will
be 90° for fault location on the boundary of the circle.
The angle β for L1 to L2 fault can be defined according to equation below.
1 2
1 2
1 2
1 2
1
arg
1
L L
L L
set
L L
L L
set
U
I
Z
U
I
Z
IECEQUATION15008 V2 EN-US
(Equation 9)
Section 7
1MRK 505 394-UEN A
Impedance protection
128
Line differential protection RED650 2.2 IEC
Technical manual
Summary of Contents for RED650
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