ABB RED650 Technical Manual page 134

Section 7
Impedance protection
128

I jX
L 1 L 2
I
IEC15000060 V1 EN-US
Figure 49: Simplified mho characteristic and vector diagram for phase L1-to-
L2 fault
Offset Mho
The characteristic for offset mho is a circle with origin as the center and magnitude
of as the radius, where
Z 1
set
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 50). 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.


U I



L L 1 2 L L 1 2
arg


 
U I

L L 1 2 L L 1 2
IECEQUATION15008 V2 EN-US


Z 1
U
L L 1 2 set
comp
U
L 1L 2
U
pol
is settable through the resistance and reactance
Z 1
set


Z 1

set



Z 1

set
1MRK 505 394-UEN A
 
U I Z 1
L 1 L 2 L 1 L 2 set

I
IEC15000060-1-en.vsdx
GUID-3E13E6D5-0832-4386-9677-9A40BFF42F8F v2
Line differential protection RED650 2.2 IEC
Technical manual

R
L 1 L 2
(Equation 9)