ABB Relion 670 series - Page 361


A
V
3 0 1
N set
I K Z
( 3 0 ) 1
comp A A N set
V V I I K Z    
pol
V
IA•R
IA•jX
1
A set
IZ
ANSI15000059-1-en.vsdx
ANSI15000059 V1 EN-US
Figure 180: Simplified offset mho characteristic and vector diagram for phase A-to-ground
fault
Operation occurs if 90 °≤β≤270 °.
Offset mho
GUID-1CD62635-A76A-41F7-A814-8BB493F5B051 v1
The condition for operation of offset mho at phase-to-earth fault is that the angle β between the
two compensated voltages is equal to or greater than 90°, see figure
181. The angle will be 90° for
fault location on the boundary of the circle.
β = − + ⋅ ⋅
( )
− − − + ⋅


)
⋅
{
arg ( ) ( ]V I I K Z V I I K Z
A A N set A A N RVset
3 0 1 3 0 1arg
}}
ANSIEQUATION15022 V1 EN-US (Equation 107)
where
Z RVset1
is the complex positive sequence impedance of the line in Ω/
phase for phase-to-ground fault opposite to zone direction and
is defined as,
Z R RvPEZx j X RvPEZx
RVset
1 1 1= + ⋅
IECEQUATION15023 V1 EN-US (Equation 108)
1MRK 502 066-UUS B Section 7
Impedance protection
355
Technical manual