ABB REG650 Technical Manual page 128

Section 6
Impedance protection
122
The characteristic for offset mho is a circle where two points on the circle are the
setting parameters ZxFwd and ZxRev. The vector ZxFwd in the impedance plane
has the settable angle ImpadenceAng and the angle for ZxRev is ImpedanceAng
+180°.
The condition for operation at phase-to-phase fault is that the angle β between the
two compensated voltages Ucomp1 and Ucomp2 is between 90° and 270° (figure
62). The angle will be 90° or 270° for fault location on the boundary of the circle.
The angle β for L1-to-L2 fault can be defined according to equation 30.
æ
- ×
U I ZxFwd
b =
Arg ç L1L2
ç
- - ×
U ( I Zx Re v)
è
L1L2
IECEQUATION2320 V1 EN
where
U
EQUATION1800 V1 EN
I X
L1L2·
× ZxFwd
I
L L
1 2
- × ZxRev
I
L L 1 2
IEC09000174 V1 EN
Figure 62: Simplified offset mho characteristic and voltage vectors for phase
L1-to-L2 fault.
Operation occurs if 90≤β≤270.
ö
÷
÷
ø
is the U
L1L2
= -
Ucomp 2 U
L L
1 2
ß
U
Ucomp
1MRK 502 034-UEN -
voltage
× ZxFwd
( I )
L L
1 2
= + × ZxRev
2 U ( I )
L L 1 2 L l 1 2
I R
L1L2·
IEC09000174_1_en.vsd
Technical Manual
(Equation 30)