The condition for operation at phase-to-phase fault is that the angle β between the two
compensated voltages Ucomp1 and Ucomp2 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
.
L1L2
L1L2
-I
ZPP
arg
U-(-I
ZRevPP)
U
×
×
b =
æ
ö
ç
÷
è
ø
EQUATION1792 V1 EN
(Equation 38)
where
U
EQUATION1800 V1 EN
is the U
L1L2
voltage
ZRevPP
is the positive sequence impedance setting for phase-to-phase fault in reverse direction
ZPP
I
2
L
1
L
•
L1L2
comp1
U
=
U
ß
I
L1L2
jX
I
L1L2
R
-
ZPP
I
2
L
1
L
•
vPP
Re
Z
2
L
1
L
I
•
U
U
2
Ucomp
=
=
-
I
F
•Z
F
=U
L1L2
en07000110.vsd
IEC07000110 V1 EN
Figure 67:
Simplified offset mho characteristic and voltage vectors for phase L1-
to-L2 fault.
Operation occurs if 90≤β≤270.
Offset mho, forward direction
When forward direction has been selected for the offset mho, an extra criteria beside
the one for offset mho (90<β<270) is introduced, that is the angle φ between the
Section 7
1MRK502052-UEN B
Impedance protection
186
Technical manual
Summary of Contents for Relion REG670
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