ABB Relion 670 Series Technical Reference Manual page 258

Section 6
Impedance protection
252
I jX
AB •
I • ZPE
A
I - • Z Re vPe
A
ANSI06000465 V1 EN
Figure 123: Simplified offset mho characteristic and voltage vector for phase A-to-
ground fault
Operation occurs if 90≤β≤270.
Offset mho, forward direction
In the same way as for phase-to-phase fault, selection of forward direction of offset
mho will introduce an extra criterion for operation. Beside the basic criteria for offset
mho according to equation
the voltage and the current must lie between the blinders in second and fourth
quadrant. See figure 124. Operation occurs if 90≤β≤270 and ArgDir≤φ≤ArgNegRes.
where
ArgDir
is the setting parameter for directional line in fourth quadrant in the directional element,
ZDMRDIR (21D).
ArgNegRes
is the setting parameter for directional line in second quadrant in the directional element,
ZDMRDIR (21D).
β is calculated according to equation
V =
comp1
ß
V
A
V
comp
en 06000465 _ansi . vsd
41 and 90≤β≤270, also the criteria that the angle φ between
41
1MRK505222-UUS C
V - A I • ZPE
A
V - (-I • ZRevPE
2 = A A
I R
•
AB
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