ABB REG670 - Page 197

ZPEI 1L •
ZPE•L1I-U=U
L1
comp1
ß
jX
IL1L2 R
vPeReZ•I- L1
UL1
)
L1= ZRevPE
•
(-I-1L2comp UU
en 06000465.vsd
2I 1L L
•
•
IEC06000465 V1 EN
Figure 71: Simplified offset mho characteristic and voltage vector for phase L1-
to-earth 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
41 and 90≤β≤270, also the criteria that the angle φ between
the voltage and the current must lie between the blinders in second and fourth
quadrant. See figure
72. 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.
ArgNegRes is the setting parameter for directional line in second quadrant in the directional element,
ZDMRDIR.
β is calculated according to equation 41
1MRK502052-UEN B Section 7
Impedance protection
191
Technical manual