ABB REL650 series Technical Manual page 120

Section 6
Impedance protection
114
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 voltage and
the current must lie between the blinders in second quadrant and fourth quadrant. See
figure 43. 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,
ZDNRDIR.
ArgNegRes
is the setting parameter for directional line in second quadrant in the directional element,
ZDNRDIR.
β is calculated according to equation
The directional information is brought to the mho distance measurement from the mho
directional element as binary coded information to the input DIRCND. See Directional
impedance quadrilateral and mho (ZDNRDIR) for information about the mho directional
element.
I jX
AB
ArgNegRes
ANSI09000118 V1 EN
Figure 43: Simplified offset mho characteristic in forward direction for phase A-to-B
fault
Offset mho, reverse direction
The operation area for offset mho in reverse direction is according to figure 44. The
operation area in second quadrant is ArgNegRes+180°.
Operation occurs if 90≤β≤270 and 180° - ArgDir ≤φ ≤ ArgNegRes + 180°
16
Z
V
AB
I
AB
ArgDir
ANSI09000118-1-en.vsd
1MRK 506 335-UUS A
Technical manual