ABB REL650 series Technical Manual page 121

1MRK 506 335-UUS A
Technical manual
The β is derived according to equation
voltage and current.
X
f
U
AB
ZRev
ANSI09000119 V1 EN
Figure 44: Operation characteristic for reverse phase A-to-B fault
Phase-to-ground fault
Mho
The measuring of ground faults uses ground-return compensation applied in a
conventional way. The compensation voltage is derived by considering the influence from
the ground-return path.
For a ground fault in phase A, the compensation voltage Vcomp can be derived, as shown
in figure 45.
- ×
=
V I
Vcomp
A
pol
EQUATION1793-ANSI V1 EN
where
V is the polarizing voltage (memorized VA for Phase A-to- ground fault)
pol
Z is the loop impedance, which in general terms can be expressed as
loop
=
Z +ZN Z
1
EQUATION1799 V1 EN
Table continues on next page
16 for the mho circle and φ is the angle between the
Z
ArgNegRes
I
AB
ArgDir
ANSI09000119-1-en.vsd
Z
loop
( )
× +
1 KN
1
Impedance protection
R
Section 6
(Equation 17)
(Equation 18)
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