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Power Automation and Protection Division
7.2.
Single Phase-to-Ground
Single phase-to-ground fault detection (see Figure 3-10) is accomplished by 3 non-directional
phase units (A, B, C). Expressions 1 and 2 (below) are for the operating and reference quantity,
respectively. The unit will produce output when the operating quantity leads the reference quan-
tity.
and
where
V
XG
I
X
I
0
Z
, Z
1L
0L
Z
FG
Z
RG
7.3.
Three-phase
Three-phase fault detection ( see Figure 3-11 ) is accomplished by the logic operation of one of
the three ground units, plus the 3øF output signal from the phase selector unit.
However, for a 3-phase fault condition, the computation of the distance units will be:
and
where
V
XG
I
X
Z
RG
7.4.
Phase-to-Phase
The Phase-to-Phase unit ( see Figure 3-12 ) responds to all forward Phase-to-Phase faults, and
some phase-phase-to-ground faults. Expressions 5 and 6 are for operating and reference
REL 352 Version 1.00
Z
0L
V
–
I
+
----------------------- I
XG
X
Z
Z
j V
+
I
+
------------------------ I
XG
X
=
V
, V
or V
AG
BG
CG
=
I
, I
or I
A
B
C
=
zero sequence relay current
=
Positive and zero sequence line impedance in relay ohms
=
Forward zone reach setting in secondary ohms for SLGF
=
Reverse reach setting in secondary ohms for SLGF
V
- I
Z
XG
X
P
[
]
j V
+
I
Z
XG
X
RG
=
V
, V
, V
AG
BG
CG
=
I
, I
or I
A
B
C
=
Phase reach setting in secondary ohms for SLGF.
–
Z
1L
Z
0
FG
1L
–
Z
Z
OL
1L
0
RG
Z
L
I.L. 40-201.9
eq. (1)
3
eq. (2)
eq. (3)
eq. (4)
3-5
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