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I.L. 40-386.3
is the direction where tripping takes place; the "reverse" reach is then in the forward
line direction.)
V
XG
(
j V
XG
Z
, Z
0L
1L
Z
, Z
CGF
These units are directionally supervised by FDOG (RDOG for reverse Zone3). Because of in-
ternal clipping of unfaulted phase voltages during phase-ground faults, use of Zero-sequence
or Dual Polariz (polarization) for DIR TYPE only is recommended when applied to resis-
tance grounded systems; calculation of V2 magnitude and angle is likely to be incorrect in this
application, causing NSEQ polarization to give false directional sense ( see Section 2.4.11 ).
2.2.2
Three-Phase Fault
Three-phase (3Ø) fault detection (Figure 2-3) is accomplished by the logic operation of
one of the three ground units, plus the 3Ø fault output signal from the faulted phase
selector unit.
However, for a 3-phase fault condition, the computation of the distance units will be:
V
- I
XG
X
(and (V
where V
I
X
Z
CP
for
V
Q
2-2
[
]Z
I
k
I
–
+
X
O
O
CG
Z
Z
–
OL
IL
k
=
----------------------- -
=
o
Z
IL
1
(
I
-- - I
I
I
=
+
+
O
A
B
C
3
[
]Z
+
I
+
k
I
X
O
O
CGR
Where V
V
=
XG
AG
,
,
I
=
I
I
or I
X
A
B
C
=
zero and positive sequence line impedance in relay ohms
=
Zone forward and reverse reach settings in secondary ohms of Z1L, for ph-
CGR
G fault (both are in angle PANG)
Z
CP
)
Q
=
V
, V
, or V
XG
AG
BG
=
I
, I
or I
A
B
C
=
Zone reach setting (Pilot Ø, Z1Ø, Z2Ø,and Z3Ø) in secondary ohms
multi-phase faults.
=
Quadrature phase voltages, i.e.,V
C units, respectively.
∠
(
Z
GANG PANG
–
R
)
)
,
,
V
or V
BG
C
CG
)
for ↓A, φB and Ø
, V
and V
CB
AC
BA
(1)
(2)
(3)
(4)
(10/94)
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