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Section 3. APPLICATIONS AND ORDERING INFORMATION
3. 1. NON-PILOT SYSTEM
The MDAR non-pilot relay system detects faults in
three zones of distance, phase and ground. Zones 1
and 2 are forward set; Zone 3 can be set to forward
or reverse. There is also a separate optional pilot
zone (see Section 3.5). The fault locator can be set
to indicate fault distance in miles or kilometers.
The R-X Diagram, shown in Figure 3-1, describes
the characteristics available with MDAR. Zone 1
phase and ground settings are chosen to provide
substantial coverage of the protected line without
overreaching the next bus. A setting of 80% of the
line impedance is typical. Faults occurring within the
reach of the Zone 1 measurement cause direct trip-
ping without regard to any action occurring at the re-
mote terminal. Zone 2 settings are chosen to assure
that faults occurring on the next bus are recognized.
Settings are chosen (independent of the Zone 1 set-
tings), generally to be 120 to 150% of the line imped-
ance. Any fault occurring on the protected line will be
recognized by this Zone 2 measurement (within the
fault resistance and current limitations of the relaying
system). Zone 2 tripping occurs with time delay (T2)
or, where equipped with pilot provisions, at high
speed, subject to the constraints imposed by the pi-
lot channel for the particular pilot system selected.
The Zone 3 measurement is directional, and may be
chosen to respond to forward or reverse faults. The
reverse sensing option is chosen for the blocking
system where the reverse fault carrier start function
is required. It is also used in conjunction with the T3
trip function, chosen to coordinate with adjacent ter-
minal Zone 2 timing. The forward sensing option pro-
duces time delayed backup to other devices sensing
forward faults. Blinder measurements (B1, B2, B3,
B4) are available as an option for out-of-step sens-
ing. The inner blinder (as a standard function) also
restricts the trip zone of each of the 3-phase fault
measuring units.
3. 2. LINE MEASUREMENT TECHNIQUES
Line measurement techniques applied to each zone
include:
• Single-Phase-To-Ground fault detection
• 3-Phase fault detection
(5/92)
• Phase-to-Phase fault detection
• Phase-to-Phase-to-Ground fault detection
3.2.1 Single-Phase-to-Ground
Single-phase-to-ground fault detection (see Figure
3-2) is accomplished by 3 quadrature polarized
phase units (φA, φB, φC). Equations 1 and 2 (below)
are for operating and reference quantity, respective-
ly. The unit will produce output when the operating
quantity leads the reference quantity.
Z
Z
–
0L
V
I
–
+
-----------------------
XG
X
Z
1L
1
(
)
I
=
-- - I
+
I
+
I
0
A
B
C
3
Vector (V
)
Q
where V
= V
, V
XG
AG
BG
I
=
I
, I
or I
X
A
B
Z
, Z
=
positive and zero sequence line
L
1L
0
impedance in relay ohms.
Z
=
Zone reach setting in secondary
CG
ohms for φGF fault
V
=
quadrature phase voltages, i.e.,
Q
V
, V
CB
AC
units, respectively.
3.2.2 Three-Phase
Three-phase fault detection (see Figure 3-3) is ac-
complished by the logic operation of one of the three
ground units, plus the 3φF output signal from the
faulted phase selector unit.
However, for a 3-phase fault condition, the computa-
tion of the distance units will be:
V
- I
Z
XG
X
CP
and (V
)
Q
where V
= V
, V
XG
AG
I
= I
, I
or I
X
A
B
I.L. 40-385.1B
I
1L
Z
CG
0
, or V
CG
C
for φA, φB and φC
and V
BA
, or V
BG
CG
C
(1)
(2)
(3)
(4)
3-1
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