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3.2.2
Three-Phase
Three-phase fault detection (see Figure 3-3, page 3-29) is accomplished 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 computation of the distance units will be:
V
- I
XG
and (V
where V
If the REL300 detects that all three voltages are less than 1 volt, the pre-fault voltages (memory
action) are used as reference for Zone 1 tripping. For Zone 2 and Zone 3, the memory action
is in effect if all three voltages are less than 7 volts.
3.2.3
Phase-to-Phase
The phase-to-phase unit (see Figure 3-4, page 3-29) responds to all phase-to-phase faults,
phase-to-phase-to-ground faults, and some single-phase-to-ground faults. Equations (5 and 6)
are for operating and reference quantity, respectively. They will produce output when the oper-
ating quantity leads the reference quantity.
(V
- I
AB
(V
- I
CB
3.3
MEASUREMENT ZONES
REL300 performs line measurement within 3 zones of the transmission line (Zone 1, Zone 2,
Zone 3), and one optional pilot zone. When the REL300 functional display "STYP" is set at
"3ZNP", it will perform the 3-zone non-pilot function.
When the REL300 trips, the trip contacts will be sealed-in as long as the trip coil current flow
exists. The trip contacts can be delayed dropout (by 50 ms) after the trip current is removed,
providing a jumper (JMP4) on the Microprocessor module is connected.
3.3.1
Zone 1 Trip
For Zone 1 phase faults, the Z1P unit will identify the fault and operate. The 3φ fault logic is
supervised by the load restriction logic via AND131C and AND 131 (Figure 3-18a) and is also
supervised by the selectable OSB, as shown in Figure 3-5 (page 3-30). Outputs of Z1P and IM
Z
X
CP
)
Q
= V
, V
, or V
XG
AG
BG
I
= I
, I
or I
X
A
B
C
Z
= Zone reach setting (PLTP, Z1P
CP
Z2P, and Z3P) in secondary ohms of Z
V
= Quadrature phase voltages, i.e.,
Q
V
, V
and V
CB
AC
Z
)
AB
CP
Z
)
CB
CP
CG
for φA, φB and φ C units, respectively
BA
for multi-phase faults
1L
I.L. 40-385.7
(3)
(4)
(5)
(6)
3-3
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