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I.L. 40-385.1B
Z
= Zone reach setting (PLTP, Z1P
CP
Z2P, and Z3P) in secondary ohms
for multi-phase faults.
V
= Quadrature phase voltages, i.e.,
Q
V
, V
CB
C units, respectively.
3.2.3 Phase-to-Phase
The phase-to-phase unit (see Figure 3-4) responds
to all phase-to-phase faults, and some single-phase-
to-ground faults. Equations (5 and 6) are for operat-
ing and reference quantity, respectively. They will
produce output when the operating quantity leads
the reference quantity.
(V
- I
Z
)
AB
AB
CP
(V
- I
Z
)
CB
CB
CP
3.3
MEASUREMENT ZONES
MDAR performs line measurement within 3 zones of
the transmission line (Zone 1, Zone 2, Zone 3), and
one optional pilot zone. When the MDAR functional
display "STYP" is set at "3ZNP", it will perform the 3-
zone non-pilot function.
When the MDAR trips, the trip contacts will be
sealed-in as along 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) is connected on the Microprocessor module.
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 select-
able OSB, as shown in Figure 3-5. Output of Z1P
satisfies AND-2 and provides a high-speed trip
(HST) signal from OR-2 to operate the trip output
telephone relay. The trip circuit is monitored by a
seal-in reed relay (S), which is in-series with each
trip contact in the tripping circuits. The S relay will
pick up if the trip current is higher than 0.5 Amp. The
operation of the "S" contact will turn-on the breaker
trip indicators (with memory), and feeds back to OR-
4 to hold the trip relay in operation until the breaker
trips and 52a contact opens (not shown in Figure 3-
5). The TRSL signal plus the output signal from
3-2
for φA, φB and φ
and V
AC
BA
AND-2 turns on the Zone 1 phase trip indicator
(Z1P). The breaker trip and Zone 1 phase trip indica-
tors are memorized. They can be reset by external
RESET voltage or through remote communication.
By pushing the RESET pushbutton, the flashing LED
will be reset, but the fault information will still remain
in memory.
The Z1P 3φ trip logic AND-131 is supervised by both
the conventional OSB and the subsequent OSB log-
ic when the OSB is set to "YES", for more security on
some special power system applications. ZIP logic
AND-2 is also supervised by the FDOP (Forward Di-
rectional Overcurrent Phase unit) when the OSB is
set to "YES" for more security on some special pow-
er system applications.
(5)
Similar operations exist for Zone 1 single-phase-to-
(6)
ground faults. The Z1G unit sees the fault and oper-
ates; the IoM and FDOG units also operate, satisfy-
ing AND-3. Tripping occurs via OR-2 with Zone 1
ground trip indication Z1G. Logic AND-3 is also su-
pervised by the signal of RDOG (reverse directional
overcurrent ground) for security purposes.
The Z1G unit is also supervised by the signal of un-
equal-pole-closing and RDOG.
A two-out-of-three "leading phase blocking" logic is
included for solving the overreach problem of the
single-phase ground distance units, which may re-
spond to a φφG fault.
The high-speed trip (HST) signal also is connected
to the reclosing initiation logic.
Either or both Zone 1 phase and Zone 1 ground
function(s) can be disabled by setting the Z1P and/
or Z1G to the position. Zone 1 trip can be delayed by
setting T1 = YES. The delay time is 2 cycles for a
non-pilot 3PT backup, with another system operat-
ing in SPT mode.
3.3.2 Zone 2 Trip
For Zone 2 phase faults, the Z2P unit will see the
faults and operate the Zone 2 phase timer (T2P).
The Z2P output plus the T2P timer output satisfy
AND-18, as shown in Figure 3-6. The AND-18 output
provides time delay trip signal TDT via OR-3. Signal
TDT picks up OR-4 (Figure 3-5) and operates the trip
relay. The tripping and targeting are similar as
(5/92)
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