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described in Zone 1 trip except for Zone 2 phase
time delay trip indicator (Z2P).
Similar operation occurs for Zone 2 single-phase-to-
ground faults. The Z2G unit sees the fault and oper-
ates. This, plus the operation of the IoM, FDOG and
T2G satisfy AND-19, and provide the TDT signal via
OR-3 with Zone 2 ground time delay trip indicator
(Z2G).
The single-phase ground distance units may re-
spond to a φφG fault. The output of the Z2G unit plus
the operation of the φφ selection will trip the Z2P via
OR-157, T2P and AND-18. Leading phase blocking
is unnecessary for an overreach Zone device.
The TDT signal can be connected to the reclosing
block logic. The settings for Zone 2 timers (phase
and ground units) are independent, as follows:
• T2P (Zone 2 phase)
• T2G (Zone 2 ground)
The range of the timers is as follows:
• T2P and T2G (0.1 to 2.99 seconds or Block)
Either or both Zone 2 phase and Zone 2 ground
function(s) can be disabled by setting Z2P and/or
Z2G to the BLK position.
3.3.3 Zone 3 Trip
For Zone 3 phase faults, the Z3P (forward or reverse
looking, depending on the Z3FR setting) unit will
identify the faults and operate the Zone 3 phase tim-
er T3P. The Z3P output plus the T3P timer output
satisfy AND-20 (as shown in Figure 3-7). The AND-
20 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 to Zone 1 trip, except for the Zone 3 phase
time delay trip indicator (Z3P).
For Zone 3 single-phase-to-ground faults, Z3G iden-
tifies the fault and operates. This, plus the operation
of the IOM, satisfies AND-7; the TDT signal then
trips via OR-3 with Zone 3 ground time delay trip in-
dicator Z3G. The TDT signal can be connected to
the reclosing block logic. For security, the Z3G unit
is also supervised by the signal of FDOG when it is
set for forward looking (or by the signal of RDOG
when it is set for reverse looking) via logic OR-171B,
AND-171C or AND 171D (as shown in Figure 3-7).
(5/92)
A similar operation for φφG faults (shown in Zone 2),
is applied to Zone 3, through OR-170, T3P and AND-
20 gates.
The settings for Zone 3 timers (phase and ground
units) are independent, as follows:
• T3P (Zone 3 phase)
• T3G (Zone 3 ground)
The range of the timers is as follows:
• T3P and T3G (0.1 to 9.99 seconds or Block)
Either or both Zone 3 phase and Zone 3 ground
function(s) can be disabled by setting Z3P and/or
Z3G to the BLK position.
3.3.4 Zone 1 Extension
This scheme provides a higher speed operation on
end zone faults without the application of pilot chan-
nel.
If the MDAR functional display "STYP" is set on Z1E
position, the Z1P/Z1G unit will provide two outputs:
one is overreach which is set at 1.25 x Z1 reach by
the microprocessor, and one is the normal Z1 reach.
A single shot instantaneous reclosing device should
be used when applying this scheme. The targets
Z1P/Z1G will indicate either Z1 trip and/or Z1E trip
operations. The other functions (e.g., Z2T, Z3T, ac
trouble monitoring, overcurrent supervision, IT, CIF,
unequal-pole closing load pickup control, load-loss
acceleration trip, etc.) would remain the same as in
the basic scheme (3ZNP).
For a remote internal fault (refer to Figure 3-8), either
Z1P or Z1G will see the fault since they are set to
overreach. High speed trip will be performed via the
normal Z1T path (Figure 3-5), i.e., AND-2 (or AND-
3), OR-2. HST signal operates the instantaneous re-
closing scheme. The breaker recloses and stays
closed if the fault is automatically cleared.
Target Z1P and/or Z1G will be displayed. Once the
breaker trip circuit carries current, it operates the log-
ic OR-5 (not shown), produces output signal TRSL,
and satisfies logic AND-26 for 5000 ms (Figure 3-8).
The output signal of AND-26 will trigger the Z1P/Z1G
reach circuit, constricting their reaches back to the
normal Zone 1 for 5000 ms. During the reach con-
stricting periods, if the breaker is reclosed on a Zone
1 permanent fault, it will retrip again. If the breaker is
I.L. 40-385.1B
3-3
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