I.L. 40-385.5
9-5
trip will be performed. HST signal operates the
instantaneous reclosing scheme. The breaker
recloses and stays closed if the fault has been iso-
lated by the adjacent line breaker.
However, if the adjacent line breaker fails to trip, the
normal remote back up will operate.
9.12 SELECTABLE LOSS-OF-LOAD
ACCELERATED TRIP (LLT)
The load loss accelerated Zone-2 trip logic senses
remote 3-pole clearing on all faults except 3Ø to
complement or substitute for the action of the pilot
channel, speeding up trip at the slow terminal. The
logic includes AND-24, AND-25, OR-13, 0/32 and the
10/0 ms timers, as shown in Figure 23. Under normal
system conditions, 3-phase load currents are bal-
anced, and the low set overcurrent units IAL, IBL, ICL
satisfy both AND-24 and OR-13. On internal end
zone faults, Z2P, Z2G and/or FDOG/I
oM
picks up and
satisfies the third input to AND-25 via OR-6. How-
ever, the signal from AND-24 is negated to AND-25,
therefore, AND-25 should have no output until the
remote end 3-pole trips.
At this time the local end current will lose one or two
phases, depending on the type of fault (except 3-
phases), and AND-24 output signal changes from “1”
to “0”, satisfying AND-25. After 10 ms this output
bypasses T2 timer and provides speedup Zone-2
trip. The 10/0 ms time delay is for coordination on
external faults with unequal pole clearing. The 0/32
ms timer is needed for security on external faults with
no load current condition. Targets LLT will turn on
after an LLT trip.
The LLT function is selected by the setting of “YES,
FDOG, NO”, where YES = LLT with Z2 supervision;
FDOG = LLT with both Z2 and (FDOG/I
OM
) supervi-
sion; and NO = LLT function is not used.
LLT is not recommended for 3-terminal line applica-
tion due to difficulty in determining proper setting of
IL and complicated infeed from the third terminal.
9.13 PROGRAMMABLE RECLOSING INITIATION
(Figure 24)
The MDAR (REL-300) system provides the following
contact output for reclose initiation (RI) and reclose
block (RB) functions:
RI1, used for reclose initiation on single pole trip.
RI2, used for reclose initiation on 3-pole trip.
RB, used for reclose block.
The operation of RI1, RI2 and RB contacts is con-
trolled by the setting of the programmable reclose ini-
tiation logic as shown in Figure 24. The operation of
either RI1, RI2 or RB must be confirmed by the signal
of TRSL, which is the trip output of MDAR (REL-300)
operation.
The External Pilot Enable Switch (refer to Figure 6,
terminals 9 and 10 on TB-5), is used for externally
enabling the pilot system.
The PLT setting is similar to the external pilot enable
switch, except it is set from the front panel (or
remotely set via the communication interface).
For pilot MDAR (REL-300) with supporting non-pilot
function, a most popular reclose initiation practice is
to have reclosing initiation on high speed trip (pilot,
Zone-1 and high set) only. Referring to Figure 24, this
can be programmed by closing the external pilot
enable switch and selecting PLT and Z1RI to YES.
AND-84 will produce logic to operate the RI2 relay
when receiving signals from TRSL and AND-89. The
use of Z1RI signal to supervise the AND-84 provides
a flexibility for disabling RI, if needed, when pilot is in-
service. The program is further controlled by the
TTYP setting.
TTYP set at OFF — 3PRN provides no output,
therefore, RI2 will not operate.
TTYP set at 1PR — 3PRN will provide output “1”
on ØG faults only (via OR-100 and
AND-51A), RI2 will operate.
TTYP set at 2PR — 3PRN will provide output “1”
on ØG fault or ØØ faults (via OR-
100B and AND-51B), RI2 will
operate.
TTYP set at 3PR — 3PRN will provide output “1”
on any type of fault (via OR-51),
and RI2 will operate.
The Z1RI, Z2RI AND Z3RI settings combining with
the logic of AND-62B, -62C, -62D and OR-62 provide
for programming applications where the reclose initi-
ation on Zone-1, Zone-2 or Zone-3 trip is desired on
a non-pilot MDAR (REL-300) system. AND-62A is
controlled by the signal 3PRN, therefore, the setting
of 1PR, 2PR and 3PR also affects the Z1RI, Z2RI
and Z3RI program.
In general, the RB relay will operate on TDT (time
delay trips) or OSB (out-of-step block condition).
However, it will be disabled by the setting of Z1RI,
