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the signal continuation will not be per-
formed if the trip is caused by a CIF
function (AND-49E and OR-49C).
(c)
Carrier Receiving Logic (Figure 28)
This logic includes a contact converter CC and logic
AND-44. Output "trip" (or unblocking) frequency sig-
nal from the carrier receiver operates the contact
converter and will produce a carrier trip, CR, signal
from AND-44.
(d)
Channel Indicators (not shown in Figure 28)
The memorized SEND indicator will be displayed
after breaker trip and frequency shift to trip or
unblocking by the transmitter during the fault. The
memorized RCVR indicator will be displayed after the
breaker trips and a carrier trip signal was received
from the receiver.
(e)
Channel Simulation (not shown in Figure 28)
The test function selection provides the capability to
simulate the TK switch function for keying action via
OR-18 and AND-35 without the operation of pilot
relay units, and to simulate the RS switches function
for receiving of a trip or unblocking frequency signal
action without the operation from the remote trans-
mitter.
(f)
TBM, Transient Block and Unblock Logic
(Figure 36)
For a loop system or paralleled line applications,
power reversal may introduce a problem to the pilot
relay system, especially when a 3-terminal line is
involved, since the distance units may have to be set
greater than 150% of ZL in order to accommodate
the infeed effect from the tapped terminal. They may
see the external fault on the parallel line when the
third source is out of service. The transient block and
unblock logic, TBM, is for solving this problem.
Field experiences show that the reverse power may
also be occurred transiently on a single circuit appli-
cation under unequal-pole external fault clearing con-
dition. On an external ground fault, when the
adjacent line breaker trips, it interrupts the faulted
phase as well as the load currents in the unfaulted
phases. Dependent on the direction of the load cur-
rent, and the asymmetry of the breaker, there can be
a short pulse of load-derived Io with possible "trip-
ping direction" polarity, which provides an electrical
forward torque to the ground directional relay. There-
fore, for security reason, the setting of "RBSW" on
MDAR (REL-300) version 2.10 has been removed
from the logic and the software (some older ver-
sions need to set RBSW to YES). Once the POTT
system is selected, the transient blocking and
unblocking logic will automatically be activated.
MDAR (REL-300) POTT scheme uses reverse-
block approach for the TBM logic, as shown in
Figure 36. For activating the TBM logic, the zone-
3 distance units should be set to reverse, i.e. set
Z3FR = REV. The TBM logic, Figure 36, consists of
the reverse setting zone-3 distance units, AND-172,
AND-9B, OR-9A, AND-45A and the 0/50 ms timer.
(g)
Programmable Reclosing Initiation, (Figure 24)
The basic programmable RI application is as
described in Chapter IX. However, on pilot systems,
to activate the RI2 on any 3-pole trip, the external
pilot enable switch should be ON, and both the PLT
and Z1RI should be set to YES. The operation will
occur via the logic AND-89, AND-84 and OR-84A, as
shown in Figure 24.
10.1.2 Permissive Underreach Transfer Trip
System (PUTT)
The basic operating principles of a PUTT system are:
(a)
The pilot relays, PLTP/PLTG, are set to over-
reach,
(b)
The pilot channel is a frequency shift type
device, and
(c)
The transmitter frequency need not to be differ-
ent at each terminal. Its signal may be through
either metallic wire or microwave.
(d)
Channel is normally operated with a guard fre-
quency. The channel frequency will be shifted
from guard to trip when the Zone-1 reach relay,
Z1P/Z1G, operates, and
(e)
Pilot trip is performed when the pilot relay(s),
PLTP and/or PLTG operates, together with the
receiving of a carrier trip signal from the remote
end.
The PUTT system includes the following logic. The
functional display STYP should be selected to PUTT.
The TBM logic is not required for this scheme
because the carrier keying units are set for under-
reach.
I.L. 40-385.5
10-3
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