Backup Mode Trip - If the RFL 9300 is configured for single-pole trip operation and the relay is operating in
backup mode, any trip signal that is calculated locally will result in all three single-pole breakers being tripped
and a reclose block signal being issued. This is the case regardless of the status of Selective Pole Relaying
which does not apply when backup mode is active. In three-terminal systems it is very possible that during a
communications outage between two of the terminals, the third terminal may still be providing differential protec-
tion. Only the two terminals experiencing the communications problem may be in backup mode (if enabled). If
the third terminal calculates a permissive trip it will transmit trip signals to the two terminals operating in backup
mode. Since the trip was not calculated locally these terminals will trip only on the faulted phase(s).
3I0 Trip Algorithm - When the RFL 9300 relay is configured for single-pole operation the GROUND DELAY func-
tion takes on an additional role. If GROUND DELAY is not enabled, trips calculated by the 3I0 controller will
have no effect. In certain applications, such as tapped loads, the ground bias may be set much more sensitive
than the phase bias and only a 3I0 trip signal will be available to clear low-level internal faults. In this case,
GROUND DELAY must be enabled to insure that there will be adequate time to allow the individual Phase Con-
trollers to trip their breakers. Then, when the 93B SV receives a trip signal from the 3I0 controller, if none of the
other Phase Controllers has issued a trip signal all three will be commanded to trip. It’s ok to do this since the
3I0 controller can’t pass its trip signal to the 93B SV unless the programmed GROUND DELAY has already ex-
pired.
When GROUND DELAY is enabled specifically for the purpose of allowing 3I0 single-pole trips it is recom-
mended that a setting of 50ms be used. Keep in mind that the ground delay timer doesn’t start until a 3I0 trip
signal would have been issued in a three-pole application i.e. after the normal 3I0 trip delay. This means that
with a 50ms setting the timer may not expire until as much as 80 to 90ms after the fault. Remember that trip sig-
nals are calculated at the conclusion of positive half-cycles of line current. Should a positive half-cycle terminate
just prior to the 50ms time-out it will be an additional 16ms before the 3I0 trip will be passed to the 93B SV
which must then pass the trip command to the phase controllers.
24.4.6 SINGLE-POLE ALARMS
The alarms listed below are specific to a single-pole system:
054 - SPT Trip General
Single-pole logic general alarm. Problem on Single-Pole chassis detected by
93B SV . Problem with (or no) serial message sent by SP logic.
055 - PH A SG POLE CS
Phase A single-pole trip alarm: Phase A dc trip current sensed for more than
500ms by single-pole logic or Phase A dc trip current sensed without a Phase
A trip signal having been issued.
056 - PH B SG POLE CS
Phase B single-pole trip alarm: Phase B dc trip current sensed for more than
500ms by single-pole logic. Phase B dc trip current sensed without a Phase B
trip signal having been issued.
057 - PH C SG POLE CS
Phase C single-pole trip alarm: Phase C dc trip current sensed for more than
500ms by single-pole logic. Phase C dc trip current sensed without a Phase C
trip signal having been issued.
RFL 9300 RFL Electronics Inc.
August 25, 2000 24 - 11 (973) 334-3100
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