RFL 9300 RFL Electronics Inc.
October 20, 2004 7 - 14 (973) 334-3100
c. The message "ALARM 34 31 60" will appear on the display.
d. The beeper will sound if it has been enabled.
This condition produces a "Local Charge Comparison Trip" (LCCT) alarm on Phase A
(31) and a Phase A Controller general alarm (61). The LCCT alarm occurs because the
arithmetic sum of 3 amperes exceeds the phase bias level, and the fault detectors have
not energized. The RFL 9300 considers this to be an alarm condition for two reasons:
a. An LCCT alarm condition cannot
occur during a real fault.
b. An LCCT alarm condition can
occur for certain failure modes in the relay, such
as an A/D converter failure.
If you leave this condition on, you will note that the alarm disappears approximately
every five seconds and then comes back. This shows that the RFL 9300 is trying to
clear the alarm.
9. Simulate an actual fault by applying the LCCT current level suddenly.
All red FD indicators on the 93B PC module will flash momentarily, and the A and G trip
indicators on the 93B DISPLAY module will light.
If the fault current is allowed to persist, all fault detectors drop out. This happens be-
cause they are based on current change. However, there will be no LCCT alarm. Once a
trip signal is issued this alarm is disabled until the fault is removed and a trip is no
longer calculated.
10. Apply a test current of 6 amperes or more.
The Phase A fault detectors are now picked up continually, since the test current is
above the phase fault detector setting.
If the test current has a full dc offset, tripping may occur at a current level that is sig-
nificantly less than the steady-state value (for example, an arithmetic sum of 2 Arms in-
stead of 3 Arms). This "overreach" effect is caused by dc offset, and is usually benefi-
cial to the RFL 9300. For internal faults, it can only help improve speed and sensitivity.
(Unfortunately, you cannot count on it, because the dc offset may not be present. Its
presence depends upon fault inception angle and the L/R ratio of system impedance).
On external faults, the dc offset has no effect at all. "Current In" is still equal to "Cur-
rent Out"; for the RFL 9300, "Charge In" equals "Charge Out."
In tapped-load applications, the dc offset that may occur for low-side faults increases
the tendency to over-trip. A higher bias level setting is required to assure security. The
RFL 9300's software includes a "DC FILT" setting that allows the user to limit the over-
reach caused by dc offset.
11. Using the timer circuit described in step 2 above, measure trip times at various current levels. At UHS
current levels, trip times will be about 5 ms faster than the times at lower currents. In general, trip
times should be 11 to 25 ms for fiber or direct digital versions of the RFL 9300, and 25 to 40 ms for the
modem version.
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