RFL 9300 RFL Electronics Inc.
October 20, 2004 8 - 14 (973) 334-3100
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 every few
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.
The red FD indicator on the 93B PC module monitoring Phase A will flash mo-
mentarily, and the A and G trip indicators and the TRIP 1 indicator on the 93B
DISPLAY module will light.
10. Apply a test current of 6 amperes or more.
The fault detector monitoring Phase A is 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
significantly less than the steady-state value (for example, an arithmetic sum of 2
Arms instead of 3 Arms). This "overreach" effect is caused by dc offset, and is
usually beneficial to the RFL 9300. For internal faults, it can only help improve
speed and sensitivity. (Unfortunately, you cannot count on it, because the dc off-
set 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 "Current Out"; for the RFL 9300, "Charge In"
equals "Charge Out."
In tapped-load applications, the dc offset that may occur for low-side faults in-
creases 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 overreach caused by dc offset. DC FILT is available only in 2-
terminal mode.
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, G.703, or direct digital, and 25 to 40 ms for
the modem version.
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