RFL Electronics RFL 9300 - Ultra High-Speed Tripping

RFL 9300 RFL Electronics Inc.
August 25, 2000 3 - 9 (973) 334-3100
3.8 ULTRA HIGH-SPEED TRIPPING
The RFL 9300's UHS (Ultra High-Speed) circuit provides a trip decision in as little as 7 ms, when the RFL 9300
is using a 56-Kbps or fiber channel. (Actual breaker tripping takes about 4 ms longer; this allows for the auxiliary
relay's pick-up time). The UHS circuit sends a high-priority message whenever a current greater than +12 A
peak
is present for 2 milliseconds. Tripping occurs at the receiving terminal, unless the UHS is blocked by at least
one current sample of -(11A - bias setting)
peak
or more. The minimum blocking current allowed is -7.5A peak for
the phase A, B, or C controller or +7.5A peak for the 3I0 controller. The sample that blocks the UHS circuit must
occur at some time during a 6-ms time window. This provides correct operation for internal and external faults,
with incorrect channel compensations up to +
3 ms. (See Figures 3-11 and 3-12.)
When the relay is configured for 3-terminal operation a UHS signal received from a remote terminal will not exe-
cute the UHS algorithm until it has been “verified” by a WCM, UHS or CCD message received from the second
remote terminal. “Verified” means that the adjusted received time-tags of the two messages must be compared
to insure that they represent the same time interval. The message from the second remote terminal may have a
time-tag that precedes or follows the UHS message. Trip speeds comparable to those observed for 2-terminal
systems are possible if the second terminal is sending a WCM or UHS message. If the second terminal is send-
ing a CCD message the trip speed will tend to be similar to a SFT since the second terminal will not transmit the
CCD message until a zero-crossing of the fault waveform is recorded.
Figures 3-11 & 3-12 represent UHS operation regardless of the system configuration. It must be understood that
if the relay is configured for 3-terminal operation the waveforms represent transient fault current waveforms after
pre-fault load subtraction.