RFL 9300 RFL Electronics Inc.
August 9, 2001 4 - 8 (973) 334-3100
4.2.8 BACKUP - SYSTEM BACKUP FUNCTIONS
Parameter #27 (BACKUP) controls the RFL 9300's system backup functions. It can either be
enabled or disabled. There are four back-up functions:
1. High-Set Overcurrent (Instantaneous)
2. Inverse Time Overcurrent (See 4.2.11 and 4.2.15)
3. Loss-Of-Load
4. Switch-Into-Fault
All back-up functions, with the exception of the Phase and Ground Inverse Time Overcurrent
functions, become active whenever the channel is lost and back-up has been enabled. The
Phase and Ground Inverse Time Overcurrent functions have an additional Enable/Disable set-
ting (Parameters #30 and #34). This allows the operator the option of disabling these functions
while the rest of the backup functions are enabled. However if parameter #27 is disabled, the
Phase and Ground Inverse Time Overcurrent functions are disabled, regardless of the settings
of Parameters #30 and #34. The current values used by all backup functions are based on the
integral of the absolute value of the true CT current samples (charge) calculated over the 8 ms
interval that includes the latest sample. They do not reference the zero-crossings of the input
current waveforms.
When stub-bus mode is active (89B disconnect switch applied to the relay) the RFL 9300 is
forced into backup mode regardless of the setting of parameter #27. While this special case
applies, only the High-Set Overcurrent (Instantaneous) function will become active. The Phase
and Ground Inverse Time Overcurrent functions will only become active if they are enabled (i.e.
parameters #30 or #40 are enabled).
For most applications, backup should be disabled. This is particularly true where there are other
"truly redundant" line protection systems that operate in parallel with the RFL 9300. Backup is
not required in applications where the RFL 9300 and the parallel protection do not have ex-
pected common failure modes.
4.2.9 PH OC BU - PHASE OVERCURRENT BACKUP
Parameter #28 (PH OC BU) is used to control the phase overcurrent backup trip setting. It can
be set anywhere from 6.0 amperes to 31.875 amperes, in 0.125-ampere steps.
The phase overcurrent backup value should be set above the maximum expected contribution to
an external fault. On very short lines, this contribution for bus faults may exceed the maximum
available setting. An overtrip of the RFL 9300 overcurrent back-up for this rare event may be ac-
ceptable. Also, faults on adjacent lines close to the bus will usually produce enough infeed effect
to prevent an overtrip.
4.2.10 G OC BU - GROUND OVERCURRENT BACKUP
Parameter #29 (G OC BU) controls the RFL 9300's ground overcurrent backup trip setting. It
can be set anywhere from 1.0 ampere to 31.0 amperes, in 0.125 ampere steps.
The ground overcurrent backup value should be set above the maximum expected 3I
0
contribu-
tion to an external fault. The comments regarding phase overcurrent back-up also apply to
ground overcurrent back-up.
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