Schweitzer Engineering Laboratories SEL-387E - Deriving Cumulative I 2 T Values for Preloading; Magnitude Limits on Through-Fault Event Data

Date Code 20080110 Metering and Monitoring 5-19
SEL-387E Instruction Manual
If the TFE command is then executed, the response shows the new preloaded values (the
through-fault events at bottom are not disturbed):
=>TFE <Enter>
XFMR 1 Date: 06/17/06 Time: 18:59:49.130
STATION A
FID=SEL-387E-R700-V0-Z101003-D20060616
Number of Through Faults: 10 Last Reset: 02/10/04 19:56:22
Winding 1 Total I-squared-t (kA^2 seconds, primary):
A-phase B-phase C-phase
147.800 303.500 237.900
# Date Time Duration IA IB IC
(seconds) (A, primary max)
1 02/14/04 18:59:22.244 5.002 241 4158 260
2 02/11/04 11:37:55.495 30.834 220 241 451
Deriving Cumulative I
2
t Values for Preloading
If cumulative I
2
t values need to be derived for preloading, refer first to the preceding subsection
Through-Fault Calculation to see how individual I
2
t calculations are made (even though this
referenced subsection refers to how the relay does the calculation automatically, the same
approach is still valid for “hand” calculations). In the referenced subsection, notice how the
example 6000 A (6 kA) fault value is handled in the calculation, so that the resultant comes out
in units of (kA)
2
seconds. All the individual I
2
t calculations, for the corresponding faults on a
specific phase, are then summed together to create a cumulative I
2
t value that can then be
preloaded for that phase. Use the previously discussed
TFE P command to preload the
cumulative I
2
t values for each phase.
Magnitude Limits on Through-Fault Event Data
In the above TFE command responses, there are limits, besides the aforementioned 1200 event
limit on stored through-fault events, to data accumulation. These limits are:
“Number of Through-Faults” counts: 65,535 counts
“Total I-squared-t” (per phase): 4,294,967.295 (kA)
2
seconds
“Duration” for through-fault event: 8191 cycles, converted to seconds
“IA, IB, IC” for through-fault event 65,535 A, primary
If any of these values exceed their limits, a plus sign (+) is appended to the above maximum
limit number in the display. If “Duration” or “IA, IB, IC” values are at their maximums or
beyond, then the monitor uses the above maximum values in performing subsequent simple I
2
t
calculations and cumulatively storing calculation results for each monitored phase.
All these through-fault event data are stored in nonvolatile memory.