Date Code 20001006 Breaker Monitor, Metering, and Load Profile Functions 8-23
SEL-351 Instruction Manual
The rolling demand meter integrates the applied signal (e.g., step current) input in 5-minute
intervals. The integration is performed approximately every 2 seconds. The average value for an
integrated 5-minute interval is derived and stored as a 5-minute total. The rolling demand meter
then averages a number of the 5-minute totals to produce the rolling demand meter response. In the
Figure 8.11 example, the rolling demand meter averages the three latest 5-minute totals because
setting DMTC = 15 (15/5 = 3). The rolling demand meter response is updated every 5 minutes,
after a new 5-minute total is calculated.
The following is a step-by-step calculation of the rolling demand response example in Figure 8.11
(bottom).
Time = 0 Minutes
Presume that the instantaneous current has been at zero for quite some time before “Time =
0 minutes” (or the demand meters were reset). The three 5-minute intervals in the sliding time-
window at “Time = 0 minutes” each integrate into the following 5-minute totals:
5-Minute Totals
Corresponding
5-Minute Interval
0.0 per unit -15 to -10 minutes
0.0 per unit -10 to -5 minutes
0.0 per unit -5 to 0 minutes
0.0 per unit
Rolling demand meter response at “Time = 0 minutes” = 0.0/3 = 0.0 per unit
Time = 5 Minutes
The three 5-minute intervals in the sliding time-window at “Time = 5 minutes” each integrate into
the following 5-minute totals:
5-Minute Totals
Corresponding
5-Minute Interval
0.0 per unit -10 to -5 minutes
0.0 per unit -5 to 0 minutes
1.0 per unit 0 to 5 minutes
1.0 per unit
Rolling demand meter response at “Time = 5 minutes” = 1.0/3 = 0.33 per unit
Courtesy of NationalSwitchgear.com
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