Date Code 20010625
Breaker Monitor and Metering Functions
8-25
SEL-311L 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 8.13 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.
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
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