Sel 751A, Instruction Manual

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4.80
SEL-751A Relay Instruction Manual Date Code 20100129
Protection and Logic Functions
Demand Metering
meter response. In the Figure 4.41 example, the rolling demand meter
averages the three latest five-minute totals because setting DMTC = 15
(15/5 = 3). The rolling demand meter response is updated every five minutes,
after a new five-minute total is calculated.
The following is a step-by-step calculation of the rolling demand response
example in
Figure 4.41 (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
five-minute intervals in the sliding time-window at “Time = 0 minutes” each
integrate into the following five-minute totals:
Rolling demand meter response at “Time = 0 minutes” = 0.0/3 = 0.0 per unit.
Time = 5 Minutes
The three five-minute intervals in the sliding time-window at “Time = 5
minutes” each integrate into the following five-minute totals:
Rolling demand meter response at “Time = 5 minutes” = 1.0/3 = 0.33 per unit.
Time = 10 Minutes
The three five-minute intervals in the sliding time-window at “Time = 10
minutes” each integrate into the following five-minute totals:
Rolling demand meter response at “Time = 10 minutes” = 2.0/3 = 0.67 per unit.
Five-Minute Totals Corresponding Five-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
Five-Minute Totals Corresponding Five-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
Five-Minute Totals Corresponding Five-Minute Interval
0.0 per unit –5 to 0 minutes
1.0 per unit 0 to 5 minutes
1.0 per unit 5 to 10 minutes
2.0 per unit