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7.7
Date Code 20171006
Instruction Manual
SEL-400 Series Relays
Metering
Demand Metering
Rolling Demand
Rolling demand is a sliding time-window arithmetic average. Rolling demand
measurement is similar to a step-sampled A/D conversion system.
shows the rolling demand response for a step input for a demand meter time con-
stant of 15 minutes (DMTC := 15). The relay divides the DMTC period into three
5-minute intervals and averages the three DMTC subinterval samples every
DMTC period.
lists the rolling demand response for four DMTC peri-
. Rolling demand metering response is at 100 percent
(1.0 per unit) of the full applied value after a time equal to the fourth DMTC
period (see (d) in
Figure 7.3
Thermal Demand Metering
Step
Current
Input
Thermal
Demand
Meter
Response
(EDEM := THM)
1.0
1.0
0.9
0.5
0
0.5
0
0
5
10
15
0
5
10
15
Time
(minutes)
DMTC Period
Time
(minutes)
R
C
—
+
Table 7.4
Rolling Demand Calculations
DMTC Period
(see Figure 9.18)
1/3 DMTC
Interval
(minutes)
Interval
Sample
(per unit)
Rolling
Demand
Total
Rolling
Demand
Calculation
Rolling
Demand
Response
(per unit)
(a)
–5 to 0
0
0
0 / 3
0
(b)
0 to 5
1
1
1 / 3
0.33
(c)
5 to 10
1
2
2 / 3
0.67
(d)
10 to 15
1
3
3 / 3
1.00
Summary of Contents for SEL-421-4
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