Sel 411L - Table 9.19 Rolling Demand Calculations

P.9.33
Date Code 20151029 Protection Manual SEL-411L Relay
Monitoring and Metering
Metering
Figure 9.17 Thermal 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. Figure 9.18
shows the rolling demand response for a step input for a demand meter time
constant of 15 minutes (DMTC := 15). The relay divides the DMTC period
into three 5-minute intervals and averages the three DMTC sub-interval
samples every DMTC period. Table 9.19 lists the rolling demand response for
four DMTC periods shown in Figure 9.18. 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 9.18).
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
510
15
Time
(minutes)
DMTC Period
Time
(minutes)
R
C
—
+
Table 9.19 Rolling Demand Calculations
DMTC Period
(see Figure 9.18)
1/3 DMTC
Interval
(minutes)
Interval
Sample
(per unit)
Rolling
Demand
Tota l
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