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E149701
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1: Three-Phase Power Measurement
As in Table 1.2, the accumulated energy for the power load profile of Figure 1.7 is
14.92 kWh.
Demand is also a time-based value. The demand is the average rate of energy use
over time. The actual label for demand is kilowatt-hours/hour but this is normally
reduced to kilowatts. This makes it easy to confuse demand with power, but demand
is not an instantaneous value. To calculate demand it is necessary to accumulate the
energy readings (as illustrated in Figure 1.7) and adjust the energy reading to an
hourly value that constitutes the demand.
In the example, the accumulated energy is 14.92 kWh. But this measurement was
made over a 15-minute interval. To convert the reading to a demand value, it must be
normalized to a 60-minute interval. If the pattern were repeated for an additional
three 15-minute intervals the total energy would be four times the measured value or
Time
Interval
(minute)
Power
(kW)
Energy
(kWh)
Accumulated
Energy
(kWh)
1
30
0.50
0.50
2
50
0.83
1.33
3
40
0.67
2.00
4
55
0.92
2.92
5
60
1.00
3.92
6
60
1.00
4.92
7
70
1.17
6.09
8
70
1.17
7.26
9
60
1.00
8.26
10
70
1.17
9.43
11
80
1.33
10.76
12
50
0.83
12.42
13
50
0.83
12.42
14
70
1.17
13.59
15
80
1.33
14.92
Table 1.2: Power and Energy Relationship over Time
Summary of Contents for Shark 200
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