GE EPM 6000 instruction manual Demand, Power and Energy Relationship Over Time

CHAPTER 2: ELECTRICAL BACKGROUND

Table 2–2: Power and Energy Relationship Over Time

Time Interval	Power	Energy	Accumulated
			Energy
1 minute	30 kW	0.50 kWh	0.50 kWh
2 minutes	50 kW	0.83 kWh	1.33 kWh
3 minutes	40 kW	0.67 kWh	2.00 kWh
4 minutes	55 kW	0.92 kWh	2.92 kWh
5 minutes	60 kW	1.00 kWh	3.92 kWh
6 minutes	60 kW	1.00 kWh	4.92 kWh
7 minutes	70 kW	1.17 kWh	6.09 kWh
8 minutes	70 kW	1.17 kWh	7.26 kWh
9 minutes	60 kW	1.00 kWh	8.26 kWh
10 minutes	70 kW	1.17 kWh	9.43 kWh
11 minutes	80 kW	1.33 kWh	10.76 kWh
12 minutes	50 kW	0.83 kWh	12.42 kWh
13 minutes	50 kW	0.83 kWh	12.42 kWh
14 minutes	70 kW	1.17 kWh	13.59 kWh
15 minutes	80 kW	1.33 kWh	14.92 kWh

As shown in the above table, the accumulated energy for the power load profile of the data in Power Use Over Time on page 2–9 is 14.92 kWh.

2.3.4Demand

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 Power Use Over Time on page 2–9) 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 59.68 kWh. The same process is applied to calculate the 15-minute demand value. The demand value associated with the example load is 59.68 kWh/hour or 59.68 kWd. Note that the peak instantaneous value of power is 80 kW, significantly more than the demand value.

2–10 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE